Inferotemporal cortex stimulation is perceived before its onset

Abstract

Neural response latency measures when stimulus-evoked activity becomes detectable, but it does not reveal when the brain assigns the causal contribution of that activity to events in the external world. We define this temporal adjustment as projected delay and measure it in the macaque inferotemporal cortex using optogenetic stimulation and behavior. Two rhesus macaques performed a cortical perturbation detection task in which a visual masker appeared at different times relative to stimulation. Detection was selectively impaired when the masker began 200 ms before stimulation. We then tested this timing using Perceptography, a method that optimizes image perturbations to mimic stimulation-evoked visual events. Image perturbations presented 200 ms before stimulation elicited higher false-alarm rates than perturbations presented at stimulation onset. Here, we show that stimulation-evoked visual events in inferotemporal cortex depend preferentially on visual information originating approximately 200 ms before the cortical perturbation. This projected delay exceeds typical inferotemporal response latencies and suggests temporally extended readout mechanisms relevant to causal models of visual perception and the timing of cortical visual prostheses.