Differentiating errors on the basis of the distinct cognitive mechanisms that may have generated them has provided neuropsychologists with useful diagnostic tools. For example, perseverative errors arising from the inability of the patient to set a new criterion for responding are considered one of the hallmarks of cognitive inflexibility. Similarly, in the task-switching paradigm it is possible to distinguish between task-confusion errors, produced by a failure in task selection, and response-confusion errors, arising when the correct task is selected, but the wrong response is given. Nonetheless, only a few studies so far have exploited the existence of different kinds of errors in multitasking situations to inform theories of cognitive flexibility. In the present study, we set out to use a variety of methodologies employed so far in the literature for disentangling errors due to task-selection failure from errors due to task-execution failure. In three experiments, we assessed the capacity of each method to produce error categories that can be mapped as clearly as possible to the cognitive mechanism(s) underlying them using multinomial processing tree modelling. Subsequently, the distinction between task- and response-confusion errors was used to test their differential impact on inhibitory mechanisms in task switching as measured by N-2 repetition costs. Our results are encouraging regarding the possibility of correctly detecting response- and task-selection failures, thus allowing us to assess their differential impact on N-2 repetition costs.
