A quantitative analysis of spontaneous kicking in two-month-old infants

Abstract

Although it is generally agreed that spontaneous movements are important for the development of motor coordination in infants, the specific role of these movements is unclear. In order to elucidate this role, the synchrony between both intralimb and interlimb joints has been examined in spontaneous kicking (Thelen, 1985). In the present study, time-series analysis was used to determine cross-correlations between joints of the same and different limbs during spontaneous kicking in 7- to 8-week-old infants. In addition, phase lags between joint angles were used to examine the degree of synchrony between the joints. Phase lags are useful to determine simultaneous (in-phase) and alternating (anti-phase) kicking patterns when both legs are kicking. Results suggest that, in infants around two months of age, there are rigid intralimb couplings during spontaneous kicking but there is little evidence of coupling between the limbs. The intralimb synchrony was discussed in terms of Bernstein's (1967) notion that in the early stages of acquisition of motor tasks, rigid couplings are formed that reduce the degrees of freedom to be controlled.