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....