Variable contributions of rods and cones to saccadic eye-movement latency in a non-foveating task

Abstract

Latencies were measured for anti saccades away from a small lit cue that steps ±10 deg in complete darkness. Cue luminance and wavelength were varied. Additional measurements were made during dark-adaptation or on backgrounds or at different retinal eccentricities. Luminance matched cues and Palmer's equivalent luminance transformation were also used. Latencies for pure rod and pure cone inputs obey Piéron's law in much the same manner as foveating saccades, except that latencies are somewhat longer. However, as judged by saccadic latency, interaction between rods and cones is quite variable in the anti task. The rod-cone transition either occurs at cue luminances well above the cone threshold and is from pure rod input to primarily cone, or occurs at the cone threshold and is from rods to rods-plus-cones. Direction errors, or reflex foveating saccades, are particularly increased for mesopic cues. The variable behaviour of subjects at the anti task is discussed in relation to temporal multiplexing of rod and cone signals from dark-adapted retinal ganglion cells, the delaying nature of the task, and attentional mechanisms.