Visual Agnosia - Symptoms

Symptoms

While most cases of visual agnosia are seen in older adults who have had extensive brain damage, there are also cases of young children with less brain damage during developmental years acquiring the symptoms. Commonly, visual agnosia presents as an inability to recognize an object by its shape, in the absence of other explanations, such as vision problems. This is most easily seen in prosopagnosia, where the individual can clearly see the faces of those people nearby, but is unable to draw the mental connections and recognize the person. Another common manifestation of visual agnosia is a difficulty to identify objects that look similar in shape, difficulty with line drawings that lack much detail, and recognizing objects that are shown from less common views.

Visual agnosia occurs after damage to the visual association cortex. This occurs even when no damage has been done to the eyes or optic tract that leads visual information into the brain. Visual agnosia is caused by damage to parts of the ventral stream of vision. The ventral stream is also known as the "what pathway of vision" because this pathway allows the individual to identify they objects they see. The other stream is the dorsal stream or "where/how" pathway; and this pathway remains undisturbed, allowing individuals with visual agnosia to show relatively normal visually guided behavior. Damage to specific areas of the ventral stream impair the ability to recognize certain categories of visual information.