Small animals face a large challenge when running. A stable head is key to maintenance of a stable gaze and a good sense of self-motion and spatial awareness. However, trunk undulations caused by the cyclic limb movements result in involuntary head movements. Hence, the head needs to be stabilized. Humans are capable of stabilizing their head up to 2–3 Hz, but small animals run at cycle frequencies that are up to six times higher. We wondered how natural selection has adapted their head stabilization control. We observed that the relative contributions of vision, on the one hand, and vestibular perception and proprioception, on the other hand, remain the same when lizards undergo fast or slow body undulations in an experimental set-up. Lizards also maintain a short phase lag at both low and high undulation frequencies. Hence, we found no indication that they use a different control mechanism at high frequencies. Instead, head stabilization probably remains possible owing to faster reflex pathways and a lower head inertia. Hence, the intrinsic physical and neurological characteristics of lizards seem to be sufficient to enable head stabilization at high frequencies, obviating the need for evolutionary adaptation of the control pathways. These properties are not unique to lizards and might, therefore, also facilitate head stabilization at high frequencies in other small, fast animals.

中文翻译：

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小型脊椎动物的头部稳定，它们以伸展的姿势高频率运转

小动物奔跑时面临巨大挑战。稳定的头部对于保持稳定的视线以及良好的自我运动和空间意识至关重要。但是，由周期性肢体运动引起的躯干起伏会导致头部非自愿运动。因此，需要使头部稳定。人类能够稳定其头部，使其频率高达2-3 Hz，但是小型动物以高达六倍的循环频率运行。我们想知道自然选择如何适应他们的头部稳定控制。我们观察到，当蜥蜴在实验设置中经历快速或缓慢的身体起伏时，一方面视觉，相对前庭感知和本体感受的相对贡献保持不变。蜥蜴在低和高起伏频率下也保持较短的相位滞后。因此，我们没有发现他们在高频使用不同的控制机制的迹象。相反，由于更快的反射路径和较低的头部惯性，头部稳定可能仍然存在。因此，蜥蜴的内在生理和神经学特征似乎足以使头部稳定在高频下，从而消除了对控制途径进行进化适应的需要。这些特性不是蜥蜴独有的，因此也可以促进其他小型快速动物的高频头部稳定。蜥蜴的内在生理和神经学特征似乎足以使其在高频下稳定，从而避免了对控制途径的进化适应。这些特性不是蜥蜴独有的，因此也可能有助于其他小型快速动物在高频下稳定头部。蜥蜴的内在生理和神经学特征似乎足以使其在高频下稳定，从而避免了对控制途径的进化适应。这些特性不是蜥蜴独有的，因此也可以促进其他小型快速动物的高频头部稳定。