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Factorial Design: Binocular and Monocular Depth Perception in Vertical and Horizontal Stimuli

This article describes a factorial experiment that is useful as a laboratory exercise in a research methods course. In the Howard–Dolman depth perception apparatus, two vertical rods are adjusted, using binocular or monocular vision, so they appear equidistant from the observer. The two rods can also be oriented horizontally, which allows a factorial design combining the factors of Viewing Condition (binocular and monocular) and Rod Orientation (vertical and horizontal). The exercise illustrates the nature of an interaction and the necessity of an additional analysis of simple main effects. It also provides a basis for understanding a perceptual problem in the real world—the difficulty of localizing horizontally extended stimuli such as power lines.