Methods for Dummies Second level Analysis (for fMRI) Chris Hardy, Alex Fellows Expert: Guillaume Flandin Overview of todays talk 1.Recap of first level analysis 2.What is second level analysis? 3.Fixed vs. random effects 4.How do we analyse random effects? 5.Practical demonstration 6.Questions 2 Overview of todays talk 1.Recap of first level analysis 2.What is second level analysis? 3.Fixed vs. random effects 4.How do we analyse random effects? 5.Practical demonstration 6.Questions 3 4 1 st Level Analysis is within subject Y = X x + fMRI scans Time (e.g. TR = 3s) Time Voxel time course 5 fMRI dataDesign MatrixContrast Images SPM{t} Subject 1 Subject 2 Subject N 6 1 st Level Analysis Spatial preprocessing Movement in scanner Fitting to standard space (MNI) Smoothing etc for statistical power 7 Overview of todays talk 1.Recap of first level analysis 2.Second level analysis 3.Fixed vs. random effects 4.How do we analyse random effects? 5.Multiple conditions 6.Practical demonstration 7.Questions 8 RealignmentSmoothing Normalisation General linear model Statistical parametric map (SPM) Parameter estimates Design matrix Template Kernel Gaussian field theory p B) c = -1 (e.g. B>A) 38 Select options for displaying results: Correct for multiple comparisons FWE/FDR. 39 40 41 42 Summary For fMRI data, usually preferable to use RFX analysis, not FFX Hierarchical models provide gold standard for RFX, BUT computationally intensive Summary statistics = robust method for RFX group analysis 43 Overview of todays talk 1.Recap of first level analysis 2.What is second level analysis? 3.Fixed vs. random effects 4.How do we analyse random effects? 5.Practical demonstration 6.Questions 44 Resources Previous MfD slides (Bex Bond and Samira Kazan) (Camilla Clark and Cat Slattery) Slides from Guillaume Flandins talk in Zurich, Feb 2014 Mumford, J. A., & Poldrack, R. A. (2007). Modeling group fMRI data. Social cognitive and affective neuroscience, 2(3), Friston, K. J., Stephan, K. E., Lund, T. E., Morcom, A., & Kiebel, S. (2005). Mixed-effects and fMRI studies. Neuroimage, 24(1),