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Humans’ Choice between Different Reinforcer Amounts and Delays: Effects of Choice Procedures and Monetary Deduction
LEARNING AND MOTIVATION ARTICLE NO.
28, 102–117 (1997)
LM960956
Humans’ Choice between Different Reinforcer Amounts and Delays: Effects of Choice Procedures and Monetary Deduction MASATO ITO, KIYOKO NAKAMURA,
AND
SHIGERU KUWATA
Osaka City University, Osaka, Japan Human subjects were exposed to concurrent-chains schedules in which reinforcer amounts or delays were varied in the terminal links and consummatory responses were required to receive points later exchangeable for money. Two independent variable-interval 30-s schedules or a single variable-interval 15-s schedule were in effect during the initial links and delay periods were defined by fixed-time schedules used in the terminal links. In addition to varying reinforcer amount and delay, two different choice procedures were studied for two different groups and a monetary deduction procedure was studied, within subjects, under independent scheduling procedure. The human subjects preferred the larger of two different reinforcer amounts and the shorter of two different reinforcer delays. The degree of preference was higher in the independent scheduling procedure than in the nonindependent scheduling procedure and there was no substantial difference in preference between the absence and presence of the monetary deduction procedure. q 1997 Academic Press
Human choice has been studied with concurrent and concurrent-chains schedules designed to resemble as closely as possible animal procedures (e.g., Belke, Pierce, & Powell, 1989; Logue, Pena-Correal, Rodriguez, & Kabela, 1986; cf. Matthews, Shimoff, Catania, & Sagvolden, 1977). Investigators have examined factors thought to influence human choice, such as qualitative differences in reinforcers (Millar & Navarick, 1984, video game; Navarick, 1982, noise; Logue et al., 1986, points), the presence or absence of a consummatory response (King & Logue, 1990; Matthews et al., 1977), changeover delay duration (Catania & Cutts, 1963; King & Logue, 1987), difference in choice procedures (Logue, King, Chavarro, & Volpe, 1990), and monetary deduction (Logue et al., 1990).
This study was supported by Grant-in-Aid for Scientific Research (C) of the Japanese Ministry of Education, Science and Culture (No. 06610080). Address reprint requests to Masato Ito, Department of Psychology, Osaka City University, 3-3-138, Sugimoto, Sumiyoshiku, Osaka 558, Japan. 102 0023-9690/97 $25.00 Copyright q 1997 by Academic Press All rights of reproduction in any form reserved.
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With respect to qualitative differences in reinforcers, Belke et al. (1989), using a concurrent-chains procedure, found that human behavior reinforced with points exchangeable for money was less sensitive to variations in reinforcer delays than pigeons’ behavior reinforced with food. This finding is consistent with the results of Logue et al.’s (1986) study obtained in a selfcontrol paradigm in which subjects chose between larger, more delayed and smaller, less delayed reinforcers (points as a reinforcer), revealing that human subjects showed self-control, that is, they chose the larger, more delayed reinforcer, whereas pigeons showed impulsiveness, that is, they chose the smaller, less delayed food reinforcer. On the other hand, humans’ impulsiveness was shown in the choice situation using video game-playing as a reinforcer (Millar & Navarick, 1984). In the context of negative reinforcement, Navarick (1982) found that most human subjects showed impulsiveness rather than self-control in a self-control paradigm using noise reduction as a reinforcer. These results indicate that secondary reinforcers such as points later exchangeable for money tend to produce self-control, whereas intrinsically accessible reinforcers (i.e., primary reinforcers) such as food, video gameplaying or noise reduction tend to produce impulsiveness in a self-control paradigm. However, a recent work by Forzano and Logue (1994) using an adjusting-delay procedure (cf. Mazur, 1988) provided inconsistent data, showing that in human subjects a higher sensitivity of reinforcer amount relative to reinforcer delay was evident irrespective of the difference in the type of reinforcers (juice vs. points) and also that the time of delivery of reinforcers affected the degree of self-control in humans. Although they used an adjusting-delay procedure, which has not usually been studied in the self-control choice situation, the results suggest that the difference in the time of delivery of reinforcers may in part explain the different effects of primary and secondary reinforcers on self-control choices. King and Logue (1987) examined the changeover delay (COD) duration in a self-control paradigm under three different COD durations (i.e., 1, 15, and 30 s). In a two-alternative choice situation, the COD insures a separation in time between a changeover response and a subsequent reinforced response, preventing the adventitious reinforcement of the changeover and the reinforced response sequence (cf. de Villiers, 1977). They found that increasing the COD duration significantly increased the subjects’ sensitivity to variation in reinforcer amount, although subjects were indifferent between two alternatives at the 1-s COD. This result is consistent with that of the previous study by Catania and Cutts (1963) who examined the effects of a COD between 2 and 15 s on human choice under concurrent schedules. The method of delivering reinforcer amount may have a significant effect on human choice. For example, King and Logue (1990) examined two different methods of reinforcer delivery in two separate experiments, and showed that human sensitivity to variation in reinforcer amount was higher in the presence of a consummatory response than in the absence of a consummatory response.
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Their results were consistent with those of the previous study (e.g., Matthews et al., 1977; Wurster & Griffiths, 1979), but inconsistent with those of some studies showing sensitivity to reinforcer amount without a consummatory response (e.g., Buskist, Oliveira-Castro, & Bennett, 1988; McDowell & Wood, 1984). King and Logue pointed out the important role of feedback that the subjects receive concerning the consequences of responding, and it was argued that the differing results with respect to the use of a consummatory response could be explained by the difference in the degree of this feedback. The effects on human choice of different types of choice (i.e., independent and nonindependent scheduling) procedures and a monetary deduction procedure have been examined in a series of experiments by Logue et al. (1990) who varied reinforcer amount and/or delay in concurrent variable-interval, variable-interval (VI VI) schedules of different types with and without a monetary deduction procedure. In the monetary deduction procedure, a random number of points was deducted from the counter every 15 s during the entire session, independently of the subject’s behavior to simulate the decrease and increase in the subject’s energy supply that occurs when food is the reinforcer, as in the pigeons. To assess the effectiveness of the choice procedures in evaluating human self-control choice, they employed two different choice procedures (i.e., independent and nonindependent scheduling procedures). For the nonindependent scheduling (i.e., forced-choice) procedure, a single VI schedule was used to equate reinforcement rate for two alternatives and the available alternative was assigned either to the right or to the left in a quasirandom sequence (e.g., Stubbs & Pliskoff, 1969), whereas two independent VI schedules were used for the independent scheduling (i.e., free-choice) procedure. Considering the experimental procedures across five experiments, however, the presence or absence of a monetary deduction procedure was used only under nonindependent concurrent schedules (e.g., Experiments 2 and 3), while two different types of a concurrent schedule were examined under the monetary deduction condition (e.g., Experiments 1 and 3). They compared the results of Experiments 2 and 3 and found that in the nonindependent scheduling procedure, there was no difference in sensitivity to variation in reinforcer amount or delay between the presence and absence of the monetary deduction. Furthermore, concerning different types of choice procedure, they showed that with the monetary deduction, sensitivity to variation in reinforcer amount or delay was higher in the independent scheduling procedure than in the nonindependent scheduling procedure. Taking these results together, it seems that the independent scheduling procedure with the monetary deduction may have a significant effect on sensitivity to variation in reinforcer amount or delay, as in the case of pigeons (Chavarro & Logue, 1988). Although the monetary deduction procedure had no significant effect on humans’ sensitivity to reinforcer amount or delay under the nonindependent scheduling procedure, it is unclear to what extent the independent scheduling procedure per se
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affects sensitivity to variations in reinforcer amount or delay without the monetary deduction, and moreover, it is not clear whether the monetary deduction procedure may increase sensitivity to reinforcer amount and delay under the independent scheduling procedure. Therefore, it would be preferable to address these questions for the understanding of human choice. In the present experiment, the effect of the monetary deduction procedure was studied, within subjects, under the independent scheduling procedure, and also the effects of two different choice procedures (i.e., independent and nonindependent scheduling procedures) were studied for two different groups when the monetary deduction is absent. METHOD
Subjects The participants were eight adult undergraduate students (four males and four females) between 18 and 22 years of age. They were recruited for participation. The participants were divided into two groups; the participants in one group were numbered 51 through 54 and those in the other group were numbered 71 through 74. None of the participants was a psychology major. Apparatus The experiment was conducted in a small room (3.6 m by 2.8 m). A 14in. color CRT monitor with a touch panel (MicroTouch Systems Inc.) was placed on the desk, and was separated by a large panel from a personal computer (NEC PC-9801U2) and the experimenter. A touch to the circles presented on the screen of the monitor was defined as a response. A personal computer was programmed to present stimuli (i.e., colored circles and counters) on the screen of the monitor, control the experiment, and record events. The screen of the monitor contained three colored circles and counters (see Fig. 1). Two colored circles, 5.0 cm in diameter, were located in the center of the screen and 11 cm apart (from center to center). A small colored circle was located 7.0 cm below the center and 13.5 cm from the sides. Of three counters, two side counters were located below the large circles and the remaining one (i.e., center counter) was above the small circle. A touch to the circles produced a brief beep as a feedback showing that response was effective. Procedure Subjects were seated before the monitor and required to leave all metal objects outside (i.e., watches and jewelry) to minimize interference with the touch panel during the session. They were then given the following minimal instructions (in Japanese) as to what they were to do: Please read repeatedly until you understand. Do not ask for additional instructions. You may play a game. Your task is to earn money as much as you can. Money will
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FIG. 1. A display of the monitor used in the experiment.
