Abstract
Background: Spatial attention modifies both visually guided manual and ocular motor responses and motor responses can be used to quantify covert attention. Given that transient covert attention accelerates the rate of visual information processing (Carrasco & McElree, 2001), here we compare the spatial trajectories of hand movements toward peripherally cued stimuli with those toward neutrally cued stimuli to investigate the effects of accelerated processing on motor control. We use a visually guided motor response task that previously has been shown to replicate keyboard response results (Faludi, Maloney, Carrasco, VSS 2004), allowing us to focus on the response trajectories.
Methods: Observers performed a 2AFC task in which they were asked to judge whether the target (2 deg, 4 cpd tilted Gabor) was present or absent. The target stimulus appeared on 50% of trials at one of eight 9 deg iso-eccentric locations, with distracters occupying the non-target locations. To direct attention, a cue appeared either adjacent to the potential target location or at the neutral fixation location (67 ms). Following an ISI (54 ms) the stimulus was presented (54 ms). These timings maximize the effects of transient attention and precluded eye movements. Observers touched the target location on the monitor or the fixation point if no target was perceived. Response trajectories were measured using an Optotrak 3020 motion capture device.
Results: As in previous experiments, we found a horizontal-vertical anisotropy (HVA) and a vertical meridian asymmetry (VMA). Pointing response trajectories revealed a difference between peripherally and neutrally cued trials. In peripherally cued trials, trajectories deviated toward the target location sooner, and arrived at a greater eccentricity than neutrally cued trials. We suggest this is the effect of temporally enhanced information accrual influencing motor response.
Grant BCS-9910734/HCP from the NSF; Grant EY08266 from the NIH