Facial configurations in monkeys and apes

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Chapter 1 endnote 19, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

If we put all the scientific evidence together, we cannot claim, with any reasonable certainty, that each emotion has a diagnostic facial expression. [...] For evidence on whether non-human primates are similar to humans in their expressions, see....

Monkeys and non-human apes do not show clear cut evidence that they make or perceive specific facial expressions that correspond to emotions one-to-one.[1] As is the case with humans, there is more research on perception than production of facial movements in these primates.

Rhesus macaque monkeys make several distinctive facial configurations:[2]

  • A "silent bared teeth" face (exposed teeth and gums, with forehead pulled back, presumed to be the expression for fear)
  • A "threat" face (open mouth, ears and forehead forward, presumed to be the expression for anger, when a monkey is threatening others)
  • A "lip smack" (lips are smacked together over and over again, presumed to be the expression for affiliation or appeasement)
  • A play face (relaxed, open mouthed)

The bared teeth face, for example, often appears in situations where fear is unlikely (e.g., during copulation), and fails to appear when monkeys come face to face with feared objects, such as a snake or a spider. For example, in one study of 14 monkeys,[3] twelve failed to make the bared teeth face when presented with snakes, spiders, lizard, etc., and two monkeys made the face rarely. Half the monkeys made the threat face occasionally. All but one (13 of the 14 monkeys) made the lip-smacking affiliation/appeasement face. Similarly, when macaque monkeys have their amygdalae lesioned as infants, they do not differ from monkeys with intact amygdalae in their frequency of bared teeth configurations. Early damage to the amygdala in these animals makes them less reactive overall, both in pleasant and unpleasant situations (e.g., to food, to aggressive animals, etc.).[4]

Chimpanzees are able distinguish a negative face (e.g., “bared teeth”) from a neutral face but have difficulty distinguishing one negative face from another (e.g., a “bared teeth face” and a “scream face”[5]). Macaque monkeys also have the greatest success differentiating between a positive face (i.e., “play face”) and either a neutral or negative face but have difficulty telling one negative face from another.[2]

Notes on the Notes

  1. For an overview, see Bliss-Moreau, Eliza and Gilda Moadab. 2017. "The faces monkeys make." In The Science of Facial Expression, edited by Jose-Miguel Fernandez Dols & James A. Russell, 153-172. New York: Oxford University Press.
  2. 2.0 2.1 For example, Parr, Lisa A., and Matthew Heintz. 2009. "Facial expression recognition in rhesus monkeys, Macaca mulatta." Animal Behavior 77 (6): 1507-1513.
  3. Bliss-Moreau, Eliza. Unpublished data.
  4. Bliss-Moreau, Eliza, Melissa D. Bauman, and David G. Amaral. 2011. "Neonatal amygdala lesions result in globally blunted affect in adult rhesus macaques."  Behavioral Neuroscience 125 (6): 848-858.
  5. Parr, Lisa A., William D. Hopkins, and Frans de Waal. 1998. "The perception of facial expressions by chimpanzees, Pan Troglodytes." Evolution of Communication 2 (1): 1-23.