Great~, thank you William for your nice help! all the best, ping
>From: Will Penny <[log in to unmask]>
>Reply-To: Will Penny <[log in to unmask]>
>To: [log in to unmask]
>Subject: Re: [SPM] what's the meaning in the desian matrix based on SPM2?
>Date: Thu, 15 Sep 2005 12:12:34 +0100
>
>Wang Ping wrote:
>
> > Dear spmer,
> >
> > I just try to use spm2 to design matrix, and finally in the figure
> > window get the design matrix. I want to know what's the meaning of
> > something like "sn(1) trial 1*bf(1)"? I don't know the meanings of
> > sn(1) and bf(1),
>
>
>
>You can put data from multiple sessions into the same design
>matrix. sn(1) means session number 1.
>
>trial 1 is the first trial in that session. If you've specified
>4 different conditions (trial types) this index will run from
>1 to 4.
>
>bf(1) is the 1st basis function. Each trial can be modelled with
>a number of basis functions eg (1) canonical HRF, (2) temporal derivative
>(3) dispersion derivative.
>
>
>I also don't know the design orthogonality.
>
>This tells you how much correlation there is between regressors.
>
>If you have two vectors, eg columns in your design matrix, say
>x1 and x2 then the inner product between them
>
>x1^T x2 = |x1| |x2| cos theta
>
>where |x1| and |x2| are the lengths of x1 and x2 and theta
>is the angle between the vectors.
>
>See section 2.5 of
>
>http://www.fil.ion.ucl.ac.uk/~wpenny/course/matrices.ps
>
>for derivation and discussion.
>
>Two vectors are orthogonal if the inner product is 0.
>This will be the case if cos theta is 0.
>
>In SPM, if you go to Review->Design->Design matrix SPM
>will plot a matrix of cos theta's where the i,j th
>entry corresponds to the value for columns i and j.
>
>Generally, experimental designs are better if your
>columns are more orthogonal.
>
>Best,
>
>Will.
>
>
>Could
>
> > anyone tell me?
> >
> > Thanks so much!
> > Ping Wang
> >
> >
>
>--
>William D. Penny
>Wellcome Department of Imaging Neuroscience
>University College London
>12 Queen Square
>London WC1N 3BG
>
>Tel: 020 7833 7475
>FAX: 020 7813 1420
>Email: [log in to unmask]
>URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
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