T he impact of wor king memory load on psychophysiological measures of mental effort and motivational disposition

Mental effort may be conceived in terms of computation (energy mobilization for cognitive tasks) or motivation disposition (decision to invest or withdraw task effort). The current study measured cardiovascular, electroencephalographic (EEG) and pupillometric data in order to capture computational and motivational aspects of mental effort. Working memory load was manipulated using a verbal version of the N-back task using 6 different load levels, ranging from 1-back (easy) to 6-back (extremely hard). 18 participants completed the task after pre-trial training. Performance and psychophysiological activity was measured during task completion along with subjective reports of motivation and workload. Results showed omnibus effects for load on performance and subjective effort, systolic blood pressure and pupil dilation. Load effects were also present on EEG anterior and parietal alpha suppression, and on theta power at anterior frontal scalp sites. Frontal EEG asymmetry, which indexes motivation, showed greater relative left activation for low and high loads compared to baseline, hypothesized to reflect expectancy at low loads and approach motivation at high loads. No effect was found for the highest load compared to baseline, thought to indicate reduced approach motivation due to overload. Results are discussed in relation to developing computer systems to detect high mental workloads using psychophysiology.