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Grapheme-color synesthetes experience graphemes as having a consistent color (e.g., “N is turquoise”). Synesthetes’ specific associations (which letter is which color) are influenced by linguistic properties (letter frequency, phonetic similarity, etc.), and plausibly reveal the characteristics of underlying letter representations. Despite their clear linguistic origin, these influences (termed “Regulatory Factors”, RFs) are almost always studied in a single language, typically English. Here, we measure the influence of three RFs (previously examined only in English) in Dutch, English, Greek, Japanese, Korean, Russian, and Spanish synesthetes. For two RFs, effect size significantly differed between languages. In contrast, an RF which we predicted to be universal (because it is shaped by prelinguistic shape-color associations) did not differ between languages. Our results suggest that monolingual synesthesia studies should be interpreted with caution. Furthermore, they show how synesthetic associations offer an exceptional opportunity to study linguistic and prelinguistic influences on letter representations in different languages.

Misophonia is a disorder of decreased tolerance to specific sounds or their associated stimuli that has been characterized using different language and methodologies. The absence of a common understanding or foundational definition of misophonia hinders progress in research to understand the disorder and develop effective treatments for individuals suffering from misophonia. From June 2020 through January 2021, a project was conducted to determine whether a committee of experts with diverse expertise related to misophonia could develop a consensus definition of misophonia. An expert committee used a modified Delphi method to evaluate candidate definitional statements that were identified through a systematic review of the published literature. Over four rounds of iterative voting, revision, and exclusion, the committee made decisions to include, exclude, or revise these statements in the definition based on the currently available scientific and clinical evidence. A definitional statement was included in the final definition only after reaching consensus at 80% or more of the committee agreeing with its premise and phrasing. The results of this rigorous consensus-building process were compiled into a final definition of misophonia that is presented here. This definition will serve as an important step to bring cohesion to the growing field of researchers and clinicians who seek to better understand and support individuals experiencing misophonia.

Grapheme-color synesthetes experience linguistic symbols (e.g., letters of the alphabet) as having a consistent color (e.g., “The letter S is burgundy red”). Intriguingly, when non-synesthetes are forced to choose colors for letters, similar non-random distributions are observed. Why are certain letters likelier to be associated with certain colors? Researchers have long sought to explain these trends, and in the past few decades numerous studies have reported correlations between synesthetic colors and various properties of letters, such as ordinal position, frequency in the language, and even pronunciation. These influences, which we call “Regulatory Factors” (RFs), each explain some fraction of the variation in observed associations. In the present work, we provide an updated review of the literature, covering all known studies of RFs. We describe each RF and the operationalization that was used to measure it. For each RF, we also replicate the results in our own database of synesthetes and non-synesthetes, in some cases testing for the first time whether the RF influences the associations of non-synesthete controls. Finally, we introduce a new statistical model of synesthetic associations, that can evaluate the effect of all RFs in a single model.

We propose that synesthetic cross-activation between the primary auditory cortex and the anatomically adjacent insula may help explain two puzzling conditions—autonomous sensory meridian response (ASMR) and misophonia—in which quotidian sounds involuntarily trigger strong emotional responses. In ASMR the sounds engender relaxation, while in misophonia they trigger an aversive response. The insula both plays an important role in autonomic nervous system control and integrates multiple interoceptive maps representing the physiological state of the body to substantiate a dynamic representation of emotional wellbeing. We propose that in ASMR cross-activation of the map for affective (sensual) touch leads to an increase in subjective wellbeing and parasympathetic activity. Conversely, in misophonia the effect of the cross-activation is to decrease emotional wellbeing and increase sympathetic activity. Our hypothesis also illuminates the connection between hearing and wellbeing more broadly and helps explain why so many people experience decreased wellbeing from modern urban soundscapes.

For individuals with misophonia, specific innocuous sensory stimuli - such as hearing another person chewing or breathing - evoke strong negative emotional and physiological responses, such as extreme anger, disgust, stress and anxiety. Instead people with misophonia do not experience or display atypical reactions to generic aversive sounds such as screams or nails scratching on a blackboard. Misophonia appears to be unrelated to neurological trauma or hearing deficit, and features a characteristic developmental pattern. Its aetiology is currently unknown.The few previous fMRI studies on misophonia showed that sufferers feature increased dorsal anterior insula activity during trigger vs. generic aversive sounds. While this effect likely reflects the saliency associated with the perception of trigger sounds in people with misophonia, in the present fMRI study we investigate the neural mechanisms underlying the emotional reaction to trigger stimuli. To this aim, we probe the task-dependent connectivity of mid-cingulate, medial premotor and ventrolateral premotor cortex. We observe that only in participants with misophonia the presentation of trigger audio-visuals prompts an increased interaction of these three brain regions with the lateral orbitofrontal cortex. This brain region is crucial for behavioural inhibition mediated by cognitive and emotional content (such as in reward-reversal learning) and is part of the temporo-amygdala-orbitofrontal network, which integrates visceral and emotional states with cognition and behaviour. We also observe that in people with misophonia trigger sounds prompt a significant increase in the interaction between mid-cingulate and the primary auditory cortex.Our study replicates previous results and expands the network of brain regions involved in misophonia. The involvement of the orbitofrontal cortex suggests a defective functioning of high-order integrative processes allowing the reappraisal of experience-dependent negative emotional association with harmless sensory stimuli, and sheds light on the mechanisms underlying the compulsive nature of the misophonic reaction. The increased interaction, rather than the overall activity, of the primary auditory cortex with the mid-cingulate supports the hypothesis that the emotional response in misophonia is subserved by an indirect auditory-limbic pathway processing the subjective valence of specific sounds, rather than their physical properties alone.

