1038 end of the speech-tapping task, the participants provided a second measure of their spontaneous tapping rate. Finally, they tapped along with a sounded metronome (IOI = 500 ms, for approximately 30 s) to assess their tapping regularity with a regular nonverbal stimulus. To control for potential effects of the language of experi- mental instructions on subsequent tapping performance, the experimenter (a native balanced bilingual) addressed the bilingual participants in the language in which they next heard stimuli in the tapping task, switching languages in the middle of the experiment. French and English monolinguals were addressed in their native language during the entire experiment. Data analyses Tapping regularity was assessed with two measures. First, the coefficient of variation (CV, SD/mean of ITIs) was computed from the tap onsets and indicates the temporal variability adjusted for tapping rate. Second, the hierarchical level at which participants aligned their taps was determined by raters who coded the alignment of taps relative to stimulus syllables (words), a subjective coding that may reflect P-centers (Morton, Marcus, & Frankish, 1976). P-centers are defined as the psychological moment of occurrence of syllables but have no consistent acoustic correlates (Marcus, 1981). A French–English balanced bilingual coder (M.M.) first categorized each participant’s tapping trials as belonging to one of the following three categories: (1) low hierarchical level, tapping with every word (11–13 taps per utterance, aligned with every word); (2) high hierarchical level, tapping with every second word (6–8 taps per utterance, aligned with every other word) or every fourth word (4 taps per utterance, aligned with every fourth word); or (3) other cases, in which none of these patterns was observed consistently across trials. The coder determined the category for 33% of each participant’s trials in each language block. Interrater reliability was assessed by two other coders, one native speaker of English (C.P.) and one native speaker of French (P.L.), who rated the same data samples from a subset of 9 participants. The interrater agreement was 94%. Results The mean ITI was similar for English-speaking (405 ms), French-speaking (360 ms), and bilingual participants (411 ms), as well as for English stimuli (383 ms) and French stimuli (383 ms), with no interaction, all Fs < 1. A two-way repeated measures ANOVA on the temporal variability of tapping to speech, measured by the CV(ITI), indicated main effects of both stimulus language and Psychon Bull Rev (2011) 18:1035–1041 participant group, as shown in Fig. 1. All participant groups tapped less variably to English speech (mean CV = 0.27) than to French speech (mean CV = 0.32), F(1, 69) = 47.17, p < .001. The main effect of participant group indicated that French monolinguals exhibited greater tapping variability than did English monolinguals and French–English bilinguals, F(2, 69) = 3.202, p < .05. No significant interaction was found between stimulus language and participant group, F < 1. Next, we correlated the stimulus metrics shown in Table 1 with the tapping variability measures for each participant. The only acoustic variable that correlated with participants’ tapping variability was the variability of the intervocalic intervals [CV(IVI); r = .47, p < .001]. An ANOVA on these individual correlations between stimulus and tapping CVs indicated a significant effect of stimulus language, F(1, 69) = 33.05, p < .001, and an interaction of stimulus language with participant group, F(2, 69) = 3.75, p < .05. As is shown in Fig. 2, participants’ tapping variability was more strongly correlated with stimulus variability for French utterances than for English utter- ances, but this difference reached significance only for French monolinguals (Tukey post hoc HSD = 4.16, p < .05), who were less sensitive to (had lower correlations for) the temporal regularities of the English utterances. Finally, we examined the hierarchical levels at which the participants tapped. Figure 3 shows the number of partic- ipants in each group (n = 24) who tapped hierarchically on alternating stressed words (every two or four words, high hierarchical level) and those who tapped with every word (low hierarchical level), which are the predominant tapping patterns (16.6% of participants used an alternate pattern). Participants were highly consistent in the hierarchical level at which they tapped: Fewer than 10% of participants switched hierarchical levels between trials or languages. A chi-squared Fig. 1 Mean coefficient of variation (SD/mean) of intertap intervals (ITIs) by participant group and stimulus language. Error bars represent the standard error of the mean