EVENT-RELATED BRAIN POTENTIALS DURING IDENTIFICATION OF TACHISTOSCOPICALLY PRESENTED PICTURES

In the present study in 20 healthy subjects, event-related potentials (ERPs) were used to investigate the identification of picture stimuli. Each of 36 landscape pictures and 36 scrambled pictures was presented by a tachistoscope repeatedly until the subject made an identificatio n response. Presentation of one picture was finished after 12 exposure s. On the average, landscapes were identified after 5.8 +/- 0.4 exposu res; identification responses to scrambles were always wrong and occur red after 11.8 +/- 0.1 exposures. Latencies and amplitude measures wer e assessed for P2, P3, N400, and the slow wave (SW), Changes in P2 acr oss stimulus presentations did not differ between landscapes and scram bles excluding this component from being indicative for the processing of stimulus meaning. Amplitude of P3 generally declined across presen tations, but increased prior to identification for landscape pictures. N400 rapidly declined across presentations of landscapes, but less ra pidly for scrambles. The SW increased across stimulus presentations. T his increase was more pronounced for landscape than scrambled pictures . The pattern of ERP changes can be interpreted in a framework of a st epwise inhibition of spreading activation within semantic memory with progressing picture identification. (C) 1996 Academic Press, Inc.