Abstract
Fear of a stimulus can distort perception of its appearance (e.g., spiders: Rachman & Cuk, 1992; heights: Stefanucci & Proffitt, 2008). These studies have not distinguished between conscious perception versus the control of visually guided action (Milner & Goodale, 1995). In this study we tested spider-phobic (n=15) and non-phobic (n=20) participants in a visually guided pointing task that measured both conscious and unconscious aspects of visual-motor control. Participants made speeded pointing actions on a touch-screen to images depicting either negative or positive emotional content (spiders vs. pets). The pointing task was performed with visual attention either focused on the image (single task) or divided because participants were also identifying letters (dual task). This dual task disrupts the conscious planning of actions (as measured by action initiation time) but not their online control (as measured in movement time, pointing accuracy, and response to target displacement during the action) (Liu, Chua, & Enns, 2008). Pointing was controlled differently by spider-phobic than non-phobic participants. In the dual task, they showed greater interference for letter identification and slower pointing movement. In the single task, they showed less accuracy and greater sensitivity to image content, specifically avoiding the negative images when pointing. Yet, when attention was divided between images and letters in the dual task, measures of unconscious motor control showed no differences related to phobia; pointing speed, accuracy, and sensitivity to target displacement were unaffected by phobia or image content. These findings support the hypothesis that spider-phobia exerts its influence on the conscious, but not unconscious, control of visually guided action. They imply that the automatic pilot of the dorsal stream (Pisella et al., 2000), which is guided by the location of the images, is not influenced by their emotional content.
UBC AURA Award, NSERC Discovery Grant.