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1 st -level analysis: Basis Functions, Parametric Modulation and Correlated Regressors

1 st -level analysis: Basis Functions, Parametric Modulation and Correlated Regressors. Sam Ereira Methods for Dummies 13 th January 2016. Basis Functions. The canonical HRF. Basis Functions.

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1 st -level analysis: Basis Functions, Parametric Modulation and Correlated Regressors

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  1. 1st-level analysis: Basis Functions, Parametric Modulation and Correlated Regressors Sam Ereira Methods for Dummies 13th January 2016

  2. Basis Functions The canonical HRF

  3. Basis Functions • Using a model to deconvolve a signal composed of successive HRFs, to estimate the structure of a single HRF. • The model that we use is composed of many temporal basis functions

  4. The General Linear (convolution) Model Basis Functions Convolution Downsample Design Matrix

  5. Basis Functions • SPM offers several options of temporal basis functions which differ in the following ways • How flexible they are • How much they offer in terms of biological interpretability • Fourier Set • Finite Impulse response • Gamma Functions • Informed Basis Set

  6. Basis Functions Fourier Set Finite Impulse Response

  7. Basis Functions Gamma Functions

  8. Basis Functions Informed Basis Set

  9. Time (scans) Regressors: 1 2 3 4 mean Parametric Modulation Factorial Design

  10. Time (scans) Time (scans) Regressors: press force mean Regressors: press force (force)2 mean Parametric Modulation Parametric Design

  11. Correlated Regressors If 2 parameters, A and B are correlated then the parametrically modulated regressors will also be correlated. Thus trial-by-trial changes in BOLD activation might be due to both the regressors, making it difficult to assign responsibility to one. I.e. they share descriptive variability. Image from Mumford et al. PLOS One 2015

  12. Correlated Regressors

  13. Resources • Lecture slides by Rik Hensen • http://www.fil.ion.ucl.ac.uk/spm/course/slides11-oct/08_Event_Related_fMRI.ppt • Review article by Mumford et al. • http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0126255 • Lectures by Sara Bengstsson and Christian Ruff • http://www.fil.ion.ucl.ac.uk/spm/course/video/#Design • Previous MfD Lecture slides • Special thanks to Guillaume Flandin Images from Mumford et al. PLOS One 2015

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