Visuomotor Organization of Pecking in the Pigeon

Abstract

The visual field of the pigeon, like that of many birds, is largely monocular and panoramic. Only a limited portion of the field immediately in front of and below the beak is binocular (Martinoya et al., 1981). This binocular portion of the field corresponds to a region in the upper temporal quadrant of the retina — the so-called red area or red field — where many of the cones contain red oil droplets. The red area has a relatively high tectal magnification factor and a ganglion cell density comparable to that of the central fovea in the monocular field (Binggeli and Paule, 1969; Clarke and Whitteridge, 1976; Galifret, 1968; Nye, 1973; Whitteridge, 1965; Yazulla, 1974), all of which suggest an area specialized for acute vision comparable to the fovea itself. The near-point of accommodation for this portion of the field, however, has been found to be much closer than that of the lateral fields (Nye, 1973). In short, there appear to be two areas of specialization within the pigeon retina: (i) a central fovea for viewing distant objects within the monocular field, and (ii) another area of acute binocular vision in the red area for viewing stimuli located only a few centimeters away from the beak.