Participants estimated proficiency on a scale from 1 (“not at all proficient: you can barely speak the language”) to 7 (“very proficient: you can speak the language like a native speaker”) for each language. We used the proficiency estimate also used by Ameel et al. (2005) for reasons of comparability. Moreover, this type of self-report measures have been shown to correspond well with performance measures of proficiency such as reaction times (Dufour and Kroll, 1995; Kroll et al., 2002). The mean French proficiency estimate of the Dutch monolinguals was 2.88 (SD 0.98), and the mean Dutch proficiency estimate of the French monolinguals was 1.80 (SD 1.32). The mean estimates for the bilingual participants were 6.35 (SD 0.84) for Dutch and 5.52 (SD 0.84) for French. Eight out of 30 participants indicated an equal degree of proficiency in both languages and are therefore considered balanced bilinguals. Of the remaining 22 participants, 19 indicate a higher level of proficiency in Dutch and three participants indicated a higher level of proficiency in French. As a group, the bilingual participants indicated a significantly higher degree of proficiency in Dutch than French, t(29) = 3.40, p < 0.01. The bilinguals also indicated a significantly lower degree of proficiency in both languages as compared to monolingual participants, t(39.18) = -2.96, p < 0.01 and t(41.78) = -8.17, p < 0.001, for Dutch and French, respectively. The characteristics of the participants in the original study are very comparable. The bilingual participants consisted of 25 people with a Dutch-speaking father and a French-speaking mother (14 out of 25) or vice versa (11 out of 25). The mean proficiency estimates in their two languages were also very high: 5.7 for French (SD 0.64) and 6.5 for Dutch (SD 0.74). The estimates for the non-native language of the monolinguals were 2.8 (SD 0.83) for the French competence of Dutch speaking monolinguals and 1.3 (SD 0.65) for the Dutch competence of the French-speaking monolinguals.