Misophonia is a newly researched condition in which specific sounds cause an intense, aversive response in individuals, characterized by negative emotions and autonomic arousal. Although virtually any sound can become a misophonic “trigger,” the most common sounds appear to be bodily sounds related to chewing and eating as well as other repetitive sounds. An intriguing aspect of misophonia is the fact that many misophonic individuals report that they are triggered more, or even only, by sounds produced by specific individuals, and less, or not at all, by sounds produced by animals (although there are always exceptions).In general, anecdotal evidence suggests that misophonic triggers involve a combination of sound stimuli and contextual cues. The aversive stimulus is more than just a sound and can be thought of as a Gestalt of features which includes sound as a necessary component as well as additional contextual information. In this study, we explore how contextual information influences misophonic responses to human chewing, as well as sonically similar sounds produced by non-human sources. The current study revealed that the exact same sound can be perceived as being much more or less aversive depending on the contextual information presented alongside the auditory information. The results of this study provide a foundation for potential cognitive based therapies.

Synaesthesia is a neurological phenomenon affecting perception, where triggering stimuli (e.g. letters and numbers) elicit unusual secondary sensory experiences (e.g. colours). Family-based studies point to a role for genetic factors in the development of this trait. However, the contributions of common genomic variation to synaesthesia have not yet been investigated. Here, we present the SynGenes cohort, the largest genotyped collection of unrelated people with grapheme–colour synaesthesia ( n = 723). Synaesthesia has been associated with a range of other neuropsychological traits, including enhanced memory and mental imagery, as well as greater sensory sensitivity. Motivated by the prior literature on putative trait overlaps, we investigated polygenic scores derived from published genome-wide scans of schizophrenia and autism spectrum disorder (ASD), comparing our SynGenes cohort to 2181 non-synaesthetic controls. We found a very slight association between schizophrenia polygenic scores and synaesthesia (Nagelkerke's R 2 = 0.0047, empirical p = 0.0027) and no significant association for scores related to ASD (Nagelkerke's R 2 = 0.00092, empirical p = 0.54) or body mass index ( R 2 = 0.00058, empirical p = 0.60), included as a negative control. As sample sizes for studying common genomic variation continue to increase, genetic investigations of the kind reported here may yield novel insights into the shared biology between synaesthesia and other traits, to complement findings from neuropsychology and brain imaging. This article is part of a discussion meeting issue ‘Bridging senses: novel insights from synaesthesia'.

In grapheme-colour synaesthesia, particular linguistic elements evoke particular colour sensations. Interestingly, when asked, non-synaesthetes can also associate colours to letters, and previous studies show that specific letter-to-colour associations have similar biases to those of synaesthetes. However, it is an open question whether the colours reported by synaesthetes and non-synaesthetes differ overall : is there a ‘synaesthetic colour palette’? In this study, we visualize the overall distribution in colour space of colour concurrents in grapheme-colour synaesthetes, and colour associations in non-synaesthetic controls. We confirm the existence of a synaesthetic colour palette: colour concurrents in synaesthetes are different from colour associations in non-synaesthetes. We quantify three factors that distinguish the colour palette of synaesthetes and non-synaesthetes: synaesthetes have an increased over-representation of ‘pure’ (unmixed) hues, an increased presence of ‘warm’ (yellow, orange, brown) colours, and an increased presence of achromatic (grey, white, black) colours. Furthermore, we demonstrate that differences in the synaesthetic colour palette can be used to train a machine learning algorithm to reliably classify single subjects as synaesthetes versus non-synaesthetes without using test–retest consistency data. As far as we know, this is the first time an individual could be ‘diagnosed’ as a synaesthete, based only on his or her colours evoked by letters. This article is part of a discussion meeting issue ‘Bridging senses: novel insights from synaesthesia’.

The recent sharp increase in studies on synesthesia has taught us a lot about this fascinating condition. Still, while we define synesthesia as 'the mixing of senses', the great majority of synesthesia studies focus on only one synesthesia type (in particular grapheme-color synesthesia). In this study, a large group of subjects are tested on the presence or absence of different types of synesthesia. Efforts to recruit a representative sample of the Dutch population, not related to or aware of synesthesia as a research topic, helped counter a selection bias or a self-report bias in our subject group. A sharp increase in synesthesia prevalence was found, at least partially due to including many different types of synesthesia in the synesthesia 'diagnoses'. The five synesthesia types reported in the Novich et al (2011) study were obtained; Colored Sequences, Colored Music, Colored Sensations, Spatial Sequences, Non-Visual Sequelae, as well as an additional synesthesia type, Sequence-Personality. No differences were found between synesthetes and non-synesthetes in education level, handedness, age, and sex. The synesthetes showed increased intelligence as compared with matched non-synesthetes. This was a general effect rather than bound to a specific cognitive domain or to a specific (synesthesia-type to stimulus-material) relationship. The expected effect of increased "Openness" in synesthetes was obtained, as well as two unexpected effects in personality traits (increased "Neuroticism" and decreased "Conscientiousness"). We also found increased "Emotionality" (experiencing emotions) and increased "Fantasizing", but synesthetes did not differ in cognitive appraisal of emotions (identifying/analyzing/verbalizing of emotions). The personality and cognitive characteristics were found related to having synesthesia (in general) rather then to particular synesthesia subtypes. This supports the existence of a general synesthetic 'trait', over the notion of relatively independent 'types' of synesthesia. In further support, exploratory analyses showed that a measurement of synesthetic strength (number of subtypes of synesthesia) correlates with stronger findings (increased "Openness", "Fantasizing", and "Emotionality", and decreased "Conscientiousness"). In conclusion, results are in line with the notion of a general synesthetic 'trait', and this synesthetic trait is associated with particular personality traits and cognitive characteristics.

