Time course and nature of stimulus evaluation in category induction as revealed by visual event-related potentials.

Category induction involves abstraction of features common to two or more stimuli. We predicted that category induction affects processing of each stimulus, before completion of perceptual analysis. Event-related potentials (ERPs) were recorded from ten 11-13-year olds while they were performing visual category-induction tasks. Subjects viewed a series of two geometric shapes belonging to the same perceptual category (size, color, or shape), defined by one or two shared features, and decided if a probe stimulus shared membership in that category. Large frontal N120, frontal-central N300 and smallest P450 were elicited by the first stimulus; number of shared features affected P150, N170, and P450 amplitudes to the second stimulus. Principal Component Analysis (PCA) indicated networks of frontal, parietal and occipital activity, different to each stimulus. Results suggest that in young adolescents category induction affects early stages of stimulus processing. Processing is based on selective analysis of stimuli for shared features, not exhaustive examination of all features of all stimuli.