Early Category-Specific Cortical Activation Revealed by Visual Stimulus Inversion
Figure 4
Source distribution of the M100 Stimulus Inversion Effect.
A. Anatomically constrained source analysis (average dSPM values across subjects; n = 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 t-tests; n = 9; df = 8) at each dipole location occurring within the 70–100-ms time-window. Significant t-values at the level of p<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 t-values of 3.35 and larger (red/dark-blue) correspond to p<0.01, absolute t-values of 4.8 and larger (yellow/light blue) to p<0.001. Abbreviations: mFG = middle Fusiform Gyrus; IOG = Inferior Occipital Gyrus; LOC = Lateral Occipital Cortex; pIFG = posterior Inferior Frontal Gyrus; mOFC = medial OrbitoFrontal Cortex.