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Symmetry Part 3: Primer on Directional Asymmetry in Faces

August 27, 2009 Leave a comment

Most faces show some measurable degree of asymmetry, or lack of perfect balance. Some of this asymmetry occurs more on one side of the face than the other. When it does, it is known as directional asymmetry (DA). Here are two examples:

This photo (Ercan, et.al., 2008) shows dominance in the left half of both faces. In this context, dominance means a tendency for asymmetries to be larger on one side of the face than the other, when the face is split down the midsaggital plane (dotted line). In this illustration, each solid line represents a separate DA. Ercan found left side dominance (because more features on the left side of the face were bigger/larger/further apart) and that women exhibited more DA than did men (as indicated by the number of solid lines).   

 

The line drawing on the right (Haraguchi et.al., 2008) shows another measurement that can show asymmetries and hemifacial dominance: facial width. In Haraguchi’s sample, the right side of the face was dominant.   

The reasons for facial DA are still unclear, but, sequelae to cerebral lateralization and different patterns of muscular activity (e.g., preferred chewing side, asymmetries in emotional expression, etc.) are candidate explanations. Several articles I’ve read recently have indicated that human faces tend to be right side dominant. This assertion seems premature. Ercan references studies showing both left and right side dominance and identifies several possible causes of these inconsistent results:

  • Population/Cultural differences
  • Age differences
  • Varying measurement techniques/locations
  • Variable head positioning when facial photographs are being taken

Smith (1998) even found consistent differences in hemifacial dominance in college faculty based on academic discipline. Clearly, we have yet to work out all the details associated with this phenomenon.

Wayne Hooke

ResearchBlogging.orgErcan, I., Ozdemir, S., Etoz, A., Sigirli, D., Tubbs, R., Loukas, M., & Guney, I. (2008). Facial asymmetry in young healthy subjects evaluated by statistical shape analysis Journal of Anatomy, 213 (6), 663-669 DOI: 10.1111/j.1469-7580.2008.01002.x

Haraguchi, S., Iguchi, Y., & Takada, K. (2008). Asymmetry of the Face in Orthodontic Patients The Angle Orthodontist, 78 (3) DOI: 10.2319/022107-85.1

Smith, W. (1998). Hemispheric and Facial Asymmetry: Faces of Academe Journal of Cognitive Neuroscience, 10 (6), 663-667 DOI: 10.1162/089892998563077

Categories: General, The Face

Symmetry Part 2: Homo Sapiens: The Asymmetric Ape?

August 24, 2009 Leave a comment

Homo Sapiens – humans – by one measure at least – are the most asymmetric of all the great apes. Frederick and Gallup (2007), using previously published data, compared fluctuating asymmetry in the teeth of humans with that of great apes and a number of fossil hominins. Humans showed more dental fluctuating asymmetries than orangutans, gorillas, and chimpanzees. No significant differences between homo sapiens and fossil hominins were found.

Implications

Humans may experience less selection pressure from environmental influences when compared to the other great apes. The idea here is that weaknesses resulting from developmental instabilities are less problematic for humans. This implication assumes a close relationship between FA and developmental instability: an assumption which has yet to be established.

The human preference for less FA may have minimal impact on human sexual selection. That is, our attraction to symmetry has not kept us from being what appears to be the least symmetric ape.

Concerns

Due to the nature of the data, there were no controls for measurement error.

Differences in levels of FA may exist between homo sapiens and at least some extinct hominins – conclusions cannot be drawn from this study.

It is unclear to what degree facial/other asymmetry can be predicted by dental asymmetries – additional comparative studies are in order.

Of potential interest: Orangutans were significantly more symmetric than any of the other great apes. Two explanatory hypotheses were offered:

  1. Canopy dwelling orangutans may have greater selection pressures for balance – which may be improved with bilateral symmetry.
  2. Orangutans are the most solitary of the apes – pathogen virulence is negatively correlated with host contact.

Wayne Hooke

Symmetry Part 1

Photo courtesy of Tom Low, Camp Leakey, 2003

ResearchBlogging.orgMichael J. Frederick, & Gordon G. Gallup, Jr. (2007). Fluctuating Dental Asymmetry in Great Apes, Fossil Hominins, and Modern Humans: Implications for Changing Stressors during Human Evolution Acta Psychologica Sinica, 39 (3), 489-494

Categories: General, The Body, The Face

Symmetry Part 1: Introduction

August 23, 2009 3 comments

“Beauty is our weapon against nature; by it we make objects, giving them limit, symmetry, proportion. Beauty halts and freezes the melting flux of nature.”

Camille Paglia 

In the study of attractiveness, symmetry almost always refers to bilateral, mirror, or reflection symmetry: each side is identical to the other when split down the middle – as is the figure on the left. The midsagittal plane – the plane that runs through the body, beginning at the head and passing through the spinal column and the navel, is the marker of mirror symmetry. Bilateral symmetry is common in vertebrates and chordates. It promotes movement, a central nervous system, and cephalization (the development of heads).

