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Contrast constancy revisited: the perceived contrast of sinusoidal gratings above threshold

Lookup NU author(s): Dr Wayne Smith

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Abstract

The contrast sensitivity function of the human visual system, measured with sinusoidal luminance gratings, has an inverted U shape with a peak around 2–4 c/deg. Above threshold, it is thought that luminance gratings of equal physical contrasts but of distinguishably different spatial frequencies are all perceived as having similar contrasts, a phenomenon that has been termed contrast constancy. However, when suprathreshold contrast matches were measured for pairs of luminance gratings whose spatial frequencies were indistinguishable, the matching curves were not flat and followed a similar inverted U shape form as the contrast sensitivity function at threshold. It was therefore suggested that contrast constancy may only be revealed when matching the contrasts of clearly distinguishable spatial frequencies. Here, observers matched the perceived contrasts of suprathreshold luminance gratings of similar but visibly different spatial frequencies between 0.25 and 16 c/deg. The results show that, much like the contrast sensitivity function at threshold, observers are more sensitive to intermediate spatial frequencies (1–6 c/deg) than they are to either higher or to lower spatial frequencies. This tuning is evident when matching reference contrasts of 30–80%, implying a significant role in everyday vision. To demonstrate that these results were not due to local adaptation, the experiment was repeated with shorter stimulus duration, producing the same results. The extent of departure from contrast constancy found in the present study is compared to previously reported suprathreshold measurements. The results are also discussed with consideration to limitations with display apparatus such as monitor blur.

Publication metadata

Author(s): Smith WS

Publication type: Article

Publication status: Published

Journal: The Quarterly Journal of Experimental Psychology

Year: 2015

Volume: 68

Issue: 2

Pages: 363-380

Print publication date: 01/02/2015

Online publication date: 15/09/2014

Acceptance date: 07/07/2014

ISSN (print): 1747-0218

ISSN (electronic): 1747-0226

Publisher: Routledge

URL: http://dx.doi.org/10.1080/17470218.2014.944919

DOI: 10.1080/17470218.2014.944919

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