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Detection of smooth three-dimensional surfaces from optic flow.

An assumption central to the study of 3-dimensional (3-D) shape perception is that sufficient information must be present to detect a 3-D surface. Three experiments were conducted to determine the variables important for the detection of 3-D surfaces from optic flow. Observers were presented with optic-flow displays simulating either points positioned on a corrugated 3-D surface or points randomly positioned within a 3-D volume. The task of the observer was to indicate whether the display appeared to be a 3-D surface. An increase in frequency of the corrugation for simple (single-frequency corrugation) surfaces resulted in a decrease in surface detection. Detection performance increased with an increase in density and amplitude for both simple and complex (multiple-frequency corrugation) surfaces. An analysis of the deformation of the displays suggests that 3-D surface detection may be based on the summed absolute value of the 2 shear components of deformation.