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Effects of variable frequency of presentation on paired-associate learning as a function of interstimulus similarity
JOUnNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR 6, 4 7 0 - - 4 7 5
(1967)
Effects of Variable Frequency of Presentation on PairedAssociate Learning as a Function of Interstimulus Similarity WILL.tm~ N. RUNQUIST University of Alberta, Edmonton, Alberta, Canada Four groups of Ss were run in a paired-associate task in which they learned to associate buttons with trigrams. Two groups had highly similar stimuli while for two groups the stimuli were dissimilar. For one group in each similarity condition, four of the eight pairs appeared three times on each trial. For the other group, all pairs appeared once. The asymmetrical presentation frequency resulted in superior performance in both high- and low-similarity tasks, although the effect appeared somewhat later under high similarity. Facilitation occurred entirely after the appearance of the first correct response and was accompanied by an increase in the proportion of overt errors among those items which were not presented more frequently.
In a recent study (Runquist, 1965.) it was shown that the learning of a pairedassociate verbal list is facilitated when some of the items in the list are presented more frequently than others. Thus, ff the relative difficulty of paired-associate tasks is due, in part, to interference among the items in the list, this result suggests that facilitation will be obtained when some of the interfering associations are stronger despite the fact that they are stronger. Actually, it appears as ff interference is reduced because S has learned to categorize the response terms on the basis of frequency of appearance, or because he is able to eliminate from consideration those response terms which are extremely well learned to other stimuli. The purpose of this research was to extend these findings in two directions. The first extension involved the use of a task in which the population of response terms
was completely delimited, thus eliminating the necessity of response learning (Underwood and Schulz, 1960). If the effects of asymmetry of presentation frequency depend upon this process, then facilitation should not occur in this task. The second direction in which this experiment extends the previous one is in the study of the effects of intralist stimulus similarity. Presumably, any variable which would make the perceptual grouping of items more difficult might be expected to delay the appearance of facilitation. Whether it is frequency of appearance or response strength which is the determining factor; the effect of similarity should be to forestall facilitation, either because it is harder to group stimuli which are highly similar or because the items appearing more frequently are less rapidly learned when they are highly similar. In this experiment, then, performance on two lists was compared. In one list, all 1 This work was supported by grants APA-88 and APT-88 from the National Research Council' items appeared once per trial; in the other list, some of the items appeared three times of Canada. Dennis Foth supervised the collection per trial. The comparison was made for of the data. 470
FBEQUENCY OF PBESENTATION lists in w h i c h stimulus similarity w a s h i g h a n d in w h i c h s i m i l a r i t y w a s low. I n all conditions response terms were available f r o m t h e b e g i n n i n g o f le a r n in g . METHOD
Apparatus. The paired-associate task consisted of associating each of eight low-association value trigrams with one of the numerals from one to eight. The apparatus consisted of a visual display on which the trigrams were presented and a response panel on which were located eight buttons in a linear arrangement. Above each button was a small white lamp. Both lamps and buttons were numbered consecutively. When being tested, S was to indicate his choice of the correct number by pressing the appropriate button. The Ss were run two at a time seated in booths 28 inches wide and separated by a partition extending 24 inches above the level of the gable. The response panels were sloping 8 X 16-inch varnished plywood and displayed the eight ~ inch black plastic buttons in a linear array 2 inches apart. A 4-inch vertical extension of each panel contained a small lamp. Panels were not attached to the table. The stimulus display units consisted of IEE Series 80000 digital display units. The trig~ams for a given list were photographed on film and mounted on the lens plate of the display unit. Lens plates containing different lists could readily be exchanged through a slot in the upper surface of the display unit. The units were located directly in front of each S and protruded from the wall 12~ inches above table level and extended from the wall 6 inches. The wall was located approximately 2 ft from the front edge of the table. The display screen was 3 X 5 inches but was masked to an aperture of 1 X 3 inches with black tape. The trigram stimuli appeared ~/2-inch square in this aperture. The anticipation method was used in this experiment, such that the trigram appeared on the screen for a fixed interval of time, and then the lamp above the correct button was lighted for a fixed interval. There was also a brief interval during which no stimuli were shown. The stimulus-light combination for a particular presentation was selected with a Western Union Model 1A Tape Transmitter operating through a relay tree. For any given tape code the stimuli and lights were fixed, but a patch panel allowed for rewaking of stimuli and lamps for a given condition. The tape transmitter was advanced with a cam operated microswitch and the delay between
