ENCODING TARGET-TRUNK RELATIVE POSITION - CERVICAL VERSUS VESTIBULAR CONTRIBUTION

The contribution of cervical and vestibular cues in signaling the chan ges in target-trunk relative positions during self-motion was investig ated. Normal subjects (Ss) were shown a LED flashed in the peripheral visual field in a dark room. Ss were then passively rotated about the vertical axis in one of three different conditions: (1) head chair-fix ed (vestibular condition); (2) head earth-fixed (relaxed neck conditio n); and (3) head earth-fixed, but with the Ss actively attempting to t urn it (activated neck condition). The Ss were then required to indica te, with their unseen index finger, the position of the previously fla shed target. It was found that pointing at the memorized target was si milarly accurate in the relaxed neck condition and in the activated ne ck condition. In the vestibular condition, pointing accuracy dropped s ignificantly. These results suggest that neck proprioceptive signals a re more effective than vestibular ones in signaling relative changes i n the position of stationary objects with respect to the body during h ead-trunk motion. The finding that cervically mediated estimates were unchanged during active contraction of the neck muscles may suggests t hat efference copy signals may help interpete the change in the affere nt signals caused by voluntary neck muscle activation.