Abstract
Saccades are typically hypometric, and this hypometria generally scales with target eccentricity. However, it is not clear how specific aspects of task demands influence the accuracy and precision of saccades. We investigated the effect of target direction, task demands at the target location and the type of saccade made (endogenous or exogenous) on the precision and accuracy of saccades.
We measured saccades for five normally sighted observers while completing two tasks. Targets were presented at 1 of 8 polar angles and the target eccentricity was blocked, ranging from 2–12°. Instead of a simple saccade task, observers were asked to make a saccade to: 1) discriminate the location of the gap in a Landolt C (4AFC) or 2) make a rapid point to a target. Additionally, we cued the saccade with either an endogenous or exogenous cue. Saccade endpoints are hypometric with respect to the target, and this error scales with target eccentricity, consistent with previous findings. Saccades are less precise in the radial direction than tangential. In conflict with Findlay (2008) we did not find an effect of exogenously versus endogenously cued saccades in the acuity task, suggesting that the targeting error is driven by the resolution of task-dependent visual information. However, there was a clear effect of task on saccade targeting. When reaching to a target, saccade endpoint errors showed the same patterning, but both accuracy and precision worsened as compared to the acuity task. For close targets (2 and 4°), more than one subject did not even make saccades on almost half of the trials. Saccade targeting error is affected by the visual resolution demands of the task. In the limiting case of an acuity task when an accurate saccade is most needed, it is irrelevant whether the saccade is made reflexively or intentionally.
NIH R01 EY018004-05 to LWR and Smith-Kettlewell Pilot Award.