471
stimulus onset and the occurrence of the information lamp was controlled by a Hunter Model 111C Decade Timer. Responses were recorded on an Esterline Angus Operations Recorder at a paper speed of 6 inches/ rain. One channel marked the onset of each stimulus. The Decade Timer in addition to delaying the onset of information also cut off the recorder input so that responses made after the anticipation interval were not recorded. Subiects and Design. The Ss were 96 undergraduate psychology students who served as part of a course requirement. Assignment to one of the four maior groups of the experiment was made according to an unbiased system whereby the conditions were listed randomly with the restriction that each condition appear once in each block of four conditions. The Ss were then assigned to the next vacant cell as they appeared at the laboratory to be tested. Two groups learned lists in which the CVC trigrams were of low intralist similarity (TYW, QIH, NIJ, XUL, CUG, KYB, VUP, ZUF) and two groups learned lists of high similarity (XIW, XIJ, XEJ, XEF, XUF, XUL, XUW, XIL). All trigrams had meaningfulness ratings of less than 25% as determined by Archer's norms (1960). For the purposes of the design, the eight stimuli were divided into two arbitrary sets of four which may be labeled Sets A and B. For half of the Ss, the items in Set A were paired with buttons 3, 4, 6, and 8, and those in Set B with buttons 1, 2, 5, and 7. For the remaining half of the Ss, this situation was reversed. Particular S-R pairing is partially confounded, however, since the first 48 Ss had the first arrangement and the second 48 Ss the second arrangement. For any given S, performance was measured on only the Set A or only the Set B items. These items are referred to further as the kernel items. Half of the Ss in each group had the Set A items as kernel items and half had Set B items in this function. The further experimental variable of interest was the relative frequency of occurrence of kernel items and nonkernel items. Thus, for half the Ss, the nonkernel items appeared three times on a given trial for every presentation of the kernel items, while for the remaining half the Ss the frequency of presentation of the two sets was identical. In summary, then, the design consisted of a 2 X 2 >( 2 X 2 factorial design with intralist stimulus similarity and symmetrical vs. asymmetrical presentation as the two main factors with Sets of Items and S-R pairing as counterbalanced factors. Thus there were 24 Ss in each of the four main groups which will
472
RUNQUIST
be referred to as HS-S, LS-S, HS-A and LS-A. Procedure. Each S received 25 anticipation trials on the list including the first trial. The anticipation interval was 1.57 see and the information lamp was lighted for .96 sec. A dark interval of .47 sec occurred between each presentation. Although the entire list was presented as a "'trial," there was no intertrial interval or other indication that one trial had ended and another begun. To the Ss, there was simply an unbroken sequence of items. The Ss were instructed to respond as soon as they knew any of the items. RESULTS
As a preliminary" analysis, the total correct anticipations for each S on the kernel items were subjected to analysis of variance according to the four-factors design. The only interaction of any consequence between the two major independent variables and a counterbalanced variable was between symmetry and S-R pairing, which approached significance, F(1, 8 0 ) ~ 3.93, p < .10. Since the interaction did not involve a reversal of the symmetry effect, this can probably be discounted. The only other counterbalanced variable which had an effect was the main effect of Item Sets, F(1, 80)--10.42, p < .005, showing that one set of stimuli was more diMcult than the other. As a result of these analyses, it seemed unlikely that the two counterbalanced variables exerted much effect on the outcome; hence, they are ignored in all subsequent analyses. The performance of the four main groups in terms of the percentage of correct anticipations on the kernel items in blocks of five trials is shown in Fig. 1. Clearly, the facilitative effect of differential frequency of presentation of kernel and nonkernel items is manifested as a superiority of performance in the asymmetry (A) groups under both high- and lowsimilarity conditions. As expected, the appearance of facilitation was delayed in the high-similarity conditions. These findings are supported by an analysis of vari-
anee in which Similarity, F( 1, 92) ~-57.76, p < .01; Symmetry, F(1, 92) = 13.12, p < .01; Trials, F(4, 368)z83.60, p < .01; Trials X Similarity, F(4, 368) = 15.58, p < .01; Trials X Symmetry, F(4, 368) = 11.73, p < .01; and the triple interaction of Trials X Similarity X Symmetry, F(4, 368 ) = 2.64, p < .05; were all significant (error mean square = 37.82 for between-Ss comparisons and 5.44 for within-Ss comparisons). In general, these effects indicate: (a) superiority of low over high similarity, (b) superiority of the asymmetrical pres100
eo
.,~.ILS-A ~ . . . . . . . LS-S
~.
