Abstract
Previous studies have shown that saccades may deviate towards or away from task irrelevant visual distractors (Van der Stigchel, Meeter, & Theeuwes, 2006). The deviation away from distractors is stronger for targets in the lower visual field (LVF) than those in the upper visual field (UVF). Using a distractor task, three experiments were conducted to elucidate the mechanism underlying this observation. Extending previous findings, stronger deviation away from distractors was observed for LVF targets, regardless of being presented on (Exp. 1) or 15° off (Exp. 2) the vertical meridian, for a large range of target-distractor distance (15°-165°). One possible explanation is that, compared to the UVF, the LVF is under-represented on oculomotor maps, such as the superior colliculus (SC). To test this hypothesis, in Experiment 3, the distractor (if presented) was put at a location that mirrored the target in the opposite visual field (upper or lower). Thus, for a given target-distractor distance (30°, 60°, 90°, 120° or 150°), the directional deviation in collicular space was comparable for targets in the UVF and LVF. Canonical mathematical model of the SC (van Gisbergen, van Opstal, & Tax, 1987) assumes symmetric representations of the UVF and LVF in the SC and thus predicts equivalent directional deviation for targets in the UVF and LVF in Experiment 3. However, stronger directional deviation was observed for targets in the LVF. Because the target-distractor distance in collicular space was the same for targets appeared in the UVF and LVF, the findings of Experiment 3 provide unambiguous behavioral evidence for the hypothesis that the LVF is under-represented in the SC.
Meeting abstract presented at VSS 2014