Visually guided motor behavior requires that the visual system provides a
representation of the physical surroundings that can be used to perform motor actions. The question arises what the nature of the representation is and how it affects the way human subjects perform motor actions. The research project reported here introduces and tests the idea that the visual system computes different types of representations independently from each other and that subjects' performance in a task will depend on the representation that they can use.
The currently dominant view (Goodale & Milner, 1992; Milner & Goodale, 2008)
on the relationship between visual perception and visually guided motor behavior
proposes that the human visual system employs two anatomically and functionally
distinct processing streams for perceptual judgment and visually guided motor action. However, studies that support the perception/action dissociation confounded the type of spatial representation that subjects could use to perform a task (topological / egocentric / allocentric), with the response mode (perceptual judgment / motor action).
Here we report five experiments that were designed to test if the spatial
representation, rather than response mode, determines task performance. The experiments systematically varied the degree to which subjects could rely on different types of spatial representations, but each experiment measured a different aspect of performance. Exp.1 and Exp.2 (Chapter 2) measured accuracy and variability of reaching movements and perceptual judgments. Exp.3 (Chapter 3) examined how movements are planned by the central nervous system and Exp.4 (Chapter 4) investigated the speed of visuo-motor processing; Exp.5 (Chapter 5) tested how subjects' reaching performance changes in response to different types of visual feedback.
The results show that subjects' performance depends on the spatial representation that they can use to perform a task, rather than on the response mode. These findings are consistent with a representation-based approach to visually guided motor action.