<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:18pt"><div><span style="font-size: 13px; "><span style="color: rgb(69, 69, 69); font-family: tahoma, 'new york', times, serif; ">> Poldrack et al. [1] mention using an intersection mask to</span><br style="color: rgb(69, 69, 69); font-family: tahoma, 'new york', times, serif; "><span style="color: rgb(69, 69, 69); font-family: tahoma, 'new york', times, serif; ">> ensure they were looking at the same voxels across subjects. </span> <br></span></div><div><br></div><div><span>As a simple alternative approach, maybe you can try the intersection of </span>(1pt)-dilated masks.</div><div><br></div><div>- Rawi</div><div><br></div><div><span style="font-size: small;"><br></span><blockquote style="border-left-width: 2px; border-left-style: solid; border-left-color: rgb(16, 16, 255); margin-left: 5px; margin-top: 5px;
padding-left: 5px; "> <div style="font-family: 'times new roman', 'new york', times, serif; "> <div style="font-family: 'times new roman', 'new york', times, serif; "> <div dir="ltr"> <font face="Arial"><span style="font-size: small;"> </span><hr size="1"> <b style="font-size: 12pt; "><span style="font-weight:bold;">From:</span></b><span style="font-size: 12pt;"> J.A. Etzel <jetzel@artsci.wustl.edu></span><br> <b style="font-size: 12pt; "><span style="font-weight: bold;">To:</span></b><span style="font-size: 12pt;"> pkg-exppsy-pymvpa@lists.alioth.debian.org </span><br> <b style="font-size: 12pt; "><span style="font-weight: bold;">Sent:</span></b><span style="font-size: 12pt;"> Wednesday, January 18, 2012 5:04 PM</span><br> <b style="font-size: 12pt; "><span style="font-weight: bold;">Subject:</span></b><span style="font-size: 12pt;"> Re: [pymvpa] question about cross-subject analysis</span><br> </font> </div> <br><span style="font-size: 12pt;">
To run multiple-subjects tests I've usually converted everyone's </span><br><span style="font-size: 12pt;">functional images to a standard space first (MNI or whatever), then </span><br><span style="font-size: 12pt;">subsetted to only have voxels with non-zero variance in all subjects.</span><br><br><span style="font-size: 12pt;">This sometimes works surprisingly well and is fairly straightforward.</span><br><br><span style="font-size: 12pt;">Jo</span><br><br><br><br><span style="font-size: 12pt;">On 1/18/2012 9:30 AM, John Magnotti wrote:</span><br><span style="font-size: 12pt;">> Hi All,</span><br><span style="font-size: 12pt;">></span><br><span style="font-size: 12pt;">> I'm trying to work build a cross-subject analysis using the Haxby et</span><br><span style="font-size: 12pt;">> al data (http://data.pymvpa.org/datasets/haxby2001/). The problem is</span><br><span style="font-size: 12pt;">> that the masks for each subject don't
necessarily cover the same</span><br><span style="font-size: 12pt;">> voxels. Poldrack et al. [1] mention using an intersection mask to</span><br><span style="font-size: 12pt;">> ensure they were looking at the same voxels across subjects. Is there</span><br><span style="font-size: 12pt;">> a way to do this in PyMVPA, and should I do something like convert to</span><br><span style="font-size: 12pt;">> standard space beforehand? I could also just use the whole timeseries,</span><br><span style="font-size: 12pt;">> but I think there is still the issue of ensuring that the voxels</span><br><span style="font-size: 12pt;">> "match" across subjects, right?</span><br><span style="font-size: 12pt;">></span><br><span style="font-size: 12pt;">> Any hints or tips would be much appreciated.</span><br><span style="font-size: 12pt;">></span><br><span style="font-size: 12pt;">></span><br><span style="font-size: 12pt;">>
Thanks,</span><br><span style="font-size: 12pt;">></span><br><span style="font-size: 12pt;">> John</span><br><br><span style="font-size: 12pt;">_______________________________________________</span><br><span style="font-size: 12pt;">Pkg-ExpPsy-PyMVPA mailing list</span><br><a ymailto="mailto:Pkg-ExpPsy-PyMVPA@lists.alioth.debian.org" href="mailto:Pkg-ExpPsy-PyMVPA@lists.alioth.debian.org" style="font-size: 12pt; ">Pkg-ExpPsy-PyMVPA@lists.alioth.debian.org</a><br><span style="font-size: 12pt;">http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/pkg-exppsy-pymvpa</span><br><br><br> </div> </div> </blockquote></div> </div></body></html>