Grapheme Color Research Articles

Is non-synesthetes’ B Blue? Grapheme–color association improves non-synesthetes’ detection in visual search

Grapheme–color synesthesia is expected to provide a clue to solving the “binding problem” of visual features. Synesthetic research uses non-synesthetes as a control group and shows that synesthetes perform better with synesthetic color congruency, while non-synesthetes’ performances do not. However, non-synesthetes also have certain grapheme–color associations. Therefore, this study examined whether non-synesthetes’ grapheme–color associations improve their performance in a visual search task. The results indicated that non-synesthetes were significantly faster at detecting congruent targets with their grapheme–color associations, such as red for “A,” blue for “B,” and yellow for “C.” However, the effect was not found in relation to numerical characters. This study has implications for future neuroscience and consciousness research regarding grapheme–color synesthesia.

Synaesthesia and Encapsulation

The concept of informational encapsulation has been important in promoting a view of the mind that has dominated cognitive science. Multisensory phenomena, such as synaesthesia, have been used as evidence for challenging this view. The main objective of this paper is to provide a more detailed understanding of the nature of such a challenge by examining the two types of grapheme–colour synaesthesia, projectors and associators. It is argued that the phenomena under consideration exemplify partial encapsulation failure and that it is expressed in three forms: intramodal, intermodal, and top-down. Additional support for these claims is provided by considering some evidence on synaesthetic-like experiences in relation to the continuity thesis.

The time course of synaesthetic colour perception

Grapheme–colour synaesthesia is a neurodevelopmental condition wherein perception of numbers and letters consistently and involuntarily elicits concurrent experiences of colour photisms. Accumulating evidence suggests that heterogeneity in the visuospatial phenomenology of synaesthesia is attributable to the operation of top-down processes underlying photisms experienced as representations in associator synaesthetes and bottom-up processes subserving photisms experienced as spatially localized in projector synaesthetes. An untested corollary of this hypothesis is that bottom-up mechanisms will actuate earlier photism perception in projector than associator synaesthetes. We tested this prediction in a pre-registered study wherein associators and projectors completed adaptive temporal order judgement tasks for graphemes, colours, and photisms. In corroboration of the hypothesis of differential photism access across subtypes, projectors displayed lower photism colour thresholds than associators whereas the two subtypes did not significantly differ in veridical colour thresholds. Synaesthetes did not differ in grapheme or colour thresholds relative to non-synaesthete controls. These results are consistent with the proposal of differential neural mechanisms underlying photism perception in subtypes of grapheme–colour synaesthesia and warrant renewed attention to heterogeneity in the mechanisms and phenomenology of this condition.

Grapheme-Color Synesthesia in an Abugida: a Bengali Case Study.

Grapheme-color synesthetes experience graphemes (e.g., letters of the alphabet) as having a specific, consistent color. Most studies of grapheme-color synesthesia have only examined synesthetes in English, leaving underexplored the question of how synesthetic phenomenology might differ in languages that do not use alphabets. In particular, grapheme-color synesthesia in an abugida (a segmental writing system in which vowels are added to consonant graphemes using 'accent'-like diacritical marks) has never been studied. Here, we present a case study of a Bengali synesthete, MJ, the first report of a grapheme-color synesthete in an abugida. First, we show that for MJ, diacritics influence the overall color of the consonant grapheme they modify, 'pulling' it toward the color she experiences for the vowel. Second, we describe and analyze the complex synesthetic experiences reported by MJ for conjunct graphemes, a unique orthographic feature of Brahmi-derived scripts (such as Bengali) in which multiple graphemes are visually combined into a single 'merged' grapheme. Finally, we show that in addition to these language-specific features, MJ's synesthetic associations are influenced by some of the same linguistic properties (such as orthography and phonology) that influence synesthetic associations in other languages. We conclude that the idiosyncratic features of MJ's synesthesia reflect unique properties of the Bengali writing system, that more studies of synesthesia in non-alphabetic scripts are needed, and that synesthetic phenomenology can offer insights into how linguistic properties shape grapheme representation in the brain.

Multivariate pattern analysis of fMRI data for imaginary and real colours in grapheme-colour synaesthesia.

