Neurophilosophy

WE all know that bats and dolphins use echolocation to navigate, by producing high frequency bursts of clicks and interpreting the sound waves that bounce off objects in their surroundings. Less well known is that humans can also learn to echolocate. With enough training, people can use this ability to do extraordinary things. Teenager Ben Underwood, who died of cancer in 2009, was one of a small number of blind people to master it. As the clip below shows, he could use echolocation not only to navigate and avoid obstacles, but also to identify objects, rollerskate and even play video games. 

Very little research has been done on human echolocation, and nothing is known about the underlying brain mechanisms. In the first study of its kind, Canadian researchers used functional magnetic resonance imaging (fMRI) to monitor the brain activity of two blind echolocation experts. Their findings, published today in the open access journal PLoS ONE, show that echolocation engages regions of the brain that normally process vision.  



Psychologist Lore Thaler of the University of Western Ontario and her colleagues recruited two expert echolocators for the new study. One, a 43-year-old man referred to as EB, was born with retinoblastoma – a form of cancer that affects cells in the retina – and had both eyes removed at 13 months of age. The other, a 27-year-old man known as LB, lost his vision at the age of 14, following degeneration of the optic nerve, which carries visual information from the eye to the brain. Both have trained themselves to be expert echolocators. Both of them use click-based echolocation on a daily basis, to navigate their home cities and explore unfamiliar ones, go hiking or play basketball. 

The researchers seated their participants in a sealed room, placed various objects in front of them, and asked them to produce echolocation clicks. As they did so, the sounds they produced – and the faint echoes – were recorded with high quality stereo equipment. They also asked the participants to do the same thing in an outdoor courtyard surrounded by buildings, and made more recordings. Some of these contained echoes produced by a tree, car or lamp-post, while others did not. 

EB and LB could accurately determine the size, shape, position and movements of objects in both situations. Crucially, they could do the same from the sound recordings when they were played back later. EB, for example, could distinguish a 3° difference in the position of a pole in the sealed room, as well as from the pre-recorded sounds. LB, was slightly less accurate, distinguishing 9° differences in position of the pole while in the room, and 22° differences from the recordings.

Thaler and her colleagues then scanned the blind participants’ brains, and those of two sighted controls of the same age and sex, while they listened to the pre-recorded sounds through earphones. They found that the recordings activated the auditory cortex, which process sounds, in all four participants. The sounds also activated parts of the visual cortex in the blind participants, but this activity was completely absent in the sighted controls. EB exhibited greater visual cortical activation than LB. This may reflect the fact that he is more experienced at using echolocation. 

The researchers observed another difference when they compared the brain activity evoked by outdoor recordings with and without echoes. The recordings without echoes produced the same pattern of activity as those used in the first experiment. Remarkably, though, the recordings containing echoes activated the visual cortex in the blind participants, but not the auditory cortex. 

Although it is somewhat limited by the small number of participants, this study suggest that EB and LB both use echolocation in a way that is very similar to vision. The exact role of the visual cortex in human echolocation is unclear, but Thaler and her colleagues suggest that it might be processing spatial information contained in the echolocation clicks.

The researchers are cautious in their interpretation of the findings. They note numerous studies which show that blindness can lead to extensive brain re-organization. Such changes can produce cross-modal activation, whereby sensations activate brain regions that would not normally process them. But the observation that the echoes in the outdoor recordings activated visual but not auditory cortices in the blind participants supports the researchers’ conclusion. 

The use of pre-recorded sounds overcomes a number of difficulties in scanning the brains of echolocating people, and could stimulate other neuroimaging experiments of the phenomenon. Future studies of blind echolocators may confirm these new findings, and comparisons with sighted people who have been trained to echolocate and blind non-echolocators with an increased sensitivity to echoes could provide further insights into the underlying neural mechanisms.

Related:


Thaler, L., et al. (2011). Neural Correlates of Natural Human Echolocation in Early and Late Blind Echolocation Experts. PLoS ONE 6 (5): e20162. doi: 10.1371/journal.pone.0020162

Comments

  1. #1 SC
    May 26, 2011

    I wonder whether non-blind people can learn echolocation.

    Also, maybe there really is an answer to “what is it like to be a bat?”

  2. #2 Emmy
    May 28, 2011

    Facinating post, and by the way when the **heck** is the medical community going to find a cure for blindness (or cancer, for that matter?) The kid’s eyes were removed? That’s horrible!

