 |
 |
ooops - indeed. On 10 Jun 2011, at 09:52, Mark Jenkinson wrote: > I agree, although you should use a linear contrast of [ -3 -1 1 3 ] and > not [ -2 -1 1 2 ] as the latter is not linear (there's a gap of +2 between > -1 and 1 but +1 between the others). > > All the best, > Mark > > On 10 Jun 2011, at 09:48, Stephen Smith wrote: > >> I would probably recommend option 1, as any nonlinearity of response (which you can then test for with other contrasts) will not damage the quality of the GLM fitting. >> Cheers. >> >> >> >> On 9 Jun 2011, at 11:03, Annouchka Van Impe wrote: >> >>> Dear FSL users, >>> >>> >>> I'm new to using FEAT and I have a question concerning parametric modulation. >>> >>> My subjects perform a mental rotation task according to 4 rotation angles (45°, 90°, 135°, 180°). I’m assuming that the BOLD-response goes up with higher rotation angles, seeing as the RTs increase linearly with rotation angle. >>> What would be the best way to model this parametric modulation? >>> >>> 1) Using a separate EV for each rotation angle and then specifying a contrast -2 -1 1 2 >>> 2) Using one EV for all rotation angles, and entering the RT in the 3rd column. >>> If so, should I demean the RTs? >>> 3) Using one EV for all rotation angles, and entering 1,2,3 or 4 in the 3rd column >>> 4) Using one EV for all rotation angles, and entering -2, -1, 1 or 2 in the 3rd column >>> >>> Thanks for the info. >>> >>> >>> Kind regards, >>> >>> Annouchka >>> >> >> >> --------------------------------------------------------------------------- >> Stephen M. Smith, Professor of Biomedical Engineering >> Associate Director, Oxford University FMRIB Centre >> >> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK >> +44 (0) 1865 222726 (fax 222717) >> [log in to unmask] http://www.fmrib.ox.ac.uk/~steve >> --------------------------------------------------------------------------- >> >> >> > --------------------------------------------------------------------------- Stephen M. Smith, Professor of Biomedical Engineering Associate Director, Oxford University FMRIB Centre FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK +44 (0) 1865 222726 (fax 222717) [log in to unmask] http://www.fmrib.ox.ac.uk/~steve ---------------------------------------------------------------------------