Grapheme-colour synaesthesia is a subjective phenomenon related to perception and imagination, in which some people involuntarily but systematically associate specific, idiosyncratic colours to achromatic letters or digits. Its investigation is relevant to unravel the neural correlates of colour perception in isolation from low-level neural processing of spectral components, as well as the neural correlates of imagination by being able to reliably trigger imaginary colour experiences. However, functional MRI studies using univariate analyses failed to provide univocal evidence of the activation of the "colour network" by synaesthesia. Applying multivariate (multivoxel) pattern analysis (MVPA) on 20 synaesthetes and 20 control participants, we tested whether the neural processing of real colours (concentric rings) and synaesthetic colours (black graphemes) shared patterns of activations. Region of interest analyses in retinotopically and anatomically defined visual areas revealed neither evidence of shared circuits for real and synaesthetic colour processing, nor processing difference between synaesthetes and controls. We also found no correlation with individual experiences, characterised by measuring the strength of synaesthetic associations. The whole brain searchlight analysis led to similar results. We conclude that revealing the neural coding of the synaesthetic experience of colours is a hard task which requires the improvement of our current methodology: for example involving more individuals and achieving higher MR signal to noise ratio and spatial resolution. So far, we have not found any evidence of the involvement of the cortical colour network in the subjective experience of synaesthetic colours.

Correction to ‘Investigating genetic links between grapheme–colour synaesthesia and neuropsychiatric traits’

Correction to ‘Investigating genetic links between grapheme–colour synaesthesia and neuropsychiatric traits’

Difference of the grapheme–color synesthesia caused by the character recognition level

Difference of the grapheme–color synesthesia caused by the character recognition level

Echoes from the past: synaesthetic colour associations reflect childhood gender stereotypes.

Grapheme-colour synaesthesia is a neurological phenomenon in which linguistic symbols evoke consistent colour sensations. Synaesthesia is believed to be influenced by both genetic and environmental factors, but how these factors interact to create specific associations in specific individuals is poorly understood. In this paper, we show that a grapheme-colour association in adult synaesthetes can be traced to a particular environmental effect at a particular moment in childhood. We propose a model in which specific grapheme-colour associations are 'locked in' during development in children predisposed to become synaesthetes, whereas grapheme-colour associations remain flexible in non-synaesthetes. We exploit Western gender-colour stereotypes to test our model: we found that young girls in general tend to associate their first initial with the colour pink. Consistent with our model, adult female synaesthetes are influenced by their childhood environment: they associate their first initial with pink. Adult female non-synaesthetes do not show this bias. Instead, in our study, non-synaesthetes tended to associate their first initial with their current favourite colour. The results thus support the 'locking in' model of synaesthesia, suggesting that synaesthetic associations can be used as a 'time capsule', revealing childhood influences on adult linguistic associations. Grapheme-colour synaesthesia may thus offer an extraordinary opportunity to study linguistic development. This article is part of a discussion meeting issue 'Bridging senses: novel insights from synaesthesia'.

Synaesthetic colour associations for Japanese Kanji characters: from the perspective of grapheme learning.

One of the fundamental questions about grapheme-colour synaesthesia is how specific associations between the graphemes and colours are formed. We addressed this question by focusing on the determinants of synaesthetic colours for Japanese Kanji characters (logographic characters) using a psycholinguistic approach. Study 1 explored the influence meaning has on synaesthetic colours for Kanji characters representing abstract meanings by examining synaesthetic colours for antonym pairs (i.e. characters with meanings opposed to each other) in Japanese synaesthetes. Results showed that semantic relations influenced the grapheme-colour associations for characters representing abstract meanings in the early stages of learning abstract Kanji, while the influence was reduced in the grapheme-colour associations for those learned later. Study 2 examined the effect that learning new sounds or meanings of graphemes has on synaesthetic colours for those graphemes. Japanese synaesthetes were taught new sounds or new meanings for familiar Kanji characters. Results indicated that acquiring new information for graphemes slightly but significantly reduced the test-retest grapheme-colour association consistency, suggesting that synaesthetic colours can be modulated to reflect the synaesthete's latest knowledge about graphemes. Implications of these findings are discussed from the perspective of the relationship between synaesthesia and grapheme learning. This article is part of a discussion meeting issue 'Bridging senses: novel insights from synaesthesia'.

Do synaesthesia and mental imagery tap into similar cross-modal processes?

