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Vision Res. 1989;29(10):1389-400.

Orientation discrimination for objects defined by relative motion and objects defined by luminance contrast.

Author information

1
Department of Psychology BSB, York University, Ontario, Canada.

Abstract

A bar-shaped area within a pattern of random dots was demarcated by moving the dots within the bar at a velocity equal and opposite to the velocity of dots outside the bar. Orientation discrimination for this motion-defined dotted bar was compared with orientation discrimination for a contrast-defined dotted bar that was created by switching off all dots outside the bar. Orientation discrimination was approximately as acute (approx. 0.5 deg) for a motion-defined bar as for a contrast-defined dotted bar, provided that dot contrast and speed were both high. Furthermore, this 0.5 deg discrimination compares with the most acute values reported for sharp-edged lines and sinewave gratings. For the motion-defined bar discrimination fell off rapidly when dot contrast was reduced, but remained acute for the contrast-defined bar for a further reduction of 0.6 log units. Thus, there was a 4:1 range of contrasts over which discrimination had collapsed for the motion-defined bar but remained acute for the contrast-defined bar. For the motion-defined bar discrimination also fell off rapidly at low dot speeds, but was almost unaffected by speed for the contrast-defined bar. These findings bear on the question whether orientation of motion-defined and contrast-defined bars are analyzed by the same or by different neural mechanisms, and pose a challenge for current theories of orientation discrimination.

PMID:
2635467
DOI:
10.1016/0042-6989(89)90194-6
[Indexed for MEDLINE]

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