Here’s how learning to echolocate changes your brain

Real-life stories of blind people, such as David Kish, using click-based echolocation to navigate their way through their environment have inspired studies into how to help others to do it. In 2021, for example, a team led by Liam Norman at Durham University reported that after just 10 weeks of dedicated training, both sighted and blind participants could develop these skills, with some even reaching the level of expert echo-locators.

In a new paper in Cerebral Cortex, Norman and colleagues now report on findings from studies of brain scans of these participants, taken before and after the training period. This work reveals some similar brain changes in both the sighted and the blind group — including in a key 'visual' area.

Fourteen sighted and 12 blind participants completed the 10-week programme, which included both computer-based and real world training. They practised using click-based echolocation to judge the size of objects around them, for example, as well as to navigate virtual and real indoor and outdoor environments. The improvements in their abilities after training were often substantial. For example, the mean time taken to navigate a virtual maze dropped from 104.1 to 40.9 seconds for the sighted participants and from 137 to 57.23 seconds for the blind group.

Before and after the training period, the participants also completed an additional task, in which they listened to a series of sound files. Some of these files were recordings of clicks and click-echoes that a person would hear if they were using echolocation while taking different routes through a maze— such a single-turn route, for example, or a two-turn route. In some sound files, though, the team had scrambled the sounds, meaning that they didn't provide any spatially helpful information. In others, they had removed the echoes, leaving only the clicks.

After listening to each sound file, the participants indicated whether they'd heard a route recording — and if so, what type — or a scrambled file. They were also asked to report when echoes were not present. After the 10-week programme, both the blind and sighted participants got better at this task, too. Though most of the trials of this task were completed in the lab, some were done while the participant's brains were being scanned during fMRI. The findings from these brain scans are the focus of the new paper. They help to explain what underpinned the participants' improvements.

The team found that, after 10 weeks of training, for the blind participants, there was an increase in the density of the grey matter in the right primary auditory cortex. For the sighted group, there as enhanced grey matter density in adjacent acoustic areas. The team also found that, after training, for both the blind and sighted groups, there were bigger increases in the response of the primary auditory cortex to sound, in general. More surprisingly, for both the sighted as well as the blind participants, their left and right primary visual cortex had become sensitive to echoes.

Earlier work has shown that, in blind echolocation experts, this key 'visual' area processes the sounds of echoes. It had been suggested that this is only the case for people who have been deprived of their sight for many years. The new findings contradict this idea. The work "provides strong evidence that the ability of a primary sensory area to exhibit sensitivity to input from a different modality (here: sound echoes) can be considered a normal characteristic of the typical adult human brain," the team writes.

One suggestion for why the primary visual cortex of the sighted group responded to echoes is that this region processes sensory information that allows us to build up a spatial understanding of our environment. Visual signals certainly provide excellent information about the location and distance of objects around us. But, with echolocation training, people can learn to use sounds to gather this type of information, too — and sounds with echoes contain more spatial-related information than sounds without echoes.

The team did find a few differences between the brains of the blind versus sighted participants after training. But, given past suggestions that some areas of the brain only handle sensory data from a particular, corresponding sensory organ, this observation of similar changes in the response of the primary visual cortex to echoes adds to the developing picture of the reality being more complex.

Read the paper in full:

Norman, L. J., Hartley, T., & Thaler, L. (2024). Changes in primary visual and auditory cortex of blind and sighted adults following 10 weeks of click-based echolocation training. Cerebral Cortex, 34(6). https://doi.org/10.1093/cercor/bhae239