An example trial from the child synaesthesia test-retest consistency experiment

ObjectiveWe aim to elucidate misophonia, a condition in which particular sounds elicit disproportionally strong aversive reactions.MethodA large online study extensively surveyed personal, developmental, and clinical characteristics of over 300 misophonics.ResultsMost participants indicated that their symptoms started in childhood or early teenage years. Severity of misophonic responses increases over time. One third of participants reported having family members with similar symptoms. Half of our participants reported no comorbid clinical conditions, and the other half reported a variety of conditions. Only posttraumatic stress disorder (PTSD) was related to the severity of the misophonic symptoms. Remarkably, half of the participants reported experiencing euphoric, relaxing, and tingling sensations with particular sounds or sights, a relatively unfamiliar phenomenon called autonomous sensory meridian response (ASMR).ConclusionIt is unlikely that another “real” underlying clinical, psychiatric, or psychological disorder can explain away the misophonia. The possible relationship with PTSD and ASMR warrants further investigation.

Grapheme-color synesthesia is a condition in which seeing letters and numbers produces sensations of colors (e.g., the letter R may elicit a sky-blue percept). Recent evidence implicates posterior parietal areas, in addition to lower-level sensory processing regions, in the neurobiological mechanisms involved in synesthesia. Furthermore, these mechanisms seem to differ for "projectors" (synesthetes who report seeing the color "out there in the real world") versus "associators" (synesthetes who report the color to be only an internal experience). Relatively little is known about possible electrophysiological characteristics of grapheme-color synesthesia. Here we used EEG to investigate functional oscillatory differences among associators, projectors, and non-synesthetes. Projectors had stronger stimulus-related alpha-band (~10 Hz) power over posterior parietal electrodes, compared to both associators and non-synesthetes. Posterior alpha activity was not statistically significantly different between associators from non-synesthetes. We also performed a test-retest assessment of the projector-associator score and found strong retest reliability, as evidenced by a correlation coefficient of .85. These findings demonstrate that the projector-associator distinction is highly reliable over time and is related to neural oscillations in the alpha band.

Grapheme-color synesthesia is a neurological phenomenon in which viewing a grapheme elicits an additional, automatic, and consistent sensation of color. Color-to-letter associations in synesthesia are interesting in their own right, but also offer an opportunity to examine relationships between visual, acoustic, and semantic aspects of language. Research using large populations of synesthetes has indeed found that grapheme-color pairings can be influenced by numerous properties of graphemes, but the contributions made by each of these explanatory factors are often confounded in a monolingual dataset (i.e., only English-speaking synesthetes). Here, we report the first demonstration of how a multilingual dataset can reveal potentially-universal influences on synesthetic associations, and disentangle previously-confounded hypotheses about the relationship between properties of synesthetic color and properties of the grapheme that induces it. Numerous studies have reported that for English-speaking synesthetes, “A” tends to be colored red more often than predicted by chance, and several explanatory factors have been proposed that could explain this association. Using a five-language dataset (native English, Dutch, Spanish, Japanese, and Korean speakers), we compare the predictions made by each explanatory factor, and show that only an ordinal explanation makes consistent predictions across all five languages, suggesting that the English “A” is red because the first grapheme of a synesthete's alphabet or syllabary tends to be associated with red. We propose that the relationship between the first grapheme and the color red is an association between an unusually-distinct ordinal position (“first”) and an unusually-distinct color (red). We test the predictions made by this theory, and demonstrate that the first grapheme is unusually distinct (has a color that is distant in color space from the other letters' colors). Our results demonstrate the importance of considering cross-linguistic similarities and differences in synesthesia, and suggest that some influences on grapheme-color associations in synesthesia might be universal.

Synaesthesia is a neurological phenomenon affecting perception, where triggering stimuli (e.g. letters and numbers) elicit unusual secondary sensory experiences (e.g. colours). Family-based studies point to a role for genetic factors in the development of this trait. However, the contributions of common genomic variation to synaesthesia have not yet been investigated. Here, we present the SynGenes cohort, the largest genotyped collection of unrelated people with grapheme–colour synaesthesia (n = 723). Synaesthesia has been associated with a range of other neuropsychological traits, including enhanced memory and mental imagery, as well as greater sensory sensitivity. Motivated by the prior literature on putative trait overlaps, we investigated polygenic scores derived from published genome-wide scans of schizophrenia and autism spectrum disorder (ASD), comparing our SynGenes cohort to 2181 non-synaesthetic controls. We found a very slight association between schizophrenia polygenic scores and synaesthesia (Nagelkerke's R(2) = 0.0047, empirical p = 0.0027) and no significant association for scores related to ASD (Nagelkerke's R(2) = 0.00092, empirical p = 0.54) or body mass index (R(2) = 0.00058, empirical p = 0.60), included as a negative control. As sample sizes for studying common genomic variation continue to increase, genetic investigations of the kind reported here may yield novel insights into the shared biology between synaesthesia and other traits, to complement findings from neuropsychology and brain imaging. This article is part of a discussion meeting issue ‘Bridging senses: novel insights from synaesthesia'.

