Emotion. A sickening feeling of revulsion, loathing, or nausea.
Usage: Disgust shows a. in a curled upper lip; b. in digestive vocalizations, e.g., of repugnance; c. in narrowed (i.e., partly closed) eyes; d. in lowered brows of the frown face; e. in backward head-jerks and side-to-side head-shakes; and f. in visible protrusions of the tongue.
Media. The green "Mr. Yuck" face sticker is a familiar graphic symbol used as a nonverbal poison-warning label for children.
RESEARCH REPORTS: 1. Signs of disgust include guttural sounds (e.g., "ach" or "ugh"), a retracted upper lip, and mouth movements "preparatory to the act of vomiting" (Darwin 1872:256). 2. In "disgust-revulsion," the brows are slightly narrowed, the upper lip is raised, the lip corners are drawn down and back, the tongue is moved forward or protruded, thenose is drawn up and wrinkled (i.e., the procerus muscle draws down the medial angle of the brows to make transverse wrinkles across the bridge of the nose; Izard 1971:243). 3.Disgust shows most clearly in the lower face (Ekman, Friesen, and Tomkins 1971). 4. Theoretically, disgust originated as a response to bad tastes, and later evolved as a moral emotion (as reflected, e.g., in college-students who judged the raised upper lip as a sign of aversion to body boundary violations, inappropriate sex, poor hygiene, and death; Rozin et al. 1994).5. Additional signs include a wrinkled nose, raised nostrils, and lowered inner corners of the eyebrows (Ekman 1998:256).
Evolution. Disgust is a mammalian elaboration of the pharyngeal gag reflex. The nerves and muscles used to close the mouth derive from the 1st pharyngeal arch, while those constricting the throat derive from the 3rd and 4th arches. From the 2nd arch, the facial nerve (cranial VII) contracts the orbital muscles to narrow the eyes, while corrugator and associated muscle groups lower the eyebrows, when we detect an offending aroma or taste cue.
Neuro-notes I. In infants a bitter taste shows in lowered brows, narrowed eyes, and a protruded tongue. The noxious taste causes baby to protectively seal off her throat and oral cavity, as cranial nerves IX and X activate the pharyngeal gag reflex. Cranial V depresses her lower jaw to expel the unpleasant mouthful, then closes the mouth to keep unpalatable food out as cranial XII protrudes her tongue. The sickening feeling we associate with disgust is mediated by the enteric brain.
Neuro-notes II. Mirror neurons: Giacomo Rizzolati has recently discovered mirror neurons in the monkey brain's insula, "a reservoir of disgust and pain" (reported in the APS Observer, Vol. 24, No. 3, March 2011).