1 2 Many aspects of human behavior are inherently rhythmic, requiring production of rhythmic 3 motor actions as well as synchronizing to rhythms in the environment. It is well-established 4 that individuals with ADHD exhibit deficits in temporal estimation and timing functions, which 5 may impact their ability to accurately produce and interact with rhythmic stimuli. In the current 6 study we seek to understand the specific aspects of rhythmic behavior that are implicated in 7 ADHD. We specifically ask whether they are attributed to imprecision in the internal 8 generation of rhythms or to reduced acuity in rhythm perception. We also test key predictions 9 of the Preferred Period Hypothesis, which suggests that both perceptual and motor rhythmic 10 behaviors are biased towards a specific personal 'default' tempo. To this end, we tested a 11 several aspects of rhythmic behavior, including spontaneous motor tapping (SMT), perceptual 12 preferences (PPT) and synchronization-continuations tapping in a broad range of rhythms, 13 from sub-second to supra-second rates. Moreover, we evaluate the intra-subject consistency of 14 rhythmic preferences, as a means for testing the reality and reliability of personal 'default-15 rhythms'. 1617 Results indicate that individuals with ADHD are primarily challenged in producing self-18 generating isochronous motor rhythms, during both spontaneous and memory-paced tapping. 19 However, they nonetheless exhibit a high degree of flexibility in synchronizing to a broad range 20 of external rhythms. These findings suggest that auditory-motor entrainment is preserved in 21 ADHD, and that the presence of an external pacer allows overcoming the inherent difficulty in 22 Some have argued that these default motor preferences also extend to the realm of auditory 64 perception. Specifically, McAuley and colleagues (2006) report a one-to-one correspondence 65 between individual SMTs and the tempo that individuals indicate is most 'comfortable' for 66 them to listen to, labeled their Preferred Perceptual Tempo (PPT). This finding prompted 67 the Preferred Period Hypothesis, suggesting that individuals have a characteristic preferred 68 rhythm, that is generalized across perception and production, and can be attributed to a 69 common internal oscillator (McAuley 2010;Michaelis et al. 2014;Provasi et al. 2014; 70 Schwartze and Kotz 2015). Moreover, according to this perspective, preferred internal rhythms 71 also influence behavior, facilitating perceptual, motor and inter-personal synchronization at 72 rhythms near one's SMT (Styns and Leman 2007;Large and Gray 2015;Zamm et al. 2015). 73 However, to date, the consistency of 'default' motor and perceptual preferences within 74 individuals and the degree to which they indeed generalize across rhythmic behaviors, has been 75 somewhat debated (van der Wel et al. 2009;McPherson et al. 2018;Qi et al. 2019). Moreover, 76 the manifestation of internal motor and perceptual rhythmic preferences in clinical populations 77 who exhibit timing-related de...