The response time paradox in functional magnetic resonance imaging analyses

Response times (RTs) are often the main signal of interest in cognitive psychology but are often ignored in functional MRI (fMRI) analyses. In fMRI analysis the intensity of the signal serves as a proxy for the intensity of local neuronal activity, but changes in either the intensity or the duration of neuronal activity can yield identical fMRI signals. Therefore, if RTs are ignored and pair with neuronal durations, fMRI results claiming intensity differences may be confounded by RTs. We show how ignoring RTs goes beyond this confound, where longer RTs are paired with larger activation estimates, to lesser-known issues where RTs become confounds in group-level analyses and, surprisingly, how the RT confound can induce other artificial group-level associations with variables that are not related to the condition contrast or RTs. We propose a new time-series model to address these issues and encourage increasing focus on what the widespread RT-based signal represents. Mumford et al. examine how response time differences can lead to confounds in functional MRI analyses, and they propose a new time-series model to account for response time effects.

Automated summary

Ignoring response times in functional MRI analyses can lead to confounds and artificial associations. A new time-series model is proposed to address these issues and emphasizes the importance of examining the RT-based signal.