Colour perception in a dichromat

Research output: Contribution to journalArticle


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.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Zoology


  • chromatic space., colour vision, horse, mammal, dichromat
Original languageEnglish
Pages (from-to)2795-2800
JournalJournal of Experimental Biology
Issue number16
Publication statusPublished - 2007
Publication categoryResearch