Reconfiguration and the bottleneck: Does task switching affect the refractory period effect?

If two stimuli are presented with a short stimulus–onset asynchrony (SOA), the response to the second stimulus is usually slower than on longer SOAs. Bottleneck theories attribute these dual-task costs, also known as the psychological refractory period (PRP) effect, to an inability for carrying out two central processes simultaneously. A delay of the second response is also observed if the instruction of the current single task is different from that of the previous single task. These costs of task switching are typically attributed to the costs of control operations. The current study investigated how task-switching costs relate to the PRP effect. In the first experiment, dual-task trials were preceded by prime tasks. In the dual task, the second task was or was not the same as the prime task. The latency of the second response was substantially reduced if the second task was primed, and the priming effect was independent of SOA. A second experiment compared the PRP effect on dual tasks with and without a task switch. Task selection was complicated by requiring the participant to vocalise a word that was compatible, incompatible, or neutral with respect to the currently relevant stimulus dimension. Again, the switch costs and the compatibility effect were constant across SOA. These experiments corroborate the conclusion of Lien, Schweickert, and Proctor (2003 Lien, M. C., Schweikert, R. and Proctor, R. W. 2003. Task switching and response correspondence in the PRP-paradigm. Journal of Experimental Psychology: Human Perception and Performance, 29: 692–712. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) that control operations involved in task switching are sensitive to capacity limitations that also give rise to the PRP effect, and show that it also applies to endogenous switch processes and ambiguous stimuli.