Principles derived from the study of animal behaviour have been
applied directly to human subjects in applied settings despite
the growing evidence that the two populations show pronounced
differences in operant performance. For example, fixed-interval
schedules where reinforcement is only obtainable after a specified
length of time has elapsed since the last reinforcement,
produce a pattern of pausing and then gradually accelerated
responding in animals; both the length of the pause and rate of
responding are sensitive to the duration of time between reinforcement
availability. In contrast, adult humans show either
high, constant rates regardless of the fixed- interval value , or
one response per interval pattern. Such differences have been
explained by the tendency for human adults to use language to
interpret their surroundings and guide subsequent behaviour.
Performance of mentally handicapped people under fixed-interval
schedules shows pronounced variability, but to date explanations
for such inter- subject differences have not been systematically
investigated. In the present study , all subjects were assessed
by means of tests of verbal regulation of behaviour described
by Luria. Their behaviour on schedules of reinforcement was
directly related to their performance on such tests. Subjects
showing good VRB ability produced fixed-interval behaviour similar
to that of normal adults, whereas subjects with immature
verbal systems were most like infra- human subjects.
Furthermore, interval-based instructions and self-instructions
resulted in marked decrease in rate only in subjects demonstrating
ability to regulate behaviour in the Lurian tasks. Providing
a clock to time the interval resulted in much lower, more
efficient responding for all subjects tested.
The results suggest a pattern of development from animal-type
performance controlled directly by the environment, to adult
human- type behaviour which is rule-governed and influenced by
speech. This is similar to that found with the developing
child.