Types Of Synaesthesia Research Articles

Chapter 22 - Auditory synesthesias

Synesthesia is experienced when sensory stimulation of one sensory modality (the inducer) elicits an involuntary or automatic sensation in another sensory modality or different aspect of the same sensory modality (the concurrent). Auditory synesthesias (AS) occur when auditory stimuli trigger a variety of concurrents, or when non-auditory sensory stimulations trigger auditory synesthetic perception. The AS are divided into three types: developmental, acquired, and induced. Developmental AS are not a neurologic disorder but a different way of experiencing one's environment. They are involuntary and highly consistent experiences throughout one's life. Acquired AS have been reported in association with neurologic diseases that cause deafferentation of anterior optic pathways, with pathologic lesions affecting the central nervous system (CNS) outside of the optic pathways, as well as non-lesional cases associated with migraine, and epilepsy. It also has been reported with mood disorders as well as a single idiopathic case. Induced AS has been reported in experimental and postsurgical blindfolding, as well as intake of hallucinogenics or psychedelics. In this chapter the three different types of synesthesia, their characteristics, and phenomologic differences, as well as their possible neural mechanisms are discussed.

Mirror-touch and ticker tape experiences in synesthesia

A fundamental question in the field of synesthesia is whether it is associated with other cognitive phenomena. The current study examined synesthesia's connections with phenomenal traits of mirror-touch and ticker tape experiences, as well as the representation of the three phenomena in the population, across gender and domain of work/study. Mirror-touch is the automatic, involuntary experience of tactile sensation on one's own body when others are being touched. For example, seeing another person's arm being stroked can evoke physical touch sensation on one's own arm. Ticker tape is the automatic visualization of spoken words or thoughts, such as a teleprompter. For example, when spoken to, a ticker taper might see mentally the spoken words displayed in front of his face or as coming out of the speaker's mouth. To explore synesthesia's associations with these phenomena, a diverse group (n = 3743) was systematically recruited from eight universities and one public museum in France to complete an online screening. Of the 1017 eligible respondents, synesthetes (across all subtypes) reported higher rates of mirror-touch and ticker tape than non-synesthetes, suggesting that synesthesia is associated with these phenomenal traits. However, effect sizes were small and we could not rule out that response bias influenced these associations. Mirror-touch and ticker tape were independent. No differences were found across gender or domain of work and study in prevalence of synesthesia, mirror-touch or ticker tape. The prevalence of ticker tape, unknown so far, was estimated at about 7%, an intermediate rate between estimates of grapheme-color (2–4%) and sequence-space synesthesia (9–14%). Within synesthesia, grapheme-personification, also called ordinal-linguistic personification (OLP) was the most common subtype and was estimated around 12%. Co-occurences of the different types of synesthesia were higher than chance, though at the level of small effect sizes.

Inside a synesthete's head: A functional connectivity analysis with grapheme-color synesthetes

Grapheme-color synesthesia is a condition in which letters are perceived with an additional color dimension. To identify brain regions involved in this type of synesthesia and to analyze functional connectivity of these areas, 18 grapheme-color synesthetes and 18 matched controls were stimulated with letters and pseudo-letters presented in black and color in an event-related fMRI experiment. Based on the activation-differences between synesthetes and non-synesthetic controls regions of interest were defined. In a second analysis step functional connectivity was calculated using beta series correlation analysis for these seed regions. First we identified one seed region in the left inferior parietal (IPL) cortex (BA7) showing activation differences between grapheme-color synesthetes and controls. Furthermore, we found activation differences in brain areas involved in processing of letters and pseudo-letters, in particular the right IPL cortex (BA7), but also two more clusters in the right hemispheric BA 18 and BA 40. Functional connectivity analysis revealed an increased connectivity between the left IPL seed region and primary/secondary visual areas (BA 18) in synesthetes. Also the right BA 7 showed a stronger connectivity with primary/secondary visual areas (BA 18) in grapheme-color synesthetes. The results of this study support the idea that the parietal lobe plays an important role in synesthetic experience. The data suggest furthermore that the information flow in grapheme-color synesthetes was already modulated at the level of the primary visual cortex which is different than previously thought. Therefore, the current models of grapheme-color synesthesia have to be refined as the unusual communication flow in synesthetes is not restricted to V4, fusiform cortex and the parietal lobe but rather involves a more extended network.

