Hello FSL List serv,
New FSL/FEAT user trying to sort out the best methodology for first level analysis. The study is a Stroop, and is basic concept is outlined here: http://en.wikipedia.org/wiki/Stroop_effect. We are concerned with finding a stroop effect and conflict adaptation effect. Briefly, a Stroop effect is found by measuring the difference between congruent trials (when both of the stimuli are similar in nature) and incongruent trials (when the stimuli are of opposite nature). Conflict adaptation occurs when an incongruent trial is followed by another incongruent trial. The subjects respond quicker in this case than when an incongruent trial is preceded by a congruent trial.
Thus, we have two types of trials for the stroop effect: Congruent and Incongruent
And four types of trials for the conflict adaptation effect: Inc-Inc, Con-Inc, Con-Con, Inc-Con
First Level Analysis
Two Proposed methods:
(1) 4 Evs with a Basic shape of Custom (3 column format), Convolution of double-gamma HRF. Each of the four Evs will be composed of trial types listed in the conflict adaptation above (II, CI, CC, IC).
Example of the 1 line in the 3 column file:
Stimuli Onset Reaction Time 1
Comparisons:
Stroop Effect:
Congruence (II EV + CI EV) > (IC EV + CC EV)
Note: that the part in parenthesis would capture all of each type of congruent or incongruent trial.
Conflict Adaptation: II EV > CI EV
(2) Three regressors/EVs:
1) An all Trial regressor (used to absorb what is the same across all trials)
2) A conflict regressor: best way I can describe it is to to describe the 3 column file:
Column 1: Stimulus Onset Column 2: Reaction time Column 3: a number between 0-1 used to approximate the level of conflict. (Find avg Rt for each condition II, IC, CI, CC, then normalize to a scale of 0-1. CC would be 0 presumably and CI would be 1 presumably)
3) A "control" regressor: same general idea as (2) except were looking for stroop effect rather than conflict adaptation
Comparisons
Compare 2 > 1 for conflict adaptation
Compare 3 > 1 for stroop effect.
I am just curious if I am on base here and what would be the preferably methodology at the first level.
Thank You,
Michael Cordell
|