Imai T, Moore S T, Raphan T, Cohen B
Department of Computer and Information Science, Brooklyn College of CUNY, NY 11210, USA.
Exp Brain Res. 2001 Jan;136(1):1-18. doi: 10.1007/s002210000533.
Body, head, and eye movements were measured in five subjects during straight walking and while turning corners. The purpose was to determine how well the head and eyes followed the linear trajectory of the body in space and whether head orientation followed changes in the gravito-inertial acceleration vector (GIA). Head and body movements were measured with a video-based motion analysis system and horizontal, vertical, and torsional eye movements with video-oculography. During straight walking, there was lateral body motion at the stride frequency, which was at half the frequency of stepping. The GIA oscillated about the direction of heading, according to the acceleration and deceleration associated with heel strike and toe flexion, and the body yawed in concert with stepping. Despite the linear and rotatory motions of the head and body, the head pointed along the forward motion of the body during straight walking. The head pitch/roll component appeared to compensate for vertical and horizontal acceleration of the head rather than orienting to the tilt of the GIA or anticipating it. When turning corners, subjects walked on a 50-cm radius over two steps or on a 200-cm radius in five to seven steps. Maximum centripetal accelerations in sharp turns were ca.0.4 g, which tilted the GIA ca.21 degrees with regard to the heading. This was anticipated by a roll tilt of the head of up to 8 degrees. The eyes rolled 1-1.5 degrees and moved down into the direction of linear acceleration during the tilts of the GIA. Yaw head deviations moved smoothly through the turn, anticipating the shift in lateral body trajectory by as much as 25 degrees. The trunk did not anticipate the change in trajectory. Thus, in contrast to straight walking, the tilt axes of the head and the GIA tended to align during turns. Gaze was stable in space during the slow phases and jumped forward in saccades along the trajectory, leading it by larger angles when the angular velocity of turning was greater. The anticipatory roll head movements during turning are likely to be utilized to overcome inertial forces that would destabilize balance during turning. The data show that compensatory eye, head, and body movements stabilize gaze during straight walking, while orienting mechanisms direct the eyes, head, and body to tilts of the GIA in space during turning.
在五名受试者直线行走和转弯时，对其身体、头部和眼睛的运动进行了测量。目的是确定头部和眼睛在空间中跟随身体直线轨迹的程度，以及头部方向是否跟随重力惯性加速度矢量（GIA）的变化。使用基于视频的运动分析系统测量头部和身体的运动，使用视频眼动描记法测量水平、垂直和扭转眼动。在直线行走过程中，身体存在以步频的横向运动，其频率为步频的一半。GIA根据与脚跟撞击和脚趾弯曲相关的加速和减速围绕前进方向振荡，并且身体与步幅同步偏航。尽管头部和身体存在直线和旋转运动，但在直线行走时头部指向身体的前进方向。头部俯仰/滚动分量似乎是为了补偿头部的垂直和水平加速度，而不是定向到GIA的倾斜或预期其倾斜。转弯时，受试者以50厘米半径走两步或以200厘米半径走五到七步。急转弯时的最大向心加速度约为0.4g，这使GIA相对于前进方向倾斜约21度。这通过头部高达8度的滚动倾斜来预期。在GIA倾斜期间，眼睛滚动1 - 1.5度并向下移动到线性加速度方向。偏航头部偏差在转弯过程中平稳移动，比身体横向轨迹的变化提前多达25度。躯干没有预期轨迹的变化。因此，与直线行走相反，在转弯时头部和GIA的倾斜轴倾向于对齐。在缓慢阶段，注视在空间中是稳定的，并且在扫视时沿着轨迹向前跳跃，当转弯角速度较大时领先更大角度。转弯时预期的头部滚动运动可能被用于克服在转弯时会破坏平衡的惯性力。数据表明，在直线行走期间，补偿性的眼睛、头部和身体运动使注视稳定，而在转弯期间，定向机制将眼睛、头部和身体引导至空间中GIA的倾斜方向。
