An investigation in the capabilities of projectors,
associators and non-synesthetes in colour
precision and colour consistency
By Jork de Kok (11644060)
Faculty of Science
BSc Psychobiology
22 June 2020
Supervisor
Dr. Romke Rouw
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Abstract
People with grapheme-colour synesthesia see certain letters in certain colours. Two types of grapheme-colour synesthetes can be distinguished, projectors and associators. Projectors see synesthetic colours in the outside world, whereas associators see synesthetic colours inside their mind’s eye. Colour consistency is the ability to distinguish synesthetic colours from each other. This is measured by instructing participants to produce a certain colour when they see a certain letter. Colour precision is the ability to distinguish “real” colours from each other. This is measured by instructing participants to produce the same colour as a shown colour stimuli. It is known that synesthetes perform better on colour consistency and colour precision in comparison with non-synesthextes. Building upon these findings, this study has looked at the capabilities of projectors, associators and non-synesthetes on a colour consistency and colour precision task. This was done to determine if there are any differences in capabilities between the three groups, and to see if there is a correlation between colour precision and colour consistency in projectors and associators. Non-synesthetes were recruited via the University of Amsterdam, whereas synesthetes were targeted via social media or personal emails. Non-synesthetes, projectors and associators were divided into different groups with the use of a questionnaire and the score on the colour consistency task. A total of 123 people participated in the experiment and 90 of those met all criteria to be included in the data analysis. The results showed that both projectors and associators were significantly more consistent on the colour consistency task in comparison with non-synesthetes. Associators showed more precise colour precision in comparison with non-synesthetes, but projectors did not. There was no correlation found between colour precision and colour consistency in both projectors and associators.
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Introduction
Background
People with synesthesia experience the world differently compared with typical individuals. Synesthesia refers to the involuntary process by which one certain type of sensory information can evoke another type of sensory information. This leads to the mixing of two different types of sensory information. There are various types of synesthesia; for example, some people with synaesthesia can tactilely feel what they taste or tactilely feel what they smell (Cytowic et al., 2002). However, this study focusses on grapheme-colour synaesthesia. People with grapheme-colour synesthesia perceive different letters in specific colours (e.g. red A, blue Z). Grapheme-colour synesthesia is relatively rare in the general population, about 1.2% has grapheme-colour synaesthesia (Carmichael et al., 2015).
People with grapheme-colour synesthesia can be divided into two distinct groups, associators and projectors (Dixon et al., 2004). These two groups report differences in how synesthetic colours are perceived. Projectors report that the synesthetic colours are present outside themselves; as if they are physically present in the outside world. Simultaneously, projectors are aware that the synesthetic colours do not “really” exist. In contrast, associators report that certain letters have certain colours in their “mind’s eye” (Dixon et al., 2004). This means that, for associators, synesthetic colours are perceived more similar to mental imagery instead of being physically present. Previous research found that during the perception of synesthetic colours projectors and associators show more activation in different brain areas (Rouw and Scholte, 2010). Projectors showed more activity in brain areas related to the perception of, and actions in, the outside world (i.e. visual cortex, auditory cortex, motor cortex and frontal brain areas). Whereas the associators showed more activation in brain areas related to memory (i.e. hippocampus and parahippocampal gyrus). This means that the differences in synesthetic colour experience underlie two distinct neural mechanisms in projectors and associators. To create a more complete understanding of the outcomes of these different mechanisms, this study focusses on two aspects of colour perception: colour consistency and colour precision.
Scientific relevance and research questions
The colour consistency is the ability to distinguish between synesthetic colour. In this study, colour consistency will always refer to synesthetic colour. In the colour consistency experiments, participants will see a letter and are instructed to produce a colour which they think seems most fitting to the letter. It is referred to as colour consistency because participants have to consistently produce a specific colour when a specific letter is shown. Colour consistency of synesthetic colour is often used as a way to identify synesthetes, e.g. the Eagleman battery test (Carmichael et al., 2015). If there is a difference in the colour consistency between projectors and associators than that could be used as a method to distinguish projectors and associators without relying on self-report.
Colour precision is the ability to distinguish between “real” colour (“real” in this sense means colours observed as by non-synesthetes). In colour precision tasks a certain colour is shown and participants are instructed to produce that particular colour. A study found that synesthetes have enhanced colour precision of “real” colours (Bannissy et al., 2009). But, it is not clear if this enhanced colour precision is present in both associators and projectors. Moreover, this is interesting to research because Bennissy et al. (2009) did a colour precision task with a relatively small sample size (eight grapheme-colour synesthetes). As such, this study will contribute to a better understanding of the differences in performance between projectors, associators and non-synesthetes on a colour precision task.
