Spatiotemporal cluster analysis of cortical current estimates.

<p>Results of the spatiotemporal cluster analysis on the cortical current estimates data for Face and Body perception, visualized on the inflated cortical surface. Columns represent different time windows, rows represent different contrasts. Each cell displays both the spatial and temporal extent of each cluster. The visualization of the inflated cortical surface is equivalent to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0071408#pone-0071408-g003" target="_blank">Figure 3</a> (see figure legend 3D), with left hemisphere on the left and right hemisphere on the right. The graphs below the cortical maps represent the temporal courses of the size of each cluster (in number of dipoles) and their p-value, in the left and right hemisphere. In the case of multiple clusters, the red, blue and green colors indicate corresponding clusters in the cortical map (circles) and time course. <b>A</b>. <i>Body Sensitivity</i> was analysed with the contrast Bodies>Scrambled Bodies (<i>n</i> = 10, one-sided, <i>α</i> = 0.05). <b>B</b>. <i>Face sensitivity</i> was analysed with the contrast Faces>Scrambled Faces (<i>n</i> = 10, one-sided, <i>α</i> = 0.05). <b>C</b>. Body and face selectivity was analysed by directly contrasting Bodies with Faces (<i>n</i> = 10, two-sided, <i>α</i> = 0.025 for each side). Clusters with preferred responses to Bodies are indicated in yellow/red; clusters with preferred responses to Faces in blue.</p

Category-specific cortical distribution of the M100 Inversion Effect.

<p>A. Overview of the cortical distribution of the Inversion Effect for the M100 component for the three different stimulus categories. The three <i>t</i>-maps of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003503#pone-0003503-g004" target="_blank">figure 4</a> were combined into a single map. Dipole positions at which the Inverted stimuli induced significantly (<i>p</i><0.01) larger currents than their canonical Upright presentation within the 70–100-ms time-window are color-coded according to stimulus category and their spatial overlap as displayed in panel C. B. Bar graph displaying the number of dipoles showing a significant Inversion Effect for Faces, Bodies and Houses. Within each stimulus category the color (color coding as in C) indicates the degree of category-specificity, i.e. the amount of spatial (non-)overlap with the other categories. The amount of spatial overlap between categories is small (see also panel C for the exact number of dipoles). C. Color coding of stimulus category and their spatial overlap as used in panels A and B, with the exact number of dipoles showing a significant Inversion Effect.</p

Examples of Stimuli and Experimental Trial.

<p>A. Examples of the nine stimulus conditions. Photographs of Faces, Bodies and Houses were presented in three different ways: Upright, Inverted, and after phase-Scrambling. B. Example of an experimental trial. Stimuli were presented for 250-ms in random order, and after a delay of 500-ms subjects had to judge by button press whether the pictures were Upright, Inverted, or Scrambled.</p

Global measures of MEG activity.

<p>A, B. The grand average (<i>n</i> = 9 subjects) of the Mean Global Field Power (MGFP) of the magnetometers (A) and gradiometers (B) showed a significant Inversion Effect for Faces only, i.e. around 170 ms. C. Source analysis (anatomically constrained MNE) revealed an early global Inversion Effect around 85-ms latency for all three stimulus categories with a larger mean overall ( = whole cortex) dipole strength for the Inverted stimuli than for the Upright stimuli. The time samples at which significant Inversion Effects occur (<i>p</i><0.05; paired <i>t</i>-tests, <i>n</i> = 9, <i>df</i> = 8) are indicated by horizontal bars with color corresponding to category (Faces = yellow; Bodies = red; Houses = blue).</p

Visually evoked magnetic fields to Upright and Inverted Stimuli.

<p>Visually evoked magnetic fields to Upright (blue) and Inverted (red) Faces, Bodies, and Houses recorded at a typical posterior planar gradiometer (MEG2123) in a representative individual. The early response peaked around ∼100-ms after picture onset, and is clearly smaller for Upright Faces as compared to Inverted Faces. Note the different vertical scale for Bodies as compared to Faces and Houses. Displayed on the right are the corresponding topographic distributions of the evoked fields at 85-ms latency for the Upright and Inverted conditions and for the Upright-Inverted difference-wave, as seen from the back and the right side of the helmet.</p

Source distribution of the M100 Stimulus Inversion Effect.

