Unintended bias in the pursuit of collinearity solutions in fMRI analysis

Brisbane Convention & Exhibition Centre 

In task-based fMRI, collinearity between design matrix regressors can impact power. Optimal task design involves evaluating multiple designs to maximize efficiency and minimize collinearity. Here, we highlight inappropriate strategies to reduce collinearity that introduce biases, impair contrast interpretability, and potentially increase false positives. Using Monetary Incentive Delay (MID) task fMRI data from the Adolescent Brain Cognitive Development (ABCD) study, we show that omitting regressors, using impulse regressors for extended activations, and ignoring response times bias contrast estimates, sometimes inflating error rates in a sample of 500 subjects. We propose a "Saturated" model that includes all stimuli and response times, eliminating bias and providing valid estimates of task-related brain activity.