Emotion and facial expression

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Facial expression and emotion

Introduction

Expression quote

Facial movements and expressions are seen by psychologists as one of the most effective and accurate ways of communicating one’s emotions. Emotions and feelings can be difficult at times to put into words but our behavioural reactions to these feelings are universally accepted as being similar and easily noticeable; like a smile which is accepted as conveying happiness, or a an upside down frown which usually represents the feeling of sadness or anger. This chapter discusses the relationship between facial expressions and emotions and discusses theories which link the two together.

Historical overview

A full history about the process and the origins of facial expression, is still yet to be written, but over the last 100 years there has been few behavioural scientists who have cemented the theories of facial expressions into the study of emotions (Russell & Fernandez Dols, 1997).Charles Darwin and Ekman and Friesen have been the most influential theorists and researchers of facial expressions and in this history section we look at their most important findings and developments in understanding facial expressions as a tool for emotion.

Work of Charles Darwin

Darwin in his later years.

The work of Charles Darwin has been the stepping stone for understanding the encoding of expressions of specific emotions and most of his published work went to be studied further by many other facial analysts. Darwin (1872) proposed that particular facial expressions represent an individual’s emotions and he made three distinctive points in explaining his reasons behind this (Coon & Mitterer, 2008). Firstly, the principle of serviceable habits was explained by Darwin about how certain behaviours lead to rewards. In observing mammals, Darwin noticed that angry animals showed the facial features of a furrowed brow and exposed teeth when under attack. Darwin observed this expression as being beneficial in aggressive encounters, as it scared off attackers in many of his observations. Darwin thus proposed that the angry facial expressions of mammals (which are very similar to humans) were successful, as they had been proven to being effective in scaring away opposing threats. The second principle of ‘Antithesis’ is explained by Fridlund (1994) as "opposing states are associated with opposing expressions". In an example when an individual is showing confidence this is usually expressed with an extended neck, chest and shoulders. Both of these first two principles suggest that a feeling is expressed through body language, a notion that has been carried through to the present study of facial expressions. Darwin's most prominent claim which was published was that facial expressions, much like all other learned human development, are universal and are seen as being expressed and identified in the same way all around the world (Coon & Mitterer, 2008).

Work of Ekman and Friesen

This third principle of Darwin's led to the further work and study of Paul Ekman and Friesen (1969) who through Darwin's principles and observations proposed the encoding and decoding hypothesis of facial recognition. The hypothesis predicts that if facial expressions are universal, then the expression and feeling should be represented and identified in the same way across every culture and country around the world (Fridlund, 1994). This hypothesis is most notably tested by Ekman and Friesen in 1969. The scientists took over 3000 photographs of different people around the world from Chile, United States, Argentina, Brazil and Japan. The photographs displayed the six main emotions, according to Ekman and Friesen, of sadness, surprise, anger, happiness, fear and disgust. The participants were asked which photographs best predicted each of the emotions and there was found to be an 80 to 90% accuracy rate across the sample of all participants associating the correct emotion with the expression.

There was one main limitation in the experiment as all of the tested countries had access to Western (American culture) media. Darwin's principle stated that facial expressions were universal across all cultures and therefore Ekman extended his study to Papua New Guinea and observed a group of people who had never watched a movie or read a Western cultured magazine. The procedure replicated the first study ()participants were asked to point out the photograph that best represented a particular emotion. The results reflected those of the first study, therefore confirming Darwin's hypothesis that all facial expression of emotions and feeling are universal (Ekman & Friesen, 1971).

Facial Coding System

Along with the study of the universal nature of facial expressions , Ekman and Friesen (1978) developed a system which measured and described particular facial behaviour. This method is known as the Facial Coding System (FACS)(Farah, Wilson, Drain & Tanaka, 1998). FACS objectively measures particular facial signals in terms of actions and these actions were determined by Ekman and Friesen through observation of videotapes and knowledge of facial anatomy. After observing the contractions of many facial muscles Ekman defined a total of 46 action facial units which can be used in the system (Ekman & Friesen).

