Vision is one of the most important sensory systems in birds.
Visual acuity has been studied in several species of birds, but no behavioural studies of visual acuity in crows have been reported so far. Subjects were trained to hold their heads in a fixed position to keep a constant observing distance. The position of the head was measured by a microsensor placed on the side panel of the cage. On each trial, a grating pattern and a uniform gray appeared on adjacent windows. When the subject pecked on the window with the grating pattern, he got food as a reward.