/
°o ,.
...-" .........
40
.....
•
n
1-5
6-10
•
11-15
,SA
....................
HSS
•
•
16-20
21-25
BLOCKSOF FIVE TRIALS Fro. 1. Percentage of correct responses in blocks of five trials.
entation frequency over symmetrical presentation, (c) more rapid performance increases under low similarity than high similarity and under asymmetrical as opposed to symmetrical presentation fiequeney, and (d) delay of the facilitative effect of asymmetry under high similarity conditions; such an effect does not appear with any magnitude until trials 15-20. The source of these effects may be further localized by considering two other response measures. In previous studies (Runquist, 1965, 1966) it has been useful to consider separately performance prior to and after the first correct response. These results are shown in Table 1 in
473
FREQUENCY OF PRESENTATION TABLE 1 MEAN ERRORS BEFORE AND AFTER FIRST CORRECT RESPONSE
Group HS-S LS-S HS-A LS-A
Mean no. of errors before
Mean % errors after
7.4 5.4 7.9 4.8
.71 .54 .58 .40
terms of the mean number of errors (overt errors plus omissions) prior to the first correct response and the mean percentage of errors on the first five trials following the first correct response for each item. Prior to the first correct response, the only notable effect is due to the fact that the high-similarity groups made more errors than the low-similarity groups. Symmetry had little influence. This was supported by the analysis of variance which resulted in a significant F for Similarity, F(1, 92) = 14.98, p < .01, but no other significant effects, F < 1.00 for both Symmetry and the interaction (error mean s q u a r e = 164.26). Following the first correct response both Similarity and Symmetry produced significant effects, F(1, 9 2 ) = 28.44 and 10.25, p < .01, respectively (error mean square = .0321). The interaction was less than 1.00. The main effects reflected better performance under low similarity and better performance with the asymmetrical frequency of occurrence of kernel and nonkernel items. There were
16 of the 384 items which were not included in this analysis because they were not gotten correct soon enough to yield five trials for analysis. These were distributed as seven in each of the two highsimilarity conditions and two in LS-S group. In view of the large and extremely reliable effects, it is doubtful whether these omissions significantly influence the results. In short, then, virtually the entire facilitative effect of asymmetry occurs after the first correct response, i.e., relatively late in acquisition. Also of interest are the overt errors (responses to incorrect buttons) which are tabulated in Table 2. The mean number of overt errors prior to and after the first correct response are shown separately as the number and percentage of "kernel" errors, i.e., errors in which the response which would be correct for one kernel item is given as the response to another kernel item. Inspection of the table shows that the high-similarity conditions and the symmetrical conditions produced more total overt errors. This was supported by analysis of variance showing both Similarity, F(1, 92) = 21.73, p < .01, and Symmetry, F (1, 92) ~-- 8.35, p < .01, significant (error mean square = 143.43). This pattern in total errors was reflected primarily in performance following the first correct response, for prior to the first correct response, Symmetry made little difference. Of major importance, however, is the percentage of kernel errors. Prior to the first
TABLE MEAN OVERT ERRORS Prior to first correct
After first correct
Group
Total
Total
Kernel
%
Total
Kernel
HS-S LS-S HS-A LS-A
38.16 £6.45 80.87 18.88
15.12 8.54 14.13 8.63
8.17 8.84 6.50 4.54
52 39 48 51
28,06 17.93 16.76 10.22
9,51 7.17 7.92 6.30
39 89 50 59
474
I~UNQUIST
correct response, there was little difference 1966). In essence, it has been postulated among the groups in these errors. Follow- that the items are grouped in such a way hag the first correct response, however, the that interference between items in difLS-A condition produced a much larger ferent groups is virtually eliminated. This proportion of these errors. Analysis of vari- process, furthermore, is conceptualized as ance was performed on the mean percent- being part of response learning in which age of kernel errors as computed from specific responses are associated with some the percentage of kernel errors made by cue which the group of items has in comeach S. The results showed that prior to mon. In this case, the cue is probably the first correct response there were no differential frequency of appearance in significant effects, F < 1.00 for Similarity the asymmetry conditions; but, as was and Symmetry and 2.95 for interaction mentioned in the introduction, differential (error mean square ~ .055). After the first response strength might also serve this correct response, Symmetry yielded an function. Once a group has been formed, F(1, 92)=12.03, p < . 0 1 (error mean the interference comes primarily from consquare--.057). Although the interaction fusions within the group; hence, although failed to attain significance, F(1, 92)--- the amount of interference is reduced, the 1.88, t-tests comparing the two symmetry proportion of overt errors which consist of groups within each similarity condition confusions of items within the group inproduced t ( 4 6 ) = 2 . 