| |
Abstract:
Normal men and women (N=15) and a 54 year-old man with
left-sided visual neglect after a right-sided CVA bisected a 430mm
long black horizontal line with the right hand and then marked the
perceived quarter point on one side of the line. On this side, they
then marked the perceived eights and (normal subjects only) the
perceived sixteenths. Next, they transected the other side of the
line in the same way. Normal subjects performed 50 trials, the
neglect patient 25; all aternated the side they transected first.
Mean relative bias of each subject was expressed as a percentage of
half segment transected. Segment lengths were measured by marks
subjects made in their previous transactions. The normal group
transected the whole line with no bias. When transecting the left
half of lines, they showed leftward bias, increasing with distance
of the segment from the midline; when transecting the right half,
they showed smaller, constant biases to the right. Thus line
segments in the left hemispace are preceived as increasingly
expanded as their distance from the midline increases. As expected,
the neglect patient's bisections were biased to the right. This
bias increased linearly as he transected segments located further
to the left and decreased as he transected segments further to the
right. Thus, perceptual constriction in this patient increases with
leftward and decreases with rightward distance from the
midline.
|
