title: Discrete bandwidth visual feedback increases structure of output as compared to continuous visual feedback in isometric force control tasks.
abstract: BACKGROUND
  Performance variability measures provide a partial picture of force control ability. Nonlinear analyses can reveal important information related to the randomness and complexity of the data, providing a more complete picture of the physiological process.
  
  
  METHODS
  We investigated the effects of visual feedback on the structure and performance of the force output from isometric force control tasks. Twelve young volunteers completed isometric force control tasks using two types of visual feedback: discrete bandwidth (+/-4% maximal voluntary contraction) and continuous line matching. We determined force signal variability (standard deviation), self-similarity (fractal dimension), and complexity (approximate entropy). Analyses of variance (feedback x muscle group x force level) were conducted and P values less than 0.05 were considered significant.
  
  
  RESULTS
  The force signal in discrete bandwidth feedback, compared to continuous line matching, had significantly a higher standard deviation (P=.000): 2.18 Nm (SD 1.98) vs. 0.99 Nm (SD 0.91); lower fractal dimension (P=.000): 1.07 (SD 0.04) vs. 1.16 (SD 0.04); and lower approximate entropy (P=.000): 0.12 (SD 0.07) vs. 0.26 (SD 0.09).
  
  
  CONCLUSIONS
  The greater self-similarity (lower fractal dimension) and greater regularity (lower approximate entropy) of the discrete bandwidth, compared to the continuous line matching, may indicate a process that required more kinesthetic (intrinsic) feedback to modulate force. Clinicians may choose to employ visual feedback paradigms that target the use of intrinsic feedback during rehabilitation. Discrete bandwidth feedback may be useful for delineating impairments in motor skill and measuring outcomes of intervention programs.
authors.affiliation: US Army Natick Soldier Center, 45 Kansas St. Bldg. 3, RM R307, Natick, MA 01760-5000, USA. Jeffrey.Schiffman@natick.Army.mil
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Schiffman
authors.forename: Carl W
authors.initials: CW
authors.lastname: Luchies
authors.forename: Louis
authors.initials: L
authors.lastname: Piscitelle
authors.forename: Leif
authors.initials: L
authors.lastname: Hasselquist
authors.forename: Karen N
authors.initials: KN
authors.lastname: Gregorczyk
mesh_terms: D000328:Adult; D004551:Elbow Joint / Q000502:physiology*; D005246:Feedback / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013314:Stress, Mechanical; D014785:Vision, Ocular / Q000502:physiology*