Pii: S0163-6383(01)00046-7

Recent progress in understanding the adult’s postural control system comes from studying the relation between the timing of postural responses and visual motion. In this study, we sought to investigate this same relation in infants by testing the postural responses of 10 9-month-old infants sitting in a moving room. Trials were defined by the walls oscillating at different frequencies ranging from 0.2 to 0.8 Hz. In contrast to previous research with infants, we tested postural sway with multiple measures including center of pressure (COP), and head and lower back movements. The results revealed that all three measures were influenced by the driving frequency of the wall movements, but the pattern of this relation differed across measures. In particular, sway coherence between the head or lower back and room movements decreased with frequency, but sway coherence between the COP and room movements remained flat. The reasons for this pattern of results are discussed in terms of the type of control system necessary for producing postural sway to visual motion. © 2000 Elsevier Science Inc. All rights reserved.