Explain why the specific quality of a disorder of expressive movement (diminished, stiff and masked, or exaggerated) is clinically useful information.

The specific quality of the disturbance helps distinguish depression, catatonia, and mania from one another. A generally limited range of movement with a sad or anxious cast to the face points toward depression; a stiff, mask-like facial expression with scanty body movement, though the eyes may remain paradoxically lively, points toward catatonia; and exaggerated, wide, expansive gestures accompanying a cheerful, overactive manner point toward mania. Because expressive movement varies enormously with mood, culture, and individual personality even in health, attending carefully to which specific quality is present, rather than simply noting that expressive movement is disturbed, gives useful diagnostic information about which underlying condition is most likely.