Synaesthesia has previously been linked with imagery abilities, although an understanding of a causal role for mental imagery in broader synaesthetic experiences remains elusive. This can be partly attributed to our relatively poor understanding of imagery in sensory domains beyond vision. Investigations into the neural and behavioural underpinnings of mental imagery have nevertheless identified an important role for imagery in perception, particularly in mediating cross-modal interactions. However, the phenomenology of synaesthesia gives rise to the assumption that associated cross-modal interactions may be encapsulated and specific to synaesthesia. As such, evidence for a link between imagery and perception may not generalize to synaesthesia. Here, we present results that challenge this idea: first, we found enhanced somatosensory imagery evoked by visual stimuli of body parts in mirror-touch synaesthetes, relative to other synaesthetes or controls. Moreover, this enhanced imagery generalized to tactile object properties not directly linked to their synaesthetic associations. Second, we report evidence that concurrent experience evoked in grapheme-colour synaesthesia was sufficient to trigger visual-to-tactile correspondences that are common to all. Together, these findings show that enhanced mental imagery is a consistent hallmark of synaesthesia, and suggest the intriguing possibility that imagery may facilitate the cross-modal interactions that underpin synaesthesic experiences. This article is part of a discussion meeting issue 'Bridging senses: novel insights from synaesthesia'.

Long-term versus short-term consistency in the grapheme-colour synaesthesia: Grapheme-colour pairings can change in adulthood.

The aim of the article is to examine the stability of grapheme-colour matchings in adulthood. We carried out a panel study using computerized tests to measure short-term and long-term consistency. We conducted three testing rounds during 1 year and a half with a resulting sample of 26 synaesthetes. Our results suggest that the colours associated with individual graphemes can change substantially (e.g. from "salmon" to "aquamarine") even during this relatively short time period. Based on a linear mixed model, we further argue that short-term and long-term consistency should be distinguished because these scores tend to differ. These results thus complement previous findings on the issue of grapheme-colour consistency and have important consequences for the study of synaesthesia in the future.

Superior learning in synesthetes: Consistent grapheme-color associations facilitate statistical learning

In synesthesia activation in one sensory domain, such as smell or sound, triggers an involuntary and unusual secondary sensory or cognitive experience. In the present study, we ask whether the added sensory experience of synesthesia can aid statistical learning—the ability to track environmental regularities in order to segment continuous information. To investigate this, we measured statistical learning outcomes, using an aurally presented artificial language, in two groups of synesthetes alongside controls and simulated the multimodal experience of synesthesia in non-synesthetes. One group of synesthetes exclusively had grapheme-color (GC) synesthesia, in which the experience of color is automatically triggered by exposure to written or spoken graphemes. The other group had both grapheme-color and sound-color (SC+) synesthesia, in which the experience of color is also triggered by the waveform properties of a voice, such as pitch, timbre, and/or musical chords. Unlike GC-only synesthetes, the experience of color in the SC+ group is not perfectly consistent with the statistics that signal word boundaries. We showed that GC-only synesthetes outperformed both non-synesthetes and SC+ synesthetes, likely because the visual concurrents for GC-only synesthetes are highly consistent with the artificial language. We further observed that our simulations of GC synesthesia, but not SC+ synesthesia produced superior statistical learning, showing that synesthesia likely boosts learning outcomes by providing a consistent secondary cue. Findings are discussed with regard to how multimodal experience can improve learning, with the present data indicating that this boost is more likely to occur through explicit, as opposed to implicit, learning systems.

Multilevel analysis of individual differences in regularities of grapheme-color associations in synesthesia.

Grapheme-color synesthesia is a neurological phenomenon where visual perception of letters and numbers stimulates perception of a specific color. Grapheme-color correspondences have been shown to be systematically associated with grapheme properties, including visual shape difference, ordinality, and frequency. However, the contributions of grapheme factors differ across individuals. In this study, we applied multilevel analysis to test whether individual differences in regularities of grapheme-color associations could be explained by individual styles of processing grapheme properties. These processing styles are reflected by the type of synesthetic experience. Specifically, we hypothesized that processing focusing on shape differences would be associated with projector synesthetes, while processing focusing on ordinality or familiarity would be associated with associator synesthetes. The analysis revealed that ordinality and familiarity factors were expressed more strongly among associators than among projectors. This finding suggests that grapheme-color associations are partly determined by the type of synesthetic experience.

