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Noncorrectional probability learning and reversal by rats: Posterior decortication influence
PhyMology and B¢lmvior, Vol. 6, pp. 613-615. Pcxgamon P r ~ l , 1971. Printed in Great Britain
BRIEF COMMUNICATION Noncorrectional Probability Learning and Reversal by Rats: Posterior Decortication Influence' F, R O B E R T T R ~ C H L E R
Department o f Psychology, Kent State University, Kent, Ohio, U.S.A. (Received 13 August 1970)
T~CHH~, F. R. Noncorrectionalprobability learning and reversal by rats: posterior decortication influence. PHY$IOL. Bm-L~V. 6 (5) 613-615, 1971.--Thirty normal and thirty posterior decorticate rats were tested on spatial probability learning and reversal at ratios of 60:40, 70:30 or 80:20. All testing employed discrete-trial noncorrectional procedures. In acquisition, both normal and lesioned subjects at 80:20 and 70:30 ratios came to select the more frequently reinforced alternative on nearly every trial. On the 60:40 ratio, asymptotic choice levels of all subjects remained at levels only slightly greater than chance. In reversal the 80:20 and 70:30 ratios yielded response strategies similar to those of acquisition, and no reliable effect of the lesion was observed. At the 60:40 ratio, lesioned animals seemed to show little influence of their prior training, while normal subjects exhibited a tendency to relinquish their choice of the previously more frequently reinforced alternative. However, neither normal nor lesioned rats showed asymptotic 60:40 reversal performance which was different from chance. Decortication
Probability learning
Reversal
Rats
A ~NT experiment by Treichler and Dengerink [2] has assessed the visual and spatial probability learning and reversal of rats which had received either anterior or posterior neocortical lesions of the type described by Hotel, Bvttinger, Royce and Meyer [1]. Although the two lesion loci did not produce different effects, a slight impairment was observed in acquisition of a 70:30 correctional probability task. However, this result was specific to the spatial probability learning task, and comparatively poorer and nondifferential performance was observed on both the acquisition and reversal of a visual task. In the report by Treichler and Dengerink [2], the correctional procedure was used exclusively. However, Uhl [3] has shown that different eventual choice strategies are employed by rats in probability learning as a consequence of the use of correctional or noncorrectional procedures. Under the former condition, matching or approximation of reinforcement probability by choice probability occurs, while under the latter condition, maximizing or consistent choice of a more frequently reinforced alternative obtains. Further, Uhl [3] reports that the use of different probability ratios, ie. 80:20, 70:30, etc., influences the level of matching for subjects receiving correctional procedures, while this manipulation merely prolongs the course of acquisition when non-correctional training is provided at probability ratios of small disparity. The present experiment was designed as an assessment of cortical lesion influences on probability learning and reversal
when non-correctional training was provided at several different probability ratios. The purpose of the experiment was to determine the generality of the finding of Treichler and Dengerink [2] which indicated an impairment in acquisition of the spatial test under correctional procedings at one probability ratio (70:30). METHOD
Sixty male Holtzman albino rats, 110-130 days old, served as subjects. All were reduced to 85 per cent of their predeprivation weights and maintained at this level by daily restriction of food rations. A specially constructed Skinner box identical to the apparatus used by Treichler and Dengerink [2] served as the test compartment. Responding required discrete-trial choices which were designed by the contact of one of two food cups. Correct choices yielded 45 nag rat diet pellets, and incorrect choices terminated the trial without reward.
Surgery The intended extent of lesion was the same as the "posterior" bilateral extirpation administered by Horel et aL, [1]. A two-week recovery period was provided after surgery, and the establishment of pre-deprivation weights was instituted after this period. Upon completion of testing, all lesioned rats were sacrificed and histological examination of both cortical surface damage and retrograde thalamic degeneration was
1This research was partially supported by funds obtained under terms of grant MH-12934. The assistance of Gary LaMonica and Frank H a i r in animal testing is acknowledged. 613
614
TREICHLER
conducted. Surface areas of the aspirative lesions conformed to the intended locus, and extensive thalamic degeneration was noted in the dorsal lateral gcniculate nuclei.