The development of FACS was highly beneficial when it was introduced as it increased the importance of facial expression study in field of behavioural science and even though the method was extremely time consuming because it is precise in the encoding of facial features (Farah, Wilson, Drain & Tanaka, 1998). FACS is still used as an effective tool in the measurement of facial expression and according to Sloan and associates(2002) the system is mainly used in showing the differences between a genuine or stimulated expressions, like pain, and also in identifying people who are lying from those who are telling the truth. One of the main advancements of the process, since FACS was developed 30 years ago, has been the incorporation of the system being used through computer software. This has made the process a lot faster in recognition and more accurate as it prevents human error (Ganel, 2010).

Theories of facial expressions

The work of Charles Darwin, Ekman and Friesen on facial expression has influenced many theories and hypotheses. Theories like the innateness of facial expressions, expression-feeling link, feedback, and the readout and behavioral ecology hypothesis, and also the spontaneity and voluntary nature of expression have all been defined by the way they are influenced by and affect emotions and how particular feelings are linked to certain facial expressions.

Voluntary and spontaneous expressions

A person’s facial expression can occur spontaneously or voluntarily, as a response to an external/emotional stimulus or is expressed due to personal force with no influences from a felt emotion (Naab & Russell, 2007). Spontaneous expressions result from an immediate reaction to stimuli, such as bursting into tears after hearing something distressing, whereas forced expressions are made solely for personal gain like in the profession of acting. It is often hard to distinguish between a voluntary and involuntary facial expression as both originate from the contraction of musclesand signals from the brain (Galati, Scherer & Ricci-Bitti, 1997 & Naab & Russell, 2007).

Expression-Feeling Link

Diagram One: example of the expression feeling link. Hypothesis one = feeling and expression occur at the same time due to the emotional stimulus of a sad movie.

Through the work of both Darwin and Ekman it is seen evident that both facial expressions and feelings are both components of emotions. Deckers (2006) describes this relationship as the Expression-feeling Link which describes how different facial movements are linked to particular feelings which represent a certain emotion. For example, producing a tear or a frown and feeling a sense of loss and despair represents the emotion of sadness (Ganel, 2010). There are two hypotheses which describe this link with the first one being the most commonly accepted and simplest notion. The first hypothesis states that both feelings and expression evolve from the influence of an environmental stimulus (Diagram One) and then these expressions and feelings form to represent a particular emotion(Coon & Mitterer, 2008).

The second hypothesis that links feelings and expressions states that it is the feelings that activate the corresponding expressions (Diagram Two). A paper written by Izard (1993) studied this hypothesis and concluded that feelings produce the onset of its corresponding facial expressions. The researcher found that feeling sad results in tears developing and suggested that the reason for this was that the feelings activate a particular brain impulse which send information to particular facial muscleswhich produces the expression of the felt emotion. Since this study this process has been called the Efference Hypothesis (Decker, 2005).

If facial emotions are a result from an environmental stimulus and if feelings produce certain expression, is it possible for the expressions to produce a feeling? This hypothesis is known as the Facial Feedback Hypothesis.

Diagram Two. Example of expression feeling link. Hypothesis two

Facial Feedback Hypothesis

The facial feedback hypothesis is one of the most controversial and widely researched facial expression hypotheses. The hypothesis holds the notion that the construction of a facial expression will produce the subjective feeling of an emotion. For example, if you were to (naturally) smile while you were reading this section you would feel a sense of happiness (Reisanzein & Studtmann, 2007). This hypothesis still relates to the expression-feeling link as there still needs to be an emotional stimulus needed to produce the expression. The only difference is instead of both the feeling and expression being components of the emotion, the feedback hypothesis suggests that the muscles which form an expression(smile), send a message to the brain which than produces the feeling(Joy) (Soussigman, 2002). Charles Darwin predicted this hypothesis when he explained that the expression of an individual will intensify any particular emotion; in other words making any expression will heighten or suppress an emotion/feeling (Deckers, 2005).

The facial feedback hypothesis has been tested rigorously over the last 20 years and a recent study conducted by Soussignan (2002) examined the effect of smiling on eliciting the feelings of joy/happiness. The study mimicked an early research paper by Strack (1988), and was conducted by asking participants to hold a pencil in their mouth while watching a humorous cartoon. Some of the participants were asked to hold the pencil with both their lips and teeth (which restricted the muscle movement around the mouth) others just held the pencil with their teeth muscles around the mouth could still be used) and finally the remainder of the participants just held the pencil in their hand. Soussignman, hypothesised that according to the feedback rule, that the participants who couldn't use the muscles around their mouth to form a smile would express nil to low feelings of happiness/joy after watching the cartoon. The hypothesis was supported as the participants holding the pencil with just their teeth or in their hand were able to smile from watching the cartoon and had higher rating of feeling happy compared to the others. The results of this study and others similar to it support the facial feedback hypothesis, however, there is an equal amount of criticism that surrounds this hypothesis. Most notably it is evident that people who suffer from permanent facial paralysis are still able to express and feel particular emotions without having the use of their facial features (Deckers, 2006 & Keillor, 2002).

