November 2002
Volume 2, Issue 7
Free
Vision Sciences Society Annual Meeting Abstract  |   November 2002
Discrimination of shifted centers-of-motion in a patient that cannot perceive radial motion
Author Affiliations
  • S.A. Beardsley
    Brain and Vision Research Laboratory, Dept. of Biomedical Engineering, Boston University, USA
Journal of Vision November 2002, Vol.2, 657. doi:10.1167/2.7.657
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      S.A. Beardsley, L.M. Vaina; Discrimination of shifted centers-of-motion in a patient that cannot perceive radial motion. Journal of Vision 2002;2(7):657. doi: 10.1167/2.7.657.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose. We use psychophysical data from a motion-impaired stroke patient, GZ (Vaina & Goldberg 2002), to challenge the generally accepted view that a precise computation of local and/or global motion information is necessary for recovering the 2D center-of-motion (COM) associated with translational direction in a 3D scene, (Reiger & Lawton 1985; Bruss & Horn 1983). Methods. Motion stimuli were represented as constant density random dot kinematograms presented within a 24 deg aperture (central 4 deg removed) for 440±40ms. In two perceptual tasks observers were presented with 30 deg/s radial (expansion/contraction) or circular (CW/CCW) motion-patterns and were required to discriminate (1) the shift in the COM, left or right, relative to a central fixation or (2) opposing motion-patterns (e.g. expansion vs. contraction) defined by a proportion of signal dots embedded in masking motion noise (Motion Pattern Coherence). Results. In normal observers (1) COM thresholds for circular motion-patterns were significantly higher than for radial motion-patterns (p<0.005; t(19)=2.92) while in (2) discrimination thresholds for radial and circular motion-patterns were comparable (∼10%). GZ was only able to discriminate moderate shifts (∼1 deg) in the COM for radial and circular motion-patterns. In contrast GZ totally failed to discriminate radial motion-patterns even at 100% coherence. However, she could discriminate CW from CCW motion and radial from circular motion-patterns. Conclusion. GZ's performance could be explained by a mechanism that computes a scalar norm from the motion-pattern for use as an error measure to localize the COM (Sundareswaran 1992). In this scheme a sparse sampling of scalar errors across the visual field provides a coarse spatial localization of the COM, independent of the type of radial motion-pattern. Discrimination with finer accuracy can be obtained through computations that use the direction information of the radial motion-patterns.

Beardsley, S. A., Vaina, L. M.(2002). Discrimination of shifted centers-of-motion in a patient that cannot perceive radial motion [Abstract]. Journal of Vision, 2( 7): 657, 657a, http://journalofvision.org/2/7/657/, doi:10.1167/2.7.657. [CrossRef]
Footnotes
 Supported by NIH grant EY-2R01-07861-07 to L.M.V.
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