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Influence of practice on response-selection and response-implementation processes involved in the response-interference effect
Acta Psychologica 109 (2002) 177±194 www.elsevier.com/locate/actpsy
In¯uence of practice on response-selection and response-implementation processes involved in the response-interference eect Melanie A. Hart a b
a,*
, T. Gilmour Reeve
b
School of Health, Physical Education and Leisure Services, 203 Wellness/Recreation Center, University of Northern Iowa, Cedar Falls, IA 50614-0241, USA Department of Health, Physical Education and Recreation, Texas Tech University, TX, USA Received 10 October 2000; received in revised form 29 May 2001; accepted 29 May 2001
Abstract In a choice reaction-time task, the response-interference eect is an increase in reaction times when the two possible responses are from the same hand compared to when the two possible responses are from dierent hands [Psychonomic Science 2 (1965) 55±56; Human Motor Control, Academic Press, San Diego, CA, 1991]. Although the in¯uence of practice on other reaction-time eects (i.e., the complexity eect and precuing) has been examined, research evaluating the in¯uence of practice on the response-interference eect is limited. Therefore, two experiments were conducted to determine the in¯uence of practice on the response-interference eect. In Experiment 1, a bilateral transfer task was used to assess the in¯uence of practice on the response-selection processes associated with the response-interference eect. The practice results indicated decreased reaction times, but did not in¯uence the response-interference eect. In Experiment 2, a priming task was used to assess the in¯uence of practice on response-implementation processes associated with the response-interference eect. The reaction time results indicated a change in the response-interference eect. The results of these two experiments suggest that with only two ®ngers on response keys, practice alters the mechanical constraints aecting the response-implementation processes and thereby decreases the response-interference eect. Ó 2002 Elsevier Science B.V. All rights reserved. PsycINFO classi®cation: 2330; 2340 Keywords: Reaction time; Practice; Interference learning; Hypothesis testing; Response interference
*
Corresponding author. Fax: +1-319-273-5958. E-mail address: [email protected] (M.A. Hart).
0001-6918/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 1 - 6 9 1 8 ( 0 1 ) 0 0 0 5 6 - 7
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In a two-choice task, response interference is the increase in reaction time created by the relationship between the alternative responses (Rosenbaum, 1991). The response-interference eect was demonstrated by Kornblum (1965), who found that reaction times were slower when the two possible responses were from the same hand (i.e., a same-hand condition) rather than from dierent hands (i.e., a dierent-hand condition). Thus, an advantage for responses from the dierent-hand condition was apparent in the reaction times. This dierent-hand advantage was attributed to the presence of competition between the responses (i.e., response interference) in the same-hand condition. Although the dierent-hand advantage is a robust ®nding when only two ®ngers are on the response keys, varying the number of ®ngers in contact with the response keys produces dierent results (Alain, Buckolz, & Taktak, 1993; Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982). For example when four ®ngers are placed on the response keys, the dierent-hand advantage is eliminated, and reaction times are equal for the two hand conditions (Alain et al., 1993; Reeve & Proctor, 1988). Various hypotheses for the source of the response-interference eect have been proposed. Rosenbaum and Kornblum (1982) concluded that the response-interference eect was due to the use of dierent response-preparation strategies (response-preparation hypothesis). According to the response-preparation hypothesis, the preparation strategies adopted determines the presence or absence of response interference. An individual preparation strategy would not produce the response-interference eect, because neither response is prepared until the presentation of the stimulus. A multiple response-preparation strategy would encourage the participant to prepare both responses prior to the presentation of the stimulus. This multiple preparation strategy results in the response-interference eect. Therefore, according to Rosenbaum and Kornblum's response-preparation hypothesis, the response-interference eect is due to the preparation strategy adopted. These preparation strategies in¯uence response-selection processes. Additional research by Reeve and Proctor (1988) supported the concept of response-preparation strategies as being the source of the response-interference eect. Although preparation strategies operating during response-selection processes have been implicated as the source of the response-interference eect (Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982), another source for the response-interference eect may involve response-implementation processes (response-implementation hypothesis). Response-implementation processes involve the motoric aspects of response production. Several theoretical accounts have posited that response implementation may be involved in the response-interference eect (Alain et al., 1993; Hasbroucq, Akamatsu, Mouret, & Seal, 1995). According to Hasbroucq et al. (1995), the response-implementation processes produce the response-interference eect due to mechanical constraints posed by the anatomical structures in the same-hand condition. The ®ngers are designed to ¯ex as a unit, and when only one ®nger is to be ¯exed more time is required to program and implement the single ®nger ¯exion when both responses are from within the same-hand resulting in the response-interference eect. Although the response-implementation hypothesis was originally proposed by Reeve and
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Proctor (1988), they rejected it because their experiments did not produce support for this hypothesis. Hasbroucq et al. (1995) utilized electromyography (EMG) to fractionate reaction times in an attempt to determine the locus of the response-interference eect. EMG data were collected from the ¯exor digitorum profundus and ¯exor digitorum sublimis for fractionating the reaction time into premotor and motor times. Premotor times are assumed to be associated with cognitive processes, such as response selection, while motor times are assumed to re¯ect motoric processes involved in response implementation. The conclusion of these researchers was that the response-interference eect is due to the degree of involvement of the motor cortex and the excitability of the spinal neurons, in other words to implementation processes. Although Hasbroucq et al. (1995) rejected the possibility of response-selection processes as the source of the response-interference eect, changes in premotor times as well as motor times were found between the two hand conditions. In their ®rst experiment, the EMG data indicated longer premotor times and motor times for the same-hand condition than the dierent-hand condition. The results of their experiment suggest the possibility of both response-selection and response-implementation processes contributing to the response-interference eect. The change in premotor time could re¯ect dierent response-selection processes associated with the two hand conditions. Additionally, although the dierent-hand advantage is a robust ®nding in the two®nger condition, Hasbroucq et al. (1995) reported only a marginally signi®cant different-hand advantage after a short practice period. However, the examination of practice eects was not the purpose of their study, and practice eects were not addressed analytically. Although practice has not been directly addressed, the study of practice eects may provide additional information about the nature of the responseinterference eect. The response-preparation hypothesis and the response-implementation hypothesis have been studied extensively as if the two were in opposition to one another (Alain et al., 1993; Hasbroucq et al., 1995; Reeve & Proctor, 1988). The purposes of these studies have been to ®nd support for one hypothesis over the other. However, as originally proposed (Rosenbaum & Kornblum, 1982), the response-preparation hypothesis suggests factors that may in¯uence the presence or absence of response interference (i.e., strategy selected for the response preparation). The response-implementation hypothesis addresses the source of the interference when it is present. Therefore, rather than the hypotheses being opposing explanations for the response-interference eect, both may provide explanations for the eect. In other words, both the response-preparation hypothesis and the response-implementation hypothesis may be necessary to adequately explain the various reaction time patterns found as a result of manipulating various factors. Practice is one factor that has been found to in¯uence the reaction time patterns associated with other eects, such as the stimulus±response compatibility eect and the complexity eect. Thus, in an attempt to build a model that incorporates both hypotheses, the in¯uence of practice on the response-interference eect needs to be addressed.