be accumulated on the counter and you will receive total amounts of money accumulated on the counter after the session ends. Each session is 20 min in duration. You may touch anything on the screen to earn money, but you have to touch with a forefinger. A brief beep sound will be provided if a response is effective. The session will begin when three white circles come on.
A concurrent-chains schedule was employed with two different types of initial-link schedules (i.e., choice phase); the independent scheduling procedure was used for one group of subjects (numbered 51 through 54), while the nonindependent scheduling procedure was used for the other group of subjects (numbered 71 through 74). During the choice phase, three white circles and the counter were presented on the screen of the monitor. Each circle was colored with white (the background color of the screen was black). After entry into either of the terminal links (i.e., delay period), only the circle not selected was darkened and the other circle was lit with either blue or yellow. Entry into either of the terminal links was arranged by two independent VI 30-s VI 30-s schedules for the independent scheduling procedure (see Fig. 2), or by the single VI 15-s schedule for the nonindependent scheduling procedure (see Fig. 3). Each interval of the VI tape was derived from the distribution of Fleshler and Hoffman (1962). As each interval in one of the VI schedules timed out, the timer stopped and reinforcement was assigned to the appropriate side. In the nonindependent scheduling procedure, however, reinforcement was assigned quasirandomly, with equal probability to either the left or the right circle (e.g., Stubbs & Pliskoff, 1969). A 3-s changeover delay (COD) was used for both the independent and nonindependent scheduling procedures. In this COD procedure, 3 s had to elapse after a changeover response from the right to the left circle or vice versa before a subsequent
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FIG. 2. A schematic diagram of the independent scheduling (free-choice) procedure used in the experiment.
response made it possible to enter into the delay period. The next response on the appropriate circle initiated the delay period defined by the fixed-time (FT) schedule. After the delay, the reinforcer access period was in effect, during which the small circle was illuminated with red and either the left- or the right-side counter was presented on the screen. Each response to the red circle accumulated a prescribed point (i.e., points were worth 1 yen) on the side counter and on the center counter in which the total number of points was accumulated. However, the side counter was always reset at the start of the next cycle. Then a timeout period followed the shorter delay. The timeout period was used to equate overall rates of reinforcement on two alternatives. In a monetary deduction procedure, the method of monetary deduction used in the present experiment was similar to that of Logue et al. (1990). The center counter was set at 720 yen at the start of the session for the
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FIG. 3. A schematic diagram of the nonindependent scheduling (forced-choice) procedure used in the experiment.
reinforcer amount condition and 780 yen for the reinforcer delay condition. These values ensured that the counter would decrease to 0 yen at the end of a 20-min session if the subject received no reinforcers. During the session, an average of 10 yen was deducted from the counter every 15 s, independently of the subject’s response, except for the reinforcer access period. The subjects numbered 51 through 54 were exposed to the monetary deduction procedure. The experiment consisted of three conditions, that is, baseline, reinforcer amount, and reinforcer delay conditions. In baseline, reinforcer amount was .03 yen and reinforcer delay was 5 s for two alternatives. For the reinforcer amount condition, reinforcer amounts were varied and delays were kept constant across two alternatives. Two different reinforcer amounts of .03 and .60 yen (for a consummatory response) were used and there were two conditions in which the side to which the larger amount was assigned was reversed to control for position and color bias. For the reinforcer delay condition, contrary
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to the reinforcer amount condition, reinforcer delays were varied and amounts were kept constant across two alternatives. Two different reinforcer delays of 5 s and 100 s were used and there were two conditions in which the side to which the shorter delay was assigned was reversed as in the reinforcer amount condition. Each condition was presented once in a random sequence except for baseline; if the subject was not indifferent between two alternatives in the baseline, however, the baseline condition was replicated. The order of the conditions is shown in Table 1. Each session was 20 min in duration and three 20-min sessions were conducted per day. The experiment was conducted over two days for each subject. At the start of the session, the subjects were exposed to four ‘‘forced-choice cycles’’ (trials) in which only one alternative was presented at once and with equal opportunity (i.e., two right and two left alternatives were presented in a random sequence) except for baseline condition. These forced-choice cycles were not included in a 20-min session and never used in data analysis. Each subject completed a questionnaire asking how he (or she) did during the experiment and they received the money earned at the end of each session. RESULTS
Table 1 shows the number of responses for both left and right circles, choice proportions, the number of cycles, and the order of conditions for each subject. The number of consummatory responses is also shown in Table 1. For all but baseline condition, data were combined across two sessions. Choice proportions for the larger of two reinforcers or the shorter of two delays were higher in the independent scheduling (free-choice) procedure than in the nonindependent scheduling (forced-choice) procedure. Figure 4 shows the choice proportions for larger reinforcers or less delayed reinforcers under the reinforcer amount and delay conditions for each subject. The left half of the figure shows the data under the independent scheduling procedure for the subjects numbered S51 through S54 and the right half of the figure shows the data under the nonindependent scheduling procedure for the subjects numbered S71 through S74. The white bars represent the absence of monetary deduction, while the shadowed bars represent the presence of monetary deduction. In addition, the black bars represent the baseline condition. Choice proportions were calculated by dividing choice responses for the larger amount or shorter delay by the total choice responses (except for the baseline). Choice proportions for the larger amount or shorter delay reinforcer were combined across two sessions for each condition. In the baseline condition, however, choice proportions were based on data from a session or the second session if the session was replicated. Choice proportions in the baseline were around .50 (i.e., indifference) for most subjects. In the nonindependent scheduling procedure, the choice proportions ranged from .52 to .68 for the reinforcer amount condition and from .51 to .67 for the reinforcer delay condition. In contrast, the choice proportions in the
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S51
Subject
.03 .60 .03 .03
6 8 7 9
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5 3 4 2 7 9 6 8
.03
.03 .60 .03 .03
4 2 5 3
1
.03
Al
1
Order
Dl
.03 5 No deduction .60 5 .03 5 .03 5 .03 100 Deduction .60 5 .03 5 .03 5 .03 100
5
Dr
lma
5 5 100 5
5 5 100 5
5
5 5 100 5
5 5 100 5
Delay (s)
.03 5 No deduction .60 5 .03 5 .03 5 .03 100 Deduction .60 5 .03 5 .03 5 .03 100
Ar
Points (yen)
317 670 130 119
366 1145 228 72
534
63 269 94 21
84 152 62 44
222
Left
632 316 70 328
923 315 87 297
541
167 42 49 113
156 112 12 64
242
Right
Responses
.666 .680 .650 .734
.716 .784 .724 .805
.503
.726 .865 .657 .843
.650 .576 .838 .593
.522
Choice prop.
