An investigation of visually guided interaction with 2-dimensional stimuli

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Langridge, Ryan W.
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This dissertation explores how vision is used to guide interactions with 2-D computer-generated targets, with the goal of furthering our understanding of how perception and action interact during visually guided action. Study 1: Participants used their right hands to grasp square targets that either remained stationary or travelled horizontally across the screen. Fixations and digit placement favoured the near side of stationary targets presented at non-central positions, and the trailing side of moving targets, suggesting participants minimized the energy required to grasp the stationary targets and selected ‘safer’ contact points when the target was moving. Gaze and grasp positions were shifted rightward when grasping target shapes that discouraged digit placement near the horizontal midline, suggesting participants tried to avoid obstructing the view of the target when grasping. Study 2: Fixations and grasp positions were compared when grasping 2-D targets versus 3-D versions of these targets. Fixations and digit placement were comparable when grasping 2-D and 3-D stimuli positioned in the center of the display. When grasping non-central stimuli however, participants fixated and placed their digits at more ‘stable’ locations near the 3-D object’s midline compared to locations biased toward the near side of the 2-D targets. Intended manipulation of each stimulus type produced similar adjustments in fixation and digit placement, suggesting participants may have attributed physical properties to the 2-D targets in response to the manipulative task demands. Study 3: The Ebbinghaus illusion was used to explore how the perceived size of an on-screen target influences cursor movements toward that target. Participants’ perceptual size judgments, but not accuracy or movement time, were influenced by the illusion. However, the illusion affected cursor trajectories toward the target, suggesting the illusion may have influenced the planning and early stages of the cursor movement. The results of each study are discussed regarding the Two Visual Streams Hypothesis (Goodale & Milner, 1992), and suggest that the context in which an action is directed toward a 2-D stimulus – particularly the target’s position and the action end-goal – may determine the degree to which the visually guided action is mediated by perceptual influences.
Perception, Action, 2-dimensional stimuli, Eye-hand coordination