The selective inability to draw horizontal lines: a peculiar constructional disorder

A patient is described who was affected by degenerative dementia and who developed severe constructional apraxia. She showed a dissociation between the construction of horizontal lines (impaired) and oblique or vertical lines (spared) which has never been reported previously. A battery of tests disclosed that this phenomenon was consistent across a range of experimental conditions and that a similar dissociation was evident in perceptual and representational domains. This peculiar clinical finding suggests that mental representations of horizontal and vertical spatial relations in an egocentric coordinate system are functionally dissociated.