Emotion-evoked synesthesia

Emotion-colour synesthesia
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Coloured auras or haloes experienced by the synesthete based on how they feel

A relatively new form of synesthesia is person or emotion-colour synesthesia which consists of coloured halos or "auras" around a person's face or body [1]. One of the earliest cases was reported in 1934, where a 7-year old synesthete associated colours with people [2]. The colours were only elicited on people, inanimate objects, such as plaster heads did not elicit any colours showing that it is based on familiarity. He described strangers as "bright orange with a black outline" and as he got to know them better the colour would become blue or pinkish purple [2]. Once the colours stopped changing, he said it was because he got to know them better [2]. This is seen when he watched the Oliver Twist movie, he associated unpleasant characters with dark, gloomier colours such as black and grey, whereas characters he liked had more saturated colours [2].

Another case study was reported in 1989 by Cytowic, with subject BB who saw coloured "auras" around people that were linked to his emotions: "The feeling lasts a few seconds…sometimes I think I see the colour and react emotionally; others it may be reversed - I get an emotion and then see this colour." [3]. Although similar cases were reported in the past on this phenomenon, some were ruled out because they may have been a result of co-occurrence with other types of synesthesia or some case studies were not specific enough [3-4]. Cross-culturally there are a lot of similar associations between certain colours with emotions (brighter and more saturated colours associated with positive emotions, etc.), which can explain why some synesthetes associate certain colours emotions too [4]. Some synesthetes can also see synesthetic colours that are different and unique than those presented in the real world [5].

Case Studies

Subject GW (2004)

Ward reported a case of subject GW who saw coloured halos in response to some people, but less to words, letters and numbers [4]. She reported having this all her life and only became aware of it around the age of 7. By getting to know a person better, the face usually elicited a synesthetic colour which appears automatically and cannot be suppressed [4]. A main factor underlying her seeing the coloured halos depended on familiarity. In a task, she was given a list of 83 words and was asked to associate colours with those words [4]. When she was first exposed to the list, she reported seeing no colours [4]. A week later, she was tested again and had a higher consistency rate in colour associations she had made a week previously compared to the controls. Even after 4 months later, she still had a higher consistency rate compared to the controls indicating that this was not based on memory [4]. Next, Ward used the synesthete variant Stroop task consisting of two parts, the first tested her ability to identify the text colour (congruent and incongruent conditions) and the second was to identify the synesthetic colour (photism) she saw (congruent and incongruent conditions) [4].

Under congruent conditions she was faster at naming the text colour and under incongruent conditions, naming the photism colour was slower due to the interference effect [4]. The interference effect is when the word colour competes with the photism colour that the synesthete sees [4-6]. The next test, GW was presented with 180 nouns and was asked to rate it on emotionality on a scale of 1-7 (1 being unemotional and 7 being highly emotional) and goodness (1 being very pleasant, 4 being neutral, and 7 being very unpleasant) [4]. When including word valency (positive or negative), positive words tended to be pink, orange, yellow and green; negative words tended to be brown, grey and black; and neutral words were blue [4]. GW was found to have a synesthetic experience regardless of how pleasant or unpleasant the word was [4]. However the higher the emotionality, the more likely she was to have a synesthetic experience [4-5]. Another study focusing on the emotional valency of synesthesia also found that congruently coloured words were rated more positive than incongruently coloured words, which makes sense because incongruently coloured words elicit an uncomfortable response because it is different from the photism that the synesthete is used to. Hence coherence or easily processed information would be favoured over hard-to-process (incongruent) information [6].

Subject R (2007)

From an earlier case study by Milán and collagues, synesthete subject R has mild colour blindness and cannot see red, green and brown [7]. His synesthesia also comes in the form of coloured auras and are based on emotional valency [7]. R is categorized as an "associator" synesthete and his synesthetic experiences cannot be controlled voluntarily and are fairly consistent over time [7]. He has synesthetic experiences even in the absence of humans. Attractive or pleasing objects are red, anything disgusting or repulsive tend to be green, happiness is purple, aggressiveness and envy are yellow, and neutral objects tend to be brown [7]. R's impression of people depends on the aura photisms he sees from them. To test how R saw colours, they first did a colour Stroop task and did not observe any significant Stroop effect meaning that his colour identification skills are lacking, which is consistent with his colour blindness [7].

