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Successive reversal learning in the bob-white quail (Colinus virginianus)
Anita. Behav.,1967, 1$, 1-5
SUCCESSIVE REVERSAL LEARNING IN T H E B O B - W H I T E (COLINUS VIRGINIANUS)
QUAIL
BY LAURENCE J. STETTNER, WILLIAM J. SCHULTZ & ALAN LEVY*
Wayne State University, and *Western Reserve University The study of reversal learning appears to be a most promising avenue for the development of a genuine comparative psychology of learning (cf. Bitterman, 1960). The reversal paradigm is readily adaptable to a wide variety of species, stimulus conditions, and response modes. The presence or absence of progressive improvement over a series of reversals is a criterion which can provide an objective basis for evaluating qualitative differences in learning ability between species. Results to date have been encouraging in that a consistent positive relationship has been found between level of successive reversal performance and phylogenetic status among the representatives of different classes that have been studied (Bitterman, 1965). To date, the least satisfactory set of reversal learning results appears to be for birds. Reid (1958) found little improvement in learning on successive visual-discrimination reversals in the pigeon. There was reduction of repetitive errors, but no reduction of frequency of initial errors on each stimulus presentation. Warren, Brookshire, Ball & Reynolds (1960), on the other hand, found that white leghorn chickens made fewer errors on the last five than on the first five spatial reversals, although no information is available in their report on the course of improvement. In an attempt to reconcile the above, Bullock & Bitterman (1962) found that pigeons did progressively improve on spatial reversals, while improvement was much more limited on visual reversals and occurred only under a specialized 'guidance' training procedure, wherein after the bird makes a defined number of perseverative errors, only the correct stimulus is presented on the next trial. Each training session was begun with a new reversal, regardless of level of performance reached on the previous session, so that we cannot really trace the course of improvement during different learning phases. Thus, it appears that birds do progressively improve on spatial reversals, but that visual reversal appears to represent some sort of particularly sensitive 'marginal' case, wherein
improvement occurs only in limited respects and/or under special conditions. The present experiment was designed to extend our knowledge of avian reversal learning to a new species, the Bob-white quail, utilizing a procedure of running each reversal to criterion so that a detailed analysis of performance at different stages of learning on successive reversals would be possible. Interest in testing the quail stems not only from general concern for broadening the species-generality of our knowledge, but also from the fact that if 'ability to show progressive improvement' truly reflects a fundamental aspect of the 'intellectual capacity' of a species, then one would expect species as similar in brain size and structure as the quail and the pigeon to be quite similar in this ability. The comparative anatomical work of Cobb (1960) and of Portmann & Stingelin (1960) has led them to place birds of the orders galliformes and columbiformes together in the 'more primitive' grouping of avian brain development, with passerines and psittaciformes representing the most advanced levels of development, and anseriformes representing an intermediate position. The current investigators in the course of histological analysis have observed the very close similarity between quail and pigeon forebrains, which are in turn easily differentiable from anseriforme, passerine, and psittaciforme forebrains. Since 'ability' in this case represents a marginal type of performance with respect to progressive improvement, this appears to represent a fairly stiff test of the phyletic generality of the successive reversal results.
