We can adjust an ongoing movement to a change in the target’s position with a latency of about 100 ms, about half of the time that is needed to start a new movement in response to the same change in target position (reaction time). In this opinion paper, we discuss factors that could explain the difference in latency between initiating and adjusting a movement in response to target displacements. We consider the latency to be the sum of the durations of various stages in information processing. Many of these stages are identical for adjusting and initiating a movement; however, for movement initiation, it is essential to detect that something has changed to respond, whereas adjustments to movements can be based on updated position information without detecting that the position has changed. This explanation for the shorter latency for movement adjustments also explains why we can respond to changes that we do not detect.
Smeets and Brenner are with the Research Institute MOVE, Dept. of Human Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, Netherlands. Oostwoud Wijdenes was with the Sobell Dept. of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK, at the time of the research and is now with the Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, Netherlands.