Inhibition in task switching: The reliability of the n - 2 repetition cost

The n - 2 repetition cost seen in task switching is the effect of slower response times performing a recently completed task (e.g. an ABA sequence) compared to performing a task that was not recently completed (e.g. a CBA sequence). This cost is thought to reflect cognitive inhibition of task representations and as such, the n - 2 repetition cost has begun to be used as an assessment of individual differences in inhibitory control; however, the reliability of this measure has not been investigated in a systematic manner. The current study addressed this important issue. Seventy-two participants performed three task switching paradigms; participants were also assessed on rumination traits and processing speed-measures of individual differences potentially modulating the n - 2 repetition cost. We found significant n - 2 repetition costs for each paradigm. However, split-half reliability tests revealed that this cost was not reliable at the individual-difference level. Neither rumination tendencies nor processing speed predicted this cost. We conclude that the n - 2 repetition cost is not reliable as a measure of individual differences in inhibitory control.