A series of six experiments was conducted, investigating the effect on temporally-based behaviour of the omission of reinforcement and variation in
the magnitude of reinforcement. In Section I, Experiments I and II examined the effect of omission of reinforcement on differential reinforcement of
low-rate schedules. The results were considered with reference to the existing theoretical accounts of the effects of reinforcement omission, namely
(i) that conditioned inhibitory control is removed in the absence of food, or (ii} that the omission of food results in a motivational state that enhances
responding. The latter part of this section, including Experiments III and IV, successfully tested the hypothesis that the degree of inhibitory control
exerted by a reinforcing stimulus is a function of the number of stimulus components comprising that event.
In the experiments reported in Section II, magnitude of reinforcement was manipulated and magnitude was found to be positively related to
post-reinforcement pause duration. It was found that contextual variables that have been previously shown to affect the relationship between stimulus intensity
and stimulus control also affected the relationship between reinforcement magnitude and the duration of the post-reinforcernent pause.
The data reported in this thesis indicated that the effects of both omission of reinforcement and manipulations of reinforcement magnitude were associated with stimulus discrimination, rather than the motivational phenomena postulated by frustration hypothesis and demotivation hypothesis. However, at least two current discriminative accounts of these effects, namely generalization decrement hypothesis and overshadowing in memory were also inadequate in
accounting for many aspects of the experimental data reported here . The data were consistent, however, with the suggestion that the effects of
reinforcement omission and variation in the magnitude of reinforcement reflect aspects of the discriminability of reinforcement as a conditioned inhibitory stimulus.