Mangalam Madhur, Conners James D, Kelty-Stephen Damian G, Singh Tarkeshwar
Department of Psychology, University of Georgia, Athens, GA, USA.
Department of Psychology, Grinelle College, Grinelle, IA, USA.
Exp Brain Res. 2019 May;237(5):1213-1226. doi: 10.1007/s00221-019-05505-2. Epub 2019 Mar 4.
The applied muscular effort to wield, hold, or balance an object shapes the medium by which action-relevant perceptual judgments (e.g., heaviness, length, width, and shape) are derived. Strikingly, the integrity of these judgments is retained over a range of exploratory conditions, a phenomenon known as perceptual invariance. For instance, judgments of length do not vary with the speed of rotation, despite the greater muscular effort required to wield objects at higher speeds. If not the amount of muscular effort alone, then what features of the neuromuscular activity implicated while wielding objects contribute to perception via dynamic touch? In the present study, we investigated how muscular activity mediates perception of heaviness and length of objects via dynamic touch. We measured EMG activity in biceps brachii and flexor carpi radialis as participants wielded objects of different moments of inertia. We found that variation in the amount of muscular effort (literally, root-mean-square values of EMG activity) predicted variations in judgments of heaviness but not length. In contrast, fluctuations in the activity of biceps brachii and flexor carpi radialis were fractal, and variation in the degree of fractality in the two muscles predicted variation in judgments of length. These findings reflect the distinct implications of dynamic touch for perception of heaviness and length. Perceptions of length can be derived from minimal effort, and muscular effort only shapes the medium from which judgments of length are derived. We discuss our findings in the context of the body as a multifractal tensegrity system, wherein perceptual judgments of length by wielding implicate, at least in part, rapidly diffusing mechanotransduction perturbations cascading across the whole body.
为了操控、握住或平衡一个物体而施加的肌肉力量塑造了一种媒介，通过这种媒介可以得出与动作相关的感知判断（例如重量、长度、宽度和形状）。令人惊讶的是，这些判断的完整性在一系列探索条件下都能得以保持，这种现象被称为感知不变性。例如，长度判断不会随旋转速度而变化，尽管以更高速度操控物体需要更大的肌肉力量。如果不是仅靠肌肉力量的大小，那么在操控物体时涉及的神经肌肉活动的哪些特征通过动态触觉有助于感知呢？在本研究中，我们调查了肌肉活动如何通过动态触觉介导对物体重量和长度的感知。当参与者操控具有不同转动惯量的物体时，我们测量了肱二头肌和桡侧腕屈肌的肌电图（EMG）活动。我们发现，肌肉力量大小的变化（确切地说是EMG活动的均方根值）预测了重量判断的变化，但没有预测长度判断的变化。相比之下，肱二头肌和桡侧腕屈肌活动的波动是分形的，并且这两块肌肉分形程度的变化预测了长度判断的变化。这些发现反映了动态触觉对重量和长度感知的不同影响。长度感知可以从最小的努力中得出，而肌肉力量只是塑造了得出长度判断的媒介。我们将在身体作为一个多分形张拉整体系统的背景下讨论我们的发现，其中通过操控对长度的感知判断至少部分涉及快速扩散的机械转导扰动在全身级联传递。
