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Biomedical subjects

L T Stoddard

Publications and source records attributed to L T Stoddard.

31 records · Page 2Linked to original sources
PubMed1971

The removal and restoration of stimulus control.

When a well-learned circle versus ellipse discrimination was made impossibly difficult for the subjects (rhesus monkeys), the controlling stimulus-response topographies were replaced by competing topographies. The identification of two training conditions sufficient to reinstate the original discrimination permitted the following inferences: the original controlling topography had merely decreased in probability of occurrence, whereas the "strength" of the stimulus-response relation remained unchanged; discriminations along the apparently continuous circle-ellipse dimension actually involved several distinct stimulus-control topographies.

Animals↗
PubMed1967

The effects of errors on children's performance on a circle-ellipse discrimination.

Children first learned by means of a teaching program to discriminate a circle from relatively flat ellipses. Children in the control group then proceeded into a program which gradually reduced the difference between the circle and the ellipses. They advanced to a finer discrimination when they made a correct choice, and reversed to an easier discrimination after making errors ("backup" procedure). The children made relatively few errors until they approached the region of their difference threshold (empirically determined under the conditions described). When they could no longer discriminate the forms, they learned other bases for responding that could be classified as specifiable error patterns. Children in the experimental group, having learned the preliminary circle-ellipse discrimination, were started at the upper end of the ellipse series, where it was impossible for them to discriminate the forms. The backup procedure returned them to an easier discrimination after they made errors. They made many errors and reversed down through the ellipse series. Eventually, most of the children reached a point in the ellipse series where they abandoned their systematic errors and began to make correct first choices; then they advanced upward through the program. All of the children advanced to ellipse sizes that were much larger than the ellipse size at the point of their furthest descent.

Achievement↗
PubMed1967

The effectiveness of fading in programming a simultaneous form discrimination for retarded children.

A non-verbal teaching program, combined with reinforcement and extinction (Program Group), was compared with reinforcement and extinction alone (Test Group) in teaching retarded children to discriminate circles from ellipses. In the Program Group, fading techniques were used to transfer stimulus control from "bright vs. dark" to "form vs. no-form" and then to "circle vs. ellipse". The Test Group had the task of learning the circle-ellipse discrimination with no prior teaching program. With the program, seven of 10 children learned the circle-ellipse discrimination. Without the program, one of nine learned. The eight Test-Group children who failed to learn circle vs. ellipse were then given the opportunity to learn the form no-form discrimination by reinforcement and extinction alone, without fading. Six of the eight learned, but only three of these six then learned circle vs. ellipse on a second test. All seven Program-Group children who had learned form vs. no-form also learned the circle-ellipse discrimination by means of fading; each of the seven made fewer errors than any of the three who succeeded on the second test. Children who failed to learn circle vs. ellipse adopted response patterns incompatible with the development of appropriate stimulus control.

Journal Article↗
PubMedDate not supplied

Studies of exclusion in individuals with severe mental retardation.

Exclusion performances in matching to sample are demonstrated when subjects select experimentally undefined comparison stimuli in the presence of undefined sample stimuli, apparently by rejecting defined comparison stimuli. Several studies have documented exclusion performances in a small number of individuals with severe mental retardation. These studies also demonstrated the potential of exclusion procedures for establishing prerequisites for emergent naming performances. The present study examined exclusion in a larger cohort of subjects. Initial experiments asked two questions. First, how reliably would exclusion performances be demonstrated? Second, would those performances be followed by emergent naming, and, if so, how reliably? Follow-up experiments examined the stimulus control basis for exclusion performances. Our findings and conclusions can be summarized as follows: First, reliable exclusion was demonstrated in nearly all subjects. Second, naming performances typically emerged. These performances were seen in the context of a recent experimental history of matching to sample and of naming baseline stimuli in the experimental format. Third, apparent exclusion may sometimes result from relating undefined sample and comparison stimuli. Together, our findings suggest potentially effective strategies for teaching people with mental retardation and point to variables that should be considered when designing exclusion-based teaching interventions.

Adolescent↗
PubMedDate not supplied

Stimulus classes in matching to sample and sequence production: the emergence of numeric relations.

We investigated interrelationships among stimulus classes established in matching-to-sample and sequence-production tasks. The analysis focused on the matching and sequencing of quantities, numerals, and arbitrary forms in two individuals with mental retardation. The basic protocol involved: (a) establishing both matching and sequencing performances with some stimuli, (b) training sequencing with a new set of stimuli and assessing whether new matching performances emerged, and (c) training matching with a new set of stimuli and assessing whether new sequencing emerged. The results showed that sequence training did not readily lead to new matching performances, unlike prior research with college students. In contrast, training in matching to sample yielded emergent sequence production; these data support prior studies involving children and adults without developmental disabilities. The results extend prior stimulus class research and suggest an important role for stimulus control processes in the production of generative numeric performances.

Adult↗