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Hi - this sounds reasonable, yes. Cheers, Steve. On Sat, 4 Sep 2004, Francois Lalonde wrote: > Hello Everyone, > > My question is similar to the one that Jack Grinband asked a few days ago > but with an added condition. > > I have a block design with three conditions and rest periods between trials. > This is a visual memory task in which subjects memorize a pattern and, > after a short delay, have to decide whether a second pattern is either the > same or different as the first. The first pattern is preceeded by an > instruction to study and the second pattern is preceeded by an instruction > to recall. For this analysis the entire sequence of study, pattern, recall, > pattern is considered as a single trial. The conditions are as follows: > > The first condition called "easy memory" follows the sequence decribed above > with an easily memorized pattern. > > The second condition called "hard memory" follows the same sequence but with > a more complex pattern. > > The third condition called "no memory" follows the same sequence but the > instructions have changed. Instead of studying the pattern subjects are > instructed to "look" at the pattern and instead of the word "recall" > subjects are given the correct answer to the following pattern. Subjects > are familiarized with the task prior to scanning and reaction times support > the assumption that they are, in fact, not making the effort to remember > during the "no memory" trials. > > If we consider the order of the conditions as no memory, easy memory, and > hard memory then, following Christian Beckman's recommendation, there should > be one regressor equal to 1 whenever a pattern or instruction is present > (1,1,1). Another regressor whenever subjects have to memorize (0,1,1) and > finally a contrast to differentiate between the 2 memory conditions (0,-1,1). > > Any feedback would be greatly appreciated. > > Francois > Stephen M. Smith DPhil Associate Director, FMRIB and Analysis Research Coordinator Oxford University Centre for Functional MRI of the Brain John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK +44 (0) 1865 222726 (fax 222717) [log in to unmask] http://www.fmrib.ox.ac.uk/~steve