Perceptual adjustments on representations of familiar patterns: change over time and relational features.

Subjects classified individual stimuli as exact copies or as distortions of previously viewed prototype letters. Perceptual adjustments were induced by the presence of difficult (subtle) distortions within the stimulus set. In Experiment 1, subjects initially made feature-based adjustments, and, with experience, adjustments became identity-based. Decisional adjustments also occurred. A similar change over time was obtained in Experiment 2; in addition, the feature-based adjustments could not be explained by overall similarity between letters. Experiment 3 indicated that feature-based adjustments can be long lasting under appropriate circumstances. Experiment 4 indicated that the relevant features are not functionally independent parts of letters, but rather relations between neighboring parts. The results are consistent with the idea that adjustments can change between levels over time, and that the adjusted features are relational in nature.