41 42 11 10
40 40 10 10
38
38 30 10 10
39 39 10 10
53
Cycles
399 570 132 140
366 543 148 72
324
195 478 123 57
139 380 148 28
381
Left
493 476 118 148
494 352 90 172
361
474 61 68 139
439 260 22 82
419
Right
Consummatory responses
TABLE 1 Values of Reinforcer Amount (A) and Delay (D) for the Left (l) and Right (r) Circles, Number of Choice Responses, Consummatory Responses, and Cycles during a 20-Min Session, Choice Proportions for the Larger, or Less Delayed Reinforcers and Order of Conditions for Each Subject
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S53 1
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.03 .60 .03 .03
5 3 4 2 1 4 2 5 3
.03 .60 .03 .03
.03
.03 .60 .03 .03
.03 .60 .03 .03
7 9 6 8
1
4 2 5 3
6 8 7 9
.03
.03 .60 .03 .03 .03
5 5 5 5 100
.03 5 No deduction .60 5 .03 5 .03 5 .03 100 Deduction .60 5 .03 5 .03 5 .03 100
.03 5 No deduction .60 5 .03 5 .03 5 .03 100 Deduction .60 5 .03 5 .03 5 .03 100
5 5 5 100 5
5 5 100 5
5 5 100 5
5
5 5 100 5
5 5 100 5
5
961 1095 1050 226 208
3 865 1104 187
1136 3542 1099 2
486
46 1390 476 93
7 934 296 1
439
894 1347 1130 222 334
4258 358 22 265
2788 617 43 1175
365
1483 308 7 245
1017 4 0 232
483
.482 .552 .482 .504 .616
.999 .707 .980 .586
.710 .852 .962 .998
.429
.970 .819 .986 .725
.993 .960 1.0 .996
.524
40 45 46 11 11
31 31 9 9
38 39 9 10
20
32 37 9 10
32 32 9 10
34
152 315 261 80 54
42 240 149 61
366 797 295 30
151
40 636 185 92
68 614 189 28
363
159 323 244 84 84
825 110 41 84
610 326 49 275
88
750 196 40 162
655 53 31 231
378
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1 3 5 2 4
1 2 4 3 5
1 5 3 4 2
Order
.03 .03 .60 .03 .03
.03 .03 .60 .03 .03
.03 .03 .60 .03 .03
Al
.03 .60 .03 .03 .03
.03 .60 .03 .03 .03
.03 .60 .03 .03 .03
Ar
5 5 5 5 100
5 5 5 5 100
5 5 5 5 100
Dl
Dr
5 5 5 100 5
5 5 5 100 5
5 5 5 100 5
Delay (s)
303 154 270 42 48
1643 1437 2139 490 348
134 550 1643 638 118
Left
323 299 142 52 62
1768 1972 1261 444 419
178 1723 1768 259 201
Right
Responses
.516 .660 .655 .447 .564
.518 .578 .629 .525 .546
.571 .758 .482 .711 .630
Choice prop.
45 51 53 11 10
58 54 59 10 11
22 44 46 9 10
Cycles
289 520 660 85 87
530 478 465 69 74
169 204 431 53 54
Left
327 677 653 101 146
568 529 495 90 96
177 388 439 68 100
Right
Consummatory responses
Note. In baseline, choice proportions for the right circle were presented. Subjects S51 through S54 were exposed to the independent scheduling procedure, while subjects S71 through S74 were exposed to the nonindependent scheduling procedure.
S74
S73
S72
Subject
Points (yen)
TABLE 1—Continued
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FIG. 4. The choice proportions for the larger amount or the shorter delay reinforcers under several conditions for each subject. The subjects numbered S51 through S54 were exposed to the independent scheduling (free-choice) procedure, while the subjects numbered S71 through S74 were exposed to the nonindependent scheduling (forced-choice) procedure.
independent scheduling procedure ranged from .61 to .995 for the reinforcer amount condition and from .72 to .998 for the reinforcer delay condition. Applied to the combined data across the reinforcer amount and delay conditions, the Wilcoxon–Mann–Whitney test (Siegel & Castellan, 1988) revealed that the difference in choice proportions between two choice procedures was significant at p õ .05 (N Å 8, Wx Å 11). Thus, it is clear that the choice proportions were higher in the independent scheduling procedure than in the nonindependent scheduling procedure. With monetary deduction, choice proportions did not change substantially from those without monetary deduction; of eight cases across two conditions (i.e., reinforcer amount and delay condition) and four subjects, there were only three cases (two conditions of S51 and the reinforcer amount condition of S54) in which choice proportions with monetary deduction were greater than those without monetary deduction. The Wilcoxon signed ranks test revealed that there was no significant difference between the presence and absence of monetary deduction for both reinforcer amount and delay conditions. Therefore, the monetary deduction procedure does not increase choice proportions for the larger amount or shorter delay reinforcers in the independent scheduling procedure.
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FIG. 5. The mean choice proportions for the larger amount or the shorter delay reinforcers across subjects. Brackets indicate one standard deviation.
