Humphreys' “Acquisition and Extinction of Verbal Expectations” Revisited: Evidence for a Partial Reinforcement Hump Effect

The present study employed the sequential prediction task to determine whether the partial reinforcement hump effect—a rise in the dependent variable curve following partial reinforcement—is a reliable phenomenon. 210 college students received one of seven sequences in which two events occurred equally often for 100 trials and in which the maximum run length was 2, 3, 4, 5, 6, 7, or 8, followed by 30 trials during which one event was always correct. A hump appeared in the post-acquisition curves of all seven groups. The location of the hump was a function of the maximum run length during Trials 1–100. These results provide strong support for an expectancy interpretation of the partial reinforcement extinction effect.