The next test they did was using the IAPS and found that his aura colour-image associations were fairly consistent overtime [7]. However, in the IAPS manual, R actually had opposite emotions elicited in response to what the manual had for certain image sets [7]. For example, a set of pictures showing the same person, one smiling, one angry, and one neutral seemed to be all green to R. Despite the different facial expressions, R said it was because the person's face was unattractive and asymmetric [7]. A possible explanation they proposed is that instead of the colour spectrum that we are usually used to seeing, he uses an inverted spectrum [7]. An example is we perceive the sky to be blue which is usually calming and serene, but he perceives the sky as exciting because he sees it as red. The next test they used was an Aura Stroop test, which consists of 21 pictures that were randomly presented, where he had to click certain keys depending on what colour he saw [7]. Unlike the colour Stroop task which did not show any significant Stroop effect, the Aura Stroop did, indicating that R sees imaginary colours, or what they termed as "phantom colours" [7]. Control subjects who did not have synesthesia and were not colour-blind did not show any Stroop effect on the Aura Stroop, but did for the colour Stroop task [7].

Subject TK (2013)

An idea of how TK sees the auras
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Presenting letters inside and outside of the aura border
and seeing how fast he is able to identify the letter [1]

Ramachandran and his colleagues came across a case stating it as a new form of synesthesia. Subject TK saw these coloured halos based on familiarity and how he feels about a person. Upon interaction with a stranger, there would be a blue halo, but as he encountered or got to know that person more, the colour of the halo changes and eventually stabilize at a certain colour [1]. TK was diagnosed with Aspergers at a young age and had difficulty identifying the emotions of others and of himself, so his parents told him to associate his emotions with colours [1]. Those close to him often had a red aura or halo. To test whether he actually saw halos, when they placed a red dot on the ear of his close friend, he failed to notice it, but when a green dot was presented, he noticed it right away. He did not notice the red dot until they mentioned it to him, but both red and green dots were noticed when they were outside the halo [1]. A close friend accompanied him in the study and when a border was drawn around where TK said he saw the halo, he said the halo was blocked by the border and did not spread out as much [1]. When they made small gaps around the border, TK reported seeing the colour leak out, which shows that the halo resides in a specific location [1]. From the picture presented, TK had to identify letters that were presented outside and inside of the halo. TK was much slower at identifying the letters inside the halo that were in a congruent colour (even much slower than the other conditions: incongruent inside the halo, incongruent outside the halo, and congruent outside the halo) [1].

He was quicker at identifying stimuli near the face than those presented near the body [1]. The colour appeared to be more concentrated around the face than the body, indicating that the fusiform gyrus may be involved because there are fewer cells in the fusiform gyrus pertaining to the limbs or body than those pertaining to the face [1]. The non-synesthete control subjects had similar reaction times as TK, but were unaffected by the location or the congruency of the colours [1]. TK and controls were quicker at identifying words that were congruently coloured and higher emotionality words [1]. However, under incongruent conditions for emotional words, TK showed more of a Stroop interference effect than the controls [1].

They were able to map the emotion-colour associations that TK had shown in the figure below [1]. An interesting result is that pride is blue and aggression is red, and arrogance is purple [1]. Arrogance is a combination of pride and aggression, hence red and blue make purple, which TK himself was not aware of [1]. This shows that his emotion-colour associations are not random but are mapped out specifically, involving areas such as the frontal cortices, insula, and the colour-processing V4 region [1]. They also found that TK can only identify a colour after he has experienced the colour and if he wanted to express a certain emotion he had to visualize a certain colour to do so (ex. To express happiness, he must think of the colour green) [1]. This article also presents a potential learning method for those with Aspergers to be better able to identify how they are feeling as well as perceiving the emotions of others [1].

A CIE colour-space map of TK's emotion colour associations
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Interesting is how some of the colours are mixtures of other colours because those emotions contain aspects of those other emotions. [1]

Associated brain regions and the involvement of affect in the synesthetic experience

There are three models proposed to be involved in synesthesia, disinhibited feedback (trigger or inducer model), enhanced neural connectivity (concurrent), and neural cross-talk (moderator or mediator model), with the cross-talk being the most common [8]. The cross-talk model includes cross-interaction between brain regions, an example is the cross-activation between the right fusiform face recognition area and the colour recognition V4 region is proposed to be a possible model underlying this type of synesthesia [4]. An example of enhanced neural connectivity is the greater activation of the retrosplenial cortex in synesthetes than controls. The retrosplenial cortex is activated in the presence of familiar stimuli [4, 6, 8, 11]. The trigger or inducer model is shown through Fitzgibbon's study on the "empathy for pain" which involves disinhibition of the "mirror systems" as a result of a traumatic event. Mirror system involves the overlapping of cortical areas allowing one to feel what the other person is feeling. The anterior cingulate cortex (ACC) is activated when one is in pain or one sees another in pain [9] (acquired-synesthesia).

