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Problem diversity and familiarity in multiple discrimination learning by monkeys
Anim. Behav ., 1968,16, 74-78
OBLEM DI E
I Y AND FAMILIA I Y IN M L I LE
DI C IMINA ION LEA NING BY MONKEY BY A
H
J.
IO ELLE*
ulane niversity Delta egional rimate esearch Center, Covington, La . 70433 AND
W . HA OLD MOONt
Auburn niversity, Auburn, Ala . 36830
hesus monkeys, given many discrimination problems daily, form efficient learning sets (Harlow, 1949), eventually attaining a high percentage of correct responses on the second and subsequent trials of the problems . Is diversity of problems a necessity or even an aid? On the one hand, sets are formed to a series of problems made up of all possible two-object combinations taken from a set of four objects ( iopelle, 1955), and problem reversal training using only three problems (1300 total trials) also permits its development in chimpanzees ( chusterman, 1962) . On the other hand, training on six difficult discrimination problems does not lead to learning-set formation in macaques, even though each problem may require many trials to be learned ( iopelle, 1953) . It would thus appear that problem diversity, i .e . the number of object-unique problems encountered, is a significant variable in learning-set formation . One purpose of the present experiment was to evaluate its importance . Opportunities for investigating two other variables emerged in developing the experimental design . First, because the design required that some animals should encounter the same stimulus pairs repeatedly, whereas others were always presented with new stimuli, we had the opportunity to compare performance on problems consisting of familiar stimuli with that on problems in which all stimuli were unfamiliar . his would tell us of the importance of the stimulus familiarity as a factor in learning-set formation . his comparison demands that some animals should be trained on completely new problems each day and that others should be trained mostly on familiar stimulus pairs but with just enough new problems each day to provide a basis for comparison with the first group.
he second opportunity then presented itself : since it was decided to present familiar stimulus pairs, why not create two groups, one trained mostly on familiar problems which did not have to be learned anew each day, i .e . problems in which the correct stimulus was the same on every trial, and the other group given the same familiar stimulus pairs as the first group but with the identity of the rewarded stimulus varying randomly from one problem to the next . he first group would merely need to remember the correct responses to each problem, whereas the second group could derive no consistent advantage from this approach . ince this last group would be required repeatedly to reverse its earlier solutions, a comparison of the two groups would tell us about the importance of this factor in learning to learn . Method ubjects welve juvenile and young-adult stumptail monkeys (Macaca speciosa) of both sexes served in this experiment. None had undergone previous discrimination learning, so all were trained to displace a single object from a food well to obtain the hidden reward before beginning the experiment . Apparatus All testing was conducted in a modified version of the Wisconsin general test apparatus (Harlow, 1949) . he stimuli consisted of several hundred pairs of multidimensionally different objects of the sort usually employed in learning-set studies. rocedure he monkeys, tested individually, sat in a cage behind an opaque screen . When this was raised, they confronted a grey tray bearing two stimuli, one of which covered food reward. o obtain it, they had merely to displace the object from the food well . he monkey's task was to discover (learn) in each problem which of the two objects covered the food during the six
* upported by grant No . F -00164 from the Division of esearch Facilities and esources, National Institutes of Health. t his study was conducted while the second author was visiting scientist at the rimate Center . 74
IO ELLE & MOON : DI C IMINA ION LEA NING BY MONKEY
