A laterality effect in isometric and isotonic labial tracking.

Hemispheric dominance for sensorimotor control of lip activity was investigated by use of a pursuit auditory tracking task. This task involves continuous frequency matching of a computer-generated target tone and a subject-controlled cursor tone. Thirty right-handed subjects were tested under isometric lip and hand control, and 20 right-handed subjects under isotonic lip control. Subjects tracked 10 1-min trials under each laterality condition--cursor/right ear, target/left ear, and vice versa. In both experiments tracking performance was better when the lip-controlled cursor tone was presented to the right ear (hence direct contralateral route to left hemisphere). A significant (p less than 0.05) cursor/right-ear advantage was found under isometric hand-tracking. Analysis routines examined relative laterality advantages across several time intervals within each 1-min trial. Consistent lateralization scores in favor of cursor/right-ear presentations (REAs) were independent of the time interval measured. For isometric tracking, 58% of subjects having laterality advantages (p less than 0.10) revealed REAs. For isotonic tracking, 71% of subjects revealed REAs. Implications of the latter finding are discussed relative to a left hemisphere mechanism specialized to integrate movement-generated auditory feedback with dynamic kinesthetic information from the articulators.