AbstractThe perception/action model (PAM) asserts that functionally and anatomically distinct cortical processing streams mediate perceptions and actions (for review see Goodale 2011: Vis Res). More specifically, the PAM contends that the dorsal cortical pathway mediates actions and processes absolute visual metrics, whereas the ventral cortical pathway serves perceptions and processes relative visual metrics. Notably, however, an important question from the dissociation of cortical processing streams is whether tactile cues (such as tactile feedback in grasping) influence putative interactions between the distinct visual pathways. To address this issue, Experiment 1 had participants initiate grasping responses towards differently sized objects in two conditions wherein vision of the grasping environment was removed prior to movement onset. In the memory-guided condition the target object was physically present for participants to grasp, whereas in the pantomime condition the object was removed (i.e., immediately after response cuing) in order to preclude tactile interaction with the object. Results showed that just noticeable difference (JNDs) scores computed at the time of peak grip aperture in the pantomime - but not the memory-guided condition - scaled linearly with increase in target size. In other words, results for the pantomime and memory-guided conditions demonstrate the respective mediation of aperture shaping via relative and absolute visual information. Accordingly, Experiment 2 involved the same pantomime condition as Experiment 1 with the exception that participants were provided terminal tactile feedback after completing the response (i.e., pantomime with tactile feedback). The results of this experiment showed a null scaling of JNDs to target size comparable to that associated with the memory-guided grasping used in Experiment 1. Thus, the combined results of our experiments indicate that introducing tactile feedback provides a reliable source of information which can be used to support on- or offline use of absolute visual cues for aperture shaping.
Acknowledgments: Natural Sciences and Engineering Research Council (NSERC)