Contrary to our hypothesis, asymmetrical decreased gradually instead of showing an inverted U-shaped trajectory, thus revealing that it did not play a bridging role in the transition between the other two frames. Only asymmetrical patterns were influenced by the fixed effect of infant’s gender (χ2[1] = 4.02, p < .05), with girls showing greater proportional durations of this pattern selleck than boys. With respect to interindividual variability (random effect at two-level variance, Table 2), dyads differed in unilateral and symmetrical patterns, both with respect to the initial status (random intercept

effects [σ2u0], χ2[1] = 4.54, p < .05; χ2[1] = 4.66, p < .05, respectively) and the growth rate (random slopes for Deforolimus linear effects

of age [σ2u1]; χ2[1] = 4.28, p < .05; χ2[1] = 4.32, p < .05, respectively). As in Figure 2, unilateral decreased very rapidly for half of the dyads (dyads 2, 7–10) and remained high and practically unaltered for the other half. Dyads also differed with respect to symmetrical trend as shown in Figure 3; all of them were quite low at the beginning, but at around 15 months half of them (dyads 2, 7–10) increased much steeper than the other half. In both cases, the initial differences became greater as a function of time. Finally, with respect to intraindividual variance—i.e., variability owing to differences within each dyad across observations (random level 1 variance)—two significant effects were found: the linear effect of age for asymmetrical patterns (σ2e1 =0.00001, χ2[1] = 23.90, p < .01) and the covariance effect between the intercept and the linear effect of age (σ2e01 =0.00013, χ2[1] = 8.79, p < .01) for symmetrical. Therefore, the variability of the proportional duration of these two frames within dyads was a function of time. To be more precise, asymmetrical intradyadic variability showed a U-shaped relationship, indicating a maximum of variability both at the beginning (11th month) and

at the end (24th month) with a minimum variability around the 18th BCKDHB month; symmetrical intradyadic variability increased with time so that the proportional durations of symmetrical patterns differed more in the latter part of the year than in the former. This greater variability between sessions at the end compared with the beginning could signal a certain degree of systematic fluctuation for symmetrical patterns. It was not found for either unilateral or asymmetrical. The second hypothesis of the study was about the age effects on each of the three different types of symmetrical coregulation. We expected that affect and action patterns would be prevalent at an earlier age and verbal exchanges would be prevalent at the end.