How many colors can rats see? - briefly
Rats have dichromatic vision, detecting mainly ultraviolet and green wavelengths, which limits their color discrimination to roughly two distinct hues. Their visual system cannot differentiate the broader spectrum observable by humans.
How many colors can rats see? - in detail
Rats possess a visual system that differs fundamentally from that of humans. Their retinas contain two functional cone types, providing a dichromatic perception rather than the trichromatic vision typical of primates. The short‑wavelength (S) cones are most sensitive to ultraviolet light around 360 nm, while the medium‑wavelength (M) cones peak near 510 nm in the green region. Consequently, rats can discriminate between at most two distinct spectral ranges, effectively perceiving a limited set of colors.
Experimental evidence supports this assessment:
- Electrophysiological recordings show distinct responses of S‑ and M‑cones to UV and green stimuli, with no measurable activity for wavelengths corresponding to red hues.
- Behavioral tests using conditioned discrimination tasks demonstrate that rats reliably differentiate UV‑rich from green‑rich environments but fail to distinguish between green and red cues.
- Genetic analyses reveal the presence of only two opsin genes (S‑opsin and M‑opsin) in the rat genome, confirming the physiological basis for dichromacy.
The functional consequence is a visual palette comprising roughly two to three perceptible colors:
- Ultraviolet – detected by S‑cones, enabling perception of patterns invisible to humans.
- Green – detected by M‑cones, representing the primary visible range for rats.
- Intermediate shades – arising from combined activation of both cone types, providing limited gradations but lacking true red or orange perception.
Rats rely heavily on non‑visual cues such as whisker touch, olfaction, and auditory signals for navigation and foraging. Their visual acuity is low, with a spatial resolution of about 1 cycle/degree, further emphasizing the limited role of color discrimination in their natural behavior.