Research ArticleANTHROPOLOGY

Universal facial expressions uncovered in art of the ancient Americas: A computational approach

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Science Advances  19 Aug 2020:
Vol. 6, no. 34, eabb1005
DOI: 10.1126/sciadv.abb1005
  • Fig. 1 Ancient American sculptures with discernible faces and contexts.

    (A) Captive from Tonina archeological site (Mexico, 690–700 CE). Photo credit: Mauricio Marat, Instituto Nacional de Antropología e Historia. (1 July 2019). (B) Tortured, scalped prisoner from Campeche (Mexico, 700–900 CE). Baltimore Museum of Art, Kerr Portfolio 2868, photo by J. Kerr. (C) Maya man carrying large stone (Mexico, 600–1200 CE). Kerr Portfolio 8237, photo by J. Kerr. (D) Joined couple (Mexico, 200–500 CE). Los Angeles County Museum of Art (LACMA) AC1996.146.21, gift of C. M. Fearing. (E) Maya woman holding child (600–800 CE). Princeton University Art Museum 2003-26, gift of G. G. Griffin. (F) Kneeling Maya warrior with facial tattoos and shield (Mexico, 600–800 CE), detail. Earthenware and pigment, 15.9 cm by 10.8 cm. Fine Arts Museums of San Francisco 2009.38.2, gift of G. Merriam and J. A. Merriam. (G) Maya ballplayer (Mexico, 700–900 CE). University of Maine HM646, William P. Palmer Collection. (H) Colima drummer (Mexico, 200 BCE–500 CE). LACMA, Proctor Stafford Collection, purchased with funds provided by Mr. and Mrs. Allan C. Balch.

  • Fig. 2 Accordance between emotions perceived in sculptures’ isolated face depictions and Western expectations for the emotions that unfold in eight portrayed contexts.

    To calculate the accordance between sculptures’ expressions and Westerners’ expectations, we correlated the participants’ average judgments of the emotions and affective features associated with each isolated face and each context across the eight contexts and divided by the maximum attainable correlation given sampling error (see Materials and Methods). Correlations are generally positive, indicating that facial muscle configurations portrayed in ancient American sculptures align, in terms of the emotions they communicate to Westerners, with Western participants’ expectations for the emotions that unfold in different contexts. Error bars represent SEs. Here, we excluded 10 emotions and 1 affective feature used seldom enough that <1/3 of the covariance in judgments was explainable, as a result of which SEs were very large.

  • Fig. 3 Dimensions shared between sculptures’ expressions and Western expectations for the emotions that unfold in eight contexts.

    (A) To extract dimensions, or varieties, of perceived facial expression in sculptures that accord with Western expectations for the emotions that might unfold in the eight portrayed contexts, we applied PPCA in a leave-one-subject-out fashion. PPCA extracts shared dimensions between two parallel datasets—in this case, judgments of isolated faces from each of the eight contexts and judgments of emotions associated with descriptions of each context. This analysis revealed three dimensions (P ≤ 0.0066, q[FDR] < 0.02; Wilcoxon signed rank tests). Principal component analysis (PCA) applied to mean expression judgments (blue) also revealed three dimensions of covariance (P = ≤0.0021, q[FDR] < 0.005), although they were not the first three PCs. This misordering, or improper rotation, of dimensions by PCA is expected, given that PCA does not optimize for reliability across datasets but for variance within a dataset (see the “PPCA versus PCA” section in Materials and Methods and movie S1 for illustration). Error bars represent SE. See fig. S1 for analysis including 13 affective features. (B) Positive and negative loadings of perceived emotions in the face on each PPCA dimension. The second and third dimensions were found to have substantial negative and positive loadings, representing two kinds of perceived facial expression. (C) To determine the contexts corresponding to the facial expressions represented by the dimensions, we projected the average ratings from each context onto each dimension. The greatest average rating for each context is outlined in black, each significantly greater than 0 (P < 0.0002; q[FDR] < 0.0002, bootstrap test). Together, (B) and (C) reveal the emotions captured by each dimension. The first dimension primarily represents expressions of pain in one direction (1+), which often occurs in the context of torture, and a number of positive emotions in the other (1−), which tend to occur in contexts of holding a baby, playing a ball game, and playing music. The second dimension most strongly represents expressions of determination and strain in one direction (2+), which occurs more often in the contexts of heavy lifting, and elation in the other (2−), which occurs in contexts of social touch. Last, the third dimension most strongly represents anger in one direction (3+), which occurs in the contexts of combat, and sadness in the other (3−), which occurs in the context of captivity. Expression categories and contexts are ordered according to maximally loading dimension.

  • Fig. 4 Mapping sculptures along dimensions of perceived facial expression that tend to accord with predicted emotions.

    To explore the distribution of ancient American artwork along the dimensions of perceived facial expression that accorded with predicted responses to each context, projections of each face onto the dimensions were subjected to t-SNE (32), which positioned each face near faces with similar projections. The dimensions are also represented with five distinct colors—one for the first dimension, which was unipolar, and two distinct colors for each the two dimensions that were bipolar. Colors assigned to individual faces are weighted averages of their loadings on each dimension. Eight example sculptures are shown. To explore all 63 sculptures, see online map: Credit, from top left down: (i) Metropolitan Museum of Art 2005.91.12, gift of the Andrall and Joanne Pearson Collection, 2005; (ii) Princeton University Art Museum 2003-26, gift of G. G. Griffin; (iii) Metropolitan Museum of Art 1979.206.578, Michael C. Rockefeller Memorial Collection, Bequest of Nelson A. Rockefeller, 1979; (iv) Kerr Portfolio 342, Jaina Figure, photo by J. Kerr; (v) Kimbell Art Museum, Fort Worth, Texas, AP 1971.07, Presentation of Captives to a Maya Ruler (detail) (39); and (vi) Photograph: Museum of Fine Arts, Boston 1983.288, gift of L. T. Clay (40).

Supplementary Materials

  • Supplementary Materials

    Universal facial expressions uncovered in art of the ancient Americas: A computational approach

    Alan S. Cowen and Dacher Keltner

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