Synaesthetic Experience Research Articles

Familial patterns and the origins of individual differences in synaesthesia

The term synaesthesia has been applied to a range of different sensory-perceptual and cognitive experiences, yet how these experiences are related to each other is not well understood. Not only are there disparate types of synaesthesia, but even within types there are vast individual differences in the way that stimuli induce synaesthesia and in the subjective synaesthetic experience. An investigation of the inheritance patterns of different types of synaesthesia is likely to elucidate whether a single underlying mechanism can explain all types. This study is the first to systematically survey all types of synaesthesia within a familial framework. We recruited 53 synaesthetes and 42% of these probands reported a first-degree relative with synaesthesia. We then directly contacted as many first-degree relatives as possible and collected complete data on synaesthetic status for all family members for 17 families. We found that different types of synaesthesia can occur within the same family and that the qualitative nature of the experience can differ between family members. Our findings strongly indicate that various types of synaesthesia are fundamentally related at the genetic level, but that the explicit associations and the individual differences between synaesthetes are influenced by other factors. Synaesthesia thus provides a good model to explore the interplay of all these factors in the development of cognitive traits in general.

Synaesthesia for Finger Counting and Dice Patterns: A Case of Higher Synaesthesia?

Synaesthesia is often triggered by numbers, although it is conceivable that different aspects of numerical representation are responsible for different variants of synaesthesia. For individuals with “higher synaesthesia” it is assumed that number meaning (or numerosity) is responsible for the elicitation of synaesthetic experiences. This study documents a case study of a synaesthete, TD, who broadly fits this profile. TD reports that the same colours are elicited from physically different representations of number (digits, dice patterns and finger counting) provided that they share the same numerosity. The authenticity of his synaesthesia is established using Stroop-like priming and interference paradigms. Not only does synaesthetic colour interfere with veridical colour judgements, but also veridical colours can interfere with numerosity judgments. This suggests a close bi-directional coupling between numerosity and colour. Together, these findings constrain theories concerning the neural basis of synaesthesia. This research is funded by the Leverhulme Trust.

Color Opponency in Synaesthetic Experiences

Grapheme-color synaesthesia is a rare condition in which perception of a letter or a digit is associated with concurrent perception of a color. Synaesthetes report that these color experiences are vivid and realistic. We used a Stroop task to show that synaesthetically induced color, like real color, is processed in color-opponent channels (red-green or blue-yellow). Synaesthetic color produced maximal interference with the perception and naming of the real color of a grapheme if the real color was opponent to the synaesthetic color. Interference was reduced considerably if the synaesthetic and real colors engaged different color channels (e.g., synaesthetic blue and real red). No dependence on color opponency was found for semantic conflicts between shape and color (e.g., a blue lemon). Thus, the neural representation of synaesthetic colors closely resembles that of real colors. This suggests involvement of early stages of visual processing in color synaesthesia and explains the vivid and realistic nature of synaesthetic experiences.

Adorno's Schreker: Charting the self-dissolution of the distant sound

Franz Schreker's opera Der ferne Klang is usually discussed using the term ‘phantasmagoria’, as a guiding thread. This article argues that this term names not one but two phenomena: as used by Theodor W. Adorno in his analysis of Wagner, the term denotes the repression of musical production in order to create a music without origin. In a lesser-known piece Adorno uses the term slightly differently, in a sense pioneered first by his friend Walter Benjamin. This second sense is interested in the repression not of musical production, but of the acoustic means of production that conspire to create a unified, synaesthetic experience (rather than an aesthetic object). This second sense, the denial of any sense data outside of the one experience to be had in an opera house, is exceedingly fruitful when applied to Der ferne Klang, since its hero is questing for the titular sound which is located in that very space the aural phantasmagoria has to pretend does not exist. Reading Schreker's opera keeping both senses of the term in mind may allow us to overcome Adorno's own somewhat negative assessment of Schreker's modernism and to locate within the opera a certain self-consciousness of phantasmagoric production.

