Alexia, or word blindness, is an acquired type of sensory aphasia where trauma to the brain causes a patient to lose the ability to read. It is also called text blindness, or visual aphasia.
Alexia is often the result of trauma to the left brain’s parietal-temporal-occipital association area. This area of the cortex lies between the processing centers for auditory, visual, and somatosensory sensory processing. It coordinates the information that is gathered from all three processing centers and assigns meaning to the stimulus. In the left brain, the P.T.O is primarily responsible for language recognition. In the right brain, the PTO mainly handles recognition of an object and its spatial characteristics.
Alexia may or may not be accompanied by expressive aphasia (the inability to produce language) such as agraphia, the loss of one’s ability to write. If damage to the brain is exclusively to the POT (an exclusively input-based locus), then output ability may not be lost. In this scenario, an individual’s ability to create language may exist without the ability to understand it.