4 According to Bannisy et al. (2009) and Mattingley et al. (2001) synesthetes have respectively more precise “real”, and more consistent synesthetic colour perception in comparison with non-synesthetes. It would be interesting to find if there is any relation between colour consistency and precision. Due to the difference in how projectors and associators see synesthetic colours, there might be differences in how colour consistency and colour precision are related to each other in projectors and associators. A relation between colour precision and colour consistency could show that abilities in “real” and synesthetic colour perception are related in projectors and associators.
In short, this study aims to answer the following questions: Are there any differences in the capabilities in colour consistency and colour precision in projectors, associators and non-synesthetes? And is there a relation between colour consistency and colour precision in projectors and associators? To answer these questions, this study uses a colour precision task, colour consistency task and two questionnaires.
Hypotheses
Previous research has shown that synesthetes perform more consistent in colour consistency task in comparison with non-synesthetes (Mattingley et al., 2001). Therefore, it is expected that both projectors and associators show more consistent results in comparison with non-synesthetes. Projectors might be more consistent because projectors can simply produce the synesthetic colour of the letter that is shown outside. Whereas associators would have to produce synesthetic colours which are shown in their mind’s eye. Therefore, it is hypothesized that projectors have a more consistent colour consistency in comparison with associators (H1).
In Bannisy et al. (2009) it is hypothesized that the enhanced precision of “real” colours is either the cause or a consequence of synesthesia. If that is true then that would mean that both projectors and associators would have enhanced “real” colour precision. Therefore, it is expected that both projectors and associators show an enhanced colour precision in comparison with non-synesthetes (H2).
Both colour consistency and colour precision are enhanced in synesthetes (Bannisy et al. 2009, Mattingley et al. 2001). The synesthetic colours might be similar experiencing “real” colour perception. Therefore, there might a positive relation between the colour consistency and colour precision in synesthetes. There might be a difference in the relation between colour consistency and precision in projectors and associators. This could be due to the differences in how they see synesthetic colour (outside or in the mind). Therefore, both projectors and associators will be tested instead of just synesthetes. It is expected that there will be a positive relation between colour consistency en colour precision in both projectors and associators (H3 and H4). In short, the following are the four main hypotheses of this study:
(H1) Projectors will show more consistent results than the associators in the colour consistency task.
(H2) Projectors and associators show more precise results than the non-synesthetes on the colour precision task.
(H3) There is a positive relation between colour consistency and colour precision in projectors
(H4) There is a positive relation between colour consistency and colour precision in associators.
Materials and Methods
RecruitmentAll the instructions during the experiments were in Dutch, therefore it was required for all participant to be fluent in Dutch. Non-synesthetes were recruited via the University of Amsterdam, these were
5 psychology and psychobiology students. These participants were rewarded with participant points, which are necessary to complete a psychology or psychobiology bachelor at the University of Amsterdam. Synesthetes were recruited by specifically targeting them via various social media platforms (i.e. Facebook, Instagram and Twitter). This was done by posting advertisements for the study in synesthesia-related, creativity-related, and art-related groups. Art-related groups were chosen because synesthesia is more prevalent in fine art students in comparison with the general population (Domino, 1989; Carmicheal et al., 2015). To identify more Dutch synesthetes the search term “synesthesie” was searched on Instagram and Twitter. People who posted synesthesia-related comments were identified and approached through personal messaging to ask if they actually were synesthetes; and willing to participate in this study. Besides personal messaging, synesthetes who have participated in research before and had indicated that they would be open to participating in research again were contacted via a personal email. The entire experiment lasted about an hour and a half, and the synesthetes were rewarded with 15 euro’s upon completion of the experiment.
