ROI-analysis of primary auditory cortex (BA 41) at the time of the N1 and P2.

<p>Data were collapsed for four adjacent loudspeaker positions, resulting in four data sets, each covering a range of 40 degrees (LE, left eccentric; LC, left central; RC, right central; RE, right eccentric; black arcs in the schematic view of the set-up). In the coronal and horizontal slices (MNI-template as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0025146#pone-0025146-g002" target="_blank">Fig. 2</a>), voxels of the ROI are marked in white. The plots show <i>t</i>-values as a function of sound location (error bars, standard errors across subjects), resulting from contrasts of activations with a 40-ms prestimulus period of silence for the whole ROI.</p

Peak activations of brain regions for all sound locations, as revealed by sLORETA analysis.

<p>Activations at the time of the N1 and P2 components of the responses to the sound onset were contrasted with a 40-ms prestimulus period of silence. Colour coding shows <i>t</i>-values, with statistically significant activations (<i>p</i><0.05) at <i>t</i>≥4.1 for N1 and <i>t</i>≥3.6 for P2. Data from all subjects were projected onto a single anatomical image (T2 MNI-template “Colin 27” of sLORETA). Horizontal and coronal slices were positioned at MNI <i>Z</i> and <i>X</i> coordinates as given in the figure (A, anterior; L, left; P, posterior; R, right). Data are as given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0025146#pone-0025146-t002" target="_blank">Table 2</a>.</p

Processing of left, right, central, and eccentric sound locations (all <i>p</i><0.05).

<p>Processing of left, right, central, and eccentric sound locations (all <i>p</i><0.05).</p

Locations of peak <i>t</i>-values for N1 and P2 responses to all sound positions vs. silence as revealed by sLORETA (all <i>p</i><0.01).

<p>Locations of peak <i>t</i>-values for N1 and P2 responses to all sound positions vs. silence as revealed by sLORETA (all <i>p</i><0.01).</p

Significant variation of activation as a function of location for six examplary areas, as revealed by different contrasts either at the time of the N1 (black bars) or at the time of the P2 (gray bars).

<p>For the voxel with maximum activation in each of the areas (coordinates taken from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0025146#pone-0025146-t003" target="_blank">Table 3</a>), the plots show the mean <i>t</i>-values as a function of sound location (error bars, standard errors across subjects), resulting from contrasts of activations with a 40-ms prestimulus period of silence (as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0025146#pone-0025146-g003" target="_blank">Figs. 3</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0025146#pone-0025146-g004" target="_blank">4</a>). Note that these <i>t</i>-values are based on statistical comparisons of the estimated current densities at a specific sound location versus baseline, whereas the images are based on comparisons between estimated current densities for different sound locations. Coordinates given in brackets indicate <i>X</i>, <i>Y</i>, <i>Z</i> MNI coordinates of the maximum activation, as are shown in horizontal slices. Areas are as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0025146#pone-0025146-t003" target="_blank">Table 3</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0025146#pone-0025146-g005" target="_blank">Fig. 5</a>.</p

Auditory-evoked potentials.

<p>(<b>A</b>) Grand-average AEPs with N1 and P2 components at a left (C3), vertex (Cz), and right (C4) electrode position, plotted as a function of time relative to sound onset for left-eccentric (LE), left-central (LC), right-central (RC), and right-eccentric (RE) ranges of sound locations. Black horizontal bars indicate stimulus duration. (<b>B</b>) Topographies for the four ranges of sound locations (LE, LC, RE, RC) at the time of N1 and P2. (<b>C</b>) Difference topographies of N1 and P2, comparing right and left sound positions, and central and eccentric sound positions. Filled circles indicate electrodes with significant differences in amplitude values (significant <i>t</i>-values according to permutation tests, all <i>p</i><0.05).</p

Experimental procedures and behavioral performance.

<p>(A) Experimental conditions. The <i>upper row</i> illustrates conditions with standard series for which the stimuli were presented in the median plane of the subject’s head, and the <i>lower row</i> illustrates conditions with standard series for which stimuli were presented laterally to the median plane of the subject’s head. The standard series (Std) was followed by a deviant (Dev) which was either craniocentric (cranDev, red) or allocentric (alloDev, blue). The angles next to the schematic heads (−12° and +12°) indicate the orientation of the head in relation to trunk median sagittal plane. The angles (−12°, +12°, +36°) adjacent to the loudspeakers and fixation targets (stars) indicate the stimulus positions. Only left to right head movements are shown. In half of the blocks, subjects had to perform right to left head orientations and the stimulation was accordingly mirror-symmetric. (B) Histogram of head positions: mean number of head positions before the deviants, averaged across subjects in one-degree-bins. Black bars indicate trials with head rotations that we deemed sufficiently accurate (within ±6°) to be included into the EEG analysis. Red bars indicate discarded trials. (C) Histogram of eye-in-head positions: mean number of eye-in-head positions at the time of deviant stimulation, averaged across subjects in one-degree-bins.</p

Event-related potentials.

<p>(A) Statistical comparisons of craniocentric deviant versus standard and the allocentric deviant versus standard with a nonparametric cluster–randomization approach (two-tailed <i>t</i>-test, corrected for multiple comparisons at a cluster-level). Only difference data from electrodes are shown that were part of a significant cluster (<i>p</i><0.05, cluster level) within the indicated period. The upper row shows significant differences between the craniocentric deviant (cranDev) and the standard (Std), and the lower row differences between the allocentric deviant (alloDev) and the standard. (B) ERP waveforms at fronto-central electrodes for the craniocentric (cranDev, left column) and allocentric deviants (alloDev, right column), and for standards (Std). Solid colored lines indicate ERPs for the deviant (red: craniocentric; blue: allocentric), black lines the standard, and dashed colored lines the difference waves between craniocentric (red) or allocentric (blue) deviants and standards. The vertical dashed gray lines indicate stimulus onset.</p

Areas related to the localization of sounds in a “cocktail-party situation”.

<p>(<b>A</b>) Activations of brain regions as revealed by the contrast of <i>“cocktail”</i>><i>“single”</i> (<i>p</i>_FWE <0.05). The contrast resulted in a major activation of auditory cortex, specifically in the planum temporale (PT). Two further small clusters in right PT and left inferior frontal gyrus (IFG) were observed. (<b>B</b>) Activation for the contrast of <i>“cocktail”</i>><i>“sequence”</i> (<i>p</i>_FWE <0.05). The only areas active with this contrast were the precuneus (PrCu) bilaterally and a small cluster in left PT.</p

Source localization.

<p>(A) sLORETA source reconstruction for the N1 component of the craniocentric deviants versus standards (measured in trials preceding the craniocentric deviants). Functional data from all subjects were projected onto the standard 3-D MNI brain template “Colin” of sLORETA. Red and yellow color coding indicates <i>t</i>-values with statistically significant activation for deviants compared to standards at <i>t</i>≥5.29; <i>p</i><0.05, corrected for multiple comparisons. (B) sLORETA source reconstruction for the craniocentric deviant compared to standards for time points with maximal MMN (mean: 182 ms). Red and yellow color coding indicates <i>t</i>-values with statistically significant activation for deviants compared to standards (<i>t</i>≥5.55; <i>p</i><0.05, corrected for multiple comparisons). Black arrows point toward significant regions in the left inferior parietal lobule. A, anterior; P, posterior; L, left; R, right. The <i>x</i>, <i>y</i>, and <i>z</i>-values indicate the position of the sagittal, coronal and horizontal slices in MNI-coordinates.</p