Page 35 - Like me, or else... - Michelle Achterberg

Social evaluation in childhood
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convolved with the hemodynamic response function (HRF). The onset of social feedback was modeled as the first event with a zero duration and with separate regressors for the positive, negative, and neutral peer feedback. The start of the noise blast was modeled for the length of the noise blast duration (i.e., length of button press) and with separate regressors for noise blast after positive, negative, and neutral feedback. Trials on which the participants failed to respond in time were modeled separately as covariate of no interest and were excluded from further analyses. On average 7.3% of the trials were invalid (pilot: 7.8%, test: 7.3%, replication: 6.5%), with similar proportions of positive (6.9%), neutral (7.2%) and negative (7.3%) invalid trials. All participants had at least 10 trials for each feedback type. To account for possible motion induced error that had not been solved by realignment and ARTrepair, we included six additional motion regressors (corresponding to the three translational and rotational directions) as covariates of no interest. The least squares parameter estimates of height of the best-fitting canonical HRF for each condition were used in pairwise contrasts. The pairwise comparisons resulted in subject-specific contrast images.
Higher-level group analyses
Subject-specific contrast images were used for the group analyses. Given that the all feedback > fixation baseline generally results in strong and robust activity, we validated our replication approach using this contrast (for results see Supplementary Material). Our main analyses focus on the condition specific contrasts (e.g. ‘positive vs. negative’ feedback), using t-tests. Results were False Discovery Rate (FDR) cluster corrected (pFDR<.05), with a primary voxel-wise threshold of p<.005 (uncorrected) (Woo et al., 2014). Cluster-extend based thresholding has relatively high sensitivity (Smith and Nichols, 2009) and takes into account that individual voxel activations are not independent of the activations of voxels nearby (Heller et al., 2006). We set the primary p-value at p<.005 to strike the balance between too liberal cluster defining primary thresholds (e.g. p<.01; which can induce Type I errors) and more conservative primary thresholds (e.g. p<.001; which can induce Type II errors). Recently, cluster corrections have been debated for potential high Type I errors (Eklund et al., 2016), but the current three-sample design should reduce the risk for coincidental findings. Coordinates for local maxima are reported in MNI space.
Region of Interest analyses
To extract patterns of activation in functionally defined clusters, SPM8’s MarsBaR toolbox (Brett et al., 2002) was used. Besides ROIs derived from whole brain comparisons, we also performed analyses on three predefined ROIs based on adult social evaluation literature. These were the amygdala (from the Automated Anatomical Labeling (AAL) atlas (Tzourio-Mazoyer et al., 2002), left and right combined, center of mass (x,y,z) right: 27,-1, -19; left: -24, -2, -19), the anterior
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