The entire experiment consisted of a questionnaire and five different tasks. The experiment was performed with the use of the software program Qualtrics. Participants agreed with an informed consent statement and were subjected to a colour consistency task. After that, the participants filled in the questionnaire; the questionnaire consisted of questions about the colour picker task and demographic information. Participants were also asked if they see certain letters always in certain colours, like the letter “J” is orange (Bepaalde letters hebben voor mij altijd een bepaalde kleur (bijvoorbeeld, de letter "J" is oranje). If participants agreed, then they would be subjected to the PA questionnaire and more statements regarding synaesthesia, which participant had to either strongly agree, agree, neutral, disagree or strongly disagree with. One of the statements was: Colours I associate with letters are a specific colour and not just a generic colour category (De kleuren die ik aan letters associeer zijn specifieke kleurschakeringen, niet slechts een generieke kleurcategorie). The data of this particular statement was analysed because it gives information on the specificity of synesthetic colours, which is related to colour consistency. After the questionnaire(s) participants were subjected to a synesthetic Stroop task, followed by a colour precision task and two colour memory tasks. At the end, participants indicated how well-concentrated they were during the experiment and filled in their bank account number to receive the compensation of 15 euro’s. The tasks that are relevant to this paper will now be discussed in greater detail.
PA questionnaire
The PA questionnaire divides synesthetes into projectors and associators (Rouw and Scholte, 2007; 2010). The PA questionnaire consists of a series of statements where participants are given the option to either (strongly) disagree, (strongly) agree or be neutral (Figure 1). Every option was matched with a number; strongly disagree 1, disagree 2, neutral 3, agree 4, and strongly agree 5. Every statement is formulated in such a way that if participants (strongly) agree with it, it will indicate that they are either a projector or an associator (Figure 2). The PA score can be derived by subtracting the mean score of the six associators statements from the means score of the six projector statements. When the PA score was higher than 0 they were considered projectors, when the PA score was lower they were considered associators (Rouw and Scholte, 2007; 2010).
6 Figure 1. PA Questionnaire. One question of the PA questionnaire as shown to participants.
Statement (in English) Statement (in Dutch) Projector/associator When I look at a certain letter or
number, I see a particular colour.
Wanneer ik naar een bepaalde letter of cijfer kijk, dan zie ik een specifieke kleur.
projector
When I look at a certain letter, the accompanying colour appears only in my thoughts and not somewhere outside my head (such as on the paper).
Wanneer ik naar een bepaalde letter kijk, verschijnt de bijbehorende kleur alleen in mijn gedachten en niet ergens buiten mijn hoofd (zoals op het papier).
associator
When I look at a certain letter, the accompanying synesthetic colour appears only in my thoughts and on the paper appears only the colour in which the letter is printed (e.g. a black letter against a white background).
Wanneer ik naar een bepaalde letter kijk, komt daarvan de bijbehorende
synesthetische kleur in mijn gedachten maar op het papier verschijnt enkel de kleur waarin de letter gedrukt is (bijv. een zwarte letter tegen een witte
achtergrond).
associator
It seems that the colour is on the paper where the letter is printed.
Het is alsof de kleur zich daadwerkelijk op het papier bevindt waarop de letter gedrukt staat.
projector
The figure itself has no colour but I am aware that it is associated with a specific colour.
De figuur zelf heeft geen kleur maar ik ben ervan bewust dat deze geassocieerd is met een specifieke kleur
associator
The colour is, if it were, projected onto the letter.
De kleur is als het ware geprojecteerd op de letter.
projector
I do not see letters literally in a colour but have a strong
feeling that I know what color belongs to a certain letter.
Ik zie letters niet letterlijk in een kleur maar heb een sterk gevoel dat ik weet welke kleur bij een bepaalde letter hoort.
associator
The colour is not on the paper but floats in space.
De kleur bevindt zich niet op het papier maar zweeft in de ruimte.
associator
The colour has the same shape as the letter.
De kleur heeft dezelfde vorm als de letter. projector
I see the colour of a letter only in my head.
Ik zie de kleur van een letter alleen in mijn hoofd.
associator
I see the synesthetic colour very clearly in the proximity of the stimulus (e.g. on top of it or behind it or above it).
Ik zie de synesthetische kleur heel duidelijk in nabijheid van de stimulus (bijv. erop of erachter of er overheen).
projector
When I look at a certain letter, the synesthetic colour appears
somewhere outside my head (such as on the paper).
Wanneer ik naar een bepaalde letter kijk, verschijnt de bijbehorende kleur ergens buiten mijn hoofd (zoals op het papier).
projector
Figure 2. PA Questionnaire. An overview of all statements in the PA questionnaire. Participants could either strongly agree, agree, be neutral, disagreed or strongly disagreed with every statement.
7 Colour consistency task
In the colour consistency task, a letter is shown in a certain colour on the top part of the screen and participants can change the colour of that letter with the tool on the bottom of the screen (as depicted in Figure 3). Participants are instructed to change the colour of the letter to what they deem most fitting to it. All 26 letters of the alphabet were shown and every letter was shown three times, making it a total of 78 trails. There was no time limit imposed on participants when they were selecting the colours. As mentioned, the participants will fill in a colour three times for each specific letter. This creates three different coordinates in the tool, and the distance between those coordinates will be quantified. The distance between the coordinates is a measure for the consistency; the smaller the distance between the three coordinates, the better the consistency and vice versa.