Misophonia is a complex neurobehavioral syndrome phenotypically characterized by heightened autonomic nervous system arousal and negative emotional reactivity, in response to a decreased tolerance for specific sounds1,2. Some people with Misophonia report aversive responses to certain visual and tactile stimuli. The small body of research on Misophonia suggests that individuals suffering from this condition experience extreme autonomic arousal1 when exposed to ordinary auditory stimuli. Sufferers report physical sensations, and actions such as teeth clenching and muscle tightening. Emotional reactions and feeling-states include extreme annoyance, anger, rage, and anxiety. Misophonia is not classified in DSM-V or ICD-10, and most people are self-diagnosed. Research from basic and applied fields are synthesized with studies explicitly designed to investigate misophonia in an effort to more specifically conceptualize this syndrome. The current study identifies several cognitive and affective aspects of Misophonia in over 300 misophones. Phonophilia, depression, anxiety, ADD, OCD and PTSD have the highest symptom overlap with Misophonia. Despite the suggested potentially clinical resemblance of Misophonia with OCSD, still the condition should be described as a separate condition2,3 in DSM-V, based on severity of the symptoms, and the distinctiveness of the combination of symptoms. Our data reveal co-morbidity with PTSD. Subjects with PTSD also report more severe Misophonic complaints than subjects without PTSD. Furthermore, according to our data, almost half of the Misophonics experience ASMR (Autonomous sensory meridian response) to various degrees. In our sample, 66 subjects report severe distress caused by their Misophonia, experiencing panic/rage reactions as well as reporting actual use of physical violence (often self-harming). Given the impairing nature of this condition, further research is clearly warranted regarding etiology, phenotypes, and cognitive and neurological properties of this condition.

Over 100,000 verbal and visuospatial immediate and delayed memory tests were presented via the Internet to over 28,000 participants in the age range of 11 to 80. Structural equation modeling pointed to the verbal versus visuospatial dimension as an important factor in individual differences, but not the immediate versus delayed dimension. We found a linear decrease of 1% to 3% per year in overall memory performance past the age of 25. For visuospatial tests, this decrease started at age 18 and was twice as fast as the decrease of verbal memory. There were strong effects of education, with the highest educated group sometimes scoring one full standard deviation above the lowest educated group. Gender effects were small but as expected: women outperformed men on the verbal memory tasks; men outperformed women on the visuospatial tasks. We also found evidence of increasing proneness to false memory with age. Memory for recent news events did not show a decrease with age. © 2012 Elsevier B.V.

Despite a recent upsurge of research, much remains unknown about the neurobiological mechanisms underlying synaesthesia. By integrating results obtained so far in Magnetic Resonance Imaging (MRI) studies, this contribution sheds light on the role of particular brain regions in synaesthetic experiences. First, in accordance with its sensory nature, it seems that the sensory brain areas corresponding to the type of synaesthetic experience are activated. Synaesthetic colour experiences can activate colour regions in occipito-temporal cortex, but this is not necessarily restricted to V4. Furthermore, sensory and motor brain regions have been obtained that extend beyond the particular type of synaesthesia studied. Second, differences in experimental setup, number and type of synaesthetes tested, and method to delineate regions of interest may help explain inconsistent results obtained in the BOLD-MRI (Blood Oxygen Level Dependent functional MRI) studies. Third, an overview of obtained results shows that a network of brain areas rather than a single brain region underlies synaesthesia. Six brain regions of overlapping results emerge, these regions are in sensory and motor regions as well as ‘higher level’ regions in parietal and frontal lobe. We propose that these regions are related to three different cognitive processes inherently part of synaesthesia; the sensory processes, the (attentional) ‘binding’ processes, and cognitive control processes. Finally, we discuss how these functional and structural brain properties might relate to the development of synaesthesia. In particular, we believe this relationship is better understood by separating the question what underlies the presence of synaesthesia (‘trait’) from what determines particular synaesthetic associations (‘type’).

Grapheme-color synesthesia is a neurological condition in which viewing numbers or letters (graphemes) results in the concurrent sensation of color. While the anatomical substrates underlying this experience are well understood, little research to date has investigated factors influencing the particular colors associated with particular graphemes or how synesthesia occurs developmentally. A recent suggestion of such an interaction has been proposed in the cascaded cross-tuning (CCT) model of synesthesia, which posits that in synesthetes connections between grapheme regions and color area V4 participate in a competitive activation process, with synesthetic colors arising during the component-stage of grapheme processing. This model more directly suggests that graphemes sharing similar component features (lines, curves, etc.) should accordingly activate more similar synesthetic colors. To test this proposal, we created and regressed synesthetic color-similarity matrices for each of 52 synesthetes against a letter-confusability matrix, an unbiased measure of visual similarity among graphemes. Results of synesthetes’ grapheme-color correspondences indeed revealed that more similarly shaped graphemes corresponded with more similar synesthetic colors, with stronger effects observed in individuals with more intense synesthetic experiences (projector synesthetes). These results support the CCT model of synesthesia, implicate early perceptual mechanisms as driving factors in the elicitation of synesthetic hues, and further highlight the relationship between conceptual and perceptual factors in this phenomenon.

