Memory mechanisms in grasping.

The availability of visual information influences the execution of goal-directed movements. This is very prominent in memory conditions, where a delay is introduced between stimulus presentation and execution of the movement. The corresponding effects could be due to a decay of the visual information or to different processing mechanisms used for movements directed at visible (dorsal stream) and remembered (ventral stream) objects as proposed by the two visual systems hypothesis. In three experiments, the authors investigated grasping under full vision and three different delay conditions with increasing memory demands. Results indicate that the visuomotor information used for grasping decays rapidly. No evidence was found for qualitative changes in movement kinematics and the use of different representations for visually guided and memory guided movements. Findings rather suggest that delayed grasping is similar to grasping directed to larger objects under full vision. Therefore, the authors propose that grasping after a delay is guided by classic memory mechanisms and that this is reflected in an increasing maximum grip aperture in grasping.