On April 28th, 2015 we learned about

Enhanced hearing in the blind may come with a cost to their… hearing

While neuroscience often aims to attribute specific functions to specific portions of the human brain, we know that brains are also strikingly adaptable. If one region of the brain becomes damaged, neighboring areas can sometimes take over the missing functionality. One intriguing scenario is that some blind people have been found to have their brains’ visual centers assisting with auditory processing. The assumption has then been that blind people must hear better than their sighted counterparts, and a recent test has looked at some of the details of that concept.

Test subjects were asked to use a laser pointer to point at where they felt a sound was coming from. The sounds came from a variety of locations meant to test both horizontal and vertical targeting. When locating a sound in the same horizontal plane as your head, the brain compares small differences in how and when sounds reach each ear. When sounds comes from vertical orientations, relative to the listener, it will most likely reach both ears at the same time. The shape of the outer ears then needs to cause small distortions in the sound waves, called spectral cues, to help the brain identify the source.

Shifting the balance of sound detection

Many blind test subjects performed these tests no better or worse than sighted test subjects. But some blind test subjects did show some distinct performance differences, with better than normal horizontal targeting, but lower than normal vertical targeting. It’s thought that rather than a baseline improvement in all forms of hearing, they’ve actually trained themselves to use those spectral cues for detecting vertical relationships to instead enhance their horizontal hearing. This specialization had a cost though, evident in the decrease in vertical hearing, although considering most human navigation doesn’t involve moving along a y-axis, it’s probably acceptable.

More tests are needed to confirm that spectral cues really were the fulcrum point in the test subjects’ hearing, as there is a chance the differences detected were actually due to the volume of the sound used in testing.

Source: For the blind, hearing the way forward can be a tradeoff by Bethany Brookshire, Scicurious

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