Hi
> suppose I have three conditions EX1, EX2, and N and let's assume I
> define two 1st-level contrasts as '1 0 0' and '-1 0 0'.
>
Fine, though if you denote by N the 'null condition' or baseline then
note that all time series get de-meaned in FEAT prior to the analysis.
You therefore would not model this explicitly.
> (a) Is it correct that thereby I test 'EX1 > 0' and -EX1 > 0?
>
Yes, i.e. you ask where the estimated amplitude associated with the
regressor is significantly larger than zero.
> (b) If (a) is correct, what exactly does '0' stand for? Is is the
> average activation of the the whole EPI-time series?
>
because it is de-meaned the timeseries will vary around zero. If EX1
does not model any signal, the amplitude associated with the best fit
of the EVs shape into the data should be close to zero (and not
significant when tested against the level of noise).
> (c) Can I infer that EX1 leads to activatins, if I only find
> significant results for '1 0 0' and vice versa (i.e. deactivates, if
> I find only significant results in '-1 0 0')?
>
Well, this sounds as if you are asking about causal relationships? In
areas where the [1 0 0] contrast
is significantly positive there is significant correlation between the
signal in a voxel and the experimental manipulation modeled by EX1
hth
Christian
> Many thanks for any help.
>
> Best,
> -Lucas
> __________________________________________________________________________
> Verschicken Sie SMS direkt vom Postfach aus - in alle deutschen und
> viele
> ausländische Netze zum gleichen Preis!
> https://produkte.web.de/webde_sms/sms
_______________________________________________
Christian F. Beckmann, DPhil
Senior Lecturer, Clinical Neuroscience Department
Division of Neuroscience and Mental Health
Imperial College London, Hammersmith Campus
Rm 419, Burlington Danes Bldg, Du Cane Road, London W12 0NN, UK
Tel.: +44 (0)20 7594 6685 --- Fax: +44 (0)20 7594 6548
Email: [log in to unmask]
http://www.imperial.ac.uk/medicine/people/c.beckmann/
Senior Research Fellow, FMRIB Centre
University of Oxford
JR Hospital - Oxford OX3 9DU
Tel.: +44 (0)1865 222551 --- Fax: +44 (0)1865 222717
Email: [log in to unmask]
http://www.fmrib.ox.ac.uk/~beckmann
|