Modeling the temporal dynamics of IT neurons in visual search: A mechanism for top-down selective attention

We propose a neural model for object-oriented attention in which various visual stimuli (shapes, colors, letters, etc.) are represented by competing, mutually inhibitory, cell assemblies. The model's response to a sequence of cue and target stimuli mimics the neural responses in infero temporal (IT) visual cortex of monkeys performing a visual search task: enhanced response during the display of the stimulus, which decays but remains above a spontaneous rate after the cue disappears. When, subsequently a display consisting of the target and several distracters is presented, the activity of all stimulus-driven cells is initially enhanced. After a short period of time, however, the activity of the cell assembly representing the cue stimulus is enhanced while the activity of the distracters decays because of mutual competition and a small top-down 'expectational' input. The model fits the measured delayed activity in IT-cortex, recently reported by Chelazzi, Miller, Duncan, and Desimone, and we suggest that such a process, which is largely independent of the number of distracters, may be used by the visual system for selecting an expected target (appearing at an uncertain location) among distracters.