Center-Surround Antagonism and the Influence of Disparity upon the Perception of Speed in Young and Aging Observers
Two experiments were designed to evaluate the influence of binocular disparity in a target’s surround upon the perceived speed of a moving target, in both young and aging observers. Contextual information is known to influence the perceived speed of a target. For example, studies have shown that contextual parameters, such as surround velocity (Norman, Norman, Todd, & Lindsey, 1996; Tynan & Sekuler, 1975), landmark presence (Brown, 1931), landmark density (Gogel & McNulty, 1983), and background texture and stimulus contrast (Blakemore & Snowden, 2000; Nguyen-Tri & Faubert, 2007) can alter an observer’s perception of target speed. Other research, using discrete center-surround type stimuli, has shown modulatory effects of surround disparity upon neuronal responses in cortical area MT (Bradley & Andersen, 1998). Experiment 1 was designed to examine the degree to which crossed, uncrossed, and zero disparities in a target’s moving surround alter the perceived speed of the target. Given the fact that aging is widely known to affect performance on motion-related tasks (e.g., Norman, Ross, Hawkes, & Long, 2003). Experiment 2 was designed to test the effects of aging upon perceived velocity under conditions equivalent to those used in Experiment 1. The results of Experiment 1 demonstrated that a target’s perceived speed is dependent upon its position in depth relative to its surround when both regions move in the same direction. Experiment 2 showed that aging alters the perceived speed of moving targets, such that perceived speed is dependent upon a target’s depth relative to its surround, this effect occurring independently of the surround’s direction of motion.