Are temporal response features prepared in fixed order? Inferences from movement-related potentials.

Using a response precuing task, we investigated whether motor preparation of temporal response features follows a fixed order as implied by the generalized motor program (GMP) view. Relative timing and overall duration of sequential key presses were factorially manipulated. Precues either provided no information, provided partial information about relative or overall duration, or fully specified the response. Reaction time decreased with the amount of advance information, reflecting the reduction of response alternatives by the precue and influences on preparatory motor processes. The contingent negative variation (CNV) over the left but not the medial and right motor regions increased with the amount of advance information provided. The foreperiod lateralized readiness potential indicated hand-specific activation for the full precue condition only. These findings disagree with the assumption that a GMP's invariant and variable response features are prepared in fixed order.