Perception of Interdependent Finger Forces During a Bimanual Finger Pressing Task

<b>Background:</b> Perception of force involves integrating sensory and motor signals to form an accurate percept. Since individual finger pressing inadvertently causes neighboring fingers to exert force involuntarily, intriguing is its contribution to proprioception considering the increased force feedback during the task. For instance, pressing with the middle finger often generates substantial involuntary force in the adjacent ring finger. Although prior studies have examined perception of finger forces during contralateral force-matching tasks, the influence of interdependent forces on force perception remains unknown.<b>Purpose:</b> This study examined the perception of unintentional interdependent forces in relation to voluntary efforts. <b>Research Design:</b> Experimental, within a subject study. Study Sample: Twelve right-handed participants without neurological and orthopedic impairments. <b>Data Collection and/or Analysis:</b> All participants performed bilateral finger-pressing tasks, producing a target force with their middle finger (reference hand) while generating an interdependent force with their ring finger. Subsequently, they matched this involuntary ring-finger force using their contralateral hand. We hypothesized that perception of interdependent forces would be less accurate than voluntary forces due to weaker coupling between motor commands and sensory feedback (efferent copy). Additionally, we expected that matching responses would reflect a bias toward the sum of instructed and interdependent forces rather than the interdependent force alone, and that variability would be greater in the absence of visual feedback.<b>Results:</b> Perception of interdependent forces was significantly less accurate, and matching accuracy improved when participants matched the summed force. Variability was notably higher without visual feedback, while visual cues reduced variability in the reference hand. <b>Conclusions:</b> These findings clarify how unintentional forces influence perception in tasks that involve multiple interdependent fingers. Unintentinal interdependent forces impair perceptual accuracy compared to voluntary forces, likely due to weaker coupling between motor commands and sensory feedback. Perceptual judgements appear biased toward the total generated force rather than isolated independent components.