ABSTRACT
The diagnosis of associative agnosia must be envisaged when the patients fail to recognise a meaningful visual stimulus, whose perceptual structure has been adequately encoded. The inability to retrieve mental images characterises a clinical pattern that bears some relation to visual agnosia and is relevant to the understanding of the processes underlying visual perception. An amnestic or associative form of prosopagnosia can be envisaged when the patient passes all perceptual tests and fails the recognition of familiar faces, though showing intact semantic knowledge of the persons to whom they refer. An interesting phenomenon, brought out in prosopagnosia, as well as in other cognitive domains, is unconscious recognition. In adults, the most common aetiology of prosopagnosia is stroke in the territory of the posterior cerebral artery. Tactile agnosia is the inability to recognise an object through palpation, in spite of preserved or minimally impaired somatosensory functions.
