People with severe vision loss can less accurately judge the distance of nearby sounds, potentially putting them more at risk of injury, according to new research published in the journal Scientific Reports.
Researchers from Anglia Ruskin University’s Vision and Eye Research Institute (VERI) tested participants with different levels of vision loss, presenting them with speech, music and noise stimuli, and different levels of reverberation (echoes).
Participants were asked to judge the distance of the different sounds, as well as the size of the room.
People with severe visual loss judged closer sounds more inaccurately compared to those whose vision loss is less severe, who in turn, were less accurate when compared to people with normal sight.
For more distant sounds, people with severe visual loss judged these to be twice as far away when compared to normal sighted individuals. Participants with severe sight loss also judged the rooms to be three times larger than the control group of normal sighted individuals.
Professor Shahina Pardhan, Director of VERI, said: “Vision loss means people rely more on their hearing for awareness and safety, communication and interaction, but it was not known how hearing is affected by the severity of partial vision loss.
“The results demonstrate that full blindness is not necessary for judged auditory distance and room size to be affected by visual loss, and that changes in auditory perception are systematic and related to the severity of visual loss.
“Our research found that more severely visually impaired people were less accurate in judging the distance of closer sounds, which may make it harder for them in real-life situations, for example such as crossing busy streets.”
The World Health Organization (WHO) estimated that globally 188.5 million people have mild visual loss, 217 million have moderate to severe losses, and 36 million are blind1.
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, see2–7).
For example, blindness often results in dramatic improvements in echolocation skills4,8 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 sounds11,12, or judge sound position with respect to external acoustic landmarks13.
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 loss5,14,15.
However, the underlying principles of what drives changes in auditory abilities following visual loss are not well understood. 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 closer16,17, demonstrating the critical role that vision plays in calibrating auditory space18.
A number of studies have also shown that partial visual deprivation affects auditory localization abilities. Myopic (short-sighted) participants are more accurate than sighted controls for azimuthal localization19 and echolocation, and show greater sensitivity to echoic spatial cues20.
Myopic and amblyopic participants have been reported to show significantly smaller self-positioning errors using sound to assess their position in a room than sighted controls21. Also, partially sighted participants self-reported better azimuthal sound localization and improved abilities to follow speech when switching between different talkers22.
Although partial loss of vision entails an increased reliance on hearing for awareness and safety, communication and interaction, and for enjoyment through sound23, it is not known how hearing is affected by the severity of partial visual loss.
We explored this by obtaining judgments of the distance of sound sources and of room size using sound for participants with a range of severities of visual loss, to test the hypothesis that crossmodal calibration is dependent on the magnitude of the sensory loss.
It was hypothesized that systematic increases in auditory judgments of distance and room size would be associated with the severity of visual loss, with greater estimates associated with more severe visual loss. To investigate whether this was true, and whether it generalized across different room environments and stimuli, participants were tested in virtual anechoic and reverberant rooms, using speech, music and noise stimuli.
The different stimuli were chosen as they varied in their spectro-temporal characteristics. It was hypothesized that in a virtual reverberant room, estimates of distance and room size would be greater than in the virtual anechoic room, as research suggests that greater reverberation is associated with increased perceived distance24 and room size estimates25,26 for normally sighted participants.
It was hypothesized that estimates would be more veridical for speech27 than for noise28 or music, as normally sighted participants were previously shown to be able to utilize their familiarity with the acoustic characteristics of speech to give more veridical distance estimates29.
References
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More information: Andrew J. Kolarik et al, The accuracy of auditory spatial judgments in the visually impaired is dependent on sound source distance, Scientific Reports (2020). DOI: 10.1038/s41598-020-64306-8
