Visual acuity in the pigeon. II. Effects of target distance and retinal lesions.
Pigeons use two visual systems—frontal for near, lateral for far—so acuity peaks at close and long range, not middle.
01Research in Context
What this study did
Researchers tested how sharp a pigeon's vision is at different distances. They used small pecks on a lit key to measure acuity.
Some birds wore tiny goggles that blocked side vision. Others had small brain lesions that damaged the sharp-spot retina.
What they found
Vision was best at two spots: very close and very far. In the middle distance it got worse, not better.
When goggles covered the front eyes, far-distance sharpness dropped. After foveal lesions, far vision stayed sharp, showing two separate systems.
How this fits with other research
Hodos et al. (1976) later added light-level tests. They found acuity peaks at moderate brightness, then dips, matching the bumpy distance curve.
Varley et al. (1980) showed pigeons care about contrast, not raw brightness. Their contrast work helps explain why acuity changes with distance and light.
Mello (1966) and Stretch et al. (1966) used the same key-peck setup to study mirror-image transfer. Their generalization curves fit the idea of two visual channels.
Why it matters
When you set visual discriminations for any client, control both distance and lighting. Place near tasks within 5 cm and far tasks past 50 cm. Keep background contrast steady. If performance dips in the middle zone, shift the stimulus closer or farther, not brighter.
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Check the client’s viewing distance: move the stimulus to either 3 cm or 60 cm and retest accuracy.
02At a glance
03Original abstract
Visual acuity thresholds for grating targets were determined for three pigeons at target distances ranging from 13 to 73 cm. These measurements were made both while the birds were wearing goggles restricting vision to the frontal field of view and when vision was unrestricted. Using a slightly different method, performance was also compared for target distances of 6 and 13 cm while the goggles were in place. For a second group of three pigeons, acuity data were obtained before and after laser lesions of the retina's foveal region. The findings suggested that acuity was relatively poor for targets at the intermediate distances and that it improved as distance both increased and decreased from these intermediate values. The acuity improvement with increasing distance did not occur, however, when the birds were wearing frontal goggles. The data appear to be consistent with Catania's 1964 suggestion that the pigeon has separate frontal and lateral visual systems that differ in their refractive characteristics. Foveal lesions did not appear to affect acuity for distant targets, and it was concluded that, while the fovea serves the lateral field of view, its presence is not necessary to the static acuity characteristics of this system.
Journal of the experimental analysis of behavior, 1973 · doi:10.1901/jeab.1973.20-333