Retinal eccentricity and the latency of eye saccades

The latency-eccentricity function, for the first saccade towards a small green or red target on the horizontal hemi-retinal meridian, is bowl-shaped with a central latency peak, a minimum plateau from 0.75 to 12 degrees, and a gradual increase in latency towards the periphery. The function is highly reproducible and the central peak is a robust finding. For our step sizes and criteria its height is around 35-75 msec. Manipulations of target intensity and colour, or the state of adaptation by a retinal bleach, show that sensory contributions to the central peak are generally small (5-15 msec) for adequately suprathreshold targets. Beyond 35 degrees in the temporal retina (nasal visual field) latencies become erratic, even for bright green targets, and there are direction errors. Frequent direction errors occur over a much wider range of eccentricities for red targets that are 1 log above the foveal threshold for perception.