Dissociation of Short- and Long-Range Apparent Motion in Visual Search

The visual search paradigm was used in four experiments to investigate apparent motion perception. The addition of distractor items led to a linear increase in reaction time under long-range (LR) conditions (> 35 min of arc displacement), whereas reaction time was independent of display size under short-range (SR) conditions (<18 min of arc). Although clear performance differences were obtained, Ss had difficulty in distinguishing between the two types of apparent motion displays when asked to make such judgments (Experiment 2). Experiments 3 and 4 explored some variables that may constrain the search process. Search times under LR conditions were reduced when some of the distractors were stationary or the motion of the distractors was homogeneous. Form and motion were found to be separable, whereas color and motion were not. Varying the color (and brightness) interfered with the processing of motion information.