A well-powered test of task difficulty effects on cardiovascular indicators of mental effort

Motivational intensity theory posits that effort is proportional to task difficulty as long as success is possible and the necessary effort is justified. Dozens of earlier studies operationalized mental effort as cardiovascular reactivity, especially systolic blood pressure (SBP), but also heart rate (HR), and diastolic blood pressure (DBP). In a highly cited paper, Richter et al. (2008) have advocated for pre-ejection period (PEP) as a more reliable indicator of mental effort because of its direct dependence on beta-adrenergic sympathetic activation. We aimed to build on and extend that past work by testing the difficulty effect in larger cell sizes to (1) address recent concerns about underpowered studies and (2) provide a more complete picture of the hemodynamic effects. N = 114 young adults worked on an easy vs. difficult memory span task while their cardiovascular activity was assessed. As expected, responses of PEP-and also cardiac output (CO), SBP, DBP, and HR-were stronger during the difficult compared to the easy task, thereby conceptually replicating and extending past research. By contrast, responses of total peripheral resistance (TPR) and heart rate variability (RMSSD & HF power) did not significantly differ between the conditions. Accordingly, task difficulty effects on cardiovascular reactivity are primarily mediated by beta-adrenergic activation. This provides a strong conceptual replication of a task difficulty effect on cardiovascular reactivity that is consistent across sexes and adds additional information about the underlying hemodynamics (i.e., myocardial response pattern).