Motivation and emotion/Book/2014/Pupil dilation and emotion

Pupil dilation and emotion:
What does pupil dilation indicate about emotion?

Multimedia presentation (5 min)

Overview The eyes are often referred to as being the windows to the soul. This chapter seeks to discuss current studies and beliefs about pupil dilation and emotion, along with the relationship between pupil dilation and deception. The aim of this chapter is to provide a better understanding of pupil dilation and emotion to influence our daily lives in a positive manner through an increased ability to recognise signals of emotion from others.

The eye

Figure 1. The eye on the left has been treated with dilating eye drops so more of the retina is visible during examination

Basic anatomy

Our eyes are the organ responsible for sight, and achieve this through many components working together.

Figure 2. Diagram of the Eye

The sclera, or white of the eye, is a layer of connective tissue that gives the eye its spherical shape (Marieb, 2003; The Five Mile Press, 2002). The cornea is the transparent layer at the front of the sclera where light initially enters the eye to be bent onto the retina (The Five Mile Press, 2002). The choroid is the middle layer of the eye that contains blood vessels that serve the eye (The Five Mile Press, 2002) and the pigment that helps prevent light from scattering within the eye (Marieb, 2003). The ciliary body holds the ciliary muscles that keep the lens in place so it is able to work with the cornea to project light onto the retina (The Five Mile Press, 2002).

In front of the lens are the iris and pupil. They are controlled by the autonomic nervous system, which is divided into the sympathetic (fight or flight) and the parasympathetic (rest and digest)(Marieb, 2003). The coloured part of the eye is the iris, which in Greek means rainbow (Marieb & Hoehn, 2007). Interestingly, there is no blue or green pigment in the eyes. Those with pigment in the stroma (fibres in the iris) have eyes appearing brown, and those without have eyes appearing variations of blue, green or hazel (Mason, 1924). The pupil is the hole within the iris through which light travels. The pupil constricts (gets smaller) and dilates (gets bigger) to regulate the amount of light entering the eye for best vision. The light that enters the eye is absorbed, resulting in the pupil appearing black (Mellerio, 1971).

The iris consists of two smooth muscle layers. The circularly arranged muscles of the iris are responsible for the constriction of the pupil in bright lights, with the radially arranged muscles constricting to cause dilation of the pupil in low light (Marieb, 2003).

The retina is the inner layer of the eye and is considered part of the brain due to its processing ability (Gowin, 2010). It absorbs light and contains the photoreceptors known as rods and cones. Rods are used in vision during dim light, while cones are activated in bright light and are also responsible for colour vision (Marieb & Hoehn, 2007).

Figure 3. Optic chiasma

The area at the back where the optic nerve exits the eye is known as the optic disk, or blind spot. This area of the eye has no photoreceptor cells, so when light focuses on this spot we are unable to see it (Marieb, 2003).

Look at the image below to see an example of how your blind spot works. First, cover your right eye and focus your left on the cross surrounded by a circle (on the right), then slowly move closer to the image until the cross on the left disappears from sight!

From the optic disk the optic nerve carries the impulses, that have been converted from light on the retina, to the brain to be processed. The optic nerve travels through the optic chiasma to the brain, with half the fibres from each side crossing to the opposite side of the brain and on to the occipital lobe (Marieb & Hoehn, 2007).

Figure 4. Blind spot example

Pupillary light reflex Figure 5. The pupillary light reflex The pupillary light reflex constricts and dilates the pupil in response to the brightness of light in order to protect the eye and allow for best possible vision (Dragoi, 1997).

Dilation and emotion

Love and attraction

Our pupils dilate when we see someone we consider attractive. Leknes et al. (2012) state that this dilation may also influence our approach behaviour. This may be due to oxytocin, which is a hormone that acts on the brain, including influencing aspects such as the nervous system and emotions. It is also often referred to as the love hormone as it triggers feelings of trust and attraction. Oxytocin has a strong relationship with child birth as it is released during labour and is an essential hormone in lactation (Carter et al., 2007).

