How rats see

Neitz and Jacobs (1986) measured the electrical response of the rat eye and found a single daylight cone mechanism, peaking at about 510 nm (green). In their behavioral test, rats showed no sign of color vision.

Later, Jacobs, Fenwick and Williams (2001) reported a second class of cone, sensitive to ultraviolet; in some daylight tests rats were about equally sensitive to green and to ultraviolet light. Rats then passed tests of telling wavelengths apart: they have two-color (dichromatic) vision. We did not read the peak of the ultraviolet cone in these papers, so the chart shows only the green-sensitive one.

A photo records red, green and blue for human eyes and holds no ultraviolet, so the rat's ultraviolet cone gets almost nothing from it. One cone gives brightness without hue: the simulator shows each color as a gray as bright as the rat's green cone finds it, so red comes out dark.

The table runs a few everyday pairs through the same model and gives the color difference (ΔE 2000) for a person and for the rat model: the smaller the number, the harder the pair is to tell apart. On the scale we use across this site, below 3 is a close match, 6 or more is a visibly different color, and 10 or more is clearly different.

The gray is built from the rat's green-sensitive cone (510 nm). For each color the simulator estimates how strongly that cone would respond, using the pigment template of Govardovskii and colleagues (2000) and daylight (CIE D65), and shows a gray of the same brightness; white and grays stay as they are. The cone signal weighs the light by its energy; weighting by photon count instead would change some grays by up to 8 of 255 in our check. It is an approximation: the eye's lens is left out, and each color's spectrum is a guess from its screen color. Everything runs on your device: the camera picture, photos and videos are not uploaded.

Prusky and colleagues (2002) tested how fine a striped pattern rats could tell apart, in six lab strains and in wild rats. Wild rats and the pigmented strains Dark Agouti and Long-Evans clustered around 1.0 cycle per degree (one cycle is a dark and a light stripe), Fisher-Norway rats reached 1.5, and the three albino strains (Fisher-344, Sprague-Dawley and Wistar) about 0.5. The simulator uses 1.0. An albino rat would see the picture about twice as blurry.

An earlier swimming test from the same lab also put Long-Evans rats near 1.0 cycle per degree (Prusky, West and Douglas, 2000).

How the blur is made: the simulator follows AcuityView, the method of Caves and Johnsen (2018). Fine detail is faded along a bell-shaped curve that leaves about 3% of the contrast at the animal's acuity limit, and coarse shapes stay. A picture does not say how wide the scene was, so the simulator assumes that the long side of the picture covers about 70°, the view of a typical phone's main camera (the iPhone 16 main camera is 26 mm in 35 mm terms, about 69° across). If you zoomed in or cropped, the scene was narrower and the animal would see it blurrier than shown. The blur stands for the sharpest part of the eye only.