Digit repetition in brain-damaged adults: clinical and theoretical implications.

Digit repetition was investigated in samples of unilaterally (N = 87) and bilaterally (N = 75) brain-damaged adults. The study was designed to investigate the hemispheric and neuropsychological factors that underlie performance on these two dissimilar tasks. Digit repetition was disproportionately depressed in such patients, especially those with left hemisphere lesions. The incidence of individually impaired digit repetition performance, especially of digits backward, was significantly higher than in normals, again particularly within the left hemisphere sample. However, impaired digit repetition was not invariably associated with brain dysfunction. The data suggest, but do not confirm, a differential function hypothesis, as well as a unilateral hemispheric hypothesis that underlies the ability to repeat forward and backward digits; this finding is consistent with some previous literature. Group performance showed considerable overlap, which limited the possibility of demonstrating a double dissociation between digits forward and verbal measures, and digits backward and nonverbal factors. Digit repetition in brain-damaged patients appears to have some theoretical value, but limited clinical utility.