Near-field visual acuity of pigeons: effects of head location and stimulus luminance.
Pigeon vision peaks at medium light levels; brighter light drops performance by lowering contrast.
01Research in Context
What this study did
Researchers tested how bright light affects pigeon eyesight.
Birds pecked a key to report seeing tiny black-and-white stripes.
The team changed screen brightness from dim to very bright while stripes stayed the same size.
What they found
Vision sharpened as light grew brighter, but only to a point.
At medium brightness, pigeons saw the finest stripes.
Brighter light past that point made vision slightly worse again.
How this fits with other research
Wilkie (1973) from the same lab showed pigeons see best at very near and very far distances.
Together, the two papers map the sweet spots for pigeon vision: best distance and best brightness.
Varley et al. (1980) later found pigeons care more about contrast than raw brightness.
That explains why extra-bright light in Hodos et al. (1976) hurt acuity: it washed out stripe contrast.
Why it matters
When you set up visual tasks for learners, think about screen or room brightness.
Too dim or too bright can both hurt discrimination.
Aim for moderate, even lighting and check that figure-ground contrast stays strong.
If a client starts missing trials, dim or raise lights a notch before you change the teaching program.
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02At a glance
03Original abstract
Two pigeons were trained to discriminate a grating stimulus from a blank stimulus of equivalent luminance in a three-key chamber. The stimuli and blanks were presented behind a transparent center key. The procedure was a conditional discrimination in which pecks on the left key were reinforced if the blank had been present behind the center key and pecks on the right key were reinforced if the grating had been present behind the center key. The spatial frequency of the stimuli was varied in each session from four to 29.5 lines per millimeter in accordance with a variation of the method of constant stimuli. The number of lines per millimeter that the subjects could discriminate at threshold was determined from psychometric functions. Data were collected at five values of stimulus luminance ranging from--0.07 to 3.29 log cd/m2. The distance from the stimulus to the anterior nodal point of the eye, which was determined from measurements taken from high-speed motion-picture photographs of three additional pigeons and published intraocular measurements, was 62.0 mm. This distance and the grating detection thresholds were used to calculate the visual acuity of the birds at each level of luminance. Acuity improved with increasing luminance to a peak value of 0.52, which corresponds to a visual angle of 1.92 min, at a luminance of 2.33 log cd/m2. Further increase in luminance produced a small decline in acuity.
Journal of the experimental analysis of behavior, 1976 · doi:10.1901/jeab.1976.25-129