9 0 , p < .01, for the creases. Presumably, the appearance of low-similarity groups and 1.51, p = .18 grouped items is indexed rather nicely by for the high-similarity groups. In general, the appearance of the first correct rethe pattern is that higher proportions of sponse. Thus, the effects of incidental cues kernel errors correlate with better per- do not appear until after the first correct formance during learning. response has appeared. The delayed occurrence of the effect Discussion resulting from highly similar stimuli apThe results of this study are almost parently results entirely from the greater completely consistent with those of the diflaculty of forming stable groups when previous experiment (Runquist, 1965) in the dominant formal characteristics of the which facilitation resulted from asymme- stimuli are so similar; i.e., it is harder to try in frequency of presentation of kernel associate a particular stimulus with the apand nonkernel items in a verbal list. The propriate group of response terms because facilitation here, as in the previous study, these stimuli generalize so readily. There was restricted t o performance following is no evidence that the facilitation prothe first correct response and was accom- duced by asymmetry was greater in the panied by an increase in the proportion low-similarity condition after the first corof kernel errors. Although the same effects rect response. Thus, the entire differential tended to appear in the task where inter- effect of asymmetry shown in Fig. i results stimulus similarity was high, the facilita- from the effect of similarity in delaying tion appeared later in learning. the appearance of the first correct reThe pattern, of results is also consistent sponse. In short, once the stable groups with the explanation developed to explain are formed, as indexed by the first correct the results of the previous study as well response, the effects of asymmetry are inas some other studies dealing with the re- dependent of similarity. With respect to this interpretation, it duction of intralist interference (Runquist,
FREQUENCY OF PRESENTATION should be pointed out that the kernel items in the asymmetrical conditions are separated by a longer time interval than those items in the symmetrical conditions. It is conceivable that the facilitation produced i n t h e former items results from distribution of practice. Several considerations lead to the rejection of this notion, although without comparable control groups the possibility cannot be entirely ignored. The main reason for preferring an explanation in terms of item grouping is that facilitation by distributed practice seldom occurs without interference in the response-learning stage (Underwood, 1961 ). It is unlikely that much interference of this kind was present in this experiment. Secondly, the pattern of errors does not appear to be predictable from a distributed practice viewpoint. Finally, it should be pointed out that the fact that similarity had a large influence on errors prior to the first correct response is not consistent with at least one other study (Runquist, 1966). The cause of this inconsistency is not entirely clear, for there were several differences between
475
the two studies. Notably in the study in which differences were not obtained, verbal responses were used and similarity was defined in terms of the pairwise similarity between a given kernel item and one nonkernel item. Whether one of these variables is important or whether the difference results from sampling error cannot be determined now. REFERENCES
ARCrIER, E. J. A re-evaluation of the meaningfulness of all possible CVC trigrams. Psychol. Monogr., 1960, 74, Whole No. 497. RUNQUIST,W. N. Order of presentation and number of items as factors in paired associate verbal learning. ]. verb. Learn. verb. Behav., 1965, 4, 585-540. RUNQUIST, W. N. Intralist interference as a fimction of list length and interstimulus similarity. J. verb. Learn. verb. Behav., 1966, 5, 713. UNDERWOOD, B. J. Ten years of massed practice on distributed practice. Psychol. Rev., 1961, 68, 229-247. UNDERx,VOOD, B. J., AND SCHULZ, R. W. Meaningfnlness and verbal learning. Chicago, Lippincott, 1960. (Received September 20, 1965)
(1967)
Effects of Variable Frequency of Presentation on PairedAssociate Learning as a Function of Interstimulus Similarity WILL.tm~ N. RUNQUIST University of Alberta, Edmonton, Alberta, Canada Four groups of Ss were run in a paired-associate task in which they learned to associate buttons with trigrams. Two groups had highly similar stimuli while for two groups the stimuli were dissimilar. For one group in each similarity condition, four of the eight pairs appeared three times on each trial. For the other group, all pairs appeared once. The asymmetrical presentation frequency resulted in superior performance in both high- and low-similarity tasks, although the effect appeared somewhat later under high similarity. Facilitation occurred entirely after the appearance of the first correct response and was accompanied by an increase in the proportion of overt errors among those items which were not presented more frequently.
