Binaural frequency-following response (FFR) to lateralization stimuli

Abstract

The cues for localization or lateralization are interaural disparities of time and intensity, and neurophysiological studies have elegantly demonstrated that lower-brain-stem neurons, in conformity with anatomical observations, are differentially sensitive to the stimulus parameters that mediate binaural phenomena. Brain-stem responses were obtained using low-frequency (500 Hz) stimuli in various combinations of interaural phase (time) and interaural phase and level presented in-concert and in-opposition through earphones. The findings show that the amplitudes and morphologies of the volume-conducted evoked FFR potentials are differentially altered as a function of time and level variables. There are significant reductions, for example, in the amplitude of the evoked responses due to interaural time differences. Furthermore, for in-concert and in-opposition time and level stimuli, the amplitude changes are distinctly different, reflecting the complex neuronal interactions at the level of the brain-stem nuclei and tracts.

Frequency-Following Response: Effects of Interaural Time and Intensity Differences

“…Figure 1 illustrates representative waveforms from one subject. The waveforms to monaural right and left stimuli, although similar, were not identical; such asymmetries have been reported previously (Ballachanda et al, 1994). The binaural response from all subjects was larger, but not by a factor of two, than either of the monaural waveforms.…”

“…The most widely studied is the auditory brainstem response (ABR), a series of waves (I-VII) evoked by brief sounds such as clicks or tone bursts that originate from neurons located caudal to the inferior colliculi (Jewett et al, 1970). The frequency-following response (FFR), another evoked potential, mimics the tonal stimulus (Marsh and Worden, 1968 ;Moushegian et al, 1973 ;Ballachanda et al, 1994) and reflects phase-locked activity from the same caudal brainstem levels (Gardi et al, 1979 ;Bledsoe and Moushegian, 1980 ;Bledsoe et al, 1982 ;Hoormann et al, 1992).…”