Unequal motor durations under simple-, go/no-go, and choice-RT tasks: extension of Miller and Low (2001).

The logic of the Subtraction Method is used implicitly or explicitly in a variety of work, ranging from traditional response-time research to functional neuroimaging. One assumption of all forms of the Subtraction Method is that components may be inserted (or deleted) without causing changes in the remaining components. We tested this assumption as it applies to the duration of late motor processing using the lag between the onset of lateralized readiness potential (LRP) and the production of the required response as the measure of late motor processing. In contrast to a similar, previous study that used this approach (Miller & Low, 2001), we found differences in the LRP lags across the types of task that are used in the Subtraction Method. The LRP lag for simple-RT was shorter than the lags for either go/no-go or choice-RT. This finding constitutes evidence against an assumption required by the Subtraction Method, at least as applied to component durations, but can be explained in terms of a supplementary (non-subtractive) inhibitory component that is only employed in the go/no-go task.