trials they were presented . pon completion of one problem, a different pair of objects was presented for another six trials . he monkeys attempted ten such problems each day for 50 days . he non-correction procedure was used throughout : when an animal displaced the unrewarded object, the tray was withdrawn, the opaque screen lowered and the tray reset for the next trial . here was one deviation from customary procedure . Instead of placing a highly preferred food morsel, such as a raisin or corn kernel, under the correct object, we used only the standard laboratory diet . On some occasions this was sweetened with saccharin to increase its appeal . he reason for using the standard laboratory diet rather than the customary special reward was that these animals were participating in the baseline phase of a concurrent nutrition experiment which imposed this demand . Experimental Design he animals were assigned randomly to three groups . he control (C) group underwent the standard learning-set procedures, receiving ten new problems each day for 50 days, making a total of 500 new problems learned . he other two groups had three new problems each day plus seven `familiar' problems which reappeared daily . For the predictable reward ( ) group, the same member of each familiar problem was always the correct one and its displacement invariably led to food reward . he unpredictable reward ( ) group, on the other hand, saw the same pairs of stimuli, but there was no way in which the animal could predict on any day which member of the pair was to be rewarded, for this was determined by a table of random nip nbers . he group had to learn the correct st , mulus of each problem whereas the group h, d only to remember the correct stimulus . he group learned 350 `familiar' problems and 150 new problems . pon completion of this phase of the experiment, all groups were tested on the control (standard learning-set) procedure for 50 problems : ten unfamiliar problems per day for 5 days (phase II) . he purpose of this was to determine whether or not performance on the new problems by the and the F groups in phase I was altered by the concurrent familiar problems . esults hase I Figure 1 shows the intraproblem learning
75
curves for the three groups . he left panels portray the results of the recurrent, familiar problems and the right panels show the performance on the novel problems . Each curve of the figures represents 5 days of testing . he first week's performance of the group on the familiar problems (left panel) varies between 50 per cent and 70 per cent correct, that for the second week between 80 per cent and 90 percent correct, and for all subsequent weeks is close to 100 per cent correct . erformance on the familiar problems by the group shows a progressive improvement such as one would expect in the formation of learning sets, but it never attains the level reached by the group . Differences between the groups far exceed the usually accepted levels of statistical significance . It is of interest to know whether or not the group's performance on the familiar problems surpasses its performance on new problems (top panels) . his difference measures the effect of stimulus familiarity on learning rate . roficiency on trials 2 to 6 of the familiar problems approximates that for novel problems . he difference which was statistically non-significant ( able I), averaged only 2 . 6 per cent during the last 15 days . able I. ummary of Analysis of ariance . npredictable eward Group. Old versus New roblems (Last 3 weeks) ource
df
M
F
roblems
1
48 . 13
3 . 33
rials
4
189 . 78
13 . 14*
Weeks
2
888 . 433
61 .06*
ooled Error
22
14 . 44
otal
29
* ignificant at 0 . 001 level
he graph of the C group (lower right panel) shows learning-set curves as they have been presented many times before . his graph is based on all ten problems of each day, hence the curves are more stable than those for the other groups . erformance on trial 1 hovers near 50 per cent, and that on trials 2 to 6 rises progressively throughout the experiment . he cardinal comparisons of this experiment are those among the performances of the three groups on the novel problems . he C group's performance surpasses that of the other two
76
ANIMAL BEHA IO OLD
, 16, 1
OBLEM
NEW
OBLEM
X
w CL
LEGEND -- I - 5 DAY ---- • 6-10 11-15 < 16-20 - • 21- 25 26-30 -- 31-35 36-40 41-45 ---- 46 - 50
s0 70
CON I
2
OL G O
3
4
5
6
IAL Fig . 1 . erformance of three groups of monkeys on familiar and novel problems, phase I . groups . For example, second-trial proficiency, which measures the amount learned on the first trial, averages 83 per cent correct for the C group, 63 per cent for the group and 71 per cent for the group during the last 2 weeks of training . he superiority of the C group persists through all trials and is highly significant ( able II) .
here is no overall difference between the performance of the and the groups . hase II Figure 2 shows the performance of the three groups on the 5 days of standard learning-set problems given during hase II . he C group's
IO ELLE & MOON : DI C IMINA ION LEA NING BY MONKEY able II.
ummary of Analysis of roblems All groups
ource
ariance for New
df
M
F
Groups (G)
2
2227 .23
17-63*
rials ( )
4
949 . 91
16 . 03*
Weeks (W)
9
961 .69
6 . 72*
G x
8
59 .25
2 .35
G x W
18
129 . 14
5 . 12*
x W
36
33 . 95
1 . 35
72
25 . 21
Gx otal
xW
149 * ignificant at 0 . 001 level
IAL
Fig . 2. erformance of monkeys on learning-set problems, phase II.