Method Subjects. Four adult male Bob-white quail (Colinus virginianus) obtained from the Georgia Quail Farm, Savannah, Georgia, served as subjects. Apparatus. Four special living quarters adjoining a Skinner-type training box were constructed, each separated from the training area by a manual guillotine door. By lifting the door, the experimenter was able to 'shoo' the subjects
ANIMAL
BEHAVIOUR,
from living quarters to training box and back again with no necessity for handling, beyond the initial placement in the living quarter from the home cage. Each living quarter and the training box was 21 in. • in. • 17 in., and had four opaque walls and a wire grid floor and ceiling, a food cup at the base of one narrow wall, and a water supply. Centred above the training box food cup, at birds' eye level, were two stimulus windows, 189 in. • 189 in. A digital display projector unit was mounted in each window behind a pecking key of transparent Plexiglass, such that the birds' pecking responses were directed at the projected stimulus. The feeding apparatus, a hollow tube, 88 in. in diameter, permitted a supply of game bird chow to fall into the food cup. The feeder was electrically activated by a solenoid-controlled valve. Each stimulus was a set of three white stripes on a black field; one set was horizontally oriented, the other vertically. The entire apparatus was designed to perform all of the following operations automatically: (1) present horizontal and vertical sets at each stimulus presentation in random arrangement spatially, varied and balanced in accordance with selected Gellerman (1933) orders; (2) programme all stimulus events with a random arrangement ofintertrial intervals of 60, 90, 120, and 180 sec; (3) terminate the presentation of stimuli after all responses; (4) reinforce each correct response with 0.2 g; (5) perform 'delayed correction' (a procedure to eliminate spatial bias as an interfering variable, to be discussed later); (6) tally the frequencies of right, left, and reinforced responses, and total possible presentations; and (7) record on an Esterline-Angus multiple-event recorder the onset, duration, and termination of stimuli, and note the occurrence and correctness of each response and each intertrial peck. Feeding schedule. While still in the home cage, each bird was deprived of food for 48 hr, after which 15 g of chow were administered. Forty-eight hours following this feeding, the subject was placed in the living quarter with 15 g in the food cup. The first morning that the food cup was observed to be empty, the subject received another 15 g ration. Twenty-four and 48 hr later, the procedure was repeated. At the 72 hr mark (the third day after the first morning the food cup in the living quarter was found empty), the bird was shuttled through the guillotine door into the training box, the food cup of which contained 2 g. At this point, acquisition training began. On occasion, to
15,
1
facilitate initial pecking responses to the stimuli, the pecking keys were 'baited' with specks of grain made inaccessible by attachment to the outside of the transparent key. This technique was unnecessary in most cases, as the birds usually began the pecking-at-window responses quite spontaneously. On the first and each following day of training, the bird was fed the difference between 20 g and the amount 'earned' in training. This daily allowance was placed in the food cup in living quarter immediately after each training session. On Friday afternoons, each subject received an additional food ration of 25 g for weekend sustenance. Training schedule. During each 2 hr training session, the maximum possible number of stimulus presentations was 83. The apparatus was programmed in a manner such that unless the subject pecked at one of the stimuli, they would remain projected. In order to eliminate the possibility of a 'spatial fixation', wherein the animal could be rewarded 50 per cent of the time by responding to either the right or left stimulus regardless of visual differentiation, a delayed correction procedure was established. The incorrect response extinguished the projector lamps, but the automatic-sequence equipment was not caused to advance to the next 'step' in the stimulus sequence. For example, on a given trial with the left stimulus positive and the right negative, a pecking response to the right side terminated the stimulus presentation for that trial; but on the subsequent stimulus presentation, the leftpositive, right-negative arrangement was repeated. Only a correct (in this case, left) response 'stepped' the stimuli to the next unit in the random sequence. Thus continued responding to the same side would result in 0 per cent rather than 50 per cent reinforcement. In acquisition, two quail were trained on horizontal-positive, and two were reinforced for pecks at the vertical. When a given subject had reached the criterion of three successive training sessions at 90 per cent or better correct responses, the next session was a reversal of the acquisition condition. This rigid criterion for initial acquisition was used in order to insure full adaptation of the birds to the situation and the task prior to the onset of the reversal series. Subsequently, the criterion for successful learning in reversals was sixteen or more correct responses in the last twenty of each session. The training day following the one in which the
STETTNER et ah SUCCESSIVE REVERSAL LEARNING IN THE QUAIL subject met this criterion, another reversal was programmed. Thus, if a bird met criterion on day 1 on condition horizontal- positive, he was reversed to condition vertical-positive on the following training day. This procedure meant that generally some degree of 'over-learning' was involved on each reversal since the subject might reach a high level of correct performance sometime before the last twenty trials of a day, but still would not be reversed until the following day. Training was continued until each bird had gone through twenty-five reversals.
