Abstract
Clinical skills in neuropsychology are closely related to hypothesis testing based on careful observation of symptoms and signs. Systematic observation is necessary to differentiate agnosia from other similar symptoms. Agnosia is defined as modality-specific disturbance of object recognition in the absence of elementary sensory dysfunction or beyond an elementary sensory failure when it exists. Anomia and impaired semantic knowledge of objects should be distinguished from agnosia.
There are two types of agnosia. Accordingly, apperceptive agnosia results from a faulty synthesis of object features, whereas associative agnosia arises when intact perceptual extraction of object features cannot associate with semantic knowledge. Furthermore, integrative agnosia has been taken into consideration for visual agnosia. Systematic investigation could reveal an impaired stage of information processing in each type of agnosia. Category-specific agnosia has been reported in visual and auditory agnosia. Prosopagnosia, i. e. agnosia for faces, and landmark agnosia are different from the other visual agnosia in that recognition of an individual face or landmark is disturbed. Patients with prosopagnosia can recognize human face, but cannot tell who he/she is.
Not only neuroimaging and neurophysiological findings in neuroscience but also careful and detailed clinical investigation with hypothesis and test cycle are essential to reveal neuronal bases of object recognition.
