Saccades to spatially extended targets: the role of eccentricity

Size and eccentricity of visual targets are known to modulate saccade parameters. Here we asked for a possible interaction between these target properties. We investigated latency and amplitude of saccades to targets of varying diameter presented at various eccentricities in the visual field. Effects of target size on saccadic eye movements highly depended on eccentricity of saccade targets. For large saccade targets, latencies increased and mean amplitudes decreased mainly at parafoveal eccentricities. By contrast, scatter of saccade amplitudes increased nearly linearly with target size and eccentricity. These effects are consistent with the known functional anatomy of the superior colliculus. Size- and eccentricity-related changes in saccade parameters may depend on distinct subpopulations of collicular neurons.