Visual information and the multiple time scales of isometric force control

Open Access
Lafe, Charley
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 14, 2014
Committee Members:
  • Karl Maxim Newell, Thesis Advisor
  • John Henry Challis, Thesis Advisor
  • Kristina A Neely, Thesis Advisor
  • Force variability
  • Intermittency
  • Timescales
  • Visual-motor Processing
The experiment was designed to examine the interaction between frequency of visual information feedback and force level on the control of isometric force production. Participants were asked to produce constant levels of isometric force using in separate conditions the index finger of their right hand, left hand, and both hands. Visual intermittency rates ranging from .8Hz to 25.6Hz were presented at three force levels of 15%, 30%, and 60% of the maximal voluntary contraction. There were significant effects of force level on the amount (Standard Deviation) and time dependent structure (Approximate Entropy) of force variability. Reduced intermittency of the frequency of visual feedback decreased the amount of force variability and increased the irregularity of force output. Visual information was found to have a force level dependent effect on frequency structure up to 12Hz, while spectral density was predominantly modulated within the 0 - 4Hz bandwidth. This pattern of findings for force level and intermittency remained consistent across all hand conditions. The study provides further evidence for the postulation that there are multiple timescales of isometric control that are scaled interactively by force level and visual information intermittency.