Both males and females were found by Tombs and Silverman (2004) to be most attracted to members of the opposite sex with more dilated pupils. They report this finding to be a biological result of dilated pupils being an indicator of sexual arousal.

Sadness

Figure 6. Constricted pupils are perceived as appearing more sad.

Constricted pupils are associated with sadness (Harrison, Singer, Rotshtein, Dolan, & Critchley, 2006). In a study by Harrison et al (2006) on pupillary contagion, it was found that not only are smaller pupils perceived as appearing sadder but also that there is a reduction in pupil size when it is observed in others. Humans often copy the body language and expressions of others, this is not always conscious and shows empathetic understanding as a result of motor mimicry. It is suggested that similar process are involved in the mirroring of both the actions and emotions of those we empathise with. Harrison et al (2006) investigated the extent to which perception-action models and mimicry apply to pupil dilation. They found some of the first evidence supporting the involvement of the autonomic nervous system in perception-action models of empathy, with perception of sad faces correlating with arousal of the autonomic nervous system and pupillary mimicking.

Motor mimicry: A social phenomena that communicates we understand or empathise with what another person is feeling, such as cringing in response seeing someone get injured (Bavelas, Black, Lemery, & Mullett, 1986). |Perception-action model: The website 'Perception-action approach to intervention for children with movement disorders' (http://p-a-approach.weebly.com/theoretical-foundation.html) explains perception-action theory as involving forming an understanding of an environment or situation based on actions driven by sensory channels. It is a cycle in that perception drives actions, and actions are needed to form perceptions.

Current research findings

Recall of words with varying emotionality

Pupil diameter is controlled by the Autonomic Nervous System and changes to dilation have been shown to be linked to emotion and cognitive effort (Babiker, Faye, & Malik, 2013). One study looked at both emotion and cognitive effort involved participants attempting to remember words from a list that were either positive, negative or neutral in emotionality (Võ et al., 2008). They were then required to indicate which words in a series were from the previous list (old) or new. Pupillary responses were measured to see the emotional responses to each word, as well as cognitive effort from memory retrieval. It was found that when an old word was presented pupil dilation will be largest for neutral words and smaller for the positive and negative words. It was also found that when a new word was presented, participants pupils dilated most for words negative in emotionality, slightly less for positive words and least to neutral words. These findings suggest words higher in emotionality involve more cognitive effort when encoding into memory, but are also easier to recall.

Response to art

The more interesting an artwork is perceived to be, the greater the dilation of the pupil (Libby, Lacey, & Lacey, 1973). In a study conducted by Kuchinke, Trapp, Jacobs, & Leder (2009) there was a relationship found between pupillary response and aesthetic pleasure. Through the use of cubist paintings they found that the higher cognitive fluency, the more aesthetic pleasing the experience of the art was perceived to be emotionally. They report that this higher cognitive fluency caused an increase in pupil dilation.

Cognitive fluency: refers to the ability to cognitively process. In this case specifically, the ability to identify objects they recognised in the paintings.

Dilation and deception

Case study Someone stole John’s sushi he had brought for lunch at work today, so he confronted two of his co workers about it. The first denied it and gestured toward an empty pizza box. The second maintained a strange amount of eye contact while she gave an indepth story as to why it could not have been her. When he wasn’t intrigued by her strangely large pupils, he was staring at the seaweed in her teeth.

Lying and deception are defined by DePaulo et al (2003) as deliberately trying to mislead someone. People often believe that someone who is lying will avoid eye contact. However, this is not always the case as when we lie we are consciously making more effort to be convincing. A study by Mann et al (2012) involved interviewing passengers at an airport about their trip and measuring the amount of eye contact that was maintained with the interviewer. They found that those who were lying were deliberately making much more eye contact, along with more (unnecessary) detail.