performance again surpasses that of the two two familiar-problem groups, but no difference exists between the group and group . Differences among groups for trials 2 to 6 are highly significant, virtually all of the variance is however, due to the superiority of the C group ( able III) . hus discrimination-learning proficiency of the two groups with only restricted experience is itself limited . Discussion he principal finding of the experiment is that diversity of problems enhances the formation of learning sets. Both the and the groups'
77
able III. ummary of Analysis of ariance, hase ource
df
Groups
2
239 . 27
16-58**
1
546 . 13
37 . 84***
1
32 . 40
2 . 25
4
95 .73
6 .63
8
14 .43
C versus
and
versus rials G x
(Error)
M
F
performances on new problems were inferior to the one of the C group which received ten novel problems daily. Explanations of learning-set formation based solely on the acquisition of strategies or skills which are independent of the range of stimuli employed, for example the `win-stay', lose-shift' hypothesis ( chusterman, 1962), or `abstract' cues related to properties of reinforcement common to all problems ( estle, 1958, pp . 79), are not sufficient . Although these theories predict the equivalence of performance by the and the groups on novel problems -the strategies being equally applicable in the and the procedures-they do not predict the inferiority of the two groups to the C group, which also is alike in these characteristics . Moreover it is difficult to see why error factors (Harlow, 1959) are eliminated at the precise rates required for these data, since the experimental procedures are equivalent except for stimulusrelated aspects . he win-stay, lose-shift strategy, if it develops, is relevant to both the and the problems . A question may be raised as to the unity of the strategy and as to whether its development depends on the number of rewards . he group made many win-stay responses and received a reward on virtually every trial, whereas the group experienced both rewarded and unrewarded trials . If the win-stay strategy is different from the lose-shift strategy, the performances of the group and group on the new problems should differ strikingly . In fact they were identical, non-rewarded trials within rather wide limits, being as informative as rewarded trials . he strategy is therefore believed to be unitary . eese (1964) accounts for one-trial learning within the Hull- pence theory which specifically requires that the subjects should be given practice on a large number of problems . his theory therefore predicts the superiority of the C
78
ANIMAL BEHA IO
group, although it does not anticipate the learning sets produced in the four-stimulus experiments with rhesus monkeys ( iopelle, 1955) or in the chimpanzee experiment ( chusterman, 1962) involving several multiple reversal problems. Diversity of stimuli must be considered in any complete explanation of this phenomenon . timulus diversity, if not crucial for learning-set formation, surely assists macaques in it . Familiarity with stimuli does not improve discrimination learning . If this were a potent variable, as would be expected from latent learning or sensory preconditioning considerations, performance on the familiar problems by the group would surpass that on the novel problems. he absence of a difference is consistent with a related finding by hell & iopelle (1958) who exposed a series of stimulus pairs to platyrrhine monkeys before using them as discriminanda . he exposure was without effect on learning rate. imilarly, repeated presentations of a single stimulus with changing partners ( iopelle, Cronholm & Addison, 1962) did not improve learning. If familiarity depresses performance, its effect is seen on the unfamiliar problems as well. It is noteworthy that the and the procedures, so different in their use of the familiar problems, produce equivalent rates of learning on the novel problems . One group ( ) must relearn the problems every day, performing successive reversals, the other group need not . he group may alternatively be thought of as performing discriminations under 50 per cent partial reinforcement, given in runs of six trials, and thus equating the cumulative reinforcements of the two stimuli in each pair . he group, on the other hand, responds consistently to one of the stimuli which is always rewarded . Evidently, both equal and widely discrepant cumulated response tendencies to the familiar stimuli have the same effect on the learning of stimuli . Also, since the learning of the familiar problems, which have (equated) high approach tendencies, proceeds at the same pace as the learning of the novel problems which have presumed low response tendencies, we can infer that magnitude of response tendencies, if they are equal, is not an important factor in monkey discrimination learning . On a first approximation, the familiar problems have no effect on the speed of learning the new problems, and perhaps the familiar problems should be ignored in plotting learning-set
