# Face fMRI data¶

As another, more sophisticated example, consider the data from a repetition priming experiment performed using event-related fMRI. Briefly, this is a 2\(\times\)2 factorial study with factors “fame” and “repetition” where famous and non-famous faces were presented twice against a checkerboard baseline (for more details, see (Henson et al. 2002)). The subject was asked to make fame judgements by making key presses. There are thus four event-types of interest; first and second presentations of famous and non-famous faces, which we denote N1, N2, F1 and F2. The experimental stimuli and timings of events are shown the next two figures.

Images were acquired using continuous Echo-Planar Imaging (EPI) with
TE=40ms, TR=2s and 24 descending slices (64\(\times\)64
3\(\times\)3 mm\(^2\)), 3mm thick with a 1.5mm gap. The data archive
is available from the SPM website. This contains 351 Analyze format
functional images `sM03953_0005_*.{hdr,img}`

of dimension
64\(\times\)64\(\times\)24 with
3\(\times\)3\(\times\)4.5 mm\(^3\) voxels. A structural image
is also provided in Analyze format (`sM03953_0007.{hdr,img}`

).

To analyse the data, first create a new directory `DIR`

eg.
`C:\data\face_rep`

, in which to place the
results of your analysis. Then create 3 subdirectories (i) `jobs`

, (ii)
`categorical`

, (iii) `parametric`

and (iv) `bayesian`

. As the analysis
proceeds these directories will be filled with job-specification files,
design matrices and models estimated using classical or Bayesian methods.

As well as the classical/Bayesian distinction we will show how this data can be analysed from a parametric as well as a categorical perspective. We will look at the main effects of fame and repetition and in the parametric analysis we will look at responses as a function of “lag”, that is, the number of faces intervening between repetition of a specific face.

Start up MATLAB, enter your `jobs`

directory and type `spm fmri`

at the
MATLAB prompt. SPM will then open in fMRI mode with three windows (1)
the top-left or “Menu” window, (2) the bottom-left or “Interactive”
window and (3) the right-hand or “Graphics” window. Analysis then takes
place in three major stages (i) spatial pre-processing, (ii) model
specification, review and estimation and (iii) inference. These stages
organise the buttons in SPM’s base window.