The Innate Nature of Facial Expression

The idea that facial expressions are innate and universal is a theory which can be dated back to work of Darwin , Ekman and Izzard. Facial expression are considered to be inherent in nature as they occur in life very early on, are universal across different cultures and countries, and also children who are born or develop blindness at a very early age still produce some facial expressions (Elfenkein & Ambady, 2002). Facial expressions are evident in newborn infants long before any other cognitive functions develop. Infants from just two weeks old are observed to smile at the sound of their mother’s voice. Within the first few months of life infants express feelings of disgust as they regularly pull faces as they react to new bitter or sour tastes (Ekman, 1972). According to Izard (1994) these facial expressions which the infants make towards an emotional stimulus are true indications of the emotion the infant is feeling at that particular time. Additional evidence supporting the innate and universal nature of expressions is through the observation of children who have become blind within the first few months of birth or who have been born with the disability. Past research has shown that these children still portray the exact expressions of smiling, crying and glaring to represent feelings of joy, sadness and anger/rage (Eibestedt, 1973 & Galati, 1997 & Thompson, 1941). Although the expressions aren't as finely tuned as 'seeing children' it still supportsu the theory that facial expressions are inherent and universal.

Readout and Behavioural Ecology Hypothesis

The behavioural functions of facial expression are hard to put into theory and for this reason there are two main hypotheses that aim to represent the functions of behavioural expressions (Russell & Fernandez Dols, 1997). So why does a tear form when we are sad? Is it because we want to show another individual our feeling or is it due to higher social motives? These concepts are explained in the readout and behavioural ecology hypothesis. The readout hypothesis explains that we express our feelings through the face, as it is a way of communicating these feelings with another individual. The hypothesis also highlights that expressing an emotion isn’t only to convey the expression to an individual (Ganel, 2010). The expression is an automated response to a stimulus, which occurs regardless of whether you are alone or in the company of others. Behavioural Ecology hypothesis on the other hand specifically refers to the behaviour of facial expressions as being tools to express one's social motives. Expressions of the face are windows into an individual’s emotions and desire for those emotions to be accepted in a social environment (Coon & Mitterer, 2008).

Table 2. Interpretation of facial expressions in relation to Readout and Behavioral Ecology Hypothesis.

Main Types of Emotions and Expression

Ekman and Tonkins in 1969 listed the main recognisable facial expressions and feelings as being happiness, sadness, anger, disgust, fear and surprise. Their study found these expressions to be universally accepted around the world and to be the most commonly expressed emotions in everyday life (Lewis, Haviland-Jones & Barrett, 2008). This section looks at the nature of these emotions paying particular attention to the facial components which express these emotions through the face.

Sadness

Sadness is an emotion that is produced from an array of visceral feelings like loss, sorrow and disadvantage (Lang, 1993). It is important to realise that the emotional state of sadness is only temporary and that the prolonged feelings of sorrow and unhappiness may be the result of an emotional disorder like depression (Haneli, Shomrat & Hess, 2009). According to Adolphs (2002), the expressions of sadness are mainly expressed more in women than men. One of the contributing factors for this is that the expressions that are associated with being sad, like expressing tears and sobbing, is considered by men to be a sign of weakness.

Ekman, Friesen and Tomkins, (1971) listed the main facial features of sadness as being:

young girl expressing sadness- dropped mouth and eyelids & formation of tears

Dropping eyelids
Lowered lips and cheeks
The formation of tears
Corners of the mouth drop downwards

The expressions which are portrayed from being sad are assisted through the contraction of the muscles around the eyes and mouth. The Orbicularis oculi muscle forces the eyelids to drop and close in the response to the formation of tears. The Depressor labii inferioris muscle is the main muscle around the mouth in which lowers and quivers the bottom lip when someone is expressing feeling of sadness (Sloan, Bradley, Dimoulas & Land, 2002).

