Simultaneous recording of brain responses indicating sensation and perception of changes in interaural phase differences

Abstract

Changing the interaural phase difference (IPD) between binaurally presented tones induces the sensation of a change of the sound source in space and elicits auditory brain responses specific for sound localization. We recorded neuromagnetic responses to IPD changes in young, middle-aged, and older listeners at various tonal frequencies. Young listeners showed brain responses below 1500 Hz according to the behavioral findings of using IPD for sound localization at low frequencies only. The upper limit for IPD detection decreased with age, and older listeners (mean age of 71 years) could make use of IPD changes only for tonal sounds below 750 Hz. The stimuli were amplitude modulated at 40 Hz and elicited synchronized brain activity at the rhythm of the amplitude modulation. Thus, 40-Hz brain activity was recorded simultaneously with the IPD change responses. Although the amplitude modulation as continuous and specifically did not change the interaural phase relation, the 40-Hz brain response was reset at the IPD change. We interpret the 40-Hz brain responses as related to sensory binding for perception. Each change in the auditory environment requires a reset and reconfiguration of the binding network, which can be observed in the reset of 40-Hz brain oscillations. Recording simultaneously brain responses to sensation and perception of IPD changes gives insight into the temporal dynamics of binaural auditory processing.