AN ELECTROPHYSIOLOGICAL STUDY OF THE SELECTION OF THE COLOR AND SHAPEOF ALPHANUMERIC CHARACTERS IN RESPONSE CHOICE

We examined the functional and temporal organization of task-directed selective processing of the color and shape of alphanumeric characters . Dependent variables were measures derived from event-related brain p otentials (onset latency of selection negativity (SN) and the laterali zed readiness potential). We found SNs related to the relevance for co rrect task-performance of the color, the global shape and the local sh ape of the characters. The onset latencies of these SNs suggested that color and global shape were identified at the same time and earlier t han local shape. The absence of an SN to global shape if the color was irrelevant suggested that selection on the basis of the global shape depended hierarchically on that of color. Selection of the local shape was independent of color relevance. The lateralized readiness potenti als suggested that response selection occurred when the conjunction of color, global shape and local shape had been identified. No evidence was found for temporal overlap between stimulus identification and res ponse selection. These findings show that selective, task-directed pro cessing can be studied at multiple levels in a single paradigm. They a re inconsistent with the central assumption of several continuous info rmation transmission models that relevant partial information is used to activate associated responses as soon as it becomes available. (C) 1997 Elsevier Science B.V.