Abstract
Depth perception is a critical aspect of the human visual system which supports localization and interactions with objects in space. Over the years, psychophysical and neuropsychological research has showed that sensory processing is modulated by the location of stimuli relative to the body. In particular, objects closer to the observer benefit from enhanced processing, appropriately termed the “close advantage” effect. Previously, evidence of the close advantage was limited to multisensory studies, with little focus on a purely visual component. However, recent investigations show that depth information modulates visuo-perceptual resolution, even when other visual attributes (such as retinal size) are held constant. While it is clear that this phenomenon is robust and generalizable across stimuli and tasks, the underlying mechanism is poorly understood. One hypothesis is that objects that are perceived as closer to the observer are more behaviorally relevant (e.g., one can grasp a hammer only if it is within arm’s reach), and therefore benefit from enhanced processing. To evaluate this proposal, we assessed the close advantage effect for shapes that either offer a potential for action (affordable – e.g., elongated) or do not potentiate action (non-affordable – e.g., non-elongated). The stimuli were presented on either the ‘close’ or ‘far’ regions of a Ponzo Illusion arrangement. A method of constant stimuli was used to measure precision and reaction times were recorded. Our results replicate previous findings by demonstrating an enhanced discrimination for both affordable and non-affordable shapes in the “close” space. Critically, and consistent with our hypothesis, affordable shapes elicited a stronger “close advantage” than non-affordable shapes. Together, these results provide novel evidence for the role of affordance in mediating the close advantage effect.