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In other studies of information processing and human performance, the use of practice and transfer designs have been utilized to understand the factors in¯uencing the various processes. Practice bene®ts have been found to in¯uence response-selection processes associated with the dierential eects of precuing (Miller, 1982; Proctor & Reeve, 1988; Proctor, Reeve, Weeks, Dornier, & Van Zandt, 1991; Reeve & Proctor, 1984). Other studies have examined the in¯uence of practice on response programming, or implementation processes associated with the complexity eect (Klapp, 1995, 1996). The results of studies on other eects indicate practice can in¯uence both response-selection (Proctor & Reeve, 1988; Proctor et al., 1991) and response-implementation processes (Klapp, 1995, 1996). Although it has been hypothesized (Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982) that the response-interference eect may arise from response-selection processes (i.e., response-preparation strategy), as well as implementation processes (Alain et al., 1993; Hasbroucq et al., 1995), extensive research examining the in¯uence of practice on the response-interference eect is lacking. In a preliminary study (Hart & Reeve, 2000), the role of practice on the responseinterference eect was examined. Following a pre-test consisting of both a samehand ®nger pairing and a dierent-hand ®nger pairing, participants were assigned to one of two practice groups, practicing with either same-hand or dierent-hand ®nger pairings. The analysis of the post-practice reaction times indicated a dierenthand advantage for the dierent-hand practice group and a same-hand advantage for the same-hand practice group. Thus, practice eects on response interference suggest the possibility of a change in either the response-selection processes or the response-implementation processes. Because practice and testing were conducted under the same conditions in the preliminary study, the results cannot distinguish between response-selection and response-implementation processes. The purpose of the current study was to examine in greater detail the changes in the response-interference eect as a result of practice. Speci®cally, two experiments using transfer designs were performed to examine the in¯uence of practice on response-selection and implementation processes associated with the response-interference eect. Experiment 1 used a bilateral transfer task to assess the eects of practice on response-selection processes, whereas Experiment 2 used an intratask transfer to assess the eects of practice on response-implementation processes. 1. Experiment 1 Practice bene®ts have been found for response-selection skills when advanced information is provided by a precue (i.e., precuing eects). Precuing is a technique that provides the participant with advanced information, which reduces the number of stimulus±response alternatives (Proctor & Reeve, 1988). Based on which alternatives are precued, dierential bene®ts are indicated (Miller, 1982; Reeve & Proctor, 1984). When practice was provided for the precuing task, the dierential precuing eect was eliminated (Proctor & Reeve, 1988; Proctor et al., 1991). After practice, the elimina-
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tion of the dierential precuing eect is assumed to be due to the increased eciency of the response-selection processes. Thus, response-selection processes are enhanced by practice. Research indicates that the processes associated with the response-selection stage require less time to perform as a result of practice (see Proctor & Dutta, 1995; for a review). Keele and colleagues (Keele, Jennings, Jones, Caulton, & Cohen, 1995) found that practice of a novel task with one set of eectors in¯uences performance when a dierent set of eectors are utilized (i.e., bilateral transfer). Bilateral transfer is assumed to be a result of changes in the response-selection processes as a result of practice (Schmidt & Lee, 1999). The purpose of Experiment 1 was to utilize a bilateral transfer task to test the possibility that the response-interference eect could be due to response-selection processes (Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982). 2. Method 2.1. Participants 48 (25 females and 23 males) volunteer undergraduate students served as participants. Each participant signed an informed consent prior to participation in this study, and general instructions were given in written and verbal form prior to the actual testing. Participants did not have prior exposure to the task (i.e., the individuals had not participated in previous response-interference experiments), nor did any have knowledge of the hypotheses being tested. 2.2. Tasks A two-choice reaction-time task was performed on an IBM compatible computer under the control of the Microcomputer Experimental Laboratory (MEL) Professional software version 2.0 (Schneider, 1995). The participants were required to make a response by pressing either the B or the N key on a standard computer keyboard. Responses were a keypress made with the left-middle, left-index, right-index, or right-middle ®ngers, with the actual ®nger pairings determined by the speci®c conditions. Participants were seated in front of the computer keyboard and monitor (approximately 50 cm from the monitor and 40 cm from the keyboard), with the midline of the participant's body aligned with the center of the monitor and between the B and the N keys of the keyboard. The presentation of the stimuli and the collection of the response data were controlled by the MEL software. Each trial was initiated by a warning signal that was a ®xation cross (5 cm high 6 cm wide) centered on the computer monitor. A cue was presented 500 ms after the presentation of the warning signal. The cue consisted of two asterisks (each asterisk measured 1.2 cm 1.2 cm), one in each of the upper quadrants of the ®xation cross. The target stimulus was a single asterisk displayed in one of the lower quadrants of the ®xation cross. The foreperiod between the cue and the presentation of the target stimulus was randomized
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from trial to trial. The duration of the foreperiod was 500, 750 or 1000 ms and each duration occurred an equal number of times within a block of trials. The random foreperiod was included to minimize anticipation. The intertrial interval was 1000 ms. 2.2.1. Pre- and post-tests For the pre- and post-test trials, a target stimulus in the lower left quadrant indicated that an index ®nger (left or right depending on hand condition) response was required, while a target stimulus in the lower right quadrant, indicated that a rightmiddle ®nger response was required. For the pre- and post-tests, the two blocks of trials each contained 12 familiarization trials followed by 36 test trials, for a total of 48 trials per block. Within a block of test trials, half of the responses required a right-middle ®nger response and the other half an index ®nger response (left or right index ®nger depending on the condition). The ®nger pairing for the same-hand condition was the right middle and index ®ngers, while the ®nger pairing for the different-hand condition was the right-middle and left-index ®ngers. To minimize any order eects, the order of the hand conditions was counterbalanced across participants. 2.2.2. Practice conditions Participants were randomly assigned to one of three conditions (N 16 per condition), either a no practice condition or one of two practice conditions (a same-hand or a dierent-hand practice condition). The participants in the no practice condition performed the pre-test on the ®rst day and the post-test on the second day, with no practice on the task between these tests. Participants in the same-hand practice condition performed all practice trials using only the left-index and left-middle ®ngers. Participants in the dierent-hand practice condition performed all practice trials using only the right-index and left-middle ®ngers. For the practice trials, a target stimulus in the lower left quadrant indicated a left-middle ®nger response while a target stimulus in the lower right quadrant would indicate an index ®nger response (right or left depending on the practice condition). By practicing with the left hand, the eectors (i.e., speci®c ®ngers) involved during the practice and the testing sessions were dierent. Therefore, any change in reaction time pattern from pre-test to post-test are assumed to be due to changes in the cognitive processes. In other words, any bilateral transfer of the changes associated with the response-interference eect are due to cognitive or response-selection processes. 2.2.3. Sessions Each participant completed two sessions. The ®rst session consisted of the pre-test and one practice session, whereas the second session consisted of the second practice session followed by the post-test. During the ®rst session, each participant in a practice group performed the pre-test followed by 10 practice blocks of 48 trials each. Participants were given a one-minute rest interval between each practice block. In the second session, the participants performed 10 practice blocks of 48 trials each with a 1 min rest interval between practice blocks. Following the practice blocks during
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the second session, the participants were given a 10-minute rest interval in which they were allowed to read. After the rest interval, the participants performed a post-test, which was identical to the pre-test. The total number of practice trials was 960, which has been shown to be sucient practice to induce a change in response-selection processes (Proctor & Dutta, 1995). The sessions were conducted on consecutive days. 3. Results The reaction time data and total error data were analyzed for the test trials and the practice trials. The reported results are those found for the right-middle ®nger on the test trials and the left-middle ®nger on the practice trials. The analysis of the reaction times for the right-middle ®nger is consistent with Kornblum's (1965) initial analysis and the analyses from more recent studies (Hart & Reeve, 2000; Hasbroucq et al., 1995; Reeve & Proctor, 1988). Trials containing timing errors (e.g., reaction times less then 100 ms or greater than 500 ms) and response errors (e.g., incorrect responses) were not repeated and were eliminated from the reaction time analyses. 3.1. Analyses of the test trials The reaction time data for both the pre- and post-tests are presented in Table 1. A preliminary analysis was performed to ensure that the three groups were not significantly dierent prior to practice and that a dierent-hand advantage was initially present. 3.1.1. Pre-test reaction times The pre-test data for the right-middle ®nger were analyzed using a 3 2 (Practice Group Finger Pairing) analysis of variance with repeated measures on the last facTable 1 Mean reaction times and standard deviations (in parentheses) in milliseconds for the test trials for Experiment 1 Finger Pairing
Pairing
Practice group
Same-hand
Dierent-hand
Dierent-hand advantage
Same-hand Pre-test Post-test
309 (24.4) 288 (22.5)
302 (35.3) 281 (31.2)
7 7
Dierent-hand Pre-test Post-test
320 (43.9) 288 (45.6)
308 (40.6) 273 (33.1)
12 15
No practice Pre-test Post-test
300 (40.1) 301 (38.1)
286 (32.4) 286 (31.2)
14 15
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tor. The three levels of Practice Group were no practice, same-hand practice and different-hand practice. The two Finger Pairing levels were same-hand and dierenthand. The results of the analysis revealed no signi®cant dierences among the groups, F 2; 45 1:45; p > 0:05. The main eect for Finger Pairing was signi®cant, F 1; 45 10:22; p < 0:05, with the reaction times being slower for the same-hand condition (M 310) than the dierent-hand condition (M 299). The interaction of Practice Group and Finger Pairing was not signi®cant, F 2; 45 < 1:00. The lack of interaction signi®es that the eects of ®nger pairing were statistically equal for the three groups. 3.1.2. Pre-test and post-test reaction times The mean reaction times for the right-middle ®nger were analyzed using a 3 2 2 (Practice Group Test Finger Pairing) analysis of variance with repeated measures on the last two factors. The two levels of Test were pre-test and post-test. The results of the analysis revealed signi®cant main eects for Test, F 1; 45 33:73; p < 0:05, and Finger Pairing, F 1; 45 21:82; p < 0:05. The mean reaction times indicated slower reaction times for the pre-test (M 304 ms) than for the post-test (M 286 ms). Also, the same-hand ®nger pairing produced slower mean reaction times than the dierent-hand ®nger pairing with the mean reaction times of 301 and 289 ms, respectively. Neither the main eect for Practice Group, F 2; 45 < 1:00, nor the two-way interactions of Practice Group Finger Pairing, F 2; 45 < 1:0; p > 0:05, and Test Finger Pairing, F 1; 45 < 1:0, were signi®cant. The two-way interaction of Practice Group Test was signi®cant, F 2; 45 9:82; p < 0:05. The Practice Group Test interaction is presented in Fig. 1. The interaction was due to the decrease in reaction times for the same-hand and dierenthand practice groups from pre-test to post-test, but no change was observed for the
Fig. 1. Mean reaction times for the Test Practice Group Interaction in Experiment 1.
