Evans Carys, Edwards Martin G, Taylor Lawrence J, Ietswaart Magdalena
Faculty of Health and Life Sciences, Department of Psychology, Northumbria University Newcastle upon Tyne, UK.
Institute of Research in the Psychological Sciences, Université catholique de Louvain Louvain-le-Neuve, Belgium.
Front Hum Neurosci. 2016 Feb 1;10:8. doi: 10.3389/fnhum.2016.00008. eCollection 2016.
Patients with apraxia perform poorly when demonstrating how an object is used, particularly when pantomiming the action. However, these patients are able to accurately identify, and to pick up and move objects, demonstrating intact ventral and dorsal stream visuomotor processing. Appropriate object manipulation for skilled use is thought to rely on integration of known and visible object properties associated with "ventro-dorsal" stream neural processes. In apraxia, it has been suggested that stored object knowledge from the ventral stream may be less readily available to incorporate into the action plan, leading to an over-reliance on the objects' visual affordances in object-directed motor behavior. The current study examined grasping performance in left hemisphere stroke patients with (N = 3) and without (N = 9) apraxia, and in age-matched healthy control participants (N = 14), where participants repeatedly grasped novel cylindrical objects of varying weight distribution. Across two conditions, object weight distribution was indicated by either a memory-associated cue (object color) or visual-spatial cue (visible dot over the weighted end). Participants were required to incorporate object-weight associations to effectively grasp and balance each object. Control groups appropriately adjusted their grasp according to each object's weight distribution across each condition, whereas throughout the task two of the three apraxic patients performed poorly on both the memory-associated and visual-spatial cue conditions. A third apraxic patient seemed to compensate for these difficulties but still performed differently to control groups. Patients with apraxia performed normally on the neutral control condition when grasping the evenly weighted version. The pattern of behavior in apraxic patients suggests impaired integration of visible and known object properties attributed to the ventro-dorsal stream: in learning to grasp the weighted object accurately, apraxic patients applied neither pure knowledge-based information (the memory-associated condition) nor higher-level information given in the visual-spatial cue condition. Disruption to ventro-dorsal stream predicts that apraxic patients will have difficulty learning to manipulate new objects on the basis of information other than low-level visual cues such as shape and size.
失用症患者在演示如何使用物体时表现不佳，尤其是在模仿动作时。然而，这些患者能够准确识别、拿起并移动物体，表明腹侧和背侧视觉运动处理通路完好。熟练使用物体的适当操作被认为依赖于与“腹-背”通路神经过程相关的已知和可见物体属性的整合。在失用症中，有人提出腹侧通路中存储的物体知识可能不太容易纳入行动计划，导致在目标导向的运动行为中过度依赖物体的视觉可供性。本研究考察了有（N = 3）和无（N = 9）失用症的左半球中风患者以及年龄匹配的健康对照参与者（N = 14）的抓握表现，参与者反复抓握重量分布不同的新型圆柱形物体。在两种条件下，物体重量分布通过与记忆相关的线索（物体颜色）或视觉空间线索（重物端上方可见的点）来表示。参与者需要结合物体重量关联来有效抓握并平衡每个物体。对照组根据每种条件下每个物体的重量分布适当地调整抓握方式，而在整个任务中，三名失用症患者中的两名在与记忆相关和视觉空间线索条件下表现都很差。第三名失用症患者似乎弥补了这些困难，但表现仍与对照组不同。失用症患者在抓握均匀重量版本的中性对照条件下表现正常。失用症患者的行为模式表明，归因于腹-背通路的可见和已知物体属性的整合受损：在学习准确抓握重物时，失用症患者既没有应用基于纯粹知识的信息（与记忆相关的条件），也没有应用视觉空间线索条件中给出的高级信息。腹-背通路的破坏预示着失用症患者将难以基于诸如形状和大小等低水平视觉线索以外的信息来学习操作新物体。