Fitzgibbon and his colleagues proposed that it is the disinhibition of pain perception pathway which explains why there is enhanced pain perception (phantom pain) in amputees. The areas involved in pain perception are the thalamus, contralateral primary somatosensory cortex (S1), secondary somatosensory cortices (S2), insula (IC), ACC, and prefrontal areas [9]. The somatosensory cortices are involved in both responses to physical and emotional pain (ex. rejection, shame, etc.) [9]. Areas such as the ACC, anterior insula (AI) are involved in the affective response of pain. Disinhibition of pain perception may be a result of the body's motor response to painful or noxious stimuli as a result of the fight or flight response [9]. Increased sensitization to a perceived threat along with a reduced pain threshold can result in an enhanced pain response. This includes both physical and emotional pain (ex. rejection or shame). It is not fully understood whether mirror system disinhibition alone results in empathy for pain, or if other factors, such as familiarity to a person is involved as well [9].

In an article by Dael and colleagues, they made two hypotheses for the basis underlying affect-related synesthesia. The first is that affect is not just influenced by emotional valency (positive or negative), but also by cognitive appraisal processes [8]. The second is that the synesthetic experiences undergoes temporary changes on a quantitative level depending on the affective response induced by the stimulus or the current emotional state of the person. By quantitative changes, it means the form, frequency and intensity at which the synesthetic experience occurs at. The affective response during synesthetic experience depends on the stability of the affective appraisal or how one feels about something. For example unpleasant experiences or smells elicit a relatively stable negative affective appraisal, but where it can change is if the affective appraisal is based on how one feels towards a person (ex. relationship versus a bad breakup). With emotion-colour associations, negative emotions such as loneliness and sadness tend to be less saturated and darker, whereas positive ones are more saturated and brighter[1,4]. Even smiling faces are reported to be brighter than not smiling faces and angry faces appear redder than non-angry faces [10].

Emotion is also involved in other types of synesthesia such as grapheme-colour-synesthesia and auditory-visual-synesthesia [10-11]. In a study done by Melero and colleagues, they focused on the emotional aspect of grapheme-colour synesthesia [11]. Using neuroimaging techniques, such as 3D diffusion tensor imaging (DTI), they found some significant anatomical differences in the brain compared to controls [10]. There appeared to be a greater amount of gray matter in the left parahippocampal gyrus (PHg), more white matter in the right temporal pole (TP), higher fractional anisotropy (FA) values in the white matter of the right anterior insula (aIN) and the cingulate gyrus (CG), and the left putamen had a greater volume of gray matter. The aIN is associated with the amygdala, TP and PHg which are involved in emotional processing of external cues (olfactory, visual, etc.); the left putamen, associated with the basal ganglia which is part of the hate circuit and is also active during pleasant feelings such as love; and the retrosplenial cortex associated with the CG is shown to have increased white matter which can explain why some studies show greater activity in the retrosplenial cortex compared to controls [11].

3D-T1 images of the emotional-related areas of the brain
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There was an increase in gray matter volume in the left PHg and an increase in white matter in the TP [11]

Mystics versus synesthetes

Are aura readers synesthetes?
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Aura readers also see coloured halos or auras around people,
but is distinct from person-colour synesthesia

Referring back to the inducer or trigger model, an "inducer" is a stimulus that elicits a synesthetic experience and "concurrent" is the phantom sensation that results from it, such as seeing or tasting colours
[12]. Psychics or aura readers believe that humans, animals, or objects all possess an energy field that is seen as an aura. The aura is based on the "seven chakras or energy centers" that branch off from the nervous system [12]. Some researchers have proposed that what aura readers experience are a result of cross-modal processes in the brain that are similar to that of synesthetes [12].

