Agnosia = loss of knowledge. It is the loss of the ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective or is there any significant memory loss. Bauer (1993) defined agnosia as a “failure of recognition that cannot be attributed to elementary sensory defects mental deterioration, attentional disturbances, aphasic misnaming or unfamiliarity with sensorially presented stimuli”
Brain damage can affect a variety of sensation such as determining the presence of absence of light, detecting changes in contrast, discriminating between or perceiving colour. Diagnosis of agnosia dictates that these sensory deficits are absent.
There are a variety of different types of agnosia Lissauer (1890), agnosia manifested itself in two distinct forms: appreciative agnosia & associative agnosia. Two types of agnosias are visual agnosia and object agnosia. Visual agnosia is the severe inability to recognize visual stimuli despite sensory abilities. Object agnosia is the inability to identify objects that are presented, in these case they can neither name or give other evidence of recognizing visually presented objects. Prosopagnosia is another form of agnosia and is sometimes also called faceblindness and facial agnosia. Patients cannot consciously recognize familiar faces, and can at times even be their own. It can sometimes be perecievd as an inability to remember names.
http://www.youtube.com/watch?v=rwQpaHQ0hYw < - Object agnosia
http://www.youtube.com/watch?v=OYW8vJ5232o <- Visual agnosia
http://www.youtube.com/watch?v=ZogbIvdgfzQ&feature=related <- Prosopagnosia
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