Efficient allocation of attentional sensitivity gain in visual cortex reduces foveal sensitivity in visual search

The human visual system has a high-resolution fovea and a low-resolution periphery. When actively searching for a target, humans perform a covert search during each fixation, and then shift fixation (the fovea) to probable target locations. Previous studies of covert search under carefully controlled conditions provide strong evidence that for simple and small search displays, humans process all potential target locations with the same efficiency that they process those locations when individually cued on each trial. Here, we extend these studies to the case of large displays, in which the target can appear anywhere within the display. These more natural conditions reveal an attentional effect in which sensitivity in the fovea and parafovea is greatly diminished. We show that this "foveal neglect" is the expected consequence of efficiently allocating a fixed total attentional sensitivity gain across the retinotopic map in the visual cortex. We present a formal theory that explains our findings and the previous findings.