Laboratory of Neuromotor Physiology, IRCCS Fondazione Santa Lucia, Rome, Italy.
Department of Systems Medicine, University of Rome Tor Vergata, Rome, Italy.
J Physiol. 2019 Apr;597(7):2021-2043. doi: 10.1113/JP277469. Epub 2019 Feb 6.
It is known that interception of targets accelerated by gravity involves internal models coupled with visual signals. Non-visual signals related to head and body orientation relative to gravity may also contribute, although their role is poorly understood. In a novel experiment, we asked pitched observers to hit a virtual target approaching with an acceleration that was either coherent or incoherent with their pitch-tilt. Initially, the timing errors were large and independent of the coherence between target acceleration and observer's pitch. With practice, however, the timing errors became substantially smaller in the coherent conditions. The results show that information about head and body orientation can contribute to modelling the effects of gravity on a moving target. Orientation cues from vestibular and somatosensory signals might be integrated with visual signals in the vestibular cortex, where the internal model of gravity is assumed to be encoded.
Interception of moving targets relies on visual signals and internal models. Less is known about the additional contribution of non-visual cues about head and body orientation relative to gravity. We took advantage of Galileo's law of motion along an incline to demonstrate the effects of vestibular and somatosensory cues about head and body orientation on interception timing. Participants were asked to hit a ball rolling in a gutter towards the eyes, resulting in image expansion. The scene was presented in a head-mounted display, without any visual information about gravity direction. In separate blocks of trials participants were pitched backwards by 20° or 60°, whereas ball acceleration was randomized across trials so as to be compatible with rolling down a slope of 20° or 60°. Initially, the timing errors were large, independently of the coherence between ball acceleration and pitch angle, consistent with responses based exclusively on visual information because visual stimuli were identical at both tilts. At the end of the experiment, however, the timing errors were systematically smaller in the coherent conditions than the incoherent ones. Moreover, the responses were significantly (P = 0.007) earlier when participants were pitched by 60° than when they were pitched by 20°. Therefore, practice with the task led to incorporation of information about head and body orientation relative to gravity for response timing. Instead, posture did not affect response timing in a control experiment in which participants hit a static target in synchrony with the last of a predictable series of stationary audiovisual stimuli.
众所周知，受重力加速的目标截获涉及与视觉信号耦合的内部模型。与重力相对的头部和身体方向的非视觉信号也可能有贡献，尽管其作用尚未得到很好的理解。在一项新的实验中，我们要求倾斜观察者击打一个以与观察者俯仰一致或不一致的加速度接近的虚拟目标。最初，定时误差很大，与目标加速度与观察者俯仰之间的相干性无关。然而，随着练习，在相干条件下，定时误差大大减小。结果表明，有关头部和身体方向的信息可以有助于模拟移动目标受重力的影响。来自前庭和躯体感觉信号的方位线索可能与假定在其中编码重力内部模型的前庭皮层中的视觉信号相整合。
移动目标的截获依赖于视觉信号和内部模型。关于相对于重力的头部和身体方位的非视觉线索的额外贡献知之甚少。我们利用伽利略沿斜面运动定律来证明前庭和躯体感觉关于头部和身体方位的线索对截获定时的影响。要求参与者击打沿水槽向眼睛滚动的球，导致图像扩展。该场景在头戴式显示器中呈现，没有任何关于重力方向的视觉信息。在单独的试验块中，参与者向后倾斜 20°或 60°，而球的加速度在试验中随机变化，以便与 20°或 60°的斜坡滚动兼容。最初，定时误差很大，与球加速度和俯仰角之间的相干性无关，这与完全基于视觉信息的响应一致，因为在两种倾斜度下视觉刺激是相同的。然而，在实验结束时，在相干条件下定时误差比非相干条件下小系统地小。此外，当参与者向后倾斜 60°时，响应明显（P=0.007）早于向后倾斜 20°时。因此，通过练习该任务，信息被整合到相对于重力的头部和身体方位，以用于响应定时。相反，在参与者与可预测的一系列静止视听刺激中的最后一个同步击打静态目标的控制实验中，姿势对响应定时没有影响。
