Allan M. Schrier

Categorization of natural stimuli by monkeys (Macaca mulatta): effects of stimulus set size and modification of exemplars.

The concept humans was studied in two experiments on rhesus monkeys, in each of which a two-choice simultaneous discrimination procedure was used. In Experiment 1, the choice was between scenes with humans and scenes without humans, with the slide set sizable enough that a large number of trials could be given without repeating any individual slide. Speed of categorization learning was faster and final level of performance was higher than in prior research in this laboratory involving a much smaller slide set. Experiment 2 was an attempt to obtain some information about the basis for the categorization by means of a series of probe trials. Probe trials involved slides of humans that were modified in one of several ways and slides in which monkeys or apes were present instead of humans. When paired with slides with humans, probe slides were seldom chosen, except when they showed a human rightside up in an upside down scene. In the latter case, choices were at the chance level. When paired with a slide with no humans in the scene, probe slides were usually chosen, except when they showed monkeys or apes or silhouettes of humans, in which case choices were again at the chance level. Possible reasons for the differences in results of category learning tests with pigeons and monkeys are discussed as are the implications of the probe tests for a concept interpretation of these results.

Learning how to learn: The significance and current status of learning set formation

In honor of the memory ofHarry F. Harlow, this paper reviews the current status of learning set formation, the discovery of which represents one ofHarlows major contributions to behavioral science. Learning set formation or “learning how to learn” refers to the learning of visual and other types of discrimination problems progressively more quickly as a function of training on a series of such problems. The general procedure thatHarlow used, his original learning set finding, and its significance are described first. A brief review of theories of learning set formation follows. Lastly, the attempt to use learning set formation as a tool for studying comparative behavior is discussed.

Observing behavior in monkeys (Macaca arctoides): Support for the information hypothesis ☆

Abstract A single lever, discrete-trials observing procedure was used with stumptailed monkeys ( Macaca arctoides ). Lever-presses during a trial produced colored key lights (IS + and IS − ) which signaled whether the trial would end with response-independent food or without food. During the baseline period, both IS + and IS − were produced on a variable-interval (VI) 15-sec schedule which began operating at the onset of the trial. The two experimental conditions involved a combination of this VI schedule and a DRL schedule. In one of these conditions, only a response that both met the VI requirement and was preceded by at least 6 sec of nonresponding could produce IS − on nonfood trials, while the schedule for IS + on food trials remained VI 15 sec. In the other experimental condition, the schedules for producing the two stimuli were the reverse. All subjects eventually learned to produce either IS + or IS − on the combined VI-DRL schedule. These data support an information hypothesis of observing in monkeys and contrast with data from pigeons which support a conditioned reinforcement hypothesis.

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.

Pretraining performance of three species of macaque monkeys

Rhesus (Macaca mulatta), Philippine cynomolgus (M. irus), and stump-tailed(M. speciosa)macaques were given the same 16-step pretraining procedure in a Wisconsin General Test Apparatus (WGTA). The stump-tailed monkeys completed pretraining in significantly fewer trials than did the rhesus and Philippine monkeys. The pretraining performance of the latter two species was about the same.

Neonatal hypoglycemia in the rhesus monkey: Effect on development and behavior☆

Abstract Neonatal hypoglycemia has been implicated as a cause of brain damage that may lead to cognitive, sensory, psychomotor, or behavioral deficits in children. Because nonhuman primates can serve as useful models of many aspects of human behavior, we have produced neonatal hypoglycemia in newborn rhesus monkeys to identify the specific nature of the deficits produced. Neonatal hypoglycemia was produced by the continuous subcutaneous delivery (begun in utero) of insulin for up to the first 4 hours after birth. A cognitive and behavioral testing program was begun under blind conditions when each animal reached 8 months of age. None of the measures of cognitive abilities or behavior distinguished experimental animals with 6.5 hours of hypoglycemia from controls. Ten hours of hypoglycemia resulted in motivational and adaptability problems that made it impossible for some animals to learn even the simplest tasks, but, when provided with additional attention and adequate motivation, these experimental animals performed as well as controls in tests designed to measure cognitive ability. We conclude that neonatal hypoglycemia of 10 hours duration results in adaptive difficulties in rhesus monkeys but, if special attention is devoted to these animals, there are no enduring cognitive or behavioral deficits.

Visuo-Motor Integration in Split-Brain Cats

Chiasm- and callosum-sectioned (split-brain) cats and controls were trained to displace the correct one of two different objects, using each forelimb half the time. During this discrimination training, vision was restricted to one eye, thus confining visual input and learning to a single hemisphere in the split-brain animals. It was found that either forelimb could be used about equally well by all the animals.

Extradimensional transfer of learning-set formation in stumptailed monkeys ☆

Abstract Stumptailed macaques were trained (original learning) on a series of two-choice discrimination problems in which form (color) was relevant and color (form) irrelevant and variable within and between problems, i.e., tow values from the irrelevant dimension were used on each trial; these values varied randomly with respect to the reinforcer and were changed from problem to problem. After the S s reached a high level of performance, the relevant and irrelevant dimensions were reversed (shift learning). Performance levels were substantially and significantly higher during shift learning than during original learning, suggesting extradimensional transfer of learning-set formation. An additional control group was given extended training on a single color discrimination problem and then a series of form discriminations. The results for this group indicated that adaptation to testing may account for some of the transfer obtained, but far from all of it.

SUCROSE CONCENTRATION AND RESPONSE RATES OF MONKEYS

Studies on rats (e.g., Collier & Myers, 1961) suggest that the relationship berween bar-press rate and log sucrose concentration is a function of, among other things, frequency of reinforcement and volume per reinforcement. The relationship tends to be linear and increasing when frequency of reinforcement is low and volume is small, but tends to become nonmonotonic (increasing to a maximum, then decreasing) when either or both of these variables are increased. In one sucrose study on rhesus monkeys, Conrad and Sidman (1956) found a nonmonotonic rate-concentration function for each of three Ss tested. The data on rhesus monkeys reported here are also concerned with sucrose concentration effects. Bar-press rates of four adolescent Ss, deprived of food 18 to 20 hr., were determined for 10, 20, 30, 40, and 50% solutions of sucrose (by weight). Reinforcements were programmed according to a VI 1 schedule, and were delivered by means of a %-cc. cup in a Lehigh Valley Liquid Dipper. Duration of dipper presentation was 3 sec. Each S was given one 30-min. test session a day, 5 days a week, for a total of 8 weeks. The first week, for 2 Ss, the concentration was increased by 10% steps on successive days starting with the 10% solution, and, for the other 2 Ss, was decreased by 10% steps starting with the 50% solution. During succeeding weeks, the order of presentation of the solutions for each S was the reverse of the previous week. The mean response rates (Rs/Min.) during the first 5 min. and the entire 30 min.

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.