The control parameters used by the CNS to guide the hand depend on the visuo-motor task: evidence from visually guided pointing.

To perform visually guided hand movements the visuo-motor system transforms visual information into movement parameters, invoking both central and peripheral processes. Central visuo-motor processes are active in the CNS, whereas peripheral processes are active at the neuromuscular junction. A major share of research attention regarding central visuo-motor processes concerns the question which parameters the CNS controls to guide the hand from one point to another. Findings in the literature are inconsistent. Whereas some researchers suggest that the CNS controls the hand displacement vector, others suggest that it controls final hand position. The current paper introduces a paradigm and analysis method designed to identify the parameters that the CNS controls to guide the hand. We use simulations to validate our analysis in the presence of peripheral visuo-motor noise and to estimate the level of peripheral noise in our data. Using our new tools, we show that hand movements are controlled either in terms of the hand displacement vector or in terms of final hand position, depending on the way visual information relevant for movement production is specified. Interestingly, our new analysis method reveals a difference in central visuo-motor processes, even though a traditional analysis of movement endpoint distributions does not. We estimate the level of peripheral noise in our data to be less than or equal to 40%. Based on our results we conclude that the CNS is flexible with regard to the parameters it controls to guide the hand; that spatial distributions of movement endpoints are not necessarily indicative of central visuo-motor processes; and that both peripheral and central noise has to be carefully considered in the interpretation of movement data.