Synesthesia, Pseudo-Synesthesia, and Irritable Bowel Syndrome

Synesthesia is a sensory disorder where the stimulation of one sensory modality can lead to a reaction in another which would not usually be expected to respond; for instance, someone might see a color on hearing a word such as a day of the week. Disordered perception of sensory information also appears to contribute to the pathophysiology of irritable bowel syndrome (IBS). The purpose of this exploratory study was to ascertain whether these two conditions might be linked in any way. Two hundred consecutive IBS outpatients were screened for synesthesia and compared with 200 matched healthy volunteers (controls). Positive responders were tested for two types of synesthesia (grapheme-color and music-color/shape) using a questionnaire which was repeated after 3 months to test for reproducibility. Of the 200 IBS outpatients screened, 26 (13%) patients and six (3%) controls claimed to be synesthetic (P < 0.001). Reproducibility was more variable in IBS patients than controls but despite this variability, 15 (7.5%) patients compared with 5 (2.5%) controls had greater than 75% consistency (P = 0.036), and 19 (9.5%) patients and 6 (3%) controls had greater than 50% consistency (P = 0.012). A reproducibility of less than 50% was observed in seven (3.5%) patients and no controls (0%) (P = 0.015), and these individuals were classified as having pseudo-synesthesia. IBS patients clearly differ from controls in terms of claiming to have synesthetic experiences. These results justify additional studies on the relationship between IBS and synesthesia to further understand the neural mechanisms underpinning these two conditions and to establish whether they may be linked.

Ordinary associations or ‘special cases’; defining mechanisms in synesthesia

A synesthete might inform you that McDonald’s is ‘all wrong’, as obviously their large letter M has the completely wrong color. While synesthesia is now well accepted as a ‘real’ phenomenon, what underlies the highly specific and consistent additional sensations is a topic of debate. What sets synesthetic mechanisms apart from those involved in ‘normal’ associations? In this presentation, we first discuss the possible neurobiological underpinnings. A review study has shown six brain regions related to synesthesia. Furthermore, results from structural as well as functional connectivity studies show hyperconnectivity in the synaesthete’s brain. Second, the behavioral characteristics that set synesthetes apart from non-synesthetes are discussed. One problem in obtaining a clear model of synesthesia is that currently, most studies are performed on particular types of synesthesia (in particular colored letters/numbers). We present rare cases of synesthesia (taste/smell with sounds) and examine how well their characteristics fit with the traditionally presented model of synesthesia.

“Blue is music to my ears”: Multimodal synesthesias after a thalamic stroke

Acquired synesthesias have been reported in association with deafferentation of the visual system, temporal lobe seizures, and the use of psychedelics. Based on our review of the literature, the appearance of synesthesias after a thalamic stroke has been reported only once. We present the case of a 45-year-old hypertensive male who, 9 months after a hemorrhagic stroke involving the left lateral posterior nucleus of the thalamus developed persistent sound–tactile, sound–color, and grapheme–gustatory synesthesias. Moreover, the patient noted that even thinking about a sensory stimulus could trigger the experience of another sensory modality, a conceptual type of synesthesia.

The neural correlates of coloured music: A functional MRI investigation of auditory–visual synaesthesia

In auditory–visual synaesthesia, all kinds of sound can induce additional visual experiences. To identify the brain regions mainly involved in this form of synaesthesia, functional magnetic resonance imaging (fMRI) has been used during non-linguistic sound perception (chords and pure tones) in synaesthetes and non-synaesthetes. Synaesthetes showed increased activation in the left inferior parietal cortex (IPC), an area involved in multimodal integration, feature binding and attention guidance. No significant group-differences could be detected in area V4, which is known to be related to colour vision and form processing. The results support the idea of the parietal cortex acting as sensory nexus area in auditory–visual synaesthesia, and as a common neural correlate for different types of synaesthesia.

Baudelaire's Syncretic Extensions of Synesthesia

The essay explores Baudelaire's application of synesthesia as a figure of fusion on the vertical and horizontal planes in order to demonstrate that the figure's extensions develop both spiritual and psychophysical dimensions of his work as literary self-portrait. The integration of different types of synesthesia is shown to contribute to the creation of a “total” autotelic artwork of which the lyric subject is at once the core and the perimeter. The analysis concerns the self-referential technique of mise en abyme because it installs the “self” as center even when the subject of the text appears to be an “other.” The role of rhetoric, symbolism, and the poet's creative imagination are also examined because they incorporate various “others” including famous artists, philosophers, and aspects of mysterious, faraway lands. Thus a “sociospiritual synesthesia” and a “synesthetic exoticism” combine to expand the lyric subject's sphere of self-reference.

