These techniques differ depending on the type of agraphia. This damage causes an extreme form of writer's block known as agraphia. Central agraphias include lexical, phonological, deep, and semantic agraphia. In the beginning stages of AD, individuals show signs of allographic agraphia and apraxic agraphia. This form of agraphia does not impair spoken language. More extensive left hemisphere damage can lead to global agraphia. Visuospatial agraphia typically has a right hemisphere pathology. A connection between AD and agraphia is the role of memory in normal writing ability. It includes right-left confusion, difficulty with writing (agraphia) and difficulty with mathematics (acalculia). Disruption of the posterior commissure can cause alexia without agraphia. The three major linguistic disorders that result from these injuries are aphasia, alexia, and agraphia. Lexical agraphia is associated with damage to the left angular gyrus and/or posterior temporal cortex. Agraphia can be broadly divided into central and peripheral categories. Agraphia is often seen in association with Alzheimer's Disease (AD). Peripheral agraphias include allographic, apraxic, motor execution, hemianoptic and afferent agraphia.