A circuit model for transsaccadic space updating and mislocalization

Abstract

We perceive a stable, continuous world despite drastic changes of retinal images across saccades. However, while persistent objects in daily life appear stable across saccades, stimuli flashed around saccades can be grossly mislocalized. We address this puzzle with our recently proposed circuit model for perisaccadic receptive-field (RF) remapping in LIP and FEF. The model uses center/surround connections to store a relevant stimulus retinal location in memory as a population activity. This activity profile is updated across each saccade by directional connections gated by the corollary discharge (CD) of the saccade command. The updating is a continuous backward (against the saccade) shift of the population activity (equivalent to continuous forward remapping of the RFs), whose cumulative effect across the saccade is a subtraction of the saccade vector. The model explains forward and backward translational mislocalization for stimuli flashed around the saccade onset and offset, respectively, as insufficient and unnecessary cumulative updating after the saccade, caused by the sluggish CD time course and visual response latency. We confirm the model prediction that for perisaccadic RFs measured with flashes before the saccades, the final forward remapping magnitudes after the saccades are smaller for later flashes. We discuss the possibility that compressive mislocalization results from a brief reduction of attentional remapping and repulsion. Although many models of RF remapping, transsaccadic updating, and perisaccadic mislocalization have been proposed, our work unifies them into a single circuit mechanism and suggests that the brain uses "unaware" decoders which do not distinguish between different origins of neurons activities.