Synaesthesia: supernormal integration?

Synaesthesia has been known to scientific research for over 100 years but has undergone something of a renaissance recently as new investigations begin to uncover its neurological basis. Rather than being an anomaly, it might offer beneficial insights into the basis of normal perception. A new study by Esterman et al. epitomises this current trend and claims to show that the posterior parietal cortex is a crucial locus of synaesthetic experience. As the posterior parietal cortex is commonly linked to normal sensory integration, Esterman et al.'s finding might lend support to the claim that synaesthesia is an extension of the normal perceptual processes assumed to occur in binding.

Pupillometry of Grapheme-Color Synaesthesia

Pupil diameters of color-grapheme synaesthetes were measured with an infrared eye-tracker while Stroop-like alphanumeric symbols were passively viewed. Pupils dilated more when synaesthetes viewed incongruently-colored symbols than congruently-colored symbols or symbols printed in the standard black ink. The results show that the physiological measure of pupillary diameter can be used as a marker of the synaesthetic experience.

What is the relationship between synaesthesia and visuo-spatial number forms?

This study compares the tendency for numerals to elicit spontaneous perceptions of colour or taste (synaesthesia) with the tendency to visualise numbers as occupying particular visuo-spatial configurations (number forms). The prevalence of number forms was found to be significantly higher in synaesthetes experiencing colour compared both to synaesthetes experiencing taste and to control participants lacking any synaesthetic experience. This suggests that the presence of synaesthetic colour sensations enhances the tendency to explicitly represent numbers in a visuo-spatial format although the two symptoms may nevertheless be logically independent (i.e. it is possible to have number forms without colour, and coloured numbers without forms). Number forms are equally common in men and women, unlike previous reports of synaesthesia that have suggested a strong female bias. Individuals who possess a number form are also likely to possess visuo-spatial forms for other ordinal sequences (e.g. days, months, letters) which suggests that it is the ordinal nature of numbers rather than numerical quantity that gives rise to this particular mode of representation. Finally, we also describe some consequences of number forms for performance in a number comparison task.

Symposium 3: Functional Magnetic Resonance Imaging: from method to madness (applications and design issues in fMRI)

For people with aphantasia, visual imagery is absent or markedly impaired. Here, we investigated the relationship between aphantasia and two other neurodevelopmental conditions also linked to imagery differences: synaesthesia, and autism. In Experiment 1a and 1b, we asked whether aphantasia and synaesthesia can co-occur, an important question given that synaesthesia is linked to strong imagery. Taking grapheme-colour synaesthesia as a test case, we found that synaesthesia can be objectively diagnosed in aphantasics, suggesting visual imagery is not necessary for synaesthesia to occur. However, aphantasia influenced the type of synaesthesia experienced (favouring ‘associator’ over ‘projector’ synaesthesia - a distinction tied to the phenomenology of the synaesthetic experience). In Experiment 2, we asked whether aphantasics have traits associated with autism, an important question given that autism – like aphantasia – is linked to weak imagery. We found that aphantasics reported more autistic traits than controls, with weaknesses in imagination and social skills.

A systematic, large-scale study of synaesthesia: implications for the role of early experience in lexical-colour associations

