Visual Prosthesis
D. The effectiveness of electrical stimulation

(b) The threshold for eliciting saccadic eye movements changes as a function of the depth of the electrode in V1.

Figure 3 demonstrates this. The gray matter of visual cortex is about 2mm thick and has several identifiable layers. As can be seen in this figure, the lowest threshold for generating a saccadic eye movements occurs in layer 5. This is the layer from which neurons project to the superior colliculus. Thresholds rise dramatically for the upper layers.