APA Dictionary of Psychology

a set of four symptoms associated with lesions of a specific area of the (usually left) parietal lobe. They are inability to recognize one’s individual fingers (finger agnosia; see tactile agnosia), inability to distinguish between the right and left sides of one’s body (right–left disorientation), inability to perform mathematical calculations (acalculia), and inability to write (agraphia). The existence of Gerstmann’s syndrome as a true independent entity is subject to debate. [Josef G. Gerstmann (1887–1969), Austrian neurologist]