Attention and probability effects in the human occipital cortex: an optical imaging study.

A new imaging technique (event-related optical signal, EROS) reveals the time course of neural activity in selected cortical areas of normal human subjects. This technique was used to study the event-related activity in striate and extrastriate occipital areas in an experiment in which spatial selective attention and stimulus probability were manipulated. The results show that attention effects are evident in the initial response in extrastriate cortex (latency < 100 ms), but not in striate cortex, confirming previous modeling effects. They also show that the initial response in striate cortex is modulated by stimulus probability, suggesting the occurrence of pre-attentive memory phenomena in primary visual cortex.