How does a pig see the world?

What the research shows

The pig's two cone classes were measured with electroretinographic flicker photometry, which records the retina's electrical response to flickering lights of different wavelengths. Neitz & Jacobs (1989) used it to place the short-wavelength cone near 439 nm and the long-wavelength cone near 556 nm, values the research notes rank among the best-established for any species in this group. Because the surviving long cone sits close to the human L cone, the page models the pig as deuteranope-like. The neutral point, the wavelength a dichromat sees as grey, is estimated at around 480 nm rather than directly measured.

Almost everything else about pig vision is estimated. Acuity is not tightly quantified: behavioural and anatomical estimates cluster around 6 cpd, held down by low ganglion-cell resolution despite a cone-rich central retina, and the simulation uses a slightly softer 5 cpd. The field of view, about 310° with 35–50° of binocular overlap, is also an estimate, and the domestic pig has no tapetum lucidum. Flicker fusion, estimated at 50–70 Hz from behavioural and electroretinographic work, points to a limit a screen cannot address: a pig may perceive flicker in some artificial lighting that looks steady to people, and no image shown to a human viewer can transfer that difference. Nor can it convey the sense a pig relies on most, which is smell.