While symmetry is expected in development, asymmetry (the absence of symmetry) is common. There are three types of asymmetry: directional asymmetry, antisymmetry, and fluctuating asymmetry (Kowner, 2001).  

 

 

Directional Asymmetry (DA): some traits develop more on one side than the other, e.g., the human brain.

 

 

 

 

  1. Antisymmetry: asymmetric development is typical, but unpredictable, e.g., claw size in fiddler crabs.

 

 

 

  1. Fluctuating Asymmetry (FA): “randomly produced deviations from perfect symmetry of two sides of quantitative traits in an individual for which the population mean of R-L differences is zero and their variability is near-normally distributed” (Kowner, 2001, p.448).  

 

 

 

By-and-large, DA and antisymmetry are understood to contribute to an organism’s fitness. FA, on-the-other-hand, is generally assumed to be an indicator of developmental instability: the inability “of the organism to resist or buffer the disruption of precise development by environmental and genetic stresses” (Kowner, 2001, p. 447). That is, perfect symmetry is the developmental expectation and organisms with genetic weaknesses in particular environments will show this weakness through FA (irregular development).  

Clear connections between facial and body symmetry and attractiveness exist. Connecting the dots:

 Thus, the preference for symmetry is a preference for good genes. This conclusion is straightforward and coherent – but may be premature:

To be clear: I am not opposed to the possibility that there is a connection between FA and DI. I am merely suggesting that beauty researchers emphasize the tentative nature of this connection.

 Wayne Hooke

 Planar image courtesy of Yassine Mrabet

 
ResearchBlogging.orgKowner, R. (2001). Psychological perspective on human developmental stability and fluctuating asymmetry: Sources, applications and implications British Journal of Psychology, 92 (3), 447-469 DOI: 10.1348/000712601162284

Categories: General, The Body, The Face

It Can Be In How You Look At It….

August 20, 2009 Leave a comment

Krupinski et.al. (2005) found that the use of LCDs to view radiographic images degrades reader performance. This work has led me to wonder if variation in human seated height, combined with the use of LCDs to present stimulus sets, might have a confounding effect on attractiveness research.

Liquid Crystal Displays – LCDs – are becoming increasingly common as computer monitors. I just checked an online electronics retailer and could not find a single CRT monitor for sale. LCDs are smaller, lighter, can last longer, and use less energy than CRTs – so the transition to the newer technology makes sense. Each type of technology has pros and cons, and there are significant performance differences between manufacturers and models. One consistent limitation of LCDs, however, is limited viewing angle: color and brightness changes occur as viewers move off-axis. Technological improvements have resulted in increased viewing angles in the latest, high-end LCDs. However, most of the improvement has been in the lateral rather than in the vertical direction. This image shows typical, vertical angle of view effects on a higher end laptop LCD screen.

LCD-Viewing-Angle-Variation

Left: iphone snap from a viewing angle of approximately 0°; Middle: snap from below; Right: snap from above.

Some observations:

  • Viewing from below primarily darkens the image while viewing from above lightens it
  • Viewing from below darkens the skin and increases contrast
  • Viewing from below can add more dimensionality to a face
  • Viewing from above primarily lightens the skin while decreasing contrast and dimensionality

While just rules of thumb, darkening the skin and increasing contrast are both masculinity enhancing photographic techniques. Lightening the skin and decreasing contrast are femininity enhancing techniques. Adding dimensionality is a technique used to make subjects appear to weigh less. Given that sexual dimorphism and apparent body mass are relevant to evaluations of attractiveness, I suggest that beauty researchers who use LCDs take steps to minimize possible confounding effects of variation in seated height when presenting stimuli on LCDs. As an initial suggestion, perhaps all subjects in beauty studies that utilize LCDs should be positioned to maintain a 0° angle between raters’ eyes and stimulus-image eyes? Possible approaches include:

  • Use of a chin rest (the technique used by Dr. Rhodes and colleagues (2007) in the study from which this image was taken)
  • Use of adjustable height seating
  • Use of adjustable height monitors

Additionally, research to investigate whether there is a measurable effect of seated height on attractiveness ratings (with LCD presentation) seems called for.

Cautions

  • Not all images will show this degree of off-axis variation
  • LCDs will show more or less off-axis variation than is visible here: each make/model is different

In closing, I will emphasize that the variations in the image above involve alterations of viewing angle that are substantially greater than would be expected given the variation in adult human seated height. Therefore, under normal research conditions the effect will not be as dramatic. However, in most/all LCDs, alterations in vertical viewing angle begin to show these changes rather quickly.