to the last. It appears that 'asymptotic' performance was reached by the second block' and that unsystematic variation beyond this point obscured the improvement that occurred early in the reversal series. Individual performance curves are shown in Fig. 1, errors to criterion for
::I/
2
#2
Results
All birds were able to acquire the discrimination fairly readily and to reverse successfully each time. However, there was only very limited indication of progressive improvement during the series of reversals. This can be seen in Table I, mean number of errors to criterion for acquisition and for each block of five reversals (for
8CI
20_
#13
.
" V 5
Table I. Mean Number Errors to Criterion for Acquisition and for Blocks of Five Reversals
Mean No. errors Acquisition
38 "2
Reversals
1- 5
38 "5
6-10
25 "5
11-15
30"6
16 - 20
34"0
21 - 25
23 "4
purposes of analysis, criterion was set at the first block of eight out of ten correct responses). On an a priori basis, a test of the hypothesis that no improvement occurred over the series was made by comparing the first and last blocks. The obtained t ratio was 2.50, with 3 df, indicating that the difference between the first and last block was significant at the 0.05 level of confidence. However, a repeated measures analysis of variance fell considerably short of statistical significance (F = 1.76, d f = 4, 12, P > 0 . 1 0 < 0-25) and no a posteriori comparisons of block means could be legitimately made. Inspection of the means in Table I helps explain this apparently contradictory state of affairs, as we can see that the second block performance was superior to the third and fourth and only slightly inferior
10
[
#15
~"
"
15 20 25
5
10
15 20
25
REVERSAL
Fig. 1. Errors to criterion on each reversalfor each subject. each reversal for each bird. These clearly show variability within each subjects' performance to the extent that they often made many more errors on later reversals than they had on considerably earlier ones. Indeed, with the exception of the record for bird No. 2, there is little progressive improvement apparent in any of the individual curves. Further, the 'best performance' level reached by the birds fell far short of anything that might be termed 'immediate reversal' since no bird was able to maintain performance at less than ten errors per reversal. This question of the absolute level of performance is a tricky one; but one we must face, as a comparison of the curve for No.2 with the others brings out. His very poor performance on the first reversal made his progressive improvement appear quite dramatic, although his 'peak performance' of fewest errors was no lower than for the other birds. (In this case, No. 2 did, ultimately, appear to be the best performer, in terms of consistently making the fewest errors. One can see clearly, however, that it is quite possible to have cases where terminal level of performance would be equal, therefore, the poorer the initial performance, the more pronounced the progressive improvement I) Further analysis of the birds' performance is provided in Fig. 2 which shows the change in percentage correct responses over the series
4
ANIMAL
801
100
f
TRIALS 1-10
n
10
15
20
BEHAVIOUR,
15,
n-2o I
25
S
10
15
20
loo
~$
21-30 I
S
1'0
lr5
sl-6o [ .,,
5,
20
/'x~
15
0
25
5
10 15 20 REVERSAL
25
5
10
. . . .
"
5
I
lO
'
15
f5
2'0
2=5
A
" / - " "
L
31--10 --/
.
