Purpose. Hemispatial neglect involves the defective deployment of visual attention toward contralesional space. Neglect patients misbisect horizontal line stimuli far to the right of veridical midpoint. Normal observers misbisect horizontal lines slightly but significantly to the left of veridical midpoint, displaying an azimuthal pseudoneglect (PN). Normals may also display altitudinal PN. Most line bisection studies of neglect and PN have used lengthy presentation and method-of-adjustment procedures where eye and limb movements are potentially confounding variables. We attempt to isolate perceptual and cognitive influences on line bisection using a tachistoscopic forced-choice paradigm. Methods. Pre-transected lines were presented for 150 ms at four orientations (|, - , / and \). Subjects made either "left-right" (for - , /, and \ lines) or "above-below" (for |, / and \ lines) discriminations in response to each line stimulus, depending upon perceived transector location relative to veridical line midpoint. Median response time and point of subjective equality (pse) were computed for each treatment condition. Results. Pse's in "left-right" conditions were significantly left of veridical; response time maxima were similarly displaced. Azimuthal PN was greatest for horizontal lines. Pse's in "above-below" conditions were displaced above veridical; response time maxima were similarly displaced. Altitudinal PN was greatest for negative diagonal lines (\). Azimuthal PN > altitudinal PN. "Left-right" responses (478.3 ms) were significantly faster than "above-below" responses (504.6 ms). Conclusions. Scanning eye and/or gross limb movements do not account for PN. Chronometric and psychometric measures of PN are in remarkable agreement. A cognitive variable (decision context) significantly influences line bisection performance.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Feb 15 1996|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience