Echolocation is probably most associated with bats and dolphins. These animals emit bursts of sounds and listen to the echoes that bounce back to detect objects in their environment and to perceive properties of the objects (e.g. location, size, material). Bats, for example, can tell the distance of objects with high precision using the time delay between emission and echo, and are able to determine a difference in distance as small as one centimeter. This is needed for them to be able to catch insects in flight.
People, remarkably, can also echolocate. By making mouth clicks, for example, and listening for the returning echoes, they can perceive their surroundings. Humans, of course, cannot hear ultrasound, which may put them at a disadvantage. Nonetheless, some people have trained themselves to an extraordinary level. Daniel Kish, who is blind and is a well-known expert echolocator, is able to ride his bicycle, hike in unfamiliar terrain, and travel in unfamiliar cities on his own. Daniel is the founder and president of World Access for the Blind, a non-profit charity in the US that offers training in echolocation alongside training in other mobility techniques such as the long cane.
Since 2011, the scientific interest in human echolocation has gained momentum. For example, technical advances have made it feasible to scan people’s brains while they echolocate. This research has shown that people who are blind and have expertise in echolocation use ‘visual’ parts of their brain to process information from echoes. It has also been found that anyone with normal hearing can learn to use echoes to determine the sizes, locations, or distance of objects or to use it to avoid obstacles during walking. Remarkably, both blind and sighted people can improve their ability to interpret and use sound echoes within a session or two.
Marina Ekkel and colleagues from Radboud University in the Netherlands showed recently that sighted people learned to echolocate size, and that people’s attentional capacity was related to their learning success. This is important because attention has also been implicated in other forms of learning. As the authors state, knowing that attentional capacity might affect echolocation learning might also be useful when devising training programs.
In their study Ekkel and colleagues trained sighted people to echolocate whilst they wore a blindfold. They did not ask people to make mouth clicks, but people were allowed to use a loudspeaker mounted on their head. People could press a button so that the loudspeaker made a brief (10ms) sound. People then made judgments about the relative sizes of objects using echoes that came back from those objects. Participants came into the lab on four separate occasions and each time the researchers measured their ability to do the task. The researchers also measured participants’ hearing ability, spatial ability, working memory and attention.
What Ekkel and colleagues found was that people’s increase in echolocation ability from session 1 to 4 was positively correlated with their attentional measures. That is, those people who had higher attentional capacity scores also showed greater improvement in their echolocation ability.
During the early days of echolocation research, in the 1940s and 1950s, the ability of people to echolocate was referred to as “facial vision” or “obstacle sense”. Scientists were not sure how it worked, but many believed that some select blind people were able to mysteriously detect subtle changes in air pressure on their skin, as they approached a wall or some other large obstacle. A series of early experiments conducted at Cornell University, however, made it clear that blind people were actually listening to the echoes of sounds bouncing off surfaces in their immediate surroundings. Subsequent research went on to show that both blind and sighted people can learn to avoid obstacles without vision, as long as they are able to use their hearing.
Research has also been aimed at identifying what predicts how much someone would be able to benefit from training in echolocation. Some of the first candidates were aspects of hearing, and it was understood that normal hearing was a requirement for learning to echolocate. Yet, one question was whether the ability to be able to hear certain sound frequencies better, or changes in sound intensity or frequency, would predict how well people would learn. From these studies no clear predictors emerged. Subsequent research focused on other aspects of cognition, and it was found that, for example, sighted people’s ability to use mental imagery (i.e. create pictures in their mind’s eye) was positively related to their ability to learn to use echolocation to perceive size.
Ekkel and colleagues’ paper follows in this line of research, confirming the learnability of echolocation, and suggesting that people’s attentional capacity might be an aspect driving the acquisition of this skill. To date, research into the cognitive variables involved in learning echolocation has been conducted with people who are sighted. Yet, loss of vision is associated with many behavioral and neural changes. We need research to determine if the variables that affect learning in sighted people are the same as those for people who are blind. Blindness affects people worldwide. Finding out more about how echolocation is learned by people who are blind, and how it affects their wellbeing, will answer important questions about how the brain adapts to vision loss. The research may also help establishing echolocation alongside other tools and techniques for people who are blind.