A Is for Apple: the Role of Letter-Word Associations in the Development of Grapheme-Colour Synaesthesia.

This study investigates the origins of specific letter-colour associations experienced by people with grapheme-colour synaesthesia. We present novel evidence that frequently observed trends in synaesthesia (e.g., A is typically red) can be tied to orthographic associations between letters and words (e.g., 'A is for apple'), which are typically formed during literacy acquisition. In our experiments, we first tested members of the general population to show that certain words are consistently associated with letters of the alphabet (e.g., A is for apple), which we named index words. Sampling from the same population, we then elicited the typical colour associations of these index words (e.g., apples are red) and used the letter → index word → colour connections to predict which colours and letters would be paired together based on these orthographic-semantic influences. We then looked at direct letter-colour associations (e.g., A→ red, B→ blue…) from both synaesthetes and non-synaesthetes. In both populations, we show statistically that the colour predicted by index words matches significantly with the letter-colour mappings: that is, A→ red because A is for apple and apples are prototypically red. We therefore conclude that letter-colour associations in both synaesthetes and non-synaesthetes are tied to early-learned letter-word associations.

Ignoring Irrelevant Information: Enhanced Intermodal Attention in Synaesthetes.

Despite the fact that synaesthetes experience additional percepts during their inducer-concurrent associations that are often unrelated or irrelevant to their daily activities, they appear to be relatively unaffected by this potentially distracting information. This might suggest that synaesthetes are particularly good at ignoring irrelevant perceptual information coming from different sensory modalities. To investigate this hypothesis, the performance of a group of synaesthetes was compared to that of a matched non-synaesthete group in two different conflict tasks aimed at assessing participants' abilities to ignore irrelevant information. In order to match the sensory modality of the task-irrelevant distractors (vision) with participants' synaesthetic attentional filtering experience, we tested only synaesthetes experiencing at least one synaesthesia subtype triggering visual concurrents (e.g., grapheme-colour synaesthesia or sequence-space synaesthesia). Synaesthetes and controls performed a classic flanker task (FT) and a visuo-tactile cross-modal congruency task (CCT) in which they had to attend to tactile targets while ignoring visual distractors. While no differences were observed between synaesthetes and controls in the FT, synaesthetes showed reduced interference by the irrelevant distractors of the CCT. These findings provide the first direct evidence that synaesthetes might be more efficient than non-synaesthetes at dissociating conflicting information from different sensory modalities when the irrelevant modality correlates with their synaesthetic concurrent modality (here vision).

What Can Illusory Conjunctions Reveal About Synaesthetic Bindings?

The visual system successfully binds the shapes and colours of objects; therefore, our visual experience regarding the objects around us is coherent. However, this binding process can break down when attention is diverted, producing illusory conjunctions (ICs); for example, when presented with a red 2 and a green 5, the observer may report a green 2 and a red 5. The strongest observation of binding in human cognition is found in synaesthesia. In grapheme-colour synaesthesia, linguistic stimuli (e.g., letters or numbers) are strongly associated with colours. It is debatable whether these highly stable bindings constitute a form of early binding that occurs outside the focus of attention. We examined for the first time the occurrence of ICs in grapheme-colour synaesthesia. Experiment 1 replicated our previous finding, showing the effects of numerical distance on ICs (Arend et al., Psychon. Bull. Rev. 2013, 20, 1181-1186). Participants viewed a display containing two centrally presented letters and two coloured numbers and were asked to report: (1) whether the letters were same/different, (2) the colour of the larger number, and (3) the level of confidence concerning the colour of the number. Experiment 2 used a modified version of this task. Synaesthetes (N=5) and controls (N=15) viewed number-colour pairs that were congruent or incongruent with that of the synaesthetic association. Grapheme-colour synaesthesia significantly affected ICs on incongruent but not on congruent trials. Our findings strongly support the notion that shape and colour are free-floating features in synaesthesia, similar to what is observed in normal cognition.

Is Synaesthesia More Prevalent in Autism Spectrum Conditions? Only Where There Is Prodigious Talent.