The tool on the bottom part of Figure 3 makes use of a colour wheel and a CIELUV colour space, as used in Rouw and Root (2019). The distance between two points in the CIELUV colour space will tell how unequal the two colours are perceived. The bigger the distance the more unequal the two colours are perceived. This is different from a colour space in which different points in the colour space corresponds to different wavelengths. The CIELUV colour space was used because it was expected to give more precise results when it comes to accurately depicting the ability to discriminate different colours. Moreover, according to Rothen et al. (2013) the CIELUV colour space is the best way to identify synesthetes. The CIELUV colour space calculates the Euclidean mean with the formula shown in Figure 4. The Euclidean mean is a measure for how big the colour distance is between the three different trails for one particular letter. Besides consistency the time it takes to finish a trail was also measured. This is to ensure participants took adequate time to be consistent.
Figure 3. Colour consistency task. Participants are instructed to make the letter the colour that they seem most fitting. The colour of the square and the letter can be adjusted with the use of the colour wheel and the space in the square.
8 Figure 4. Formula Euclidean mean. The d stands for the Euclidean mean and the L for brightness, U for relatively how much green in comparison with red is present and V for relatively how much blue in comparison with yellow. The i refers to that all three different trails for one particular letter will be compared. So, trail 1 compared with trail 2, trial 1 compared trail 3 and trail 2 compared with trail 3. In the case of the colour precision task, the colour of the shown stimuli is compared to the produced colour; instead of comparing different trails.
Colour precision task
The colour precision task consists of two squares and a colour picker with distractors in the background (see Figure 5). The distractors were there to make it more difficult to be precise. Participants were instructed to adjust the colour of the top right square and to make it the same colour as the square on the top left (Figure 5). The was no time limit imposed to fill in an answer. The time it took to answer was also measured; to control if participants took adequate time to be precise. The colour of the top left square was not generated randomly; four different types of colour were shown (primary colour, fully-saturated non-primary colour, darker version of primary colour and darker version of non-primary colour). All participants were shown six of each type of colour; making a total of 24 trails. The order of the trail are semi-randomized, meaning that the order was the same for all participants and the same colour types were not shown one after another. The precision in the colour precision task is measured by how similar the colours in both top squares are. The difference was calculated with the formula in Figure 4. The difference between the calculations is that in the colour precision task the coordinated of the shown colour is compared to how precise it is recreated; and in the colour consistency task, three different trails are compared.
Figure 5. Colour precision task. Participants are instructed to make the top right square the same colour as the top left square. The colour of the top right square is adjusted with the colour picker tool underneath the two top squares.
9 Defining groups
The questionnaire, PA score and scores on the colour consistency task were important in defining the different groups. In other words, self-report and quantitative data was used to identify projectors, associators and non-synesthetes. According to Rothen et al. (2013), a CIELUV colour consistency task is the best way to identify synesthetes. It showed that just 90% (sensitivity) of the self-reported synesthetes scored lower than 135, and just 94% (specificity) the participants that scored lower than 135 were synesthetes. Therefore, Rothen et al. (2013) recommends using a cut-off value of 135 to identify synesthetes. The questionnaire in the experiment is designed in such a way that participants will be directed to the PA questionnaire when they agree with the following statement: certain letters always have certain colours, for example, the letter “J” is orange. Therefore, to be considered a non-synesthete participants had to score higher than 135 on the colour consistency task, and had to disagree with the statement: certain letters always have certain colours. This double safeguard ensured that self-reported non-synesthetes with a score lower than 135 were not identified as projectors nor associators. Participants were considered projectors when PA score is higher than 0 and had a score lower than 135 on the colour consistency task. Associators were defined as participants who had a PA score lower than 0 and score lower than 135 on the colour consistency task. In the case of projectors and associators, the criteria of a lower score on the colour consistency task ensured that all associators and projects were consistent enough to be considered synesthetes. An overview of all the criteria for all the groups are shown below (Figure 6).
group Colour consistency score Certain letters have certain colours
PA score
Projectors Lower than 135 Agree Higher than 0
Associators Lower than 135 Agree Lower than 0
Non-synesthetes Higher than 135 Disagree NA Figure 6. Overview of all criteria of the different groups.
