Response to H.C. Howland, "Orbital orientation is not visual orientation"

Abstract

We have hypothesized that the size of the binocular field among mammals has been selected to maximize the visually surveyable region around the animal (Changizi and Shimojo, 2008). At first glance it may seem that this hypothesis should always predict lateral pointing eyes, and a consequently small binocular field width. However, the hypothesis does not predict lateral pointing eyes in cases where the environment is filled with leafy occlusions and the animal's interpupillary distance surpasses the typical widths of the leaves (when both of these apply, we call the environment "cluttered"). In such cases, within an animal's binocular region the eyes tend to sample the scene independently. Laterally directed eyes also sample the scene independently, but the binocular region benefits from a variety of binocular summation, lowering the threshold for the recognition of objects in the binocular field. Our hypothesis predicts that mammals outside of leafy environments should have small binocular fields, independent of the size of the animal; but it predicts that for animals in leafy environments, whereas small animals should have small binocular fields (because their interpupillary distance is small compared to the typical occlusion width), large animals should have large binocular fields (because the binocular region begins to become more powerful at object recognition). Our paper provided evidence consistent with these predictions.

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