Roland -
There is no problem entering categorical (eg binary) variables as parametric
modulators.
Rik
--------------------------------------------------------
DR RICHARD HENSON
MRC Cognition & Brain Sciences Unit
15 Chaucer Road, Cambridge,
CB2 2EF England
EMAIL: [log in to unmask]
URL: http://www.mrc-cbu.cam.ac.uk/~rik.henson
TEL +44 (0)1223 355 294 x522
FAX +44 (0)1223 359 062
MOB +44 (0)794 1377 345
--------------------------------------------------------
>-----Original Message-----
>From: SPM (Statistical Parametric Mapping)
>[mailto:[log in to unmask]] On Behalf Of Roland Zahn
>Sent: 06 January 2006 22:09
>To: [log in to unmask]
>Subject: [SPM] SPM5 parametric modulation of event-related fMRI
>
>
>Dear SPM experts,
>
>
>My question might be trivial to the community, but I just
>wanted to make
>sure not to get something wrong here. It concerns whether I
>can enter a
>categorical variable (nominal scale) as a "parametric
>modulation" of the
>trial-specific HRF, although it is not a continuous variable.
>
>I am using SPM5 to analyze a study using 3 different
>conditions of word
>pairs and null events.
>
>I have several psycholinguistic parameters, which I want to use as
>parametric regressors. Some as regressors of interest, some of
>no interest.
>
>Under fMRI model specification -> Data & Design -> Conditions
>
>There is the option "parametric modulation" to enter a vector
>of values
>for each trial of a given condition (say word pair type 1)
>
>I figured this was the best way to enter my parameters, since
>I want to
>test whether they interact with the HRF to a specific type of
>word pair.
>
>Most of my parametric variables are continuous and most of
>them normally
>distributed.
>
>However I have one non-parametric factor (word class, e.g. verb, noun,
>adjective, overall there are 6 different levels of this
>factor) which I
>would like to include as a confound. Each condition (word pair type)
>contains different types of words.
>
>Would it be correct to enter this categorical factor as a "parametric
>modulation" ?
>
>Thanks for any help !
>
>Best,
>Roland
>
>Roland Zahn, Dr. med.
>NIH / NINDS
>Cognitive Neuroscience Section
>Building 10, 5C206
>10 Center Drive, MSC 1440
>Bethesda, MD 20892-1440
>Tel.: (+1)-301-402-6392
>Fax.: (+1)-301-480-2909
>
>
>
>
>
|