Wayne Hooke
ResearchBlogging.orgKrupinski EA, Johnson J, Roehrig H, Nafziger J, & Lubin J (2005). On-axis and off-axis viewing of images on CRT displays and LCDs: observer performance and vision model predictions. Academic radiology, 12 (8), 957-64 PMID: 16023384

Rhodes, G., Peters, M., & Ewing, L. (2007). Specialised higher-level mechanisms for facial-symmetry perception: Evidence from orientation-tuning functions Perception, 36 (12), 1804-1812 DOI: 10.1068/p5688

Categories: Methodology, The Face

Size UK

August 13, 2009 Leave a comment

Wells, et. al. (2007), have published data from 3D body scans taken from a 9617 member, cross-sectional sample of UK adults (stratified by age and SES). The study seems intended to gather commercial (garment sizing information) and health related information, but does have some implications for beauty research.

Implications:

  • Body shape correlates with age in females more obviously than in males.
  • Females more likely to become “apples” – or proportionally more similar to males – with age.
  • BMI is not a good predictor of body shape/proportion or waist circumference: at least at the border of the overweight range. Male subjects with a BMI between 24-25 had waist circumferences ranging from 29.7″ to 43.3″ while female subjects ranged from 28.6″ to 44.8″ (a 3.5 standard deviation range in waist circumference for a narrow range of BMI).
  • BMI is insensitive to age associated body weight redistributions.
  • Height and circumference explains most of the variance in weight in both men (91.7%) and women (94.8%). Thus, visual cues are strong predictors of weight.    

Beauty relevant findings:

  • Rank order of strongest predictors of weight in women: height, hip, bust, thigh, and waist.
  • Rank order of strongest predictors of weight in men: height, waist, chest, and thigh.
  • Thigh, arm, and waist girths are strongly(?) related to body fat – implied but not directly addressed in this article.
  • After age 30, mean male waist-hip-chest measurements maintain relatively constant ratios (see Fig. 2A).
  • After age 30, mean female waist circumference increases relative to hip, chest, and bust: leading to a decreased tendency toward hourglass figures with age (see Fig. 2B).

  • Average male waist circumference increases about 0.2″ per decade.
  • Average female waist circumference increases about 1.1″ per decade.

Strengths

  • Total body measurements from 3D scans accurate to 0.2″ were used
  • Large sample
  • Point-cloud data may be accessible to future research on attractiveness

Limitations

  • Sample may not be representative
  • Cross-sectional data do not identify individual developmental trajectories: some of the relationships in the data could be cohort specific

 

Wayne Hooke

ResearchBlogging.orgWells JC, Treleaven P, & Cole TJ (2007). BMI compared with 3-dimensional body shape: the UK National Sizing Survey. The American journal of clinical nutrition, 85 (2), 419-25 PMID: 17284738

Ready for Action

August 11, 2009 5 comments

Action figures have gotten bigger and more muscular over the last 25 years. In a straightforward bit of research, Baghurst et.al. (2006) measured changes in the relative sizes of action figures that have been in production for more than 25 years (G.I. Joe, Batman, Hulk, Spiderman, and Superman). Their data are summarized in the table below. Given that research on the effects of media and male body image is relatively young, it is unclear what effects these bulked-up and unrealistically proportioned toys will have. We can guess that some will be inspired to attain the muscular ideal and that others will develop higher levels of body dissatisfaction.  

Wayne Hooke

G.I. Joe Photo: H.P.Holland, 2006

ResearchBlogging.orgBAGHURST, T., HOLLANDER, D., NARDELLA, B., & HAFF, G. (2006). Change in sociocultural ideal male physique: An examination of past and present action figures Body Image, 3 (1), 87-91 DOI: 10.1016/j.bodyim.2005.11.001

Categories: Media Influence

Low Brow Is More Attractive When You Can Look Down On It

August 8, 2009 Leave a comment

Sybil Geldart (2008) has found that taller people prefer faces with longer foreheads and shorter people prefer faces with longer chins. She had subjects place facial features (brows, eyes, nose, and mouth) inside the outlines of their respective faces, and found that taller subjects placed the features lower in the face while shorter subjects placed the features higher in the face. Geldart concluded that an observer’s typical viewing angle influences their sense of what is the most attractive facial configuration. That is, taller people tend to look down at others and therefore see more apparent forehead. Shorter people, on the other hand, see more apparent chin as a result of more often seeing faces from below. The effect was stronger when the ears were fully or partially visible in the stimulus (as on the left), r = .51 than when ears were not visible, r = .38. There was more variance in feature positioning when the ears were occluded: probably the result of ears functioning as configural anchors for the other features.

Upper and lower face heights appear to maintain consistent proportions throughout adult development and I have not seen data suggesting significant sex differences in these facial areas. Pending replication, Geldart seems to have found another source of individual difference in the evaluation of attractiveness.

Wayne Hooke

ResearchBlogging.orgGeldart, S. (2008). Tall and Good-Looking? Journal of Individual Differences, 29 (3), 148-156 DOI: 10.1027/1614-0001.29.3.148

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