Definitions for agnosia

Agnosia (a-gnosis, "non-knowledge") is a loss of ability to recognize objects, persons, sounds, shapes or smells. However, the specific sense involved is not defective, there is no significant memory loss and knowledge of the characteristics of those objects or persons exist (So I may know that my keys are flat objects with a round or square head connected by a ring, but I can't tell you that the things dangling in front of my face are my keys) . Agnosia can result from strokes, dementia, or other neurological disorders. Most of the time agnosia is due to parietal or occipital lobe injury in the brain.
What are parietal and occipital lobes you ask? Well the occipital lobe is the very back part of your brain. In the picture below it is colored orange. As for the parietal lobe there are on the side of the brain. In the picture it is colored pink.

Source: http://www.mrc-cbu.cam.ac.uk/personal/daniel.bor/memorymachine/background.html
People with agnosia may have difficulty recognizing the geometric features of an object or face (I know they are my keys, but I cannot describe their shape) or may be able to perceive the geometric features but not know what the object is used for or whether a face is familiar or not. Agnosia can be limited to one sense such as vision or hearing. For example, a person may have difficulty in recognizing an object as a cup or identifying a sound as a cough. People with agnosia may retain their cognitive abilities in other areas, like memory, ability to learn and conversation skills.
Visual agnosia is the inability to understand the meaning of visual stimuli despite apparently normal vision. There is a loss of recognition of visual perception. Visual agnosia is associated with lesion of the left occipital lobe and temporal lobes. Many patients who have visual agnosia also have a severe problems with their visual field.

This website is brought to you by Katie, Hanin, Aaron, Emlyn and Kat.
Thank you