Journal
MOTOR CONTROL
Volume 12, Issue 2, Pages 151-172Publisher
HUMAN KINETICS PUBL INC
DOI: 10.1123/mcj.12.2.151
Keywords
variability; force; synergy; Fitts's law
Categories
Funding
- NIA NIH HHS [R01 AG018751, AG-018751, R01 AG018751-07] Funding Source: Medline
- NINDS NIH HHS [R01 NS035032, NS-035032, R01 NS035032-11] Funding Source: Medline
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We explored possible effects of negative covariation among finger forces in multifinger accurate force production tasks on the classical Fitts's speed-accuracy trade-off. Healthy subjects performed cyclic force changes between pairs of targets as quickly and accurately as possible. Tasks with two force amplitudes and six ratics of force amplitude to target size were performed by each of the four fingers of the right hand and four finger combinations. There was a close to linear relation between movement time and the log-transformed ratio of target amplitude to target size across all finger combinations. There was a close to linear relation between standard deviation of force amplitude and movement time. There were no differences between the performance of either of the two radial fingers (index and middle) and the multifinger tasks. The ulnar fingers (little and ring) showed higher indices of variability and longer movement times as compared with both radial fingers and multifinger combinations. We conclude that potential effects of the negative covariation and also of the task-sharing across a set of fingers are counterbalanced by an increase in individual finger force variability in multifinger tasks as compared with single-finger tasks. The results speak in favor of a feed-forward model of multifinger synergies. They corroborate a hypothesis that multifinger synergies are created not to improve overall accuracy, but to allow the system larger flexibility, for example to deal with unexpected perturbations and concomitant tasks.
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