The mouse has dichromatic colour vision based on two different types of opsins: short (S)-and middle (M)-wavelength-sensitive opsins with peak sensitivity to ultraviolet (UV; 360 nm) and green light (508 nm), respectively. In the mouse retina, the cone photoreceptors that predominantly express the S-opsin are more sensitive to contrasts, and denser towards the ventral retina, preferentially sampling the upper part of the visual field. In contrast, the expression of the M-opsin gradually increases towards the dorsal retina that encodes the lower visual field. Such distinct retinal organizations are assumed to arise from a selective pressure in evolution to efficiently encode the natural scenes. However, natural image statistics of UV light have never been examined beyond the spectral analysis. Here we developed a multi-spectral camera and examined the UV and green image statistics of the same natural scenes. We found that the local contrast and the spatial correlation were higher in UV than in green for images above the horizon, but lower in UV than in green for those below the horizon. This suggests that the mouse retina is not necessarily optimal for maximizing the bandwidth of information transmission. Factors besides the coding efficiency, such as visual behavioural requirements, will thus need to be considered to fully explain the characteristic organization of the mouse retina.
bioRxiv Subject Collection: Neuroscience