SURROGATION ANALYSIS REVEALS DEVELOPMENT OF DETERMINISTIC STRUCTURE IN THE CONTROL OF POSTURE
Surrogation analysis is used to identify deterministic structure in postural control, typically by comparing a characteristic measure of a data series (i.e. approximate entropy) to the same measure of a surrogate time series of that data. For surrogation, a temporally randomized time series is produced from the original, without severely altering its standard properties (i.e. mean and variance). Report of deterministic structure suggests that control is enacted by the central nervous system to regulate body position. We sought to uncover the development of this deterministic control of human posture. Center of pressure (COP) was recorded (AMTI Accusway, 200Hz) from 20 infants, throughout development of sitting proficiency. Six trials were collected at 3 developmental stages for each infant; from the earliest expression of sitting (Stage 1) to fully independent (Stage 3). Surrogates were produced using Theiler et al.’s (1992) algorithm, while approximate entropy characterized the temporal structure of each series. In cases where the ApEn values were significantly larger (Mann-Whitney comparison data v. surrogate), the presence of deterministic structure was concluded. Our results demonstrate that the control of sitting posture changes across development, supporting the theoretical perspective of optimal movement variability; that motor learning leads to a more organized structure of movement variability which allows for successful yet maximally adaptive behavior. Interestingly, the results additionally suggest that deterministic control develops differently for the AP and ML postural axes, indicating that the emergence of control of sitting in the AP direction precedes that of control in the ML direction.
Listed In: Biomechanics, Posturography,
Tagged In: Infant Sitting, Motor Development, Postural control
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