See inline responses.
Best Regards, Donald McLaren
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Office: (773) 406-2464
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On Tue, Jul 12, 2011 at 2:35 AM, Karen Chan <[log in to unmask]> wrote:
> Hi all,
> I have a question. My study design is as follows:
> Memory Task
> Old words (emo, neu) + New words (not presented before)
> Subject's performance measured: hits/misses/false alarms/correct rejections
> I would like to compare hit-neu words with hit-emo words, neu words with emo words, hits vs correct rejections, & old vs new.
> I've started by specifying 6 conditions hit-neu, miss-neu, hit-emo, miss-emo, cr and fa. Note that some subjects have 0 misses.
> I've also created contrasts:
> #1 hitneu > hitemo
> #2 hitemo > hitneu
> Q1: How can I create contrasts for the comparisons hits vs cr, old vs new and neu vs emo? The problem is that when I try to create a contrast for emo vs neu by using the vector [-1 -1 1 1 0 0), it says invalid contrast. What could be the issue here?
Hard to say without seeing the design matrix. Did you put the ) at the
end? That is the only thing that I can see might be wrong. It should
> Q2: Some subjects have 0 misses (hit prob = 1). Since there are no onsets specified for the 'miss' condition, doesn't that pose a problem in the GLM?
No. It just means that you need to have different contrasts for those subjects.
> Q3: I want to compare hitneu vs hitemo (emotion is a within-subject variable). Under 2nd level analysis, should I use the one-sample t-test option or the paired-samples t-test option?
They are identical. If you have the contrast image for hitneu-hitemo,
then the one-sample will work; if you have hitneu>fix and hitemo>fix
use the paired-samples.