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Concept: Synesthesia


Synesthesia 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.

Concepts: Light, Color, Green, Blue, Purple, Qualia, Synesthesia, Azure


Although the arbitrariness of language has been considered one of its defining features, studies have demonstrated that certain phonemes tend to be associated with certain kinds of meaning. A well-known example is the Bouba/Kiki effect, in which nonwords like bouba are associated with round shapes while nonwords like kiki are associated with sharp shapes. These sound symbolic associations have thus far been limited to nonwords. Here we tested whether or not the Bouba/Kiki effect extends to existing lexical stimuli; in particular, real first names. We found that the roundness/sharpness of the phonemes in first names impacted whether the names were associated with round or sharp shapes in the form of character silhouettes (Experiments 1a and 1b). We also observed an association between femaleness and round shapes, and maleness and sharp shapes. We next investigated whether this association would extend to the features of language and found the proportion of round-sounding phonemes was related to name gender (Analysis of Category Norms). Finally, we investigated whether sound symbolic associations for first names would be observed for other abstract properties; in particular, personality traits (Experiment 2). We found that adjectives previously judged to be either descriptive of a figuratively ‘round’ or a ‘sharp’ personality were associated with names containing either round- or sharp-sounding phonemes, respectively. These results demonstrate that sound symbolic associations extend to existing lexical stimuli, providing a new example of non-arbitrary mappings between form and meaning.

Concepts: Male, Female, Sex, Linguistics, Metaphysics, Synesthesia, Sound symbolism, Bouba/kiki effect


This case report offers rare insights into crossmodal responses to psychedelic drug use in a congenitally blind (CB) individual as a form of synthetic synesthesia. BP’s personal experience provides us with a unique report on the psychological and sensory alterations induced by hallucinogenic drugs, including an account of the absence of visual hallucinations, and a compelling look at the relationship between LSD induced synesthesia and crossmodal correspondences. The hallucinatory experiences reported by BP are of particular interest in light of the observation that rates of psychosis within the CB population are extremely low. The phenomenology of the induced hallucinations suggests that experiences acquired through other means, might not give rise to “visual” experiences in the phenomenological sense, but instead gives rise to novel experiences in the other functioning senses.

Concepts: Sensory system, Hallucination, Psychosis, Synesthesia, Psychedelic drug, Psychedelics, dissociatives and deliriants, Hallucinations in the sane, Psychedelic


Grapheme-colour synaesthesia is an atypical condition characterized by the perception of colours when reading achromatic text. We investigated the level of colour processing responsible for these experiences. To do so, we tapped a central characteristic of colour perception. In different lighting conditions the same wavelength of light can prompt the perception of different colours. This helps humans recognize distinctive coloured objects despite changes in illumination. We wanted to see if synaesthetic colours were generated at a neural locus that was susceptible to colour constancy analyses. We used colour matching and naming tasks to examine interactions between simulated coloured illuminants and synaesthetic colours. Neither synaesthetic colour matching or naming was impacted. This contrasted with non-synaesthetic control participants, who performed the colour-matching task with graphemes physically coloured to mimic synaesthesia. Our data suggest that synaesthetic colour signals are not generated at lower-levels of colour processing, but are introduced at higher levels of analysis and are therefore not impacted by the processes responsible for perceptual constancy.

Concepts: Light, Color, Lighting, Qualia, Synesthesia, International Commission on Illumination, Color constancy, Subjective constancy


Synaesthetic people are probably more numerous than usually thought. This unique sensory phenomenon may concern up to 4% of the general population. Physicians are not very aware of synaesthesias because synaesthetes ignore themselves and most often consider this perceptive faculty as common and not pathological. We report in detail a grapheme-phoneme to colour developmental synaesthesia in a 54-year-old woman. The major contribution of research over the last two decades is also summarized.

Concepts: Psychology, Greek loanwords, Color, Major, Qualia, Synesthesia, Women's suffrage, Field officer


Recently, swimming-style colour synaesthesia was introduced as a new form of synaesthesia. A synaesthetic Stroop test was used to establish its genuineness. Since Stroop interference can occur for any type of overlearned association, in the present study we used a modified Stroop test and psychophysiological synaesthetic conditioning to further establish the genuineness of this form of synaesthesia. We compared the performance of a swimming-style colour synaesthete and a control who was trained on swimming-style colour associations. Our results showed that behavioural aspects of swimming-style colour synaesthesia can be mimicked in a trained control. Importantly, however, our results showed a psychophysiological conditioning effect for the synaesthete only. We discuss the theoretical relevance of swimming-style colour synaesthesia according to different models of synaesthesia. We conclude that swimming-style colour synaesthesia is a genuine form of synaesthesia, can be mimicked behaviourally in non-synaesthetes, and is best explained by a re-entrant feedback model.

