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A M Schrier

Publications and source records attributed to A M Schrier.

13 recordsLinked to original sources
PubMed1987

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.

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PubMed1985

Biological and behavioural assessments of young rhesus monkeys after intrauterine exposure to high phenylalanine concentrations.

Nineteen pregnant Macaca mulatta were fed a special diet throughout the gestational period in an attempt to render them hyperphenylalaninaemic. Group C (control group) received a regular diet, group Lo was given a 'low' phenylalanine diet, group Me a 'median' phenylalanine diet, and group Hi a 'high' phenylalanine diet. Nearly all monkeys had an uncomplicated pregnancy and an uneventful delivery. Biological measurements were obtained shortly after the birth of the infants and behavioural assessments were done when the offspring were between 6 and 18 months of age. The results of the biological and behavioural evaluations revealed that there was no statistically significant difference among the respective study groups. We concluded that a combination of factors inherent in an imperfect animal model may account for the negative results of this study.

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PubMed1982

Eye movements of monkeys during discrimination learning: role of visual scanning.

Four experiments were conducted on stumptailed monkeys (Macaca arctoides) to determine whether the high levels of visual scanning (shifts in fixation from one discriminative stimulus to the other) seen during discrimination learning play a necessary role in this learning. In Experiments 1 and 2, the monkeys were given a series of two-choice, dot-pattern discrimination reversal problems. Normal visual scanning before a choice response was allowed during all but the reversal trials of half of the problems. On these latter trials, the discriminative stimuli were replaced by an uninformative stimulus after the animals made more than one visual fixation on each discriminative stimulus. Thus, on these trials, the animals were limited, in terms of the information received, to the empirically determined minimum number of scans necessary to maintain high levels of performance on such problems. In both experiments, which differed primarily in the number and type of uninformative stimuli used, the rate of reversal learning was markedly retarded by the experimental condition, with the effect persisting over a long series of problems. The magnitude of the effect was unrelated to the similarity of the uninformative stimulus to the discriminative stimuli. In Experiment 3, the monkeys were given a series of discrimination problems without reversals, during half of which the experimental condition was in effect. The results were similar to those of the first two experiments. Experiment 4 was similar to the preceding experiment except that, under the experimental condition, each trial began with the uninformative stimuli, which were replaced by the discriminative stimuli when visual scanning occurred. The uninformative stimuli had no clear-cut effect on discrimination learning in this experiment. These experiments indicate that the information provided by above-minimum levels of scanning is not necessary for discrimination learning per se, but it dose appear necessary for efficient discrimination learning.

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PubMed1980

Conditional discrimination learning: a critique and amplification.

Carter and Werner recently reviewed the literature on conditional discrimination learning by pigeons, which consists of studies of matching-to-sample and oddity-from-sample. They also discussed three models of such learning: the "multiple-rule" model (learning of stimulus-specific relations), the "configuration" model, and the "single-rule" model (concept learning). Although their treatment of the multiple-rule model, which seems most applicable to the pigeon data, is generally excellent, their discussion of the other two models is incomplete and sometimes inaccurate. Potential problems of terminology are discussed in the present paper, as are additional lines of research that deserve consideration by those interested in further work in this area. The issue of response versus stimulus selection (configuration versus compound-cue learning) is discussed in connection with the configuration model. Particular attention is given to Carter and Werner's criticism of the application, in studies with other species, of the learning set procedure in testing for single-rule learning. Some of the important related issues are: the bias for improvement on new problems in a series, the adequacy of a multiple-rule model to explain learning set formation, and evidence in favor of the single-rule model, at least in primates. Consideration of these additional contributions to the study of conditional discrimination learning emphasizes the usefulness of this task in the comparative study of cognitive processes.

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PubMed1978

Eye movements of monkeys during learning-set formation.

Eye movements of stump-tailed monkeys were measured during learning of a long series of two-choice pattern discrimination problems. The amount of scanning per trial (shifts in visual fixation from one pattern to the other) and the duration of individual fixations on the patterns increased during the course of learning-set formation and (except for the amount of scanning by some animals) remained high during the prolonged training following learning-set formation. Some of the changes in eye movements were different from those seen during the learning of single discrimination problems, a difference that possibly reflects cognitive processes specific to the learning-set task.

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PubMed1967

Discrimination learning by Macaca mulatta with option to switch between S+ and S-.

Three rhesus monkeys were trained to press either of two response keys. A response on the reinforcement key during presentation of the reinforced stimulus produced a sucrose pellet followed by an intertrial interval, but during presentation of the unreinforced stimulus produced only the intertrial interval. A response on the switching key changed the discriminative stimulus from reinforced to unreinforced or from unreinforced to reinforced. The reinforced stimulus was presented automatically on half the trials, but could be produced only by a switching response on the other half. Switching tended to occur in three distinct stages during acquisition of discriminative behavior. The first stage was identified as "nondiscriminative switching"; the second as "nonswitching"; and the third as "discriminative switching".

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