Did you get the joke? Physiological, subjective and behavioral responses to mirth

Mirth is elicited by the perception of humor, which requires the resolution of an incongruity in an unexpected and playful manner. Previous psychophysiological research using affective pictures is scarce, and did not elucidate the cognitive and affective components of the humor process. In this study, the passive viewing paradigm is applied to mirthful, incongruent, neutral and erotic pictures to characterize the emotional response of mirth. Physiological (zygomaticus major [ZM] activity, skin conductance response [SCR] and heart rate [HR]), behavioral (free viewing time) and subjective responses (mirthful ratings) were recorded from 63 participants. The presence of an inflection change in the ZM response and mirthfulness ratings were used as markers of humor comprehension. Participants showed the greatest ZM and HR in response to mirthful compared to incongruent, erotic and neutral pictures, as well as a stronger SCR response to mirthful compared to incongruent and neutral pictures. The overall results shed light on the temporal course of the humor process, suggesting that humor comprehension (cognitive component) occurred around 1000-1500 ms after picture onset, according to the ZM and SCR responses; and the humor appreciation stage (emotional component) occurred at around 3500 ms after stimulus onset, according to the HR and SCR changes. Moreover, marked interindividual variability was observed in the number of smiles, and in the pictures that provoked them. This points to the complexity of the humor process, and suggests the need to develop methods to elicit mirth and elucidate the factors potentially underlying individual differences in humor.