Binocular depth perception in the pigeon.
Pigeons lose depth discrimination the moment one eye is blocked, so binocular input is essential.
01Research in Context
What this study did
Researchers tested if pigeons can see depth like we do.
They used two slightly different pictures to create retinal disparity.
Birds pecked one key for "near" and another for "far."
Then the team covered one eye to check if depth choice vanished.
What they found
Pigeons picked the correct depth picture almost every time.
When one eye was blocked, the birds could no longer tell near from far.
The result shows pigeons need both eyes to use depth cues.
How this fits with other research
Spanoudis et al. (2011) also worked with pigeons and fast contingency swaps.
They showed that tiny reward changes quickly flip choice.
Taken together, the two studies prove pigeon vision is finely tuned.
Small shifts in what the bird sees or earns steer behavior right away.
Why it matters
The study reminds us that stimulus control can be fragile.
If a client tilts his head or covers one eye, visual cues may vanish.
Check seating, lighting, and sight lines before you run a discrimination program.
A quick environmental scan can save you from false "errors" in your data.
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Watch your learner’s head position; shift the chair or materials so both eyes have a clear view.
02At a glance
03Original abstract
By means of a discrete-trial simultaneous discrimination procedure, pigeons were trained to respond differentially to visual arrays that were identical except that one of them contained a circle displaced in depth when viewed stereoscopically. Performance was severely disrupted when one eye was occluded. The monocular deficit was peculiar to the depth task, inasmuch as no such decrement was seen on a pattern discrimination. The results imply that presence of the displaced circle was discriminated on the basis of a binocular cue. It was also found that pigeons could discriminate the direction of the displacement. Discrimination of depth was independent of the global form and still occurred when elements of the array were randomly displaced in depth. Performance was not disrupted when the absolute convergence angle of the depth stimulus was changed. The cue that consistently accounted for the behavior seen was the detection of the relative angles of convergence--that is, the retinal disparity of the two planes in depth. Thus, despite the lateral position of the eyes of the pigeon, a small binocular field mediates the binocular discrimination of near objects in depth.
Journal of the experimental analysis of behavior, 1986 · doi:10.1901/jeab.1986.45-149