Happiness

Children displaying happy facial expressions.

Happiness is an individual’s self-reported evaluation of their feelings of love, joy, pleasure and contentment (Young & Hugenberg, 2007). Harre and Parrott (1996) explain that the emotion of happiness comes from many positive interactions within an environmental stimulus, with the main influences being relationships, social networks, a healthy mind and body and financial stability. According to a study conducted by Wolf and Mass (2005), the main facial expressions which convey a happy face are:

Smile
Wide eyes
Lifted eyebrow and cheekbone

Wolf and Mass (2005), explains that lifting and accentuating these features is a result of positive arousal of the muscles around these features. Wikipedia outlines these main muscles and highlights that the use of the zygomaticus major is the muscle around the mouth which lifts to form a smile. Forming a smile also causes the raising of the cheekbones which is assisted by the buccinator muscle and the lifting and widening of the eyes and eyebrows is the result of the expansion of the occipito frontalis muscle.

Anger

Muscles of the face A=Frontalis, B=Procerus, C=Nasalis,G=Zygomaticus major, K=Depressor labii inferoris.

[w:Anger|Anger]] is known as the ugly emotion which can range from annoyance to intense rage. This emotion is associated with many negative feelings of frustration and hurt, disappointment, worry and embarrassment and as a result all of these feelings are accompanied by many biological changes in your body (Harre & Parrott, 1996). When you get angry, your heart rate and blood pressure rise and stress hormones are released causing you to shake, feel out of control and become hot and sweaty. The main way a person or animal communicates this emotion is through external expressions of the face. The prominent facial changes of expressing anger are through (Aviezer, 2008 & Haneli, Shomrat & Hess, 2009):

Lowered eyebrows
Creased forehead
Wide exaggerated mouth
Tight chin

The muscles associated with this expression are strained and exaggerated to emphasise the intense feeling. The procerus muscle is the dominant muscle used in the expression of anger, as it forces the frown in between the eyes and lowers the brows making an angry person look extremely menacing. The mentalis muscle which is located near the chin and mouth is tightened to emphasis the lower face during anger (Sloan, Bradley, Dimoulas & Land, 2002).

Disgust

Young girl expressing disgust. She has a wrinkled nose, frowned eyebrows and pressed lips and chin.

Disgust is the emotion which is more or so associated with the feelings annoyance, dislike, or repulsiveness to an emotional stimulus which displeases a person (Aviezer, 2008). Expressions of disgust are most commonly used as communicative tools of reacting to unwanted personal advances from others, the disliking of foods or the unappreciative response to gifts, other's lifestyles and even another person’s personality (Lang, 1993). Zeichner (2010) explains that the main physical features of someone whose disgusted are a wrinkled nose, pressed lips and frowning of the forehead. Zeichner states that the levator labii superioris muscle is the main facial contraction of disgust as it wrinkles the nose and raises the upper lip to express the feeling of dislike and revulsion. Like in anger, the mentalis muscle is also tightened to form the pressed lips and lifted chin.

Surprise

Two surprised ladies.

Surprise is another basic emotion which consists of a sudden feeling of surprise and astonishment (Lewis, Haviland-Jones & Barrett, 2008). The unexpected facial expression which this emotion evokes makes it one of the most dramatic and instantaneous expressions. The emotional state experienced when being surprised can range from being pleasant to unpleasant or even neutral in valence. Due to this reason, the emotion of being surprised usually only lasts for an instant before the valence of being surprised is transferred to another emotional state; for an example an unpleasant surpise may develop into fear or a pleasant surprise may form the feelings of happiness and joy (Haneli, Shomrat & Hess, 2009). Due to surprise being one of the more exaggerated emotions there are many ways in which the face expresses this:

Eyebrows are high and curved
Wrinkles are formed across the forehead
Wide open mouth which is formed by a dropped jaw (Reisanzein & Studtmann, 2007)

The high and curved eyebrows which a surprised face portrays is formed from the lifting and arousal of the occipito frontalis muscle. The wrinkles across the forward are formed from the lifting of the occipito frontalis muscle, which then contracts the frontalis muscle in the forehead forming a series of horizontal wrinkles (Reisanzein & Studtmann, 2007).

