Evaluating the Sensitivity to Virtual Characters Facial Asymmetry in Emotion Synthesis

Figures & data

Figure 1. Summary of the results from (Ahn et al. 2013). Results are the same for both the male (James) and the female characters (Kamila). Basic emotions were rated as less realistic with asymmetry whereas complex emotions were rated as more realistic with degree of asymmetry.

Figure 2. Facial expressions for a basic emotion (sadness). This asymmetric facial expression (left) is slightly amplified on the character’s left side of the face. It is built by biasing a single emotion (right).

Figure 3. Facial expressions for a complex emotion (vicious) combining two distinct VAD states for the asymmetric facial expression (left). The symmetric facial expression is obtained by averaging the VAD coordinates of the two asymmetric components (right).

Figure 4. (left) One of the four illustrations of a keyword showing a symmetric and an asymmetric facial expression on the male agent. The other three combinations for this agent and keyword were obtained by swapping the location of the two faces (a) and by mirroring the left and right sides of the asymmetrical face (b). (Right) The stimuli display setup on a 30” screen.

Table 1. Screen location influence (p-value).

	Basic		Complex
	Sym score	Asym score	Sym score	Asym score
p-value	0.449	0.506	0.112	0.267

Table 2. Side of the facial asymmetry influence (p-value).

	Basic		Complex
	Sym score	Asym score	Sym score	Asym score
p-value	0.261	0.958	0.281	0.161

Table 3. Subject gender and character gender (p-value), different scores of symmetry and asymmetry given by male and female subjects.

	James		Kamila
	Sym score	Asym score	Sym score	Asym score
Sadness	0.503	0.846	0.937	0.906
Peaceful	0.841	0.956	0.876	0.580
Fear	0.542	0.579	0.879	0.874
Smirk	0.733	0.552	0.967	0.910
Vicious	0.918	0.915	0.840	0.664
P2bCool	0.868	0.800	0.823	0.856
Good2b	0.736	0.977	0.910	0.664
Suspicious	0.994	0.489	0.988	0.692

Table 4. Subject gender and asymmetry (p-value).

	Male Sym/Asym	Female Sym/Asym
Sadness	<0.001	<0.001
Peaceful	<0.001	<0.001
Fear	0.984	0.800
Smirk	<0.001	<0.001
Vicious	<0.001	<0.001
P2bCool	0.095	0.156
Good2b	0.036	0.003
Suspicious	<0.001	<0.001

Table 5. keywords and the associated short definitions.

[Keyword]	Short definition
[Sadness]	Emotions experienced when not in a state of well-being
[Peaceful]	Free from disturbance
[Fear]	An unpleasant emotion caused by the belief that someone or something is dangerous, likely to cause pain, or a threat
[Smirk]	A forced smile expressing self-satisfaction or disdain rather than pleasure.
[Vicious]	Deliberately cruel or violent, as if enjoying negative feelings
[Pretend to be cool or okay]	Anxious deep inside but try to show off his/her calm
[Too good to be true]	A positive surprise but hard to believe
[Suspicious]	Having or showing a cautious distrust of someone or something

Keywords and short definitions provided for the eight facial expressions in the experiment:

VAD coordinates of asymmetric expressions: As explained before, the basic expressions are built from a single asymmetrically biased reference emotion, whereas complex expressions are built from two distinct emotions. The symmetric expression is given by the average of left and right VAD coordinates. Table 6 indicates the ANEW keywords (indicated in italics) (Bradley and Lang 1999) that were directed used or edited with the VAD-based system from (Ahn et al. 2013):

Table 6. VAD coordinates of ANEW keywords exploited for building the asymmetric expressions. LR indicates the left-biased asymmetric expression.

[Keyword]	ANEW keywords VAD coordinates used for the asymmetric expressions
[Sadness]	LR: sad [−0.85,-0.22,-0.39] with side weights: 0.75 on the left, 0.25 on the right
[Peaceful]	LR: peace [0.68,-0.51,0.11] with side weights: 0.75 on the left, 0.25 on the right
[Fear]	LR: Afraid [−0.75,0.42,-0.56] with side weights: 0.75 on the left, 0.25 on the right
[Smirk]	L: VAD space origin [0,0,0] = neutral, R: happy [1,0.48,0.53] * 1.3
[Vicious]	L: pleasure [0.66,-0.42,0.8] R: jealousy [−0.31,-0.14,0.5]
[Pretend to be cool or okay]	L: Anxious [−0.12,0.46,-0.26] R: relaxed [0.3,-0.54,-0.3]
[Too good to be true]	L: happy [0.5,0.5,0.06] R: sad [−0.59,0.24,-0.56]
[Suspicious]	L: serious [0.3,-0.1,0.1] R: passion [−0.3,0.6,0.6]

The RL is obtained by mirroring the LR expression.

Table 7. One of the four combinations of each of the eight keywords for the male and female agent’s facial expressions. Facial expression stimuli (one of the four possible combinations per character) for the eight emotions:

Figure 5. Experimental conditions. The four layout possibilities of an emotion combining the location of the symmetric facial expression either on the left or the right side of the screen (screen location), and the two possible designs of the asymmetric expression (facial asymmetry).

Figure 6. Evaluation of basic and complex emotions depending on the two cases of facial asymmetry as depicted in Figure 5.

Figure 7. Lack of influence of subject’s gender and virtual character gender in the evaluation of the eight emotional words.

Ahn, J., S. Gobron, D. Thalmann, and R. Boulic. 2013. Asymmetric facial expressions: Revealing richer emotions for embodied conversational agents. Computer Animation and Virtual Worlds 24 (6):539–51. doi:10.1002/cav.1539.

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Bradley, M. M., and P. J. Lang. 1999. Affective Norms for English Words (ANEW): Stimuli, instruction manual and affective ratings (Tech. Report C-1). Gainesville: University of Florida, Center for Research in Psychophysiology.

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