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Laurent Madelain, Mark R. Harwood, Richard J. Krauzlis, Joshua Wallman; Spatial scale of attention influences saccade latencies. Journal of Vision 2004;4(8):644. doi: 10.1167/4.8.644.
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Purpose: We previously showed that, when viewing two concentric rings (0.8 and 8 deg diameter) that together undergo a step displacement (< 8 deg), subjects make saccades at shorter latencies if they attend to the inner ring. We proposed that saccades are triggered faster when the target object leaves the spotlight of attention. We now test three other explanations. First, the difference in latency could simply be an effect of stimulus eccentricity. Second, subjects may divide their attention when instructed to attend to the large ring, causing an increase in latency. Third, ring size may determine latency regardless of whether the stimulus steps outside of the field of attention. Experiment 1: Large and small stimuli with the same eccentricity. Two pairs of lines, one spanning 2 deg, the other 8 deg, oscillated side-to-side 2 deg from the fixation point. At a random time, they stepped and the lines briefly changed orientation. Subjects reported whether the lines of the assigned pair were transiently parallel. In the three subjects, saccades occurred later when attending large (288 ms) than small (205 ms). Experiment 2: Rings of various sizes stepping by various distances. At a random time, a single, segmented ring stepped, and briefly changed its number of segments. Subjects reported the number of segments during the change. We varied the size of the ring (from 2 to 8 deg) and the amplitude of the step (from 1 to 9 deg). For each ring size, the saccade latencies were longer for steps much smaller than the ring diameter and shorter for steps as large or larger than the ring diameter. Conclusions: Neither eccentricity nor divided attention nor ring size can explain the changes in saccade latency we observed. We conclude that saccades are delayed if the position error is smaller than the size of the field of attention.
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