Human auditory steady-state responses to changes in interaural correlation.
Steady-state responses were evoked by noise stimuli that alternated between two levels of interaural correlation rho at a frequency fm. With rho alternating between +1 and 0, responses at fm dropped steeply above 4 Hz, but persisted up to 64 Hz. Two time constants of 47 and 4.4 ms with delays of 198 and 36 ms, respectively, were obtained by fitting responses to a transfer function based on symmetric exponential windows. The longer time constant, possibly reflecting cortical integration, is consistent with perceptual binaural "sluggishness". The shorter time constant may reflect running cross-correlation in the high brainstem or primary auditory cortex. Responses at 2fm peaked with an amplitude of 848+/-479 nV (fm=4 Hz). Investigation of this robust response revealed that: (1) changes in rho and lateralization evoked similar responses, suggesting a common neural origin, (2) response was most dependent on stimulus frequencies below 1000 Hz, but frequencies up to 4000 Hz also contributed, and (3) when rho alternated between [0.2-1] and 0, response amplitude varied linearly with rho, and the physiological response threshold was close to the average behavioral threshold (rho=0.31). This steady-state response may prove useful in the objective investigation of binaural hearing.