Karnath H O, Niemeier M, Dichgans J
Department of Neurology, University of Tübingen, Germany.
Brain. 1998 Dec;121 ( Pt 12):2357-67. doi: 10.1093/brain/121.12.2357.
The present study investigated the gaze as well as the head and the eye-in-head movements of neglect patients while they were exploring their surroundings. A random configuration of letters was presented on the inner surface of a sphere that surrounded the subject, requiring free exploratory eye and head movements. The subjects were requested to search for a single (non-existent) target letter. The co-ordination of eye and head movements in patients with neglect resembled the pattern usually observed in healthy subjects orienting to eccentric visual targets. They performed hypometric head movements with additional shifts of eye-in-head position. Moreover, like healthy subjects, the patients with neglect explored space with gaze, with head and eye-in-head movements that were symmetrically distributed around preferred orientations in space. However, in contrast to controls, these centres of exploration were shifted towards the right. The average horizontal position of gaze and of head movements lay right of the body's mid-sagittal plane, the average eye-in-head position right of the head midline. The preferred orientations were located far away from the anatomical limits of horizontal gaze, head and eye-in-head movements. The decrease of exploration towards more eccentric locations left and right of these orientations thus could not be explained by anatomical restrictions. The results argue against a model of neglect that proposes a lateral gradient of attentional orienting towards the ipsilesional side. Exploring the surroundings, the patients did not orient gaze, the head or the eyes in the head towards the extreme ipsilesional side, nor even close to it. The results favour a deviation model suggesting a shift of the whole frame for exploratory behaviour towards the ipsilesional side. In addition to this shift, we found a second component of altered visual exploration in neglect. The patients' head and gaze movements exhibited a reduced variability around the deviated centre of exploration. The variability was not generally reduced but rather concerned specifically the horizontal dimension. The latter was found even when the area of exploration was paralleled between the groups, requiring the control subjects to search only in that part of the letter array that the neglect patients had explored spontaneously. Possible mechanisms, such as a disturbed ability to update the spatial representation of visual targets or an altered neural representation of space in the horizontal dimension, are discussed.
本研究调查了忽视症患者在探索周围环境时的注视以及头部和眼球在头部内的运动情况。在围绕受试者的球体内表面呈现一组随机排列的字母，要求受试者自由地进行探索性眼球和头部运动。受试者被要求寻找一个单一的（不存在的）目标字母。忽视症患者的眼球和头部运动协调情况类似于健康受试者在定向于偏心视觉目标时通常观察到的模式。他们进行的头部运动幅度不足，并伴有眼球在头部内位置的额外偏移。此外，与健康受试者一样，忽视症患者通过注视、头部和眼球在头部内的运动来探索空间，这些运动在空间中的偏好方向周围呈对称分布。然而，与对照组相比，这些探索中心向右偏移。注视和头部运动的平均水平位置位于身体矢状中平面右侧，眼球在头部内的平均位置位于头部中线右侧。偏好方向远离水平注视、头部和眼球在头部内运动的解剖学极限。因此，在这些方向左右更偏心位置处探索减少不能用解剖学限制来解释。这些结果与一种忽视症模型相悖，该模型提出注意力定向存在向患侧的侧向梯度。在探索周围环境时，患者不会将注视、头部或头部内的眼睛朝向患侧极端方向，甚至不会接近该方向。这些结果支持一种偏差模型，该模型表明探索行为的整个框架向患侧偏移。除了这种偏移之外，我们还发现忽视症患者视觉探索改变的第二个成分。患者的头部和注视运动在偏离的探索中心周围表现出变异性降低。变异性并非普遍降低，而是特别涉及水平维度。即使在两组之间使探索区域平行，即要求对照组受试者仅在忽视症患者自发探索的字母阵列部分进行搜索时，也发现了后者。文中讨论了可能的机制，如更新视觉目标空间表征的能力受损或水平维度空间的神经表征改变。