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no practice group. The three-way interaction was not signi®cant F 2; 45 < 1:00. Thus, practice resulted in faster reaction times for the bilateral transfer post-test, demonstrating that practice did enhance the response-selection processes. However, the magnitude of the dierent-hand advantage remained constant from pre-test to post-test for the three groups (e.g., no change in the response-interference eect). 3.1.3. Errors The analysis of the percent of total errors (response errors and timing errors) for the right-middle ®nger were analyzed using a 3 2 2 (Practice Group Test Finger Pairing) analysis of variance with repeated measures on the last two factors. The results of the analysis revealed a signi®cant main eect for Finger Pairing F 1; 45 5:76; p < 0:05. The errors were higher for the same-hand ®nger pairing (7.2%) than for the dierent-hand ®nger pairing (4.6%). No other main eect or interaction was signi®cant. 3.2. Analyses of practice trials Mean reaction times for the left-middle ®nger were analyzed by a 2 20 (Practice Group Block) analysis of variance with repeated measures on the last factor. The two levels of Practice Group were same-hand practice and dierent-hand practice. The Block levels were the 20 blocks of practice trials. Neither the main eect for Practice Group, F 1; 30 2:15; p 0:15, nor the two-way interaction of Group Block, F 19; 570 < 1:00, was found to be signi®cant. The reaction times for both groups tended to become faster as a function of practice, which was revealed by the signi®cant main eect for Block, F 19; 570 7:10; p < 0:05. The analysis of the percent of total errors did not reveal any signi®cant dierences of the main eects or the interaction. 4. Discussion The purpose of Experiment 1 was to examine the in¯uence of practice on the response-selection processes associated with the response-interference eect. The prediction was that if response-selection processes are the locus of the response-interference eect, then positive bilateral transfer should be observed on the response-interference eect. The signi®cant interaction of test and practice group revealed that bilateral transfer did occur indicating a change in the response-selection processes. The participants who were allowed to practice signi®cantly reduced their reaction times compared to the group of participants who did not receive practice trials. Although response-selection processes were in¯uenced by practice from pre- to post-test as shown by positive bilateral transfer, practice did not in¯uence the response-interference eect. The lack of a three-way interaction indicated that after practice, the dierent-hand advantage was still present for both of the groups receiving practice. Therefore, the response-interference eect was not in¯uenced by
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practice. These results suggest the speci®city of practice eect found by Hart and Reeve (2000) appears not to be due to response-selection processes. 5. Experiment 2 In a previous study of the response-interference eect, Reeve and Hart (in press) had participants perform a two-choice task with two hand conditions and two priming conditions. For the primed trials, the required response was signaled prior to the presentation of the target stimulus. For the unprimed trials, the required response was not signaled until the presentation of the target stimulus. The results of their study indicated a same-hand advantage for the primed trials and a dierent-hand advantage for the unprimed trials. It was concluded that for the primed trials, the response-selection processes were minimal during the reaction time interval, therefore resulting in a dierent preparation strategy (i.e., individual response-preparation strategy). The primed trials eliminated the need to use a multiple preparation strategy, resulting in the elimination and even the reversal of the dierent-hand advantage. In the present study, Experiment 2 examined changes on unprimed trials that result as a function of practice on primed trials. The purpose of Experiment 2 was to examine the in¯uence of practice on the response-implementation processes that have been proposed to be associated with the response-interference eect (Alain et al., 1993; Hasbroucq et al., 1995; Reeve & Proctor, 1988). A priming technique was used to allow response-selection processes to be completed prior to the presentation of the stimulus (Rosenbaum & Kornblum, 1982). Thus, providing practice of primarily the response-implementation processes during the reaction-time interval. If the eciency of the implementation processes is improved with practice, then a change in the response-interference eect (i.e., the different-hand advantage) should be observed on unprimed test trials. 6. Method 6.1. Participants 48 (36 females and 12 males) volunteer undergraduate students served as participants. Each participant signed an informed consent prior to participation in this study, and general instructions were given in written and verbal form prior to the actual testing. Participants did not have prior exposure to the task (i.e., the individuals had not participated in previous response-interference experiments), nor did any have knowledge of the hypotheses being tested. 6.2. Tasks For the pre-test and the post-test, the tasks were the same as that used in Experiment 1. However, for all practice trials the participants were informed (e.g., primed)
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prior to the presentation of the stimulus, which response would be required. Also, unlike Experiment 1, the ®nger pairings used for practice trials were the same as those used for the test trials. 6.2.1. Pre- and post-tests For all three groups, two hand conditions (a same-hand and a dierent-hand condition) were tested in two blocks of trials in both the pre- and post-tests. The foreperiods, stimulus patterns, and ®nger pairings for the two hand conditions were the same as those used in Experiment 1. The order of the blocks was counterbalanced across participants to minimize any potential order eects. 6.2.2. Practice conditions Participants were randomly assigned to one of three conditions, either a no practice (control) condition or one of two practice conditions, a same-hand practice or a different-hand practice. The participants in the no practice condition performed the pre-test on the ®rst day and the post-test on the second day, with no practice on the task between these tests. Participants in the same-hand practice condition performed all practice trials with only the right index and middle ®ngers on the response keys, while participants in the dierent-hand practice condition performed all practice trials with only the left-index and right-middle ®ngers on the response keys. The practice sessions and the total number of trials were the same as those used in Experiment 1. For the practice blocks, all responses were primed with half of the responses requiring a right-middle ®nger response with the other half requiring an index ®nger response (left or right index ®nger depending on the practice condition). The warning stimulus (the ®xation cross) for the primed trials was the same as used for the unprimed trials, but the cue contained only one asterisk (i.e., the prime) in either the upper left or right quadrant of the ®xation cross (see Fig. 2). As in Experiment 1, variable foreperiods of 500, 750, and 1000 ms were used to reduce the ability of the participants to anticipate the presentation of the stimulus. The prime indicated the target stimulus, which was presented directly under the cue. Thus, the prime was entirely valid on all practice trials. 7. Results The reaction time data and total error data were analyzed for the test trials and the practice trials as in Experiment 1 with the exception of the practice trials. Unlike Experiment 1, the right-middle ®nger data were used for the practice trials. 7.1. Analyses of test trials The mean reaction time data for both the pre- and post-tests are presented in Table 2. A preliminary analysis was performed to ensure that the three groups were not signi®cantly dierent prior to practice and that a dierent-hand advantage was initially present.
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Fig. 2. An illustration of the warning, cue, and target stimulus patterns for primed trials. The target in the left column indicates that a keypress would be made by the index ®nger, while the right column indicates that a keypress would be made by the right-middle ®nger. (Note. The cue serves as the prime.)
7.1.1. Pre-test reaction times The pre-test data for the right-middle ®nger were analyzed using a 3 2 (Practice Group Finger Pairing) analysis of variance with repeated measures on the last factor. The results of the analysis revealed no signi®cant main eect for Practice Group, F 2; 45 < 1:00. The main eect for Finger Pairing was signi®cant, F 1; 45
Table 2 Mean reaction times and standard deviations (in parentheses) in milliseconds for the test trials for Experiment 2 Pairing
Finger Pairing Practice group
Same-hand
Dierent-hand
Same-hand Pre-test Post-test
Dierent-hand advantage
321 (41.3) 295 (24.0)
313 (29.4) 292 (21.4)
8 3
Dierent-hand Pre-test Post-test
311 (22.3) 304 (25.4)
302 (21.9) 284 (21.3)
9 20
No practice Pre-test Post-test
315 (33.2) 302 (25.6)
304 (30.2) 301 (27.2)
11 1
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8:54; p < 0:05, with the reaction times being slower for the same-hand condition M 316 than the dierent-hand condition (M 306). The interaction of Practice Group and Finger Pairing was not signi®cant, F 2; 45 < 1:00. The lack of interaction signi®es that the eects of ®nger pairing were statistically equal for the three groups. 7.1.2. Pre-test and post-test reaction times Because the preliminary analysis revealed a dierent-hand advantage for the three groups and no dierences among the groups, the reaction time analysis for all the test trials was conducted. The mean reaction times for the right-middle ®nger were analyzed using a 3 2 2 (Practice Group Test Finger Pairing) analysis of variance with repeated measures on the last two factors. The results of the analysis revealed signi®cant main eects for Test, F 1; 45 22:38; p < 0:05, and Finger Pairing, F 1; 45 12:41; p < 0:05. The means indicated slower reaction times for the pre-test (M 311 ms) than for the post-test (M 296 ms). Also, the same-hand ®nger pairing produced slower mean reaction times than the dierent-hand ®nger pairing with mean reaction times of 308 and 299 ms, respectively. Neither the main eect for Group, F 2; 45 < 1:00, nor the two-way interactions of Group Paring, F 2; 45 1:41; p > 0:05, Group Test, F 2; 45 2:26; p > 0:05 and Test Finger Pairing F 1; 45 < 1:00, were found to be signi®cant. However, the three-way interaction was signi®cant, F 2; 45 3:85; p < 0:05. The three-way interaction is shown in Fig. 3. Practice with the same-hand ®nger pairing reduced the magnitude of the dierent-hand advantage from 8 ms on the pre-test to 3 ms on the post-test. The opposite eect was found for the group that practiced using the dierent-hand ®nger pairing. The magnitude of the dierent-hand advantage increased from 9 ms on the pre-test to 20 ms on the posttest. 1 7.1.3. Errors For the test trials, the percent of total errors (response errors and timing errors) for the right-middle ®nger were analyzed using a 3 2 2 (Practice Group Test Finger Pairing) analysis of variance with repeated measures on the last two factors. The results of the analysis revealed no signi®cant main eects or interactions.
1
The dierent-hand advantage for the no practice group was 11 ms for the pre-test but only 1 ms for the post-test. However, for this group the overall reaction times did not decrease as they did for the same-hand and dierent-hand practice groups. Additionally, a separate 2 2 (Test Finger Pairing) analysis of variance with repeated measures for the data from the no practice group indicated no signi®cant eects. These results indicated that there were no signi®cant changes in the reaction time patterns for the no practice condition. Similar analyses for the other two groups indicated a signi®cant main eect for Test (same-hand practice, F 1; 15 13:36; p < 0:05, and dierent-hand practice, F 1; 15 4:71; p < 0:05. Thus, the signi®cant three-way interaction indicated a speci®city of practice in¯uence on the responseinterference eect for the two groups that received practice.
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Fig. 3. Three-way Interaction for Practice Group Test Finger Pairing in Experiment 2.