A more subtle indication of deceptive behaviour is pupil dilation. When we deceive, or lie, there is a higher amount of cognitive effort involved in creating the lie than recalling the truth (Mann et al., 2012). During times of higher cognitive effort, and higher levels of adrenaline, our pupils will naturally dilate (Babiker, Faye, & Malik, 2013). This helps to explain why when we lie our pupils dilate, because we are experiencing the resulting stress, anxiety, and mental effort as we try to create a believable story, that is consistent with what others know, in our minds (DePaulo, 2003).

The dilation of the pupils can help with lie detection further through pupillometry, which is the measurement of pupil diameter. Using pupillometry is a highly practical meted as it is non-invasive, able to be recorded without participant awareness, and is less expensive than many other psychological research methods, such as MRI's. It also provides reliable results as, for the most part, pupil diameter cannot be consciously controlled by most (Laeng, Sirois, & Gredebäck, 2012).

“ "Oh! What a tangled web we weave, when first we practise to deceive."
(Sir Walter Scott, Marmion) ”

Conclusion

This chapter initially looked into the basic anatomy of the eye in order to create a better understanding of the involvement of the pupil. Following this, the pupil and studies on the relationships between dilation and arousal, attraction and cognitive effort, along with the indication of empathy from perceived sadness that is influenced by the perception of constricted pupils, were covered. By applying this knowledge to everyday life we may be better able to recognise, and empathise with, emotions of others. The relationship between dilation and deception has also been explored, with a focus on the indicators of deception. The method of pupillometry to measure dilation in lie detection provides individuals (such as those in law enforcement) with a reliable and non-intrusive method of testing the honesty of those in question.

In conclusion, there is still a lot more we do not know about the relationship between pupil dilation and emotion. However, from the studies mentioned in this chapter we can see that the eyes may really be the windows to the soul… Or at least to our emotions.

Summary

• The many structures of the eye work together to allow for best possible vision.
• The iris is composed of two layers of smooth muscle that dilate or constrict the pupil (Marieb, 2003).
• Dilation and constriction is often to regulate light entering the eye (Marieb, 2003).
• The pupillary light reflex controls this regulation and is triggered by the autonomic nervous system (Dragoi, 1997).
• Dilation of the pupils often occurs when we see someone we find attractive (Leknes et al, 2012), and we also deem people with more attractive when their pupils are dilated. This is because it indicates both sexual arousal and mutual interest (Tombs & Silverman, 2004). Our pupils have also been found to dilate in response to aesthetically pleasing artworks (Kuchinke, 2009).
• Constriction of the pupils influences as to see someone as more sad, and when we empathise with them our pupils also constrict in response. This is known as motor mimicry (Harrison et al, 2006). The perception-action model and the autonomic nervous system trigger this constriction.
• The perception-action model is about perceptions driving actions, and actions developing perceptions.
• Contrary to popular belief, liars do not always avoid eye contact.
• Due to the high cognitive load and stress of creating a lie, our pupils will often dilate (Mann et al, 2012).
• Pupillometry is a reliable method of lie detection as, for the most part, dilation of the pupils is not a voluntary action (Laeng, Sirois, & Gredebäck, 2012).

Quiz

Point added for a correct answer:    Points for an incorrect answer: Ignore the questions' coefficients: 1 The iris of the eye has _________ smooth muscle layers, they are _________ arranged. 2, vertically and horizontally 2, circularly and radially 3, vertically, horizontally and circularly 3, horizontally, circularly and radially 2 When the pupil is constricted, the ________ arranged muscles are contracting. horizontally circularly vertically radially 3 When see someone and our pupils dilate what do we perceive them as? Attractive Unattractive Neutral 4 When we see a friend who is sad, what might our pupils do to mimic them? Constrict Dilate Don't change 5 What do our pupils do when we are telling a lie? Constrict Dilate Don’t change

See also

Here are some links to related resources:

1. Emotion
2. Empathy
3. Eye scanning lie detector
4. Pupil
5. Pupillary light reflex
6. Pupillometry

References

Babiker, A., Faye, I., & Malik, A. (2013). Non-conscious behavior in emotion recognition: Gender effect. Paper presented at the 258-262. doi:10.1109/CSPA.2013.6530052

