Constancy of Head Turning Recorded in Healthy Young Humans

Abstract

This study evaluated the 'constancy' of head turning as recorded two-dimensionally by accelerometers. Fourteen healthy participants turned the head with his/her natural and comfortable speed. Maximum inclination angles (MIA) during head turning were measured in four (anterior, posterior, right, and left) directions of clockwise (CW) and counter-clockwise (CCW) conditions. Three indices were used for the evaluation: (1) standard deviations of MIA as an index of 'spatial constancy,' (2) anterior/posterior and right/left ratios from intervals among four MIA as indices of 'temporal constancy,' and (3) first derivatives from head turning trajectories as an index of 'angular velocity.' The spatial index varied from 0.15 degrees to 9.96 degrees (CW condition) and from 0.56 degrees to 10.6 degrees (CCW condition). The temporal index in the anterior-posterior direction varied from 0.711 to 1.103 (CW condition) and from 1.071 to 1.905 (CCW condition). The index in the right-left direction varied from 0.773 to 2.081 (CW condition) and from 0.842 to 1.226 (CCW condition). Characteristic hollows or protrusions were detected from the first derivatives of head turning trajectories and were regarded as abrupt changes in angular velocity during head turning. The results suggest that these three indices are appropriate tools for evaluation of the constancy of head turning.