Thank you Rik.
Therefore it is right to conclude that whatever activation comes with
contrast "-1" its always a decrease?
But there is no way to have the correct plot with SPM or some other tools?
Best Regards.
Dorian.
2009/2/11 Rik Henson <[log in to unmask]>:
>
> It is because the parametric plot in the bottom right of plotarea2 refers to
> the signal at 15.8s, which is normal undershoot of the HRF (not its peak
> like in plotarea1). But because this region shows a "negative" HRF vs
> baseline, the parametric function is reversed - ie the region in plotarea2
> does show a decreasing (more negative) response with increasing parameter
> values, as in the bottom left panel, but the plot on the bottom right
> reverses this. I agree this is very confusing, and generally ignore the plot
> on the bottom right. The contrast and results pertain to the parameter
> estimate for your HRF, and are consistent.
>
> Rik
>
> Dorian P wrote:
>>
>> Dear all,
>>
>> I am running an analysis with parametric modulations. The contrast "1"
>> is supposed to reveal areas with
>> increasing signal while "-1" with decreasing signal
>> (https://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind05&L=SPM&P=R168802).
>>
>> However, when I plot the contrast "-1", I am getting some areas with
>> increasing
>> activation and other areas decreasing. You can see the effect at the
>> attached pictures. How is this possible?
>>
>> I have observed that the attached examples are one for for response at
>> 5.1 seconds and the other at 15.8 seconds. This is
>> how SPM plots that, I just used the plot button.
>>
>> Any clue on what kind of modulations I am getting?
>>
>> Dorian.
>> PhD Student
>> Ruhr University Bochum.
>>
>> ------------------------------------------------------------------------
>>
>>
>> ------------------------------------------------------------------------
>>
>
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