2h5
"V'
._
I0
1
" "
20
i
25
Fig. 2. Mean per cent correct responses for different phases of each reversal. of reversals for different portions of each reversal session. This analysis shows that progressive improvement is confined entirely to the first four reversals, and that the maximum improvement over these reversals was in the twenty-one to sixty trial range, where performance went from below 50 per cent on the initial reversal to consistently above 50 per cent after the fourth. Within this range, there is a consistency not found in the overall reversal data. The improvement which occurred only on these middle trials and during the first few reversals is all but washed out when we consider performance over all trials and over all twentyfive reversals. As suggested by McIntosh (1965), analysis of performance over different portions of each reversal is more revealing than the overall analysis of errors to criterion. Just as performance during trials 21-60 suggests progressive improvement, performance on trials 1-20 indicates the quite limited nature of the improvement. Performance remained in the 20-30 per cent correct range over all twenty-five reversals for trials 1-10 and never exceeded 50 per cent correct on trials 11-20. Finally, we must consider the possibility that the extra training given on initial acquisition led to greater difficulty on the first reversal than on any of the others, and that improvement is due solely to this factor. Elimination of consideration of the first reversal would, in fact, attenuate the improvement in errors to criterion shown by No. 2 and No. 15, but it would lead to greater indication of improvement for No. 12 and No. 13. Moreover, the difference between first and last blocks would still be significant (t=5.46, df--3, P < 0 . 0 1 ) if we eliminate the first
reversal and divide the remaining twenty-four reversals into six equal blocks. Furthermore, the trends revealed in the analysis of different portions of each reversal (Fig. 2) would be essentially unchanged if the first reversal was eliminated. Throughout the range from 21-30 up through 51-60 trials, the major inflection point in the curves occurred between the fourth and fifth reversal. Discussion
The results of this study are essentially consistent with the findings reviewed by Bitterman (1965), and provide some support for the phyletic generality of results obtained with the successive reversal task. What might be termed limited or 'marginal' progressive improvement was found under conditions designed to facilitate detection of any genuine improvement. This is essentially the same type of finding reported for the pigeon. It should be noted, however, that the quail, pigeon, and domestic fowl are by no means representative of the highest level of avian development, but on the contrary, have been ranked among the lowest on the basis of comparative brain development (Cobb, 1960). A proper assessment of the learning capacity of birds as a class cannot be made without careful experimental study of the performance of representatives of the 'higher' birds, such as the crow, canary, or parrot forms. Although the general tenor of the results supports the use of reversal learning as a technique for comparative learning investigations, some basic methodological questions were brought out by the detailed analysis of the quail's
STETTNER et al.: SUCCESSIVE REVERSAL LEARNING IN THE QUAIL 'marginal' progressive improvement. 'Progressive improvement' might well be considered a generic term which could apply to many different patterns of performance and underlying mechanisms. It is clear that procedures should be designed to optimize performance on the initial reversal(s), or else a spurious progressive improvement can occur. Bitterman (1965) has recently come up against one aspect of this problem in his consideration of the likelihood that 'warm-up' effects may well have accounted for what initially looked like successive improvement in the cockroach, earthworm, and fish. It is also clear that in using reversal learning for phyletic comparison we must allow for some consideration of the ultimate level of performance reached, as well as the progressive trend.
Summary Four Bob-white quail (Colinus virginianus) were run on a series of twenty-five reversals of a discrimination involving simultaneous presentation of horizontal and vertical stripes. Analysis of five reversal blocks revealed a decrease in errors to criterion between the first and last block (t=2.50, P<0.05). Closer analysis indicated that there was no improvement after the fourth reversal, and little improvement at all on the first twenty trials of each reversal. This 'limited' improvement is consistent with previous results for the pigeon, thus providing some support for use of reversal learning as a tool in comparative learning studies. Analysis of individual performances, however, brought out
certain methodological problems primarily involving consideration of the influence of absolute levels of performance on progressive improvement trends.
