Bottom–Up Clues in Target Finding: Why a Dalmatian May Be Mistaken for an Elephant

Abstract

We provide informal psychophysical support for a strategy where bottom–up features guide attention toward a target, and the top–down path interprets hypothetical shapes at the target location—as opposed to a dominant top–down approach. In our survey, for which we used the familiar picture of a Dalmatian dog against a dappled background, (i) 75% of subjects initially found a bulging body which overlaps that of the dog, but final ‘top–down’ percepts were unexpected: nearly all subjects assigned an incorrect head and limbs to the body; (ii) after random rotation of texture elements overlapping computed features only 45% of subjects reported a bulging body, with a few adding limbs etc. The picture of the Dalmatian dog must therefore contain many bottom–up features—a top–down strategy may find ‘incorrect’ targets at correct target locations. Computational support for these claims is more easily constructed than one may expect. We could compute at least two bottom–up features, both useful in 3-D surface interpolation from 2-D scenes, which yielded significant values at the location of the Dalmatian dog: anisotropic texture compression and affine texture distortion cues. We therefore conclude that the role of top–down processing is overstated in a traditional example such as the Dalmatian dog picture.