Fear

Artwork work of a man expressing fear

Fear is considered to be one the most distressing emotions in in response to either a real or imagined threat, danger or pain (Aviezer, 2008). Along with many physical reactions like increased heart rate and blood pressure, dilated pupils and higher production of sweat this emotion is predominately recognisable through a few particular facial features (Harre & Parrott, 1996):

Wide open mouth which is formed by the raising of the upper lip
Wide open/exaggerated eyes
The forehead and eyebrows are wrinkled and pull towards the center of the face
Stretched lips (Sloan, Bradley, Dimoulas & Lang, 2002)

The levator labii is the facial muscle which raises the upper lip and forms the wide exaggerated mouth. Another prominent facial change associated with fear is the frowning of the forehead and eyebrows to the middle of the face; this facial contraction is done through the frontalis and corrugators muscles. Finally the action of stretching lips is assisted through the buccinators muscle which pulls the lip outwards (Marsh, Kozale & Ambady, 2007).

Table of Emotions, Feelings & Facial Muscles. This table summarises the different expressions of feelings and the muscles in which form these expressions.

Artwork showing different facial expressions.

Summary

History and General Facts

Facial expressions and movements are seen by psychologists as one of the most effective and accurate ways of communicating someone’s emotions.
A person’s facial expression has the ability to occur spontaneously or voluntarily, and either occurs as a result to an external/emotional stimulus or is expressed due to personal force and no influences from a felt emotion.
Darwin (1872) started the phenomenon that particular facial expressions represent an individual's emotions and he made three distinctive points in explaining his reasons behind this.
Darwin's most prominent claim which was published was that facial expressions, much like all other learned human development, are universal and are seen as being expressed and identified around the world.
Paul Ekman (), and Friesman () who through Darwin's principles and observations proposed the encoding and decoding hypothesis of facial recognition. The hypothesis predicts that if facial expressions are universal, then the expression and feeling should be represented and identified in the same way across every culture and country around the world.
Along with the study of the universal nature of facial expressions, Ekman and Friesman, developed a system which measured and described particular facial behaviour, this method is known as Facial Coding System (FACS).
FACS objectively measures particular facial signals in terms of actions.
Ekman and Tonkins in 1969 listed the main recognizable facial expressions and feelings as being happiness, sadness, anger, disgust, fear and surprise. Their study found that these expressions to be universally accepted around the world and to be the most commonly expressed emotions in everyday life.

Theories of Facial Expression

Expression-feeling Link describes how different facial movements are linked to particular feelings which represent a certain emotion. For an example producing a tear or a frown and feeling a sense of loss and despair represents the emotion of sadness.
The Facial feedback hypothesis is one of the most controversial and widely researched facial hypotheses. The hypothesis holds the notion that the construction of an expression will produce the subjective feeling of an emotion.
Facial expression are considered to be inherent in nature as they occur in life very early on, they are proven to be universal across different cultures and countries and also children who are born or develop blindness at a very early age still produce some facial expressions.
The readout hypothesis explains that we express our feelings through the face, as it is a way of communicating these feelings with another individual. The hypothesis also highlights that expressing an emotion isn’t only to convey the expression to an individual. The expression is an automated response to a stimulus, which occurs regardless of whether you are alone or in the company of others.
Behavioural Ecology hypothesis on the other hand specifically refers to the behaviour of facial expressions as being tools to express ones social motives.

Quiz

Please Review all Diagrams and Tables before attempting the quiz.

References

Adolphs, R. (2002). Recognizing emotion from facial expressions: Psychological and neurological mechanisms. Behavioral and Cognitive Neuroscience Reviews, 1, 21–62. doi:10.1177/1534582302001001003

Aviezer, H., Hassin, R. & Ryan, J. (2008). Anger, Disgusted or afraid. Psychological Science, 19, 724-732

Coon, D. & Mitterer, J. (2008). Introduction to psychology: gateways to the mind and behaviour. (12th Ed). Belmont, CA: Wadsworth Pub inc

Deckers, L. (2005). Motivation: biological, psychological and environmental (2nd Ed). Boston, MA: Pearson Inc

Ekman, P. & Friesen, W. (1971). Constants across cultures in the face and emotion. Journal of Personality and Social Psychology, 17, 124-129

Ekman, P. (1972). Universals and cultural differences in facial expressions of emotion. In J. Cole (Ed.), Nebraska Symposium on Motivation (Vol.19, pp. 207–283). Lincoln, NE: University of Nebraska Press.

