Spatial processing in human auditory cortex: The effects of 3D, ITD, and ILD stimulation techniques

Abstract

Here, the perception of auditory spatial information as indexed by behavioral measures is linked to brain dynamics as reflected by the N1m response recorded with whole-head magnetoencephalography (MEG). Broadband noise stimuli with realistic spatial cues corresponding to eight direction angles in the horizontal plane were constructed via custom-made, individualized binaural recordings (BAR) and generic head-related transfer functions (HRTF). For comparison purposes, stimuli with impoverished acoustical cues were created via interaural time and level differences (ITDs and ILDs) and their combinations. MEG recordings in ten subjects revealed that the amplitude and the latency of the N1m exhibits directional tuning to sound location, with the amplitude of the right-hemispheric N1m being particularly sensitive to the amount of spatial cues in the stimuli. The BAR, HRTF, and combined ITD + ILD stimuli resulted both in a larger dynamic range and in a more systematic distribution of the N1m amplitude across stimulus angle than did the ITD or ILD stimuli alone. Further, the righthemispheric source loci of the N1m responses for the BAR and HRTF stimuli were anterior to those for the ITD and ILD stimuli. In behavioral tests, we measured the ability of the subjects to localize BAR and HRTF stimuli in terms of azimuthal error and front-back confusions. We found that behavioral performance correlated positively with the amplitude of the N1m. Thus, the activity taking place already in the auditory cortex predicts behavioral sound detection of spatial stimuli, and the amount of spatial cues embedded in the signal are reflected in the activity of this brain area. D

Neuronal representations of distance in human auditory cortex

“…Previous neurophysiological (8,11) and human neuroimaging studies (43,44) generally suggest that nonprimary regions, including PT/posterior STG, process progressively more complex sounds than the primary "core" regions of auditory cortex. These observations are in line with a previous MEG study (45) that systematically compared activations to individual and combined 3D sound features, and showed that ILD alone is not sufficient for producing direction-specific activations at the cortical level. It is also worth noting that in humans, no consistent evidence on ILD-specific fMRI activations in PT/posterior STG exists.…”

Neurophysiological Correlate of Binaural Auditory Filter Bandwidth and Localization Performance Studied by Auditory Evoked Fields

“…The main effect of the ITDs was significant (P < 0.005). This result is consistent with previous findings Sams et al, 1993;Palomäki et al, 2005). The main effect of the hemispheres on the N1m amplitude was not significant.…”

“…That is, ipsilaterally localized stimuli produced shorter latencies in the case of right-leading stimuli. This result is consistent with previous findings (McEvoy et al, 1994;Palomäki et al, 2005). Figures 11 show the N1m amplitude as a function of ITD.…”

Lateralization and Binaural Interaction of Middle-Latency and Late-Brainstem Components of the Auditory Evoked Response

“…Whether such functional neuroanatomical gradients nevertheless result in lateralized MLRs remains unclear. Although it is well established that later components of the auditory evoked response-especially the N1-can be lateralized in response to both monaural (Scherg and Von Cramon 1986;Woldorff et al 1999;Hine and Debener 2007;Königs and Gutschalk 2012) and lateralized binaural (McEvoy et al 1993;McEvoy et al 1994;Palomäki et al 2005;Johnson and Hautus 2010;Königs and Gutschalk 2012) stimuli, previous studies examining the MLR are inconclusive. While some have reported balance for monaural stimulation (Peters and Mendel 1974;Scherg and Von Cramon 1986;Kileny et al 1987;Jacobson and Grayson 1988), others have indicated varying degrees of contralateral dominance for the N19 (Woods and Clayworth 1985), the N19-P30 pair (Woods et al 1987), the P30 and P50 , or the P50-N100 pair (Pantev et al 1986), but not for binaural stimuli lateralized by interaural time differences (ITDs) (McEvoy et al 1994).…”