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Biomedical subjects

G V Thomas

Publications and source records attributed to G V Thomas.

27 records · Page 2Linked to original sources
PubMed1983

The role of marking when reward is delayed.

Two-choice spatial discrimination by rats is enhanced if a salient stimulus marker occurs immediately after every choice response and again after a delay interval (Lieberman, McIntosh & Thomas, 1979). Three experiments further explore this effect. Experiment 1 found that the second marker is unnecessary. Experiment 2 found that a marker presented before a response is as effective as one presented after. Both effects could be explained in terms of markers focusing attention on subsequent cues. Experiment 3, however, found that markers after choice enhance learning even when no discriminative cues are present following the marker. Markers thus appear to initiate both a backward search through memory and attention to subsequent events; both processes help to identify events that might be related to the unexpected marking stimulus.

Animals↗
PubMed1979

Learning when reward is delayed: a marking hypothesis.

Rats were trained on spatial discriminations in which reward was delayed for 1 min. Experiment 1 tested Lett's hypothesis that responses made in the home cage during the delay interval are less likely to interfere with learning than responses made in the maze. Experimental subjects were transferred to their home cages during the delay interval, and control subjects were picked up but then immediately replaced in the maze. Contrary to Lett's hypothesis, both groups learned. Further experiments suggested that handling following a choice response was the crucial variable in producing learning: No learning occurred when handling was delayed (Experiment 2) or omitted (Experiment 3). One possible explanation for the fact that handling facilitated learning is that it served to mark the preceding choice response in memory so that subjects were then more likely to recall it when subsequently reinforced. In accordance with this interpretation, learning was found to be just as strong when the choice response was followed by an intense light or noise as by handling (Experiment 4). The implication of marking for other phenomena such as avoidance, quasi-reinforcement, and the paradoxical effects of punishment is also discussed.

Animals↗
PubMed1974

Response rate, reinforcement frequency, and behavioral contrast.

Pigeons responded for food on a multiple schedule in which periods of green-key illumination alternated with periods of red-key illumination. When behavior had stabilized with a variable-interval 2-min schedule of reinforcement operating during both stimuli, low rates of responding (interresponse times greater than 2 sec) were differentially reinforced during the green component. Conditions during the red stimulus were unchanged. Response rates during the green component fell without changing the frequency of reinforcement but there were no unequivocal contrast effects during the red stimulus. The frequency of reinforcement during the green component was then reduced by changing to a variable-interval 8-min schedule without reducing the response rates in that component, which were held at a low level by the spacing requirement. Again, the conditions during the red stimulus were unchanged but response rates during that stimulus increased. These results show that reductions in reinforcement frequency, independently of response rate, can produce interactions in multiple schedules.

Journal Article↗
PubMedDate not supplied

Observations of young normal and handicapped children.

An observational study was made of 1-2-year-old children, and of mentally handicapped children functioning at a similar level, to determine the extent to which they involved themselves in play with toys and other objects and the extent to which their day was "empty". Observations of normal children were made in their homes and in day nurseries; observations of mentally handicapped children were made at home, in day care centres (special schools) and in the schools and wards of subnormality hospitals. In no setting were children interacting with adults for more than 20% of their non-routine time. These findings seem to justify concern over independent play with toys and other objects. The handicapped children in all settings had "emptier" days than the normal children, this being accounted for by greater amounts of inattentive handling of objects and self-stimulation and lesser amounts of social interaction and attentive play. However, attentive play scores for the handicapped children varied markedly with setting. In appropriate circumstances, there can be as much spontaneous contact with objects in handicapped children as in normal children at a similar development level. Despite current concern over the effects of day care on the development of very young children, normal children in day nurseries did not differ from normal children at home, either in attentive play scores or in the proportion of nonroutine time spent interacting with adults.

Adolescent↗
PubMedDate not supplied

Some conditions affecting manipulative play with objects in severely mentally handicapped children.

Four experiments investigated contact and manipulative activity with play materials in severely handicapped children functioning at the 1--2-year-old stage of normal development. Experiment 1 found that many mentally handicapped children were as quick to contact and manipulate a novel object as were comparable normal children and that auditory (or visual) feedback seemed to be effective in sustaining attentive activity with an object. A small minority of the handicapped children, however, were very slow to contact either familiar conventional toy or a novel object. Experiments 2 and 3 found that adding stimulus features such as lights, sounds or bright colours to an object had no consistent effect on the latencies of these 'slow responders' to contact the object. Experiment 4 found that the amount and kinds of manipulative play of mentally handicapped children differed from the normal children only in that they interacted less with an attendant adult and displayed less frequent representational use of toys in pretend play. The play of both normal and handicapped children was relatively unaffected by whether only a few (four) or many (15) toys were provided.

Acoustic Stimulation↗
PubMedDate not supplied

Play materials for mentally handicapped children.

A range of experimental play materials are described which were designed to aid the development of manipulative skills such as posting, threading, fitting and matching in mentally handicapped children functioning at the 1-2-year-old stage of normal development. The play materials are designed to withstand rough treatment and they can be securely mounted on adjustable frames so that they can be presented to children with physical handicaps. There are few detachable parts to be thrown or dropped out of reach, and appropriate manipulations produce "rewarding' auditory feedback. A preliminary assessment of the experimental play materials suggested that they prompted more developmentally productive kinds of manipulative play than did a selection of comparable conventional toys.

Acoustic Stimulation↗