Visual memory can be strong despite impairment from "summary" of The Mind's Eye by Oliver Sacks
In describing visual agnosias, I have often pointed out that the ability to recognize familiar faces, or objects, or scenes may be lost, while the ability to perceive, to see, remains intact. I have described patients who can draw objects they cannot recognize, who can copy a drawing without understanding what it represents. Such patients have what is called apperceptive agnosia, a loss of the ability to apprehend the visual world, which is quite different from a loss of the ability to see. Apperceptive agnosia is sometimes seen in people with severe dementia. Such patients may recognize nothing, not even their own faces in the mirror, and are often surprised or frightened by movements or changes in their environment. They may be unable to organize their visual world, to see objects as distinct from their backgrounds, or to see objects in correct perspective. They may be unable to recognize even simple shapes or forms, or to recognize the simplest objects. Apperceptive agnosia is a profound disorder, a breakdown of the most basic elements of visual perception. It is a disorder of the most essential, primitive, "low-level" aspects of vision. But even in the total absence of recognition, or of any understanding of the visual world, there may still be some sort of visual memory. Patients with apperceptive agnosia may lose the ability to see specific objects, or to recognize specific faces, or even to recognize their own faces. They may be unable to name or visualize objects or faces, yet they may be able to draw them, or to draw them with remarkable accuracy. There seems to be a profound disconnection between the visual and linguistic areas in these patients, a disconnection that allows them to draw or copy what they cannot name or recognize. They may reproduce objects, or faces, in an almost photographic way, in great detail, and yet be totally unable to recognize them. This can extend to the copying of faces—often a rather difficult task for normal people—as well as to the copying of complex scenes or patterns. Such patients may be able to draw, or copy, a scene, a landscape, in an astonishing way, with great detail and accuracy, and yet be quite unable to recognize, or to say what they have drawn. Their drawing, their copying, is purely perceptual, and not impeded by any lack of visual memory.
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