Sue Barry and The Quale of Stereopsis


It has been 10 years since we blogged about Stereo Sue’s exploration into the quale of stereopsis. Simply put, quale is the quality or property of a phenomenon as perceived or experienced by a person. I had hoped that somewhere along the way, someone outside of Optometry would pick up on the significance of what Sue had achieved in acquiring stereopsis and writing so eloquently about it in Fixing My Gaze. I was therefore delighted to come across a book authored in 2020 by E. Bruce Goldstein, Associate Professor Emeritus of Psychology at the University of Pittsburgh, writer of the award-winning textbook Sensation and Perception now in its tenth edition.

MIT Press publishes Goldstein’s psychology textbook, and it is the publisher of his most recent work, The Mind: Consciousness, Prediction, and the Brain in which he delves into the story of Stereo Sue. The widespread penetration of MIT Press should draw influential minds and eyes toward this important story.

On page 46 in his chapter on Consciousness and Experience, Professor Goldstein has a section titled: Can Experience (Qualia) Be Inferred From Scientific Knowledge? He begins with the conundrum as to whether it is possible to know what qualia another person is experiencing, made famous by the thought experiment about color vision by the philosopher Frank Jackson. The thought experiment is known in Philosophy and Psychology circles as “Mary the Color Scientist”.

“This thought experiment”, Goldstein writes on page 47, “would not be relevant to our quest for understanding qualia except that a real ‘Mary’ has recently been discovered. Her name is Dr. Susan Barry, and she is a professor of neurobiology at Mount Holyoke College.” Goldstein proceeds to relate the story of Stereo Sue as it unfolded in her interactions with Dr. Oliver Sacks, and notes that “Susan had gone to an optometrist, who prescribed eye exercises designed to make her eyes work together. These exercises changed her perception, and her book Fixing My Gaze describes what started happening as her eyes began working together … So Susan had become the ‘Mary” of depth perception. Despite all her scientific knowledge and her confidence that she knew what the experience of depth perception would be like, she was nonetheless amazed when she first experienced binocular depth perception. Scientific knowledge was not enough. She needed to actually experience binocular depth perception, not just know about it.”

We may be more accurate in speaking about the qualia of depth in the plural form. There is of course a sense of depth imparting a quale that can be based on monocular cues as mastered by artists. But Professor Goldstein builds the case both in his textbook on Sensation and Perception, as well as in his comparatively short book on The Mind, that disparity driven binocular stereopsis is a quale all its own that affords unique a window into neuroplasticity of the visual system. On page 49 of The Mind he invites the reader to think about what this means: “In addition to the idea that experience must be experienced, we can draw another message from Susan’s story … Somehow the brain had transformed two flat images into a single three-dimensional perception. What this means is that activity in the nervous system creates experiences.” Or as our friend and colleague Bob Sanet is fond of saying, in order for our interventions to be most effective, we must speak to the neurology. Goldstein’s latest book provides a wonderful narrative for that conversation.

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