Independence of fingertip force coordination to interference from common tasks
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The purpose of this thesis was to investigate if the integrity of object lifting and holding with one hand can be affected by the use of the other hand, by speaking out loud, or by watching a similar object being lifted by someone else. One chapter examined if the performance of one hand lifting and holding an object could be influenced by the other hand lifting another object or performing resource-heavy tasks. Results suggest that the fingertip forces of one hand experience no overflow from the other’s. The other chapter investigated how auditory processing or production could affect fingertip forces. This series of studies explored (1) if sound cues such as objects impacting on a table surface, or (2) if lexical cues of manual or lifting action such as words with lifting-relevant context, could prime the planning component of object lifting and, additionally, (3) if the production of speech can affect online force control when holding an object. Neither of the priming experiments showed any effect on planning forces. Regarding articulation, participants applied more force on the held object while speaking than when they silently read words, but context of the word showed no effect. This chapter’s findings echo those of the first’s; no significant overflow of auditory input or output, on fingertip forces. This chapter also examined the consequences of watching another person lift a variety of object sizes whilst participants were holding a similar object. They gradually decreased their grip force on the object, both when watching videos or a real person lifting similar objects. The combined results suggest that the phenomenon of action observation does not extend to physically executing force-related motor commands. Overall, this thesis discusses the findings which suggest that fingertip forces are (1) impervious to direct influence from speaking, using the other hand, and watching object lifting, as well as (2) considerably more isolated in terms of overflow than kinematic systems are.