58 blind participants
Fifty-eight adults with total or near-total blindness—including 28 who reported normal hearing and 30 who reported impaired hearing—participated in the study, published in February.
The researchers had previously developed a detailed questionnaire for people with either visual or hearing impairment or both, in order to assess their perceived difficulties with spatial localization in daily tasks involving both vision and hearing.
These tasks included familiar situations such as locating an ambulance by its siren, finding a ringing phone in another room, and identifying a child playing with a ball in a park.
Tasks of this type require subjects to process multiple pieces of information simultaneously in environments that are often noisy or visually cluttered. It is in these situations that real difficulties emerge.
A clear link
The responses to the questionnaire initially showed there was a clear link between participants’ actual sensory abilities and their ability to perform the selected everyday tasks under real-world conditions.
The researchers then investigated participants’ perceptions of their own (dis)abilities
The subjects were generally aware of the impact of their visual impairment. Those with partial vision knew, for example, that they would struggle to recognize someone from a distance.
Those who also had hearing loss were sometimes less aware of their own limitations.
This, even though “many could not confidently perform certain tasks, such as identifying a person in a noisy environment like a cafeteria, even when wearing a hearing aid,” Nemargut said.
Hearing aids are often optimized to improve the user’s understanding of speech in relatively quiet settings. However, in real-world settings, hearing aids can muffle important sounds, such as traffic noise, making it harder to move around safely.
Using sound to navigate
The study found that participants who reported good sound localization skills also reported better echolocation abilities, regardless of their hearing status.
Echolocation is the ability to use sound to navigate. It is the technique bats use to fly around and hunt in the dark, but it operates somewhat differently in humans.
All humans possess “passive” echolocation, Nemargut explained. The human brain constantly uses ambient sounds—ventilation, echoes, background noise—to map out space.
“For example, entering a tunnel immediately gives you a feeling of confinement, even with your eyes closed,” he said. In some people, particularly those with visual impairments, this ability can be much more developed.
There is also “active” echolocation, which involves producing sounds (such as clicks or taps) to capture echoes and detect obstacles. This skill relies on the perception of subtle sound features and is heavily dependent on the quality of hearing.
The study also found that the timing of visual impairment is important. People born blind often develop effective auditory strategies at an early age, thanks to early support.
On the other hand, those who lose their sight later in life rarely receive such intensive auditory training. As a result, they may feel less competent, even if those abilities are present.
Hearing loss and its onset are important factors in self-reported sound localization abilities as well as the likelihood that a person will use echolocation.
Towards better rehabilitation
“It is essential to take hearing status into account in rehabilitation for blind people in order to preserve and improve their spatial localization abilities,” Nemargut said.
The study underscores the fact that sensory difficulties don’t simply add up, but interact with each other, he noted. “Even today, vision and hearing impairments are often treated separately, even though these two senses work closely together."
Nemargut advocates for an integrated approach to rehabilitation, tailored to real-life situations.
For example, hearing aids could be better adjusted to specific situations. Sometimes, that will mean amplifying useful sounds such as traffic or doors opening on public transit, while muting others, such as background conversations.
Similarly, orientation and mobility specialists—who support people with visual impairment—could collaborate more closely with audiologists to better address each individual’s needs.
“Support should be comprehensive, not limited to compensating for sensory loss,” Nemargut concluded. “It should fully leverage all available resources.”
