Binocular field in pigeons: behavioral measures of stimulus detection and coding.

The extension of the binocular visual field of pigeons is measured using a pecking behavioral method. Our estimate of the binocular field derived at the animal near point of accommodation indicates a 50 degrees width on the horizontal axis and more than 50 degrees on the vertical axis. Within the binocular field there is a core of about 24 degrees, named coding area, in which the stimulus is detected and coded by only one head fixation before accomplishing the pecking response, in both binocular and monocular viewing conditions. Outside the coding area, lies the detection area, in which the stimulus can be detected, but it needs a second head fixation to be coded in all viewing conditions. Our results are in agreement with the hypothesis that the coding area corresponds to the red field projection of each retina. In binocular vision an overlap of the two areas occurs, thus promoting the image fusion useful for a stereoscopic vision during the pecking to the seed.