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We investigated to what extent participants can acquire the mastery of an auditory-substitution-of-vision device ('The vOICe') using dynamic tasks in a three-dimensional environment. After extensive training, participants took part in four experiments. In the first experiment we explored locomotion and localisation abilities. Participants, blindfolded and equipped with the device, had to localise a target by moving a hand-held camera, walk towards the target, and point at it. In the second experiment, we studied the localisation ability in a constrained pointing task. In the third experiment we explored participants' ability to recognise natural objects via their auditory rendering. In the fourth experiment we tested the ability of participants to discriminate objects belonging to the same category. We analysed participants' performance from both an objective and a subjective point of view. The results showed that participants, through sensorimotor interactions with the perceptual scene while using the hand-held camera, were able to make use of the auditory stimulation to obtain the information necessary for locomotor guidance, localisation, and pointing, as well as for object recognition. Furthermore, analysis from a subjective perspective yielded insights into participants' qualitative experience and into the strategies they used to master the device, and thus to pass from a kind of deductive reasoning to a form of immediate apprehension of what is being perceived.

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Sensory substitution devices provide through an unusual sensory modality (the substituting modality, e.g., audition) access to features of the world that are normally accessed through another sensory modality (the substituted modality, e.g., vision). In this article, we address the question of which sensory modality the acquired perception belongs to. We have recourse to the four traditional criteria that have been used to define sensory modalities: sensory organ, stimuli, properties, and qualitative experience (Grice, 1962), to which we have added the criteria of behavioral equivalence (Morgan, 1977), dedication (Keeley, 2002), and sensorimotor equivalence (O'Regan & Noë, 2001). We discuss which of them are fulfilled by perception through sensory substitution devices and whether this favors the view that perception belongs to the substituting or to the substituted modality. Though the application of a number of criteria might be taken to point to the conclusion that perception with a sensory substitution device belongs to the substituted modality, we argue that the evidence leads to an alternative view on sensory substitution. According to this view, the experience after sensory substitution is a transformation, extension, or augmentation of our perceptual capacities, rather than being something equivalent or reducible to an already existing sensory modality. We develop this view by comparing sensory substitution devices to other ''mind-enhancing tools'' such as pen and paper, sketchpads, or calculators. An analysis of sensory substitution in terms of mind-enhancing tools unveils it as a thoroughly transforming perceptual experience and as giving rise to a novel form of perceptual interaction with the environment.

Sensory substitution constitutes an interesting domain of study to consider the philosopher's classical question of distal attribution: how we can distinguish between a sensation and the perception of an object that causes this sensation. We tested the hypothesis that distal attribution consists of three distinct components: an object, a perceptual space, and a coupling between subjects' movements and stimulation. We equipped sixty participants with a visual-to-auditory substitution device, without any information about it. The device converts the video stream produced by a head-mounted camera into a sound stream. We investigated several experimental conditions: the existence or not of a correlation between movements and resulting stimulation, the direct or indirect manipulation of an object, and the presence of a background environment. Participants were asked to describe their impressions by rating their experiences in terms of seven possible "scenarios". These scenarios were carefully chosen to distinguish the degree to which the participants attributed their sensations to a distal cause. Participants rated the scenarios both before and after they were given the possibility to interrupt the stimulation with an obstacle. We were interested in several questions. Did participants extract laws of co-variation between their movements and resulting stimulation? Did they deduce the existence of a perceptual space originating from this coupling? Did they individuate objects that caused the sensations? Whatever the experimental conditions, participants were able to establish that there was a link between their movements and the resulting auditory stimulation. Detection of the existence of a coupling was more frequent than the inferences of distal space and object.

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