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SPM converts your p-value to a T-stastistic to determine the threshold - thus avoiding computing and storing all the p-values. spm_Tcdf.m could be used to get the lower tail p-value. Since you want the upper tail for positive values, you need to use 1-p. This will give you the one-tailed p-value that the test is greater than 0. You'll need to write a function to read the T-map, call spm_Tcdf function, do the subtraction, then write out the new image. Unless you plan to use the p-values outside of SPM, I don't see much value in computing and saving the p-values. 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 Sat, Oct 26, 2013 at 9:56 AM, Joćo Abrantes <[log in to unmask]>wrote: > Hello everyone, > > When I do a GLM I get the file "spmT_0001.hdr" containing the t-value for > each voxel, I want to get a file containing the p-value for each voxel how > can this be done? Using the GUI I'm able to decide a threshold for the > p-value of each voxel, which function does the GUI call when computing this > p-value? > Thanks for the help, > Joćo Abrantes > >