The event-related optical signal (EROS) in visual cortex: replicability, consistency, localization, and resolution.

We previously reported a fast and localized noninvasive event-related optical signal (EROS) elicited by visual field quadrant stimulation in occipital brain areas (Gratton, Corballis, Cho, Fabiani, & Hood, 1995). We now present a replication and extension of that experiment. In addition, we propose a new method for estimating the cross-validity of the results based on intersubject correlations, report further data on the localization of EROS, and present an analysis of its spatial resolution. The results replicate our original findings. The intersubject correlation is generally quite high (r = .6-.8). The spatial resolution analysis indicates that activities from cortical areas located approximately 1.5 cm apart are measurable independently without cross talk. This study provides further support for the idea that noninvasive optical imaging can be used to derive images of brain activity combining good spatial and temporal resolution.