7.2. Analyses of practice trials Mean reaction times for the right-middle ®nger were analyzed by a 2 20 (Practice Group Block) analysis of variance with repeated measures on the last factor. The two levels of Practice Group were same-hand practice and dierent-hand practice. The Block levels were the 20 blocks of practice trials. Neither the main eect for Practice Group, F 1; 30 < 1:00, nor the two-way interaction of Practice Group Block, F 19; 570 1:40; p > 0:05, was found to be signi®cant. The reaction times for both groups tended to become faster as a function of practice which was revealed by the signi®cant main eect for Block, F 19; 570 8:45; p < 0:05.
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The percent of total errors were calculated for the right-middle ®nger and analyzed by a 2 20 (Practice Group Block) analysis of variance with repeated measures on the last factor. The main eect of Block was found to be signi®cant, F 19; 570 1:98; p < 0:05. The percentage of errors increased over the practice blocks. The increase in the percentage of errors was not due to response errors (incorrect response), but was due to the timing errors associated with anticipation (reaction times less than 100 ms). Therefore, the increase in total errors was a result of faster responses by the participants as a result of practice, which is consistent with the reaction time data found in other studies (Dutta & Proctor, 1992; Proctor & Dutta, 1995). No other signi®cant dierences were revealed. 7.3. Discussion The purpose of this second experiment was to examine response-implementation processes associated with the response-interference eect. The reaction time results from the pre-test to the post-test indicated a speci®city of practice eect (Schmidt & Lee, 1999). After practicing with the dierent-hand condition, an 11 ms increase in the magnitude of the dierent-hand advantage was found from pre-test to posttest. More importantly, practice under the same-hand condition resulted in a change in the response-interference eect as indicated by a decrease in the dierent-hand advantage. The magnitude of the dierent-hand advantage decreased 5 ms from the pre-test to the post-test. These results suggest that the response-interference eect was in¯uenced speci®cally as a function of the practice. Because the practice trials were primed, the response-selection processes during the reaction time interval were minimized (Klapp, 1996). Therefore, the processes that were in¯uenced by practice are assumed to be the implementation processes. The results of this study indicate that the response-implementation processes associated with the response-interference eect are in¯uenced by practice. 8. General discussion In a two-choice task, the response-interference eect is an increase in reaction times when the two possible responses are from the same hand rather than from different hands (Kornblum, 1965; Reeve & Proctor, 1988). The response-interference eect, as illustrated by a dierent-hand advantage in reaction times for two-choice tasks is a robust ®nding (Alain et al., 1993; Hasbroucq et al., 1995; Reeve & Hart, in press; Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982). The present study examined the role of response-selection and response-implementation processes, which have been proposed to explain the source of the response-interference eect. In Experiment 1, a bilateral transfer design was used to examine the in¯uence of practice on the response-interference eect. In a bilateral design, positive transfer is assumed to be due to changes in response-selection processes (Magill, 1998). Therefore, positive bilateral transfer occurring after practice would be taken as a change in the response-selection processes in¯uencing the response-interference eect. The
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results of the reaction time data indicated that practice resulted in faster reaction times for the post-test than the pre-test. Therefore, changes in response-selection processes did occur which are consistent with other studies (Dutta & Proctor, 1992; Pashler & Baylis, 1991; Proctor & Dutta, 1995; Proctor & Reeve, 1988; Proctor et al., 1991), but those processes involved in the response-interference eect were not in¯uenced by practice. Thus, the results of Experiment 1 did not support responseselection processes as the source of the response-interference eect with only two ®ngers in contact with the response keys. Experiment 2 was designed to examine the in¯uence of practice on response-implementation processes associated with the response-interference eect. To minimize the response-selection processes during the reaction time interval for this experiment, all practice trials were primed. Thus, practice of the response-implementation processes was maximized. The results of Experiment 2 indicated a speci®city of practice eect (Schmidt & Lee, 1999). The participants who practiced under the same-hand condition decreased the magnitude of the dierent-hand advantage, whereas the participants who practiced under the dierent-hand condition increased the magnitude of the dierent-hand advantage. These results of practice in¯uencing response-implementation processes are consistent with other studies that have examined the response-complexity eect (Klapp, 1995, 1996). For the two-®nger condition, the combined results of these two experiments provide support for the response-implementation hypothesis (Hasbroucq et al., 1995). The results of these two experiments suggest that the response-interference eect when only two ®ngers are in contact with response keys is due to mechanical constraints associated with the anatomical similarities between the two responses in the same-hand condition. The results of the ®rst experiment suggest that the response-selection processes are similar for the two hand conditions and are not in¯uenced by practice, while the results of the second experiment suggest dierent response-implementation processes for the two hand conditions. The conclusion that response-implementation processes are the source of the response-interference eect is consistent with the conclusion found in other research (Alain et al., 1993; Hasbroucq, Guiard, & Kornblum, 1989; Hasbroucq et al., 1995; Shulman & McConkie, 1973). The combined results of the two experiments negate the role of response-selection processes as the source of the response interference when it is present, such as when two ®ngers are in contact with the response keys. However, the results do not provide an explanation as to what factors determine when response interference will be present. The response-preparation hypothesis (Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982) was proposed to explain when response interference would be present. Therefore, to completely accept the response-implementation hypothesis and discount the response-preparation hypothesis (i.e., response-selection processes) entirely, may be premature. In one aspect, the response-preparation hypothesis has not been tested for more dicult choice reaction-time situations (i.e., when four ®ngers are in contact with response keys). The response-preparation hypothesis (Reeve & Proctor, 1988) proposes that the number of ®ngers placed on the response keys determines which preparation strategy is adopted. When two ®ngers are on the
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response keys it is proposed that a multiple preparation strategy is adopted. However, when more than two ®ngers are contacting the response keys an individual preparation strategy is adopted. When two ®ngers are in contact with the response keys, a multiple preparation strategy would be used for both hand conditions. Therefore, Experiment 1 determined that the response-selection processes were essentially the same for the two hand conditions. However, the response-preparation hypothesis cannot be completely discarded as a possible explanation for the changes that occur in the response-interference eect when more than two ®ngers are in contact with the response keys (Reeve & Hart, in press). As suggested by the response-preparation hypothesis, the selection of dierent preparation strategies will determine when response interference will be present. The dierent preparation strategies were not directly tested in the present study, nor have they been directly tested in other studies (Hasbroucq et al., 1995). This fact combined with the results of other studies (Reeve and Hart, 2000; Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982) would seem to indicate that the rejection of the response-preparation hypothesis is premature. Therefore, to adequately explain the response-interference eect and the changes that occur due to various manipulations, a hypothesis that combines both the response-preparation hypothesis and the response-implementation hypothesis may be required. In conclusion, the results of these studies do point to the importance of responseimplementation processes in two-choice situations such as those studied by Kornblum (1965) and others (Hart & Reeve, 2000; Hasbroucq et al., 1995; Reeve & Hart, in press; Reeve & Proctor, 1988). More importantly, the present study demonstrated that response-implementation processes are subject to change with practice, which is consistent with other studies (Klapp, 1995, 1996). Further research is needed to better understand the response-interference eect. Speci®cally, the response-preparation hypothesis needs to be more thoroughly examined. One method to gain a greater understanding of the response-interference eect is to examine the in¯uence of practice on the reaction time patterns for choice tasks which use the same-hand and dierent-hand ®nger pairings when more than two ®ngers are involved. The goal of future research should be to build a model that accounts for the response-interference eect under all conditions. The model should address the factors that predict the presence or absence of response interference. This model may need to include both response-selection and response-implementation processes to resolve the inconsistent results among the various studies of the response-interference eect. References Alain, C., Buckolz, E., & Taktak, K. (1993). Same-hand and dierent-hand ®nger pairings in two-choice reaction time: Presence or absence of response competition. Journal of Motor Behavior, 25, 45±51. Dutta, A., & Proctor, R. W. (1992). Persistence of stimulus±response compatibility eects with extended practice. Journal of Experimental Psychology: Learning, Memory, and Cognition, 18, 801±809. Hart, M. A., & Reeve, T. G. (2000). Speci®city of practice eects on response interference in a two-choice task. Journal of Human Movement Studies, 38, 225±234.