For individuals with synaesthesia, stimuli in one sensory modality elicit anomalous experiences in another modality. For example, the sound of a particular piano note may be ‘seen’ as a unique colour, or the taste of a familiar food may be ‘felt’ as a distinct bodily sensation. We report a study of 192 adult synaesthetes, in which we administered a structured questionnaire to determine the relative frequency and characteristics of different types of synaesthetic experience. Our data suggest the prevalence of synaesthesia in the adult population is approximately 1 in 1150 females and 1 in 7150 males. The incidence of left-handedness in our sample was within the normal range, contrary to previous claims. We did, however, find that synaesthetes are more likely to be involved in artistic pursuits, consistent with anecdotal reports. We also examined responses from a subset of 150 synaesthetes for whom letters, digits and words induce colour experiences (‘lexical-colour’ synaesthesia). There was a striking consistency in the colours induced by certain letters and digits in these individuals. For example, ‘R’ elicited red for 36% of the sample, ‘Y’ elicited yellow for 45%, and ‘D’ elicited brown for 47%. Similar trends were apparent for a group of non-synaesthetic controls who were asked to associate colours with letters and digits. Based on these findings, we suggest that the development of lexical-colour synaesthesia in many cases incorporates early learning experiences common to all individuals. Moreover, many of our synaesthetes experienced colours only for days of the week, letters or digits, suggesting that inducers that are part of a conventional sequence (e.g. Monday, Tuesday, Wednesday…; A, B, C…; 1, 2, 3…) may be particularly important in the development of synaesthetic inducer-colour pairs. We speculate that the learning of such sequences during an early critical period determines the particular pattern of lexical-colour links, and that this pattern then generalises to other words.

The noetic connection: synaesthesia, psychedelics, and language

The literatures that touch on synaesthesias-scientific, art-historical, literary, phenomenological, ethnographic, psychodelic-vary widely in their definitions, their interpretations, and their degree of comfort with the first-person, subjective nature of experiential reports. The significances given to synaesthetic experiences are similarly wide-ranging. This paper explores the relationships among synaesthesias, psychedelic experience, and language, highlighting Terence McKenna's synaesthetic language experiences on DMT and magic mushrooms. We describe the complexities of creating and performing with the Synestheater, a system that provides the means to weave together, in multiple mappings, two or more complex visual, aural, and linguistic systems in live performance.

Sacred Colors and Shamanic Vision among the Huichol Indians of Mexico

Color and the visionary abilities of the shaman may be related. Interviews with a shaman-artist of the Huichol Indians of northwest Mexico reveal that color is conceptualized as a language which the gods and spirits of sacred sites use to communicate with the shaman. Colors are perceived by the shaman as part of a synaesthetic experience in which color may convert to both songs and language. This visionary color language is depicted in Huichol arts and even in art such as yarn paintings made for sale. These findings suggest further lines of inquiry into entoptic phenomena and other theories of how shamans visualize. The interviews, conducted as part of the author's ongoing research with the Huichol since 1988, also provide a new perspective on the well-known association of sacred colors and cardinal directions.

Unconscious priming eliminates automatic binding of colour and alphanumeric form in synaesthesia.

Synaesthesia is an unusual perceptual phenomenon in which events in one sensory modality induce vivid sensations in another. Individuals may 'taste' shapes, 'hear' colours, or 'feel' sounds. Synaesthesia was first described over a century ago, but little is known about its underlying causes or its effects on cognition. Most reports have been anecdotal or have focused on isolated unusual cases. Here we report an investigation of 15 individuals with colour-graphemic synaesthesia, each of whom experiences idiosyncratic but highly consistent colours for letters and digits. Using a colour-form interference paradigm, we show that induced synaesthetic experiences cannot be consciously suppressed even when detrimental to task performance. In contrast, if letters and digits are presented briefly and masked, so that they are processed but unavailable for overt report, the synaesthesia is eliminated. These results show that synaesthetic experiences can be prevented despite substantial processing of the sensory stimuli that otherwise trigger them. We conclude that automatic binding of colour and alphanumeric form in synaesthesia arises after initial processes of letter and digit recognition are complete.

Five plus two equals yellow.

Mental arithmetic in people with synaesthesia is not coloured by visual experience. In synaesthesia, ordinary stimuli elicit extraordinary experiences. For example when C., who is a digit–colour synaesthete, views black digits, each number elicits a photism — a visual experience of a specific colour. It has been proposed that synaesthetic experiences differ from imagery in their consistency1, automaticity2,3 and reliance on external stimuli to induce them4. Here we demonstrate that C.'s photisms are both consistent and automatic, but we find that an externally presented inducing stimulus is not necessary to trigger a photism and that simply activating the concept of a digit is sufficient.