In a recent study (Runquist, 1965.) it was shown that the learning of a pairedassociate verbal list is facilitated when some of the items in the list are presented more frequently than others. Thus, ff the relative difficulty of paired-associate tasks is due, in part, to interference among the items in the list, this result suggests that facilitation will be obtained when some of the interfering associations are stronger despite the fact that they are stronger. Actually, it appears as ff interference is reduced because S has learned to categorize the response terms on the basis of frequency of appearance, or because he is able to eliminate from consideration those response terms which are extremely well learned to other stimuli. The purpose of this research was to extend these findings in two directions. The first extension involved the use of a task in which the population of response terms
was completely delimited, thus eliminating the necessity of response learning (Underwood and Schulz, 1960). If the effects of asymmetry of presentation frequency depend upon this process, then facilitation should not occur in this task. The second direction in which this experiment extends the previous one is in the study of the effects of intralist stimulus similarity. Presumably, any variable which would make the perceptual grouping of items more difficult might be expected to delay the appearance of facilitation. Whether it is frequency of appearance or response strength which is the determining factor; the effect of similarity should be to forestall facilitation, either because it is harder to group stimuli which are highly similar or because the items appearing more frequently are less rapidly learned when they are highly similar. In this experiment, then, performance on two lists was compared. In one list, all 1 This work was supported by grants APA-88 and APT-88 from the National Research Council' items appeared once per trial; in the other list, some of the items appeared three times of Canada. Dennis Foth supervised the collection per trial. The comparison was made for of the data. 470
FBEQUENCY OF PBESENTATION lists in w h i c h stimulus similarity w a s h i g h a n d in w h i c h s i m i l a r i t y w a s low. I n all conditions response terms were available f r o m t h e b e g i n n i n g o f le a r n in g . METHOD
Apparatus. The paired-associate task consisted of associating each of eight low-association value trigrams with one of the numerals from one to eight. The apparatus consisted of a visual display on which the trigrams were presented and a response panel on which were located eight buttons in a linear arrangement. Above each button was a small white lamp. Both lamps and buttons were numbered consecutively. When being tested, S was to indicate his choice of the correct number by pressing the appropriate button. The Ss were run two at a time seated in booths 28 inches wide and separated by a partition extending 24 inches above the level of the gable. The response panels were sloping 8 X 16-inch varnished plywood and displayed the eight ~ inch black plastic buttons in a linear array 2 inches apart. A 4-inch vertical extension of each panel contained a small lamp. Panels were not attached to the table. The stimulus display units consisted of IEE Series 80000 digital display units. The trig~ams for a given list were photographed on film and mounted on the lens plate of the display unit. Lens plates containing different lists could readily be exchanged through a slot in the upper surface of the display unit. The units were located directly in front of each S and protruded from the wall 12~ inches above table level and extended from the wall 6 inches. The wall was located approximately 2 ft from the front edge of the table. The display screen was 3 X 5 inches but was masked to an aperture of 1 X 3 inches with black tape. The trigram stimuli appeared ~/2-inch square in this aperture. The anticipation method was used in this experiment, such that the trigram appeared on the screen for a fixed interval of time, and then the lamp above the correct button was lighted for a fixed interval. There was also a brief interval during which no stimuli were shown. The stimulus-light combination for a particular presentation was selected with a Western Union Model 1A Tape Transmitter operating through a relay tree. For any given tape code the stimuli and lights were fixed, but a patch panel allowed for rewaking of stimuli and lamps for a given condition. The tape transmitter was advanced with a cam operated microswitch and the delay between
471