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Hasbroucq, T., Guiard, Y., & Kornblum, S. (1989). The additivity of stimulus±response compatibility with the eects of sensory and motor factors in a tactile choice reaction time task. Acta Psychologica, 72, 139±144. Hasbroucq, T., Akamatsu, M., Mouret, I., & Seal, J. (1995). Finger pairing in two choice reaction time tasks: Does the between-hands advantage re¯ect response preparation? Journal of Motor Behavior, 27, 251±262. Keele, S. W., Jennings, P., Jones, S., Caulton, D., & Cohen, A. (1995). On the modularity of sequence respresentation. Journal of Motor Behavior, 27, 17±30. Klapp, S. T. (1995). Motor response programming during simple and choice reaction time: The role of practice. Journal of Experimental Psychology: Human Perception and Performance, 21, 1015±1027. Klapp, S. T. (1996). Reaction time analysis of central motor control. In H. N. Zelaznik (Ed.), Advances in motor learning and control (pp.13±36). Champaign, IL: Human Kinetics. Kornblum, S. (1965). Response competition and/or inhibition in two-choice reaction time. Psychonomic Science, 2, 55±56. Magill, R. A. (1998). Motor learning concepts and applications (5th ed.). Boston: WCB McGraw-Hill. Miller, J. (1982). Discrete versus continuous stage models of human information processing: In search of partial output. Journal of Experimental Psychology: Human Perception and Performance, 8, 273±296. Pashler, H., & Baylis, G. (1991). Procedural learning: 1. Locus of practice eects in speeded choice tasks. Journal of Experimental Psychology: Learning, Memory, and Cognition, 19, 20±32. Proctor, R. W., & Dutta, A. (1995). Acquisition and transfer of response-selection skill. In A. F. Healy, & L. E. Bourne (Eds.), Learning and memory of knowledge and skills: Durability and speci®city (pp. 300± 319). Thousand Oaks, CA: Sage. Proctor, R. W., & Reeve, T. G. (1988). The acquisition of task-speci®c productions and modi®cation of declarative representations in spatial-precuing tasks. Journal of Experimental Psychology: General, 117, 182±196. Proctor, R. W., Reeve, T. G., Weeks, D. J., Dornier, L., & Van Zandt, T. (1991). Acquisition retention, and transfer of response-selection skill in choice reaction tasks. Journal of Experimental Psychology: Learning, Memory, and Cognition, 17, 497±506. Reeve, T. G., & Hart, M.A. (in press). Contributions of response-selection processes to the responseinterference eect. Journal of Human Movement Studies. Reeve, T. G., & Proctor, R. W. (1984). On the advance preparation of discrete ®nger responses. Journal of Experimental Psychology: Human Perception and Performance, 10, 541±553. Reeve, T. G., & Proctor, R. W. (1988). Determinants of two-choice reaction-time patterns for same-hand and dierent-hand ®nger pairings. Journal of Motor Behavior, 20, 317±340. Rosenbaum, D. A. (1991). Human motor control. San Diego, CA: Academic Press. Rosenbaum, D. A., & Kornblum, S. (1982). A priming method for investigating the selection of motor responses. Acta Psychologica, 51, 223±243. Schmidt, R. A., & Lee, T. D. (1999). Motor control and learning: A behavioral emphasis (third ed.). Champaign, IL: Human Kinetics. Schneider, W. (1995). MEL professional user's guide. Pittsburgh: Psychology Software Tools. Shulman, H. G., & McConkie, A. (1973). S R compatibility, response discriminability, and response codes in choice reaction time. Journal of Experimental Psychology, 98, 375±378.
In¯uence of practice on response-selection and response-implementation processes involved in the response-interference eect Melanie A. Hart a b
a,*
, T. Gilmour Reeve
b
School of Health, Physical Education and Leisure Services, 203 Wellness/Recreation Center, University of Northern Iowa, Cedar Falls, IA 50614-0241, USA Department of Health, Physical Education and Recreation, Texas Tech University, TX, USA Received 10 October 2000; received in revised form 29 May 2001; accepted 29 May 2001
Abstract In a choice reaction-time task, the response-interference eect is an increase in reaction times when the two possible responses are from the same hand compared to when the two possible responses are from dierent hands [Psychonomic Science 2 (1965) 55±56; Human Motor Control, Academic Press, San Diego, CA, 1991]. Although the in¯uence of practice on other reaction-time eects (i.e., the complexity eect and precuing) has been examined, research evaluating the in¯uence of practice on the response-interference eect is limited. Therefore, two experiments were conducted to determine the in¯uence of practice on the response-interference eect. In Experiment 1, a bilateral transfer task was used to assess the in¯uence of practice on the response-selection processes associated with the response-interference eect. The practice results indicated decreased reaction times, but did not in¯uence the response-interference eect. In Experiment 2, a priming task was used to assess the in¯uence of practice on response-implementation processes associated with the response-interference eect. The reaction time results indicated a change in the response-interference eect. The results of these two experiments suggest that with only two ®ngers on response keys, practice alters the mechanical constraints aecting the response-implementation processes and thereby decreases the response-interference eect. Ó 2002 Elsevier Science B.V. All rights reserved. PsycINFO classi®cation: 2330; 2340 Keywords: Reaction time; Practice; Interference learning; Hypothesis testing; Response interference
*
Corresponding author. Fax: +1-319-273-5958. E-mail address: [email protected] (M.A. Hart).
0001-6918/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 1 - 6 9 1 8 ( 0 1 ) 0 0 0 5 6 - 7
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In a two-choice task, response interference is the increase in reaction time created by the relationship between the alternative responses (Rosenbaum, 1991). The response-interference eect was demonstrated by Kornblum (1965), who found that reaction times were slower when the two possible responses were from the same hand (i.e., a same-hand condition) rather than from dierent hands (i.e., a dierent-hand condition). Thus, an advantage for responses from the dierent-hand condition was apparent in the reaction times. This dierent-hand advantage was attributed to the presence of competition between the responses (i.e., response interference) in the same-hand condition. Although the dierent-hand advantage is a robust ®nding when only two ®ngers are on the response keys, varying the number of ®ngers in contact with the response keys produces dierent results (Alain, Buckolz, & Taktak, 1993; Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982). For example when four ®ngers are placed on the response keys, the dierent-hand advantage is eliminated, and reaction times are equal for the two hand conditions (Alain et al., 1993; Reeve & Proctor, 1988). Various hypotheses for the source of the response-interference eect have been proposed. Rosenbaum and Kornblum (1982) concluded that the response-interference eect was due to the use of dierent response-preparation strategies (response-preparation hypothesis). According to the response-preparation hypothesis, the preparation strategies adopted determines the presence or absence of response interference. An individual preparation strategy would not produce the response-interference eect, because neither response is prepared until the presentation of the stimulus. A multiple response-preparation strategy would encourage the participant to prepare both responses prior to the presentation of the stimulus. This multiple preparation strategy results in the response-interference eect. Therefore, according to Rosenbaum and Kornblum's response-preparation hypothesis, the response-interference eect is due to the preparation strategy adopted. These preparation strategies in¯uence response-selection processes. Additional research by Reeve and Proctor (1988) supported the concept of response-preparation strategies as being the source of the response-interference eect. Although preparation strategies operating during response-selection processes have been implicated as the source of the response-interference eect (Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982), another source for the response-interference eect may involve response-implementation processes (response-implementation hypothesis). Response-implementation processes involve the motoric aspects of response production. Several theoretical accounts have posited that response implementation may be involved in the response-interference eect (Alain et al., 1993; Hasbroucq, Akamatsu, Mouret, & Seal, 1995). According to Hasbroucq et al. (1995), the response-implementation processes produce the response-interference eect due to mechanical constraints posed by the anatomical structures in the same-hand condition. The ®ngers are designed to ¯ex as a unit, and when only one ®nger is to be ¯exed more time is required to program and implement the single ®nger ¯exion when both responses are from within the same-hand resulting in the response-interference eect. Although the response-implementation hypothesis was originally proposed by Reeve and
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Proctor (1988), they rejected it because their experiments did not produce support for this hypothesis. Hasbroucq et al. (1995) utilized electromyography (EMG) to fractionate reaction times in an attempt to determine the locus of the response-interference eect. EMG data were collected from the ¯exor digitorum profundus and ¯exor digitorum sublimis for fractionating the reaction time into premotor and motor times. Premotor times are assumed to be associated with cognitive processes, such as response selection, while motor times are assumed to re¯ect motoric processes involved in response implementation. The conclusion of these researchers was that the response-interference eect is due to the degree of involvement of the motor cortex and the excitability of the spinal neurons, in other words to implementation processes. Although Hasbroucq et al. (1995) rejected the possibility of response-selection processes as the source of the response-interference eect, changes in premotor times as well as motor times were found between the two hand conditions. In their ®rst experiment, the EMG data indicated longer premotor times and motor times for the same-hand condition than the dierent-hand condition. The results of their experiment suggest the possibility of both response-selection and response-implementation processes contributing to the response-interference eect. The change in premotor time could re¯ect dierent response-selection processes associated with the two hand conditions. Additionally, although the dierent-hand advantage is a robust ®nding in the two®nger condition, Hasbroucq et al. (1995) reported only a marginally signi®cant different-hand advantage after a short practice period. However, the examination of practice eects was not the purpose of their study, and practice eects were not addressed analytically. Although practice has not been directly addressed, the study of practice eects may provide additional information about the nature of the responseinterference eect. The response-preparation hypothesis and the response-implementation hypothesis have been studied extensively as if the two were in opposition to one another (Alain et al., 1993; Hasbroucq et al., 1995; Reeve & Proctor, 1988). The purposes of these studies have been to ®nd support for one hypothesis over the other. However, as originally proposed (Rosenbaum & Kornblum, 1982), the response-preparation hypothesis suggests factors that may in¯uence the presence or absence of response interference (i.e., strategy selected for the response preparation). The response-implementation hypothesis addresses the source of the interference when it is present. Therefore, rather than the hypotheses being opposing explanations for the response-interference eect, both may provide explanations for the eect. In other words, both the response-preparation hypothesis and the response-implementation hypothesis may be necessary to adequately explain the various reaction time patterns found as a result of manipulating various factors. Practice is one factor that has been found to in¯uence the reaction time patterns associated with other eects, such as the stimulus±response compatibility eect and the complexity eect. Thus, in an attempt to build a model that incorporates both hypotheses, the in¯uence of practice on the response-interference eect needs to be addressed.
