Fuller J H
Department of Oral Anatomy, University of Illinois at Chicago 60612, USA.
J Vestib Res. 1996 Jan-Feb;6(1):1-13.
Head movement propensity-the pattern of head saccades dependent on methods of target presentation-varies among individuals. The present group of 9 young adults was previously ranked in a visual saccadic task according to this propensity. The present report examines how and why this propensity changes if the saccades are made to auditory targets. 1) Spatially identical, interleaved, auditorily and visually elicited horizontal saccadic gaze shifts (jumps) differed in amplitude and in starting and/or ending position. The jumps were executed in two head movement modes: first, the non-aligned mode was a standard reaction-time single gaze step between two points. Second, the head-aligned mode required alignment of the head with the fixation (starting) point; thereafter both modes were identical. All results in the auditory task are expressed relative to the visual results. 2) In the non-aligned mode, head movement amplitudes were increased on average by 15% (for example, an 80 degrees jump elicited a 12 degrees larger head movement), and velocity decreased by 12%, reflecting the increased demands of the auditory task. More importantly, the differences between subjects was narrowed; that is, head movement propensity was homogenized in the auditory task. In the visual task, head-movers willingly move their heads off and across the midline, whereas non-movers are unwilling to leave the midline from eccentric starting points or to eccentric ending points. This is called the midline attraction effect and was previously linked to spatial reference frames. The homogenization in the auditory task was characterized by head-movers increasing, and non-movers decreasing, their midline attraction, suggesting altered spatial reference frames. 3) For heuristic purposes, the ideal head-mover is defined by a gain of 1.0 in the visual task, and by external earth-fixed reference frames. Similarly, the ideal non-mover has a gain of 0.0 and has a bias toward body (or some par of the body)-fixed reference frames. In the auditory task these gains (and reference frames) in head movers and non-movers are homogenized (close to 0.5), either by the participation of the head (movement of the ears in space) in sensory acquisition or by differences in central nervous processing of the two modalities, or both.
头部运动倾向——即依赖于目标呈现方式的头部扫视模式——因人而异。在之前的一项视觉扫视任务中，根据这种倾向对当前这组9名年轻人进行了排名。本报告探讨了如果扫视针对听觉目标，这种倾向会如何以及为何发生变化。1) 在空间上相同、交错出现的听觉和视觉诱发的水平扫视注视转移（跳跃）在幅度以及起始和/或结束位置上存在差异。这些跳跃以两种头部运动模式执行：首先，非对齐模式是两点之间标准的反应时单注视步。其次，头部对齐模式要求头部与注视（起始）点对齐；此后两种模式相同。听觉任务中的所有结果均相对于视觉结果表示。2) 在非对齐模式下，头部运动幅度平均增加了15%（例如，80度的跳跃引发了大12度的头部运动），速度降低了12%，这反映了听觉任务的需求增加。更重要的是，受试者之间的差异缩小了；也就是说，在听觉任务中头部运动倾向变得均匀了。在视觉任务中，头部运动者愿意将头部移离并越过中线，而非运动者则不愿意从偏心起始点或到偏心终点离开中线。这被称为中线吸引效应，之前与空间参考框架有关。听觉任务中的均匀化表现为头部运动者增加，而非运动者减少他们的中线吸引，这表明空间参考框架发生了改变。3) 出于启发式目的，理想的头部运动者在视觉任务中由增益为1.0以及外部地球固定参考框架定义。同样，理想的非运动者增益为0.0且偏向身体（或身体的某个部分）固定参考框架。在听觉任务中，头部运动者和非运动者的这些增益（以及参考框架）通过头部参与（耳朵在空间中的运动）感官获取或两种模式的中枢神经处理差异或两者兼而有之而变得均匀（接近0.5）。
