Bizygomatic Width and its Association with Social and Personality Traits in Males/Distancia Bicigomatica y su Asociacion con Habilidades Sociales y Rasgos de Personalidad en Hombres.
Since Gall's publication (Gall, 1835) there has been a persistent interest in finding a direct relationship between the temperamental, behavioral, emotional, moral and ethical traits of an individual and their physical appearance, particularly centered upon the craniofacial shape. There is little scientific literature studying straightforward connections between behavioral and psychological traits and facial appearance. There is research treating birth disorders and syndromes (Kelly et al, 2005; Jones, 2007), where specific morphogenetic variants relating to the different disorders and syndromes has been found. Non-pathological studies have found associations between the forehead angle and impulsivity (Guerrero et al., 2016) or the more studied maxillary width-to-height ratio (fWHR) as a marker for male dominance (Stirrat et al., 2012; Valentine et al., 2014).
The shape of the brain can be predicted from the craniofacial shape (Richtsmeier & Flaherty, 2013) and from the early stages of neurodevelopment shows a special interconnection with the face (Kjaer, 1995). The prenatal face and brain, both stem from the same layer of the notochord, the ectoderm, and both structures occur within a very close time span of one another (Donovan-Lepore et al., 2006), finding that the face is essentially supported by the growing brain which undergoes extensive morphogenetic changes (Diewert & Lozanoff, 1993).
Corman (1970) observed that areas of the face that were in expansion (wider) were related to extroversion, interest/motivation, the need of affirmation and hyposensitivity, and contracted areas were related to inhibition, disinterest/non-motivation, less need of affirmation, and hypersensitivity. He divided the face into three levels for analysis and gave to each face level width an area of interest (Fig. 1) and proposed that each face level interacts with the others and it can only be evaluated in comparison with the others (or at least with one other level). This proposal matches MacLean's hypothesis of the triple brain (1970 and 1990), later supported by research in Neuropsychology (Rains, 2004), Embriology (Kjaer) and the mainly accepted idea among scientists that more neural tissue means greater computational capacity (Goldberg, 2002). The scientific literature has found a close relationship between emotions and the different areas of the limbic system at different ages (Suzuki etal, 2013; Bartholomeusz et al., 2014), which is contained behind the maxillary area. The aim of this paper is to study the influence of the maxillary width (bizygomatic arch), when compared to the mandibular width (bigonial arch), on the individual's approach to socio-emotional aspects, such as the need for interaction with others (independence/gregariousness) or the ability or lack thereof to express emotions (expressiveness/alexithymia).
MATERIAL AND METHOD
The present study meets the ethical standards and has been approved by the University Ethical Committee (CEEAH - Universitat Autonoma de Barcelona). In addition, we had the written consent of the participants, provided that the results were anonymous. Nevertheless, there were no ethical violations in testing the subjects underwent, nor were they subjected to any physical or psychological harm.
Participants. The total sample consisted of 82 subjects. The average age was 38.07 years (10.66). Everyone was of an adult age and in good health and all signed a document of consent agreeing to participate in the study which included tests, evaluations, photographs and measurements for research purposes only.
Participants were divided into two groups according to their bizygomatic arch characteristics (Fig. 2).
* Group A, (bizygomatic arch in contraction): Distance between Zy's at least 0.5 cm. narrower than distance between Go's (55 subjects).
* Group B, (bizygomatic arch in expansion): Distance between Zy's at least 0.5 cm wider than distance between Go's (27 subjects).
In order to determine which subjects were to participate in the study searches were carried out in a large shopping center of Barcelona. For three days, three independent collaborators asked passers-by at a designated entrance, to participate in the study.
Those who accepted had their bizygomatic and bigonial arches measured in situ, using calipers (see in Instruments and procedure). The volunteers that meet the criterion of minimum difference (0.5 cm) were included in the study. Of the 116 who initially agreed to participate, 87 met the inclusion criteria. These subjects were given an appointment to proceed with the testing in the near future at the Institute of Craniofacial Psychology. Five of the 87 volunteers did not come to proceed with the testing. The final size of our sample consisted of 82 subjects.
Instruments. Once participants were classified as belonging to one group or another and their participation confirmed, they were given the following tests in the order shown below:
Anthropometric measurements: Using calipers and following the methodology developed by Farkas (1994) the distance was again measured between anthropometric points Zy and compared that with the measurement of the distance between anthropometric points Go (Fig. 3). With the help of an assistant the distance Zy-Zy and Go-Go were measured twice, the mean of these two readings being the final figure used. The maximum observed discrepancy between the two measurements was 1 mm.