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In other studies of information processing and human performance, the use of practice and transfer designs have been utilized to understand the factors in¯uencing the various processes. Practice bene®ts have been found to in¯uence response-selection processes associated with the dierential eects of precuing (Miller, 1982; Proctor & Reeve, 1988; Proctor, Reeve, Weeks, Dornier, & Van Zandt, 1991; Reeve & Proctor, 1984). Other studies have examined the in¯uence of practice on response programming, or implementation processes associated with the complexity eect (Klapp, 1995, 1996). The results of studies on other eects indicate practice can in¯uence both response-selection (Proctor & Reeve, 1988; Proctor et al., 1991) and response-implementation processes (Klapp, 1995, 1996). Although it has been hypothesized (Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982) that the response-interference eect may arise from response-selection processes (i.e., response-preparation strategy), as well as implementation processes (Alain et al., 1993; Hasbroucq et al., 1995), extensive research examining the in¯uence of practice on the response-interference eect is lacking. In a preliminary study (Hart & Reeve, 2000), the role of practice on the responseinterference eect was examined. Following a pre-test consisting of both a samehand ®nger pairing and a dierent-hand ®nger pairing, participants were assigned to one of two practice groups, practicing with either same-hand or dierent-hand ®nger pairings. The analysis of the post-practice reaction times indicated a dierenthand advantage for the dierent-hand practice group and a same-hand advantage for the same-hand practice group. Thus, practice eects on response interference suggest the possibility of a change in either the response-selection processes or the response-implementation processes. Because practice and testing were conducted under the same conditions in the preliminary study, the results cannot distinguish between response-selection and response-implementation processes. The purpose of the current study was to examine in greater detail the changes in the response-interference eect as a result of practice. Speci®cally, two experiments using transfer designs were performed to examine the in¯uence of practice on response-selection and implementation processes associated with the response-interference eect. Experiment 1 used a bilateral transfer task to assess the eects of practice on response-selection processes, whereas Experiment 2 used an intratask transfer to assess the eects of practice on response-implementation processes. 1. Experiment 1 Practice bene®ts have been found for response-selection skills when advanced information is provided by a precue (i.e., precuing eects). Precuing is a technique that provides the participant with advanced information, which reduces the number of stimulus±response alternatives (Proctor & Reeve, 1988). Based on which alternatives are precued, dierential bene®ts are indicated (Miller, 1982; Reeve & Proctor, 1984). When practice was provided for the precuing task, the dierential precuing eect was eliminated (Proctor & Reeve, 1988; Proctor et al., 1991). After practice, the elimina-
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tion of the dierential precuing eect is assumed to be due to the increased eciency of the response-selection processes. Thus, response-selection processes are enhanced by practice. Research indicates that the processes associated with the response-selection stage require less time to perform as a result of practice (see Proctor & Dutta, 1995; for a review). Keele and colleagues (Keele, Jennings, Jones, Caulton, & Cohen, 1995) found that practice of a novel task with one set of eectors in¯uences performance when a dierent set of eectors are utilized (i.e., bilateral transfer). Bilateral transfer is assumed to be a result of changes in the response-selection processes as a result of practice (Schmidt & Lee, 1999). The purpose of Experiment 1 was to utilize a bilateral transfer task to test the possibility that the response-interference eect could be due to response-selection processes (Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982). 2. Method 2.1. Participants 48 (25 females and 23 males) volunteer undergraduate students served as participants. Each participant signed an informed consent prior to participation in this study, and general instructions were given in written and verbal form prior to the actual testing. Participants did not have prior exposure to the task (i.e., the individuals had not participated in previous response-interference experiments), nor did any have knowledge of the hypotheses being tested. 2.2. Tasks A two-choice reaction-time task was performed on an IBM compatible computer under the control of the Microcomputer Experimental Laboratory (MEL) Professional software version 2.0 (Schneider, 1995). The participants were required to make a response by pressing either the B or the N key on a standard computer keyboard. Responses were a keypress made with the left-middle, left-index, right-index, or right-middle ®ngers, with the actual ®nger pairings determined by the speci®c conditions. Participants were seated in front of the computer keyboard and monitor (approximately 50 cm from the monitor and 40 cm from the keyboard), with the midline of the participant's body aligned with the center of the monitor and between the B and the N keys of the keyboard. The presentation of the stimuli and the collection of the response data were controlled by the MEL software. Each trial was initiated by a warning signal that was a ®xation cross (5 cm high 6 cm wide) centered on the computer monitor. A cue was presented 500 ms after the presentation of the warning signal. The cue consisted of two asterisks (each asterisk measured 1.2 cm 1.2 cm), one in each of the upper quadrants of the ®xation cross. The target stimulus was a single asterisk displayed in one of the lower quadrants of the ®xation cross. The foreperiod between the cue and the presentation of the target stimulus was randomized
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from trial to trial. The duration of the foreperiod was 500, 750 or 1000 ms and each duration occurred an equal number of times within a block of trials. The random foreperiod was included to minimize anticipation. The intertrial interval was 1000 ms. 2.2.1. Pre- and post-tests For the pre- and post-test trials, a target stimulus in the lower left quadrant indicated that an index ®nger (left or right depending on hand condition) response was required, while a target stimulus in the lower right quadrant, indicated that a rightmiddle ®nger response was required. For the pre- and post-tests, the two blocks of trials each contained 12 familiarization trials followed by 36 test trials, for a total of 48 trials per block. Within a block of test trials, half of the responses required a right-middle ®nger response and the other half an index ®nger response (left or right index ®nger depending on the condition). The ®nger pairing for the same-hand condition was the right middle and index ®ngers, while the ®nger pairing for the different-hand condition was the right-middle and left-index ®ngers. To minimize any order eects, the order of the hand conditions was counterbalanced across participants. 2.2.2. Practice conditions Participants were randomly assigned to one of three conditions (N 16 per condition), either a no practice condition or one of two practice conditions (a same-hand or a dierent-hand practice condition). The participants in the no practice condition performed the pre-test on the ®rst day and the post-test on the second day, with no practice on the task between these tests. Participants in the same-hand practice condition performed all practice trials using only the left-index and left-middle ®ngers. Participants in the dierent-hand practice condition performed all practice trials using only the right-index and left-middle ®ngers. For the practice trials, a target stimulus in the lower left quadrant indicated a left-middle ®nger response while a target stimulus in the lower right quadrant would indicate an index ®nger response (right or left depending on the practice condition). By practicing with the left hand, the eectors (i.e., speci®c ®ngers) involved during the practice and the testing sessions were dierent. Therefore, any change in reaction time pattern from pre-test to post-test are assumed to be due to changes in the cognitive processes. In other words, any bilateral transfer of the changes associated with the response-interference eect are due to cognitive or response-selection processes. 2.2.3. Sessions Each participant completed two sessions. The ®rst session consisted of the pre-test and one practice session, whereas the second session consisted of the second practice session followed by the post-test. During the ®rst session, each participant in a practice group performed the pre-test followed by 10 practice blocks of 48 trials each. Participants were given a one-minute rest interval between each practice block. In the second session, the participants performed 10 practice blocks of 48 trials each with a 1 min rest interval between practice blocks. Following the practice blocks during
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the second session, the participants were given a 10-minute rest interval in which they were allowed to read. After the rest interval, the participants performed a post-test, which was identical to the pre-test. The total number of practice trials was 960, which has been shown to be sucient practice to induce a change in response-selection processes (Proctor & Dutta, 1995). The sessions were conducted on consecutive days. 3. Results The reaction time data and total error data were analyzed for the test trials and the practice trials. The reported results are those found for the right-middle ®nger on the test trials and the left-middle ®nger on the practice trials. The analysis of the reaction times for the right-middle ®nger is consistent with Kornblum's (1965) initial analysis and the analyses from more recent studies (Hart & Reeve, 2000; Hasbroucq et al., 1995; Reeve & Proctor, 1988). Trials containing timing errors (e.g., reaction times less then 100 ms or greater than 500 ms) and response errors (e.g., incorrect responses) were not repeated and were eliminated from the reaction time analyses. 3.1. Analyses of the test trials The reaction time data for both the pre- and post-tests are presented in Table 1. A preliminary analysis was performed to ensure that the three groups were not significantly dierent prior to practice and that a dierent-hand advantage was initially present. 3.1.1. Pre-test reaction times The pre-test data for the right-middle ®nger were analyzed using a 3 2 (Practice Group Finger Pairing) analysis of variance with repeated measures on the last facTable 1 Mean reaction times and standard deviations (in parentheses) in milliseconds for the test trials for Experiment 1 Finger Pairing
Pairing
Practice group
Same-hand
Dierent-hand
Dierent-hand advantage
Same-hand Pre-test Post-test
309 (24.4) 288 (22.5)
302 (35.3) 281 (31.2)
7 7
Dierent-hand Pre-test Post-test
320 (43.9) 288 (45.6)
308 (40.6) 273 (33.1)
12 15
No practice Pre-test Post-test
300 (40.1) 301 (38.1)
286 (32.4) 286 (31.2)
14 15
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tor. The three levels of Practice Group were no practice, same-hand practice and different-hand practice. The two Finger Pairing levels were same-hand and dierenthand. The results of the analysis revealed no signi®cant dierences among the groups, F 2; 45 1:45; p > 0:05. The main eect for Finger Pairing was signi®cant, F 1; 45 10:22; p < 0:05, with the reaction times being slower for the same-hand condition (M 310) than the dierent-hand condition (M 299). The interaction of Practice Group and Finger Pairing was not signi®cant, F 2; 45 < 1:00. The lack of interaction signi®es that the eects of ®nger pairing were statistically equal for the three groups. 3.1.2. Pre-test and post-test reaction times The mean reaction times for the right-middle ®nger were analyzed using a 3 2 2 (Practice Group Test Finger Pairing) analysis of variance with repeated measures on the last two factors. The two levels of Test were pre-test and post-test. The results of the analysis revealed signi®cant main eects for Test, F 1; 45 33:73; p < 0:05, and Finger Pairing, F 1; 45 21:82; p < 0:05. The mean reaction times indicated slower reaction times for the pre-test (M 304 ms) than for the post-test (M 286 ms). Also, the same-hand ®nger pairing produced slower mean reaction times than the dierent-hand ®nger pairing with the mean reaction times of 301 and 289 ms, respectively. Neither the main eect for Practice Group, F 2; 45 < 1:00, nor the two-way interactions of Practice Group Finger Pairing, F 2; 45 < 1:0; p > 0:05, and Test Finger Pairing, F 1; 45 < 1:0, were signi®cant. The two-way interaction of Practice Group Test was signi®cant, F 2; 45 9:82; p < 0:05. The Practice Group Test interaction is presented in Fig. 1. The interaction was due to the decrease in reaction times for the same-hand and dierenthand practice groups from pre-test to post-test, but no change was observed for the
Fig. 1. Mean reaction times for the Test Practice Group Interaction in Experiment 1.