, 16, 1
formation. hus, the group was 69 per cent correct on problems 106 to 150, the group 70 per cent and the C group was 66 per cent correct on problems 101 to 150 . aking this approach, we would conclude that either the animals effectively segregated the two types of problems and suppressed any transfer between them, solving them totally independently, or the dissimilarity of the old and the new problems was so great that transfer between them was impossible . But one should not accept this conclusion too hastily, since the comparability of performance is difficult to determine precisely when learning curves have gentle slopes . ummary hree groups of four stumptail macaques were trained in a learning-set experiment . wo groups saw seven familiar and three unfamiliar problems daily ; the third group saw ten problems, all new . eward was always under certain familiar stimuli for the group but unpredictably located for the group . Control group performance surpassed that of the familiar problem groups on novel problems . Familiarproblem performance equalled novel-problem performance in the group . roficiency on novel problems was identical for the two familiar-problem groups . EFE ENCE Harlow, H . F . (1949) . he formation of learning sets . sychol . ev ., 56, 51-65 . Harlow, H. F . (1959) . Learning set and error factor theory . In sychology : A tudy of a cience (ed . by . Koch), ol . 2 . pp . 492-537 . New York : McGraw-Hill . Levine, M . (1959) . A model of hypothesis behaviour in discrimination learning sets . sychol. ev ., 66, 353-366 . eese, H . W. (1964) . Discrimination learning sets in rhesus monkeys . sychol. Bull., 61, 321-340. estle, F . (1958) . oward a quantitative description of learning set data . sychol. ev., 65, 77-91 . iopelle, A . J . & Copelan, E . L . (1954) . Discrimination reversal to a sign . J. comp . physiol. sychol., 48, 143-145 . iopelle, A . J . (1955). Learning sets from minimum stimuli . J. exp . sychol., 49, 28-32. iopelle, A . J., Cronholm, J. N . & Addison, . G . (1962) . timulus familiarity and multiple djscrimination learning . J. comp . physiol. sychol., 55, 274-278. chusterman, . J . (1962). ransfer effects of successive discrimination-reversal training in chimpanzees . cience, 137, 422-423 . hell, W . F. & iopelle, A . J . (1958) . rogressive discrimination learning in platyrrhine monkeys . J. comp. physiol . sychol., 51, 467-470 . ( eceived 25 April 1967 ; revised 14 July 1967 ; Ms. number: A575)
OBLEM DI E
I Y AND FAMILIA I Y IN M L I LE
DI C IMINA ION LEA NING BY MONKEY BY A
H
J.
IO ELLE*
ulane niversity Delta egional rimate esearch Center, Covington, La . 70433 AND
W . HA OLD MOONt
Auburn niversity, Auburn, Ala . 36830
hesus monkeys, given many discrimination problems daily, form efficient learning sets (Harlow, 1949), eventually attaining a high percentage of correct responses on the second and subsequent trials of the problems . Is diversity of problems a necessity or even an aid? On the one hand, sets are formed to a series of problems made up of all possible two-object combinations taken from a set of four objects ( iopelle, 1955), and problem reversal training using only three problems (1300 total trials) also permits its development in chimpanzees ( chusterman, 1962) . On the other hand, training on six difficult discrimination problems does not lead to learning-set formation in macaques, even though each problem may require many trials to be learned ( iopelle, 1953) . It would thus appear that problem diversity, i .e . the number of object-unique problems encountered, is a significant variable in learning-set formation . One purpose of the present experiment was to evaluate its importance . Opportunities for investigating two other variables emerged in developing the experimental design . First, because the design required that some animals should encounter the same stimulus pairs repeatedly, whereas others were always presented with new stimuli, we had the opportunity to compare performance on problems consisting of familiar stimuli with that on problems in which all stimuli were unfamiliar . his would tell us of the importance of the stimulus familiarity as a factor in learning-set formation . his comparison demands that some animals should be trained on completely new problems each day and that others should be trained mostly on familiar stimulus pairs but with just enough new problems each day to provide a basis for comparison with the first group.