REFERENCES Bitterman, M. E. (1960). Toward a comparative psychology of learning. Am. Psyehol., 15, 705-712. Bitterman, M. E. (1965). Phyletic differences in learning. Am. Psyehol., 20, 396-410. Bitterman, M. E., Wodinsky, J. & Candland, D. K. (1958). Some comparative psychology. Am. J. PsychoL, 71, 94-110. Bullock, D. H. & Bitterman, M. E. (1962). Habit reversal in the pigeon. J. comp. physiol. Psychol., 55, 958-962. Cobb, S. S. (1960). Observations on the comparative anatomy of the avian brain. Perspect. Biol. Med., 3, 383-408. Gellerman, L. W. (1933). Chance orders of alternating stimuli in visual discrimination experiments. J. genet. Psychol., 42, 207-208. McIntosh, N. J. (1965). Selective attention in animal discrimination learning. Psychol. Bull., 64, 124150. Portmann, A. & Stingelin, W. (1960). The central nervous system. Biology and Comparative Physiology of Birds, Vol. 2 (Ed. by A. J. Marshall). New York: Academic Press. Reid, R. L. (1958). Visual discrimination in pigeons. J. comp. physiol. Psyehol., 51, 716-720. Warren, J. M., Brookshire, K. H., Ball, G. C. & Reynolds, D. V. (1960). Reversal learning by white leghorn chicks. J. eomp. physiol. Psyehol., 53, 371-375. (Received 19 August 1965, revised 13 July 1966; Ms. number: A369)
SUCCESSIVE REVERSAL LEARNING IN T H E B O B - W H I T E (COLINUS VIRGINIANUS)
QUAIL
BY LAURENCE J. STETTNER, WILLIAM J. SCHULTZ & ALAN LEVY*
Wayne State University, and *Western Reserve University The study of reversal learning appears to be a most promising avenue for the development of a genuine comparative psychology of learning (cf. Bitterman, 1960). The reversal paradigm is readily adaptable to a wide variety of species, stimulus conditions, and response modes. The presence or absence of progressive improvement over a series of reversals is a criterion which can provide an objective basis for evaluating qualitative differences in learning ability between species. Results to date have been encouraging in that a consistent positive relationship has been found between level of successive reversal performance and phylogenetic status among the representatives of different classes that have been studied (Bitterman, 1965). To date, the least satisfactory set of reversal learning results appears to be for birds. Reid (1958) found little improvement in learning on successive visual-discrimination reversals in the pigeon. There was reduction of repetitive errors, but no reduction of frequency of initial errors on each stimulus presentation. Warren, Brookshire, Ball & Reynolds (1960), on the other hand, found that white leghorn chickens made fewer errors on the last five than on the first five spatial reversals, although no information is available in their report on the course of improvement. In an attempt to reconcile the above, Bullock & Bitterman (1962) found that pigeons did progressively improve on spatial reversals, while improvement was much more limited on visual reversals and occurred only under a specialized 'guidance' training procedure, wherein after the bird makes a defined number of perseverative errors, only the correct stimulus is presented on the next trial. Each training session was begun with a new reversal, regardless of level of performance reached on the previous session, so that we cannot really trace the course of improvement during different learning phases. Thus, it appears that birds do progressively improve on spatial reversals, but that visual reversal appears to represent some sort of particularly sensitive 'marginal' case, wherein
improvement occurs only in limited respects and/or under special conditions. The present experiment was designed to extend our knowledge of avian reversal learning to a new species, the Bob-white quail, utilizing a procedure of running each reversal to criterion so that a detailed analysis of performance at different stages of learning on successive reversals would be possible. Interest in testing the quail stems not only from general concern for broadening the species-generality of our knowledge, but also from the fact that if 'ability to show progressive improvement' truly reflects a fundamental aspect of the 'intellectual capacity' of a species, then one would expect species as similar in brain size and structure as the quail and the pigeon to be quite similar in this ability. The comparative anatomical work of Cobb (1960) and of Portmann & Stingelin (1960) has led them to place birds of the orders galliformes and columbiformes together in the 'more primitive' grouping of avian brain development, with passerines and psittaciformes representing the most advanced levels of development, and anseriformes representing an intermediate position. The current investigators in the course of histological analysis have observed the very close similarity between quail and pigeon forebrains, which are in turn easily differentiable from anseriforme, passerine, and psittaciforme forebrains. Since 'ability' in this case represents a marginal type of performance with respect to progressive improvement, this appears to represent a fairly stiff test of the phyletic generality of the successive reversal results.
