When deprived of a sense, the brain may go to extraordinary lengths to compensate for the particular lack of input. For example, some blind individuals become human echolocators, using sound cues from the environment that naturally occur along with self-emitted clicks to create a spatial map of their environment. One such human echolocator is Daniel Kish. Born with bilateral retinoblastomas (cancer of the retina), he lost his vision while still an infant after doctors radiated both eyes in an attempt to save his life. Many years later, Daniel is able to run, bike and camp just like sighted people through his skill of echolocation. Daniel’s earliest memory is of him sneaking out of his bedroom late at night and exploring the neighborhood through the many clicks he emitted over a several-hour period. He has no memory of not being able to echolocate—it appears the skill just developed naturally as a response to sensory deprivation. His parents cannot provide any insight on how this skill developed, since it was always just something he seemed to do.
Daniel Kish is able to run, bike and camp.
Daniel Kish, World Access for the Blind website.
Echolocation is one of the amazing abilities the brain might be capable of in extreme situations. One of the primary functions of the brain is to create phenomenal experience using, among other things, sensory data. When this sensory data is lacking in quality, the brain has different methods of filling in the missing details. Have you ever jumped out of the shower to pick up the ringing phone only to find it silent? This is one example of the brain compensating for a lack of sensory data. The monotonous white noise of the shower deprives the brain of normally rich sound cues from the environment. It responds by generating phantom sounds that typically comprise those one might anticipate hearing from the shower, such as ringing telephones, knocks on the door and someone calling your name. But don’t live in fear
of ghosts—it’s just your crazy brain!
Although echolocation is a natural skill for many of the blind, others can be taught how to do it. And sighted people can learn as well. One of the oldest experiments on human echolocation involved blindfolding sighted subjects, teaching them to sense the distance of their faces from a board. After walking into the board multiple times, subjects learned to stop just shy of giving themselves repeated nosebleeds (I’ve considered replicating the experiment but my IRB thinks the paradigm is cruel and unusual). Another study showed that blindfolded sighted people started hallucinating imagery in response to sound after just one week of being blindfolded. These studies suggest that echolocation is a skill the brain is primed to master, given the right circumstances.
Drawing of whisker experiment setup.
Ehud Ahissar, Weizman Institute of Science
A recent study
showed that the brain is also primed to receive spatial information from the sensorimotor system. Researchers attached two “whiskers” to the fingers of participants and observed their ability to determine the anterior-posterior position of poles located in the vicinity of their outstretched arms. After several training sessions, participants were able to accurately determine which poles were more posterior even when the difference between anterior-posterior location of the two poles was very small. All eight participants exhibited the same sort of behavior after training with whiskers: when the location of a pole was completely unknown, participants would scan the environment using very slow, sweeping motions. But as participants were required to discriminate among very small differences, whisker movement sped up to become light tapping. The fact that all participants exhibited the same behavior when locating suggests that these sensory processes are hardwired into our brains.
It is unlikely that participants in the above study started scratching at the corners of furniture and exclaiming to every opening of a tuna can after only a few sessions, but one might wonder what it would be like if whiskers became a part of everyday spatial experience. We can gather some insight from people like Daniel. While he has no memory of what it’s like to see, Daniel says that he does experience spatial phenomenology. Echolocation is much less like the estimative whisker experience and much more like seeing. And this is what functional magnetic resonance images (fMRI) of the echolocating brain indicate. Although sound information used to generate a spatial map doesn’t travel down the optic pathway, it shows up in the visual cortex, the part of the brain responsible for processing visual information for visual experience. So then, much to the dismay of philosopher Thomas Nagel, there is something it’s like to be a bat.