Early visual deprivation prompts the use of body-centered frames of reference for auditory localization

Ubiquitous enhancement of spatial hearing in congenitally blind people

“…Early blind people, due to their acute auditory skills (as demonstrated here) may be especially sensitive to such spatio-temporal incongruencies resulting in altered performance (Gori, Amadeo, & Campus, 2018). Second, spatial bisection tasks require a metric representation of external space (Vercillo et al, 2018). Indeed, early blind people have qualitative alterations in their perception of external space (Crollen et al, 2017), which may explain their specific difficulties in resolving spatial bisection tasks independently of their intrinsic spatial hearing abilities (Collignon et al, 2009).…”

“…Supporting this view, it was shown that severe deficits of early blind participants to localize brief auditory stimuli with respect to external acoustic landmarks (using a spatial bisection task) can be simply alleviated when participants had to localize the exact same sounds with respect to their own hand (using a body-centered reference frame; Vecillo et al, 2018). These results suggest that the spatial deficit of early blind individuals in the spatial bisection task is not perceptual in nature but rather the by-product of an altered representation of metric relationships in external space (Crollen, Spruyt, Mahau, Bottini, & Collignon, 2019;Vercillo et al, 2018). In contrast, the minimum audible angle task can be proficiently performed by relying on a mere topographical representation of sounds and therefore assesses the capability to perceptually localize sounds in space without being confounded by advanced metric computations in the external space.…”

“…Several previous studies have required the participants to point towards the source of sounds either with their hand or head (Finocchietti et al, 2015;Lewald, 2013;Vercillo et al, 2018;Voss et al, 2015;Zwiers et al, 2001), which is an action particularly unnatural to perform by blind participants who rarely point toward the source of events in the absence of visuo-motor guidance. Moreover, visual impairment is associated with changes in the development of motor behavior using upper limbs (Pardhan et al, 2011).…”

“…Moreover, visual impairment is associated with changes in the development of motor behavior using upper limbs (Cappagli, Cocchi, & Gori, 2017;Pardhan, Gonzalez-Alvarez, & Subramanian, 2011). Therefore, one cannot rule out that, in the previous studies that required participants to point towards sound with their arms and hands, blind people performed worse than sighted people simply due to the changes in goal directed hand movements, and not due to the changes in their spatial hearing abilities 1 (Finocchietti, Cappagli, & Gori, 2015;Lewald, 2002Lewald, , 2013Vercillo, Tonelli, & Gori, 2018;Voss, Tabry, & Zatorre, 2015;Zwiers et al, 2001).…”

The accuracy of auditory spatial judgments in the visually impaired is dependent on sound source distance

“…It has now been well established that full blindness (total visual loss or light perception only) can result in enhancement of certain auditory spatial abilities and worsening of others (for reviews, see 2-7 ). For example, blindness often results in dramatic improvements in echolocation skills 4,8 and the ability to locate sounds in azimuth (left-front-right judgments) 9,10 , but leads to significantly poorer ability to judge the vertical position of sounds 11,12 , or judge sound position with respect to external acoustic landmarks 13 . It has been suggested that the changes underlying enhanced performance are fundamentally related to adaptations within the occipital cortex, where visual areas of the brain are recruited to process auditory inputs in the event of visual loss 5,14,15 .…”