Savant syndrome is a condition where prodigious talent co-occurs with developmental difficulties such as autism spectrum conditions (ASC). To better understand savant skills, we previously proposed a link with synaesthesia: that savant syndrome may arise in ASC individuals who also happen to have synaesthesia. Asecond, unrelated claim is that people with autism may have higher rates of synaesthesia. Here we ask whether synaesthesia is indeed found more often in autism per se, or only in cases where autism co-occurs with savant skills. People with autism in previous studies when tested for synaesthesia were not differentiated into those with and without savant abilities. Here we tested three groups: people with autism who also have savant skills (n=40), people with autism without savant skills (n=34), and controls without autism (n=29). We used a validated test to diagnose grapheme-colour synaesthesia. Results show a significantly higher prevalence of synaesthesia in people with ASC, but only those who also have savant skills. This suggests that synaesthesia in autism is linked to those with savant abilities rather than autism per se. We discuss the role of synaesthesia in the development of prodigious talent.

Social perception in synaesthesia for colour

ABSTRACTSynaesthesia is a rare phenomenon in which stimulation in one modality (e.g., audition) evokes a secondary percept not associated with the first (e.g., colour). Prior work has suggested links between synaesthesia and other neurodevelopmental conditions that are linked to altered social perception abilities. With this in mind, here we sought to examine social perception abilities in grapheme–colour synaesthesia (where achromatic graphemes evoke colour experiences) by examining facial identity and facial emotion perception in synaesthetes and controls. Our results indicate that individuals who experience grapheme–colour synaesthesia outperformed controls on tasks involving fine visual discrimination of facial identity and emotion, but not on tasks involving holistic face processing. These findings are discussed in the context of broader perceptual and cognitive traits previously associated with synaesthesia for colour, with the suggestion that performance benefits shown by grapheme–colour synaesthetes may be related to domain-general visual discrimination biases observed in this group.

Mirror-Touch Synaesthesia Is Not Associated with Heightened Empathy, and Can Occur with Autism.

Research has linked Mirror-Touch (MT) synaesthesia with enhanced empathy. We test the largest sample of MT synaesthetes to date to examine two claims that have been previously made: that MT synaesthetes (1) have superior empathy; and (2) only ever experience their MT synaesthesia in response to viewing a person being touched. Given that autism has been suggested to involve deficits in cognitive empathy, we also test two predictions: that MT synaesthetes should (3) be less likely than general population individuals without MT synaesthesia to have an autism spectrum condition (ASC), if MT is characterized by superior empathy; and (4) have fewer autistic traits. We selected three groups: a pure MT synaesthesia group (N = 46), a pure grapheme-colour (GC) synaesthesia group (N = 36), and a typical control group without synaesthesia (N = 46). Participants took three measures of empathy and one measure of autistic traits. MT synaesthetes did not show enhanced empathy. In addition, 30% of all MT synaesthetes recruited into this study (N = 135) reported also having ASC, and MT synaesthetes showed higher autistic trait scores than controls. Finally, some MT experiences were reported in response to viewing objects being touched. Our findings dispute the views that MT synaesthesia is linked with enhanced empathy, is less likely to occur with ASC or elevated autistic traits, and is specific to seeing a person being touched.

Biases and regularities of grapheme-colour associations in Japanese nonsynaesthetic population.

Associations between graphemes and colours in a nonsynaesthetic Japanese population were investigated. Participants chose the most suitable colour from 11 basic colour terms for each of 40 graphemes from the four categories of graphemes used in the Japanese language (kana characters, English alphabet letters, and Arabic and kanji numerals). This test was repeated after a three-week interval. In their responses, which were not as temporally consistent as those of grapheme-colour synaesthetes, participants showed biases and regularities that were comparable to those of synaesthetes reported in past studies. Although it has been believed that only synaesthetes, and not nonsynaesthetes, tended to associate graphemes with colours based on grapheme frequency, Berlin and Kay's colour typology, and colour word frequency, participants in this study tended in part to associate graphemes with colours based on the above factors. Moreover, participants that were nonsynaesthetes tended to associate different graphemes that shared sounds and/or meanings (e.g., Arabic and kanji numerals representing the same number) with the same colours, which was analogous to the findings in Japanese synaesthetes. These results support the view that grapheme-colour synaesthesia might have its origins in cross-modal association processes that are shared with the general population.