he second opportunity then presented itself : since it was decided to present familiar stimulus pairs, why not create two groups, one trained mostly on familiar problems which did not have to be learned anew each day, i .e . problems in which the correct stimulus was the same on every trial, and the other group given the same familiar stimulus pairs as the first group but with the identity of the rewarded stimulus varying randomly from one problem to the next . he first group would merely need to remember the correct responses to each problem, whereas the second group could derive no consistent advantage from this approach . ince this last group would be required repeatedly to reverse its earlier solutions, a comparison of the two groups would tell us about the importance of this factor in learning to learn . Method ubjects welve juvenile and young-adult stumptail monkeys (Macaca speciosa) of both sexes served in this experiment. None had undergone previous discrimination learning, so all were trained to displace a single object from a food well to obtain the hidden reward before beginning the experiment . Apparatus All testing was conducted in a modified version of the Wisconsin general test apparatus (Harlow, 1949) . he stimuli consisted of several hundred pairs of multidimensionally different objects of the sort usually employed in learning-set studies. rocedure he monkeys, tested individually, sat in a cage behind an opaque screen . When this was raised, they confronted a grey tray bearing two stimuli, one of which covered food reward. o obtain it, they had merely to displace the object from the food well . he monkey's task was to discover (learn) in each problem which of the two objects covered the food during the six
* upported by grant No . F -00164 from the Division of esearch Facilities and esources, National Institutes of Health. t his study was conducted while the second author was visiting scientist at the rimate Center . 74
IO ELLE & MOON : DI C IMINA ION LEA NING BY MONKEY
trials they were presented . pon completion of one problem, a different pair of objects was presented for another six trials . he monkeys attempted ten such problems each day for 50 days . he non-correction procedure was used throughout : when an animal displaced the unrewarded object, the tray was withdrawn, the opaque screen lowered and the tray reset for the next trial . here was one deviation from customary procedure . Instead of placing a highly preferred food morsel, such as a raisin or corn kernel, under the correct object, we used only the standard laboratory diet . On some occasions this was sweetened with saccharin to increase its appeal . he reason for using the standard laboratory diet rather than the customary special reward was that these animals were participating in the baseline phase of a concurrent nutrition experiment which imposed this demand . Experimental Design he animals were assigned randomly to three groups . he control (C) group underwent the standard learning-set procedures, receiving ten new problems each day for 50 days, making a total of 500 new problems learned . he other two groups had three new problems each day plus seven `familiar' problems which reappeared daily . For the predictable reward ( ) group, the same member of each familiar problem was always the correct one and its displacement invariably led to food reward . he unpredictable reward ( ) group, on the other hand, saw the same pairs of stimuli, but there was no way in which the animal could predict on any day which member of the pair was to be rewarded, for this was determined by a table of random nip nbers . he group had to learn the correct st , mulus of each problem whereas the group h, d only to remember the correct stimulus . he group learned 350 `familiar' problems and 150 new problems . pon completion of this phase of the experiment, all groups were tested on the control (standard learning-set) procedure for 50 problems : ten unfamiliar problems per day for 5 days (phase II) . he purpose of this was to determine whether or not performance on the new problems by the and the F groups in phase I was altered by the concurrent familiar problems . esults hase I Figure 1 shows the intraproblem learning
75
curves for the three groups . he left panels portray the results of the recurrent, familiar problems and the right panels show the performance on the novel problems . Each curve of the figures represents 5 days of testing . he first week's performance of the group on the familiar problems (left panel) varies between 50 per cent and 70 per cent correct, that for the second week between 80 per cent and 90 percent correct, and for all subsequent weeks is close to 100 per cent correct . erformance on the familiar problems by the group shows a progressive improvement such as one would expect in the formation of learning sets, but it never attains the level reached by the group . Differences between the groups far exceed the usually accepted levels of statistical significance . It is of interest to know whether or not the group's performance on the familiar problems surpasses its performance on new problems (top panels) . his difference measures the effect of stimulus familiarity on learning rate . roficiency on trials 2 to 6 of the familiar problems approximates that for novel problems . he difference which was statistically non-significant ( able I), averaged only 2 . 6 per cent during the last 15 days . able I. ummary of Analysis of ariance . npredictable eward Group. Old versus New roblems (Last 3 weeks) ource
df
M
F
roblems
1
48 . 13
3 . 33
rials
4
189 . 78
13 . 14*
Weeks
2
888 . 433
61 .06*
ooled Error
22
14 . 44
otal
29
* ignificant at 0 . 001 level
he graph of the C group (lower right panel) shows learning-set curves as they have been presented many times before . his graph is based on all ten problems of each day, hence the curves are more stable than those for the other groups . erformance on trial 1 hovers near 50 per cent, and that on trials 2 to 6 rises progressively throughout the experiment . he cardinal comparisons of this experiment are those among the performances of the three groups on the novel problems . he C group's performance surpasses that of the other two
76
ANIMAL BEHA IO OLD
, 16, 1
OBLEM
NEW
OBLEM
X
w CL
LEGEND -- I - 5 DAY ---- • 6-10 11-15 < 16-20 - • 21- 25 26-30 -- 31-35 36-40 41-45 ---- 46 - 50
s0 70
CON I
2
OL G O
3
4
5
6
IAL Fig . 1 . erformance of three groups of monkeys on familiar and novel problems, phase I . groups . For example, second-trial proficiency, which measures the amount learned on the first trial, averages 83 per cent correct for the C group, 63 per cent for the group and 71 per cent for the group during the last 2 weeks of training . he superiority of the C group persists through all trials and is highly significant ( able II) .
