Aftereffects of Approaching and Receding Sound Sources on Postural Responses in Humans

The intersensory effects of auditory adaptation to motion have thus far been studied only in relation to visual perception, though auditory adaptation can also influence other sensory systems. We report here the first attempts to demonstrate the reaction of the postural regulatory system during and after 45-sec adaptation to an approaching and receding sound source, which was modeled in conditions of a free field using sequences of rhythmic tonal bursts of changing amplitude and frequency. A stabilometric method identified oscillations of the center of pressure in the sagittal plane during the stimulation rhythm, more marked for approach than recession. These oscillations led to increases in the length of the trajectory of the center of pressure and the mean linear speed of motion. While listening to approaching sound sources, the center of pressure was displaced in the direction of motion; during the 20 sec following the end of the stimulus, displacement in the opposite direction was seen – a typical “negative” aftereffect. These data are consistent with results from studies of postural reactions to moving visual stimuli, where “negative” effects are also observed.