Slide 27

Figure 28. From these demonstrations, we see that the perception of visual stimuli is dependent both on space (lateral interactions) and time (adaptation). Our laboratory is now investigating the time-dependence of lateral interactions. A prominent example of this is the FILL-IN of artificial scotomas. We hypothesize that fill in of artificial scotomas occurs, over a few seconds, through the expansion of receptive fields, both as determined by the action potential discharge (discharge receptive field) and perhaps as determined by the synaptic inputs (synaptic receptive field) (see part A). Specifically, we hypothesize that the membrane potential of the cell is constantly varying, depending in part on the discharge state of the cell (part B). When the cell is excited, it slowly hyperpolarizes and this underlies adaptation (to contrast in the visual cortex) and causes the receptive field to shrink. When the cell is not stimulated, such as with an artificial scotoma, the membrane potential depolarizes over a few seconds, causing the receptive field to expand, thus leading to "fill-in". We are currently testing this hypothesis.