Line drawing of a person facing a rig supporting two circular echo reflectors

Human Echolocation

What is echolocation? Sometimes, the surrounding world is too dark and silent for typical vision and hearing. This is true in deep caves, for example, or in murky water where little light penetrates. Animals living in these environments often have the ability to echolocate: They make sounds and listen for their reflections. Like turning on a flashlight in a dark room, echolocation is a way to illuminate objects and spaces actively.

Sonar for people

Similarly to many bats and marine mammals, some blind humans echolocate as well. Using acoustic reflections from tongue clicks or other pulses, such as cane taps or footfalls, echolocating practitioners have demonstrated remarkable precision in navigation and object perception. What information does echolocation afford its practitioners? What are the factors contributing to learning it? How broadly is it accessible to blind, and sighted, people? Continuing past work from MIT and UC Berkeley, at Smith-Kettlewell I am investigating these and other questions: what spatial resolution is available to people using echoes to perceive their environments, how well echoes promote orientation and mobility in blind persons, and how this ability is mediated in the brain. Previous work has shown that sighted blindfolded people can readily learn some echolocation tasks with a small amount of training, but that blind practitioners possess a clear expertise advantage, sometimes distinguishing the positions of objects to an angular precision of around 2 degrees — about the width of a thumbnail held at arm's length. Identifying the factors that might lead a novice toward that level of precision would clarify our understanding of human perception and be a valuable resource for Orientation & Mobility instructors promoting greater independent mobiity in blind travelers.

Assisted echolocation

Inspired by both human and non-human echolocators, we are also investigating artificial echoes as a perceptual aid for blind persons and other people unable to use vision. Ultrasonic echoes, silent to humans, carry higher-resolution information than audible echoes; an assistive device could make the perceptual advantages of ultrasonic echolocation available to human listeners. Previously, initial tests of a prototype showed that untrained listeners can quickly make spatial judgments using the echoes, and we are working on making artificial echolocation more perceptually useful as well as more ergonomic and convenient.