Inhibition in Task Switching: The Reliability of the NN2 Repetition Cost

The n–2 repetition cost (Mayr & Keele, 2000) 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 has been well replicated (Koch, Gade, Schuch, & Philipp, 2010). As such, the n–2 repetition cost has started to be used as a measure of individual differences in inhibitory control (e.g. Whitmer & Banich, 2007); 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, alongside the Rumination Responses Scale and the Digit-Symbol substitution processing speed task — which measures 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. Neither rumination 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.