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Colour perception in a dichromat

  • Lina Roth
  • Anna Balkenius
  • Almut Kelber
Publishing year: 2007
Language: English
Pages: 2795-2800
Publication/Series: Journal of Experimental Biology
Volume: 210
Issue: 16
Document type: Journal article
Publisher: The Company of Biologists Ltd

Abstract english

Most mammals have dichromatic colour vision based on

two different types of cones: a short-wavelength-sensitive

cone and a long-wavelength-sensitive cone. Comparing the

signal from two cone types gives rise to a one-dimensional

chromatic space when brightness is excluded. The so-called

‘neutral point’ refers to the wavelength that the animal

cannot distinguish from achromatic light such as white or

grey because it stimulates both cone types equally. The

question is: how do dichromats perceive their chromatic

space? Do they experience a continuous scale of colours or

does the neutral point divide their chromatic space into two colour categories, i.e. into colours of either short or long wavelengths?

We trained horses to different colour combinations in a

two-choice behavioural experiment and tested their

responses to the training and test colours. The horses chose

colours according to their similarity/relationship to

rewarded and unrewarded training colours. There was no

evidence for a categorical boundary at the neutral point or


This study suggests that dichromats perceive their

chromatic space as a continuous scale of colours, treating

the colour at the neutral point as any other colour they can distinguish.


  • Zoology
  • chromatic space.
  • colour vision
  • horse
  • mammal
  • dichromat


  • Lund Vision Group
  • ISSN: 1477-9145
E-mail: anna [dot] balkenius [at] biol [dot] lu [dot] se


Functional zoology

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Lund Vision Group