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.
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.
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.