Ph.D Thesis

Ph.D StudentBigman Zehavah
SubjectThe Time Course of Category Induction: A Visual Event-
Related Potential Study
DepartmentDepartment of Medicine
Supervisor PROFESSOR EMERITUS Hillel Pratt


Category induction involves determination of features common to two or more stimuli.  This study analyzed  Event-Related Potentials  to examine the characteristics of the interaction between frontal, parietal and occipital activity during category induction and  classification on the basis of a known category.

Ten 11 - 13 year old subjects participated in variations of visual ERP category induction and classification tasks. All stimuli were geometric shapes, which varied by size, color, and shape.  For the category induction tasks the subjects were shown a series of two stimuli belonging to the same category and were to decide if a probe stimulus shared membership in that category.  The tasks varied as to the number of attributes defining the category (one or two), and prior knowledge of these attributes.  For the parallel classification tasks the subjects identified stimuli containing designated target feature/s.

ANOVA of the latencies and amplitudes of early (P80, N120, P150, N170, P200) and late (N300, P450) components, as well as PCA, showed differential effects of task conditions on the different stimuli. Results indicate multiple frontal processes during early and late stages of category induction and classification.  Results suggest that during induction and classification, stimuli are analyzed in relation to others. Detail of analysis is related to the number of shared features.  Knowledge of the attribute category constrains cortical activity before perceptual processing; while complexity of analysis    is critical only after adaptation to this   knowledge. 

Results are consistent with use of exemplar-similarity strategy during category induction and classification.