Visual-tactile shape perception in the visually restored with artificial vision.

Retinal prostheses partially restore vision to late blind patients with retinitis pigmentosa through electrical stimulation of still-viable retinal ganglion cells. We investigated whether the late blind can perform visual-tactile shape matching following the partial restoration of vision via retinal prostheses after decades of blindness. We tested for visual-visual, tactile-tactile, and visual-tactile two-dimensional shape matching with six Argus II retinal prosthesis patients, ten sighted controls, and eight sighted controls with simulated ultra-low vision. In the Argus II patients, the visual-visual shape matching performance was significantly greater than chance. Although the visual-tactile shape matching performance of the Argus II patients was not significantly greater than chance, it was significantly higher with longer duration of prosthesis use. The sighted controls using natural vision and the sighted controls with simulated ultra-low vision both performed the visual-visual and visual-tactile shape matching tasks significantly more accurately than the Argus II patients. The tactile-tactile matching was not significantly different between the Argus II patients and sighted controls with or without simulated ultra-low vision. These results show that experienced retinal prosthesis patients can match shapes across the senses and integrate artificial vision with somatosensation. The correlation of retinal prosthesis patients' crossmodal shape matching performance with the duration of device use supports the value of experience to crossmodal shape learning. These crossmodal shape matching results in Argus II patients are the first step toward understanding crossmodal perception after artificial visual restoration.