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WIREs Cogn Sci
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Echolocation in humans: an overview

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Bats and dolphins are known for their ability to use echolocation. They emit bursts of sounds and listen to the echoes that bounce back to detect the objects in their environment. What is not as well‐known is that some blind people have learned to do the same thing, making mouth clicks, for example, and using the returning echoes from those clicks to sense obstacles and objects of interest in their surroundings. The current review explores some of the research that has examined human echolocation and the changes that have been observed in the brains of echolocation experts. We also discuss potential applications and assistive technology based on echolocation. Blind echolocation experts can sense small differences in the location of objects, differentiate between objects of various sizes and shapes, and even between objects made of different materials, just by listening to the reflected echoes from mouth clicks. It is clear that echolocation may enable some blind people to do things that are otherwise thought to be impossible without vision, potentially providing them with a high degree of independence in their daily lives and demonstrating that echolocation can serve as an effective mobility strategy in the blind. Neuroimaging has shown that the processing of echoes activates brain regions in blind echolocators that would normally support vision in the sighted brain, and that the patterns of these activations are modulated by the information carried by the echoes. This work is shedding new light on just how plastic the human brain is. WIREs Cogn Sci 2016, 7:382‐393. doi: 10.1002/wcs.1408

Waveforms, plotting amplitude (a.u. = arbitrary units) against time (ms) and spectrograms denoting frequency (kHz) content as function of time (ms). In spectrograms warmer colors indicate more energy in that frequency band at that moment in time. All figures are based on binaural recordings of clicks and echoes for four different echolocators (a–d). Recordings were made either at the entrance of the echolocators’ earcanals (a, c, and d) or next to their ears, that is, on each side of the head, but placed outside the pinna, (b), while they made clicks and listened to echoes. Red arrows in waveform plots highlight clicks, and green arrows highlight echoes. The recording sample frequency was 96 kHz for data shown on the right (b and d), and 44.1 kHz for data on the left (a and c). Spectrograms were calculated using a 1‐ms window with 0.8‐ms overlap in steps of 1 kHz. For (a) and (c), a sound‐reflecting surface was located 60° to their right at a distance of 50 cm. For (b), a sound‐reflecting surface was located straight ahead at a distance of 150 cm. For (d), a sound‐reflecting surface was located straight ahead at a distance of 85 cm.
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Illustration of results from Ref . For the echolocation expert who had lost vision very early in life (left side panels) areas highlighted in warm colors show an increase in BOLD signal when the participant listened to sound containing background sounds, clicks and echoes as compared to sounds that contained background sounds and clicks, but no echoes. The echolocation expert shows a relative increase in ‘visual’ cortex, including BA17/18. Interestingly, for the same contrast we did not observe an increase in activity in early auditory areas (i.e., Heschl's gyrus and surround). For the age‐ and gender‐matched sighted control participant we did not observe any increase in BOLD for the same contrast.
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