Little is known about how the properties of our private mental world relate to the physical and functional properties of our brain. Studying synesthesia, where a particular experience evokes a separate additional sensory experience, offers the unique opportunity to study phenomenological experiences as a stable trait in healthy subjects. A common form of synesthesia is grapheme–color synesthesia, where a particular letter or number evokes a particular color experience. We studied the neural basis of qualitative different properties of the synesthetic experience by using individual differences in grapheme–color synesthesia. Specifically, the synesthetic color can be experienced “in the mind” (associator synesthetes) or “in the outside world” (projector synesthetes). Gray matter structure and functioning (imaged using voxel-based morphometry and functional magnetic resonance imaging, respectively) were examined in grapheme–color synesthetes (N= 42, 16 projectors and 26 associators) and nonsynesthetes. Results indicated partly shared mechanisms for all grapheme–color synesthetes, particularly in posterior superior parietal lobe, which is involved in the integration of sensory information. In addition, the nature of synesthetic experience was found to be mediated by distinct neural mechanisms. The outside-world experience is related to brain areas involved in perceiving and acting in the outside world (visual cortex, auditory cortex, motor cortex) as well as frontal brain areas. In contrast, the in-the-mind experience is related to the hippocampus and parahippocampal gyrus, known for their role in memory. Thus, the different subjective experiences are related to distinct neural mechanisms. Moreover, the properties of subjective experiences are in accordance with functional properties of the mediating brain mechanisms.

One of the most astonishing properties of synesthesia is that the evoked concurrent experiences are perceptual. Is it possible to acquire similar effects after learning cross-modal associations that resemble synesthetic mappings? In this study, we examine whether brain activation in early visual areas can be directly related to letter-color associations acquired by training. Non-synesthetes read specially prepared books with colored letters for several weeks and were scanned using functional magnetic resonance imaging. If the acquired letter-color associations were visual in nature, then brain activation in visual cortex while viewing the trained black letters (compared to untrained black letters) should predict the strength of the associations, the quality of the color experience, or the vividness of visual mental imagery. Results showed that training-related activation of area V4 was correlated with differences in reported subjective color experience. Trainees who were classified as having stronger 'associator' types of color experiences also had more negative activation for trained compared to untrained achromatic letters in area V4. In contrast, the strength of the acquired associations (measured as the Stroop effect) was not reliably reflected in visual cortex activity. The reported vividness of visual mental imagery was related to veridical color activation in early visual cortex, but not to the acquired color associations. We show for the first time that subjective experience related to a synesthesia-training paradigm was reflected in visual brain activation.

We studied intact and impaired processes in a prosopagnosic patient (RP). In Experiment 1, RP showed an inversion superiority effect with both faces and objects, with better performance when stimul...

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There is a current debate over the possibility and validity of synesthesia training experiments (Deroy and Spence, 2013; Rothen and Meier, 2014). In order to test whether a trainee should be considered to have acquired a trained form of synesthesia, a precise definition and specific diagnostic criteria of synesthesia are necessary. There is currently not one specific checklist available including all specific diagnostic methods and criteria, exacerbating the determination and interpretation of differences between (potentially) trained and genuine synesthesia. In order to facilitate communication surrounding these issues, we propose a practical guideline for diagnosing the specific characteristics that are typical of grapheme-color synesthesia (GCS). These guidelines can be applied to developmental cases of GCS, cases of trainees who may show synesthetic traits, and other types of acquired forms of GCS at the level of a single individual.

While colors are commonplace in everyday metaphors, relatively little is known about implicit color associations to linguistic or semantic concepts in a general population. In this study, we test color associations for ordered linguistic concepts (letters and days). The culture and language specificity of these effects was examined in a large group (457) of Dutch-speaking participants, 92 English-speaking participants, and 49 Hindi-speaking participants. Non-random distributions of color choices were revealed; consistencies were found across the three language groups in color preferences for both days and letters. Interestingly, while the Hindi-speaking participants were presented with letter stimuli matched on phonology, their pattern of letter-to-color preferences still showed similarities with Dutch- and English-speaking participants. Furthermore, we found that that the color preferences corresponded between participants indicating to have conscious color experiences with letters or days (putative synesthetes) and participants who do not (non-synesthetes). We also explored possible mechanisms underlying the color preferences. There were a few specific associations, including red for "A," red for "Monday," and white for "Sunday." We also explored more general mechanisms, such as overall color preferences as shown by Simner et al. (2005). While certainly not all variation can be explained or predicted, the results show that regularities are present in color-to-letter or color-to-day preferences in both putative synesthetes and non-synesthetes across languages. Both letter-to-color and day-to-color preferences were influenced by multiple factors. The findings support a notion of abstract concepts (such as days and letters) that are not represented in isolation, but are connected to perceptual representational systems. Interestingly, at least some of these connections to color representations are shared across different language/cultural groups.

