A direct comparison of sound and vibration as sources of stimulation for a sensory substitution glove

Sensory substitution devices (SSDs) facilitate the detection of environmental information through enhancement of touch and/or hearing capabilities. Research has demonstrated that several tasks can be successfully completed using acoustic, vibrotactile, and multimodal devices. The suitability of a substituting modality is also mediated by the type of information required to perform the specific task. The present study tested the adequacy of touch and hearing in a grasping task by utilizing a sensory substitution glove. The substituting modalities inform, through increases in stimulation intensity, about the distance between the fingers and the objects. A psychophysical experiment of magnitude estimation was conducted. Forty blindfolded sighted participants discriminated equivalently the intensity of both vibrotactile and acoustic stimulation, although they experienced some difficulty with the more intense stimuli. Additionally, a grasping task involving cylindrical objects of varying diameters, distances and orientations was performed. Thirty blindfolded sighted participants were divided into vibration, sound, or multimodal groups. High performance was achieved (84% correct grasps) with equivalent success rate between groups. Movement variables showed more precision and confidence in the multimodal condition. Through a questionnaire, the multimodal group indicated their preference for using a multimodal SSD in daily life and identified vibration as their primary source of stimulation. These results demonstrate that there is an improvement in performance with specific-purpose SSDs, when the necessary information for a task is identified and coupled with the delivered stimulation. Furthermore, the results suggest that it is possible to achieve functional equivalence between substituting modalities when these previous steps are met.