Synesthetic colors are elicited by sound quality in Japanese synesthetes

Determinants of synesthetic color choice for Japanese phonetic characters were studied in six Japanese synesthetes. The study used Hiragana and Katakana characters, which represent the same set of syllables although their visual forms are dissimilar. From a palette of 138 colors, synesthetes selected a color corresponding to each character. Results revealed that synesthetic color choices for Hiragana characters and those for their Katakana counterparts were remarkably consistent, indicating that color selection depended on character-related sounds and not visual form. This Hiragana–Katakana invariance cannot be regarded as the same phenomenon as letter case invariance, usually reported for English grapheme-color synesthesia, because Hiragana and Katakana characters have different identities whereas upper and lower case letters have the same identity. This involvement of phonology suggests that cross-activation between an inducer (i.e., letter/character) brain region and that of the concurrent (i.e., color) area in grapheme-color synesthesia is mediated by higher order cortical processing areas.     

Is “Σ” purple or green? Bistable grapheme-color synesthesia induced by ambiguous characters

People with grapheme-color synesthesia perceive specific colors when viewing different letters or numbers. Previous studies have suggested that synesthetic color experience can be bistable when induced by an ambiguous character. However, the exact relationship between processes underlying the identity of an alphanumeric character and the experience of the induced synesthetic color has not been examined. In the present study, we explored this by focusing on the temporal relation of inducer identification and color emergence using inducers whose identity could be rendered ambiguous upon rotation of the characters. Specifically, achromatic alphabetic letters (W/M) and digits (6/9) were presented at varying angles to 9 grapheme-color synesthetes. Results showed that grapheme identification and synesthetically perceived grapheme color covary with the orientation of the test stimulus and that synesthetes were slower naming the experienced color than identifying the character, particularly at intermediate angles where ambiguity was greatest.     

联觉的发展与习得

联觉具有基因遗传性, 基因遗传在决定联觉中起到重要作用, 但并不意味着基因遗传就是决定联觉的唯一因素, 联觉具有在后期发展的可能, 并且这种发展呈现倒U形曲线。既然联觉是发展的, 那么联觉可否通过训练习得呢？目前不少研究对非联觉者进行了配对关联训练, 发现训练后的非联觉者具有类似于联觉者的表现, 也发现训练后的非联觉者与真正的联觉者具有一定的差异。但目前研究还没有直接或强有力的证据表明训练所致的配对关联就是一种联觉, 训练后的非联觉者就能变成联觉者。相反地, 越来越多的证据显示非联觉者经过配对关联训练后可能无法成为真正的联觉者。     

Association between synesthetic colors and sensitivity to physical colors changed by type of synesthetic experience in grapheme-color synesthesia

Grapheme-color synesthesia is a condition in which visual perception of letters induces simultaneous perception of a specific color. Previous studies indicate that grapheme-color synesthetes are more sensitive to physical colors than non-synesthetes. Synesthetic colors are found to be concentrated in multiple regions of the color space, forming “synesthetic color clusters”. The present study investigated whether color sensitivity corresponding to synesthetic color clusters (clustered colors) is higher than color sensitivity that does not correspond to synesthetic color clusters (non-clustered colors). However, we found no difference in the color sensitivity for clustered and non-clustered colors. We also investigated whether the color sensitivity is dependent on the synesthetic experience (associators and projectors). We found that the greater the tendency toward associator characteristics, the greater the sensitivity for clustered colors compared to that for non-clustered colors. Our findings suggest an association between synesthetic colors and physical color sensitivity that is modulated by synesthetic experience.     

Personality traits in people with synaesthesia: Do synaesthetes have an atypical personality profile?

People with synaesthesia not only have – by definition – unusual experiences (e.g., numbers triggering colour), they also have a different cognitive profile (e.g., in terms of their memory and perceptual abilities) and a bias towards certain interests and activities (e.g., towards the arts). However, virtually nothing is known about whether synaesthetes have an atypical personality profile. In this study, a standard measure of personality was administered (Big Five Inventory) along with two questionnaire measures of empathy. Synaesthetes, relative to demographically matched controls, reported higher levels of ‘Openness to Experience’ which is known to be related to imagination and artistic tendencies. They also reported higher levels of ‘Fantasizing’ on one of the empathy measures, which is conceptually related to Openness, although their self-reported empathy did not differ in other respects. In addition, synaesthetes reported lower levels of Agreeableness which we did not predict in advance.     

Varieties of grapheme-colour synaesthesia: a new theory of phenomenological and behavioural differences

Recent research has suggested that not all grapheme-colour synaesthetes are alike. One suggestion is that they can be divided, phenomenologically, in terms of whether the colours are experienced in external or internal space (projector–associator distinction). Another suggestion is that they can be divided according to whether it is the perceptual or conceptual attributes of a stimulus that is critical (higher–lower distinction). This study compares the behavioural performance of 7 projector and 7 associator synaesthetes. We demonstrate that this distinction does not map on to behavioural traits expected from the higher–lower distinction. We replicate previous research showing that projectors are faster at naming their synaesthetic colours than veridical colours, and that associators show the reverse profile. Synaesthetes who project colours into external space but not on to the surface of the grapheme behave like associators on this task. In a second task, graphemes presented briefly in the periphery are more likely to elicit reports of colour in projectors than associators, but the colours only tend to be accurate when the grapheme itself is also accurately identified. We propose an alternative model of individual differences in grapheme-colour synaesthesia that emphasises the role of different spatial reference frames in synaesthetic perception. In doing so, we attempt to bring the synaesthesia literature closer to current models of non-synaesthetic perception, attention and binding.     

数形联觉——数字空间表征研究“新”取向

数字空间表征是人类对数字进行表征的重要方式。数形联觉（number-form synesthesia）是一种数字可以有意识地引起空间知觉的独特现象,与此类似的是非联觉者中广泛存在的无意识的心理数字线（mental number line）现象。两者在行为和脑机制上存在着很多重叠,也存在着值得思考的差异。数形联觉的研究能够提供实质性的行为和脑机制数据,用以解决数字空间表征研究中出现的问题,加强对于数字空间表征的理解;也为更加全面深入地开展进一步研究提供了新的启示,成为数字空间表征研究中值得推崇的新取向。     

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.     

Are synesthetes exceptional beyond their synesthetic associations? A systematic comparison of creativity,personality, cognition,and mental imagery in synesthetes and controls

Synesthesia has historically been linked with enhanced creativity, but this had never been demonstrated in a systematically recruited sample. The current study offers a broad examination of creativity, personality, cognition, and mental imagery in a small sample of systematically recruited synesthetes and controls (n = 65). Synesthetes scored higher on some measures of creativity, personality traits of absorption and openness, and cognitive abilities of verbal comprehension and mental imagery. The differences were smaller than those reported in the literature, indicating that previous studies may have overestimated group differences, perhaps due to biased recruitment procedures. Nonetheless, most of our results replicated literature findings, yielding two possibilities: (1) our study was influenced by similar biases, or (2) differences between synesthetes and controls, though modest, are robust across recruitment methods. The covariance among our measures warrants interpretation of these differences as a pattern of associations with synesthesia, leaving open the possibility that this pattern could be explained by differences on a single measured trait, or even a hidden, untested trait. More generally, this study highlights the difficulty of comparing groups of people in psychology, not to mention neuropsychology and neuroimaging studies. The requirements discussed here – systematic recruitment procedures, large battery of tests, and large cohorts – are best fulfilled through collaborative efforts and cumulative science.