In seven case histories, Sacks (The Man Who Mistook His Wife Fora Hat, 1985, etc.) once again presents the bizarre both clinically and lyrically, challenging assumptions about the landscape of human reality. The fascination of Dr. Sacks's approach to neurological disorder is his attempt to empathize with patients whose realities can't be described in normal terms. He dares to wonder how pathology can shape consciousness and the concept of self. To him, a patient is not a broken machine, but an inhabitant of an unfamiliar world. And sometimes those alien worlds are more hospitable than the one we are used to. After an accident, a successful artist (referred to as Mr. I) loses the ability to experience color: Not only can't he see it, he can't dream it, remember it, or even imagine it. After a period of extreme depression and uncertainty, he comes to think of his condition as "a strange gift" that allows him to experience the physical world in a unique way. Virgil, whose sight is restored after a lifetime of blindness, is crushed by the bewilderment of vision; his brain has never learned to see, but his comfortable life as a blind person is irrevocably over. And then there is Temple Grandin, an animal-science professor and a high-functioning autistic who has only learned the rules of interpersonal relationships by memorizing them like complex math problems, though her empathy with animals is astonishing. Occasionally, Sacks provides too much technical detail -- long riffs on the mechanics of vision, for instance -- but these are minor distractions. (The essays have been previously published in the New Yorker and the New York Review of Books.) Readers may come to Sacks's work as voyeurs, but they will leave it with new and profound respect for the endless labyrinth of the human mind.