Photometric Measurements: To take measurements of the distances (Zy-Zy and Go-Go), using photometry and ImageJ software version 1.42q (Rasband, 2009) standardized digital photographs of the subjects were taken with a Canon 400 D Digital using a 17-85mm lens, fixed to a height adjustable tripod at a fixed distance of 1.5 m from the individual to be photographed. The same 67mm zoom was always used and two halogen spot lights were fixed on a black background to avoid any shadows appearing in the photographs. Each subject was seated in a chair of fixed height and placed in the same position and a wall mounted support held the head in the correct position. Those wearing glasses were asked to remove them and all subjects were encouraged to maintain a neutral and relaxed facial expression.
Visual assessment: For a total period of 15 hours, two judges were trained as observers in the visual assessment of morphological types (group A and group B).
Each judge viewed the subjects as they were sat facing them and always from the same distance. The judges were given sufficient time to conduct the analysis and afterwards the resulting scores for each subject were noted on a template. The possible scores were -3, -2, -1, 0, +1, +2, +3. The maximum positive score (+3) indicated that the subject had maximum retraction in the mid zone of the face, while the maximum negative score (-3) indicated a minimum retraction in the mid zone of the face. A score of zero indicated that the judges observed no difference between the width of the mid zone of the face and the mandible / jawbone. In order to verify that both judges had been properly trained, their level of agreement in the classification of subjects belonging to group A or B was calculated, giving a kappa value = 0.63 (p <0.0005) which is considered good (Landis & Koch, 1977).
Psychological evaluation instruments: Each subject was subjected to 5 psychological assessment tests:
* Personality Factor Questionnaire - 16PF, version adapted to Spanish (Seisdedos et al., 1989). The Q2 factor was used, which measures the subject's ability to incorporate himself into and work within a group plus their level of self-sufficiency.
* Attitudes and cognitive strategies - AECS (Moraleda et al., 2004). The Apathy-Withdrawal scale was used which corresponds to the category of Social Attitude.
* Personality Inventory Pedagogical Institute "Saint Georges" using the Sociable Misanthropic scale - Inv. SG (Universite de Montreal, 1971).
* Toronto Alexithymia Scale (TAS-20) for the Spanish sample (Moral de la Rubia & Retamales, 2000).
* Emotional Expressivity Scale (EES) (Kring et al., 1994).
Procedure. Statistical analysis was done using SPSS 19 (2010). For agreement in participant's classification in the two defined groups, the Kappa index was used. The agreement between quantitative measures was calculated with the intraclass correlation coefficient for absolute agreement (ICC). For comparison of the two groups in psychological measures, analysis of covariance was employed, with age as adjusting variable. In this last analysis effect size was obtained through Cohen's D. With a type I error probability of 0.05 and the estimates obtained using our sample size, we obtained a statistical power of 0.82 for detecting differences greater than 2 points in 16 PF.
Descriptive results of demographical, facial and psychological measures are presented in Table I.
Before doing any statistical test the normality of the variables in each group was tested employing Shapiro-Wilk test and visual examination of box-plots. All the variables showed Gaussian distributions with insignificant deviations from normality.
The concordance in the classification in the two groups from the visual, anthropometric and photographic information was absolute (Kappa = 1). The ICC for the difference between Zygonions and Gonions obtained with anthropometric and photographic procedures was 0.978 (CI95 % 0.957 to 0.987).
Table II shows the comparison of psychological measures between groups. Raw differences (Group A minus Group B) are first presented, followed by adjusted differences by age. All the comparisons are very significant from a statistical point of view, with lower limits for confidence intervals very far from zero value. Cohen's D values are very large, ranging from 1.16 to 5.26.
A high degree of correspondence has been found between visual, anthropometric and photometric measurements used to measure the bizygomatic and bigonial arch widths. Although it is necessary to conduct more studies of this type, these results support the idea that it is possible to use any of these measurement methods, when dealing with bizygomatic and bigonial arch measurements.
Regarding the comparison of groups with previously assessed psychological characteristics, subjects with the bizygomatic arch in contraction (group A) were more self-sufficient and showed less inclination to join in with the group. They also displayed a reluctance or reduced ability to describe and express their emotions and had greater difficulty displaying these emotions outwardly compared with the subjects with the bizygomatic arch in expansion (group B).
Subjects with a facial morphology with the bizygomatic arch in contraction are more independent and display a reduced capacity to join in with a group compared with the group of subjects who have the bizygomatic arch in expansion; the latter cooperated more readily and found it easier to connect with the group. To illustrate this, let us look at the standardized test 16 PF percentiles obtained by the 55 subjects in the test group, which would appear to be sufficiently revealing: the vast majority of subjects (85.2 %) were in the 10 percentile and the rest were between 8 and percentile 9.
