Wednesday, February 24, 2010

How Far Away Is the Television Screen of Visual Experience?

... not that I think there really is one, even in a loose, metaphorical sense. (See here.) But:

David Boonin (a visiting speaker from Colorado) and UCR graduate students Alan Moore and Matt Braich and I were hiking up Mt. Rubidoux. From the top, we could see several miles across town to the UCR campus. We pointed out to Boonin the clock tower, and then Alan said that the humanities building housing the philosophy department was also visible nearby, down and to the right, "about an inch and a half away".

What, an inch and a half away?! Alan's statement -- as I'm sure he knew -- sharply conflicted with my published views about the nature of the visual experience of perspective. And yet I knew exactly what Alan meant. He had effectively pointed out the spot. It seemed to me that "an inch and a half" was a much better description of the apparent distance than, say, a millimeter or twenty feet. (Of course the real distance is much larger than any of those.)

My thumb is about 3/4 of an inch wide. Holding it at arm's length, I saw that it almost perfectly occluded the distance between the clock tower and the humanities building. Thus, if the television screen of visual experience were arm's length away, Alan should have said that the distance was 3/4 of an inch. From the fact that the building's apparent distance (in some sense of "apparent distance"!) was an inch and a half, I thus geometrically derive the conclusion that the television screen of visual experience is about five feet away.

There, proved!


  1. Must have been a quiet walk down that mountain. - DG

  2. Hah.
    But if you told me something was an inch and a half away on, say, a painting in a gallery or the opposite wall of a smallish room, I would think of it in actual inches. I wonder what the threshold distance is at which we switch over to measuring on the 'visual TV screen' instead.

  3. I vaguely recall that medieval philosophers remarked similarly on the apparent size of the moon in the visual field. If I remember who and in what texts, I'll post, if there's interest. (Probably Roger Bacon, probably in his writings on *perspectiva*, but I don't have Bacon handy at the moment. Or it could be a commonplace in commentaries on De anima, the POsterior analytics, and the like.)

  4. Thanks, folks!

    No, DG, I couldn't shut up.

    David: Yes, good question!

    Kurt: I would be interested in references, if it's not too hard, although I think the moon might be an unusual case. In the ancient West it was sometimes said (including by Aristotle) that the sun looks about a foot wide. But that was often held to be sui generis, a special fact about the sun rather than about visual perspective in general.

  5. You’re the professor, right? Couldn’t you have said to the student ‘no, it’s the width-of-my-thumb away, which is 3/4 inches, so you are wrong’. Or did ‘1 and 1/2 inches’ better convey the apparent distance than ‘3/4 inches’?

  6. It struck me that 1 1/2 inches seems a better description than 3/4 inch. Neither response appeals to me theoretically, which is why I found that inclination interesting.

  7. Any chance that you were standing about 5 feet from eachother ?


  8. Interesting thought, GNZ. I would say that our distance varied from about 5 to 10 feet.

    Alan also confirmed this with a second test yesterday, getting four people independently to say that a distant object was about half an inch (3 said half inch, one said 1 cm) -- again geometrically implying about a five-foot distant projection. When Alan demonstrated with me, he was standing about 5 feet away. It would be interesting to see if the reports vary with distance between interlocutors. I'd guess not, or not very much, but worth checking!