Permutation testing of orthogonal factorial effects in a language‐processing experiment using fMRI

Abstract

The block-paradigm of the Functional Image Analysis Contest (FIAC) dataset was analysed with the Brain Activation and Morphological Mapping software. Permutation methods in the wavelet domain were used for inference on cluster-based test statistics of orthogonal contrasts relevant to the factorial design of the study, namely: the average response across all active blocks, the main effect of speaker, the main effect of sentence, and the interaction between sentence and speaker. Extensive activation was seen with all these contrasts. In particular, different vs. same-speaker blocks produced elevated activation in bilateral regions of the superior temporal lobe and repetition suppression for linguistic materials (same vs. different-sentence blocks) in left inferior frontal regions. These are regions previously reported in the literature. Additional regions were detected in this study, perhaps due to the enhanced sensitivity of the methodology. Within-block sentence suppression was tested post-hoc by regression of an exponential decay model onto the extracted time series from the left inferior frontal gyrus, but no strong evidence of such an effect was found. The significance levels set for the activation maps are P-values at which we expect <1 false-positive cluster per image. Nominal type I error control was verified by empirical testing of a test statistic corresponding to a randomly ordered design matrix. The small size of the BOLD effect necessitates sensitive methods of detection of brain activation. Permutation methods permit the necessary flexibility to develop novel test statistics to meet this challenge.

White Matter Abnormalities in Patients With Obsessive-Compulsive Disorder and Their First-Degree Relatives

“…To assess our primary hypothesis of white matter abnormalities in OCD patients in relation to healthy comparison subjects, differences between patients and comparison subjects were estimated by fitting an analysis of variance (ANOVA) model at each voxel in standard space within the white matter mask. The null hypothesis of no difference in fractional anisotropy between patients and comparison subjects (N=30 per group) was tested with permutation at the level of three-dimensional, spatially contiguous voxel clusters, as described in detail elsewhere (41,42). For each between-group comparison, we used probability thresholds for cluster-level testing (p<0.017), adjusted such that the average number of false positive tests was <1.…”

The neuro/PsyGRID calibration experiment

“…Full details of the processing pipeline are given in the Supporting Information. In brief, following spatial and temporal correction for participant motion and removal of the global signal, a regression of the general linear model [Suckling et al, 2006] estimated the contrast of one-back and two-back working memory active task blocks versus zero-back blocks. Maps of the estimated responses, b (linear model coefficients), and standardized responses, b/SE(b), (i.e.…”

“…Maps of the estimated responses, b (linear model coefficients), and standardized responses, b/SE(b), (i.e. model coefficients divided by their standard errors; a t-statistic) were registered into MNI stereotactic space by an affine transformation maximizing the intra-cerebral correlation between the image and the ''EPI'' template (available at: http://www.fil.ion.ucl.ac.uk/spm) [Suckling et al, 2006].…”

MRI Predicts Remission at 1 Year in First-Episode Schizophrenia in Females with Larger Striato-Thalamic Volumes

“…Subsequently, voxel-wise statistical analysis of grey matter images was undertaken in Cambridge Brain Analysis [23,24,27,28] using a cluster-based approach and permutation inference with a probabilistic threshold for significance corrected for multiple comparisons by family-wise error level of p < 0.001, with less than 1 false-positive cluster. Montreal Neurological Institute co-ordinates observed were converted to Talairach co-ordinates.…”