Wednesday, January 24, 2007

Human Echolocation

Can you echolocate? -- that is, hear the locations and properties of silent objects by noticing how sound reflects off them? Most people say no -- perhaps none more eminently than the philosopher Thomas Nagel in his influential essay “What Is It Like to Be a Bat?”:

bat sonar [echolocation], though clearly a form of perception, is not similar in its operation to any sense that we possess, and there is no reason to suppose that it is subjectively like anything we can experience or imagine.

It's clear, though, that we sometimes gain information about things by noticing how sound reflects from them. You can tell the difference in sound when a wall by the freeway suddenly ends, then starts again. We're all familiar with the sound difference between a footfall or shout heard in a large room and one heard in a small room (an auditorium vs. a bathroom, say). In such cases, we detect the distance of silent walls by hearing the sound reflected from them. Larry Rosenblum (a psychologist here at UCR) has tested this more formally with ordinary blindfolded undergraduates. Much to the surprise of most of them, they could distinguish differences in distance between walls 36 to 144 inches away.

Close your eyes and hold your hand in front of your face. Say "shhhh" while moving your hand up and down, forward and back, right and left. Better, get a friend to move her hand around while you do this. You can hear where the hand is, no? Close your eyes and walk toward a wall, saying "hi, hi, hi, hi...". Can't you hear how far the wall is? With a couple of practice trials, most people find it fairly easy to stop within a few inches of the wall without touching it.

Other researchers have found that ordinary people can use echolocation to discriminate the shapes of objects of equal surface area (circle vs. square vs. triangle) and in some cases the texture of objects (fabric, plexiglass, carpet, wood). Apparently, you can hear if that thing in front of you is circular!

(I've replicated some of these last results informally in my office, and I'm not entirely certain that subjects aren't just hearing differences in loudness -- e.g., a triangle with its apex up reflects more sound when you talk at it from a relatively lower position and less sound when you raise your mouth higher, while circles and squares are more symmetrical. On the other hand, sometimes it seems to me that I have an almost instantaneous impression of the shape in these experiments.)

If you're really good -- for example if you're blind and rely upon echolocation as one of your principal means of navigating the world, you might be able to do even this.

Sometime in the next week or so, I'll post on some of the philosophical issues I see arising from these facts....


Anonymous said...

Hi Eric-

A couple of months ago when the newswires were running the stories about echolocating people, there was a round of "take that Tom Nagel!" posts. Imagine my surprise when re-reading "What is it Like to be a Bat?" a few weeks ago and discover this passage from footnote 8: "It may be easier than I suppose to transcend interspecies barriers with the aid of the imagination. For example, blind people are able to detect objects near them by a form of sonar, using vocal clikcs or taps of a cane."

So, clearly Nagel knew about these cases. This isn't to deny that some of what he says in the article is really hard to square with this footnote, but I do think it isn't completely obvious that he thinks that we can't echolocate at all, as opposed to thinking that we can't echolocate in the same fashion BATS do. Alternately, he may be trying to run some sort of distinction between echolocation and other "forms of sonar."

Eric Schwitzgebel said...

Thanks for the comment, Manuel! Notice how Nagel's footnote continues, though. Here's the next sentence: "Perhaps if one knew what that was like, one could by extension imagine roughly what it was like to possess the much more refined sonar of a bat."

Implicit in the subjective conditional form of that sentence, and indeed throughout the article, is the assumption that we (ordinary, sighted folk) don't echolocate.

But the point of my post here is not to criticize Nagel. The argument in his famous article succeeds or fails, I think, independently of the specific example of bat "sonar". He could have mounted the argument as well or poorly with any of a number of other species with exotic sensory modalities (e.g., magnetic orientation -- assuming we don't do that!).

My point in this post is not about blind people's now well-known capacity to echolocate (which I mention only very briefly at the end) but our own. Few people have much cognizance of this; Nagel is just an eminent example.

Clark Goble said...

I always thought Nagel's point could be expanded to "what is it like to be an other person." Since a lot of the same logic applies. Take the bat which, per the footnote, has "much more refined sonar." But one might then ask what is it like to be blind, or to have more refined sight, or so forth. Nagel's point seems to be (at least to my eyes) expound the traditional problem of other minds via an extreme case like a bat.

It is a great paper though that everyone ought read. It's just that after a while you realize it's an old argument simply put in an interesting form.

Eric Schwitzgebel said...

I'm not sure I agree with you about this, Clark. There's a sense in which Nagel's article turns on the traditional "problem of other minds"; but his idea of focusing a kind of experience *radically* different from our own adds a twist, and perhaps a difference in kind (though he partly takes it back in the footnote Manuel cites). It creates a new sort of problem, maybe, for the argument that we can know others' experience by analogy from our own.

Clark Goble said...

Certainly the less analogy there is the bigger the problem of comprehending the other minds. And it seems to me that this is partially what I find so baffling about zombie arguments. How do we know others are zombies? We can conceive of it but can we comprehend it?

By taking an experience that is more radical though you are right it raises the issue to more prominence. The same idea has been used for decades in science fiction though. Say someone evolves some new sense. What would it be like to be them?

So I suppose I'd say it is less a different in kind than a difference in degree.

Unknown said...
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Unknown said...

I'm a seeing person, but have recently taken an affinity to echolocation. I think the concept has profound implications on what we know about human capabilities. The fact that we have the ability to do this and simply do not do it because we didn't know about it baffles me.
I'm practicing and documenting my findings and progress on my blog, and if you're interested you can check it out at my "Learning Echolocation" blog.

Unknown said...

In my early years, I read a book about parapsychology. One chapter referred to "Shadow Vision." An exercise for this was to walk in a dark room toward a wall and when you feel a tight feeling perhaps in your forehead you should stop. I practiced this for quite a time and found it to work. It seemed to me that this was sensing the ambient sound in a room reflecting off of the wall. All these years later reading about human echolocation kind of validates my childhood theory. Thanks.