Auditory time-intensity cues in the binaural interaction component of the auditory evoked potentials

Abstract

Binaural interaction in the brainstem and middle latency auditory evoked potentials to intensity (dl) and timing differences (dT) between the two ears was studied in 10 normal hearing young adults. A component reflecting binaural interaction in the brainstem potentials occurred at approximately 7 ms and was of largest amplitude when d I and dT were 0. The latency of the binaural interaction component gradually shifted and its amplitude decreased as dl or dT increased and binaural interaction became undetectable when dI = 16 dB or when dT_> 1.6 ms. In the middle latency potentials binaural interaction components peaking at 20, 32, and 45 ms were defined that were also largest when dl and dT = 0. The latency of the interaction did not shift with changes in dT and dl whereas the amplitude gradually decreased but binaural interaction components were still evident even at the largest values of dl (30 dB) and dT (3 ms). Psychophysical judgments of binaural perceptions showed binaural fusion of the stimuli to persist with dT values up to 1.6 ms and that lateralization of the intracranial image was complete when either dT = 1.6 ms or when dl = 16 dB. The results suggest that the presence of a binaural interaction component of auditory brainstem potentials correlates with the fusion of binaural click stimuli and the amplitude of the binaural interaction component correlates inversely with the degree of lateralization of the intracranial image. Binaural interaction components of middle latency potentials persist and continue to change even after the binaural stimuli cannot be fused.

Auditory brain stem responses evoked by lateralized clicks: is lateralization extracted in the human brain stem?

“…1 point into the approximate direction of the lateralization of the stimuli. Both an ITD of 0.4 ms and an ILD of 12 dB cause a strong, but not extreme lateralization of about 70³ (Furst et al, 1985;McPherson and Starr, 1995). A stronger, almost complete lateralization is produced by the synergistic stimuli L33 and R++ whose ILDs and ITDs point into the same direction.…”

“…Brantberg et al (1999a) studied DN1 as a function of the ITD and found approximately constant amplitudes for ITDs up to 1 ms. In contrast, McPherson and Starr (1995) reported that the DN1 component gradually decreased with increasing ILD and ITD, and became undetectable for ILD s 16 dB and ITD s 1.6 ms. They stated an inverse correlation between DN1 amplitude and the psychophysical lateralization (introduced by either ILD or ITD).…”

“…This has been used in other studies to avoid ACT (Jones and van der Poel, 1990;McPherson and Starr, 1995;Brantberg et al, 1999a). Instead, following Levine (1981) and Ito et al (1988), left, right and binaural stimuli were presented randomly without contralateral masking.…”

“…Any signi¢cant deviation from BD = 0 is understood as hint to some non-linearity, i.e., a functional coupling of left and right signals. The BD was analyzed in a number of studies, often as a function of ILD and ITD (Dobie and Berlin, 1979;Dobie and Norton, 1980 ;Ainslie and Boston, 1980;Levine, 1981;Wrege and Starr, 1981;Gerull and Mrowinski, 1984;KellyBallweber and Dobie, 1984;Furst et al, 1985;Ito et al, 1988;McPherson et al, 1989;Jones and van der Poel, 1990;McPherson and Starr, 1995;Jiang, 1996 ;Cone-Wesson et al, 1997;Brantberg et al, 1999a,b). Using 2000 sweeps per stimulus condition Gerull and Mrowinski (1984) contended the null hypothesis BD = 0, i.e., that the binaural response B can be perfectly predicted by the sum of the monaural responses L+R, supporting the view of two independent channels.…”

“…It can be measured either by subjectively matching the respective lateralization produced by ILD and ITD or by trading ILD against ITD resulting in a centered image. TIRs were measured for a variety of stimuli and levels (e.g., Durlach and Colburn, 1978;Nordby et al, 1982 ;Furst et al, 1985 ;McPherson and Starr, 1995;Damaschke et al, 2000).…”