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Keith Stroyan; Computation of the geometric inputs to depth perception. Journal of Vision 2008;8(6):92. doi: 10.1167/8.6.92.
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© ARVO (1962-2015); The Authors (2016-present)
We have written flexible software to compute various stimulus quantities for depth perception. It uses 2D “pin hole” optics of the eyes, and has a easily controlled variables to help inform research questions by giving precise computations.
One set of sample computations compares retinal disparity, parallax due to “head bobbing,” and parallax due to walking 1 m/sec while observing pairs of objects. When the objects are in the 10m range, all these are useful in fine depth discriminations with the smallest on the order of 10 min of arc. In the 100m range, retinal disparity and head bobbing parallax are in the 1 minute of arc range, near the threshold of perception, while walking parallax is an order of magnitude larger. In the 1km range, retinal disparity and head bobbing parallax are sub-threshold (less than 0.1 min), while walking parallax is still in the 5 minute of arc per second range. At the viewing distances and speeds of the automobile driving, motion parallax provides input quantities two orders of magnitude larger than binocular stereopsis or head bobbing.
The software can also compute horopter and curves of constant retinal disparity. For a fixate at 400m farther objects need to be almost 4km away to be perceived as more distant. This demonstrates that retinal disparity is not useful at such long distances.
The horopter is also computed for an observer with her head aimed at the fixate and again with her head aimed in a different direction, but still fixed on the same point. The curves are markedly different. Perhaps this kind of head turning could contribute to depth perception at longer distances.
Various other kinds of head or eye motion could be easily computed with the software to help decide which sorts of geometric inputs are perceivable.
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