Figure 5 summarizes the results in which data were averaged across four subjects for each condition. Mean choice proportions for the larger reinforcer were .79 for the independent scheduling procedure and .61 for the nonindependent scheduling procedure. Similarly, mean choice proportions for the shorter delay were .81 for the independent scheduling procedure and .58 for the nonindependent scheduling procedure. With respect to the monetary deduction, choice proportions did not change substantially depending on the presence or absence of the monetary deduction; mean choice proportions for the larger reinforcer and shorter delay were .82 and .80, respectively, with monetary deduction, while mean choice proportions were .79 and .81 without monetary deduction. These results thus support the conclusion that choice proportions for the larger reinforcer or shorter delay are greater in the independent scheduling procedure than in the nonindependent scheduling procedure, and that the monetary deduction procedure does not increase choice proportions in the independent scheduling procedure. DISCUSSION
One of the purposes of the present study was to assess the effect of the monetary deduction on humans’ choice in the independent scheduling procedure. Choice proportions for larger reinforcers or shorter delay reinforcers did not differ substantially between the presence and absence of the monetary deduction when the independent scheduling procedure was used. This finding
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is consistent with the results of Logue et al. (1990) which showed that when the reinforcer amount and delay were varied separately under the nonindependent scheduling procedure, there was no significant difference in sensitivity to reinforcer amount or delay between the presence and absence of the monetary deduction procedure. Thus, it is clear that the monetary deduction procedure does not increase preference for the larger amount or shorter delay reinforcer under the independent and nonindependent scheduling procedures. A second purpose of the present study was to examine the effects of choice procedures on humans’ choice between two alternatives differing in reinforcer amount or delay. The present results demonstrated that choice proportions were higher in the independent scheduling procedure than in the nonindependent scheduling procedure when the monetary deduction was absent. This finding is consistent with the results of the matching analysis (see below), showing that human subjects are more sensitive to reinforcer amount and delay in the independent scheduling procedure than in the nonindependent scheduling procedure. In this respect, the present results extended those of Logue et al. (1990) to the situation where the monetary deduction is absent and to the situation where the points are exchangeable for yen rather than dollars, although the subjective values of points (money) may be different between two studies. Furthermore, the present results are in accordance with those of Chavarro and Logue (1988), who examined pigeons’ sensitivity to reinforcer amount and delay in two different types of concurrent VI VI schedules of reinforcement, by showing that when the choice procedures changed from the independent to the nonindependent scheduling procedures, there was a decrease in sensitivity to reinforcer amount and delay. In Logue et al.’s (1990) study with human subjects and Chavarro and Logue’s (1988) study with pigeons, only one condition of the reinforcer amount or delay was used and each condition was presented twice; the side to which the larger amount or shorter delay was assigned was reversed for each presentation. To obtain sensitivity values, a linear regression was applied to the log-transformed data by the following generalized matching equation (Baum, 1974):
SD
SD
(1)
SD
SD
(2)
log
R1 A1 Å Salog / log k R2 A2
or log
R1 D2 Å Sdlog / log k R2 D1
where A is the reinforcer amount, D is the delays to reinforcers, R is the number of responses to that alternative, and k, Sa and Sd are empirical constants. The parameters Sa and Sd represent the sensitivity to variations in reinforcer amount and delay, respectively.
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By using the matching analysis, for example, Logue et al. (1990) showed that, in the independent scheduling procedure, the averaged humans’ sensitivity values were 1.0 and .7 for the reinforcer amount and delay, respectively, while they were .6 and .3 in the nonindependent scheduling procedure. A similar result was also obtained in Chavarro and Logue (1988), who showed that in the independent scheduling procedure the averaged pigeons’ sensitivity values were 1.43 and .97 for the reinforcer amount and delay, respectively, and were .65 and .50 in the nonindependent scheduling procedure. Applied to the present results, the matching analysis revealed that the averaged sensitivity values obtained in the independent scheduling procedure were .67 and 1.02 for the reinforcer amount and delay, respectively, and the averaged sensitivity values were .16 and .10 in the nonindependent scheduling procedure. From these results, it seems that the sensitivity values for the reinforcer amount and delay are generally greater in the independent scheduling procedure than in the nonindependent scheduling procedure for human subjects and pigeons. Although these results support the conclusion that human subjects are more sensitive to the reinforcer amount or delay in the independent scheduling procedure, however, there is a limitation concerning the generality of the results since, as mentioned above, the regression analysis was based on a small number of points (only one condition or two conditions if the reversed condition was included) to determine sensitivity values by the matching analysis. It is, therefore, preferable to use more than three conditions for determining sensitivity values Sa and Sd . In summary, the present study demonstrated that the independent scheduling procedure per se had a significant effect on human choice between different reinforcer amounts or delays in terms of both choice proportions and sensitivity values, and that the monetary deduction procedure had no significant effect on humans’ choice proportions under the independent scheduling procedure. These results indicates that the independent scheduling procedure is useful for studying human choice without the monetary deduction procedure. REFERENCES Baum, W. H. (1974). On two types of deviation from the matching law: Bias and undermatching. Journal of the Experimental Analysis of Behavior, 22, 231–242. Belke, T. W., Pierce, W. D., & Powell, R. A. (1989). Determinants of choice for pigeons and humans on concurrent-chains schedules of reinforcement. Journal of the Experimental Analysis of Behavior, 52, 97–109. Buskist, W., Oliveira-Castro, J., & Bennett, R. (1988). Some effects of response-correlated increases in reinforcer magnitude on human behavior. Journal of the Experimental Analysis of Behavior, 49, 87–94. Catania, A. C., & Cutts, D. (1963). Experimental control of superstitious responding in humans. Journal of the Experimental Analysis of Behavior, 6, 203–208. Chavarro, A., & Logue, A. W. (1988). Sensitivity to amount and delay of reinforcement: Effects of different types of concurrent variable-interval schedules. The Psychological Record, 38, 421–435.
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de Villiers, P. (1977). Choice in concurrent schedules and a quantitative formulation of the law of effect. In W. K. Honig & J. E. R. Staddon (Eds.), Handbook of operant behavior (pp. 233–287). Englewood Cliffs, NJ: Prentice-Hall. Fleshler, M., & Hoffman, H. S. (1962). A progression for generating variable-interval schedules. Journal of the Experimental Analysis of Behavior, 5, 529–530. Forzano, L. B., & Logue, A. W. (1994). Self-control in adult humans: Comparison of qualitatively different reinforcers. Learning and Motivation, 25, 65–82. King, G. R., & Logue, A. W. (1987). Choice in a self-control paradigm with human subjects: Effects of changeover delay duration. Learning and Motivation, 18, 421–438. King, G. R., & Logue, A. W. (1990). Humans’ sensitivity to variation in reinforcer amount: Effects of the method of reinforcer delivery. Journal of the Experimental Analysis of Behavior, 53, 33–45. Logue, A. W., King, G. R., Chavarro, A., & Volpe, J. S. (1990). Matching and maximizing in a self-control paradigm using human subjects. Learning and Motivation, 21, 340–368. Logue, A. W., Pena-Correal, T. E., Rodriguez, M. L., & Kabela, E. (1986). Self-control in adult humans: Variation in positive reinforcer amount and delay. Journal of the Experimental Analysis of Behavior, 46, 159–173. Matthews, B. A., Shimoff, E., Catania, A. C., & Sagvolden, T. (1977). Uninstructed human responding: Sensitivity to ratio and interval contingencies. Journal of the Experimental Analysis of Behavior, 27, 453–467. Mazur, J. E. (1988). Estimation of indifference points with an adjusting-delay procedure. Journal of the Experimental Analysis of Behavior, 49, 37–47. McDowell, J. J., & Wood, H. M. (1984). Confirmation of linear system theory prediction: Changes in Herrnstein’s k as a function of changes in reinforcer magnitude. Journal of the Experimental Analysis of Behavior, 41, 183–192. Millar, A., & Navarick, D. J. (1984). Self-control and choice in humans: Effects of video game playing as a positive reinforcer. Learning and Motivation, 15, 203–218. Navarick, D. J. (1982). Negative reinforcement and choice in humans. Learning and Motivation, 13, 361–377. Siegel, S., & Castellan, Jr., N. J. (1988). Nonparametric statistics for the behavioral sciences (2nd ed.). New York: McGraw-Hill. Stubbs, D. A., & Pliskoff, S. S. (1969). Concurrent responding with fixed relative rate of reinforcement. Journal of the Experimental Analysis of Behavior, 12, 887–895. Wurster, R. M., & Griffiths, R. R. (1979). Human concurrent performances: Variation of reinforcer magnitude and rate of reinforcement. The Psychological Record, 29, 341–354. Received December 6, 1995 Revised June 21, 1996
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Humans’ Choice between Different Reinforcer Amounts and Delays: Effects of Choice Procedures and Monetary Deduction MASATO ITO, KIYOKO NAKAMURA,
AND
SHIGERU KUWATA
Osaka City University, Osaka, Japan Human subjects were exposed to concurrent-chains schedules in which reinforcer amounts or delays were varied in the terminal links and consummatory responses were required to receive points later exchangeable for money. Two independent variable-interval 30-s schedules or a single variable-interval 15-s schedule were in effect during the initial links and delay periods were defined by fixed-time schedules used in the terminal links. In addition to varying reinforcer amount and delay, two different choice procedures were studied for two different groups and a monetary deduction procedure was studied, within subjects, under independent scheduling procedure. The human subjects preferred the larger of two different reinforcer amounts and the shorter of two different reinforcer delays. The degree of preference was higher in the independent scheduling procedure than in the nonindependent scheduling procedure and there was no substantial difference in preference between the absence and presence of the monetary deduction procedure. q 1997 Academic Press
Human choice has been studied with concurrent and concurrent-chains schedules designed to resemble as closely as possible animal procedures (e.g., Belke, Pierce, & Powell, 1989; Logue, Pena-Correal, Rodriguez, & Kabela, 1986; cf. Matthews, Shimoff, Catania, & Sagvolden, 1977). Investigators have examined factors thought to influence human choice, such as qualitative differences in reinforcers (Millar & Navarick, 1984, video game; Navarick, 1982, noise; Logue et al., 1986, points), the presence or absence of a consummatory response (King & Logue, 1990; Matthews et al., 1977), changeover delay duration (Catania & Cutts, 1963; King & Logue, 1987), difference in choice procedures (Logue, King, Chavarro, & Volpe, 1990), and monetary deduction (Logue et al., 1990).