Bavelas, J. B., Black, A., Lemery, C. R., & Mullett, J. (1986). I show how you feel: Motor mimicry as a communicative act. Journal of Personality and Social Psychology, 50(2), 322-329. doi:10.1037/0022-3514.50.2.322

Carter, S. C., Pournajafi-Nazarloo, H., Kramer, K. M., Ziegler, T. E., White-Traut, R., Bello, D., & Schwertz, D. (2007). Oxytocin. Annals of the New York Academy of Sciences, 1098(1), 312-322. doi:10.1196/annals.1384.006

DePaulo, B. M., Lindsay, J. J., Malone, B. E., Muhlenbruck, L., Charlton, K., & Cooper, H. (2003). Cues to deception. Psychological Bulletin, 129(1), 74-118. doi:10.1037/0033-2909.129.1.74

Dragoi, V. (1997). Ocular motor system. Neuroscience Online. Retrieved on October 27, 2014, from http://neuroscience.uth.tmc.edu/s3/chapter07.html

Gowin, J. (2010). Beauty is in the eye. Psychology Today. Retrieved on October 18, 2014, from http://www.psychologytoday.com/blog/you-illuminated/201007/beauty-is-in-the-eye

Harrison, N. A., Singer, T., Rotshtein, P., Dolan, R. J., & Critchley, H. D. (2006). Pupillary contagion: Central mechanisms engaged in sadness processing. Social Cognitive and Affective Neuroscience, 1(1), 5-17. doi:10.1093/scan/nsl006

Laeng, B., Sirois, S., & Gredebäck, G. (2012). Pupillometry: A window to the preconscious? Perspectives on Psychological Science, 7(1), 18-27. doi:10.1177/1745691611427305

Leknes, S., Wessberg, J., Ellingsen, D., Chelnokova, O., Olausson, H., & Laeng, B. (2013). Oxytocin enhances pupil dilation and sensitivity to 'hidden' emotional expressions. Social Cognitive and Affective Neuroscience, 8(7), 741-749. doi:10.1093/scan/nss062

Mann, S., Vrij, A., Leal, S., Granhag, P. A., Warmelink, L., & Forrester, D. (2012) Windows to the soul? Deliberate eye contact as cue to deceit. Journal of Nonverbal Behaviour, 36, 205-215. doi:10.1007/s10919-012-0132-y

Marieb, E. N. (2003). Essentials of human anatomy & physiology (7th ed.). San Francisco: Benjamin Cummings.

Marieb, E. N., & Hoehn, K. (2007). Human anatomy & physiology (7th ed.). San Francisco: Pearson Benjamin Cummings.

Mason, C. W. (1924). Blue eyes. The Journal of Physical Chemistry, 28(5), 498-501. doi: 10.1021/j150239a007

Mellerio, J. (1971). Light absorption and scatter in the human lens. Vision research, 11(2), 129-141. doi: 10.1016/0042-6989(71)90229-X

The Five Mile Press. (2002). The Complete Guide to the Human Body. Victoria, Australia: The Five Mile Press Pty Ltd.

Theoretical foundation (n.d.). Perception-Action Approach to Intervention for Children with Movement Disorders. Retrieved on October 26, 2014, from http://p-a-approach.weebly.com/theoretical-foundation.html

Tombs, S., & Silverman, I. (2004). Pupillometry. Evolution and Human Behavior, 25(4), 221-228. doi:10.1016/j.evolhumbehav.2004.05.001

Võ, M. L., Jacobs, A. M., Kuchinke, L., Hofmann, M., Conrad, M., Schacht, A., & Hutzler, F. (2008). The coupling of emotion and cognition in the eye: Introducing the pupil old/new effect. Psychophysiology, 45(1), 130-140. doi:10.1111/j.1469-8986.2007.00606.x