Evidence is given for a special, canonical, status of one specific view in the identification of familiar faces. In the first experiment, subjects identified by name the fully frontal or profile poses of briefly familiarised individuals less efficiently than an intermediate pose. In addition, in a matching experiment using faces seen in different poses, it was found that one specific intermediate pose (corresponding to 22.5 degrees of angle from the full frontal view) was matched more efficiently in the right visual field (RVF) than in the left visual field (LVF). This finding supports the hypothesis of a superiority of the left hemisphere (LH) over the right hemisphere (RH) in processing a familiar face's canonical view. The other tested "noncanonical" views (i.e., full frontal, 45 degrees, and profile) of these same familiar faces were better matched in the LVF (i.e., the RH); especially at low levels of familiarity. We conclude that, for each familiar face, a viewer-centred representation of the canonical (22.5 degrees ) view is stored in the LH's memory system, whereas multiple views of familiar faces are stored in a memory system of the RH. With increasing levels of familiarity other views are increasingly more efficiently encoded by the LH, and in fact for facial self-recognition the full-front view is superior to any of the other tested views. These findings taken together suggest that complementary lateralised memory subsystems in the two cerebral hemispheres store different sets, only partially overlapping, of view-centred face representations.

After decades of research the notion that faces are special is still at the heart of heated debates. New techniques like brain imaging have advanced some of the arguments but empirical data from brain-damaged patients like paradoxical recognition effects have required more complex explanations aside from localisation of the face area in normal adults. In this paper we focus on configural face processes and discuss configural processes in prosopagnosics in the light of findings obtained in brain-imaging studies. In order to account for data like paradoxical face recognition effects we propose a dual route model of face recognition. The model is based on the distinction between two separate aspects of face recognition, detection and identification, considered as dynamical and interrelated. In this perspective the face detection system appears as the stronger candidate for face-specific processes. The face identification system on the other hand is part of the object recognition system but derives its specificity in part from interaction with the face-specific detection system. The fact that face detection appears intact in some patients provides us with a possible explanation for the interference of configural processes on feature-based identification.

Selective impairment in recognition of faces (prosopagnosia) has been advanced as an argument for a brain module dedicated to face processing and focusing on the specific configural properties of faces. Loss of the inversion effect supposedly strengthened the argument ([10]: de Gelder B, Bachoud-Levi AC, Degos JD. Inversion superiority in visual agnosia may be common to a variety of orientation polarised objects besides faces. Vision Research, 1998;38:2855-61; [20]: Farah MJ, Wilson K, Drain H, Tanaka J. The inverted face inversion effect in prosopagnosia: Evidence for mandatory, face-specific perceptual mechanisms. Vision Research 1995b;35:2089-93). The present study of prosopagnosic patient LH reports that he has lost the normal pattern of superior performance with upright faces and objects and shows instead paradoxical inversion effect for faces but also for objects. Experiment 2 investigated whether LH's use of features based route for processing upright objects would be hindered by the whole-based encoding when processing upright objects. The data show the same context effect for objects as was found for faces. Therefore the inversion effect does not present decisive evidence for the existence of a face module. Moreover, the importance of configuration-based recognition known to be crucial for face processing, must also be taken seriously for object recognition.

This discussion paper forms an insightful addition to the synesthesia literature. Accompanying a steep increase in recent publications on synesthesia, it helps remedy the conspicuous paucity of mechanistic process models explaining the condition. The paper furthermore addresses what is arguably among the most interesting questions: Why do most synesthetes *not* get confused by their additional sensations? This is particularly interesting when phrased in a broader context: What are the mechanisms for deciding which of the sensations we experience reflect something "real" (phenomena in the outside world) and which reflect something that is "not real" (internally generated and private phenomena).

Synesthesia is a rare condition in which a stimulus from one modality automatically and consistently triggers unusual sensations in the same and/or other modalities. A relatively common and well-studied type is grapheme-color synesthesia, defined as the consistent experience of color when viewing, hearing and thinking about letters, words and numbers. We describe our method for investigating to what extent synesthetic associations between letters and colors can be learned by reading in color in nonsynesthetes. Reading in color is a special method for training associations in the sense that the associations are learned implicitly while the reader reads text as he or she normally would and it does not require explicit computer-directed training methods. In this protocol, participants are given specially prepared books to read in which four high-frequency letters are paired with four high-frequency colors. Participants receive unique sets of letter-color pairs based on their pre-existing preferences for colored letters. A modified Stroop task is administered before and after reading in order to test for learned letter-color associations and changes in brain activation. In addition to objective testing, a reading experience questionnaire is administered that is designed to probe for differences in subjective experience. A subset of questions may predict how well an individual learned the associations from reading in color. Importantly, we are not claiming that this method will cause each individual to develop grapheme-color synesthesia, only that it is possible for certain individuals to form letter-color associations by reading in color and these associations are similar in some aspects to those seen in developmental grapheme-color synesthetes. The method is quite flexible and can be used to investigate different aspects and outcomes of training synesthetic associations, including learning-induced changes in brain function and structure.

Gustatory forms of synesthesia involve the automatic and consistent experience of tastes that are triggered by non-taste related inducers. We present a case of lexical-gustatory and sound-gustatory synesthesia within one individual, SC. Most words and a subset of non-linguistic sounds induce the experience of taste, smell and physical sensations for SC. SC's lexical-gustatory associations were significantly more consistent than those of a group of controls. We tested for effects of presentation modality (visual vs. auditory), taste-related congruency, and synesthetic inducer-concurrent direction using a priming task. SC's performance did not differ significantly from a trained control group. We used functional magnetic resonance imaging to investigate the neural correlates of SC's synesthetic experiences by comparing her brain activation to the literature on brain networks related to language, music, and sound processing, in addition to synesthesia. Words that induced a strong taste were contrasted to words that induced weak-to-no tastes ("tasty" vs. "tasteless" words). Brain activation was also measured during passive listening to music and environmental sounds. Brain activation patterns showed evidence that two regions are implicated in SC's synesthetic experience of taste and smell: the left anterior insula and left superior parietal lobe. Anterior insula activation may reflect the synesthetic taste experience. The superior parietal lobe is proposed to be involved in binding sensory information across sub-types of synesthetes. We conclude that SC's synesthesia is genuine and reflected in her brain activation. The type of inducer (visual-lexical, auditory-lexical, and non-lexical auditory stimuli) could be differentiated based on patterns of brain activity.