This study was supported by Grant-in-Aid for Scientific Research (C) of the Japanese Ministry of Education, Science and Culture (No. 06610080). Address reprint requests to Masato Ito, Department of Psychology, Osaka City University, 3-3-138, Sugimoto, Sumiyoshiku, Osaka 558, Japan. 102 0023-9690/97 $25.00 Copyright q 1997 by Academic Press All rights of reproduction in any form reserved.
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With respect to qualitative differences in reinforcers, Belke et al. (1989), using a concurrent-chains procedure, found that human behavior reinforced with points exchangeable for money was less sensitive to variations in reinforcer delays than pigeons’ behavior reinforced with food. This finding is consistent with the results of Logue et al.’s (1986) study obtained in a selfcontrol paradigm in which subjects chose between larger, more delayed and smaller, less delayed reinforcers (points as a reinforcer), revealing that human subjects showed self-control, that is, they chose the larger, more delayed reinforcer, whereas pigeons showed impulsiveness, that is, they chose the smaller, less delayed food reinforcer. On the other hand, humans’ impulsiveness was shown in the choice situation using video game-playing as a reinforcer (Millar & Navarick, 1984). In the context of negative reinforcement, Navarick (1982) found that most human subjects showed impulsiveness rather than self-control in a self-control paradigm using noise reduction as a reinforcer. These results indicate that secondary reinforcers such as points later exchangeable for money tend to produce self-control, whereas intrinsically accessible reinforcers (i.e., primary reinforcers) such as food, video gameplaying or noise reduction tend to produce impulsiveness in a self-control paradigm. However, a recent work by Forzano and Logue (1994) using an adjusting-delay procedure (cf. Mazur, 1988) provided inconsistent data, showing that in human subjects a higher sensitivity of reinforcer amount relative to reinforcer delay was evident irrespective of the difference in the type of reinforcers (juice vs. points) and also that the time of delivery of reinforcers affected the degree of self-control in humans. Although they used an adjusting-delay procedure, which has not usually been studied in the self-control choice situation, the results suggest that the difference in the time of delivery of reinforcers may in part explain the different effects of primary and secondary reinforcers on self-control choices. King and Logue (1987) examined the changeover delay (COD) duration in a self-control paradigm under three different COD durations (i.e., 1, 15, and 30 s). In a two-alternative choice situation, the COD insures a separation in time between a changeover response and a subsequent reinforced response, preventing the adventitious reinforcement of the changeover and the reinforced response sequence (cf. de Villiers, 1977). They found that increasing the COD duration significantly increased the subjects’ sensitivity to variation in reinforcer amount, although subjects were indifferent between two alternatives at the 1-s COD. This result is consistent with that of the previous study by Catania and Cutts (1963) who examined the effects of a COD between 2 and 15 s on human choice under concurrent schedules. The method of delivering reinforcer amount may have a significant effect on human choice. For example, King and Logue (1990) examined two different methods of reinforcer delivery in two separate experiments, and showed that human sensitivity to variation in reinforcer amount was higher in the presence of a consummatory response than in the absence of a consummatory response.
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Their results were consistent with those of the previous study (e.g., Matthews et al., 1977; Wurster & Griffiths, 1979), but inconsistent with those of some studies showing sensitivity to reinforcer amount without a consummatory response (e.g., Buskist, Oliveira-Castro, & Bennett, 1988; McDowell & Wood, 1984). King and Logue pointed out the important role of feedback that the subjects receive concerning the consequences of responding, and it was argued that the differing results with respect to the use of a consummatory response could be explained by the difference in the degree of this feedback. The effects on human choice of different types of choice (i.e., independent and nonindependent scheduling) procedures and a monetary deduction procedure have been examined in a series of experiments by Logue et al. (1990) who varied reinforcer amount and/or delay in concurrent variable-interval, variable-interval (VI VI) schedules of different types with and without a monetary deduction procedure. In the monetary deduction procedure, a random number of points was deducted from the counter every 15 s during the entire session, independently of the subject’s behavior to simulate the decrease and increase in the subject’s energy supply that occurs when food is the reinforcer, as in the pigeons. To assess the effectiveness of the choice procedures in evaluating human self-control choice, they employed two different choice procedures (i.e., independent and nonindependent scheduling procedures). For the nonindependent scheduling (i.e., forced-choice) procedure, a single VI schedule was used to equate reinforcement rate for two alternatives and the available alternative was assigned either to the right or to the left in a quasirandom sequence (e.g., Stubbs & Pliskoff, 1969), whereas two independent VI schedules were used for the independent scheduling (i.e., free-choice) procedure. Considering the experimental procedures across five experiments, however, the presence or absence of a monetary deduction procedure was used only under nonindependent concurrent schedules (e.g., Experiments 2 and 3), while two different types of a concurrent schedule were examined under the monetary deduction condition (e.g., Experiments 1 and 3). They compared the results of Experiments 2 and 3 and found that in the nonindependent scheduling procedure, there was no difference in sensitivity to variation in reinforcer amount or delay between the presence and absence of the monetary deduction. Furthermore, concerning different types of choice procedure, they showed that with the monetary deduction, sensitivity to variation in reinforcer amount or delay was higher in the independent scheduling procedure than in the nonindependent scheduling procedure. Taking these results together, it seems that the independent scheduling procedure with the monetary deduction may have a significant effect on sensitivity to variation in reinforcer amount or delay, as in the case of pigeons (Chavarro & Logue, 1988). Although the monetary deduction procedure had no significant effect on humans’ sensitivity to reinforcer amount or delay under the nonindependent scheduling procedure, it is unclear to what extent the independent scheduling procedure per se
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affects sensitivity to variations in reinforcer amount or delay without the monetary deduction, and moreover, it is not clear whether the monetary deduction procedure may increase sensitivity to reinforcer amount and delay under the independent scheduling procedure. Therefore, it would be preferable to address these questions for the understanding of human choice. In the present experiment, the effect of the monetary deduction procedure was studied, within subjects, under the independent scheduling procedure, and also the effects of two different choice procedures (i.e., independent and nonindependent scheduling procedures) were studied for two different groups when the monetary deduction is absent. METHOD
Subjects The participants were eight adult undergraduate students (four males and four females) between 18 and 22 years of age. They were recruited for participation. The participants were divided into two groups; the participants in one group were numbered 51 through 54 and those in the other group were numbered 71 through 74. None of the participants was a psychology major. Apparatus The experiment was conducted in a small room (3.6 m by 2.8 m). A 14in. color CRT monitor with a touch panel (MicroTouch Systems Inc.) was placed on the desk, and was separated by a large panel from a personal computer (NEC PC-9801U2) and the experimenter. A touch to the circles presented on the screen of the monitor was defined as a response. A personal computer was programmed to present stimuli (i.e., colored circles and counters) on the screen of the monitor, control the experiment, and record events. The screen of the monitor contained three colored circles and counters (see Fig. 1). Two colored circles, 5.0 cm in diameter, were located in the center of the screen and 11 cm apart (from center to center). A small colored circle was located 7.0 cm below the center and 13.5 cm from the sides. Of three counters, two side counters were located below the large circles and the remaining one (i.e., center counter) was above the small circle. A touch to the circles produced a brief beep as a feedback showing that response was effective. Procedure Subjects were seated before the monitor and required to leave all metal objects outside (i.e., watches and jewelry) to minimize interference with the touch panel during the session. They were then given the following minimal instructions (in Japanese) as to what they were to do: Please read repeatedly until you understand. Do not ask for additional instructions. You may play a game. Your task is to earn money as much as you can. Money will
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FIG. 1. A display of the monitor used in the experiment.
