Does Age-dynamic Movement Accelerate Facial Age Impression? Perception Of Age From Facial Movement: Studies Of CHinese Women

Results 

Specification of the facial location for age estimation by analyzing gaze data

The percentages of gaze-fixing times for six ROIs where the observers evaluated the age of the models are depicted in Fig 6. The observation or angles of the face were integrated and analyzed. In summary, during the estimation of the ages, the results were confirmed that the gazes were focused not only on the eyes, nose, and mouth but also on the facial skin area, especially on the cheeks [F (1, 111) = 523.567, p < .001, η2 = 0.825]. 

Age perception test 

Our assessment confirmed that the effects of skin movement on age judgment differ depending on the age of the face model and that skin movement increases the age impression as the age of the model increases. Specifically, the two-way ANOVA with models’ age groups (five: in their 20s, 30s, 40s, 50s, and 60s) and facial movements (two: dynamic and static) as independent variables on perceived age (the estimated ratio of “the latter half” of the age group; 25–29 years old in the 20s group) was performed. The result showed a significant interaction between age groups and facial movements [F (4, 444) = 4.081, p = 0.003, ηp 2 = 0.035]. A simple main effect of the movement was confirmed, indicating that only models in their 50s experienced a strong effect of dynamics [F (1,444) = 11.753, p = 0.001, ηp 2 = 0.096]. The 60s group was considerably higher in the dynamic condition, though the difference was not statistically significant [F (1,444) = 2.224, p = 0.139, ηp 2 = 0.020] (Fig 7).

As faces are observed from various angles in our daily life, facial stimuli were also recorded and presented from various viewing angles. The effects of facial movement on the impression of being perceived as older diminished in some specific viewing angles. Specifically, the more the face orientation increased in the lateral (yaw) direction, the weaker the effects of the dynamics became. This tendency was especially confirmed with face models in their 50s (Fig 8). As a result, only in the frontal view (the angle of the yaw direction being zero), the facial movement shows a significant increase in age impression [t (111) = 3.040, p = 0.003, d = 0.431]. When observed from the upper right and lower right observation angles (both angles in the yaw directions at 33 degrees), marginal effects were found; upper right [t (111) = 1.927, p = 0.056, d = 0.243], lower right [t (111) = 1.817, p = 0.072, d = 0.259]. Moreover, at the observation angle of 45 degrees to the right (yaw direction), there was no effect of facial movement [t (111) = 0.673, p = 0.503, d = 0.080].

Discussion

Previous studies have mainly focused on static faces, reporting that aging characteristics of the skin, such as wrinkles, spots, and sagging, affect age impression [9–16]. In this study, we examined the effects of facial movement on age impression, based on the hypothesis that dynamic skin condition has a significant influence on judged age impression. In order to identify face areas considered important for age judgment, the observer’s gaze was also measured during trials. The results clearly suggested that the cheek skin is frequently observed when humans estimate a person’s age. The results demonstrated that facial movement affects age impressions and that the impressions increased depending on the person’s age. This confirmed that in the facial models aged 50 years, the person tends to be regarded as older when the face moves.

The gazes of all participants were recorded to specify the facial regions where observers subconsciously look for estimating the age of others. Previous studies have reported that with a few racial differences, human gazes are concentrated on facial features such as the eyes, nose, and mouth for identifying others [30–33]. The present findings showed that when humans judge the ages of others, they observe not only areas with high visual prominence, such as the eyes, nose, and mouth but also areas including skin, especially cheeks. 

Previous studies have reported that human gaze behavior is affected not only by the saliency of visual information (bottom-up processing) but also by exploratory tasks during observation (top-down processing) [34]. When people identify others by their faces, although this may vary due to cultural differences, the gaze typically concentrates on the eyes, noses, and mouths of the observed persons. In adult faces, the relative arrangement and individual morphology of the facial structure hardly change after the growth of the skeleton. Therefore, the eyes, nose, and mouth provide important information for identifying an individual. Conversely, when judging the age of an adult face, skin with more pronounced aging changes, especially the cheek area with laugh lines and sagging skin, and the area surrounding the eyes that is constantly moving, maybe a useful source of age-related information. This study found that the observers’ gaze was concentrated on the cheeks when judging the age of others, indicating that humans empirically use the skin for judging age.

