The saccadic size-latency phenomenon explored: Proximal target size is a determining factor in the saccade latency

Saccade latencies are known to increase for targets presented close to fixation. Recently, it was shown that not only target eccentricity, but the size of a proximal saccade target also plays a crucial role: latencies increase rapidly with increasing target size. Interestingly, these latency increases are greater than those typically found for other supra-threshold manipulations of target properties. Here we evaluate to what extent this phenomenon is distinct from known delays in saccade initiation and whether the phenomenon is truly related to the size of a proximal target. In Experiment 1 we focus on the importance of the required amplitude. Employing a saccade adaptation paradigm we find that the required amplitude is not a determining factor. Focusing on the role of size, in Experiment 2, we find that while latency increases are strongest for targets elongated in the direction of the fovea, elongations perpendicular to this direction also lead to an increase in latencies. Finally, in Experiment 3 we verify that the latency increases are driven by the properties of the saccade target rather than visual input in general. Together these experiments provide converging evidence that the current phenomenon is both novel and a consequence of the relation between proximal target size and its eccentricity.