1. Here and in the following, we comply with terminological usage in the literature on rhythm perception in referring to only the very simplest of small-integer ratios (1:1, 2:1, and 3:1) as “simple.” By contrast, we speak of 3:2, 4:3, or larger integer ratios as “(mildly) complex” rhythms. This may appear mathematically dubious; for instance, the ratio of 3:2 consists of very small integers and is mathematically simple. However, its dividend is not an integer multiple of the divisor; in other words, the quotient is not also an integer. This involves a somewhat higher degree of rhythmic complexity. For instance, 1:1, 2:1, and 3:1 are simple in that their greatest common divisor (gcd = 1) can be used as a unit of measure for interpolation-based coordination of the two durations (1:1 = xx, 2:1 = x.x, 3:1 = x.x). This property is advantageous, as it affords a metric subdivision benefit for rhythm perception (London, 2012; Martens, 2011; Repp, 2003, 2008). By contrast, a gcd-based mental plotting of a 3:2 pattern would require quintuplet subdivision (x..x.). The gcd (= 1) here is not directly suggested by any of the two sounding intervals (= 2, 3) and requires more interpolations (= 3) relative to the realized onsets (= 2); furthermore, it is more rapid relative to the rhythmic pattern. These features can be assumed to result in a drastic decrease of potential subdivision benefit for processing this rhythm.
2. The mean asynchrony did not show a significant group effect, F(3, 66) = 1.65, p = .19, ηp2 = .07, or a group-ratio interaction, F(7.98, 173.74) = 1.71, p = .10, ηp2 = .07, but we did find a small significant main effect of ratio, F(2.63, 173.74) = 8.17, p < .001, ηp2 = .11.
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