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Bird colour vision: behavioural thresholds reveal receptor noise.

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Author

Summary, in English

Birds have impressive physiological adaptations for colour vision, including tetrachromacy and coloured oil droplets, yet it is not clear exactly how well birds can discriminate the reflecting object colours that they encounter in nature. With behavioural experiments, we determined colour discrimination thresholds of chickens in bright and dim light. We performed the experiments with two colour series, orange and green, covering two parts of chicken colour space. These experiments allowed us to compare behavioural results with model expectations and determine how different noise types limit colour discrimination. At intensities ranging from bright light to those corresponding to early dusk (250-10 cd m(-2)), we describe thresholds accurately by assuming a constant signal-to-noise ratio, in agreement with an invariant Weber fraction of Weber's law. Below this intensity, signal-to-noise ratio decreases and Weber's law is violated because photon-shot noise limits colour discrimination. In very dim light (below 0.05cd m(-2) for the orange series or 0.2 cd m(-2) for the green series) colour discrimination is possibly constrained by dark noise, and the lowest intensity at which chickens can discriminate colours is 0.025 and 0.08 cd m(-2) for the orange and green series, respectively. Our results suggest that chickens use spatial pooling of cone outputs to mitigate photon-shot noise. Surprisingly, we found no difference between colour discrimination of chickens and humans tested with the same test in bright light.

Publishing year

2015

Language

English

Pages

184-193

Publication/Series

Journal of Experimental Biology

Volume

218

Issue

2

Document type

Journal article

Publisher

The Company of Biologists Ltd

Topic

  • Philosophy
  • Zoology

Keywords

  • Animal behaviour
  • Bird vision
  • Gallus gallus
  • Psychophysics
  • Visual modelling

Status

Published

Research group

  • Lund Vision Group

ISBN/ISSN/Other

  • ISSN: 1477-9145