Abstract
Purpose: :
The visual pathway is organized in a hierarchical manner, in such a way that the visual information reaches different areas with different delays. In the monkey, cells of area V1 show eye dominance, which implies different synaptic inputs from each eye. We wish to know whether the latency of the visual information reaching cells in this area changes when the stimulus is presented to the left, right or both eyes.
Methods: :
In two behaving rhesus monkeys, we flashed a square made of dynamic random dots over the receptive field of the cell in 76 cells of V1 and measured the response latency when the stimulus was presented to both, left and right eyes. In forty cells showing clear eye dominance (ANOVA, p<0.05), a normalization of the ANOVA was used to calculate a Dominance Sensitivity Index (DSI). To measure response latency we constructed a post–stimulus histogram with a bin size of 4 ms. Response latency was defined as the time elapsed from stimulus onset to the second consecutive post–stimulus bin containing a number of spikes higher than expected (Poisson, 95%, p<0.05).
Results: :
Latencies of the non–dominant eye (mean: 107.0 ms) were longer that those of the dominant eye (mean: 79.5 ms). There was no difference between the latency of the dominant eye and that obtained when both eyes were stimulated simultaneously (mean: 76.6 ms). Correlation analysis between DSI and latency showed that the higher the DSI the shorter the latency (p>0.05). We failed to find statistically significant latency differences between ipsi– and contra–lateral inputs (temporal vs. nasal retina). Similarly, there was no relationship between eccentricity of the receptive field and latency.
Conclusions: :
Our preliminary data shows that the dominant eye determines the latency of the cortical cell and the latency of binocular stimulation does not modify the latency of the cell.
Keywords: binocular vision/stereopsis • visual cortex • electrophysiology: non-clinical