Although multilinguals select their output language with apparent facility (Costa et al. 2000; Costa & Santesteban 2004), frequently selecting one language over another in everyday life has been found to lead to processing differences between multilinguals and monolinguals (Prior & MacWhinney 2010; Bialystok & Barac 2012) — hence the hypothesis of multilingualism-induced cognitive benefits. If different types of language use modulate cognitive control, then attending to auditory input while producing verbal output — a defining feature of SI — could potentially induce further processing changes in simultaneous interpreters. One such change might concern the efficiency of EC mechanisms on which higher cognitive functions rely (Gilbert & Burgess 2008; Royall et al. 2002). Although the construct of EC has received substantial attention in the context of SI, it remains difficult to define. EC manifests itself in a multitude of actions but eludes direct measurement and encompasses a variety of subcategories of control that interact depending on task demands (Miyake et al. 2000; Miyake & Friedman 2012). Inhibitory control and the ability to shift task sets are particularly relevant to manage multi- lingual in- and output. They constitute two of three EC categories proposed by Miyake et al. (2000). As these categories can apply to verbal and non-verbal control, longitudinally comparing interpreters' to non- interpreters' performance on verbal and non-verbal tasks assumed to tap these mechanisms is of relevance for two reasons. First, this approach seems most promising to help better understand how these control mechanisms might be affected by SI as extreme language use (De Groot 2011; Hervais-Adelman et al. 2015). Second, it could shed additional light on the extent to which the implicated cognitive control mechanisms are language-specific.