Moving Towards and Reaching a 3-D Target by Embodied Guidance: Parsimonious Vs Explicit Sound Metaphors.

Sensory Substitution Devices (SSDs) assist Visually Impaired People (VIP) by providing information usually acquired by vision through another functional sensory modality. Here, we evaluate a SSD that aims to guide visually impaired people to a target by converting spatial information into sound. A balance must be struck between parsimonious and explicit guidance, so that it is precise but not imposing an excessive cognitive load. Here, we express the deviation from the target to the participant’s hand. We compared three sound metaphors: 1) Binary (BI) gives only the right direction by white noise, 2) Angle-to-Pitch (AP) converts the 3-D angular deviation between a pointed direction and the right direction into sound pitch according to a continuous function, 3) Dissociated Vertical-Horizontal (DVH) dissociates the 3-D deviation into two dimensions, using pitch to provide the angular deviation projected on the horizontal plane (a continuous metaphor) and a superimposed white noise to indicate the right height (a binary metaphor). We conducted “hot and cold game” type tests in a 3-D environment. Participants, with eyes closed, moved to search and reach virtual spheres with their index finger. Each metaphor was evaluated by the time taken to reach the target, and by a questionnaire. The results show the advantage of AP over BI: it allowed a faster target hit and was considered easier to use, more efficient, and more comfortable than BI. They also show an advantage of the DVH metaphor over AP: the times to target hit were shorter, and it was considered easier to use than AP. The DVH metaphor is a good trade-off between parsimonious (use of binary information) and explicit (dissociation of the two axes) guidance. It is a first step towards smartphone SSDs applications to help find objects in a situation of visual impairment.