Method Subjects. Four adult male Bob-white quail (Colinus virginianus) obtained from the Georgia Quail Farm, Savannah, Georgia, served as subjects. Apparatus. Four special living quarters adjoining a Skinner-type training box were constructed, each separated from the training area by a manual guillotine door. By lifting the door, the experimenter was able to 'shoo' the subjects
ANIMAL
BEHAVIOUR,
from living quarters to training box and back again with no necessity for handling, beyond the initial placement in the living quarter from the home cage. Each living quarter and the training box was 21 in. • in. • 17 in., and had four opaque walls and a wire grid floor and ceiling, a food cup at the base of one narrow wall, and a water supply. Centred above the training box food cup, at birds' eye level, were two stimulus windows, 189 in. • 189 in. A digital display projector unit was mounted in each window behind a pecking key of transparent Plexiglass, such that the birds' pecking responses were directed at the projected stimulus. The feeding apparatus, a hollow tube, 88 in. in diameter, permitted a supply of game bird chow to fall into the food cup. The feeder was electrically activated by a solenoid-controlled valve. Each stimulus was a set of three white stripes on a black field; one set was horizontally oriented, the other vertically. The entire apparatus was designed to perform all of the following operations automatically: (1) present horizontal and vertical sets at each stimulus presentation in random arrangement spatially, varied and balanced in accordance with selected Gellerman (1933) orders; (2) programme all stimulus events with a random arrangement ofintertrial intervals of 60, 90, 120, and 180 sec; (3) terminate the presentation of stimuli after all responses; (4) reinforce each correct response with 0.2 g; (5) perform 'delayed correction' (a procedure to eliminate spatial bias as an interfering variable, to be discussed later); (6) tally the frequencies of right, left, and reinforced responses, and total possible presentations; and (7) record on an Esterline-Angus multiple-event recorder the onset, duration, and termination of stimuli, and note the occurrence and correctness of each response and each intertrial peck. Feeding schedule. While still in the home cage, each bird was deprived of food for 48 hr, after which 15 g of chow were administered. Forty-eight hours following this feeding, the subject was placed in the living quarter with 15 g in the food cup. The first morning that the food cup was observed to be empty, the subject received another 15 g ration. Twenty-four and 48 hr later, the procedure was repeated. At the 72 hr mark (the third day after the first morning the food cup in the living quarter was found empty), the bird was shuttled through the guillotine door into the training box, the food cup of which contained 2 g. At this point, acquisition training began. On occasion, to
15,
1
facilitate initial pecking responses to the stimuli, the pecking keys were 'baited' with specks of grain made inaccessible by attachment to the outside of the transparent key. This technique was unnecessary in most cases, as the birds usually began the pecking-at-window responses quite spontaneously. On the first and each following day of training, the bird was fed the difference between 20 g and the amount 'earned' in training. This daily allowance was placed in the food cup in living quarter immediately after each training session. On Friday afternoons, each subject received an additional food ration of 25 g for weekend sustenance. Training schedule. During each 2 hr training session, the maximum possible number of stimulus presentations was 83. The apparatus was programmed in a manner such that unless the subject pecked at one of the stimuli, they would remain projected. In order to eliminate the possibility of a 'spatial fixation', wherein the animal could be rewarded 50 per cent of the time by responding to either the right or left stimulus regardless of visual differentiation, a delayed correction procedure was established. The incorrect response extinguished the projector lamps, but the automatic-sequence equipment was not caused to advance to the next 'step' in the stimulus sequence. For example, on a given trial with the left stimulus positive and the right negative, a pecking response to the right side terminated the stimulus presentation for that trial; but on the subsequent stimulus presentation, the leftpositive, right-negative arrangement was repeated. Only a correct (in this case, left) response 'stepped' the stimuli to the next unit in the random sequence. Thus continued responding to the same side would result in 0 per cent rather than 50 per cent reinforcement. In acquisition, two quail were trained on horizontal-positive, and two were reinforced for pecks at the vertical. When a given subject had reached the criterion of three successive training sessions at 90 per cent or better correct responses, the next session was a reversal of the acquisition condition. This rigid criterion for initial acquisition was used in order to insure full adaptation of the birds to the situation and the task prior to the onset of the reversal series. Subsequently, the criterion for successful learning in reversals was sixteen or more correct responses in the last twenty of each session. The training day following the one in which the
STETTNER et ah SUCCESSIVE REVERSAL LEARNING IN THE QUAIL subject met this criterion, another reversal was programmed. Thus, if a bird met criterion on day 1 on condition horizontal- positive, he was reversed to condition vertical-positive on the following training day. This procedure meant that generally some degree of 'over-learning' was involved on each reversal since the subject might reach a high level of correct performance sometime before the last twenty trials of a day, but still would not be reversed until the following day. Training was continued until each bird had gone through twenty-five reversals.
