Validity of a New Stress Induction Protocol using Speech Improvisation (IMPRO)

This paper proposes a novel stress induction protocol utilizing speech improvisation -- Interactive Multitask Performance Response Observation (IMPRO) -- in front of an audience. This approach aims to induce stress through a combination of public speaking, cognitive effort, and challenge to maintain a spontaneous narrative. We investigate the validity of this novel approach by examining physiological responses of 35 healthy participants aged 18 to 38. Saliva cortisol was measured as the ground truth for mental stress assessment. In addition, electrodermal activity (EDA) was used as a non-invasive measure of sympathetic activation, offering real-time data with high resolution. Functional near-infrared spectroscopy (fNIRS) measurement was performed to assess the cortical hemodynamic responses induced by the IMPRO protocol. We focused on hemodynamics in the prefrontal cortex (PFC), a region associated with stress processing. We found that cortisol levels and EDA significantly increased in response to the stress task compared to the baseline. We also observed a significant change in PFC hemodynamic levels in a set of channels compared to the baseline, with a higher overall increase in the right frontopolar area compared to the left. In conclusion, our findings validated IMPRO as an effective and easy to perform method for mental stress induction.