FACIAL STEREOTYPIC MOVEMENTS AND TARDIVE-DYSKINESIA IN A MENTALLY-RETARDED POPULATION

The facial stereotypies of adults diagnosed as having mental retardati on and tardive dyskinesia were examined through a kinematic analysis o f videotaped lip and tongue motions. A control group of healthy adult subjects without mental retardation was also examined in the productio n of preferred rates of lip and tongue oscillatory motions to provide a basis to assess the degree of movement variability in the stereotypi es. The inter- and intraindividual variability of the movement form ch aracteristics of the lip and tongue stereotypic motions was higher in the subjects with mental retardation. Results suggest that the low var iability of discrete properties of movement kinematics may not be a de fining feature of stereotypies. The concept of invariance in stereotyp ies may relate only to the topological kinematic properties of the mov ement sequence that provide the basis to infer that the same stereotyp ic movement sequence was reproduced from observation to observation.