Two Aspects of Feed-Forward Control of Action Stability: Effects of Action Speed and Unexpected Events

Research Poster Health & Life Sciences 2025 Graduate Exhibition

Presentation by Sayan De

Exhibition Number 65

Abstract

We explored two types of anticipatory synergy adjustments (ASA) during accurate four-finger total force production task. The first type is a change in the index of force-stabilizing synergy during a steady state when a person is expecting a signal to produce a quick force change, which is seen even when the signal does not come (steady-state ASA). The other type is the drop in in the synergy index prior to a planned force change starting at a known time (transient ASA). The subjects performed a task of steady force production at 10% of maximal voluntary contraction (MVC) followed by a ramp to 20% MVC over 1 s, 3 s, and as a step function (0 s). In another task, in 50% of the trials during the steady-state phase, an unexpected signal could come requiring a quick force pulse to 20% MVC (0-surprise). Inter-trial variance in the finger force space was used to quantify the index of force-stabilizing synergy within the uncontrolled manifold hypothesis. We observed significantly lower synergy index values during the steady state in the 0-ramp trials compared to the 1-ramp and 3-ramp trials. There was also larger transient ASA during the 0-ramp trials. In the 0-surprise condition, the synergy index was significantly higher compared to the 0-ramp condition whereas the transient ASA was significantly larger. The finding of transient ASA scaling is of importance for clinical studies, which commonly involve populations with slower actions, which can by itself be associated with smaller ASAs. The participants varied the sharing pattern of total force across the fingers more in the task with “surprises”. This was coupled to more attention to precision of performance, i.e., inter-trial deviations from the target as reflected in smaller variance affecting total force, possibly reflecting higher concentration on the task, which the participants perceived as more challenging compared to a similar task without surprise targets.

Importance

Our study explores how the human nervous system prepares for and responds to expected and unexpected changes during precise force production with the fingers. We identified two types of anticipatory adjustments in motor coordination: one during steady force maintenance while expecting a signal and another just before a planned force change. Notably, unexpected signals led to stronger motor adjustments and increased focus on task accuracy. These findings enhance our understanding of motor control and could inform clinical assessments of populations with slower movements, such as individuals with neurological disorders. By revealing how the brain manages motor variability, our work contributes to developing more sensitive tools for diagnosing and monitoring motor impairments.

DEI Statement

My research in motor control explores how neurological disorders like Parkinson’s disease and essential tremor affect movement coordination, with the goal of developing accessible and affordable biomarkers for early diagnosis. By focusing on populations often underserved in clinical research, my work contributes to reducing healthcare disparities. Additionally, my efforts to promote diversity in science through outreach, mentoring, and cultural events foster inclusion within academia. My research embraces the complexity of individual differences in motor function, ensuring that diverse populations are represented in scientific inquiry, ultimately aiming to improve equitable access to early diagnosis and personalized rehabilitation strategies for all individuals, regardless of socioeconomic or demographic background.