Everybody has heard about echolocation in bats and dolphins. These creatures emit bursts of sounds and listen to the echoes that bounce back to detect objects in their environment. What is less well known is that people can echolocate too. In fact, there are blind people who have learned to make clicks with their mouths and to use the returning echoes from those clicks to sense their surroundings.
Some of these people are so adept at echolocation that they can use this skill to go mountain biking, play basketball, or navigate unknown environments.
Working together with two of my former postdocs, Lore Thaler (Durham) and Steve Arnott (Toronto), I was able to show that blind echolocation experts use what is normally the ‘visual’ part of their brain to process the clicks and echoes. Our study was the first to investigate the neural basis of natural human echolocation. We first made recordings of the clicks and their very faint echoes using tiny microphones in the ears of the blind echolocators as they stood outside and tried to identify different objects such as a car, a flag pole, and a tree. We then played the recorded sounds back to the echolocators while their brain activity was being measured in our 3 T fMRI brain scanner. Remarkably, when the echolocation recordings were played back to the blind experts, not only did they perceive the objects based on the echoes, but they also showed activity in those areas of their brain that normally process visual information in sighted people. Most interestingly, the brain areas that process auditory information were no more activated by sound recordings of outdoor scenes containing echoes than they were by sound recordings of outdoor scenes with the echoes removed. Only ’visual’ cortex showed differential activation to the faint echoes. Importantly, when the same experiment was carried out with sighted control people who did not echolocate, these individuals could not perceive the objects, and neither did their brain show any echo-related activity.
Our data clearly show that echolocation can be used in a way that seems uncannily similar to vision. Our findings also show that echolocation can provide blind people with a high degree of independence and self-reliance in their daily lives.
Thaler, L. Arnott, S.R. & Goodale, M.A. (2011). Neural correlates of natural human echolocation in early and late blind echolocation experts. PloS ONE, 6: e20162. PDF