Misophonia is a relatively unexplored chronic condition in which a person experiences autonomic arousal (analogous to an involuntary "fight-or-flight" response) to certain innocuous or repetitive sounds such as chewing, pen clicking, and lip smacking. Misophonics report anxiety, panic, and rage when exposed to trigger sounds, compromising their ability to complete everyday tasks and engage in healthy and normal social interactions. Across two experiments, we measured behavioral and physiological characteristics of the condition. Interviews (Experiment 1) with misophonics showed that the most problematic sounds are generally related to other people's behavior (pen clicking, chewing sounds). Misophonics are however not bothered when they produce these "trigger" sounds themselves, and some report mimicry as a coping strategy. Next, (Experiment 2) we tested the hypothesis that misophonics' subjective experiences evoke an anomalous physiological response to certain auditory stimuli. Misophonic individuals showed heightened ratings and skin conductance responses (SCRs) to auditory, but not visual stimuli, relative to a group of typically developed controls, supporting this general viewpoint and indicating that misophonia is a disorder that produces distinct autonomic effects not seen in typically developed individuals.

In grapheme-color synesthesia, a number or letter can evoke two different and possibly conflicting (real and synesthetic) color sensations at the same time. In this study, we investigate the relationship between synesthesia and executive control functions. First, no general skill differences were obtained between synesthetes and non-synesthetes in classic executive control paradigms. Furthermore, classic executive control effects did not interact with synesthetic behavioral effects. Third, we found support for our hypothesis that inhibition of a synesthetic color takes effort and time. Finally, individual differences analyses showed no relationship between the two skills; performance on a ‘normal’ Stroop task does not predict performance on a synesthetic Stroop task. Across four studies, the current results consistently show no clear relationship between executive control functions and synesthetic behavioral effects. This raises the question of which mechanisms are at play in synesthetic ‘management’ during the presence of two conflicting (real and synesthetic) sensations.

BackgroundSynesthesia is a phenomenon where a stimulus produces consistent extraordinary subjective experiences. A relatively common type of synesthesia involves perception of color when viewing letters (e.g. the letter ‘a’ always appears as light blue). In this study, we examine whether traits typically regarded as markers of synesthesia can be acquired by simply reading in color.Methodology/Principal FindingsNon-synesthetes were given specially prepared colored books to read. A modified Stroop task was administered before and after reading. A perceptual crowding task was administered after reading. Reading one book (>49,000 words) was sufficient to induce effects regarded as behavioral markers for synesthesia. The results of the Stroop tasks indicate that it is possible to learn letter-color associations through reading in color (F(1, 14) = 5.85, p = .030). Furthermore, Stroop effects correlated with subjective reports about experiencing letters in color (r(13) = 0.51, p = .05). The frequency of viewing letters is related to the level of association as seen by the difference in the Stroop effect size between upper- and lower-case letters (t(14) = 2.79, p = .014) and in a subgroup of participants whose Stroop effects increased as they continued to read in color. Readers did not show significant performance advantages on the crowding task compared to controls. Acknowledging the many differences between trainees and synesthetes, results suggest that it may be possible to acquire a subset of synesthetic behavioral traits in adulthood through training.Conclusion/SignificanceTo our knowledge, this is the first evidence of acquiring letter-color associations through reading in color. Reading in color appears to be a promising avenue in which we may explore the differences and similarities between synesthetes and non-synesthetes. Additionally, reading in color is a plausible method for a long-term ‘synesthetic’ training program.

Despite a recent upsurge of research, much remains unknown about the neurobiological mechanisms underlying synaesthesia. By integrating results obtained so far in Magnetic Resonance Imaging (MRI) studies, this contribution sheds light on the role of particular brain regions in synaesthetic experiences. First, in accordance with its sensory nature, it seems that the sensory brain areas corresponding to the type of synaesthetic experience are activated. Synaesthetic colour experiences can activate colour regions in occipito-temporal cortex, but this is not necessarily restricted to V4. Furthermore, sensory and motor brain regions have been obtained that extend beyond the particular type of synaesthesia studied. Second, differences in experimental setup, number and type of synaesthetes tested, and method to delineate regions of interest may help explain inconsistent results obtained in the BOLD-MRI (Blood Oxygen Level Dependent functional MRI) studies. Third, an overview of obtained results shows that a network of brain areas rather than a single brain region underlies synaesthesia. Six brain regions of overlapping results emerge, these regions are in sensory and motor regions as well as 'higher level' regions in parietal and frontal lobe. We propose that these regions are related to three different cognitive processes inherently part of synaesthesia; the sensory processes, the (attentional) 'binding' processes, and cognitive control processes. Finally, we discuss how these functional and structural brain properties might relate to the development of synaesthesia. In particular, we believe this relationship is better understood by separating the question what underlies the presence of synaesthesia ('trait') from what determines particular synaesthetic associations ('type').