to the last. It appears that 'asymptotic' performance was reached by the second block' and that unsystematic variation beyond this point obscured the improvement that occurred early in the reversal series. Individual performance curves are shown in Fig. 1, errors to criterion for
::I/
2
#2
Results
All birds were able to acquire the discrimination fairly readily and to reverse successfully each time. However, there was only very limited indication of progressive improvement during the series of reversals. This can be seen in Table I, mean number of errors to criterion for acquisition and for each block of five reversals (for
8CI
20_
#13
.
" V 5
Table I. Mean Number Errors to Criterion for Acquisition and for Blocks of Five Reversals
Mean No. errors Acquisition
38 "2
Reversals
1- 5
38 "5
6-10
25 "5
11-15
30"6
16 - 20
34"0
21 - 25
23 "4
purposes of analysis, criterion was set at the first block of eight out of ten correct responses). On an a priori basis, a test of the hypothesis that no improvement occurred over the series was made by comparing the first and last blocks. The obtained t ratio was 2.50, with 3 df, indicating that the difference between the first and last block was significant at the 0.05 level of confidence. However, a repeated measures analysis of variance fell considerably short of statistical significance (F = 1.76, d f = 4, 12, P > 0 . 1 0 < 0-25) and no a posteriori comparisons of block means could be legitimately made. Inspection of the means in Table I helps explain this apparently contradictory state of affairs, as we can see that the second block performance was superior to the third and fourth and only slightly inferior
10
[
#15
~"
"
15 20 25
5
10
15 20
25
REVERSAL
Fig. 1. Errors to criterion on each reversalfor each subject. each reversal for each bird. These clearly show variability within each subjects' performance to the extent that they often made many more errors on later reversals than they had on considerably earlier ones. Indeed, with the exception of the record for bird No. 2, there is little progressive improvement apparent in any of the individual curves. Further, the 'best performance' level reached by the birds fell far short of anything that might be termed 'immediate reversal' since no bird was able to maintain performance at less than ten errors per reversal. This question of the absolute level of performance is a tricky one; but one we must face, as a comparison of the curve for No.2 with the others brings out. His very poor performance on the first reversal made his progressive improvement appear quite dramatic, although his 'peak performance' of fewest errors was no lower than for the other birds. (In this case, No. 2 did, ultimately, appear to be the best performer, in terms of consistently making the fewest errors. One can see clearly, however, that it is quite possible to have cases where terminal level of performance would be equal, therefore, the poorer the initial performance, the more pronounced the progressive improvement I) Further analysis of the birds' performance is provided in Fig. 2 which shows the change in percentage correct responses over the series
4
ANIMAL
801
100
f
TRIALS 1-10
n
10
15
20
BEHAVIOUR,
15,
n-2o I
25
S
10
15
20
loo
~$
21-30 I
S
1'0
lr5
sl-6o [ .,,
5,
20
/'x~
15
0
25
5
10 15 20 REVERSAL
25
5
10
. . . .
"
5
I
lO
'
15
f5
2'0
2=5
A
" / - " "
L
31--10 --/
.
