Toward Workload-Based Adaptive Automation: The Utility of fNIRS for Measuring Load in Multiple Resources in the Brain

We investigate the utility of functional near-infrared spectroscopy (fNIRS) for workload-based adaptive automation through the lens of multiple resource theory. We focus on the criteria of unobtrusiveness, responsiveness, load sensitivity (low vs high load), and load diagnosticity (differentiating types of load). We report a large meta-review, in which we conclude that only a few studies were suitable for evaluating sensitivity and diagnosticity in complex real-world tasks. While these reveal that the fNIRS signal is adequately sensitive to gradations of load level changes (sensitivity), the diagnosticity of fNIRS to different sources of cognitive load remained uncertain. We manipulated mental load of a complex shape sorting task via working memory load (WM) and visual perceptual load (VL), while a secondary auditory task was present throughout. We measured the effect of these manipulations at the group-level using conventional secondary and eyetracking workload measures, as well as hemodynamic response in specific functional regions in the brain, including regions involved in multi-tasking (MT), VL, WM, and auditory load (AL). Our findings revealed that fNIRS is both sensitive and diagnostic to load in complex tasks, with greater sensitivity revealed by deoxyhemoglobin than oxyhemoglobin and the brain regions associated with diagnosticity align with neuroscience literature on perceptual load, WM, and goal-directed multitasking.