Repeatability of magnitude production in isometric, hand-grip force estimation: a working-memory approach.

Magnitude production has been used in ergonomics research to quantify hand-grip and finger-pinch force exertions. The repeatability of this psychophysical method may be affected by a memory component if the subject must recall multiple, previously performed force exertions. This investigation tested the hypothesis that the number of different to-be-remembered hand-grip force exertions would affect the repeatability of force productions obtained via magnitude production for 12 male students. Four levels of force were examined (20%, 35%, 50%, and 65% of subject's individual maximum) at low and high memory loads (two versus four forces to be remembered concurrently). Amount of force had a significant effect on the variance among a sample of five observations; however, memory load showed no effect on the variance measure. Thus, it is concluded that four forces do not pose a significantly greater memory load than two forces for perceived force in hand-grip magnitude productions.