Pretraining and discrimination reversal learning by rhesus monkeys

Groups of five to seven macaques were trained on repeated reversals of a visual (or spatial) discrimination habit after no pretraining, extended discrimination training, or repeated reversal training on spatial (or visual) cues. Neither sort of pretraining had a significant effect on reversal learning on the second cue. These results indicate that monkeys’ capacity to develop generalized “win-stay, lose-shift” hypotheses may have been exaggerated in previous experiments.     

Visual discrimination learning of random figure problems by rhesus monkeys

In a two-choice discrimination learning paradigm, a U-shaped function was found between trials to criterion and the number of sides comprising the random figure discriminanda. These data are consistent with results from human Ss and suggest similar information processing capabilities in the two species. Changing the orientation of the stimulus figures after the discrimination had been learned only partially disrupted subsequent discrimination performance. Any single difference in selected form attributes between the two figures comprising a problem was not a good predictor of learning speed, suggesting that monkeys use a combination of such factors.     

Airblast avoidance learning sets in rhesus monkeys

Five rhesus monkeys were tested across a series of object discrimination problems requiring avoidance of noxious pressurized air. Each S displayed a progressive reduction in the number of trials to reach criterion on particular problems, eventually achieving 82% and 88% correct performance on Trials 2–6 and Trial 6. respectively. Certain error factors also appearing in appetitive discrimination learning set research (stimulus perseveration and differential cue) were identified, as well as a factor of relative unimportance in appetitive set (positional responding). A most persistent appetitive error factor presumably reflecting a tendency to explore the unchosen object (response shift) did not appear. In addition, the results extend the effectiveness of aversive airblasts to a relatively complex discrimination task.     

Partial reinforcement effects on discrimination learning

Rats were trained on a series of reversals of a successive discrimination in which the percentage of S+ trials ending in food was varied. Changes in the discrimination index occurred more slowly with 50% reinforcement than with 100% reinforcement when the number of training trials was equated across conditions, but were approximately invariant when the conditions were equated with respect to the number of obtained reinforcements. Presentation of free reinforcement during the intertrial intervals reduced the overall rate of discrimination acquisition, but left this invariance unaffected. Invariance in reinforcements necessary to attain acquisition also occurred when different discriminations correlated with different percentages of reinforcement were intermixed within experimental sessions. The failure of the invariance effect to be disrupted by either manipulation suggests that previous accounts of the invariance effect in terms of “comparator” models of conditioning (e.g., Gibbon & Balsam, 1981) are inadequate.     

Conditioned inhibition in feature negative discrimination learning with pigeons

Discrimination performance was investigated with pigeons using feature negative (FN) discrimination procedures which differed in the temporal arrangement of the stimuli on S? trials. In both procedures, a single common element was presented on reinforced (S+) trials. In thesimultaneous FN procedure, a distinguishing element was presented simultaneously with the common element of S? trials. In thesequential FN procedure, the distinguishing element preceded onset of the common element on S? trials. In two experiments, the sequential FN procedure yielded better discrimination performance. In Experiment 1, a summation test designed to separate learning and performance variables indicated that sequential FN subjects had learned the negative relationship between the distinguishing element and reinforcement while simultaneous FN subjects had not. In Experiment 2, summation and acquisition tests indicated that the distinguishing element developed inhibitory properties in the sequential FN procedure but not in the simultaneous FN procedure.     

Latent discrimination learning under a regular schedule of partial reinforcement

In this investigation, which employed rats in a runway, discriminative responding consisted of faster running on the reinforced than on the nonreinforced trials of either the 4NR or R4N schedule, both schedules containing fixed, repeated sequences of nonreinforced and reinforced trials. Under the 4NR schedule, four nonreinforced trials preceded a reinforced trial each day, and under the R4N schedule, a reinforced trial was followed by four nonreinforced trials each day. The major finding obtained was that under the 4NR schedule, discriminative responding was improved very substantially by a shift to extinction. Rats maintained on the 4NR schedule did not show improved discriminative responding, nor did discriminative responding improve in extinction following training under either the R4N schedule or a schedule of consistent reinforcement. Latent discrimination learning was defined as discriminative responding which fails to reflect adequately the amount of discrimination learning accomplished. The present findings demonstrate latent discrimination learning for regular schedules of partial reinforcement, something already demonstrated for brightness differential conditioning and possibly DRL schedules, as well.     

