The Psychophysics of Cognitive Workload: A Novel Methodology for the Continuous Assessment of Cognitive Demand

Background : Cognitive workload (CWL), a crucial concept in aviation human factors, has been described as the interplay between the aviator’s multidimensional, limited cognitive resources and the simultaneous dynamic task demands. The literature reports three general approaches to measuring CWL, task performance metrics, psychophysiological biomarkers, and relatively standardized CWL self-report ratings. The present study assesses a fourth method adapted from standard classic sensory psychophysics. Methods : Subjects were three study-team members highly trained on a surrogate aviation task. Random sequences of 10 CWL task demand levels (DL) spanning the range from low to high were presented to each subject. Using a 2-alternative forced-choice (2AFC) psychophysical thresholding paradigm, the minimum difference in DL a subject could reliably discriminate was measured at each DL. This method of measuring CWL DL differences is analogous to a psychophysical measurement of just noticeable sensory differences (JND). Results : Unexpectedly, the JND size for high-to-low DL transitions was much smaller than that of low-to-high DL transitions. Conclusions : The study demonstrated the feasibility of adapting a quantitative sensory psychophysical testing paradigm to develop an analogous psychophysics of CWL. The results identified an unexpected difference in CWL JND size that depends on the direction of transition. This difference suggests that the CWL demand experienced at a given demand level may depend on whether the demand level was approached from a lower or higher direction. This difference may have practical implications for implementing dynamic adaptive automation. These results support the value of further studies to elaborate the concept of a CWL psychophysics.