Hi Will! Thanks for your email! I have some more questions:
I redid the approach 1 and did no high pass filtering and the data did not
change for 1d...so it can't be the high pass filtering that leads to the
differences between 2d and 1d.
Then I chose NONE for the Global intensity normalization and 2d=1d (empty
brain). So I would like to redo approach 2 but somehow do the scaling
(remove Global effects). Is that possible? How can I do that?

I don't have 1a-1d in one design matrix ...I am comparing ROIs for some
regions in 1a-1d and get different results for the two approaches...

Thanks
Nadine


 Dear Nadine,
>
> I think you should choose model 1 - the fMRI option.
>
> This is because this includes high pass filtering.
>
> The simple regression does not.
>
> Without filtering your data you're unlikely to see
> strong effects.
>
> Best,
>
> Will.
>
> What i was going to write (I typed it in - so
> I thought I'd sent it anyway !):
>
> The t-values can be different in either
> the numerator or the denominator.
>
> Differences in the numerator are due to differences in
> estimated effect sizes. You should see these differences
> in the beta images or contrast images.
>
> Differences in the denominator are due to differences in
> the estimate of the variability of the effect. This is related to the
> error of the model as a whole, which is shown in the ResMS image.
>
> These differences usually arise from differences in the specified
> design matrix.
>
> If model 1 is the same as model 2 then the design matrices should look
> the same. Try imagesc(SPM.xX.X) to have a look.
>
> Its not clear to me whether or not you're including all four effects
> in a single model or whether you have four different models.
>
> Nadine Gaab wrote:
>
>> Hi Will!
>> Yes, the number of images were the same...With my last sentence I was
>> referring to the increase in t-values (see:
>>
>>>I got similar activations in 2a-2c in comparison to 1a-1c but the
>>>t-values for conditions 2a and 2b are much higher (ROI analysis).)
>>
>> Any idea why I get different results for 2a-2c?
>> I should also mention that
>> 1a and 2a had TR =6
>> 1b and 2b had TR = 2
>> 1c and 2c had TR = 16
>> Any help is appreciated
>> Thanks
>> nadine
>>
>>
>> "If we knew what it was we were doing, it would not be called research,
>> would it?"
>>
>> A. Einstein (1879-1955)
>>
>> Nadine Gaab, PhD
>>
>> Dept. of Psychology
>>
>> Stanford University
>>
>> 420 Jordan Hall
>>
>> Stanford,CA 94305-2130
>>
>> e-mail: [log in to unmask]
>>
>> http://gablab.stanford.edu/
>>
>>
>> Nadine Gaab wrote:
>>
>>>>Hello list!
>>>>
>>>>I am trying to convolve four sets of images with a "hand made"
>>>>hemodynamic
>>>>response function (covariate A-C) using a simple regression analysis
>>>>
>>>>I tried two approaches and got two different results and now I hope
>>>> that
>>>>someone can explain the differences between the approaches to me
>>>>
>>>>1) fMRI models, no conditions, one regressor (the "hand made" hr
>>>>function), applied high pass filter and furthermore I chose finite
>>>>impulse
>>>>function but thought that will not influence the design matrix since I
>>>>only have a regressor and 0 conditions (*stupid me?*)
>>>>
>>>>I used four sets
>>>>
>>>>1a) 160 images covariate A
>>>>
>>>>1b) 516 images  covariateB
>>>>
>>>>1c) 66 images covariate C
>>>>
>>>>1d) 66 images taken from 1b and covariate C
>>>>I got nice activations that fit my hypothesis in 1a-1d
>>>>
>>>>
>>>>Then I used the what I thought more straight forward way
>>>>
>>>>2)basic models/simple regression
>>>>
>>>>I used the four sets
>>>>
>>>>2a) 160 images covariate A
>>>>
>>>>2b) 516 images  covariateB
>>>>
>>>>2c) 66 images covariate C
>>>>
>>>>2d) 66 images taken from 1b and covariate C
>>>>
>>>>I got similar activations in 2a-2c in comparison to 1a-1c but the
>>>>t-values
>>>>for conditions 2a and 2b are much higher (ROI analysis).
>>>>
>>>>I get much lower t-values for 2c than 1c...(again ROI) could this be a
>>>>result of the number of images? Or what?
>>>>
>>>
>>>But the number of images is the same for approach 1 as for
>>>approach 2. Am I understanding this
>>>correctly ?
>>>
>>>Best,
>>>
>>>Will.
>>>
>>>--
>>>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/
>>>
>>
>>
>>
>
> --
> 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/
>