Title
Hammering Does Not Fit Fitts' Law.
Abstract
While movement is essential to human wellbeing, we are still unable to reproduce the deftness and robustness of human movement in automatons or completely restore function to individuals with many types of motor impairment. To better understand how the human nervous system plans and controls movements, neuromechanists employ simple tasks such as upper extremity reaches and isometric force tasks. However, these simple tasks rarely consider impacts and may not capture aspects of motor control that arise from real-world complexity. Here we compared existing models of motor control with the results of a periodic targeted impact task extended from Bernstein's seminal work: hammering a nail into wood. We recorded impact forces and kinematics from 10 subjects hammering at different frequencies and with hammers with different physical properties (mass and face area). We found few statistical differences in most measures between different types of hammer, demonstrating human robustness to minor changes in dynamics. Because human motor control is thought to obey optimality principles, we also developed a feedforward optimal simulation with a neuromechanically inspired cost function that reproduces the experimental data. However, Fitts' Law, which relates movement time to distance traveled and target size, did not match our experimental data. We therefore propose a new model in which the distance moved is a logarithmic function of the time to move that yields better results (R-2 >= 0.99 compared to R-2 >= 0.88). These results support the argument that humans control movement in an optimal way, but suggest that Fitts' Law may not generalize to periodic impact tasks.
Year
DOI
Venue
2017
10.3339/fncom.2017.00045
FRONTIERS IN COMPUTATIONAL NEUROSCIENCE
Keywords
Field
DocType
motor control,biomechanics,upper extremity,optimal control,arm movement,impact,Fitts' Law
Fitts's law,Kinematics,Optimal control,Computer science,Robustness (computer science),Motor control,Hammer,Artificial intelligence,Logarithm,Feed forward
Journal
Volume
ISSN
Citations 
11
1662-5188
0
PageRank 
References 
Authors
0.34
11
4
Name
Order
Citations
PageRank
Tadej Petric117820.60
Cole S Simpson201.35
Ales Ude389885.11
Auke Jan Ijspeert43546282.93