here is no overall difference between the performance of the and the groups . hase II Figure 2 shows the performance of the three groups on the 5 days of standard learning-set problems given during hase II . he C group's
IO ELLE & MOON : DI C IMINA ION LEA NING BY MONKEY able II.
ummary of Analysis of roblems All groups
ource
ariance for New
df
M
F
Groups (G)
2
2227 .23
17-63*
rials ( )
4
949 . 91
16 . 03*
Weeks (W)
9
961 .69
6 . 72*
G x
8
59 .25
2 .35
G x W
18
129 . 14
5 . 12*
x W
36
33 . 95
1 . 35
72
25 . 21
Gx otal
xW
149 * ignificant at 0 . 001 level
IAL
Fig . 2. erformance of monkeys on learning-set problems, phase II.
performance again surpasses that of the two two familiar-problem groups, but no difference exists between the group and group . Differences among groups for trials 2 to 6 are highly significant, virtually all of the variance is however, due to the superiority of the C group ( able III) . hus discrimination-learning proficiency of the two groups with only restricted experience is itself limited . Discussion he principal finding of the experiment is that diversity of problems enhances the formation of learning sets. Both the and the groups'
77
able III. ummary of Analysis of ariance, hase ource
df
Groups
2
239 . 27
16-58**
1
546 . 13
37 . 84***
1
32 . 40
2 . 25
4
95 .73
6 .63
8
14 .43
C versus
and
versus rials G x
(Error)
M
F
performances on new problems were inferior to the one of the C group which received ten novel problems daily. Explanations of learning-set formation based solely on the acquisition of strategies or skills which are independent of the range of stimuli employed, for example the `win-stay', lose-shift' hypothesis ( chusterman, 1962), or `abstract' cues related to properties of reinforcement common to all problems ( estle, 1958, pp . 79), are not sufficient . Although these theories predict the equivalence of performance by the and the groups on novel problems -the strategies being equally applicable in the and the procedures-they do not predict the inferiority of the two groups to the C group, which also is alike in these characteristics . Moreover it is difficult to see why error factors (Harlow, 1959) are eliminated at the precise rates required for these data, since the experimental procedures are equivalent except for stimulusrelated aspects . he win-stay, lose-shift strategy, if it develops, is relevant to both the and the problems . A question may be raised as to the unity of the strategy and as to whether its development depends on the number of rewards . he group made many win-stay responses and received a reward on virtually every trial, whereas the group experienced both rewarded and unrewarded trials . If the win-stay strategy is different from the lose-shift strategy, the performances of the group and group on the new problems should differ strikingly . In fact they were identical, non-rewarded trials within rather wide limits, being as informative as rewarded trials . he strategy is therefore believed to be unitary . eese (1964) accounts for one-trial learning within the Hull- pence theory which specifically requires that the subjects should be given practice on a large number of problems . his theory therefore predicts the superiority of the C
78
ANIMAL BEHA IO
group, although it does not anticipate the learning sets produced in the four-stimulus experiments with rhesus monkeys ( iopelle, 1955) or in the chimpanzee experiment ( chusterman, 1962) involving several multiple reversal problems. Diversity of stimuli must be considered in any complete explanation of this phenomenon . timulus diversity, if not crucial for learning-set formation, surely assists macaques in it . Familiarity with stimuli does not improve discrimination learning . If this were a potent variable, as would be expected from latent learning or sensory preconditioning considerations, performance on the familiar problems by the group would surpass that on the novel problems. he absence of a difference is consistent with a related finding by hell & iopelle (1958) who exposed a series of stimulus pairs