<p>A. Anatomically constrained source analysis (average dSPM values across subjects; <i>n</i> = 9) for Upright (top trace) and Inverted Faces (bottom trace) from 70–100-ms after stimulus onset visualized on the inflated cortical surface (gyri appear in light grey, sulci in dark grey). For each time-instant, four different views are presented to depict the whole cortical surface, with left hemisphere on the left and right hemisphere on the right of each quadruplet. The two top images of each quadruplet show the lateral aspects of the brain and a little strip of the ventral aspect (lateral view, 11° tilted towards the bottom view); the two bottom images show the medial and ventral aspects of the brain (medial view, 45° tilted towards bottom view). Only values of dSPM>2.5 are visualized. A grey opaque mask was placed over the midbrain. B. Differential activation related to the Inversion Effects, i.e. the contrast between the Upright and Inverted condition of Faces, Bodies and Houses. Displayed are the largest positive or negative t-values (two-tailed paired <i>t</i>-tests; <i>n</i> = 9; <i>df</i> = 8) at each dipole location occurring within the 70–100-ms time-window. Significant t-values at the level of <i>p</i><0.01 are thresholded with respect to baseline noise and visualized only if the dipole strength exceeds a signal-to-noise ratio of 2.5 (i.e. dSPM>2.5) in at least one of the single stimulus conditions. The red and yellow colors denote locations at which the dipole strength is stronger for Upright than for Inverted stimuli. Blue colors denote locations in which the dipole strength is stronger for the Inverted stimuli. Absolute <i>t</i>-values of 3.35 and larger (red/dark-blue) correspond to <i>p</i><0.01, absolute <i>t</i>-values of 4.8 and larger (yellow/light blue) to <i>p</i><0.001. Abbreviations: mFG = middle Fusiform Gyrus; IOG = Inferior Occipital Gyrus; LOC = Lateral Occipital Cortex; pIFG = posterior Inferior Frontal Gyrus; mOFC = medial OrbitoFrontal Cortex.</p

Cortical source distribution during face and body perception.

<p>Group (n = 10 subjects) results of the anatomically constrained distributed source analysis (dSPM) for Face and Body perception, visualized on the inflated cortical surface at different time instants. The first column shows the source distribution at the latency of the M140 peak response in the lateral posterior sensors (135 ms for Faces, 145 ms for Bodies). The second, third and fourth column show the source distribution at the latencies of GFP maxima for bodies at 250 ms, 400 ms and 550 ms. <b>A</b> The dSPM values for the evoked responses elicited by intact Bodies (top row) and Faces (bottom). <b>B</b>. Folded cortical maps and their corresponding inflated cortical curvature maps. Gyri and sulci are indicated in light and dark gray respectively. Both the lateral and medial surfaces are rotated towards the ventral view (11° tilted and 45° tilted respectively) to enable the depiction of the entire cerebral cortex in one quadruplet of surfaces. Major sulci are marked in the inflated maps as anatomical reference points. CS = central sulcus; STS = superior temporal gyrus; COS = collateral sulcus; CCS = calcarine sulcus.</p

Time courses of MEG source estimates in anatomical regions of interest from the right hemisphere.

<p>Grand average (<i>n</i> = 10 subjects) time courses of the mean estimated current strength (thick lines) for intact (solid lines) Faces (blue), Bodies (red) and Houses (green) and their Fourier-scrambled versions (dashed lines), extracted from several large anatomical cortical regions. The thin line curves show the corresponding <i>t</i>-values for planned comparisons. The dotted black horizontal lines indicate the t-thresholds that correspond to <i>α</i>-values of 0.05, 0.01 and 0.001. <b>A</b>. <i>Category sensitivity</i>: The thin lines display the <i>t</i>-values for the contrasts between each intact stimulus category and its own scrambled counterpart (paired t-tests, one-sided, <i>n</i> = 10 subjects, <i>df</i> = 9) in blue (Faces>Scrambled Faces), red (Bodies>Scrambled Bodies) and green (Houses>Scrambled Houses). The dotted black horizontal lines indicate the <i>t</i>-thresholds that correspond to p-values of 0.05, 0.01 and 0.001. <b>B</b>. <i>Category selectivity</i>: The thin lines represent the t-values for the following contrasts: Faces>Bodies (blue solid line), Faces>Houses (blue dotted line), Bodies>Faces (red solid line) and Bodies>Houses (red dotted line). The contrasts were tested two-sided (<i>n</i> = 10, <i>df</i> = 9), but only one side is presented in the graph. Consequently, the p-values correspond to <i>α</i>/2. The dotted black horizontal lines indicate the t-thresholds that correspond to <i>p</i>-values of 0.025, 0.005 and 0.0005. Note that the vertical scales on the left axis for mne-values, and on the right axis for the <i>t</i>-values vary between graphs.</p