The purpose was to propose an alternative data analysis for functional near-infrared spectroscopy (fNIRS)-derived hemodynamics as a function of cortical activation changes. We evaluated hemodynamic responses from the prefrontal cortex region while 38 participants performed a cognitive task. The task consisted of an arithmetic calculation with three levels of complexity (i.e., easy, medium and difficult). These task-dependent hemodynamic responses were analyzed by the slope method (i.e. using a linear regression through the cognitive task) and were compared with the corresponding responses obtained with a traditional approach of the amplitude method. Subjective scales of task loading (assessed by DP15 and NASA-TLX) and behavioral outcomes (performance and reaction time) were also recorded in response to the task complexity. Results revealed that the proposed slope method allowed a better discrimination in terms of cortical activation among all levels of mental workload. There was no significant increase in cortical activation between the medium and difficult levels (p = .30; d = 0.09) with the amplitude method while the slope coefficient was sensitive to the different levels (p < .01; d = 0.32). These preliminary results from a large sample size demonstrated that the slope method appears suitable for discriminating the changes in cortical activation with respect to the mental workload.
Mandrick, K., Derosiere, G., Dray, G., Coulon, D., Micallef, J.-P., & Perrey, S. (2013). Utilizing slope method as an alternative data analysis for functional near-infrared spectroscopy-derived cerebral hemodynamic responses. International Journal of Industrial Ergonomics, 43(4), 335-341. https://doi.org/10.1016/j.ergon.2013.05.003 (Original work published 2013)