Ekman, P. & Friesen, W. V. (1978). The Facial Acting Coding System: A Technique for the measurement of facial movement. Palo Alto, CA: Consulting Psychologists Press.

Elfenbein, H. A., & Ambady, N. (2002). On the universality and cultural specificity of emotion recognition: A meta-analysis. Psychological Bulletin, 128, 203–235. doi:10.1037/0033-2909.128.2.203

Farah, M. J., Wilson, K. D., Drain, K., & Tanaka, J. N. (1998). What is “special” about face perception? Psychological Review, 105, 482–498. doi:10.1037/0033-295X.105.3.482

Fridlund, A. J. (1994). Human facial expression: an evolutionary overview. San Deigo: Academic Press

Galati, D. Scherer, K. & Ricci-Bitti, P. (1997). Voluntary facial expressions of emotion: comparing congenitally blind with normal sight encoders. Journay of Personality & Social Psychology, 73, 1363-1379

Ganel, T. (2010). Revisiting the relationship the between the processing of gaze and the processing of facial expressions. Journal of Experimental Psychology: Human Perception and Performance. Doi: 10.1037/a0019962

Haneli, S., Shomrat, N. & Hess, U. (2009). Emotional verus neutral expressions and perception of social domiance and submissivness. Journal of Emotion, 9, 378-384. Doi: 10.1037/a0015958

Harre, R. & Parrott, W. The emotion: social, cultural and biological dimensions. Thousand Oaks, CA: Sage Publications

Izard, C. (1994). Innate and universal facial expressions: evidence from developemental and cross-cultural research. Psychological Bulletin, 115, 288-299.

Keillor, J. & Barret, A. (2002). Emotional experience and perception in the absence of facil feedback. Journal of the International Neuropsychological Society, 2, 130-135

Lang, P. (1993). Looking at pictures: Affective, facial, visceral, and behavioral reactions .Psychophysiology, 30, 261–273.

Lewis, M. Haviland-Jones, J. & Barrett, L. (2008). Handbook of emotions (3rd Ed). New York, NY: Guilford Publications Inc

Marsh, A. A., Kozak, M. N., & Ambady, N. (2007). Accurate identification of fear facial expressions predicts prosocial behavior. Emotion, 7, 239–251.

Naab. P. & Russell. J. (2007). Judgements of emotion from spontaneous facial expressions of the expressions of New Guineans. Journal of Emotion, 1, 736-744. Doi: 10.1037/1528-3542.7.4736

Reisanzein, R. & Studtmann, M. (2007). One the expression and experience of surprise: facial feedback hypothesis. Emotion Journal, 7, 612-627. Doi 10.1037/1528-3542

Russell, J & Fernandez Dols, M. (1997). The psychology of facial expression. New York, NY: Cambridge University Press

Soussignan, R. (2002). Duchenne smile, emotional, experience, and autonomic reactivity. Emotion Journal, 2, 52-74. Doi: 10.1037/1528-3542

Sloan, D. M., Bradley, M. M., Dimoulas, E., & Lang, P. J. (2002). Looking at facial expressions: Dysphoria and facial EMG. Biological Psychology,60, 79–90.

Thompson, J. (1941). Development of facial expression of emotion in blind and seeing children. Archives of Psychology, 247, 2-47

Wolf, R. & Mass, R. (2005). The facial pattern of disgust, appetence, excited joy and relaxed joy: An improved facial EMG study, Scandinavian Journal of Psychology, 46, 403–409.

Young, S. G., & Hugenberg, K. Mere Social Categorization Modulates Identification of Facial Expressions of Emotion. Journal of Personality and Social Psychology. doi:10.1037/a0020400

	sobbing causes the onset of grief
	smile results in a person feeling more happy
	feeling sad results in tears and frowning of the eyebrows
	viewing cartoons evokes the expression of a smile and then the feelings of joy and happiness.

	Behavioral Ecology Hypothesis
	Feedback hypothesis
	Expression- feeling link
	Theory of innateness.

	Zygomaticus minor
	Frontalis muscle
	Zygomaticus major
	The lips.

	both expressions are produced from muscle contractions
	the involuntary and voluntary expressions are influenced by signals in the brain
	both a and b
	none of the above.

Motivation and emotion/Textbook/Emotion/Facial expression