P3D Re: Depth perception cues

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Mon, 8 Mar 1999 20:16:38 -0700
>From: Gabriel Jacob <jacob@xxxxxxxxxxxxxx>
>Subject: P3D Re: Depth perception cues

>John Roberts gave a pretty comprehensive list of depth perception cues
>and then some! 

>>Primary sources of human depth perception:
>> -binocular stereo: determining the distance (or relative distance) of an
>>    object based on the convergence of the eyes, and the disparity (if any)
>>    of the two views. Note that you don't have to converge on a particular
>>    object to get an idea of its distance (change in disparity with change
>>    in convergence is another source of information). (When done properly,
>>    the Pulfrich effect produces true binocular stereo, though it is
>>    produced by motion.)

>Regarding binocular stereo, my understanding is, this relies only on
>disparity. Convergence does play a role in depth determination but
>only by sensing the eye muscle contractions.

I've had a lot of discussions with John Bercovitz and Jim Crowell on this
subject. The cue from convergence would be similar to (though not quite
the same as) judging the weight of an object by how hard you have to exert
your muscles to hold it up. The consensus of researchers in this field seems
to be that convergence is a "minor" cue for depth perception. I find this
somewhat disturbing, because it implies that the ability of humans to judge
absolute depth by binocular stereo in the absense of other visual references
is not very good.

I can think of a possible way to test it - when viewing a monochromatic
"point" light source (of adjustable brightness) in otherwise total darkness, 
sufficiently far away that accommodation doesn't provide a good cue, and with 
the test subject not allowed to move their head, then convergence should be 
just about the only cue, and the accuracy in judging distance can be
evaluated. Of course even that can be tricky - if the light source is
moved by a person or machine, the subject might hear the sounds of the
moving. (The light would be turned off or the subject's eyes would be
closed during transitions, of course.)

>Here is a list of major depth perception cues as outlined in the 
>book, "Perception."

Thanks for posting that. One thing readers may have noticed about the list
I posted is that it's very poorly organized. I'll see if I can get better
organization for it.

Is "interposition" broken down any further?

John R


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