Head movement : Recording and significance.

Abstract

A recording apparatus to determine head movement has been developed and a basic study was done to obtain normal values of head movement and to estimate the significance of head movement as a righting reflex.Twenty healthy adults were included in the present experiment. The cephalographic system consists of an industrial television which picks up the movement of a light emitting diode (LED) on the helmet which the standing subject is wearing and transmits the movements in terms of voltage to a preamplifier connected to a wave control unit and finally to an X-Y recorder. The information obtained can at the same time be fed into a data recorder, which separately stores the data on anteroposterior and lateral displacement on the magnetic tape. The recorded data on the tape were fed into a digital computer for further analysis.1. The locus traced by LED closely resembled that of the center of gravity (CG) in the same subject.2. The total length of the locus during 1 minute of standing was 36.8±8.0cm with the eyes open and 69.7±10.5cm with the eyes closed. Those figures were smaller than those of CG.3. The anteroposterior component of the head movement was larger than the lateral component as compared with CG.4. Time course of the position of LED was similar to that of CG during standing with the eyes open, while it was different from that of CG during standing with the eyes closed.5. The frequency spectra of the head movement showed a dominantly slower frequency and the averaged divisional frequencies were 0.39±0.05Hz (lateral component) and 0.34±0.04Hz (anteroposterior component) with the eyes open and there were frequency shifts to faster frequency when the subject stood with his eyes closed.The above-mentioned results suggest that the head movement is controlled by CG movement and that CG works to keep the head steady and maintain the eyes in a normal position.