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.

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Prior evidence has shown a reduction of neglect on line bisection tasks as a function of altered hemispace presentation and left cueing. The present study was conducted to examine the effect of these factors in reducing symptoms of neglect on measures of general cognitive functioning. To examine proposed changes, revised versions of the Raven's Coloured Progressive Matrices and the Memory-for-Designs (MFD) Test were constructed by placing the target stimuli in the right hemifield. Two experimental presentations, a right hemispace condition and a right hemispace plus left cue prompt condition, were compared to the standard presentation format. The primary hypotheses predicted that RBD neglect patients would reveal enhanced performance on the criterion measures as a result of these manipulations. Significant correlations were predicted between the neglect measures and between the two scoring systems for the MFD. The sample was comprised of 54 hospitalized patients, assigned to either a RBD neglect group (N = 18), a RBD nonneglect group (N = 18) , or an orthopedic control group (N = 18) . Both RBD groups were administered the Mini Inventory of Right Brain Injury, to document the presence and severity of right brain injury. Presence of neglect was assessed via the Schenkenberg Line Bisection Task and the Bells Test for Visual Neglect. Subjects were examined under all three conditions by administering one third of the items for each condition. Neglect subjects demonstrated significantly poorer performance on both criterion measures than the two comparison groups. However, no significant improvement in performance was revealed with right hemispace presentation of stimuli or left cue prompts combined with the right hemispace version. Ancillary predictions concerning correlations for the neglect measures and MFD scoring systems were confirmed. Results are interpreted in terms of increased attentional demands and task complexity. These results suggest that, despite the frequent clinical use of these manipulations in the cognitive assessment of this population, support for the efficacy of these procedures is lacking.

- / Doctorat en Sciences Psychologiques et de l'éducation / info:eu-repo/semantics/nonPublished

Doctorat en sciences psychologiques / info:eu-repo/semantics/nonPublished