| Popis: |
Pseudoneglect (PN) reveals a contralateral bias in the deployment of visuospatial attention by the dominant (right) hemisphere. The magnitude of PN is phasically modulated by transient exogenous visual cues which automatically recruit attention to cued locations. Optimal cue-line onset asynchrony (SOA), cue-contrast of this cueing effect and the relative effectiveness of cue locations relative to line endpoints are unknown. Similarly, the direction of line scanning modulates the tonic bias, although the origin of this modulation is unknown. The present experiments aim at informing theories about visuospatial attention as well as some neurological conditions such as hemispatial neglect. Four experiments were conducted where observers performed a tachistoscopic visual line bisection task. In experiments 1-3, pretransected lines were preceded by peripheral cues delivered to the left and right line ends at a variety of (1) stimulus onset asynchronies (SOAs), (2) contrasts and (3) horizontal positions relative to the line endpoints. Experiment 4 used a tachistoscopic line bisection protocol to manipulate the type (saccadic, smooth pursuit) and direction (leftward, rightward) of attentional scanning, executed with or without eye movements (overt, covert) while performing eye-tracking. Experiment 1 demonstrated early attentional capture with optimal cue-line SOA of 60 ms. Experiment 2 demonstrated that cue contrasts below 12% were ineffective in modulating perceived midpoint and the maximal effect occurred for cues of 100% contrast. Experiment 3 demonstrated modulation of the spatial error resulting from cues at all locations except the one lying completely beyond the line endpoints. Experiment 4 showed that leftward scanning resulted in leftward error and rightward scanning resulted in rightward error. Smooth pursuit scanning was more potent than saccadic scanning. Overt scanning was more potent than covert scanning and overall the strongest effects were found in leftward overt smooth pursuit scanning. Results from the cueing experiments suggest that the mechanisms subserving exogenous attentional capture in line bisection are fast, predominantly parvocellular-mediated and exert their effects at least partially in an object-referenced coordinate system. Experiment 4 suggests attentional magnification of the left line halve where visuospatial attention is deployed asymmetrically ahead of a scanned target. |
