Infants' use of multisensory information for postural control

Two measures were used to assess to what extent infant's head position was affected by the movements of the apparatus: cross-correlations and fast Fourier transforms (FFTs). Cross-correlations can indicate to what degree the head movements follow the sinusoidal movements of the apparatus and whether the infants' head movements display a systematic reactive or predictive pattern in relation to the machine's movements (the lag). FFTs on the other hand can display in how far the head movements adopt the same frequency (0.25 Hz) as the seat and/or the wall, regardless of the shape of the movement profile of the head and regardless of the lag.