Memory-driven processing in human medial occipital cortex: an event-related optical signal (EROS) study.

Memory-driven processing in medial occipital areas (Area V1 and immediately adjacent structures) was investigated noninvasively using the event-related optical signal (EROS). Subjects viewed two letter stimuli presented in the left and right hemifields, respectively. They then viewed a centrally presented test letter and had to indicate whether this letter was the same as either of the letters presented earlier. The initial EROS response to the test stimulus in medial occipital areas (latency: 50-150 ms) was unilaterally suppressed in the hemisphere previously exposed to the same stimulus. This finding suggests that medial occipital cortex activity is modulated by a rapidly adapting hemispheric-specific pattern recognition mechanism.