Frequency-dependent integration of auditory and vestibular cues for self-motion perception.

Recent evidence has shown that auditory information may be used to improve postural stability, spatial orientation, navigation, and gait, suggesting an auditory component of self-motion perception. To determine how auditory and other sensory cues integrate for self-motion perception, we measured motion perception during yaw rotations of the body and the auditory environment. Psychophysical thresholds in humans were measured over a range of frequencies (0.1-1.0 Hz) during self-rotation without spatial auditory stimuli, rotation of a sound source around a stationary listener, and self-rotation in the presence of an earth-fixed sound source. Unisensory perceptual thresholds and the combined multisensory thresholds were found to be frequency-dependent. Auditory thresholds were better at lower frequencies and vestibular thresholds were better at higher frequencies. Expressed in terms of peak angular velocity, multisensory vestibular + auditory thresholds ranged from 0.39°/s at 0.1 Hz to 0.95°/s at 1.0 Hz, and were significantly better over low frequencies than either the auditory-only (0.54°/s to 2.42°/s at 0.1 and 1.0 Hz, respectively) or vestibular-only (2.00°/s to 0.75°/s at 0.1 and 1.0 Hz, respectively) unisensory conditions. Monaurally presented auditory cues were less effective than binaural cues in lowering multisensory thresholds. Frequency independent thresholds were derived assuming that vestibular thresholds depended on a weighted combination of velocity and acceleration cues, while auditory thresholds depended on displacement and velocity cues. These results elucidate fundamental mechanisms for the contribution of audition to balance and help explain previous findings indicating its significance in tasks requiring self-orientation.