be accumulated on the counter and you will receive total amounts of money accumulated on the counter after the session ends. Each session is 20 min in duration. You may touch anything on the screen to earn money, but you have to touch with a forefinger. A brief beep sound will be provided if a response is effective. The session will begin when three white circles come on.
A concurrent-chains schedule was employed with two different types of initial-link schedules (i.e., choice phase); the independent scheduling procedure was used for one group of subjects (numbered 51 through 54), while the nonindependent scheduling procedure was used for the other group of subjects (numbered 71 through 74). During the choice phase, three white circles and the counter were presented on the screen of the monitor. Each circle was colored with white (the background color of the screen was black). After entry into either of the terminal links (i.e., delay period), only the circle not selected was darkened and the other circle was lit with either blue or yellow. Entry into either of the terminal links was arranged by two independent VI 30-s VI 30-s schedules for the independent scheduling procedure (see Fig. 2), or by the single VI 15-s schedule for the nonindependent scheduling procedure (see Fig. 3). Each interval of the VI tape was derived from the distribution of Fleshler and Hoffman (1962). As each interval in one of the VI schedules timed out, the timer stopped and reinforcement was assigned to the appropriate side. In the nonindependent scheduling procedure, however, reinforcement was assigned quasirandomly, with equal probability to either the left or the right circle (e.g., Stubbs & Pliskoff, 1969). A 3-s changeover delay (COD) was used for both the independent and nonindependent scheduling procedures. In this COD procedure, 3 s had to elapse after a changeover response from the right to the left circle or vice versa before a subsequent
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FIG. 2. A schematic diagram of the independent scheduling (free-choice) procedure used in the experiment.
response made it possible to enter into the delay period. The next response on the appropriate circle initiated the delay period defined by the fixed-time (FT) schedule. After the delay, the reinforcer access period was in effect, during which the small circle was illuminated with red and either the left- or the right-side counter was presented on the screen. Each response to the red circle accumulated a prescribed point (i.e., points were worth 1 yen) on the side counter and on the center counter in which the total number of points was accumulated. However, the side counter was always reset at the start of the next cycle. Then a timeout period followed the shorter delay. The timeout period was used to equate overall rates of reinforcement on two alternatives. In a monetary deduction procedure, the method of monetary deduction used in the present experiment was similar to that of Logue et al. (1990). The center counter was set at 720 yen at the start of the session for the
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FIG. 3. A schematic diagram of the nonindependent scheduling (forced-choice) procedure used in the experiment.
reinforcer amount condition and 780 yen for the reinforcer delay condition. These values ensured that the counter would decrease to 0 yen at the end of a 20-min session if the subject received no reinforcers. During the session, an average of 10 yen was deducted from the counter every 15 s, independently of the subject’s response, except for the reinforcer access period. The subjects numbered 51 through 54 were exposed to the monetary deduction procedure. The experiment consisted of three conditions, that is, baseline, reinforcer amount, and reinforcer delay conditions. In baseline, reinforcer amount was .03 yen and reinforcer delay was 5 s for two alternatives. For the reinforcer amount condition, reinforcer amounts were varied and delays were kept constant across two alternatives. Two different reinforcer amounts of .03 and .60 yen (for a consummatory response) were used and there were two conditions in which the side to which the larger amount was assigned was reversed to control for position and color bias. For the reinforcer delay condition, contrary
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to the reinforcer amount condition, reinforcer delays were varied and amounts were kept constant across two alternatives. Two different reinforcer delays of 5 s and 100 s were used and there were two conditions in which the side to which the shorter delay was assigned was reversed as in the reinforcer amount condition. Each condition was presented once in a random sequence except for baseline; if the subject was not indifferent between two alternatives in the baseline, however, the baseline condition was replicated. The order of the conditions is shown in Table 1. Each session was 20 min in duration and three 20-min sessions were conducted per day. The experiment was conducted over two days for each subject. At the start of the session, the subjects were exposed to four ‘‘forced-choice cycles’’ (trials) in which only one alternative was presented at once and with equal opportunity (i.e., two right and two left alternatives were presented in a random sequence) except for baseline condition. These forced-choice cycles were not included in a 20-min session and never used in data analysis. Each subject completed a questionnaire asking how he (or she) did during the experiment and they received the money earned at the end of each session. RESULTS
Table 1 shows the number of responses for both left and right circles, choice proportions, the number of cycles, and the order of conditions for each subject. The number of consummatory responses is also shown in Table 1. For all but baseline condition, data were combined across two sessions. Choice proportions for the larger of two reinforcers or the shorter of two delays were higher in the independent scheduling (free-choice) procedure than in the nonindependent scheduling (forced-choice) procedure. Figure 4 shows the choice proportions for larger reinforcers or less delayed reinforcers under the reinforcer amount and delay conditions for each subject. The left half of the figure shows the data under the independent scheduling procedure for the subjects numbered S51 through S54 and the right half of the figure shows the data under the nonindependent scheduling procedure for the subjects numbered S71 through S74. The white bars represent the absence of monetary deduction, while the shadowed bars represent the presence of monetary deduction. In addition, the black bars represent the baseline condition. Choice proportions were calculated by dividing choice responses for the larger amount or shorter delay by the total choice responses (except for the baseline). Choice proportions for the larger amount or shorter delay reinforcer were combined across two sessions for each condition. In the baseline condition, however, choice proportions were based on data from a session or the second session if the session was replicated. Choice proportions in the baseline were around .50 (i.e., indifference) for most subjects. In the nonindependent scheduling procedure, the choice proportions ranged from .52 to .68 for the reinforcer amount condition and from .51 to .67 for the reinforcer delay condition. In contrast, the choice proportions in the
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.03 .60 .03 .03
6 8 7 9
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5 3 4 2 7 9 6 8
.03
.03 .60 .03 .03
4 2 5 3
1
.03
Al
1
Order
Dl
.03 5 No deduction .60 5 .03 5 .03 5 .03 100 Deduction .60 5 .03 5 .03 5 .03 100
5
Dr
lma
5 5 100 5
5 5 100 5
5
5 5 100 5
5 5 100 5
Delay (s)
.03 5 No deduction .60 5 .03 5 .03 5 .03 100 Deduction .60 5 .03 5 .03 5 .03 100
Ar
Points (yen)
317 670 130 119
366 1145 228 72
534
63 269 94 21
84 152 62 44
222
Left
632 316 70 328
923 315 87 297
541
167 42 49 113
156 112 12 64
242
Right
Responses
.666 .680 .650 .734
.716 .784 .724 .805
.503
.726 .865 .657 .843
.650 .576 .838 .593
.522
Choice prop.
