The project’s aim is to study how the human motor system generates movements to objects that are not visible during movement execution. It is well-known that the planning, execution and control of goal-directed hand movements (such as reaching and grasping) strongly depends on the availability of visual information [1-4]. In order to successfully grasp a target object, visual information about the object’s position in the workspace as well as its orientation, size and shape needs to be processed. This visual representation then needs to be transformed into appropriate motor coordinates based on which kinematic parameters of the intended movement are specified. However, accurate reaching and grasping is obviously not limited to situations in which we are able to see the target object. In many everyday situations we are able to safely grasp objects without looking at them, such as when picking up the coffee mug in the morning whilst reading the newspaper. When target vision is absent during movement programming and execution, motor programming has to rely on stored visual representations.
While most recent studies on memory- guided hand movements have focussed on the question of whether or not visually-guided and memory-guided movements rely on dissociable visual representations that are processed in anatomically different brain areas (i.e., dorsal stream vs. ventral stream processing), almost no attention has been paid to the question of which aspects of the visual information decay over time and whether decay functions are similar for all relevant visual features (i.e. size information vs. position information).
The aim of the proposed project is to investigate:
(1) how different visual characteristics of the target object are affected by the introduction of pre-response delays, and
(2) whether or not the information decay is similar for representation of object size and object position. Generally, the proposed studies will provide a better understanding of how humans interact with objects that are not seen. Moreover, the proposed research may clarify why, in the existing literature, the reported findings on temporary features of the visual representations in reaching and grasping are ambiguous. The findings will have important implications for the existing theories on how visual information for goal-directed movements is retained and processed after delay.
In order to successfully reach for and grasp an object, its position in space relative to the hand needs to be specified. Additionally, the size of the target object has to be taken into account in order to adjust the hand opening accordingly when approaching the object. In our research project we investigate whether the representation of target size (intrinsic feature) is more long-lived than the representation of object position (extrinsic feature) in the visuomotor system. If intrinsic properties are stored for longer time periods then the grasp component that is based on these intrinsic object properties will be less affected by the introduction of a pre-response delay than the transport component that is based on extrinsic information about the object’s position.