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no practice group. The three-way interaction was not signi®cant F 2; 45 < 1:00. Thus, practice resulted in faster reaction times for the bilateral transfer post-test, demonstrating that practice did enhance the response-selection processes. However, the magnitude of the dierent-hand advantage remained constant from pre-test to post-test for the three groups (e.g., no change in the response-interference eect). 3.1.3. Errors The analysis of the percent of total errors (response errors and timing errors) for the right-middle ®nger were analyzed using a 3 2 2 (Practice Group Test Finger Pairing) analysis of variance with repeated measures on the last two factors. The results of the analysis revealed a signi®cant main eect for Finger Pairing F 1; 45 5:76; p < 0:05. The errors were higher for the same-hand ®nger pairing (7.2%) than for the dierent-hand ®nger pairing (4.6%). No other main eect or interaction was signi®cant. 3.2. Analyses of practice trials Mean reaction times for the left-middle ®nger were analyzed by a 2 20 (Practice Group Block) analysis of variance with repeated measures on the last factor. The two levels of Practice Group were same-hand practice and dierent-hand practice. The Block levels were the 20 blocks of practice trials. Neither the main eect for Practice Group, F 1; 30 2:15; p 0:15, nor the two-way interaction of Group Block, F 19; 570 < 1:00, was found to be signi®cant. The reaction times for both groups tended to become faster as a function of practice, which was revealed by the signi®cant main eect for Block, F 19; 570 7:10; p < 0:05. The analysis of the percent of total errors did not reveal any signi®cant dierences of the main eects or the interaction. 4. Discussion The purpose of Experiment 1 was to examine the in¯uence of practice on the response-selection processes associated with the response-interference eect. The prediction was that if response-selection processes are the locus of the response-interference eect, then positive bilateral transfer should be observed on the response-interference eect. The signi®cant interaction of test and practice group revealed that bilateral transfer did occur indicating a change in the response-selection processes. The participants who were allowed to practice signi®cantly reduced their reaction times compared to the group of participants who did not receive practice trials. Although response-selection processes were in¯uenced by practice from pre- to post-test as shown by positive bilateral transfer, practice did not in¯uence the response-interference eect. The lack of a three-way interaction indicated that after practice, the dierent-hand advantage was still present for both of the groups receiving practice. Therefore, the response-interference eect was not in¯uenced by
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practice. These results suggest the speci®city of practice eect found by Hart and Reeve (2000) appears not to be due to response-selection processes. 5. Experiment 2 In a previous study of the response-interference eect, Reeve and Hart (in press) had participants perform a two-choice task with two hand conditions and two priming conditions. For the primed trials, the required response was signaled prior to the presentation of the target stimulus. For the unprimed trials, the required response was not signaled until the presentation of the target stimulus. The results of their study indicated a same-hand advantage for the primed trials and a dierent-hand advantage for the unprimed trials. It was concluded that for the primed trials, the response-selection processes were minimal during the reaction time interval, therefore resulting in a dierent preparation strategy (i.e., individual response-preparation strategy). The primed trials eliminated the need to use a multiple preparation strategy, resulting in the elimination and even the reversal of the dierent-hand advantage. In the present study, Experiment 2 examined changes on unprimed trials that result as a function of practice on primed trials. The purpose of Experiment 2 was to examine the in¯uence of practice on the response-implementation processes that have been proposed to be associated with the response-interference eect (Alain et al., 1993; Hasbroucq et al., 1995; Reeve & Proctor, 1988). A priming technique was used to allow response-selection processes to be completed prior to the presentation of the stimulus (Rosenbaum & Kornblum, 1982). Thus, providing practice of primarily the response-implementation processes during the reaction-time interval. If the eciency of the implementation processes is improved with practice, then a change in the response-interference eect (i.e., the different-hand advantage) should be observed on unprimed test trials. 6. Method 6.1. Participants 48 (36 females and 12 males) volunteer undergraduate students served as participants. Each participant signed an informed consent prior to participation in this study, and general instructions were given in written and verbal form prior to the actual testing. Participants did not have prior exposure to the task (i.e., the individuals had not participated in previous response-interference experiments), nor did any have knowledge of the hypotheses being tested. 6.2. Tasks For the pre-test and the post-test, the tasks were the same as that used in Experiment 1. However, for all practice trials the participants were informed (e.g., primed)
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prior to the presentation of the stimulus, which response would be required. Also, unlike Experiment 1, the ®nger pairings used for practice trials were the same as those used for the test trials. 6.2.1. Pre- and post-tests For all three groups, two hand conditions (a same-hand and a dierent-hand condition) were tested in two blocks of trials in both the pre- and post-tests. The foreperiods, stimulus patterns, and ®nger pairings for the two hand conditions were the same as those used in Experiment 1. The order of the blocks was counterbalanced across participants to minimize any potential order eects. 6.2.2. Practice conditions Participants were randomly assigned to one of three conditions, either a no practice (control) condition or one of two practice conditions, a same-hand practice or a different-hand practice. The participants in the no practice condition performed the pre-test on the ®rst day and the post-test on the second day, with no practice on the task between these tests. Participants in the same-hand practice condition performed all practice trials with only the right index and middle ®ngers on the response keys, while participants in the dierent-hand practice condition performed all practice trials with only the left-index and right-middle ®ngers on the response keys. The practice sessions and the total number of trials were the same as those used in Experiment 1. For the practice blocks, all responses were primed with half of the responses requiring a right-middle ®nger response with the other half requiring an index ®nger response (left or right index ®nger depending on the practice condition). The warning stimulus (the ®xation cross) for the primed trials was the same as used for the unprimed trials, but the cue contained only one asterisk (i.e., the prime) in either the upper left or right quadrant of the ®xation cross (see Fig. 2). As in Experiment 1, variable foreperiods of 500, 750, and 1000 ms were used to reduce the ability of the participants to anticipate the presentation of the stimulus. The prime indicated the target stimulus, which was presented directly under the cue. Thus, the prime was entirely valid on all practice trials. 7. Results The reaction time data and total error data were analyzed for the test trials and the practice trials as in Experiment 1 with the exception of the practice trials. Unlike Experiment 1, the right-middle ®nger data were used for the practice trials. 7.1. Analyses of test trials The mean reaction time data for both the pre- and post-tests are presented in Table 2. A preliminary analysis was performed to ensure that the three groups were not signi®cantly dierent prior to practice and that a dierent-hand advantage was initially present.
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Fig. 2. An illustration of the warning, cue, and target stimulus patterns for primed trials. The target in the left column indicates that a keypress would be made by the index ®nger, while the right column indicates that a keypress would be made by the right-middle ®nger. (Note. The cue serves as the prime.)
7.1.1. Pre-test reaction times The pre-test data for the right-middle ®nger were analyzed using a 3 2 (Practice Group Finger Pairing) analysis of variance with repeated measures on the last factor. The results of the analysis revealed no signi®cant main eect for Practice Group, F 2; 45 < 1:00. The main eect for Finger Pairing was signi®cant, F 1; 45
Table 2 Mean reaction times and standard deviations (in parentheses) in milliseconds for the test trials for Experiment 2 Pairing
Finger Pairing Practice group
Same-hand
Dierent-hand
Same-hand Pre-test Post-test
Dierent-hand advantage
321 (41.3) 295 (24.0)
313 (29.4) 292 (21.4)
8 3
Dierent-hand Pre-test Post-test
311 (22.3) 304 (25.4)
302 (21.9) 284 (21.3)
9 20
No practice Pre-test Post-test
315 (33.2) 302 (25.6)
304 (30.2) 301 (27.2)
11 1
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8:54; p < 0:05, with the reaction times being slower for the same-hand condition M 316 than the dierent-hand condition (M 306). The interaction of Practice Group and Finger Pairing was not signi®cant, F 2; 45 < 1:00. The lack of interaction signi®es that the eects of ®nger pairing were statistically equal for the three groups. 7.1.2. Pre-test and post-test reaction times Because the preliminary analysis revealed a dierent-hand advantage for the three groups and no dierences among the groups, the reaction time analysis for all the test trials was conducted. The mean reaction times for the right-middle ®nger were analyzed using a 3 2 2 (Practice Group Test Finger Pairing) analysis of variance with repeated measures on the last two factors. The results of the analysis revealed signi®cant main eects for Test, F 1; 45 22:38; p < 0:05, and Finger Pairing, F 1; 45 12:41; p < 0:05. The means indicated slower reaction times for the pre-test (M 311 ms) than for the post-test (M 296 ms). Also, the same-hand ®nger pairing produced slower mean reaction times than the dierent-hand ®nger pairing with mean reaction times of 308 and 299 ms, respectively. Neither the main eect for Group, F 2; 45 < 1:00, nor the two-way interactions of Group Paring, F 2; 45 1:41; p > 0:05, Group Test, F 2; 45 2:26; p > 0:05 and Test Finger Pairing F 1; 45 < 1:00, were found to be signi®cant. However, the three-way interaction was signi®cant, F 2; 45 3:85; p < 0:05. The three-way interaction is shown in Fig. 3. Practice with the same-hand ®nger pairing reduced the magnitude of the dierent-hand advantage from 8 ms on the pre-test to 3 ms on the post-test. The opposite eect was found for the group that practiced using the dierent-hand ®nger pairing. The magnitude of the dierent-hand advantage increased from 9 ms on the pre-test to 20 ms on the posttest. 1 7.1.3. Errors For the test trials, the percent of total errors (response errors and timing errors) for the right-middle ®nger were analyzed using a 3 2 2 (Practice Group Test Finger Pairing) analysis of variance with repeated measures on the last two factors. The results of the analysis revealed no signi®cant main eects or interactions.