41 42 11 10
40 40 10 10
38
38 30 10 10
39 39 10 10
53
Cycles
399 570 132 140
366 543 148 72
324
195 478 123 57
139 380 148 28
381
Left
493 476 118 148
494 352 90 172
361
474 61 68 139
439 260 22 82
419
Right
Consummatory responses
TABLE 1 Values of Reinforcer Amount (A) and Delay (D) for the Left (l) and Right (r) Circles, Number of Choice Responses, Consummatory Responses, and Cycles during a 20-Min Session, Choice Proportions for the Larger, or Less Delayed Reinforcers and Order of Conditions for Each Subject
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.03 .60 .03 .03
5 3 4 2 1 4 2 5 3
.03 .60 .03 .03
.03
.03 .60 .03 .03
.03 .60 .03 .03
7 9 6 8
1
4 2 5 3
6 8 7 9
.03
.03 .60 .03 .03 .03
5 5 5 5 100
.03 5 No deduction .60 5 .03 5 .03 5 .03 100 Deduction .60 5 .03 5 .03 5 .03 100
.03 5 No deduction .60 5 .03 5 .03 5 .03 100 Deduction .60 5 .03 5 .03 5 .03 100
5 5 5 100 5
5 5 100 5
5 5 100 5
5
5 5 100 5
5 5 100 5
5
961 1095 1050 226 208
3 865 1104 187
1136 3542 1099 2
486
46 1390 476 93
7 934 296 1
439
894 1347 1130 222 334
4258 358 22 265
2788 617 43 1175
365
1483 308 7 245
1017 4 0 232
483
.482 .552 .482 .504 .616
.999 .707 .980 .586
.710 .852 .962 .998
.429
.970 .819 .986 .725
.993 .960 1.0 .996
.524
40 45 46 11 11
31 31 9 9
38 39 9 10
20
32 37 9 10
32 32 9 10
34
152 315 261 80 54
42 240 149 61
366 797 295 30
151
40 636 185 92
68 614 189 28
363
159 323 244 84 84
825 110 41 84
610 326 49 275
88
750 196 40 162
655 53 31 231
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1 2 4 3 5
1 5 3 4 2
Order
.03 .03 .60 .03 .03
.03 .03 .60 .03 .03
.03 .03 .60 .03 .03
Al
.03 .60 .03 .03 .03
.03 .60 .03 .03 .03
.03 .60 .03 .03 .03
Ar
5 5 5 5 100
5 5 5 5 100
5 5 5 5 100
Dl
Dr
5 5 5 100 5
5 5 5 100 5
5 5 5 100 5
Delay (s)
303 154 270 42 48
1643 1437 2139 490 348
134 550 1643 638 118
Left
323 299 142 52 62
1768 1972 1261 444 419
178 1723 1768 259 201
Right
Responses
.516 .660 .655 .447 .564
.518 .578 .629 .525 .546
.571 .758 .482 .711 .630
Choice prop.
45 51 53 11 10
58 54 59 10 11
22 44 46 9 10
Cycles
289 520 660 85 87
530 478 465 69 74
169 204 431 53 54
Left
327 677 653 101 146
568 529 495 90 96
177 388 439 68 100
Right
Consummatory responses
Note. In baseline, choice proportions for the right circle were presented. Subjects S51 through S54 were exposed to the independent scheduling procedure, while subjects S71 through S74 were exposed to the nonindependent scheduling procedure.
S74
S73
S72
Subject
Points (yen)
TABLE 1—Continued
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FIG. 4. The choice proportions for the larger amount or the shorter delay reinforcers under several conditions for each subject. The subjects numbered S51 through S54 were exposed to the independent scheduling (free-choice) procedure, while the subjects numbered S71 through S74 were exposed to the nonindependent scheduling (forced-choice) procedure.
independent scheduling procedure ranged from .61 to .995 for the reinforcer amount condition and from .72 to .998 for the reinforcer delay condition. Applied to the combined data across the reinforcer amount and delay conditions, the Wilcoxon–Mann–Whitney test (Siegel & Castellan, 1988) revealed that the difference in choice proportions between two choice procedures was significant at p õ .05 (N Å 8, Wx Å 11). Thus, it is clear that the choice proportions were higher in the independent scheduling procedure than in the nonindependent scheduling procedure. With monetary deduction, choice proportions did not change substantially from those without monetary deduction; of eight cases across two conditions (i.e., reinforcer amount and delay condition) and four subjects, there were only three cases (two conditions of S51 and the reinforcer amount condition of S54) in which choice proportions with monetary deduction were greater than those without monetary deduction. The Wilcoxon signed ranks test revealed that there was no significant difference between the presence and absence of monetary deduction for both reinforcer amount and delay conditions. Therefore, the monetary deduction procedure does not increase choice proportions for the larger amount or shorter delay reinforcers in the independent scheduling procedure.
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FIG. 5. The mean choice proportions for the larger amount or the shorter delay reinforcers across subjects. Brackets indicate one standard deviation.
