Response selection difficulty and asymmetrical costs of switching between tasks and stimuli: no evidence for an exogenous component of task-set reconfiguration.

Four task-switching experiments examined the notion of an exogenous component of task-set reconfiguration (i.e., a process needed to shift task set that is not initiated in the absence of a task-associated figuration stimulus). The authors varied the complexity and familiarity of stimulus-response (SR) mapping rules to produce differentially time-consuming reconfiguration demands. Tasks with more complex or less familiar rules did not display increased switch costs, given that stimulus repetitions were excluded from the analysis. These results do not support the idea of exogenous reconfiguration. Moreover, stimulus repetitions inflated task-switch costs and did so disproportionately for tasks with increased response selection difficulty, thereby demonstrating that insufficient control of the sequence of stimuli may yield results that mimic those predicted by exogenous reconfiguration accounts.

Task switching and backward inhibition in obsessive-compulsive disorder.

The presumed involvement of the prefrontal cortex in the pathogenesis of obsessive-compulsive disorder (OCD) has fueled growing interest in cognitive paradigms with a putative sensitivity to this brain region. Measures of inhibition and executive functioning are thought to be promising in this regard. To our knowledge, this is the first study that has investigated task switching in OCD captures an important aspect of a paradigm that executive control, namely the preparation for an upcoming task. It was speculated that task switching costs would be enhanced in OCD patients, reflecting a fundamental deficit to quickly control the stream of thoughts. In addition, the paradigm allowed the measurement of backward inhibition, that is the time costs afforded for the re-engagement of a previously irrelevant task. A sample of 40 OCD patients, 20 psychiatric controls with anxiety disorders other than OCD as well as 20 healthy controls was investigated. Contrary to expectation, task switching costs were not elevated in OCD patients. Although anxiety control patients failed to display robust backward inhibition, group comparisons did not reach significance. Implications for future research are discussed.

Task preparation and stimulus-evoked competition.

The authors investigated how task competition evoked by a stimulus that affords both a currently relevant and a temporarily irrelevant task is affected by invalid preparation, i.e., preparation for the irrelevant task. Although invalid preparation was associated with a general performance cost, effects of stimulus-cued task competition were not enhanced on invalidly prepared trials. This result suggests that either preparation activates representations different from the ones by which stimulus cuing is mediated or that stimulus processing is postponed until invalid preparation has been corrected. In addition, invalid preparation resulted in impaired performance of the respective task when it became relevant on a subsequent trial. This result is consistent with the idea that competition due to invalid preparation is countered by task-specific inhibition.

Backward inhibition as a means of sequential task-set control: evidence for reduction of task competition.

Endogenously initiated transitions between tasks are associated with inhibition of the attentional set for the task preceding the transition, as demonstrated by slowed reactions to a task most recently switched away from (U. Mayr & S. W. Keele, 2000). Using an altered methodological approach, the authors found that this backward inhibition counteracts perseverative tendencies when switching to a new task in that it selectively reduces interference exerted by the preceding task set. The reduction of interference was dependent on endogenous preparation for the new task and did not occur for unpredictable task switches or for task switches that were precued without information about the identity of the new task.