P3D Re: Permissible Depth Range (was: "Too much depth")

[Gabriel Jacob <jacob@xxxxxxxxxxxxxx>]

>Chris Jones writes,

>There isn't a boundary in the sense that there is a switching from one mode
>of stereopsis to another. But it seems that different mechanisms dominate
>at different distances.

I would agree that there are different mechanisms at work at different
distances but stereopsis would predominate in all cases.

>For distant objects, the eyes are nearly parallel and each eye sees an
>almost identical image of the object - stereopsis arises from the
>horizontal disparities of the images.

Makes sense.

>For close objects the mechanism appears more complex, and appears to rely
>more on vergence movements, proprioception (here the feedback of eye
>position) and some implicit interpretation of the object's structure.

Stereopsis still predominates.

>For very close objects, you can get a pretty good idea of depth just from
>shadows and perspective through a single eye.

Not true. Try this. Hold up two pencils with the leads pointing toward
each other. Close one eye and try bringing them together till they touch.
Now try it with both eyes. Which way was easier?

Gabriel