Vision substitution and depth perception: early blind subjects experience visual perspective through their ears.

AIM: Sensory substitution (SS) represents a unique opportunity to provide congenitally blind persons with visual-like experience. Although visual experience influences the way we perceive the external world, little is known about the effects of SS experience.
PURPOSE: To investigate the effects of perceptual experience (visual versus sensory substitution) on depth perception through an SS system, object localization abilities of early blind (n = 10), and blindfolded sighted control subjects (n = 20) were assessed before and after a practicing period with a visual-to-auditory SS device.
METHOD: During the pre- and post-test, subjects had to replace, by hand, an object previously localized using the device. The practicing phase consisted of three sessions during which subjects tried to localize and grasp an object using the device. Results. At the pre-test, sighted subjects spontaneously used efficiently different pictorial depth cues to estimate object distance while the blind subjects were affected by their lack of visual experience and were significantly less accurate. Post-test showed that the brief practicing phase sufficed to enable blind subjects to acquire the rules of visual depth and to use them efficiently with the device.
CONCLUSIONS: These results suggest the possibility to compensate for some effects of early and long-lasting blindness by providing visual-like experience via SS. Theoretical implications are discussed.