Role of vision on haptic length perception

When a human recognize length of an object while exploring it with their index finger, haptic and visual sensation both provide information for estimating the length of the object. The present study examined the contribution of haptic and visual cues to the subjective estimation of object length while the subject's index finger passively moved. We conducted two experiment (1) to compare performance of unimodal and bimodal length perception and (2) to assess the effect of visual noise on bimodal length perception. The results were as follows; (1) multisensory enhancement was not observed when the visual and haptic presented length was congruent and (2) visual cues were weighted more than haptic cues in the bimodal judgments when noise was 50% or less, haptic cues were weighted more than visual cues when noise was 75% or more, and adding noise to visual stimulus did not decline the performance of length perception. These results suggest that adding noise to visual stimulus contributes to directing attention to either modality but not to weighting sensory inputs.