Noninformative vision improves haptic spatial perception.

Previous studies have attempted to map somatosensory space via haptic matching tasks and have shown that individuals make large and systematic matching errors, the magnitude and angular direction of which vary systematically through the workspace. Based upon such demonstrations, it has been suggested that haptic space is non-Euclidian. This conclusion assumes that spatial perception is modality specific, and it largely ignores the fact that tactile matching tasks involve active, exploratory arm movements. Here we demonstrate that, when individuals match two bar stimuli (i.e., make them parallel) in circumstances favoring extrinsic (visual) coordinates, providing noninformative visual information significantly increases the accuracy of haptic perception. In contrast, when individuals match the same bar stimuli in circumstances favoring the coding of movements in intrinsic (limb-based) coordinates, providing identical noninformative visual information either has no effect or leads to the decreased accuracy of haptic perception. These results are consistent with optimal integration models of sensory integration in which the weighting given to visual and somatosensory signals depends upon the precision of the visual and somatosensory information and provide important evidence for the task-dependent integration of visual and somatosensory signals during the construction of a representation of peripersonal space.