Fig 8. Viewpoint depended on the effects of facial movement on age impression. The graph shows the percentages of 112 observers who perceived the models in their 50s to be in the latter half of this decade based on the models’ age impressions using the dynamic and static cognitive stimulations as a function of four directions: (a) 0˚rotation (front), (b) 45˚ rotated right in the yaw (right side), (c) 33˚ rotated right in the yaw and pitch above (right upward), and (d) 33˚ rotated right in the yaw and pitch below (right downward). The closed columns (■) and open columns (□) show the percentages of observers stimulated by dynamic and static stimulations, respectively. The marks and vertical lines on the marks signify mean values and standard errors, respectively.

Our experiments suggested that skin movements change skin appearance and affect age impression. We discuss that this happens mainly due to the following two reasons.

First, changes in the skin’s physical properties may reduce the motility of the skin's surface. The movement of the facial skin surface is caused by deeper layers of active facial muscle, as radiated through the inside of the subcutaneous tissue and skin. Structures involved in viscoelasticity, such as collagen, elastin, and dermal papilla, run throughout and are known to undergo qualitative and quantitative changes with aging [35–38]. Therefore, with age, changes in the physical properties of the subcutaneous tissue and skin affect the smooth motility of the skin surface. It has been reported that humans can perceive the activity of the subcutaneous tissue simply from the motility of points on the body surface as “biological motion” [39]. In this study, facial movement was caused by the skin around the cheek, not the edge around the features such as eyes and mouth, as surface information increased age impression in facial models aged in their 50s. This result suggests that when making an age judgment, humans perceive sensitively subtle changes in the physical properties of the skin that decrease the motility of the skin surface. Human perceivers expect the smooth movement of an expressive face. Younger people in static pictures are recognized almost in the same manner as with dynamic moving faces. However, elder skin is probably detected through rough and unsmooth movement and arise a sense of discomfort in the motion.

Second, the cheek skin movement may expose a static aged appearance. In general, wrinkles that occur as a sign of aging is confirmed on a static face by plastic deformation due to the degeneration of elastic fibers. However, when we consider facial expressions, temporary wrinkles due to elastic deformation also occur by the contraction of the skin surface. The appearance of temporary wrinkles due to this elastic deformation becomes more frequent due to changes in the physical properties of the skin [40]. This study confirmed that facial movement increases age impression in elderly models. The prominent temporary wrinkles in the aged skin are considered to cause the aged impression. 

The results of the present study partly show that there are some reasons, which cannot be explained only by dynamics. For example, the effect of movement on age impression peaks in the 50s and weakens in the 60s. It is known that wrinkles and sagging suddenly become apparent both histologically and as appearance changes in women in their 60s [22,35,41,42]. Therefore, it is considered that aging characteristics that appear in a static state, such as wrinkles and sagging, attenuate the apparent aging effect of movement in one’s 60s.

We also examined the factors associated with the observation angle in models in their 50s whose facial movements increased the age impression. The effect of movement on age impression was significant for the frontal face but decreased as the face was inclined in the lateral (yaw) direction. Previous studies have reported that the symmetry of facial movement affects age impression [43]. This indicates that the effect of the movement on age impression was maximized in the frontal face, as the lateral symmetry of facial movement was easily detected. 

This study has some limitations. First, in order to verify the effect of facial movements on age impression, the models in our experiment were asked to make simple facial movements, such as expansion and contraction, swelling, shrinking, and exercises with high expression intensity. However, it is worth considering that actual quotidian conditions, such as smiles and facial expressions when speaking, may vary from the expressions used in this experiment. Next, to prioritize the effect of facial movement on age impressions, the effect of the face observation angle was mentioned only for models in their 50s who had significantly older impressions in the dynamic condition. In the future, the relationship between facial movement and observation angle should be examined in more detail for more suitable and real-life conditions. Furthermore, this study was conducted with Chinese women, and in order to eliminate the influence of individual differences in make-up, the models were asked to participate in this experiment without make-up. The observers were limited to females because it was assumed that men and women would have different opportunities to come into contact with female faces with no make-up, which would have some effect on perceived age. Further study is needed to determine whether the present results are similar for different races, sexes, and make-up faces. Finally, we discussed the effects on age impressions based on the hypothesis that cheek skin movement and its appearance change with age. In the future, the changes in cheek skin movement and appearance with aging need to be clarified metrologically.

In this study, we examined the effect of facial movement on age impression and drew the following conclusions based on the findings. Women in their 50s may give an age impression while talking to others. This age impression is a result of the dynamic features of the cheek skin. Many of us may only recognize our own static faces in mirrors and photographs on a daily basis. However, this study elucidates the importance of targeting dynamic faces based on which others make age impressions. In the future, if we can clarify the characteristics of the skin’s physical properties that cause differences in skin appearance due to facial movements, we will be able to provide measures to maintain a younger impression on a daily basis.

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