2h5
"V'
._
I0
1
" "
20
i
25
Fig. 2. Mean per cent correct responses for different phases of each reversal. of reversals for different portions of each reversal session. This analysis shows that progressive improvement is confined entirely to the first four reversals, and that the maximum improvement over these reversals was in the twenty-one to sixty trial range, where performance went from below 50 per cent on the initial reversal to consistently above 50 per cent after the fourth. Within this range, there is a consistency not found in the overall reversal data. The improvement which occurred only on these middle trials and during the first few reversals is all but washed out when we consider performance over all trials and over all twentyfive reversals. As suggested by McIntosh (1965), analysis of performance over different portions of each reversal is more revealing than the overall analysis of errors to criterion. Just as performance during trials 21-60 suggests progressive improvement, performance on trials 1-20 indicates the quite limited nature of the improvement. Performance remained in the 20-30 per cent correct range over all twenty-five reversals for trials 1-10 and never exceeded 50 per cent correct on trials 11-20. Finally, we must consider the possibility that the extra training given on initial acquisition led to greater difficulty on the first reversal than on any of the others, and that improvement is due solely to this factor. Elimination of consideration of the first reversal would, in fact, attenuate the improvement in errors to criterion shown by No. 2 and No. 15, but it would lead to greater indication of improvement for No. 12 and No. 13. Moreover, the difference between first and last blocks would still be significant (t=5.46, df--3, P < 0 . 0 1 ) if we eliminate the first
reversal and divide the remaining twenty-four reversals into six equal blocks. Furthermore, the trends revealed in the analysis of different portions of each reversal (Fig. 2) would be essentially unchanged if the first reversal was eliminated. Throughout the range from 21-30 up through 51-60 trials, the major inflection point in the curves occurred between the fourth and fifth reversal. Discussion
The results of this study are essentially consistent with the findings reviewed by Bitterman (1965), and provide some support for the phyletic generality of results obtained with the successive reversal task. What might be termed limited or 'marginal' progressive improvement was found under conditions designed to facilitate detection of any genuine improvement. This is essentially the same type of finding reported for the pigeon. It should be noted, however, that the quail, pigeon, and domestic fowl are by no means representative of the highest level of avian development, but on the contrary, have been ranked among the lowest on the basis of comparative brain development (Cobb, 1960). A proper assessment of the learning capacity of birds as a class cannot be made without careful experimental study of the performance of representatives of the 'higher' birds, such as the crow, canary, or parrot forms. Although the general tenor of the results supports the use of reversal learning as a technique for comparative learning investigations, some basic methodological questions were brought out by the detailed analysis of the quail's
STETTNER et al.: SUCCESSIVE REVERSAL LEARNING IN THE QUAIL 'marginal' progressive improvement. 'Progressive improvement' might well be considered a generic term which could apply to many different patterns of performance and underlying mechanisms. It is clear that procedures should be designed to optimize performance on the initial reversal(s), or else a spurious progressive improvement can occur. Bitterman (1965) has recently come up against one aspect of this problem in his consideration of the likelihood that 'warm-up' effects may well have accounted for what initially looked like successive improvement in the cockroach, earthworm, and fish. It is also clear that in using reversal learning for phyletic comparison we must allow for some consideration of the ultimate level of performance reached, as well as the progressive trend.
Summary Four Bob-white quail (Colinus virginianus) were run on a series of twenty-five reversals of a discrimination involving simultaneous presentation of horizontal and vertical stripes. Analysis of five reversal blocks revealed a decrease in errors to criterion between the first and last block (t=2.50, P<0.05). Closer analysis indicated that there was no improvement after the fourth reversal, and little improvement at all on the first twenty trials of each reversal. This 'limited' improvement is consistent with previous results for the pigeon, thus providing some support for use of reversal learning as a tool in comparative learning studies. Analysis of individual performances, however, brought out
certain methodological problems primarily involving consideration of the influence of absolute levels of performance on progressive improvement trends.
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