[Homer-users] Question regarding baseline subtraction and neutral cue subtraction

[Perdue, Katherine]

Hi Jared,

To add to Ted’s detailed response, there is a difference in what scientific questions you are addressing with your suggestions.

Suggestion 1 is asking “What is the mean response during your EXP condition?”  Usually the question is not asked this way in NIRS research because we are more interested in a relative response to a particular stimulus.

Suggestion 2 is asking “How is the activation in the EXP condition different from baseline/before the stimulus is presented?” Usually this is designed to answer things like “where is brain activation to my stimulus located?” This processing method is often the simplest to interpret because we have an expectation for what a brain activation looks like, but assumes that “brain activation to EXP” is a meaningful concept.

Suggestion 3 is asking “How is the brain response to EXP different from the brain response to NEUT?” Theoretically you could have more than two conditions here and have the same question. The brain response could be different between the two conditions without having a statistically significant activation (what you would find by processing like your Suggestion 2). Another argument for using this method would be if you don’t think it is possible to interpret the response to EXP without considering the response to NEUT.

The method you choose will depend on the scientific question you want to answer, or how you want the result to relate to other variables of interest.

best,
Katherine


-------------
Katherine Perdue, PhD
Research Fellow in Pediatrics
Labs of Cognitive Neuroscience
Division of Developmental Medicine
Boston Children's Hospital
Office Phone: 857-218-5214

On Jul 23, 2015, at 11:10 AM, Jared Dempsey <dempsey at recoveryscience.org<mailto:dempsey at recoveryscience.org>> wrote:

All:

I’ve talked to many different sources and can’t really get an answer on this one.  I’m hoping that the group of individuals using fNIR technology may have some opinions.  It involves the use of cue-baseline subtraction and neutral cue subtraction.  Here goes…

I’m studying prefrontal cortex activation to a specific cue (EXP).  I also randomly present a neutral cue (NEUT).  Each of my cues last 10 seconds.  There is also an intertrial period (black screen, no presentation) of 10 seconds.  For example:
*EXP____10s* *ITI____10s* *NEUT____10s*  *ITI____10s**EXP____10s* etc, etc.

So, it seems from scanning the literature on fNIR everyone is doing something a bit differently.  Also, the editors of journals have their preferred method.  Honestly, it is screaming for one of us to publish some methodology work on cue presentation and give some concrete suggestions.  I digress…  My question involves how to come to a tangible variable for my EXP cue.  Here are some of the different suggestions I have received:

1)      Take the average activation during 10s of EXP across all presentations
OR
2)      Take the average activation during EXP and subtract the average activation of 5 seconds before that specific EXP presentation.  Then average all the EXP values
OR
3)      Take the average activation during EXP and subtract the average activation of 5 seconds before that specific EXP presentation. AVERAGE ALL THESE FOR GLOBAL EXP.  Then average all of your NEUT cues, subtract the average 5 seconds before each NEUT cue. AVERAGE ALL THESE FOR GLOBAL NEUT.  Lastly, subtract your global average NEUT from your global average EXP.

I fully recognize that it depends on the study (etc., etc., etc.).  All things being equal.  How would you proceed with multiple EXP cue presentations and multiple NEUT cue presentations?

(Human study, visual/photograph presentation, Prefrontal cortex).

Thank you so much in advance for any tips you may have!!!


Best,

Jared P. Dempsey, Ph.D.
Addiction Recovery Research Institute
1001 Main Street, Suite 603
Lubbock, TX 79401
Email: dempsey at recoveryscience.org<mailto:dempsey at recoveryscience.org>
Cell: (405) 269-3440
Skype: jareddempsey

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