to platyrrhine monkeys before using them as discriminanda . he exposure was without effect on learning rate. imilarly, repeated presentations of a single stimulus with changing partners ( iopelle, Cronholm & Addison, 1962) did not improve learning. If familiarity depresses performance, its effect is seen on the unfamiliar problems as well. It is noteworthy that the and the procedures, so different in their use of the familiar problems, produce equivalent rates of learning on the novel problems . One group ( ) must relearn the problems every day, performing successive reversals, the other group need not . he group may alternatively be thought of as performing discriminations under 50 per cent partial reinforcement, given in runs of six trials, and thus equating the cumulative reinforcements of the two stimuli in each pair . he group, on the other hand, responds consistently to one of the stimuli which is always rewarded . Evidently, both equal and widely discrepant cumulated response tendencies to the familiar stimuli have the same effect on the learning of stimuli . Also, since the learning of the familiar problems, which have (equated) high approach tendencies, proceeds at the same pace as the learning of the novel problems which have presumed low response tendencies, we can infer that magnitude of response tendencies, if they are equal, is not an important factor in monkey discrimination learning . On a first approximation, the familiar problems have no effect on the speed of learning the new problems, and perhaps the familiar problems should be ignored in plotting learning-set
, 16, 1
formation. hus, the group was 69 per cent correct on problems 106 to 150, the group 70 per cent and the C group was 66 per cent correct on problems 101 to 150 . aking this approach, we would conclude that either the animals effectively segregated the two types of problems and suppressed any transfer between them, solving them totally independently, or the dissimilarity of the old and the new problems was so great that transfer between them was impossible . But one should not accept this conclusion too hastily, since the comparability of performance is difficult to determine precisely when learning curves have gentle slopes . ummary hree groups of four stumptail macaques were trained in a learning-set experiment . wo groups saw seven familiar and three unfamiliar problems daily ; the third group saw ten problems, all new . eward was always under certain familiar stimuli for the group but unpredictably located for the group . Control group performance surpassed that of the familiar problem groups on novel problems . Familiarproblem performance equalled novel-problem performance in the group . roficiency on novel problems was identical for the two familiar-problem groups . EFE ENCE Harlow, H . F . (1949) . he formation of learning sets . sychol . ev ., 56, 51-65 . Harlow, H. F . (1959) . Learning set and error factor theory . In sychology : A tudy of a cience (ed . by . Koch), ol . 2 . pp . 492-537 . New York : McGraw-Hill . Levine, M . (1959) . A model of hypothesis behaviour in discrimination learning sets . sychol. ev ., 66, 353-366 . eese, H . W. (1964) . Discrimination learning sets in rhesus monkeys . sychol. Bull., 61, 321-340. estle, F . (1958) . oward a quantitative description of learning set data . sychol. ev., 65, 77-91 . iopelle, A . J . & Copelan, E . L . (1954) . Discrimination reversal to a sign . J. comp . physiol. sychol., 48, 143-145 . iopelle, A . J . (1955). Learning sets from minimum stimuli . J. exp . sychol., 49, 28-32. iopelle, A . J., Cronholm, J. N . & Addison, . G . (1962) . timulus familiarity and multiple djscrimination learning . J. comp . physiol. sychol., 55, 274-278. chusterman, . J . (1962). ransfer effects of successive discrimination-reversal training in chimpanzees . cience, 137, 422-423 . hell, W . F. & iopelle, A . J . (1958) . rogressive discrimination learning in platyrrhine monkeys . J. comp. physiol . sychol., 51, 467-470 . ( eceived 25 April 1967 ; revised 14 July 1967 ; Ms. number: A575)