stimulus onset and the occurrence of the information lamp was controlled by a Hunter Model 111C Decade Timer. Responses were recorded on an Esterline Angus Operations Recorder at a paper speed of 6 inches/ rain. One channel marked the onset of each stimulus. The Decade Timer in addition to delaying the onset of information also cut off the recorder input so that responses made after the anticipation interval were not recorded. Subiects and Design. The Ss were 96 undergraduate psychology students who served as part of a course requirement. Assignment to one of the four maior groups of the experiment was made according to an unbiased system whereby the conditions were listed randomly with the restriction that each condition appear once in each block of four conditions. The Ss were then assigned to the next vacant cell as they appeared at the laboratory to be tested. Two groups learned lists in which the CVC trigrams were of low intralist similarity (TYW, QIH, NIJ, XUL, CUG, KYB, VUP, ZUF) and two groups learned lists of high similarity (XIW, XIJ, XEJ, XEF, XUF, XUL, XUW, XIL). All trigrams had meaningfulness ratings of less than 25% as determined by Archer's norms (1960). For the purposes of the design, the eight stimuli were divided into two arbitrary sets of four which may be labeled Sets A and B. For half of the Ss, the items in Set A were paired with buttons 3, 4, 6, and 8, and those in Set B with buttons 1, 2, 5, and 7. For the remaining half of the Ss, this situation was reversed. Particular S-R pairing is partially confounded, however, since the first 48 Ss had the first arrangement and the second 48 Ss the second arrangement. For any given S, performance was measured on only the Set A or only the Set B items. These items are referred to further as the kernel items. Half of the Ss in each group had the Set A items as kernel items and half had Set B items in this function. The further experimental variable of interest was the relative frequency of occurrence of kernel items and nonkernel items. Thus, for half the Ss, the nonkernel items appeared three times on a given trial for every presentation of the kernel items, while for the remaining half the Ss the frequency of presentation of the two sets was identical. In summary, then, the design consisted of a 2 X 2 >( 2 X 2 factorial design with intralist stimulus similarity and symmetrical vs. asymmetrical presentation as the two main factors with Sets of Items and S-R pairing as counterbalanced factors. Thus there were 24 Ss in each of the four main groups which will
472
RUNQUIST
be referred to as HS-S, LS-S, HS-A and LS-A. Procedure. Each S received 25 anticipation trials on the list including the first trial. The anticipation interval was 1.57 see and the information lamp was lighted for .96 sec. A dark interval of .47 sec occurred between each presentation. Although the entire list was presented as a "'trial," there was no intertrial interval or other indication that one trial had ended and another begun. To the Ss, there was simply an unbroken sequence of items. The Ss were instructed to respond as soon as they knew any of the items. RESULTS
As a preliminary" analysis, the total correct anticipations for each S on the kernel items were subjected to analysis of variance according to the four-factors design. The only interaction of any consequence between the two major independent variables and a counterbalanced variable was between symmetry and S-R pairing, which approached significance, F(1, 8 0 ) ~ 3.93, p < .10. Since the interaction did not involve a reversal of the symmetry effect, this can probably be discounted. The only other counterbalanced variable which had an effect was the main effect of Item Sets, F(1, 80)--10.42, p < .005, showing that one set of stimuli was more diMcult than the other. As a result of these analyses, it seemed unlikely that the two counterbalanced variables exerted much effect on the outcome; hence, they are ignored in all subsequent analyses. The performance of the four main groups in terms of the percentage of correct anticipations on the kernel items in blocks of five trials is shown in Fig. 1. Clearly, the facilitative effect of differential frequency of presentation of kernel and nonkernel items is manifested as a superiority of performance in the asymmetry (A) groups under both high- and lowsimilarity conditions. As expected, the appearance of facilitation was delayed in the high-similarity conditions. These findings are supported by an analysis of vari-
anee in which Similarity, F( 1, 92) ~-57.76, p < .01; Symmetry, F(1, 92) = 13.12, p < .01; Trials, F(4, 368)z83.60, p < .01; Trials X Similarity, F(4, 368) = 15.58, p < .01; Trials X Symmetry, F(4, 368) = 11.73, p < .01; and the triple interaction of Trials X Similarity X Symmetry, F(4, 368 ) = 2.64, p < .05; were all significant (error mean square = 37.82 for between-Ss comparisons and 5.44 for within-Ss comparisons). In general, these effects indicate: (a) superiority of low over high similarity, (b) superiority of the asymmetrical pres100
eo
.,~.ILS-A ~ . . . . . . . LS-S
~.
