The Logic of (Visual) Perception


Plenty of time these days to do spring cleaning, during which a copy of Irvin Rock’s The Logic of Perception surfaced.  Rock was one of the world’s leading authorities on visual perception until his death in 1995 from pancreatic cancer, at the age of 73.  One of my favorite courses in undergraduate school at Yeshiva University was Physiological Psychology, and unfortunately I missed having Rock as my teacher – who had departed the faculty several years earlier for Rutgers.  From there he moved to U.C. Berkeley in the 1990s, where he coined the term “inattentional blindness” with his colleague Arien Mack.

But before his seminal book on Inattentional Blindness came The Logic of Perception, published in 1983.  Every page is a gem, beginning with the Preface which opens with this observation:  “If some of my former students with whom I have lost touch should happen to come across this book, they may find it hard to believe it was written by me … This is a rather speculative book, and at times I feel uncomfortable about it.”  How refreshingly open and intellectually honest of Professor Rock!

Among the many interesting and useful points in the book, one that particularly caught my eye was a section on the intelligence of perception.  Rock writes:  “For reasons not fully understood by students of perception, depth based on stereopsis alone as given by viewing stereograms takes time to emerge.  There may be a period of 15 or 30 seconds before depth is experienced … I will assume that there is some change in the neural events in the brain that accounts for (or underlies) the transition from two- to three-dimensional experience in viewing the stereogram despite the absence of any change in incoming stimulation from the retina. … One can consider the effects in these examples as the result of a problem-solving process rather than simply an inference process … When the solution occurs, it is usually based on unconscious events; it is sudden and insightful and even pleasurable.  It then seems impossible to revert to the resolution percept and difficult to understand why the pattern could not be identified immediately.”

JBO Cover 1991

The concept of stereoscopic delay, or the speed at which stereopsis can be perceived,  was elaborated for Optometry by Dr. Selwyn Super (may he rest in peace) in his seminal article in the Journal of Behavioral Optometry in 1991.


In his Ph.D. thesis from the same year at Rand Afrikaans University on the Educational Significance of Stereopsis, Dr. Super writes: “The development of stereopsis in man and other species may be regarded as an intelligent adaptation to an environment where more and more attention has had to be paid to details of space and time in order to survive and to advance. If it can be accepted that stereopsis, in this respect, is a part of intelligence, then the degree to which an individual can appreciate and react to stereopsis, should relate in some way to that individual’s intelligence. Likewise, there should be some relationship between stereopsis and scholastic achievement in general and some school subjects in particular, where space and time concepts may be critical to such learning.”

High on my wish list is the desire to pick up on the emergence/speed of stereopsis, where Professors Rock and Super left off.  Stay tuned …

2 thoughts on “The Logic of (Visual) Perception

  1. Professor Rock’s statement about change in perception “despite the absence of any change in incoming stimulation from the retina. …” is not entirely correct even though I frequently say the same thing. I constantly point out that perception does not agree with retinal images, size and shape constancy both demonstrating that we can get the same perception from vastly different retinal images and thus vastly different neural events. Still, theoretically at least, while the visual target is not changing, the retinal images are constantly changing as the eyes and body move.
    How the illusions of dichoptic stereopsis come about and how much time it takes the viewer to form the illusion are fascinating questions. If visual illusions are, as I suppose, the result of doing vision in a new environments the same way we did vision in earlier environments, the time to see the “analogy” between the two environments could as Dr. Super suggested, well be related to intelligence. I’ll look forward, Len, to your sharing future explorations on the subject.

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