Switching tasks costs time. Allowing time to prepare reduces the cost, but usually leaves an irreducible "residual cost". Most accounts of this residual cost locate it within the responseselection stage of processing. To determine which processing stage is affected, we measured event-related potentials (ERPs) as participants performed a reading or a perceptual judgment task and examined the effect of a task-switch on early markers of lexical processing. A task cue preceding a string of blue and red letters instructed the participant either to read the letter string (for a semantic classification in Experiment 1, a lexical decision in Experiment 2), or to judge the symmetry of its color pattern. In Experiment 1, having to switch to the reading task delayed the evolution of the effect of word frequency on the reading task ERP by a substantial fraction of the effect on RT. In Experiment 2, a task switch delayed the onset of the effect of lexical status on the ERP to about the same extent that it prolonged the RT. These effects indicate an early locus of (most of) the residual switch cost: we propose that this reflects a form of task-related attentional inertia. Other findings have implications for the automaticity of lexical access: effects of frequency, lexicality and orthographic familiarity on ERPs in the symmetry task indicated involuntary but attenuated orthographic and lexical processing even when attention was focused on a non-lexical property.
3It is generally harder to switch among several cognitive tasks than to continue to perform just one. A popular way to capture at least part of this multitasking overhead in the laboratory is to conduct a reaction time (RT) experiment in which, on each of a series of trials, a stimulus is presented, and the participant must perform one of several possible tasks. On some trials the task changes, on others it does not, other things being equal. Several such "task-switching" paradigms have been developed and extensively explored over the last two decades. (For reviews see Kiesel, Steinhauser, Wendt, Falkenstein, Jost, Philipp, & Koch, 2010;Monsell, 2003;Vandierendonck, Liefooghe, & Verbruggen, 2010). The most obvious phenomenon they reveal is the substantial cost to performance of a switch of task: the average RT for a correct response is longer (and there are usually more errors) when the task changes than when it does not.The opportunity to prepare for a task before presentation of the stimulus generally reduces this switch cost, but does not eliminate it (Meiran, 1996;Rogers & Monsell, 1995). To manipulate preparation time unconfounded by the time elapsing since the previous performance of a task, task-cuing can be used (Meiran, 1996): each stimulus follows the previous response by a standard interval, and a task cue precedes the stimulus by an interval which is independently manipulated to vary preparation time. As the cue-stimulus interval (CSI) is increased from zero, the RT switch cost reduces to an asymptotic residual cost, usually reached at a CSI of bet...