Procedure Half the 60 animals were initially designated to serve as posterior decorticate subjects, while the other half remained as normal controls. The 30 rats in each group were then assigned randomly with the restriction of equal group size to receive training at probabilty ratios of 80:20, 70:30 or 60:40. All such training was conducted by a noncorrectional procedure. Upon reduction to appropriate weight level each rat was placed in the test compartment for an adaptation session. Several pellets were available in the food cups and contacting the cup yielded further pellet delivery. When contact responses had been thoroughly established, adaptation to the discrete response requirement of the procedure was instituted. Under these conditions contacting either cup yielded one pellet, terminated illumination of food cups, and initiated a 4 sec ITI during which the contact circuits were inoperative. Fifty such trials were presented in the first adaptation session. A second adaptation session provided 50 further discrete trials, using a trial rerun correction procedure for the first 25 trials and simple non-correctional training for the last 25 trials. This provided a deterrent to the establishment of position responding during pre-training. Upon completion of these phases, assigned reinforcement ratios were instituted on Day 3. Half the animals under each condition had the right position assigned as the more frequently reinforced alternative. The occurrence of trials rewarding choice of the less frequently reinforced alternative was determined randomly with the restriction that at least one such trial occur within successive blocks of ten trials.
Each rat received 50 trials per day for 28 days in acquisition. In a subsequent 20 day test period, reinforcement contingencies were changed so that the previously more-frequently reversed alternative became the less-frequently rewarded alternative, and reversal performances were assessed.
Results and Discussion Figure 1 depicts the mean proportional choice of the more frequently reinforced (majority) alternative by normal and lesioned rats trained at the different probability ratios. Analyses of variance using arcine transformed proportion scores yielded no main effect or interaction influence of the lesion variable (all ps > 0.05). However, a significant main effect of both probability ratio and blocks was indicated. While the block effect appeared to represent acquisition through the course of training, the influence of probability ratio was indicated to be entirely dependent upon the differential results observed under the 60:40 ratio. Additionally, a significant (p < 0.05) interaction was obtained for the blocks × probability ratio term. This appeared to represent the relatively slow course of majority choice adoption on the 60:40 ratio. Figure 2 displays information about the mean proportion of majority choice for the normal and lesioned groups during reversal on the various ratios. As in the acquisition phase, no main effect of the lesion variable was observed, while both blocks and probability ratios did yield significant main effects. Further, a significant blocks × probability ratio interaction was obtained. A significant blocks × lesion × probability ratio interaction was also observed. This result appeared to be a consequence of the performance of lesioned animals on the reversal of the 60:40 task. Apparently, little effect of original training was evident in these animals when reinforcement
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FIG. 1. Mean proportional choice of the more frequently reinforced alternative by normal and posterior lesioned rats tested on the acquisition of throe different probability ratios (six independent groups with n = 10 per group).
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PROBABILITY LEARNING AND DECORTICATION
615
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FIG. 2. Mean proportional choice of the more frequently reinforced alternative by normal and posterior lesioned rats tested on the reversal of three different probability ratios (six independent groups with n = 10 per group).
contingencies were reversed. In contrast, normal animals, although they displayed similar asymptotic choice levels in acquisition, did show continued choice of the former majority alternative in the early blocks of reversal with subsequent improvement in choice of the newly designated higher probability alternative. It should be noted that acquisition on the 60:40 probability ratio was difficult for both normal and lesioned animals, but performance on the last five blocks for both groups was significantly different (p < 0.05) from chance as measured by a t for specific alternatives. Conversely, reversal performances of both groups were highly variable and terminal performance did not differ from chance according to statistical tests like those applied to the acquisition data. In the present test situation, acquisition of probability learning under non-correctional procedures appeared strikingly like that reported by Uhl [3] with the exception that the 60:40 probability ratio required an unduly large number of training trials in this test. The results from reversal of the
60:40 ratio are difficult to interpret, but they do suggest some impairment of reversal perfomances. This property of performance by lesioned animals is also indicated at the other probability ratios and may decline in severity as ratios providing greater reward disparity are used as assessment tasks. The present results indicate that acquisition of noncorrectional probability learning, unlike its correctionally presented counterpart, is not influenced by posterior neodecortication. Subsequent non-correctional reversal seems to yield a very slight indication of differential performances by lesioned and normal subjects especially when there is little disparity in probability of reward of the alternatives. The overall impression gained from this study and the one by Treichler and Dengerink [2] is that cortical lesion influences upon probability learning and reversal are not demonstrated in gross performance measures. Rather, such influences appear only as subtle differences in limited aspects of the behavior assessed in our test situation.
REFERENCES 1. Horel, J. A., L. A. Bettinger, C. J. Royce and D. R. Meyer, Role of neocortex in the learning and relearning of two visual habits by the rat. J. comp. physiol. Psychol. 61: 66-78, 1966. 2. Treichler, F. R. and H. A. Dengednk. Visual and spatial probability learning by the rat: Selective decortication influences. Physiol. Behav. 5: 1229-1233, 1970.
