Zhaoping, L; Geisler, WS; May, KA; (2011) Human wavelength discrimination of monochromatic light explained by optimal wavelength decoding of light of unknown intensity. PLoS One , 6 (5) , Article e19248. 10.1371/journal.pone.0019248.
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We show that human ability to discriminate the wavelength of monochromatic light can be understood as maximum likelihood decoding of the cone absorptions, with a signal processing efficiency that is independent of the wavelength. This work is built on the framework of ideal observer analysis of visual discrimination used in many previous works. A distinctive aspect of our work is that we highlight a perceptual confound that observers should confuse a change in input light wavelength with a change in input intensity. Hence a simple ideal observer model which assumes that an observer has a full knowledge of input intensity should over-estimate human ability in discriminating wavelengths of two inputs of unequal intensity. This confound also makes it difficult to consistently measure human ability in wavelength discrimination by asking observers to distinguish two input colors while matching their brightness. We argue that the best experimental method for reliable measurement of discrimination thresholds is the one of Pokorny and Smith, in which observers only need to distinguish two inputs, regardless of whether they differ in hue or brightness. We mathematically formulate wavelength discrimination under this wavelength-intensity confound and show a good agreement between our theoretical prediction and the behavioral data. Our analysis explains why the discrimination threshold varies with the input wavelength, and shows how sensitively the threshold depends on the relative densities of the three types of cones in the retina (and in particular predict discriminations in dichromats). Our mathematical formulation and solution can be applied to general problems of sensory discrimination when there is a perceptual confound from other sensory feature dimensions.
|Title:||Human wavelength discrimination of monochromatic light explained by optimal wavelength decoding of light of unknown intensity.|
|Open access status:||An open access version is available from UCL Discovery|
|Additional information:||© 2011 Zhaoping et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the Gatsby Charitable Foundation and a Cognitive Science Foresight grant BBSRC #GR/E002536/01. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.|
|UCL classification:||UCL > School of BEAMS > Faculty of Engineering Science > Computer Science|
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