Research Topics

Artificial Vision & Neural Engineering

Visual Neuroscience

01 Retinal Neurophysiology

To make electrically-elicited artificial vision more ‘natural’, it is essential to understand response patterns arising from complex ‘natural’ stimulus in each type of retinal ganglion cells (RGCs). Typically, however, high contrast spot flashes and moving bars have been used for analysis of RGC responses. In contrast to these laboratory stimuli, our visual world is remarkably complex. During the study of their responses to natural movies, we found an interesting feature of directionally selective (DS) ganglion cells; The DS ganglion cells of the retina respond preferentially to movement in a preferred direction, but under laboratory conditions, they are also sensitive to changes in the luminance. This raises the classic problem of how the cells can reliably signal the direction of motion if the responses are confounded by both direction and luminance. Thus, during situations in which both stimuli are found, e.g. natural viewing, the brain must determine if a given burst of spikes carries information about motion or about luminance. We developed a method to separate motion and luminance responses and found that in striking contrast to much previous work, luminance responses in DS cells are strongly suppressed during natural viewing (Im and Fried, Sci. Rep., 2016). As a result, spiking from the DS cell conveys a relatively pure signal of direction to be transmitted to the brain and downstream processing is greatly simplified. This study assured that RGC responses to natural stimuli are markedly different from those to laboratory stimuli. We are going to explore the retinal neural circuitry to better understand how this complex computation is possible.