3. Uhl, C. N. Two-choice probability learning in the rat as a function of incentive, probability of reinforcement and training procedure. J. exp. Psychol. 66: 443-449, 1963.
BRIEF COMMUNICATION Noncorrectional Probability Learning and Reversal by Rats: Posterior Decortication Influence' F, R O B E R T T R ~ C H L E R
Department o f Psychology, Kent State University, Kent, Ohio, U.S.A. (Received 13 August 1970)
T~CHH~, F. R. Noncorrectionalprobability learning and reversal by rats: posterior decortication influence. PHY$IOL. Bm-L~V. 6 (5) 613-615, 1971.--Thirty normal and thirty posterior decorticate rats were tested on spatial probability learning and reversal at ratios of 60:40, 70:30 or 80:20. All testing employed discrete-trial noncorrectional procedures. In acquisition, both normal and lesioned subjects at 80:20 and 70:30 ratios came to select the more frequently reinforced alternative on nearly every trial. On the 60:40 ratio, asymptotic choice levels of all subjects remained at levels only slightly greater than chance. In reversal the 80:20 and 70:30 ratios yielded response strategies similar to those of acquisition, and no reliable effect of the lesion was observed. At the 60:40 ratio, lesioned animals seemed to show little influence of their prior training, while normal subjects exhibited a tendency to relinquish their choice of the previously more frequently reinforced alternative. However, neither normal nor lesioned rats showed asymptotic 60:40 reversal performance which was different from chance. Decortication
Probability learning
Reversal
Rats
A ~NT experiment by Treichler and Dengerink [2] has assessed the visual and spatial probability learning and reversal of rats which had received either anterior or posterior neocortical lesions of the type described by Hotel, Bvttinger, Royce and Meyer [1]. Although the two lesion loci did not produce different effects, a slight impairment was observed in acquisition of a 70:30 correctional probability task. However, this result was specific to the spatial probability learning task, and comparatively poorer and nondifferential performance was observed on both the acquisition and reversal of a visual task. In the report by Treichler and Dengerink [2], the correctional procedure was used exclusively. However, Uhl [3] has shown that different eventual choice strategies are employed by rats in probability learning as a consequence of the use of correctional or noncorrectional procedures. Under the former condition, matching or approximation of reinforcement probability by choice probability occurs, while under the latter condition, maximizing or consistent choice of a more frequently reinforced alternative obtains. Further, Uhl [3] reports that the use of different probability ratios, ie. 80:20, 70:30, etc., influences the level of matching for subjects receiving correctional procedures, while this manipulation merely prolongs the course of acquisition when non-correctional training is provided at probability ratios of small disparity. The present experiment was designed as an assessment of cortical lesion influences on probability learning and reversal
when non-correctional training was provided at several different probability ratios. The purpose of the experiment was to determine the generality of the finding of Treichler and Dengerink [2] which indicated an impairment in acquisition of the spatial test under correctional procedings at one probability ratio (70:30). METHOD
Sixty male Holtzman albino rats, 110-130 days old, served as subjects. All were reduced to 85 per cent of their predeprivation weights and maintained at this level by daily restriction of food rations. A specially constructed Skinner box identical to the apparatus used by Treichler and Dengerink [2] served as the test compartment. Responding required discrete-trial choices which were designed by the contact of one of two food cups. Correct choices yielded 45 nag rat diet pellets, and incorrect choices terminated the trial without reward.
Surgery The intended extent of lesion was the same as the "posterior" bilateral extirpation administered by Horel et aL, [1]. A two-week recovery period was provided after surgery, and the establishment of pre-deprivation weights was instituted after this period. Upon completion of testing, all lesioned rats were sacrificed and histological examination of both cortical surface damage and retrograde thalamic degeneration was
1This research was partially supported by funds obtained under terms of grant MH-12934. The assistance of Gary LaMonica and Frank H a i r in animal testing is acknowledged. 613
614
TREICHLER
conducted. Surface areas of the aspirative lesions conformed to the intended locus, and extensive thalamic degeneration was noted in the dorsal lateral gcniculate nuclei.