Figure 5 summarizes the results in which data were averaged across four subjects for each condition. Mean choice proportions for the larger reinforcer were .79 for the independent scheduling procedure and .61 for the nonindependent scheduling procedure. Similarly, mean choice proportions for the shorter delay were .81 for the independent scheduling procedure and .58 for the nonindependent scheduling procedure. With respect to the monetary deduction, choice proportions did not change substantially depending on the presence or absence of the monetary deduction; mean choice proportions for the larger reinforcer and shorter delay were .82 and .80, respectively, with monetary deduction, while mean choice proportions were .79 and .81 without monetary deduction. These results thus support the conclusion that choice proportions for the larger reinforcer or shorter delay are greater in the independent scheduling procedure than in the nonindependent scheduling procedure, and that the monetary deduction procedure does not increase choice proportions in the independent scheduling procedure. DISCUSSION
One of the purposes of the present study was to assess the effect of the monetary deduction on humans’ choice in the independent scheduling procedure. Choice proportions for larger reinforcers or shorter delay reinforcers did not differ substantially between the presence and absence of the monetary deduction when the independent scheduling procedure was used. This finding
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is consistent with the results of Logue et al. (1990) which showed that when the reinforcer amount and delay were varied separately under the nonindependent scheduling procedure, there was no significant difference in sensitivity to reinforcer amount or delay between the presence and absence of the monetary deduction procedure. Thus, it is clear that the monetary deduction procedure does not increase preference for the larger amount or shorter delay reinforcer under the independent and nonindependent scheduling procedures. A second purpose of the present study was to examine the effects of choice procedures on humans’ choice between two alternatives differing in reinforcer amount or delay. The present results demonstrated that choice proportions were higher in the independent scheduling procedure than in the nonindependent scheduling procedure when the monetary deduction was absent. This finding is consistent with the results of the matching analysis (see below), showing that human subjects are more sensitive to reinforcer amount and delay in the independent scheduling procedure than in the nonindependent scheduling procedure. In this respect, the present results extended those of Logue et al. (1990) to the situation where the monetary deduction is absent and to the situation where the points are exchangeable for yen rather than dollars, although the subjective values of points (money) may be different between two studies. Furthermore, the present results are in accordance with those of Chavarro and Logue (1988), who examined pigeons’ sensitivity to reinforcer amount and delay in two different types of concurrent VI VI schedules of reinforcement, by showing that when the choice procedures changed from the independent to the nonindependent scheduling procedures, there was a decrease in sensitivity to reinforcer amount and delay. In Logue et al.’s (1990) study with human subjects and Chavarro and Logue’s (1988) study with pigeons, only one condition of the reinforcer amount or delay was used and each condition was presented twice; the side to which the larger amount or shorter delay was assigned was reversed for each presentation. To obtain sensitivity values, a linear regression was applied to the log-transformed data by the following generalized matching equation (Baum, 1974):
SD
SD
(1)
SD
SD
(2)
log
R1 A1 Å Salog / log k R2 A2
or log
R1 D2 Å Sdlog / log k R2 D1
where A is the reinforcer amount, D is the delays to reinforcers, R is the number of responses to that alternative, and k, Sa and Sd are empirical constants. The parameters Sa and Sd represent the sensitivity to variations in reinforcer amount and delay, respectively.
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By using the matching analysis, for example, Logue et al. (1990) showed that, in the independent scheduling procedure, the averaged humans’ sensitivity values were 1.0 and .7 for the reinforcer amount and delay, respectively, while they were .6 and .3 in the nonindependent scheduling procedure. A similar result was also obtained in Chavarro and Logue (1988), who showed that in the independent scheduling procedure the averaged pigeons’ sensitivity values were 1.43 and .97 for the reinforcer amount and delay, respectively, and were .65 and .50 in the nonindependent scheduling procedure. Applied to the present results, the matching analysis revealed that the averaged sensitivity values obtained in the independent scheduling procedure were .67 and 1.02 for the reinforcer amount and delay, respectively, and the averaged sensitivity values were .16 and .10 in the nonindependent scheduling procedure. From these results, it seems that the sensitivity values for the reinforcer amount and delay are generally greater in the independent scheduling procedure than in the nonindependent scheduling procedure for human subjects and pigeons. Although these results support the conclusion that human subjects are more sensitive to the reinforcer amount or delay in the independent scheduling procedure, however, there is a limitation concerning the generality of the results since, as mentioned above, the regression analysis was based on a small number of points (only one condition or two conditions if the reversed condition was included) to determine sensitivity values by the matching analysis. It is, therefore, preferable to use more than three conditions for determining sensitivity values Sa and Sd . In summary, the present study demonstrated that the independent scheduling procedure per se had a significant effect on human choice between different reinforcer amounts or delays in terms of both choice proportions and sensitivity values, and that the monetary deduction procedure had no significant effect on humans’ choice proportions under the independent scheduling procedure. These results indicates that the independent scheduling procedure is useful for studying human choice without the monetary deduction procedure. REFERENCES Baum, W. H. (1974). On two types of deviation from the matching law: Bias and undermatching. Journal of the Experimental Analysis of Behavior, 22, 231–242. Belke, T. W., Pierce, W. D., & Powell, R. A. (1989). Determinants of choice for pigeons and humans on concurrent-chains schedules of reinforcement. Journal of the Experimental Analysis of Behavior, 52, 97–109. Buskist, W., Oliveira-Castro, J., & Bennett, R. (1988). Some effects of response-correlated increases in reinforcer magnitude on human behavior. Journal of the Experimental Analysis of Behavior, 49, 87–94. Catania, A. C., & Cutts, D. (1963). Experimental control of superstitious responding in humans. Journal of the Experimental Analysis of Behavior, 6, 203–208. Chavarro, A., & Logue, A. W. (1988). Sensitivity to amount and delay of reinforcement: Effects of different types of concurrent variable-interval schedules. The Psychological Record, 38, 421–435.
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de Villiers, P. (1977). Choice in concurrent schedules and a quantitative formulation of the law of effect. In W. K. Honig & J. E. R. Staddon (Eds.), Handbook of operant behavior (pp. 233–287). Englewood Cliffs, NJ: Prentice-Hall. Fleshler, M., & Hoffman, H. S. (1962). A progression for generating variable-interval schedules. Journal of the Experimental Analysis of Behavior, 5, 529–530. Forzano, L. B., & Logue, A. W. (1994). Self-control in adult humans: Comparison of qualitatively different reinforcers. Learning and Motivation, 25, 65–82. King, G. R., & Logue, A. W. (1987). Choice in a self-control paradigm with human subjects: Effects of changeover delay duration. Learning and Motivation, 18, 421–438. King, G. R., & Logue, A. W. (1990). Humans’ sensitivity to variation in reinforcer amount: Effects of the method of reinforcer delivery. Journal of the Experimental Analysis of Behavior, 53, 33–45. Logue, A. W., King, G. R., Chavarro, A., & Volpe, J. S. (1990). Matching and maximizing in a self-control paradigm using human subjects. Learning and Motivation, 21, 340–368. Logue, A. W., Pena-Correal, T. E., Rodriguez, M. L., & Kabela, E. (1986). Self-control in adult humans: Variation in positive reinforcer amount and delay. Journal of the Experimental Analysis of Behavior, 46, 159–173. Matthews, B. A., Shimoff, E., Catania, A. C., & Sagvolden, T. (1977). Uninstructed human responding: Sensitivity to ratio and interval contingencies. Journal of the Experimental Analysis of Behavior, 27, 453–467. Mazur, J. E. (1988). Estimation of indifference points with an adjusting-delay procedure. Journal of the Experimental Analysis of Behavior, 49, 37–47. McDowell, J. J., & Wood, H. M. (1984). Confirmation of linear system theory prediction: Changes in Herrnstein’s k as a function of changes in reinforcer magnitude. Journal of the Experimental Analysis of Behavior, 41, 183–192. Millar, A., & Navarick, D. J. (1984). Self-control and choice in humans: Effects of video game playing as a positive reinforcer. Learning and Motivation, 15, 203–218. Navarick, D. J. (1982). Negative reinforcement and choice in humans. Learning and Motivation, 13, 361–377. Siegel, S., & Castellan, Jr., N. J. (1988). Nonparametric statistics for the behavioral sciences (2nd ed.). New York: McGraw-Hill. Stubbs, D. A., & Pliskoff, S. S. (1969). Concurrent responding with fixed relative rate of reinforcement. Journal of the Experimental Analysis of Behavior, 12, 887–895. Wurster, R. M., & Griffiths, R. R. (1979). Human concurrent performances: Variation of reinforcer magnitude and rate of reinforcement. The Psychological Record, 29, 341–354. Received December 6, 1995 Revised June 21, 1996
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