A large number of technical devices attempt to help blind persons improve their spatial perception and facilitate their mobility. We wish to present here the principles on which these prosthetic perceptual devices function, the conditions of their appropriation, and the general perspectives they open concerning the role of technical objects and systems in the constitution of human experience. A technical device for assisting perception has to compensate for a sensory deficit by mobilizing other subsisting sensory modalities which remain available. We therefore have to understand the relationship between perceptual activity and sensory input. In addition, we shall see that the technical devices which assist perceptual activity can in return serves as tools for experimental scientific research on the mechanisms of perception in general.

The analyses presented in the preceding chapter seem to show that perceptual experience of the space which surrounds us is the experience of the availability of a system of actions, in other words an organized set of possible journeys and operations that can be performed in the world. Whatever the sensory modalities that a subject has at her disposition (be they visual, auditory or tactile), we can suppose that her perception of a space which surrounds her corresponds for her to the presence of a field of possibilities of this sort, which enables her to localize objects, to choose gestures and movements, to decide which actions to perform, etc. The tools and prosthetic devices she can use aim at modifying and enriching this field of possibilities, which will give access to new actions and perceptions. Our aim in this chapter is to propose several hypotheses to explain the mechanisms by which