Procedure Half the 60 animals were initially designated to serve as posterior decorticate subjects, while the other half remained as normal controls. The 30 rats in each group were then assigned randomly with the restriction of equal group size to receive training at probabilty ratios of 80:20, 70:30 or 60:40. All such training was conducted by a noncorrectional procedure. Upon reduction to appropriate weight level each rat was placed in the test compartment for an adaptation session. Several pellets were available in the food cups and contacting the cup yielded further pellet delivery. When contact responses had been thoroughly established, adaptation to the discrete response requirement of the procedure was instituted. Under these conditions contacting either cup yielded one pellet, terminated illumination of food cups, and initiated a 4 sec ITI during which the contact circuits were inoperative. Fifty such trials were presented in the first adaptation session. A second adaptation session provided 50 further discrete trials, using a trial rerun correction procedure for the first 25 trials and simple non-correctional training for the last 25 trials. This provided a deterrent to the establishment of position responding during pre-training. Upon completion of these phases, assigned reinforcement ratios were instituted on Day 3. Half the animals under each condition had the right position assigned as the more frequently reinforced alternative. The occurrence of trials rewarding choice of the less frequently reinforced alternative was determined randomly with the restriction that at least one such trial occur within successive blocks of ten trials.
Each rat received 50 trials per day for 28 days in acquisition. In a subsequent 20 day test period, reinforcement contingencies were changed so that the previously more-frequently reversed alternative became the less-frequently rewarded alternative, and reversal performances were assessed.
Results and Discussion Figure 1 depicts the mean proportional choice of the more frequently reinforced (majority) alternative by normal and lesioned rats trained at the different probability ratios. Analyses of variance using arcine transformed proportion scores yielded no main effect or interaction influence of the lesion variable (all ps > 0.05). However, a significant main effect of both probability ratio and blocks was indicated. While the block effect appeared to represent acquisition through the course of training, the influence of probability ratio was indicated to be entirely dependent upon the differential results observed under the 60:40 ratio. Additionally, a significant (p < 0.05) interaction was obtained for the blocks × probability ratio term. This appeared to represent the relatively slow course of majority choice adoption on the 60:40 ratio. Figure 2 displays information about the mean proportion of majority choice for the normal and lesioned groups during reversal on the various ratios. As in the acquisition phase, no main effect of the lesion variable was observed, while both blocks and probability ratios did yield significant main effects. Further, a significant blocks × probability ratio interaction was obtained. A significant blocks × lesion × probability ratio interaction was also observed. This result appeared to be a consequence of the performance of lesioned animals on the reversal of the 60:40 task. Apparently, little effect of original training was evident in these animals when reinforcement
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FIG. 1. Mean proportional choice of the more frequently reinforced alternative by normal and posterior lesioned rats tested on the acquisition of throe different probability ratios (six independent groups with n = 10 per group).
50 trial blocks
PROBABILITY LEARNING AND DECORTICATION
615
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FIG. 2. Mean proportional choice of the more frequently reinforced alternative by normal and posterior lesioned rats tested on the reversal of three different probability ratios (six independent groups with n = 10 per group).
contingencies were reversed. In contrast, normal animals, although they displayed similar asymptotic choice levels in acquisition, did show continued choice of the former majority alternative in the early blocks of reversal with subsequent improvement in choice of the newly designated higher probability alternative. It should be noted that acquisition on the 60:40 probability ratio was difficult for both normal and lesioned animals, but performance on the last five blocks for both groups was significantly different (p < 0.05) from chance as measured by a t for specific alternatives. Conversely, reversal performances of both groups were highly variable and terminal performance did not differ from chance according to statistical tests like those applied to the acquisition data. In the present test situation, acquisition of probability learning under non-correctional procedures appeared strikingly like that reported by Uhl [3] with the exception that the 60:40 probability ratio required an unduly large number of training trials in this test. The results from reversal of the
60:40 ratio are difficult to interpret, but they do suggest some impairment of reversal perfomances. This property of performance by lesioned animals is also indicated at the other probability ratios and may decline in severity as ratios providing greater reward disparity are used as assessment tasks. The present results indicate that acquisition of noncorrectional probability learning, unlike its correctionally presented counterpart, is not influenced by posterior neodecortication. Subsequent non-correctional reversal seems to yield a very slight indication of differential performances by lesioned and normal subjects especially when there is little disparity in probability of reward of the alternatives. The overall impression gained from this study and the one by Treichler and Dengerink [2] is that cortical lesion influences upon probability learning and reversal are not demonstrated in gross performance measures. Rather, such influences appear only as subtle differences in limited aspects of the behavior assessed in our test situation.
REFERENCES 1. Horel, J. A., L. A. Bettinger, C. J. Royce and D. R. Meyer, Role of neocortex in the learning and relearning of two visual habits by the rat. J. comp. physiol. Psychol. 61: 66-78, 1966. 2. Treichler, F. R. and H. A. Dengednk. Visual and spatial probability learning by the rat: Selective decortication influences. Physiol. Behav. 5: 1229-1233, 1970.
3. Uhl, C. N. Two-choice probability learning in the rat as a function of incentive, probability of reinforcement and training procedure. J. exp. Psychol. 66: 443-449, 1963.