The extent and the impact of spared processing of facial stimuli in the prosopagnosic patient LH is examined using the inversion effect and the face context effect. Our study asked how the deficit in individual face recognition is related to two perceptual abilities that are spared in this patient but between which there is interference when both are applied to the face stimulus, i.e. structural encoding of the face and parts-based matching procedures. Three experiments studied this relationship with task demands and stimulus properties designed to trigger the parts-based processes. In the first experiment, human and animal faces are presented upright or inverted with good performance only for the inverted condition. In Experiment 2 normals show a clear face context effect (matching of upright faces easier than scrambled or inverted ones) in the full face matching task whereas in the parts matching task the face superiority effect disappears. In contrast, LH shows a face inferiority effect when matching full faces but also when matching an isolated face part to a face part in a full face context. The results show that structural encoding of the face overrules parts-based procedures that could otherwise be helpful to tell individual faces apart.

Diffusion tensor imaging allowed us to validate for the first time the hypothesis that hyperconnectivity causes the added sensations in synesthesia. Grapheme-color synesthetes (n = 18), who experience specific colors with particular letters or numbers (for example, 'R is sky blue'), showed greater anisotropic diffusion compared with matched controls. Greater anisotropic diffusion indicates more coherent white matter. Anisotropy furthermore differentiated subtypes of grapheme-color synesthesia. Greater connectivity in the inferior temporal cortex was particularly strong for synesthetes who see synesthetic color in the outside world ('projectors') as compared with synesthetes who see the color in their 'mind's eye' only ('associators'). In contrast, greater connectivity (as compared with non-synesthetes) in the superior parietal or frontal cortex did not differentiate between subtypes of synesthesia. In conclusion, we found evidence that increased structural connectivity is associated with the presence of grapheme-color synesthesia, and has a role in the subjective nature of synesthetic color experience.

Configural face processes were tested using face recognition and face detection tasks in a comparison of acquired and developmental prosopagnosia. In the recognition task the two patients showed a very different pattern. The developmental patient does not show an inversion effect while the acquired prosopagnosia patient is better at matching inverted than normal stimuli. Moreover, there is no effect of face context on matching features in the developmental case while the acquired prosopagnosia patient shows a strong negative effect of context. However, in a speeded face detection task both patients are similarly unimpaired. The results are consistent with the existence of two separate face systems, one involved in face detection and the other in face recognition.

In this article we provide further evidence that visual mental imagery and visual perception share modality-specific mechanisms, and we find that representing visual information in a mental image (activating stored information to create a picture-like mental representation) preserves relatively low-level visual detail. Subjects either saw or visualized simple pictures, and evaluated them for the presence or absence of six types of non-accidental properties. These properties varied from very 'low-level' ones, such as T junctions, to very 'high-level' ones, such as global symmetry. The question was whether both sorts of information are equally accessible in percepts and mental images. If mental images are equivalent to descriptions of perceptual units and their organization, as some have argued, then subjects should have greater difficulty accessing low-level properties in a mental image compared to the difficulty they experience when the drawing is visible. The results of two experiments were clearcut: Subjects could evaluate high-level properties more easily than low-level ones, but this difference was the same in imagery and perception. These findings suggest that mental images preserve relatively low-level visual features, and are not simply descriptions of a pattern.

The condition synesthesia offers an extraordinary opportunity to study mechanisms involved in (hyper)-binding across different modalities. Currently, the majority of synesthesia research is aimed at a few types of synesthesia; colors evoked by written or spoken language and spatial arrangements evoked by sequential concepts. We do not yet know whether the processes involved in multisensory binding are similar or different across different types of synesthesia. In this project, brain structure measurements (connectivity and volume) were obtained from a large group of subjects (over 350 individuals). Furthermore, the subjects were presented with an extensive synesthesia questionnaire. In this subject group, different types of synesthetes were present; the inducers and concurrent ranged across perceptual modalities (e.g., visual, auditory, taste, tactile) but also involved non-sensory concepts (e.g., ‘personality’). This allows studying which of the previously obtained white-matter and grey-matter differences in synesthesia are specific to that (i.e., linguistic–color) type of synesthesia, and which are related more generally to having synesthesia. Furthermore, it allows examining whether synesthetes are, as a group, categorically different from all non-synesthetic subjects. Alternatively, each synesthete is only different from a non-synesthete in the binding of his or her specific inducer to his or her specific concurrent.

Grapheme–color synesthesia is defined as the experience of color in relation to letters, words and numbers. This form of synesthesia is a relatively common type and has received the most attention in the research field in terms of the neural basis of the synesthetic experience and behavioral features of synesthesia such as attention and memory. Grapheme–color and linguistic–color synesthesia have a genetic component. Still, language (the most common synesthetic inducer) is acquired through an interaction between genes and the environment. In order to probe this interaction, we compared relatives of grapheme–color synesthetes to a group of matched controls in a reading-in-color training paradigm. All participants read specially prepared books in which four high-frequency letters were paired with four high-frequency colors. Magnetic resonance images (MRI) were acquired before and after training, including diffusion tensor imaging (DTI). In this sample, there was no evidence of increased acquisition of the letter–color associations by the relatives of synesthetes. No group differences were found in behavior, while there are differences in functional activation on the Stroop task. Imaging results showed significant differences in brain activation in regions known to be involved in grapheme–color synesthesia across both groups. These regions include temporal–occipital cortex, inferior and superior parietal lobe, precentral gyrus, and frontal pole. We conclude that the neural basis of the effects of reading in color relies primarily on the same brain regions as the experience of (authentic) grapheme–color synesthesia.