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The contrast [1 1] makes no sense. It's the average of the slope estimate and the mean estimate. For your question, you need a conjunction of the two contrasts. Additionally, make sure you mean center your covariate, otherwise the group term will represent the value when the covariate is 0. Best Regards, Donald McLaren ================= D.G. McLaren, Ph.D. Research Fellow, Department of Neurology, Massachusetts General Hospital and Harvard Medical School Postdoctoral Research Fellow, GRECC, Bedford VA Website: http://www.martinos.org/~mclaren Office: (773) 406-2464 ===================== This e-mail contains CONFIDENTIAL INFORMATION which may contain PROTECTED HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is intended only for the use of the individual or entity named above. If the reader of the e-mail is not the intended recipient or the employee or agent responsible for delivering it to the intended recipient, you are hereby notified that you are in possession of confidential and privileged information. Any unauthorized use, disclosure, copying or the taking of any action in reliance on the contents of this information is strictly prohibited and may be unlawful. If you have received this e-mail unintentionally, please immediately notify the sender via telephone at (773) 406-2464 or email. On Thu, Sep 25, 2014 at 6:21 AM, Robin Shao <[log in to unmask]> wrote: > Dear all, > > I have a maybe basic question about 2nd-level ttest with covariate. > Suppose I assess a contrast A and a covariate B with a 1-sample t-test, so > my design matrix will consist of one column for the group contrast effect > and another column for the group variation on the covariate, and a contrast > of [1 0] gives me brain clusters activated to the contrast and [0 1] gives > me brain clusters whose activities elicited by the contrast are > significantly (and positively) modulated by the covariate. > > My question is, if I want to find areas which are both significantly > activated by the contrast and whose activities elicited by the contrast are > significantly modulated by the covariate, what is the most appropriate way? > Should I look at the 2 activation maps and find overlapping regions? Or if > I set the contrast as [1 1] does it give me the same (or very similar) > results? > > Thanks, > Robin >