Modality and Direction-Location Coherence of Instructions Modulate Long-Latency Reflex Amplitudes
E. Shushku (TU Delft - Mechanical Engineering)
W Mugge – Mentor (TU Delft - Biomechatronics & Human-Machine Control)
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Abstract
Stable upper limb movements are essential for tasks, and the sensorimotor system utilizes the stretch reflex and voluntary control to counter unexpected mechanical perturbations, ensuring skilled motor behaviour. The stretch reflex is composed of two distinctive components, the short-latency (SLR) and long-latency (LLR) responses. Given their unique modulation and the mysterious neural circuitry underlying them, much remains to be discovered about LLRs. The task dependency of the long-latency response has been a focus of research since its discovery, though further exploration of the impact of a broader range of instruction characteristics is still needed. To tackle this gap in LLR research, this study investigated how changes in instruction modality and coherence of instruction direction and location influenced the LLR amplitude. An experimental paradigm with two identical tasks was designed, where subjects were instructed to reach a target visually or audibly. Furthermore, both logical and conflicting instructions were used. Mechanical countering perturbations were applied to the subjects, eliciting stretch reflexes. It is hypothesized that the LLR response amplitude estimate will show dependency on the varying instruction characteristics. The results revealed new insights into the relationship between LLRs and their dependence on task instructions. LLR amplitude estimations revealed differences between modalities. The effect of instruction coherence was not present in both modalities. The findings of this study suggest that changes in response time between modalities lead to discrepancies in LLR amplitudes. Also, the effect instruction logic and clarity have on subject confidence influences reaction times and intent, leading to differences in LLR strength. The differences in neural pathways that localize, recognize and then transform stimuli to perceptual information are seen as new potential contributors to the long-latency stretch component.