Results
ParticipantsNotably, 123 participants participated in this study; of which four participants did not complete one of the following elements: questionnaire on synesthetic experience, PA questionnaire, colour consistency or colour precision task. In total 93 participants reported that they do see certain letters in certain colours. However, 25 out of those 93 scored higher than 135 on the colour consistency task. These participants did not meet the criteria depicted in Figure 6. Moreover, three participants reported they do not see certain letters in certain colours and scored lower than 135 on the colour consistency task. Which was, also, not in coherence with the criteria shown in Figure 6. Noticeably, 73 participants scored lower than 135 on the colour consistency task and of those 70 were self-reported synesthetes. This means there was a sensitivity of 73% (68 out of 93) and a specificity of 96% (70 out of 73). There was one participant that scored a 0 on the PA questionnaire. The time that participants took to finish a trail was measured, and the mean – 2*SD was used to check if participants took adequate time. No participants were faster than mean – 2*SD in the colour consistency task nor the colour precision task. The participants that did not complete all tasks or scored 0 at the PA questionnaire or did not meet the specific criteria (shown in Figure 6) were excluded from data analysis. This resulted in that 90 out of the 123 participants were used in the data analysis.
10 Of the 90 participants, 67 did report they see certain letters in certain colours and 23 did not. Therefore, 23 participants (mean age = 22.0; range 18-53) were identified as non-synesthetes; three were male and 20 were female. The PA scores of the 67 synesthetes are shown in Figure 7; nine were considered projectors (mean age = 39.2; rang 29-55) and 58 were considered associators (mean age = 36.0; range 18-66). The group of projectors consisted of one male and eight females; and the group of associators consisted of seven males, 49 females and two participants who rather not share their gender.
Self-report on specificity of synesthetic colours
The answers to the statements if synesthetic colours are specific colours and not just in a generic colour category are shown for projectors in Figure 8, and associators in Figure 9. Four out of the nine projectors (44%) either agreed or strongly agreed with the statement, and 45 out of 58 associators (78%) either agreed or strongly agreed with the statement.
Figure 7. PA score of all projectors and associators. The self-reported synesthetes that scored lower than 135 on the colour consistency task are shown here. The one participant that scored a 0 on the PA questionnaire is not included in the graph.
Figure 8. Specificity of synesthetic colour in projectors. Answers of the projectors to the question if synesthetic colour are specific or a generic colour category (De kleuren die ik aan letters associeer zijn
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Figure 9. Specificity of synesthetic colour in associators. Answers of the associators to the question if synesthetic colour are specific or a generic colour category (De kleuren die ik aan letters associeer zijn specifieke kleurschakeringen, niet slechts een generieke kleurcategorie).
Colour consistency task
The Shapiro-Wilk normality tests were performed and showed that projectors (p < 0.05) and non-synesthetes (p < 0.05) were normally distributed; however, associators (p > 0.05) were not. Levene’s test showed that variances between groups (p < 0.0001) were not equal. Consequently, a Kruskal-Wallis test was performed to determine if there were any significant differences between the projectors (M±SD: 53.9 ± 15.9), associators (M±SD: 69.7 ± 28.4) and non-synesthetes (M±SD: 228.7, 55.8). The Kruskal-Wallis test showed significant differences between the three groups on the colour consistency task (H(2) = 52.4; p < 0.0001). Dunn’s test was done to determine which specific groups differed significantly from each other. The Dunn’s test found that there is a significant difference between non-synesthetes and projectors (Z = 5.4; p < 0.0001) and there is a significant difference between non-synesthetes and associators (Z = -6.7; p < 0.0001), shown in Figure 10. Remarkably, there was no significant difference found between associators and projectors.
Figure 10. Colour consistency of synesthetic colours per group. The arrows show the standard deviation of each group. The Euclidean mean is a measure for the relative distance in colour space. There were significant differences between non-synesthetes and projectors, and non-synesthetes and associators.
12 Colour precision task
The Shapiro-Wilk normality showed that non-synesthetes (M±SD; 14.4 ± 11.6; p < 0.05) and associators (M±SD; 9.4 ± 3.2; p < 0.05) were distributed normally. The projectors (M±SD; 8.8 ± 3.7; p > 0.05) did not show a normal distribution. The Levene’s test also showed that variances between the three groups were not equal (p > 0.001). Therefore, a Kruskal-Wallis test was performed to determine if there are any significant differences between the projectors, associators and non-synesthetes. The Kruskal-Wallis test showed that the groups differ significantly from each other (H(2) = 7.6; p < 0.05). A Dunn’s test was done to determine which specific groups differ from each other significantly. Dunn’s test showed that there is a significant difference between the associators and nonsynesthetes (Z = -2.6; p < 0.05), as shown in Figure 11. Notably, there was no significant difference between the projectors and non-synesthetes.
