Abstract
A visual-to-auditory sensory substitution device initially developed for the blind is known to allow visual-like perception through sequential exploratory strategies. Here we used functional magnetic resonance imaging (fMRI) to test whether processing the location versus the orientation of simple (elementary) “visual” stimuli encoded into sounds using the device modulates the brain activity within the dorsal visual stream in the absence of sequential exploration of these stimuli. Location and orientation detection with the device induced a similar recruitment of frontoparietal brain areas in blindfolded sighted subjects as the corresponding tasks using the same stimuli in the same subjects in vision. We observed a similar preference of the right superior parietal lobule for spatial localization over orientation processing in both sensory modalities. This provides evidence that the parietal cortex activation during the use of the prosthesis is task related and further indicates the multisensory recruitment of the dorsal visual pathway in spatial processing.
Highlights
When deprived of its natural input, the “visual” cortex of early-blind subjects is widely activated during a variety of perceptual and cognitive tasks and its cross-modal recruitment may account for the improved perceptual abilities of these subjects in the auditory and tactile modalities
One may hypothesize that the brain activations elicited during the use of an substitution device (SSD) are partly driven by mechanisms specific to sensory substitution and depend on the nature of the task performed with the SSD [12, 13]
The mean percentages of correct responses were 80.3, 78.5, and 91.06 in the acoustic association experiment and 91.06, 92.84, and 96.42 in the visual control experiment for the localization, the orientation detection, and the control condition, respectively (all P values > 0.05, there was a trend towards better scores in the control condition compared to the orientation condition (P = 0.09) during the acoustic association experiment only)
Summary
When deprived of its natural input, the “visual” cortex of early-blind subjects is widely activated during a variety of perceptual and cognitive tasks and its cross-modal recruitment may account for the improved perceptual abilities of these subjects in the auditory and tactile modalities. Using an SSD often requires stimulus exploration strategies and a sequential perception and memorization of each single constituting element of a more complex object (due to the relatively narrow perceptual field of the SSD and its low resolution) All these aspects of SSD use involve working memory and spatial components. To reduce the importance of the spatial and working memory components inherent to the use of the SSD and to minimize the brain activation relating to decoding the SSD signal during the tasks, we used very simple stimuli: a horizontal and a vertical bar that were presented separately at the middle top or middle bottom of the SSD perceptual field Such simple stimuli did not require any exploration strategies or self-generated exploratory movements from the subject, and they could be apprehended globally and almost instantly
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