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Abstract:
Previous studies reported an ipsilesional deficit in visual
motion discrimination in patients suffering from unilateral
posterior brain damage. However, this deficit was only described
with respect to threshold elevations (TE) and along the horizontal
axis. Directional motion perception errors (DMPE, i.e. motion
stimulus: left, perceived motion: up) and TE along the vertical
axis have not been analyzed systematically. We investigated visual
motion perception in patients suffering from unilateral posterior
brain damage and determined visual motion thresholds and the number
of DMPE in the four cardinal directions. Random dot patterns were
presented in the central visual field. Patients replied whether
they perceived the direction of the motion as left, right, up,
down, or not at all. We report three principle findings. Unilateral
lesions lead to a motion discrimination deficit (TE), which is
greater along the horizontal than the vertical axis and largest in
the ipsilesional horizontal direction. DMPE are direction-specific,
depend on tested movement direction and are most often in the
vertical direction. DMPE are negatively correlated with the visual
motion threshold. These results show that posterior brain lesions
modify visual motion perception not only quantitatively but also
qualitatively leading to a systematic misperception of a given
stimulus direction. Our results are discussed in light of recent
findings in visual motion processing in man and monkey.
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