Power Law Model for Subjective Mental Workload and Validation through Air Traffic Control Human-in-the-Loop Simulation

We provide evidence for a power law relationship between the subjective one-dimensional Instantaneous Self Assessment workload measure (five level ISA-WL scale) and the radio communication of air traffic controllers (ATCOs) as an objective task load variable. It corresponds to Stevens’ classical psychophysics relationship between physical stimulus and subjective response, with characteristic power law exponent gamma of the order of 1. The theoretical model was validated in a human-in-the loop air traffic control simulation experiment with traffic flow as environmental stimulus that correlates positively with ATCOs frequency and duration of radio calls (task load, RC-TL) and their reported ISA-WL. The theoretical predictions together with non-linear regression based model parameter estimates expand previously published results that quantified the formal logistic relationship between the subjective ISA measure and simulated air traffic flow (Fürstenau, Radüntz, & Mühlhausen, Model Based Development of a Mental Workload Sensitivity Index for Subject Clustering, 2020). The present analysis refers to a psychophysics approach to mental workload suggested by (Gopher & Braune 1984) and that was recently used by (Bachelder & Godfroy-Cooper, 2019) for pilot workload estimation, with a corresponding power law exponent estimate in the typical range of Stevens’ exponents. Based on the hypothesis of cognitive resource limitation we derived the power law by combination of the two logistic models for ISA-WL and communication TL characteristics respectively. Despite large inter-individual variance the theoretically predicted logistic and power law parameter values exhibit surprisingly close agreement with the regression based estimates (for averages across participants). Significantly different logistic WL and TL scaling parameters and the corresponding Stevens exponents as ratio of these parameters quantify the TL/WL dissociation with regard to traffic flow. The sensitivity with regard to work conditions of the logistic WL-scaling parameter as well as the power law exponent was revealed by traffic scenarios with a non-nominal event: WL-sensitivity increased significantly for traffic flow larger than a critical value. Initial analysis of a simultaneously measured new neurophysiological (EEG) load index (dual frequency head maps, DFHM, (Radüntz, Dual Frequency Head Maps: A New Method for Indexing Mental Workload Continuously during Execution of Cognitive Tasks, 2017)) provided evidence for the power law to be applicable to the DFHM load measure as well

Research Design to Access the Mental Workload of Air Traffic Controllers

The German Federal Institute of Occupational Safety and Health in Berlin developed a method for neuronal mental workload monitoring. The so-called Dual Frequency Head Maps (DFHM) method allows defining the workload range of each person individually. The current research project describes the evaluation and condition-related verification of the DFHM method in a simulated realistic environment of an air traffic control center. During an interactive real-time simulation at the Air Traffic Validation Center of the German Aerospace Center, the load level for the controllers was varied by means of two independent variables: the traffic demand and the occurrence of a priority request. Dependent variables for registering mental workload were the DFHM index, heart rate, subjective questionnaires, and air traffic performance data