agnosia [Grk agnōsía ‘ignorance’]

In neuropsychology, term referring to partial or complete inability, whether it be congenital or acquired, to recognize objects or persons despite the absence of any sensory loss in the respective organ. Thus, a noise (e.g. the rattling of keys) may be perceived, but its source cannot be identified (auditory imperception) or the distance and direction of a sound or noise may not be identified (acoustic allesthesia); or the minimal acoustic contrast between phonemes may not be recognized (partial weakness in differentiation, acoustic agnosia) or linguistic sound sequences may not be differentiated (‘word deafness’ or verbal agnosia). Similarly, in visual and tactile agnosia, objects may not be identified despite normal vision or sense of touch.