Dear Gemma,

That function is really simple minded, it takes a scalp x time image and extracts all time values from a particular point on the scalp. You give it the image and coordinates for that point. You can find out the coordinates by opening the image in Display/image clicking on the scalp map and looking at the first two numbers where it says 'mm:' Yes, you just get the waveform and you should process it yourself in Matlab or Excel. Now what those waveforms mean depends on you and the image you provide. If you have a regressor per condition then providing the beta images for those regressors will give you something like condition-specific average (maybe not exactly depends what else is in the design matrix). If you have a con image then it will possibly be difference between conditions etc. So the burden of interpretation is on you in this case.

Best,

Vladimir

On Tue, Feb 26, 2013 at 3:16 PM, Gemma Barnacle <[log in to unmask]> wrote:

Hi Vladimir,

Last year you sent me a reply through the SPM mailing list regarding how to extract a time course from a scalp x time image (function Y = spm_eeg_img2timecourse(xyz)). I didn't come to use this function at the time but would like to use it now, but need a little clarification:

1. When I run the command it asks for an input image. Please can you clarify which image should be input here? (I had assumed that this meant an image from the ANOVA I had computed, but wasn't sure which to select from the beta / ess / spmF images? I have been using the beta files so far...)

2. After selecting an image I am prompted to enter scalp coordinates (N x 2). I understand from the spm_eeg_img2timecourse script that these should be in mm. Please can you clarify which coordinates need to be input? (I had assumed that it was the coordinates of the significant clusters generated from the ANOVA?)

Following my assumptions (above) spm gives me an output of 139 data points (as expected based on my sampling rate and epoch time). I have plotted these points (using excel) and get what looks like an ERP.

3. Is this the intended use for this output or can I plot these points using spm?

4. This only generates one data output (one ERP if I am correct) but I would like to extract the time course of the separate conditions so that I can compare results from my experimental manipulations. Is it possible to extract time courses relating to particular conditions?

Thanks for your help,

Gemma.

Miss Gemma Barnacle

PhD Student

School of Psychology

Room 119, Zochonis Building

University of Manchester

M13 9PL.