Concepts: Color, Stroop effect, Synesthesia, John Ridley Stroop


Are synaesthetic experiences congenital and so hard-wired, or can a functional analogue be created? We induced an equivalent of form-colour synaesthesia using hypnotic suggestions in which symbols in an array (circles, crosses, squares) were suggested always to have a certain colour. In a Stroop type-naming task, three of the four highly hypnotizable participants showed a strong synaesthesia-type association between symbol and colour. This was verified both by their subjective reports and objective eye-movement behaviour. Two resembled a projector- and one an associator-type synaesthete. Participant interviews revealed that subjective experiences differed somewhat from typical (congenital) synaesthesia. Control participants who mimicked the task using cognitive strategies showed a very different response pattern. Overall, the results show that the targeted, preconsciously triggered associations and perceptual changes seen in association with congenital synaesthesia can rapidly be induced by hypnosis. They suggest that each participant’s subjective experience of the task should be carefully evaluated, especially when studying hypnotic hallucinations. Studying such experiences can increase understanding of perception, automaticity, and awareness and open unique opportunities in cognitive neuroscience and consciousness research.

Concepts: Psychology, Cognition, Perception, Color, Consciousness, Suggestion, Qualia, Synesthesia


Grapheme-color synesthesia is a perceptual phenomenon where single graphemes (e.g., the letter “E”) induce simultaneous sensations of colors (e.g., the color green) that were not objectively shown. Current models disagree as to whether the color sensations arise from increased short-range connectivity between anatomically adjacent grapheme- and color-processing brain structures or from decreased effectiveness of inhibitory long-range connections feeding back into visual cortex. We addressed this issue by examining neural synchrony obtained from EEG activity, in a sample of grapheme-color synesthetes that were presented with color-inducing versus non-color-inducing graphemes. For color-inducing graphemes, the results showed a decrease in the number of long-range couplings in the theta frequency band (4-7 Hz, 280-540 msec) and a concurrent increase of short-range phase-locking within lower beta band (13-20 Hz, 380-420 msec at occipital electrodes). Because the effects were both found in long-range synchrony and later within the visual processing stream, the results support the idea that reduced inhibition is an important factor for the emergence of synesthetic colors.

Concepts: Brain, Human brain, Electroencephalography, Visual perception, Color, Green, Qualia, Synesthesia


Synaesthesia is a condition that gives rise to unusual secondary sensations (e.g., colours are perceived when listening to music). These unusual sensations tend to be reported as being stable throughout adulthood (e.g., Simner & Logie, 2007, Neurocase, 13, 358) and the consistency of these experiences over time is taken as the behavioural hallmark of genuineness. Our study looked at the influence of mood states on synaesthetic colours. In Experiment 1, we recruited grapheme-colour synaesthetes (who experience colours from letters/digits) and elicited their synaesthetic colours, as well as their mood and depression states, in two different testing sessions. In each session, participants completed the PANAS-X (Watson & Clark, 1999) and the BDI-II (Beck, Steer, & Brown, 1996, Manual for Beck Depression Inventory-II), and chose their synaesthetic colours for letters A-Z from an interactive colour palette. We found that negative mood significantly decreased the luminance of synaesthetic colours. In Experiment 2, we showed that synaesthetic colours were also less luminant for synaesthetes with anxiety disorder, versus those without. Additional evidence suggests that colour saturation, too, may inversely correlate with depressive symptoms. These results show that fluctuations in mood within both a normal and clinical range influence synaesthetic colours over time. This has implications for our understanding about the longitudinal stability of synaesthetic experiences, and of how mood may interact with the visual (imagery) systems.

Concepts: Psychology, Color, Selective serotonin reuptake inhibitor, Qualia, Hue, Synesthesia, Colorfulness, Secondary color


Abstract Synesthesia is a condition in which stimulation of one sensory modality causes unusual experiences in a different, unstimulated modality. Recent findings suggest that research on synesthesia offers a unique opportunity to study the neural basis of subjective experiences in healthy and pathological brains. This review summarizes and reflects current knowledge concerning synesthesia in its various aspects, including its cognitive, neural, and behavioral aspects. In this context, recent data suggest new connections between specific conditions related to synesthesic mechanisms and association processes linked to construction of synesthetic cross-modal metaphors that may play a role in psychopathological thinking and imagination.

Concepts: Psychology, Cognition, Perception, Mind, Knowledge, Synesthesia, Olivier Messiaen, Wassily Kandinsky