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Journal of the Optical Society of America A

Journal of the Optical Society of America A

| OPTICS, IMAGE SCIENCE, AND VISION

  • Vol. 17, Iss. 8 — Aug. 1, 2000
  • pp: 1382–1387

Thresholds for detecting slowly changing Ganzfeld luminances

Holger Knau  »View Author Affiliations


JOSA A, Vol. 17, Issue 8, pp. 1382-1387 (2000)
http://dx.doi.org/10.1364/JOSAA.17.001382


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Abstract

Detection thresholds for luminance increments or decrements are normally related to rapid light changes. The goal of this study was to determine detection thresholds for slowly changing achromatic Ganzfeld luminances before and after adaptation to a constant Ganzfeld illumination, subsequently called Ganzfeld adaptation. During Ganzfeld adaptation, perceived brightness decreased slowly and leveled off (on average after 5–7 min), despite constant illumination of the retina. The state of adaptation was characterized by using magnitude estimation. Comparing detection thresholds for changing light intensities before and after Ganzfeld adaptation showed that the sensitivity for luminance changes is independent of the perceived brightness. A further issue addressed was the time dependence of the luminance change. Is there a limit below which a change of luminance is no longer perceivable? Even for the slowest gradient tested (0.01 log/min), subjects were able to detect the change of luminance, although they were not able to perceive a continuous brightness change. Similar thresholds (ca. 0.24 log unit) for shallow and steep luminance gradients suggest an absolute luminance detection mechanism. Possible underlying mechanisms and neurophysiological substrates are discussed.

© 2000 Optical Society of America

OCIS Codes
(330.1880) Vision, color, and visual optics : Detection
(330.5510) Vision, color, and visual optics : Psychophysics
(330.7320) Vision, color, and visual optics : Vision adaptation

History
Original Manuscript: October 14, 1999
Revised Manuscript: April 18, 2000
Manuscript Accepted: April 18, 2000
Published: August 1, 2000

Citation
Holger Knau, "Thresholds for detecting slowly changing Ganzfeld luminances," J. Opt. Soc. Am. A 17, 1382-1387 (2000)
http://www.opticsinfobase.org/josaa/abstract.cfm?URI=josaa-17-8-1382

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