/
°o ,.
...-" .........
40
.....
•
n
1-5
6-10
•
11-15
,SA
....................
HSS
•
•
16-20
21-25
BLOCKSOF FIVE TRIALS Fro. 1. Percentage of correct responses in blocks of five trials.
entation frequency over symmetrical presentation, (c) more rapid performance increases under low similarity than high similarity and under asymmetrical as opposed to symmetrical presentation fiequeney, and (d) delay of the facilitative effect of asymmetry under high similarity conditions; such an effect does not appear with any magnitude until trials 15-20. The source of these effects may be further localized by considering two other response measures. In previous studies (Runquist, 1965, 1966) it has been useful to consider separately performance prior to and after the first correct response. These results are shown in Table 1 in
473
FREQUENCY OF PRESENTATION TABLE 1 MEAN ERRORS BEFORE AND AFTER FIRST CORRECT RESPONSE
Group HS-S LS-S HS-A LS-A
Mean no. of errors before
Mean % errors after
7.4 5.4 7.9 4.8
.71 .54 .58 .40
terms of the mean number of errors (overt errors plus omissions) prior to the first correct response and the mean percentage of errors on the first five trials following the first correct response for each item. Prior to the first correct response, the only notable effect is due to the fact that the high-similarity groups made more errors than the low-similarity groups. Symmetry had little influence. This was supported by the analysis of variance which resulted in a significant F for Similarity, F(1, 92) = 14.98, p < .01, but no other significant effects, F < 1.00 for both Symmetry and the interaction (error mean s q u a r e = 164.26). Following the first correct response both Similarity and Symmetry produced significant effects, F(1, 9 2 ) = 28.44 and 10.25, p < .01, respectively (error mean square = .0321). The interaction was less than 1.00. The main effects reflected better performance under low similarity and better performance with the asymmetrical frequency of occurrence of kernel and nonkernel items. There were
16 of the 384 items which were not included in this analysis because they were not gotten correct soon enough to yield five trials for analysis. These were distributed as seven in each of the two highsimilarity conditions and two in LS-S group. In view of the large and extremely reliable effects, it is doubtful whether these omissions significantly influence the results. In short, then, virtually the entire facilitative effect of asymmetry occurs after the first correct response, i.e., relatively late in acquisition. Also of interest are the overt errors (responses to incorrect buttons) which are tabulated in Table 2. The mean number of overt errors prior to and after the first correct response are shown separately as the number and percentage of "kernel" errors, i.e., errors in which the response which would be correct for one kernel item is given as the response to another kernel item. Inspection of the table shows that the high-similarity conditions and the symmetrical conditions produced more total overt errors. This was supported by analysis of variance showing both Similarity, F(1, 92) = 21.73, p < .01, and Symmetry, F (1, 92) ~-- 8.35, p < .01, significant (error mean square = 143.43). This pattern in total errors was reflected primarily in performance following the first correct response, for prior to the first correct response, Symmetry made little difference. Of major importance, however, is the percentage of kernel errors. Prior to the first
TABLE MEAN OVERT ERRORS Prior to first correct
After first correct
Group
Total
Total
Kernel
%
Total
Kernel
HS-S LS-S HS-A LS-A
38.16 £6.45 80.87 18.88
15.12 8.54 14.13 8.63
8.17 8.84 6.50 4.54
52 39 48 51
28,06 17.93 16.76 10.22
9,51 7.17 7.92 6.30
39 89 50 59
474
I~UNQUIST
correct response, there was little difference 1966). In essence, it has been postulated among the groups in these errors. Follow- that the items are grouped in such a way hag the first correct response, however, the that interference between items in difLS-A condition produced a much larger ferent groups is virtually eliminated. This proportion of these errors. Analysis of vari- process, furthermore, is conceptualized as ance was performed on the mean percent- being part of response learning in which age of kernel errors as computed from specific responses are associated with some the percentage of kernel errors made by cue which the group of items has in comeach S. The results showed that prior to mon. In this case, the cue is probably the first correct response there were no differential frequency of appearance in significant effects, F < 1.00 for Similarity the asymmetry conditions; but, as was and Symmetry and 2.95 for interaction mentioned in the introduction, differential (error mean square ~ .055). After the first response strength might also serve this correct response, Symmetry yielded an function. Once a group has been formed, F(1, 92)=12.03, p < . 