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Abstract:
Abstract: The purpose of this study is to examine how the
competing spatial coordinates of visual stimuli influence
orientation recognition. We used a modified rod-and-frame-illusion
task. The stimuli were two triangular figures positioned
side-by-side, each surrounded by a rectangular frame. The
orientation of the two frames was varied so that the coordinates of
the frames competed with each other. The task required
same/different decision of the figure orientation inside the
frames. We tested normal subjects and a patient (Y.M.) with
bilateral occipito-parietal atrophy. A previous study indicated
that Y.M. could line up cylinders diagonally, but not cubic blocks.
This may be due to the competition of coordinates between the
intrinsic orientation of the cubes (vertical and horizontal) and
the line-up direction (diagonal). Therefore, Y.M. may have a marked
difficulity to recognize the orientation of shapes under competing
coordinates. The results showed that, for both Y.M.and normal
subjects, as the difference in angles between the left and right
frames grew, both error rate and reaction time (RT) significantly
increased(p<.001). Furthermore, especially for Y.M., the
error rate and RT were influenced by whether one frame-and-figure
was the mirror image of the other. The results show that for Y.M.
and even for normal subjects, orientation recognition is influenced
by competition of spatial coordinates in visual stimuli. In
addition, left-to-right symmetry of the configuration may also
influence recognition of figure orientation.
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