Figure 11. Colour precision of real colours per group. The arrows show the standard deviation of each group. The Euclidean mean is a measure for the relative distance in colour space. There was a significant difference between associators and non-synesthetes.
Correlations
As mentioned, the projectors (p > 0.05) were not normally distributed on the precision task; and associators (p > 0.05) were not normally distributed on the consistency task. Therefore, Spearman correlation tests were performed to determine if there is a correlation between colour consistency and colour precision in projectors and associators. There was no significant correlation between the colour consistency and colour precision in projectors (Rs(7) = -0.52; p > 0.05), as shown in Figure 12. There was no a significant correlation between colour consistency and colour precision in associators (Rs(56) = 0.02; p > 0.05), as shown in Figure 13.
13 Figure 12. Non-significant correlation between colour precision and colour consistency in projectors. The red line is the line that best fits the data.
Figure 13. Non-significant correlation between colour precision and colour consistency in associators. The red line is the line that best fits the data.
Discussion
The results in this study show that the differences in how projectors and associators see synesthetic colours (outside or inside the world) does not affect colour consistency or colour precision. It was expected that the projectors might have better colour consistency due to the nature of the how the synesthetic colour appear to them (H1). However, the results from the projectors on the colour consistency task did not show any significant results in comparison with the associators. So, a colour consistency task cannot be used as a way to distinguish projectors and associators. Most of the associators (78%) agreed or strongly agreed that the synesthetic colours are specific colours instead of generic colour category and just 44% of the projectors also agreed with that statement. This is an interesting finding because it suggests that synesthetic colours are more specific in associators in
14 comparison with projectors. However, the difference in seeing more specific synesthetic colours did not result in a significant difference in colour consistency between projectors and associators. Moreover, the difference in self-reported specificity of synesthetic colour can also be explained by the small sample size of the projectors. In addition, the colour consistency task did show that non-synesthetes scored significantly higher in the colour consistency task in comparison with both projectors and associators. This was not very surprising since the low colour consistency scores are commonly used to distinguish synesthetes from non-synesthetes (Carmicheal et al., 2015). Also, the specific criteria depicted in Figure 6 dictate that participants were considered non-synesthetes when they scored higher than 135, and projectors and associators when they scored lower than 135.
It was expected that both projectors and associators would perform better on the colour precision task in comparison with non-synesthetes (H2). Associators did show significantly better results in comparison with the non-synesthetes, but the projectors did not. This suggests that associators are mainly responsible for the enhanced colour precision that synesthetes have shown in Bannisy et al. (2009). There was no significant difference between projectors and non-synesthetes. This was surprising because in Bannisy et al. (2009) it was suggested that enhanced colour precision is a characteristic of grapheme-colour synaesthesia. Thus, the results in this study suggest that this might not be the case for projectors. The absence of a significant difference between non-synesthetes and projectors could also be explained by the small sample size of the projectors. Future research could explore this further by testing with a bigger sample size of projectors. Such a study could also compare between different colour precision tasks. For example, in Bannisy et al. (2009) a Farnsworth–Munsell Colour Hue Test was used to measure the colour precision.
It was also expected that colour consistency and colour precision would depend on each other in both projectors and associators (H3 and H4). However, there was no correlation found between colour consistency and colour precision in projectors nor associators. That implies that synesthetic colour and “real” colour experience is not dependent on each other in projectors and associators.
When Rothen et al. (2013) tested colour consistency with a CIELUV colour space and a cut-off of 135 Euclidean mean it resulted in a 90% sensitivity and a 94% specificity. However, the cut-off showed a 73% sensitivity and 96% specificity in this study. Therefore, this method was more precise, but less sensitive in selecting synesthetes compared with the study in Rothen et al. (2013). Future researches on synesthesia could choose a higher cut-off value to make the method of identifying synesthetes more sensitive. The preciseness could be ensured when the participants have to additionally report if they can see synesthetic colours.
In summary, this study made clear that projectors and associators do not show differences in colour consistency; associators have a better colour precision in comparison with non-synesthetes, but projector not; and that there is no correlation in colour precision and colour consistency in both projectors and associators.
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