Auditory spatial representations of the world are compressed in blind humans

Abstract

Compared to sighted listeners, blind listeners often display enhanced auditory spatial abilities such as localization in azimuth. However, less is known about whether blind humans can accurately judge distance in extrapersonal space using auditory cues alone. Using virtualization techniques, we show that auditory spatial representations of the world beyond the peripersonal space of blind listeners are compressed compared to those for normally sighted controls. Blind participants overestimated the distance to nearby sources and underestimated the distance to remote sound sources, in both reverberant and anechoic environments, and for speech, music, and noise signals. Functions relating judged and actual virtual distance were well fitted by compressive power functions, indicating that the absence of visual information regarding the distance of sound sources may prevent accurate calibration of the distance information provided by auditory signals.

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

“…It is not yet known how severe the visual loss needs to be before significant alterations in auditory abilities are observed, or whether the relationship between severity of visual loss and changes in auditory abilities is systematic. If it is systematic, then people with more modest visual losses should exhibit smaller changes in auditory abilities than those with more severe visual losses.Previous work showed that compared to sighted controls, individuals with total vision loss estimate near sound sources to be farther away and estimate farther sound sources to be closer 16,17 , demonstrating the critical role that vision plays in calibrating auditory space 18 . A number of studies have also shown that partial visual deprivation affects auditory localization abilities.…”

“…Previous work showed that compared to sighted controls, individuals with total vision loss estimate near sound sources to be farther away and estimate farther sound sources to be closer 16,17 , demonstrating the critical role that vision plays in calibrating auditory space 18 . A number of studies have also shown that partial visual deprivation affects auditory localization abilities.…”

“…Stimuli were presented using Sennheiser HD219 headphones. The stimuli were generated using methods described in our previous studies 16,17,[31][32][33] . A virtual room measuring 35 m (length) x 30 m (width) x 10 m (height), that was either anechoic (where only sound level information about distance was available 24,28,34 ) or reverberant (where both level and echoic direct-to-reverberant energy ratio [DRR] distance cues were available 33,35,36 ), was generated using an image-source model (ISM) 37 .…”

“…A virtual room measuring 35 m (length) x 30 m (width) x 10 m (height), that was either anechoic (where only sound level information about distance was available 24,28,34 ) or reverberant (where both level and echoic direct-to-reverberant energy ratio [DRR] distance cues were available 33,35,36 ), was generated using an image-source model (ISM) 37 . The reverberation time T 60 (the time taken for the sound level to fall by 60 dB) was 700 ms, as used in previous studies 16,35 . The ISM produced a room impulse response (RIR) between a virtual auditory source and a receiver positioned a set virtual distance away.…”

“…Participants heard speech, music, and broadband noise stimuli, as used in our previous work 16,31 . Speech stimuli had a duration of 1.5 s, were sampled at 22.05 kHz, and were single sentences spoken at a conversational level by a male, selected randomly from the Bench-Kowal-Bamford corpus 16,31,38,39 . Music stimuli had a duration of 7.3 s, were sampled at 22.05 kHz, and played by a jazz trio of piano, bass and drums 16,31,40 .…”