| dc.contributor.author | Losier, Bruno J. W. | en_US |
| dc.date.accessioned | 2014-10-21T12:33:50Z | |
| dc.date.available | 1999 | |
| dc.date.issued | 1999 | en_US |
| dc.identifier.other | AAINQ49279 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55660 | |
| dc.description | Line bisection and covert orienting were explored in patients with neglect using stimuli presented within (peripersonal space) and beyond (extrapersonal space) arm's reach. | en_US |
| dc.description | Methods. Forty-three young subjects, 9 older subjects and 13 individuals with right-hemisphere damage, seven of whom were classified as showing left neglect, participated in the study. In one task, subjects used a hand-held device to remotely bisect computer-generated horizontally and vertically oriented lines that were placed centrally or away from center (above, below, center for horizontal lines; to the left, right of center for vertical lines). To direct the subject's attention, the bisecting cursor that was controlled by the subject was initially presented near the center of the line or towards one or the other end. In a second task, subjects detected the presentation of a target presented in one of 4 quadrants (top left; top right; bottom left; bottom right) following informative peripheral cues designed to elicit covert orienting of visual attention. All stimuli were presented at distances of 28 cm peripersonal space) and 224 (extrapersonal space) cm. | en_US |
| dc.description | Results: Line Bisection. In patients with neglect a significant rightward bias (i.e., >10%) on horizontal lines was noted, as expected. Interestingly, cuing the left end of the horizontal line significantly reduced the rightward bias to near normal level, while cuing the middle or right end of the line resulted in the expected significant rightward deviations. In contrast, vertical lines yielded a non-significant downward bias and the bisection cursor starting position did not significantly alter the bias. Viewing distances did not significantly alter bisection biases for either horizontal or vertical lines. In normal controls, the bisecting cursor significantly altered the bias in the direction of its initial starting position on both horizontal (left-right ends of lines) and vertical lines (top-bottom ends of lines). As well, a viewing distance by line location interaction was obtained for horizontal lines only. The direction of the bias differed significantly between lines displayed above and below eye levels in peripersonal space, but it did not in extrapersonal space. | en_US |
| dc.description | Visual Orienting. All groups responded more rapidly to targets presented at the cued location (valid cuing condition) than to targets at uncued locations (invalid cuing condition). Patients with neglect manifested a disengage deficit between hemifields, as expected wherein the reaction time delay on an invalid trial was much greater for targets presented in the neglected hemifield following cues in the non-neglected hemifield, than vice versa. However, evidence of a within field disengage deficit in the contralesional hemifield was not substantiated here. Moreover, following the presentation of a cue within the contralesional hemifield patients with or without neglect responded equally quickly to poor field targets at the cued and uncued locations. Viewing distance did not alter the manifestation of the disengage deficit pattern in patients with neglect. In normal controls, detection of the cued target was fastest to the lower field in peripersonal space than at any other location or viewing distance. Finally, a correlational analysis performed on the entire sample of patients with right-hemisphere damage suggested a relationship between rightward deviations on line bisection and the disengage. | en_US |
| dc.description | Conclusion. The outcome of these studies provides partial support of Previc's (1990) model of upper and lower visual field specialization. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 1999. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Psychology, Experimental. | en_US |
| dc.subject | Psychology, Cognitive. | en_US |
| dc.title | Line bisection and visual orienting within and beyond arm's reach in patients with visuospatial neglect. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