However, a study done by Milán and his colleagues find distinct differences between aura readers and synesthetes. The human aura is based on the person's physical and mental state of mind and the colours can change too, which indicates a change in mood of a person. Auras can be interpreted on a very complex level, where various characteristics are analyzed, such as the "thickness, shape, and shades of colours" [12]. Experts in the aura reading field often agree with the aura appearance they see emitted from an object, whereas various synesthetes can have see different coloured halos for specific objects or people. There are similarities between the two, including increased occurrence of psychic experiences, such as lucid dreaming or higher levels of empathy; aura-reading can be taught and the current case from Ramachandran's study of subject TK on person-colour synesthesia appears to be one that was a learned behaviour; hynopsis or meditation can inhibit synesthesia; and finally, both aura-reading and person-colour synesthesia appear to be emotionally mediated [12]."

A study done by Cytowic and Eagleman observed a case where statues did not elicit any colours whereas friends and family of the synesthetes did - indicating that emotion and familiarity is associated with the synesthetic experience [13]. In order to ensure that the four synesthetes had genuine person-colour synesthesia, they ran a total of five tests. They had to receive positive results on all five in order to be considered as one. The first test done was a Synaesthesia Battery standardized, online questionnaire, that can be found at http://www.synesthete.org. This test is discreet, because it allows only the subject and the researcher to see the results and no one else; and is efficient because both the subject and researcher can go back whenever to access the information and results [13]. The questionnaire is composed of 80 questions which on average takes about 10 minutes to finish. Some questions ask about specific traits to categorize them into a specific type of synesthesia, others enable researchers to gather information on whether they have any other phenomenons or conditions, such as autism or dyslexia [13]. Synesthetes can be categorized as "projectors" and "associators," which used to be termed as "localizers" and "non-localizers." Projectors tend to see colours in a specific location, whereas associators do not have a have a specific location to where they see the colour [13].

Another commonly used test in the battery is the synesthete variant Stroop task, however it is possible for a person to cheat on the test, by making a cheat-sheet to help with memory - which can be easily done because there is no time limit to when they should answer [13]. So, the speeded congruency test can be used in place of it [13]. The subjects are presented with a grapheme very briefly and they have to answer it as quickly as possible (half of the presented graphemes are congruently coloured - meaning it has the same colour that the synesthete associates the grapheme with and the other half is incongruently coloured). The synesthetes are first presented with a series of the same graphemes as presented in Figure A, but in different shades with varying background colours [13]. They have to answer whether they experience different or identical synesthetic colours in each of the graphemes series. If the colours they see are different, this means the synesthetic colours they see depend on the contrast the graphemes are presented with. In Figure B, it can be seen that the middle column (column4) of the chart is of lowest contrast, where the grapheme and background colour are quite similar.

The purpose of this test is to distinguish whether the synesthete is a "higher" or "lower level" synesthete [13-14]. "Higher level" synesthetes will see the same grapheme colour regardless of the background colour it is presented with, meaning the synesthetic colour they experience is contrast-independent. A typical "lower level" synesthete will put down "no colour" under column 4 because their synesthetic colour experience is based on contrast [13-14]. The second test they did was to ask whether their synesthesia was acquired or genuine [12]. The third test, the subjects were presented with a series of photos from the International Affective Pictures System (IASP) and were asked to identify the colour of the photisms they saw from the images [12]. Usually the individual with person-colour synesthesia does not fully know whether it is their emotional state or the stimulus itself that gives rise to the photisms [12]. The fourth test was an interview and the fifth test was an Aura Stroop task [12].

Speeded Congruency Test
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Figure A: Same series of graphemes presented with different background shades
Figure B: No colour is a typical result of lower level synesthetes whose synesthetic experience is contrast-dependent [13]

Those with person-colour synesthetes see different aura colours from a stimulus, whereas aura readers see the same colour elicited [12]. A photo can elicit a synesthetic response, but aura readers cannot see an aura [12]. Synesthetes's photisms are based on their emotional state, whereas aura readers see colours based on what is believed to represent certain physical or mental states [12]. Synesthetes see auras with only one colour compared to aura readers which see multiple layers or shades present [12]. Synesthesia is usually from birth, whereas aura reading can be learned with proper training [12]. However, referring back to subject TK, it is unclear whether the colours he saw was because his parents trained him to do so or because he actually was born with synesthesia [12]. Person-colour synesthetes experiences colour halos automatically, whereas aura reading requires lots of concentration and certain conditions (ex. dimmed lights). Finally, the synesthetic experience is activated quickly if the stimulus or inducer is when the synesthete is looking directly at it, whereas aura readers make use of peripheral vision to see the aura [12].

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