1
The dierent-hand advantage for the no practice group was 11 ms for the pre-test but only 1 ms for the post-test. However, for this group the overall reaction times did not decrease as they did for the same-hand and dierent-hand practice groups. Additionally, a separate 2 2 (Test Finger Pairing) analysis of variance with repeated measures for the data from the no practice group indicated no signi®cant eects. These results indicated that there were no signi®cant changes in the reaction time patterns for the no practice condition. Similar analyses for the other two groups indicated a signi®cant main eect for Test (same-hand practice, F 1; 15 13:36; p < 0:05, and dierent-hand practice, F 1; 15 4:71; p < 0:05. Thus, the signi®cant three-way interaction indicated a speci®city of practice in¯uence on the responseinterference eect for the two groups that received practice.
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Fig. 3. Three-way Interaction for Practice Group Test Finger Pairing in Experiment 2.
7.2. Analyses of practice trials Mean reaction times for the right-middle ®nger were analyzed by a 2 20 (Practice Group Block) analysis of variance with repeated measures on the last factor. The two levels of Practice Group were same-hand practice and dierent-hand practice. The Block levels were the 20 blocks of practice trials. Neither the main eect for Practice Group, F 1; 30 < 1:00, nor the two-way interaction of Practice Group Block, F 19; 570 1:40; p > 0:05, was found to be signi®cant. The reaction times for both groups tended to become faster as a function of practice which was revealed by the signi®cant main eect for Block, F 19; 570 8:45; p < 0:05.
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The percent of total errors were calculated for the right-middle ®nger and analyzed by a 2 20 (Practice Group Block) analysis of variance with repeated measures on the last factor. The main eect of Block was found to be signi®cant, F 19; 570 1:98; p < 0:05. The percentage of errors increased over the practice blocks. The increase in the percentage of errors was not due to response errors (incorrect response), but was due to the timing errors associated with anticipation (reaction times less than 100 ms). Therefore, the increase in total errors was a result of faster responses by the participants as a result of practice, which is consistent with the reaction time data found in other studies (Dutta & Proctor, 1992; Proctor & Dutta, 1995). No other signi®cant dierences were revealed. 7.3. Discussion The purpose of this second experiment was to examine response-implementation processes associated with the response-interference eect. The reaction time results from the pre-test to the post-test indicated a speci®city of practice eect (Schmidt & Lee, 1999). After practicing with the dierent-hand condition, an 11 ms increase in the magnitude of the dierent-hand advantage was found from pre-test to posttest. More importantly, practice under the same-hand condition resulted in a change in the response-interference eect as indicated by a decrease in the dierent-hand advantage. The magnitude of the dierent-hand advantage decreased 5 ms from the pre-test to the post-test. These results suggest that the response-interference eect was in¯uenced speci®cally as a function of the practice. Because the practice trials were primed, the response-selection processes during the reaction time interval were minimized (Klapp, 1996). Therefore, the processes that were in¯uenced by practice are assumed to be the implementation processes. The results of this study indicate that the response-implementation processes associated with the response-interference eect are in¯uenced by practice. 8. General discussion In a two-choice task, the response-interference eect is an increase in reaction times when the two possible responses are from the same hand rather than from different hands (Kornblum, 1965; Reeve & Proctor, 1988). The response-interference eect, as illustrated by a dierent-hand advantage in reaction times for two-choice tasks is a robust ®nding (Alain et al., 1993; Hasbroucq et al., 1995; Reeve & Hart, in press; Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982). The present study examined the role of response-selection and response-implementation processes, which have been proposed to explain the source of the response-interference eect. In Experiment 1, a bilateral transfer design was used to examine the in¯uence of practice on the response-interference eect. In a bilateral design, positive transfer is assumed to be due to changes in response-selection processes (Magill, 1998). Therefore, positive bilateral transfer occurring after practice would be taken as a change in the response-selection processes in¯uencing the response-interference eect. The
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results of the reaction time data indicated that practice resulted in faster reaction times for the post-test than the pre-test. Therefore, changes in response-selection processes did occur which are consistent with other studies (Dutta & Proctor, 1992; Pashler & Baylis, 1991; Proctor & Dutta, 1995; Proctor & Reeve, 1988; Proctor et al., 1991), but those processes involved in the response-interference eect were not in¯uenced by practice. Thus, the results of Experiment 1 did not support responseselection processes as the source of the response-interference eect with only two ®ngers in contact with the response keys. Experiment 2 was designed to examine the in¯uence of practice on response-implementation processes associated with the response-interference eect. To minimize the response-selection processes during the reaction time interval for this experiment, all practice trials were primed. Thus, practice of the response-implementation processes was maximized. The results of Experiment 2 indicated a speci®city of practice eect (Schmidt & Lee, 1999). The participants who practiced under the same-hand condition decreased the magnitude of the dierent-hand advantage, whereas the participants who practiced under the dierent-hand condition increased the magnitude of the dierent-hand advantage. These results of practice in¯uencing response-implementation processes are consistent with other studies that have examined the response-complexity eect (Klapp, 1995, 1996). For the two-®nger condition, the combined results of these two experiments provide support for the response-implementation hypothesis (Hasbroucq et al., 1995). The results of these two experiments suggest that the response-interference eect when only two ®ngers are in contact with response keys is due to mechanical constraints associated with the anatomical similarities between the two responses in the same-hand condition. The results of the ®rst experiment suggest that the response-selection processes are similar for the two hand conditions and are not in¯uenced by practice, while the results of the second experiment suggest dierent response-implementation processes for the two hand conditions. The conclusion that response-implementation processes are the source of the response-interference eect is consistent with the conclusion found in other research (Alain et al., 1993; Hasbroucq, Guiard, & Kornblum, 1989; Hasbroucq et al., 1995; Shulman & McConkie, 1973). The combined results of the two experiments negate the role of response-selection processes as the source of the response interference when it is present, such as when two ®ngers are in contact with the response keys. However, the results do not provide an explanation as to what factors determine when response interference will be present. The response-preparation hypothesis (Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982) was proposed to explain when response interference would be present. Therefore, to completely accept the response-implementation hypothesis and discount the response-preparation hypothesis (i.e., response-selection processes) entirely, may be premature. In one aspect, the response-preparation hypothesis has not been tested for more dicult choice reaction-time situations (i.e., when four ®ngers are in contact with response keys). The response-preparation hypothesis (Reeve & Proctor, 1988) proposes that the number of ®ngers placed on the response keys determines which preparation strategy is adopted. When two ®ngers are on the
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response keys it is proposed that a multiple preparation strategy is adopted. However, when more than two ®ngers are contacting the response keys an individual preparation strategy is adopted. When two ®ngers are in contact with the response keys, a multiple preparation strategy would be used for both hand conditions. Therefore, Experiment 1 determined that the response-selection processes were essentially the same for the two hand conditions. However, the response-preparation hypothesis cannot be completely discarded as a possible explanation for the changes that occur in the response-interference eect when more than two ®ngers are in contact with the response keys (Reeve & Hart, in press). As suggested by the response-preparation hypothesis, the selection of dierent preparation strategies will determine when response interference will be present. The dierent preparation strategies were not directly tested in the present study, nor have they been directly tested in other studies (Hasbroucq et al., 1995). This fact combined with the results of other studies (Reeve and Hart, 2000; Reeve & Proctor, 1988; Rosenbaum & Kornblum, 1982) would seem to indicate that the rejection of the response-preparation hypothesis is premature. Therefore, to adequately explain the response-interference eect and the changes that occur due to various manipulations, a hypothesis that combines both the response-preparation hypothesis and the response-implementation hypothesis may be required. In conclusion, the results of these studies do point to the importance of responseimplementation processes in two-choice situations such as those studied by Kornblum (1965) and others (Hart & Reeve, 2000; Hasbroucq et al., 1995; Reeve & Hart, in press; Reeve & Proctor, 1988). More importantly, the present study demonstrated that response-implementation processes are subject to change with practice, which is consistent with other studies (Klapp, 1995, 1996). Further research is needed to better understand the response-interference eect. Speci®cally, the response-preparation hypothesis needs to be more thoroughly examined. One method to gain a greater understanding of the response-interference eect is to examine the in¯uence of practice on the reaction time patterns for choice tasks which use the same-hand and dierent-hand ®nger pairings when more than two ®ngers are involved. The goal of future research should be to build a model that accounts for the response-interference eect under all conditions. The model should address the factors that predict the presence or absence of response interference. This model may need to include both response-selection and response-implementation processes to resolve the inconsistent results among the various studies of the response-interference eect. References Alain, C., Buckolz, E., & Taktak, K. (1993). Same-hand and dierent-hand ®nger pairings in two-choice reaction time: Presence or absence of response competition. Journal of Motor Behavior, 25, 45±51. Dutta, A., & Proctor, R. W. (1992). Persistence of stimulus±response compatibility eects with extended practice. Journal of Experimental Psychology: Learning, Memory, and Cognition, 18, 801±809. Hart, M. A., & Reeve, T. G. (2000). Speci®city of practice eects on response interference in a two-choice task. Journal of Human Movement Studies, 38, 225±234.
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