The role of audition in the scaling of grasping

Abstract

Although there is some work that has investigated the role of haptic and olfactory cues in the control of grasping, there has been little investigation of the role of natural auditory cues. The aim of our study therefore was to investigate how natural auditory cues about object size and location affect grip aperture in normal right-handed participants. The experiment required participants to pick up two objects of different sizes but in the same position (task 1) or to pick up the same object located near or far from subject's hand (task 2). In both tasks, participants were tested with and without vision — and with and without hearing the sound of the object being placed on the table. Hand and finger movements were tracked at 100 Hz using OPTOTRAK©. In task 1, hearing the sound of the object being placed on the table improved performance when vision was not available; that is, participants showed evidence of grip scaling for object size (which did not occur without vision and auditory cues). With vision, of course, grip scaling was always better, but even here auditory information improved performance. In task 2, the sound of objects being placed at different distances on the table did not improve localization when vision was blocked; participants simply ‘guessed’ the distance at which the object had been placed. Taken together these results suggest that auditory cues can be used to estimate the size of objects in a grasping task, but not the distance of those objects in peripersonal space. Vision contributes a great deal more to accurate scaling, but audition still plays a small role even when vision is available. Future experiments will address how these visual and natural auditory cues are weighted and integrated in the scaling of grip aperture.