The sample shows a trend towards the contraction of the bizygomatic arch width, which highlights the possibility of this being a more common trait among men. In our sample the contraction of the bizygomatic arch showed a significant correlation with higher scores of alexithymia, which has also been previously identified as a more prevalent symptom among men than among women (Levant et al., 2009).
Besides the most studied facial width-to-hight ratio (fWHR) (Stirrat et al.; Valentine et al.), the variable taken in this study (width differences between bizygomatic and bigonial arches) seem to be another good marker to be taken into consideration in further research.
Limitations to our study included a relatively small sample size and consequently the generalization of our results; however, the data gained from the study shows a strong correlation between anthropometrical measurements and psychological variables. In addition, we did not take into account additional elements of the face described by Corman as moderator variables and do not know their effect on the studied correlations, although the results show a strong relation between the bizygomatic arch and the pychological traits defined above. This strong relationship is confirmed with the high values of the Cohen's D.
To our knowledge this paper is one of the first studies that shows a correlation between the comparison of bizygomatic and bigonial arch widths and some socioemotional aspects and personality traits. Viewing the results carefully, the data shown suggests that craniofacial structure can predict some personality traits, opening up the possibility of continuing with this methodology to address in a future, more in-depth studies, the relationship between the face and other personality traits.
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Institute of Craniofacial Psychology
c/ Pau Claris 120, 3 2a 08009
Julian Gabarre-Mir (1); Jose B. Navarro-Pastor (2); Cristina Gabarre-Armengol (1) & Santiago Estaun-Ferrer (3)
(1) Institute of Craniofacial Psychology, Barcelona, Spain.
(2) Department of Psychobiology and Methodology, Universitat Autonoma de Barcelona, Bellaterra, Spain.
(3) Department of Basic, Evolutive and Educational Psychology, Universitat Autonoma de Barcelona, Bellaterra, Spain.
Caption: Fig. 1. Levels/Zones of the face--Areas of interest
Caption: Fig. 2. Group A with contracted bizygomatic arch (right) and Group B, with expanded bizygomatic arch (left).  Zygion (Zy) is the most lateral point of each zygomatic arch. It is identified by physical palpation.  Gonion (Go) is the most lateral point of the mandibular angle. It is identified by physical palpation.
Caption: Fig. 3. Faciall measurements with compass/calipers.
Table I. Description of demographical, facial and psychological measures. Group A - n=55 Mean St.Dev. Min./Max. Age 35.67 10.38 20 / 58 Anthropometric 137.05 7 120 / 146 Zy-Zy distance (mm) Anthropometric 129.50 7.20 116 / 142.5 Go-Go distance (mm) Anthropometric distance - 7.74 5.19 -20.50 / -5 difference (mm) Photographic 137.74 7.16 122/150 Zy-Zy distance (mm) Photographic 130.29 7.71 117 / 143 Go-Go distance (mm) Photographic distance - 7.44 4.88 -19 / 0 difference mm) 16PF 12.37 2.77 6 / 17 AECS 22.22 7.35 10 / 38 Inv.SG 18.89 4.3 6 / 25 TAS-20 42.37 11.12 23 / 62 EES 74.07 13.62 42 / 97 Group B - n=27 Mean St.Dev. Min./Max. Age 39.25 10.69 19 / 66 Anthropometric 124.38 6.52 105 / 137.5 Zy-Zy distance (mm) Anthropometric 147.40 9.36 125/ 173 Go-Go distance (mm) Anthropometric distance 22.68 5.63 10 / 36 difference (mm) Photographic 126.89 7.09 109/141 Zy-Zy distance (mm) Photographic 147.85 9.52 129/ 171 Go-Go distance (mm) Photographic distance 20.6 6.29 8 / 37 difference (mm) 16PF 30.51 3.43 22 / 36 AECS 43.18 9.69 18 / 61 Inv.SG 7.91 4.29 0 / 17 TAS-20 56.62 12.89 31 / 79 EES 49.24 16.7 25 / 97 Table II. Raw and adjusted comparison of groups in psychological measures. Raw results N=82 Mean Diff ** Mean Diff. ** 16PF 18.14 18.06 AECS 20.96 21.23 Inv.SG -10.98 -11.49 TAS-20 14.25 14.97 EES -24.83 -26.40 Adjusted results * N=82 p 95% CI Cohens'D 16PF <.0005 16.52 to 19.6 5.26 AECS <.0005 16.96 to 25.5 2.23 Inv.SG <.0005 -13.45 to -9.53 2.64 TAS-20 <.0005 9.17 to 20.77 1.16 EES <.0005 -33.59 to -19.21 1.64 * Adjusted by age ** Group A minus group B