Eye movements of stumptailed monkeys during discrimination learning: VTE revisited

Eye movements of stumptailed monkeys were measured during learning of a pattern discrimination problem. Amount of scanning (shifts in visual fixation from one pattern to the other) increased once learning began and reached a maximum either at about the point that frequency of correct responses reached asymptote or just after that. These results, taken together with earlier findings on vicarious trial and error and operant observing behavior, suggest that this is the characteristic pattern of change in frequency of observing during visual discrimination learning. A change in information processing strategy is proposed as one explanation for these results. Duration of the last fixation on a discriminative stimulus during a trial showed similar, though not identical, changes with practice. The decrease in duration of the last fixation following learning contrasts with results of prior studies involving more complex tasks, and supports our conclusion that the duration of the last fixation is particularly sensitive to the cognitive processing requirements of the discriminative task.     

Crying and infant abuse in rhesus monkeys

This study investigated the relation between crying and infant abuse in group-living rhesus monkeys (Macaca mulatta). The subjects were 10 abusive mothers with their infants and 10 control mother-infant pairs. Abused infants cried more frequently than controls in the first 12 weeks of life, even when cries immediately following abuse were excluded from the analysis. The coos of 5 abused infants differed from those of 5 controls in several acoustic parameters, whereas their screams and geckers were acoustically similar, when recorded in the same context. Abusive mothers were less likely than control mothers to respond positively to the cries of their infants. Although infant cries may increase the probability of abuse being repeated, infant crying per se does not appear to be a major determinant of abuse.     

Gradual acquisition of visual discrimination tasks in a social group of rhesus monkeys (Macaca mulatta)

An established, captive colony of 74 rhesus monkeys (Macaca mulatta) was group-tested on a simultaneous visual discrimination problem and three reversals of the initial discrimination. The task incorporated important aspects of rhesus foraging behavior. Although other studies of communal groups of nonhuman primates have reported rapid learning, subjects in the present study showed no evidence of one-trial acquisition of the initial problem or of rapid learning-set formation across the reversal series. Instead, mean and individual performance, on all variables measured, improved gradually, both within and across series. Subjects appeared to “learn how to learn,” consistent with findings of traditional studies of individual discrimination learning. Our finding of gradual learning in group-living animals argues that the source of rapid learning in previous reports is not attributable to social influence or ecological relevance, but may reflect specific procedural or species differences between studies.     

Serial discrimination reversal learning in pigeons as a function of intertrial interval and delay of reinforcement

Pigeons learned a series of reversals of a simultaneous red-green visual discrimination. Delay of reinforcement (0 vs. 2 sec) and intertrial interval (ITI; 4 vs. 40 sec) were varied across blocks of reversals. Learning was faster with 0-sec than with 2-sec delays for both ITI values and faster with 4-sec ITIs than with 40-sec ITIs for both delays. Improvement in learning across successive reversals was evident throughout the experiment, furthermore, even after more than 120 reversals. The potent effects of small differences in reinforcement delay provide evidence for associative accounts and appear to be incompatible with accounts of choice that attempt to encompass the effects of temporal parameters in terms of animals’ timing of temporal intervals.     

Eye movements of monkeys during brightness discrimination and discrimination reversal

Eye movements of two stump-tailed monkeys were measured during performance on an easy and a difficult brightness discrimination problem with and without a relatively long fixation required at the beginning of each trial for purposes of calibration. The duration of an individual fixation of the discriminative stimuli was unrelated to most of the variables that were examined, including problem difficulty, response outcome, whether the S+ or the S? was fixated, and presence or absence of a long fixation at the beginning of a trial. Duration of fixation increased markedly, though temporarily, following reversal of the hard problem. The animals tended to do a minimal amount of scanning of the discriminative stimuli and to fixate most frequently on S+ before responding. In general, the results did not support an account of observing behavior in terms of conventional reinforcement.     

Irrelevant cues and shape discrimination learning by cats

Experimentally naive eats learned to discriminate a pair of objects (circle and triangle) that differed in external contour, with no irrelevant cues (N = 30), with irrelevant brightness cues (N = 26), and with irrelevant size and brightness cues (N = 26). In a second experiment, naive cats were trained to discriminate bidimensional patterns (circle and triangle) with no irrelevant visual cues (N = 24) or with irrelevant size and brightness cues (N = 26). Irrelevant cues did not significantly affect the rate of shape discrimination learning in either experiment. The findings disagree with the results of several similar experiments with rats.     

Learning of the insoluble conditional reaction problem by rhesus monkeys

Spiker’s modification of the Hull-Spence learning theory predicts that one particular type of conditional reaction problem is insoluble. However, a context-sensitive theory of discrimination learning developed by Medin predicts that this problem is soluble. Eight rhesus monkeys were trained on this previously uninvestigated problem for 36 days. Seven of the eight monkeys learned the problem, thus supporting the context-sensitive theory of discrimination learning.     