Individuals with Grapheme-Color Associations Exhibit Creativity

Synesthesia occurs when a single stimulus triggers two or more sensations simultaneously in different modalities. Grapheme-color association is a frequently reported type of synesthesia. Two types of grapheme-color associations have been identified: associators and projectors. Associators experience the colors conceptually, while projectors report actually perceiving the colors. Here, we evaluated the frequency of both types of grapheme-color association among a college sample. Our findings indicate that 8% of the sample demonstrated grapheme-color associator tendencies and 3% demonstrated grapheme-color projector tendencies. No participants demonstrated both associator and projector synesthetic tendencies. Additionally, as the relation between creativity and synesthesia has been the subject of interest of many experts in the field, participants' creative abilities were assessed through use of the Alternate Uses Test and self-report. The results support the link between synesthesia and creativity in projectors, but not associators.

A self-organizing learning account of number-form synaesthesia

Some people automatically and involuntarily “see” mental images of numbers in spatial arrays when they think of numbers. This phenomenon, called number forms, shares three key characteristics with the other types of synaesthesia, within-individual consistency, between-individual variety, and mixture of regularity and randomness. A theoretical framework called SOLA (self-organizing learning account of number forms) is proposed, which explains the generation process of number forms and the origin of those three characteristics. The simulations replicated the qualitative properties of the shapes of number forms, the property that numbers are aligned in order of size, that discontinuity usually occurs at the point of carry, and that continuous lines tend to have many bends.

MusiCam: an instrument to demonstrate chromaphonic synesthesia

Inspired by a type of synesthesia where colour typically induces musical notes the MusiCam project investigates this unusual condition, particularly the transition from colour to sound. MusiCam explores the potential benefits of this idiosyncrasy as a mode of human computer interaction (HCI), providing a host of meaningful applications spanning control, communication and composition. Colour data is interpreted by means of an off-the-shelf webcam, and music is generated in real-time through regular speakers. By making colour-based gestures users can actively control the parameters of sounds, compose melodies and motifs or mix multiple tracks on the fly. The system shows great potential as an interactive medium and as a musical controller. The trials conducted to date have produced encouraging results, and only hint at the new possibilities achievable by such a device.

Variants of synesthesia interact in cognitive tasks: Evidence for implicit associations and late connectivity in cross-talk theories

This study examines the interaction between two types of synesthesia: ordinal linguistic personification (OLP; the involuntary association of animate qualities such as gender/personality to linguistic units such as letters/numbers/days) and grapheme-color synesthesia (the involuntary association of colors to letters and/or numbers). By examining both variants in the same individual we aim to: (a) show that features of different synesthetic variants interact in cognitive tasks, (b) provide a cognitive model of this interaction, and (c) constrain models of the underlying neurological roots of this connectivity. Studies have shown inhibition in Stroop-type tasks for naming font colors that clash with synesthetic colors (e.g. slower naming of green font for synesthetically red letters). We show that Stroop-type slow-down occurs only when incongruent colors come from other letters with matching (but not mis-matching) gender (experiment 2). We also measure the speed of OLP gender judgments (e.g. a=female; experiment 1) and show that response times are slowed by incongruent colors from other letters with mis-matching (but not matching) genders. Our studies suggest that synesthetic variants interact and that their concurrents can become implicitly connected without mediation from inducing stimuli. We interpret these findings in light of recent developmental data showing protracted heterochronous neuronal development in humans, which continues through adolescence in parietal, frontal and perisylvian areas.

When coloured sounds taste sweet

Synaesthesia is the involuntary physical experience of a cross-modal linkage--for example, hearing a tone (the inducing stimulus) evokes an additional sensation of seeing a colour (concurrent perception). Of the different types of synaesthesia, most have colour as the concurrent perception, with concurrent perceptions of smell or taste being rare. Here we describe the case of a musician who experiences different tastes in response to hearing different musical tone intervals, and who makes use of her synaesthetic sensations in the complex task of tone-interval identification. To our knowledge, this combination of inducing stimulus and concurrent perception has not been described before.

Types of synaesthesia.

Synaesthesia is defined by Vernon (1937) as a phenomenon in which “a stimulus presented in one mode seems to call up imagery of another mode as readily as that of its own”. The discovery of synaesthesia has sometimes been wrongly attributed to Galton. Galton (1883) certainly describes instances, but reports on earlier descriptions, for example those published in 1881 by Bleuler and Lehmann.

Number Forms: A Common Type of Synesthesia

Any teacher who has from thirty to forty pupils in her classroom can reasonably expect that at least one of them will possess the type of synesthesia known as number forms. The frequency of occurrence is not definitely known, due to conflicting investigations, but it appears to be more prevalent in girls than in boys and to be somewhat associated with an imaginative approach to life's problems.

Tone Shapes: A Novel Type of Synaesthesia

Cet article est une enquěte de deux cas de synesthesie ou les tons de divers instruments musicaux sont accompagnes de formes de trois dimensions. Bien que ces formes ne sont pas les měme chez les d...