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Metacontrast masking is specific to luminance polarity Mark W. Becker a,*, Stuart Anstis b
 

Summary: Metacontrast masking is specific to luminance polarity
Mark W. Becker a,*, Stuart Anstis b
a
Department of Psychology, Lewis and Clark College, 0615 SW Palatine Hill Road, Portland, OR 97219-7899, USA
b
Department of Psychology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0109, USA
Received 4 August 2003; received in revised form 7 May 2004
Abstract
A 1°-spot was flashed up on a screen, followed by a snugly fitting annular mask. We measured the amount of masking as a func-
tion of stimulus luminance. The surround was always mid-gray, the masking ring was either black or white, and the luminance of the
spot target ranged from 0% to 100% of white in 4% steps. Observers reported the apparent lightness of the masked spot by adjusting
a matching spot. Results: A black annular mask made all spots that were darker than the gray surround appear to be transparent,
that is, of the same luminance as the surround (complete masking). The black ring had virtually no masking effect on spots that were
lighter than the surround. Conversely, a white ring made all spots that were lighter than the gray surround look apparently the same
luminance as the surround (complete masking), but had virtually no masking effect on spots that were darker than the surround. In
summary, a black ring masked spatial decrements but not increments, whilst a white ring masked spatial increments but not dec-
rements. Thus masking occurred only when the spot and the ring had the same luminance polarity. This same-polarity masking still
occurred when the target spot was larger than the Ôdonut holeĠ of the masking ring, so that the target and ring partly overlapped.
This ruled out simple edge-cancellation theories. Instead, masking disrupts the filling-in process that normally propagates inward
from the edges of a spot [Vision Res. 31 (7­8) (1991) 1221]. We conclude that metacontrast masking occurs within, but not between,

  

Source: Anstis, Stuart - Department of Psychology, University of California at San Diego

 

Collections: Biology and Medicine