Why phosphenes are not always dots: modeling the shapes elicited 1by intracortical stimulation of human V1

Abstract

The majority of visual cortical prosthetic devices currently implanted in patients or under development rely on small depth electrodes. Reports from patients implanted with these devices suggest that stimulation with tiny electrodes does not reliably produce small punctate spots, with some patients reporting a variety of percepts, including larger spots and irregularly shaped phosphenes. Here, we compare drawings and descriptions made by a cortical implant recipient to predicted phosphene patterns, generated using a 'virtual patient' simulation based on a simple model of V1. We find that this model successfully reproduces the wide variety of percepts reported by this patient and further suggests that, for a subset of electrodes, stimulation may activate multiple locations -- possibly as a result of axonal activation.