    I was led to understand that echolocation in humans was discovered quite a while ago. Sorry, I did not yet bother to search for the study – but a professor of ours (in 2005) told us about participants blindfolded and told to walk through 2 types of rooms – carpeted and uncarpeted. The participants, with no vision impairments to speak of, were able to find their way around objects in the non-carpeted room but not the carpeted one. Does this not suggest that brain readjustment has little to do with it – and would it not be plausible that all mammals echolocate, but we just have not discovered it yet? :)

  3. #3 dmabs
    May 29, 2011

    Sunday Sacrilege pz’s blaspheming head

    debunkingskeptics.com/forum/viewtopic.php?f=7&t=1756

  4. #4 Tirso
    May 30, 2011

    I don’t understand why didn’t they use blind non-echolocators as control subjects.

  5. #5 David H. Eisenberg
    May 31, 2011

    Really? I’m having a hard time believing this. This reminds me of Clever Hans, the horse people thought could count for a while. Think I’ll wait a few years for the ECHOLOCATION IN HUMANS SHOWN TO BE A HOAX article before I buy it.

  6. #6 Torbjörn Larsson, OM
    June 2, 2011

    Illuminating. =D

    @ Tirso: What would be the difference? (Except maybe that the non-blind references are more likely not to rely on echolocation.)

    @ @ DHE: But a) these people rely on echolocation at times b) there are measurable differences. Argument from ignorance is a fallacy.

  7. #7 russell
    June 3, 2011

    its probably just the auditory cortex creeping into the visual regions as a result of plasticity…the guy who could discern object location better through sound just had more area of the cortex devoted towards sound processing and hence a more accurate representation.

  8. #8 Alexa S
    June 15, 2011

    Human Echolocation sounds fascinating! I’m sure Dr. Peggy Drexler would be interested in this subject. To find out more about her and her studies, check out this link http://bit.ly/mpJIW6

  9. #9 Anna
    June 17, 2011

    I suspect that everybody can learn to be ‘expert echolocaters’ if they need to, and that we all use echolocation to some extend.

    We don’t go around clicking like dolphins, but what do you do if you are in a dark room and don’t know where the walls are and where there are major obstacles. Don’t you whistle, knock on a wall or similar to get an idea? or if you come across a well/deep hole in the ground… don’t you try to create echoes in it (like throw something in and listen or whistle into it) to estimate its depth and shape etc?

    I would say that is also echolocation, or maybe it is more complex than that.

    I wonder if the reason the blind people used the visual cortex is simply that they are blind and their brains have reorganised to utilise the space for non-visual things because it would be a waste of space to let it be idle. It may be that blind people use their visual cortex for many kinds of non-visual sensory processing, and that sighted people in fact use their auditory cortex for echolocation.

  10. #10 Anna
    June 17, 2011

    It could also be interesting to compare with what part of their brains dolphins use to process echolocation – visual or auditory cortex, or do they have a different solution?

    Also, can humans use echolocation to navigate under water? Sounds produced under water (e.g. talking or calling under water) would seem to be absorbed and disappear and reveal nothing about the surroundings.

  11. #11 peter
    June 24, 2011

    fascinating read than kyou very much

  12. #12 EvoDivas
    July 25, 2011

    Umm… Video games? How does that work with echolocation? I get the ability to use a controller pad – every blind person could do that. But how would he actually play?

    Something is amiss.

    That very fact should bring insane levels of skeptical attention to every other claim.

  13. #13 K
    August 6, 2011

    Unbelievable!

    I wonder, can a seeing person develop this ability to use echolocation? Or does this only work if the part of the brain that is responsible for sight is not operating properly?

  14. #14 Tim Johnson
    August 7, 2011

    This is definitely a skill that we all have, blind or not. It’s just a matter of understanding it and then becoming sensitized to it. I’m not blind but I’ve been working on honing my understanding and usage of this amazing phenomenon ever since I first heard of Ben Underwood several years ago. There are several ways that we can create noises from which to perceive the size, shape and construct of a room or other environment. I’ve been successful in using my footsteps or my pants rubbing together. There are also several different types of clicks you can use as a signal.

    I’ve been documenting my successes, failures and lessons learned on my blog. If anyone is interested in learning more or contributing your thoughts to my effort, please do so: http://learnecholocation.blogspot.com

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