Discrimination and generalization along a simple dimension: Peak shift and rule-governed responding.

Abstract

In 2 experiments, participants learned to discriminate between a pair of simply related, but very similar, colors in a 2-choice categorization task. They were then tested over a wider range of isoluminant hues. Over these test values, both experiments yielded a postdiscrimination gradient that was initially peak-shifted but became monotonic through the course of testing. In Experiment 2, the presence of this early peak shift and subsequent change in gradient form were related to participants' inability to verbally characterize the difference between the training stimuli. This suggests a transition from generalization based on simple physical similarity to generalization based on a "verbalizable" rule, as a consequence of additional relevant information becoming available during test. An explanation appealing to both associative and strategically controlled verbal processes provides an accurate account of the results.