Pilots and other aircrew members are often required to perform tasks involving a substantial amount of mediational or cognitive activity. Generally speaking, workload estimation techniques have not been tested to determine their relative sensitivity and intrusion to mediational piloting tasks.

An experiment comparing the sensitivity and intrusion of eight workload estimation techniques was conducted using a mediational loading task in a three-degrees-of-freedom moving-base aircraft simulator. The primary task mediational loading required the pilots to solve a variety of navigational problems while maintaining straight-and-level flight. The presented problems were sorted prior to the experiment into low, medium, and high difficulty problems. The eight techniques included opinion measures (modified Cooper-Harper rating scale and multi-descriptor rating scale), spare mental capacity measures (time estimation and tapping regularity), primary task measures (mediational reaction time and control movements per unit time), and physiological measures (pulse rate variability and pupil dilation).

A sensitive technique was defined as a technique which indicated statistical differences of scores across the three mediational load levels. An intrusive technique was defined as a technique which significantly changed the primary task measures compared to the primary task measures obtained in a control condition. One opinion measure (modified Cooper-Harper measure (time (mediational rating scale), one estimation), and one spare mental capacity primary task measure reaction time) demonstrated sensitivity. Mediational reaction time demonstrated sensitivity to all levels of load. The other two showed partial sensitivity to load. One spare mental capacity measure (time estimation) demonstrated intrusion on two primary task measures (mediational reaction time and percent error response).