NEUROPHYSIOLOGICAL EVIDENCE FOR VISUAL PERCEPTUAL CATEGORIZATION OF WORDS AND FACES WITHIN 150 MS

The nature and early time course of the initial processing differences between visually matched linguistic and nonlinguistic images were stu died with event-related potentials (ERPs). The first effect began at 9 0 ms when ERPs to written words diverged from other objects, including faces. By 125 ms, ERPs to words and faces were more positive than tho se to other objects, effects identified with the P150. The amplitude a nd scalp distribution of P150s to words and faces were similar. The P1 50 seemed to be elicited selectively by images resembling any well-lea rned category of visual patterns. We propose that (a) visual perceptua l categorization based on long-term experience begins by 125 ms, (b) P 150 amplitude varies with the cumulative experience people have discri minating among instances of specific categories of visual objects (e.g ., words, faces), and (c) the P150 is a scalp reflection of letterstri ng and face intracranial ERPs in posterior fusiform gyrus.