Extending the Failure-to-Engage theory of task switch costs.

Failure-to-Engage (FTE, De Jong, 2000) theory explains slowed response time after switching tasks as in part due to participants sometimes failing to prepare. Brown et al. (2006) rejected FTE because, in an alternating-runs paradigm, they did not observe fixed crossing point between response-time distributions that it predicts. We replicated these findings in a cued-task paradigm that allowed us to separately examine the effects of response-to-target interval and cue-to-target interval. These results guided an extension of FTE that was tested in a further experiment and shown to be able to accommodate the effects of the interval manipulations as well as both task and cue switching. We then apply a new modeling approach to obtain direct estimates of the probability of preparation and conclude that De Jong's insights about preparation failure provide a tractable framework that can explain aspects of all of the four major task-switching phenomena identified by Monsell (2003).

ERPs dissociate the effects of switching task sets and task cues.

Recent studies have suggested that reaction time (RT) costs associated with switching tasks do not reflect an endogenous control process of task set reconfiguration [Logan, G. D., Bundesen, C., 2003. Clever Homunculus: Is There an Endogenous Act of Control in the Explicit Task-Cuing Procedure? J. Exp. Psychol. Hum. Percept. Perform. 29 (3), 575-599]. Participants randomly switched between two simple tasks. Task was cued 600 ms prior to stimulus presentation using either a color or shape cue. A significant RT task switch cost was found when controlling for either a repeat or switch in cue category. In comparison, a switch in cue category had no effect on RT, even when examined across a cumulative distribution. Electrophysiological data revealed early cue processing effects within the first 300 ms after cue onset. However, replicating previous findings, an increased parietal positivity was found for task switch relative to task repeat trials that emerged prior to stimulus onset. This suggests that task set reconfiguration processes are activated when switching between tasks and supports the usefulness of task-switching paradigms in investigating cognitive control processes.

A critical test of the failure-to-engage theory of task switching.

When people switch between two tasks, their performance on each is worse than when they perform that task in isolation. One theory of this "switch cost" is the failure-to-engage (FTE) theory, which posits that observed responses are a simple mixture of prepared and unprepared response strategies. The probability that participants use prepared processes can be manipulated experimentally (e.g., by changing preparation time). The FTE theory is a binary mixture model and therefore makes a strong prediction about the existence of fixed points in response time distributions. We found evidence contradicting this prediction, using data from 20 participants in a standard task-switching paradigm. In this article, we examine reasons for the failure of the FTE theory, and we demonstrate that a generalized version of FTE theory accommodates our data.

Electrophysiological correlates of anticipatory task-switching processes.

Recent studies show a differential switch-related positivity emerging before a switch trial and reflecting anticipatory task-set reconfiguration processes. In this study, the switch-related positivity was examined in a cued task-switching paradigm. Cue-stimulus and response-stimulus intervals were independently manipulated to dissociate between the effects of anticipatory preparation and passive dissipation of task-set interference. Reaction time switch cost declined with increasing cue-stimulus and response-stimulus intervals, suggesting a contribution from both active preparation and passive interference processes. In cue-related difference waveforms, a switch positivity peaked around 350-400 ms and is interpreted as reflecting differential activation of task-set reconfiguration. In stimulus-related difference waveforms, a switch-related negativity is believed to indicate the role of S-R priming and response interference in task-switching.