Yes, those are the maps I"ve been comparing.  I've been comparing it to BV sort of, but that analysis is not surface based and I"m not used to it, so I can't quite tell which is more accurate, though Version 2 gives a much smaller area of activity, which fits with the description of what I've been given about what to expect in BV.  Attached is two pictures of the difference I get for Version 1:1v0 (labeled with "single" in the image name) and Version 2:2v0 (labeled with "double" in the name).  As you can see, Version1 activates a much larger area than Version 2.

I guess part of my problem is that I'm having trouble understanding exactly what these two versions are telling me about the data and what the differences is.  Can you try to give me a sort of layman's explanation?

Katie


On Tue, Feb 22, 2011 at 11:45 AM, Douglas N Greve <greve@nmr.mgh.harvard.edu> wrote:
I assume that you are comparing maps of Version1:1v0 and Version2:2v0 ? I could imagine it going either way. If the true slope is 0 but the offset is non-0, then Version1 will give you an artificially high slope (and Verion2 will give you the correct slope at 0, and so no activation). Are you comparing this to a BV analysis?

doug


Katie Bettencourt wrote:
So I created a weighted regression analysis to look at the effect of memory load in a particular brain region. Basically, I weighted the paradigms by a behavioral measure that reflected the number of items actually remembered (as set size was increased).  As far as Doug told me there are basically 2 ways to weight your paradigm files.

Version 1:
Have 2 conditions, baseline (condition 0) and all the set sizes (condition 1).  Condition 1 would then be weighted by the behavioral measure.

Version 2:
Have 3 conditions, baseline (condition 0), and then I represented each presentation as two different conditions, one with a weight that is always 1 (condition 1), the other weighted according to the behavioral measure (condition 2).


The difference, as far as I understand it, in version 1, it is assumed that the response amplitude is ) when the weight is 0 (ie. that when you are attending to 0 items, brain activity = 0).  Whereas, version 2, tests the slope of the HRF amplitude vs weight without the assumption above.

However, I'm a bit confused as to the results I got.  When I looked at the data from both versions, version 1 provided a much higher amount of activation and more areas activated than version 2.  However, I believe version 2 better fits with the multiple regression analysis that is done in Brain Voyager.
Can anyone give me a better explanation of what the difference between these analysis models is?

Katie




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Douglas N. Greve, Ph.D.
MGH-NMR Center
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