Which end is up? Two representations of orientation in visual search

AbstractWhat is the orientation of an object? A simple line has an axis of orientation. That line, turned upside-down, is indistinguishable from the original line. Thus, the possible orientations of a line range from 0 to 180°. Most objects, however, have an axis and a polarity. A polar object, turned upside-down, looks upside-down. Accordingly, the orientations of a polar object range from 0 to 360°. A series of visual search experiments were run to determine if preattentive processes represent orientation in a 180 or a 360° framework. Results suggest that preattentive orientation is represented in 180°. Experiments 1 and 4 show that search for a target rotated 90° from the distractors is more efficient than search for a target rotated 180° from the distractors. Experiments 2, 3, and 5 use a variety of different stimuli to demonstrate that search for targets rotated 180° from distractors is inefficient