Kuntz Jessica R, Karl Jenni M, Doan Jon B, Whishaw Ian Q
Department of Neuroscience, Canadian Centre for Behavioral Neuroscience, University of Lethbridge, 4401 University Drive West, Lethbridge, AB T1K 3M4, Canada.
Department of Psychology, Thompson Rivers University, Kamloops, Canada.
Exp Brain Res. 2018 Apr;236(4):1091-1103. doi: 10.1007/s00221-018-5196-4. Epub 2018 Feb 13.
Reach-to-grasp movements feature the integration of a reach directed by the extrinsic (location) features of a target and a grasp directed by the intrinsic (size, shape) features of a target. The action-perception theory suggests that integration and scaling of a reach-to-grasp movement, including its trajectory and the concurrent digit shaping, are features that depend upon online action pathways of the dorsal visuomotor stream. Scaling is much less accurate for a pantomime reach-to-grasp movement, a pretend reach with the target object absent. Thus, the action-perception theory proposes that pantomime movement is mediated by perceptual pathways of the ventral visuomotor stream. A distinguishing visual feature of a real reach-to-grasp movement is gaze anchoring, in which a participant visually fixates the target throughout the reach and disengages, often by blinking or looking away/averting the head, at about the time that the target is grasped. The present study examined whether gaze anchoring is associated with pantomime reaching. The eye and hand movements of participants were recorded as they reached for a ball of one of three sizes, located on a pedestal at arms' length, or pantomimed the same reach with the ball and pedestal absent. The kinematic measures for real reach-to-grasp movements were coupled to the location and size of the target, whereas the kinematic measures for pantomime reach-to-grasp, although grossly reflecting target features, were significantly altered. Gaze anchoring was also tightly coupled to the target for real reach-to-grasp movements, but there was no systematic focus for gaze, either in relation with the virtual target, the previous location of the target, or the participant's reaching hand, for pantomime reach-to-grasp. The presence of gaze anchoring during real vs. its absence in pantomime reach-to-grasp supports the action-perception theory that real, but not pantomime, reaches are online visuomotor actions and is discussed in relation with the neural control of real and pantomime reach-to-grasp movements.
伸手抓握动作的特点是将由目标的外在（位置）特征引导的伸手动作与由目标的内在（大小、形状）特征引导的抓握动作整合在一起。动作-感知理论表明，伸手抓握动作的整合与缩放，包括其轨迹和同时进行的手指塑形，是依赖于背侧视觉运动通路在线动作路径的特征。对于模拟伸手抓握动作（即目标物体不存在时的假装伸手动作），缩放的准确性要低得多。因此，动作-感知理论提出，模拟动作是由腹侧视觉运动通路的感知路径介导的。真实伸手抓握动作的一个显著视觉特征是注视锚定，即参与者在整个伸手过程中视觉上固定在目标上，并在大约抓住目标时通过眨眼或看向别处/转头来脱离注视。本研究调查了注视锚定是否与模拟伸手动作有关。记录了参与者伸手去拿位于一臂距离处基座上三种大小之一的球时的眼动和手动，或者在球和基座不存在的情况下模拟相同伸手动作时的眼动和手动。真实伸手抓握动作的运动学测量与目标的位置和大小相关联，而模拟伸手抓握动作的运动学测量虽然大致反映了目标特征，但有显著改变。注视锚定在真实伸手抓握动作中也与目标紧密相关，但在模拟伸手抓握动作中，无论是与虚拟目标、目标的先前位置还是参与者的伸手手相关，都没有系统的注视焦点。真实伸手抓握动作中存在注视锚定而模拟伸手抓握动作中不存在注视锚定，这支持了动作-感知理论，即真实的而非模拟的伸手动作是在线视觉运动动作，并结合真实和模拟伸手抓握动作的神经控制进行了讨论。
