Beyond the classical receptive field in the visual cortex

We have investigated the organization of regions outside the classical receptive field (CRF) for neurons in the visual cortex. First, we have determined the incidence and nature of interactions from outside the CRF. We find interaction from regions outside the CRF for a majority of cortical cells and it is almost always of a suppressive nature. Second, we have determined that most interaction is from specific well-defined regions outside the CRF. These regions are generally as effective as what is found for a complete annulus. Third, it is possible to reverse the inhibition from outside the CRF by the addition of a second grating that is orthogonal to the preferred orientation. This disinhibition may completely offset the suppressive influence of the surround. Additional experiments suggest that this process is not necessarily involved in figure/ground analysis.