Bernard Mendiburu isn’t a household name. That’s okay, neither you nor I stir instant name recognition in most households, but we’ve done okay for ourselves. Of what relevance is Mendiburu to stereoscopic media? Quite a great deal, actually – and he’s managed to put his experience to good use in a marvelous book published last year by Elsevier.
In preparation for becoming Doctors of Optometry, optometric students learn a great deal about monocular cues to depth in their courses on physiological optics. Mendiburu reviews these concepts in his pleasant style, referring to non-stereoscopic cues to depth as monoscopic.
Where Mendiburu really shines, and illuminates the subject particularly for lay audiences, is in his discussion about vergence and accommodation. Pleasantly surprised? So was I. He notes that to obtain information about the absolute distance from you to the objects you’re looking at, you need to gather it from your visual motor system. To gaze with parallel alignment of the eyes is relatively relaxing; to converge the eyes for any sustained period is relatively more uncomfortable. Understanding this, Mendiburu writes, together with the concept of parallax, is the cornerstone of making good 3D stereoscopic movies.
But what about accommodation, you ask? Isn’t that a factor in coupling with the vergence system? Now here’s where the discussion really gets interesting. Mendiburu writes: “To the best of my knowledge and experience, humans cannot feel the focus plane they’re accommodating to.” And that’s a good thing, because our accommodation or focus is at the plane of the screen, while our vergence systems is positioned elsewhere.
Sound familiar? Absolutely! The visual symptoms that arise from the mismatch between the plane of vergence and accommodation are what Marty Banks and his colleagues have been investigating, as we reviewed in our introduction below, where focal distance is the distance between you and the screen, and vergence distance is where the 3D stereosopic plane requires you to look.
Mendiburu refers to this as a focus/convergence de-synchronization. He notes that the decorrelation between accommodation and convergence is not a natural function of our visual system, and that our brain has to force our eyes to do it. For those viewers who find the experience troublesome or even painful, he suggests that the ability to control accommodation and vergence separately can be learned.
Mendiburu writes: “As with any muscular activity, decorrelation increases in efficiency and comfort with exercise. Training reduces the eyestrain and processing time in assembling the pairs of 2D images into one 3D scene.”
After discussing the range of fusion, retinal rivalry, and the optimal viewing space in a movie theater to minimize viewing discomfort, Mendiburu provides several exercises that can be practiced which are essentially building “JNDs” in the separation between objects and in motion parallax. He misses the opportunity to point out, as did Schubin in his cafe below, that optometrists specialize in this field therapeutically.
After all, what is the essence of doing SILO and motion parallax with vectograms projected in space? And of spatial localization with eccentric circles, coupled with movement?
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