Proprioceptive influences on directional hearing: dependence on the movement type

Proprioceptive effects (PE) on directional hearing, i.e., sound image shifts relatively to the sound source, produced by changes in head position, were studied in their dependence on head movement type in two groups of listeners. The first group included subjects in whom horizontal head deviation to the right or to the left, performed on instruction before the presentation of clicks, caused sound image displacement of 10-15 degrees. When the same sounds were made signals of movement direction, i.e., of pointing with the head at the sound source, PE became fully inhibited in all subjects. The second group included listeners in whom PE was either absent or only very small; substitution of passive head deviations for active turns resulted (in 63 percent of cases) in PEs which presumably had been previously inhibited. Thus identical muscle activities play different roles in auditory spatial perception depending on the type of movement and on the significance of the acoustic signal for the motor act.