We used a modied version of the “roving standard” frequency paradigm also described in Baldeweg et al. (2004) and Costa-Faidella
et al. (2011a). Trains of three, twelve, and 24 equal tones were randomly
delivered at a constant stimulus-onset-asynchrony (SOA) of 500 ms,
with no inter-train pauses (Fig. 1). In total, 198 trains of three, twelve,
and 24 tone repetitions were delivered, which resulted in threefold
stimuli from 1st to 3rd positions, and twofold stimuli from 4th to 12th