Auditorysame/different concept learning by monkeys

Two rhesus monkeys learned the auditory abstract concept ofsame/different. They were trained with 38 different environmental and natural sounds, which were arranged in different combinations as training progressed. Upon transfer to 138 different novel stimuli, they performed as well (78.8% correct) on the first exposure to the novel stimuli as they did (77.3%) with their training stimuli. The comparatively large set of training sounds, contact with the sound source, and a special fading procedure are thought to have contributed to the monkeys’ being able to learn this concept. Implications for species’ similarities/differences in cognitive processing are discussed.     

Preference effects on acquisition and retention of concurrent discriminations by rhesus monkeys

Ten rhesus monkeys were trained on five tasks, each of which consisted of eight concurrently presented object discrimination problems. Sequences of presentation were devised to allow one, two, or three new tasks to intervene between acquisition and retention tests or to provide a 30-day period of no testing. Equivalent and proficient performances were obtained in all retention tests, and no relationship was observed between retention and the initial preference characteristics of various objects. Object pReferences did produce significant influences upon acquisition, but these effects were not as pronounced in early tasks as in later ones. An additional retention test provided support for the contention that monkeys do not necessarily process information about specific object pair discriminations. Rather, they appeared to retain a list of previously rewarded objects even when object pairings were different from those provided during acquisition. Concurrent discriminations involving many distinct objects were resistant to interference and independent of preference characteristics over long retention periods.     

Socially biased learning in monkeys

We review socially biased learning about food and problem solving in monkeys, relying especially on studies with tufted capuchin monkeys (Cebus apella) and callitrichid monkeys. Capuchin monkeys most effectively learn to solve a new problem when they can act jointly with an experienced partner in a socially tolerant setting and when the problem can be solved by direct action on an object or substrate, but they do not learn by imitation. Capuchin monkeys are motivated to eat foods, whether familiar or novel, when they are with others that are eating, regardless of what the others are eating. Thus, social bias in learning about foods is indirect and mediated by facilitation of feeding. In most respects, social biases in learning are similar in capuchins and callitrichids, except that callitrichids provide more specific behavioral cues to others about the availability and palatability of foods. Callitrichids generally are more tolerant toward group members and coordinate their activity in space and time more closely than capuchins do. These characteristics support stronger social biases in learning in callitrichids than in capuchins in some situations. On the other hand, callitrichids’ more limited range of manipulative behaviors, greater neophobia, and greater sensitivity to the risk of predation restricts what these monkeys learn in comparison with capuchins. We suggest that socially biased learning is always the collective outcome of interacting physical, social, and individual factors, and that differences across populations and species in social bias in learning reflect variations in all these dimensions. Progress in understanding socially biased learning in nonhuman species will be aided by the development of appropriately detailed models of the richly interconnected processes affecting learning.     

Protein deprivation and food-related risk-taking preferences of rhesus monkeys

The relative preferences of four rhesus monkeys for reward probability versus reward amount when they were maintained on a low-protein (3.35%) diet were compared with those demonstrated when they were fed an adequate (13.4%) protein diet. Four stimulus objects, each signifying a different combination of reward frequency and amount (100%-one piece, 50%-2 pieces, 33%-three pieces, or 25%-four pieces), were presented in pairs, one pair per daily session, with trial schedules providing the same amount of reward within each set of 12 trials. Selections of the more frequently rewarded objects, but with lesser amounts per trial, were significantly higher during the low-protein phase than during either the preceding or the following normal-diet phases. Protein deprivation produces a changed motivational state making these animals less tolerant of infrequent or postponed reinforcement.     

Visual observing by rhesus monkeys: Some relationships with social dominance rank

Five rhesus monkeys were tested in a visual exploration situation to determine whether the mean frequency or mean duration of visual observing were systematically related to the dominance status of the observing animal. A dominance hierarchy among the five subjects was first determined by means of a competitive food-getting task. Following dominance testing, visual exploration testing was begun. All subjects were permitted to observe all other subjects in a round-robin pairing system involving two animals at a time. In each pairing, one animal served as the experimental subject (observer); the other as the stimulus (visual incentive). A highly significant linear effect of dominance was found in regard to duration of observing. Subjects high in the dominance hierarchy observed for significantly shorter durations than low-dominant subjects. Significant effects of dominance on the frequency of observing were also found, with animals intermediate in the hierarchy viewing more frequently than animals at either extreme. The data were interpreted in terms of the arousal and reduction of fear as a function of dominance and also through the notion of dominance distance.