July 14, 2004 - People blind since infancy have at least 10 times sharper hearing than sighted people, a study of hearing skills shows.
People blinded at later ages don't seem to have this gift. However, the study showed that the earlier people lose their sight, the sharper their hearing. FrÃ©dÃ©ric Gougoux of the University of Montreal and colleagues report the findings in the July 15 issue of Nature.
"Blind people are better at judging the direction of pitch change between sounds, even when the speed of change is 10 times faster than that perceived by [sighted people] -- but only if they became blind at an early age," Gougoux and colleagues write.
The researchers studied three groups:
- The "early blind" group included seven people aged 21-40 who were blind at birth or up to age 2 years.
- The "late blind" group included seven people aged 24-46 who were blind since age 5 to 45 years.
- Twelve sighted people aged 21 to 37 served as controls.
Each subject put on headphones and indicated on a keyboard whether two tones were rising or falling in pitch. The tones started out one eighth of an octave apart and the duration of the change in pitch was 333 milliseconds. During the experiment, the tones became closer in pitch (up to 1/128th of an octave) or shorter in change of pitch (down to 20.8 milliseconds).
The early-blind subjects did as well at the most rapid condition as sighted subjects did at the slowest condition -- even though the sounds came 10 times closer together.
In many cases, late-blind subjects did a bit worse than the sighted subjects, although these differences were not significant. However, the earlier a person became blind, the better that person did on the tests.
It's already known that blind people can orient themselves to a sound better than sighted people can. The new findings show that when the brain is still young enough, it can compensate for the loss of sight.