30 rats were trained in a runway for 16 days at 5 trials a day. During acquisition (10 days) Ss were trained on an irregular 50% partially delayed reward schedule. The duration of delay was 30 sec. and 2 pellets of reward were given on all delayed trials. The magnitude of immediate reward was varied over three levels (2, 10, 24 pellets) as a between-groups factor. Although the larger rewards developed somewhat faster acquisition speeds than the small reward the results did not reach statistical reliability. During extinction, however, the larger magnitudes of reward significantly increased resistance to extinction. These results were discussed in terms of aftereffects, frustration, and dissonance theories of extinction.
