In Experiment 1 the response that terminated the postreinforcement
pauses occuring under a fixed-interval 60-sec schedule was reinforced,
if the pause duration exceeded 30 sec. 'The percentage of
such pauses, rather than increasing, decreased. 'There were complex
effects on the discriminative control of the pause by the reinforcer
terminating the previous fixed-interval, depending on whether the
fixed-interval and the added reinforcer were the same or different.
In Experiments 2 and 3 each reinforcement initiated an alternative
fixed-interval interresponse-time-greater-than-t-sec schedule, the
schedule values being systematically varied. When the response
following a pause exceeding a given duration was reinforced, fewer
such pauses occurred than when they were not reinforced, i.e. on
the comparable simple fixed-interval schedule. There was no systematic
relationship between mean interreinforcement interval and duration of
the post-reinforcement pause. The pause duration initiated by reinforcement
was directly related to the dependency controlling the shortest pause at that time, regardless of changes in mean interreinforcement
interval.
In Chapter 7, the performance of rats was studied on different
values of the fixed-interval (FI) schedule. When postreinforcement
pause measures were related to schedule value it was found that the
pause was not a constant proportion of the schedule parameter but
rather the relationship was best described by a power function with
an exponent of less than one. Also, pigeons were trained on different
FI values under two conditions: (i) where the reinforcer was of 3 sec
duration and (ii) where the reinforcer duration was one-tenth of the
value of the interval. It was found that at the highest FI values,
longer pauses occurred .following the longer reinforcer duration than
following the shorter reinforcer duration; power functions with
exponents less than one provided a good description of both types of
pause-interval relationship. Two further experiments investigated
reinforcement magnitude effects on FI when (i) only a single reinforcer
duration occurred in a session, and when (ii) different reinforcer
durations occurred within the same session. The postreinforcement
pause was directly related to the duration of the preceding reinforcer,
the effect being enhanced when different reinforcers occurred within
the same session and when the schedule parameter was increased. The
duration of the postreinforcement pause on FI schedules is shown to be
the product of a complex interaction between interval length and
reinforcement magnitude.