0 1 (error mean the interference comes primarily from consquare--.057). Although the interaction fusions within the group; hence, although failed to attain significance, F(1, 92)--- the amount of interference is reduced, the 1.88, t-tests comparing the two symmetry proportion of overt errors which consist of groups within each similarity condition confusions of items within the group inproduced t ( 4 6 ) = 2 . 9 0 , p < .01, for the creases. Presumably, the appearance of low-similarity groups and 1.51, p = .18 grouped items is indexed rather nicely by for the high-similarity groups. In general, the appearance of the first correct rethe pattern is that higher proportions of sponse. Thus, the effects of incidental cues kernel errors correlate with better per- do not appear until after the first correct formance during learning. response has appeared. The delayed occurrence of the effect Discussion resulting from highly similar stimuli apThe results of this study are almost parently results entirely from the greater completely consistent with those of the diflaculty of forming stable groups when previous experiment (Runquist, 1965) in the dominant formal characteristics of the which facilitation resulted from asymme- stimuli are so similar; i.e., it is harder to try in frequency of presentation of kernel associate a particular stimulus with the apand nonkernel items in a verbal list. The propriate group of response terms because facilitation here, as in the previous study, these stimuli generalize so readily. There was restricted t o performance following is no evidence that the facilitation prothe first correct response and was accom- duced by asymmetry was greater in the panied by an increase in the proportion low-similarity condition after the first corof kernel errors. Although the same effects rect response. Thus, the entire differential tended to appear in the task where inter- effect of asymmetry shown in Fig. i results stimulus similarity was high, the facilita- from the effect of similarity in delaying tion appeared later in learning. the appearance of the first correct reThe pattern, of results is also consistent sponse. In short, once the stable groups with the explanation developed to explain are formed, as indexed by the first correct the results of the previous study as well response, the effects of asymmetry are inas some other studies dealing with the re- dependent of similarity. With respect to this interpretation, it duction of intralist interference (Runquist,
FREQUENCY OF PRESENTATION should be pointed out that the kernel items in the asymmetrical conditions are separated by a longer time interval than those items in the symmetrical conditions. It is conceivable that the facilitation produced i n t h e former items results from distribution of practice. Several considerations lead to the rejection of this notion, although without comparable control groups the possibility cannot be entirely ignored. The main reason for preferring an explanation in terms of item grouping is that facilitation by distributed practice seldom occurs without interference in the response-learning stage (Underwood, 1961 ). It is unlikely that much interference of this kind was present in this experiment. Secondly, the pattern of errors does not appear to be predictable from a distributed practice viewpoint. Finally, it should be pointed out that the fact that similarity had a large influence on errors prior to the first correct response is not consistent with at least one other study (Runquist, 1966). The cause of this inconsistency is not entirely clear, for there were several differences between
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the two studies. Notably in the study in which differences were not obtained, verbal responses were used and similarity was defined in terms of the pairwise similarity between a given kernel item and one nonkernel item. Whether one of these variables is important or whether the difference results from sampling error cannot be determined now. REFERENCES
ARCrIER, E. J. A re-evaluation of the meaningfulness of all possible CVC trigrams. Psychol. Monogr., 1960, 74, Whole No. 497. RUNQUIST,W. N. Order of presentation and number of items as factors in paired associate verbal learning. ]. verb. Learn. verb. Behav., 1965, 4, 585-540. RUNQUIST, W. N. Intralist interference as a fimction of list length and interstimulus similarity. J. verb. Learn. verb. Behav., 1966, 5, 713. UNDERWOOD, B. J. Ten years of massed practice on distributed practice. Psychol. Rev., 1961, 68, 229-247. UNDERx,VOOD, B. J., AND SCHULZ, R. W. Meaningfnlness and verbal learning. Chicago, Lippincott, 1960. (Received September 20, 1965)