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PloS one2008; 3(11); e3711; doi: 10.1371/journal.pone.0003711

The absolute threshold of colour vision in the horse.

Abstract: Arrhythmic mammals are active both during day and night if they are allowed. The arrhythmic horses are in possession of one of the largest terrestrial animal eyes and the purpose of this study is to reveal whether their eye is sensitive enough to see colours at night. During the day horses are known to have dichromatic colour vision. To disclose whether they can discriminate colours in dim light a behavioural dual choice experiment was performed. We started the training and testing at daylight intensities and the horses continued to choose correctly at a high frequency down to light intensities corresponding to moonlight. One Shetland pony mare, was able to discriminate colours at 0.08 cd/m(2), while a half blood gelding, still discriminated colours at 0.02 cd/m(2). For comparison, the colour vision limit for several human subjects tested in the very same experiment was also 0.02 cd/m(2). Hence, the threshold of colour vision for the horse that performed best was similar to that of the humans. The behavioural results are in line with calculations of the sensitivity of cone vision where the horse eye and human eye again are similar. The advantage of the large eye of the horse lies not in colour vision at night, but probably instead in achromatic tasks where presumably signal summation enhances sensitivity.
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Publication Date: 2008-11-12 PubMed ID: 19002261PubMed Central: PMC2577923DOI: 10.1371/journal.pone.0003711Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research explores whether horses, known for their large eyes and activity patterns unrestricted to day or night, possess the ability to see colours in dim light or night conditions. The findings reveal that horses can indeed discriminate colours at light intensities equivalent to moonlight, with their colour vision threshold closely resembling that of humans.

Experiment Design

  • The researchers conducted a behavioural dual choice experiment to determine whether horses could differentiate between colours in dim light. This type of experiment typically involves presenting the subject with two contrasting stimuli and observing their choice.
  • The trial was initiated at daylight intensities, gradually transitioning to lighter intensities corresponding to moonlight.

Results

  • The results indicated that horses continued to make the correct choice at a high frequency even when the light was equivalent to moonlight.
  • A Shetland pony mare was able to discriminate colours at a light intensity of 0.08 cd/m^2, while a half blood gelding did so at an intensity as low as 0.02 cd/m^2.
  • For comparison, human subjects tested under the same conditions also demonstrated a colour vision limit of 0.02 cd/m^2 which corresponds closely with the horse’s ability.

Interpretation and Conclusion

  • The results obtained align with calculations of the sensitivity of cone vision, a part of the eye’s physiology responsible for colour detection, wherein the horse and human eye demonstrated comparable sensitivities.
  • Rather than aiding in colour vision at night, the study suggests that the large size of the horse’s eye contributes more significantly to achromatic tasks, where the ability to sum signals likely improves light sensitivity.

In summary, this research provides significant evidence to suggest not only that horses are capable of seeing colour in low light conditions, but also that their colour vision sensitivity is akin to that of humans. This is potentially attributed to the similarities in the sensitivities of horse and human cone vision. Further, the study surmises that the larger size of the horse eye is favourable for non-colour tasks of vision where increased sensitivity to light is advantageous.

Cite This Article

APA
Roth LS, Balkenius A, Kelber A. (2008). The absolute threshold of colour vision in the horse. PLoS One, 3(11), e3711. https://doi.org/10.1371/journal.pone.0003711

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 3
Issue: 11
Pages: e3711
PII: e3711

Researcher Affiliations

Roth, Lina S V
  • Department of Cell and Organism Biology, Vision Group, Lund University, Lund, Sweden. lina.roth@cob.lu.se
Balkenius, Anna
    Kelber, Almut

      MeSH Terms

      • Adaptation, Physiological
      • Animals
      • Behavior, Animal
      • Color Perception / physiology
      • Color Vision / physiology
      • Discrimination Learning
      • Horses
      • Humans
      • Photic Stimulation
      • Retinal Cone Photoreceptor Cells / metabolism
      • Sensory Thresholds

      Conflict of Interest Statement

      The authors have declared that no competing interests exist.

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      Citations

      This article has been cited 9 times.
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