Congenitally blind adults can learn to identify face-shapes via auditory sensory substitution and successfully generalize some of the learned features

Unlike sighted individuals, congenitally blind individuals have little to no experience with face shapes. Instead, they rely on non-shape cues, such as voices, to perform character identification. The extent to which face-shape perception can be learned in adulthood via a different sensory modality (i.e., not vision) remains poorly explored. We used a visual-to-auditory Sensory Substitution Device (SSD) that enables conversion of visual images to the auditory modality while preserving their visual characteristics. Expert SSD users were systematically taught to identify cartoon faces via audition. Following a tailored training program lasting ~ 12 h, congenitally blind participants successfully identified six trained faces with high accuracy.

Furthermore, they effectively generalized their identification to the untrained, inverted orientation of the learned faces. Finally, after completing the extensive 12-h training program, participants learned six new faces within 2 additional hours of training, suggesting internalization of face-identification processes. Our results document for the first time that facial features can be processed through audition, even in the absence of visual experience across the lifespan. Overall, these findings have important implications for both non-visual object recognition and visual rehabilitation practices and prompt the study of the neural processes underlying auditory face perception in the absence of vision.