There is the associative component as described by Goldsmith and Liu (2001). This is less severe because a limited understanding of the relevance of a face is retained. Patients can copy drawings of faces but remain unaware of who the drawing is of. Some patients can also draw their own pictures of generic faces accurately with the correct positioning of eyes, nose, and mouth. Associative prosopagnosia is the more common of the two and is thought to occur as the result of direct damage to the neural units required for face-recognition (Bill Choisser). Special contrast sensitivity has been found to be within normal limits in some people with prosopagnosia (Goldsmith and Liu, 2001). Some people with prosopagnosia also have the ability to interpret and imitate facial expressions correctly (Goldsmith and Liu, 2001).
There is also the appreceptive component to prosopagnosia. This is more severe and represents an inability to name or place people that they see· The person may be unable to distinguish features of faces even of a familiar person. People with apperceptive agnosia have difficulty copying drawings of faces. In some instances prosopagnosia can be explained by an inability to perceive enough detail to properly store or retrieve information associated with the face (Goldsmith and Liu, 2001). For example, people with prosopagnosia can find it difficult to perceive curved stimuli, or may show weakness in recognizing face related features such as eye gaze (Goldsmith and Liu, 2001). Apperceptive prosopagnosia is thought to result from the disconnection of functional face-recognition units. There is some evidence that individuals with apperceptive prosopagnosia still have some implicit ability to recognize faces
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