Those whose familiarity with Oliver Sacks extends only to his vivid book titles — “The Island of the Color­blind,” “An Anthropologist on Mars,” “The Man Who Mistook His Wife for a Hat” — may picture his writing as a gallery of grotesques, a parade of the exotically impaired. Sacks, a practicing neurologist, does specialize in case studies of highly unusual patients. But even as he entertains and diverts with his dramatic tales, Sacks has always been up to something else: he is gently educating us about the frailties and flaws — and the strengths and capacities — of “normal” people, those whose afflictions are of the most ordinary sort. You may never have confused your spouse for an item of outerwear, but have you ever failed to recognize the face of an acquaintance? Fumbled for a word that eluded your grasp? Read a sentence three times and still didn’t get it?

Such familiar slips, and how we handle them, are the stealth subjects of Sacks’ latest book. “The Mind’s Eye” is a collection of essays — some of which have already appeared in The New Yorker — but it has a remarkably graceful coherence of theme, tone and approach. Once again, Sacks explores our shared condition through a series of vivid characters: the woman who couldn’t talk, the man who couldn’t read, the “prosopagnosic” who couldn’t identify her own face in a photograph. (For those who wonder just how Sacks locates such people, it soon becomes clear that many of his patients find him, after recognizing themselves in his writing. They enter his care through the pages of his books, and in turn become characters in his next round of stories.)

The sufferers who write to Sacks receive a deeply empathetic response. Of one correspondent, a woman who has lost the capacity to read (but, remarkably, retains the ability to write), Sacks notes that he responded to her by telephone. “I normally would have written back,” he tells us, but in this case calling “seemed to be the thing to do.” Over time this patient, afflicted with a degenerative brain condition called posterior cortical atrophy, loses her ability to recognize objects and people, though she retains a keen sense of color and shape. When Sacks meets her in person to see how she navigates her everyday life, he dresses head to toe in red so she can keep track of him in a crowd.

Given to such un-self-consciously generous gestures, Sacks would seem to be the ideal doctor: observant but accepting, thorough but tender, training his full attention on one patient at a time. For the patient’s benefit and for ours, he illuminates every uncanny detail, brings out every excruciating irony. The woman for whom Sacks dresses in red, for example, is a virtuoso pianist, and the first sign of her malady is a sudden inability to read music. She is joined in these pages by a novelist who wakes up one morning unable to read, and an intensely sociable woman who is suddenly struck dumb. But Sacks is not primarily interested in documenting pathology, or even curing disease, which in most cases is impossible. There are no miraculous “awakenings” here.