Problems In Depth Perception

This is a comprehensive survey of binocular vision, with an emphasis on its role in the perception of a three-dimensional world. The central theme is biological vision. Machine vision and computational models are discussed where they contribute to an understanding of living systems.

In The Mind’s Eye, Oliver Sacks tells the stories of people who are able to navigate the world and communicate with others despite losing what many of us consider indispensable senses and abilities: the power of speech, the capacity to recognize faces, the sense of three-dimensional space, the ability to read, the sense of sight. For all of these people, the challenge is to adapt to a radically new way of being in the world. There is Lilian, a concert pianist who becomes unable to read music and is eventually unable even to recognize everyday objects, and Sue, a neurobiologist who has never seen in three dimensions, until she suddenly acquires stereoscopic vision in her fifties. There is Pat, who reinvents herself as a loving grandmother and active member of her community, despite the fact that she has aphasia and cannot utter a sentence, and Howard, a prolific novelist who must find a way to continue his life as a writer even after a stroke destroys his ability to read. And there is Dr. Sacks himself, who tells the story of his own eye cancer and the bizarre and disconcerting effects of losing vision to one side. Sacks explores some very strange paradoxes—people who can see perfectly well but cannot recognize their own children, and blind people who become hyper-visual or who navigate by “tongue vision.” He also considers more fundamental questions: How do we see? How do we think? How important is internal imagery—or vision, for that matter? Why is it that, although writing is only five thousand years old, humans have a universal, seemingly innate, potential for reading? The Mind’s Eye is a testament to the complexity of vision and the brain and to the power of creativity and adaptation. And it provides a whole new perspective on the power of language and communication, as we try to imagine what it is to see with another person’s eyes, or another person’s mind.

The equidistance tendency is the tendency for objects or other inhomogeneities in the field-of-view to appear at the same distance as each other with the strength of this tendency being inversely related to directional separation. The evidence for the existence of the equidistance tendency and for its ability to modify the perceived depth resulting from size or stereoscopic cues is reviewed. The equidistance tendency is discussed as a disturbing factor in visual experimentation and as a necessary factor in the understanding of Emmert's law, the moon illusion, and similar phenomena. Several possible explanations for the equidistance tendency are evaluated in terms of the range of phenomena with which it is identified. (Author).

A revelatory account of the brain's capacity for change When neuroscientist Susan Barry was fifty years old, she experienced the sense of immersion in a three dimensional world for the first time. Skyscrapers on street corners appeared to loom out toward her like the bows of giant ships. Tree branches projected upward and outward, enclosing and commanding palpable volumes of space. Leaves created intricate mosaics in 3D. Barry had been cross-eyed and stereoblind since early infancy. After half a century of perceiving her surroundings as flat and compressed, on that day she saw the city of Manhattan in stereo depth for first time in her life. As a neuroscientist, she understood just how extraordinary this transformation was, not only for herself but for the scientific understanding of the human brain. Scientists have long believed that the brain is malleable only during a "critical period" in early childhood. According to this theory, Barry's brain had organized itself when she was a baby to avoid double vision - and there was no way to rewire it as an adult. But Barry found an optometrist who prescribed a little-known program of vision therapy; after intensive training, Barry was ultimately able to accomplish what other scientists and even she herself had once considered impossible. Dubbed "Stereo Sue" by renowned neurologist Oliver Sacks, Susan Barry tells her own remarkable journey and celebrates the joyous pleasure of our senses.