Physiological Changes

SNS/PNS Activation

In two studies by Levenson and colleagues, participants completed the directed facial action task for disgust while physiological measures were taken.  In Levenson et al.’s (1990) study on American participants, disgust facial expressions caused an increase in skin conductance, and no change from baseline for heart rate, finger temperature, and muscle activity.  Anger resulted in a significantly greater increase in heart rate and finger temperature than disgust, suggesting these two emotions might be different. In a later study (Levenson et al., 1992), American and Minangkabau participants made a disgust facial expression.  For both groups, making a disgust expression resulted in similar increases in heart rate and finger temperature, but American participants showed significantly greater increases in skin conductance than Minangkabau participants.  Remember that skin conductance is a pure measure of SNS activity.  Taken together, these findings indicate that displaying a disgust facial expression activates the SNS system and causes an increase in physiological arousal.  Keep in mind that the type of disgust facial expression displayed depends on the type of disgust elicited (Rozin et al., 1994a).  Because Ekman was involved in these two studies, we could assume that the facial expressions participants displayed included the following action unit changes: AU 10 – Retraction of Upper Lip; AU 9 – Nose Wrinkle; and AU 17 – Chin Raiser (Ekman & Friesen, 1978).  Based on Rozin et al’s (1994a) work, the facial expression used in these two studies most likely elicited core disgust due to the nose wrinkle.  But, the chin raiser occurs with core, animal-nature, and interpersonal contamination.

Kreibig’s review (2010) discusses that physiological changes depend on the type of disgust elicited.  Photos and videos of core disgust/contamination/pollution elicit PNS activation and SNS activation.  Remember, heart-rate variability (HRV) is a pure measure of PNS activation, while skin conductance (SCR) is a pure measure of SNS activation.  Physiological changes for body envelope violations are less consistent.  The PNS system is not activated because HRV did not change.  Yet, disgust elicited by mutilation does seem to activate the SNS system as demonstrated by the increase in SCR.  Researchers do not know yet why this type of disgust increase SCR, but decreases heart rate.  One reason some of the physiological changes contradict each other may be the timing at which heart rate increased or decreased.  For instance, maybe heart rate decreased halfway through viewing time of the clip or maybe it decreased at the end of the clip.

Another study investigated the changes in physiology for physical disgust (including core, animal-nature, and interpersonal) compared to moral disgust.  Using audio clips (Ottaviani et al., 2013),  researchers elicited physical or moral disgust in participants. Moral disgust caused an increase in heart rate while physical disgust did not.  Physical disgust caused an increase in HRV and demonstrated other physiological indicators of parasympathetic activation, while moral disgust did not.  Taken together, these physiological changes suggest physical disgust activated the PNS, whereas moral disgust deactivated the PNS and activated the SNS.

For subjective feelings, both moral and physical disgust groups reported equally high levels of disgust.  Moral disgust participants reported feeling more scornful and more indignant, whereas physical disgust participants reported feeling more dirty.