The mechanisms underlying conditioning of phantom percepts differ between those with hallucinations and synesthesia.

There are many different kinds of 'phantom' percepts but it is unknown whether they are united by common mechanisms. For example, synaesthesia (e.g., numbers evoking colour) and hallucinations appear conceptually and phenomenologically similar: both result in a percept that does not have an environmental correlate. Here, people with synaesthesia (n = 66) performed a conditioned hallucinations paradigm known to be sensitive to hallucination susceptibility, and we asked whether synaesthetes would show the same behavioural profile as hallucinators in this task. Repeated pairing of checkerboards with tones, and gratings with colours encourages the participant to draw on prior knowledge when asked to report on the presence of the difficult-to-detect target stimulus. Synaesthetes show increased modelled expectancies for the stimulus association across the board, resulting in a higher number of detections at all stimulus intensities. This is in contrast to the pattern observed in hallucinators, who weigh their prior beliefs more strongly than controls, giving rise to more conditioned hallucinations. Results indicate that fundamentally different perceptual processes may be at the core of these seemingly similar experiences.

Synesthetic Correspondence: An Overview.

Intramodal and cross-modal perceptual grouping based on the spatial proximity and temporal closeness between multiple sensory stimuli, as an operational principle has built a coherent and meaningful representation of the multisensory event/object. To implement and investigate the cross-modal perceptual grouping, researchers have employed excellent paradigms of spatial/temporal ventriloquism and cross-modal dynamic capture and have revealed the conditional constraints as well as the functional facilitations among various correspondence of sensory properties, with featured behavioral evidence, computational framework as well as brain oscillation patterns. Typically, synesthetic correspondence as a special type of cross-modal correspondence can shape the efficiency and effect-size of cross-modal interaction. For example, factors such as pitch/loudness in the auditory dimension with size/brightness in the visual dimension could modulate the strength of the cross-modal temporal capture. The empirical behavioral findings, as well as psychophysical and neurophysiological evidence to address the cross-modal perceptual grouping and synesthetic correspondence, were summarized in this review. Finally, the potential applications (such as artificial synesthesia device) and how synesthetic correspondence interface with semantics (sensory linguistics), as well as the promising research questions in this field have been discussed.

Induced awareness of synesthetic sensations in synesthetically predisposed "Borderline Non-synesthetes".

A long-standing issue concerning synesthesia is whether the trait is continuous or discontinuous with ordinary perception. Here, we found that a substantial proportion of non-synesthetes (>10 % out of >200 unselected participants) spontaneously became aware of their synesthesia by participating in an online survey that forced them to select colors for stimuli that evoke color sensations in synesthetes. Notably, the test-retest consistencies of color sensation in these non-synesthetes were comparable to those in self-claimed synesthetes, revealing their strong though latent synesthetic dispositions. The effect was absent or weak in a matched control survey that did not include the color-picking test. Therefore, the color-picking task likely provided the predisposed "borderline non-synesthetes" with an opportunity to dwell on their tendency toward synesthesia and allowed their subconscious sensations to become conscious ones. The finding suggests that the general population has a continuum of synesthetic disposition that encompasses both synesthetes and non-synesthetes.

Action, emotion, and music-colour synaesthesia: an examination of sensorimotor and emotional responses in synaesthetes and non-synaesthetes.

Synaesthesia has been conceptualised as a joining of sensory experiences. Taking a holistic, embodied perspective, we investigate in this paper the role of action and emotion, testing hypotheses related to (1) changes to action-related qualities of a musical stimulus affect the resulting synaesthetic experience; (2) a comparable relationship exists between music, sensorimotor and emotional responses in synaesthetes and the general population; and (3) sensorimotor responses are more strongly associated with synaesthesia than emotion. 29 synaesthetes and 33 non-synaesthetes listened to 12 musical excerpts performed on a musical instrument they had first-hand experience playing, an instrument never played before, and a deadpan performance generated by notation software, i.e., a performance without expression. They evaluated the intensity of their experience of the music using a list of dimensions that relate to sensorimotor, emotional or synaesthetic sensations. Results demonstrated that the intensity of listeners' responses was most strongly influenced by whether or not music is performed by a human, more so than familiarity with a particular instrument. Furthermore, our findings reveal a shared relationship between emotional and sensorimotor responses among both synaesthetes and non-synaesthetes. Yet it was sensorimotor intensity that was shown to be fundamentally associated with the intensity of the synaesthetic response. Overall, the research argues for, and gives first evidence of a key role of action in shaping the experiences of music-colour synaesthesia.

When small effect sizes become huge: Synaesthesia is linked to very large differences in cognition.

The replication crisis has taught us to expect small-to-medium effects in psychological research. But this is based on effect sizes calculated over single variables. Mahalanobis D, the multivariate equivalent of Cohen's d, can enable very large group differences to emerge from a collection of small-to-medium effects (here, reanalysing multivariate datasets from synaesthetes and controls). The use of multivariate effect sizes is not a slight of hand but may instead be a truer reflection of the degree of psychological differences between people that has been largely underappreciated.

Is non-synesthetes' B Blue? Grapheme-color association improves non-synesthetes' detection in visual search.

Grapheme-color synesthesia is expected to provide a clue to solving the "binding problem" of visual features. Synesthetic research uses non-synesthetes as a control group and shows that synesthetes perform better with synesthetic color congruency, while non-synesthetes' performances do not. However, non-synesthetes also have certain grapheme-color associations. Therefore, this study examined whether non-synesthetes' grapheme-color associations improve their performance in a visual search task. The results indicated that non-synesthetes were significantly faster at detecting congruent targets with their grapheme-color associations, such as red for "A," blue for "B," and yellow for "C." However, the effect was not found in relation to numerical characters. This study has implications for future neuroscience and consciousness research regarding grapheme-color synesthesia.

An Open Science MRI Database of over 100 Synaesthetic Brains and Accompanying Deep Phenotypic Information.

We provide a neuroimaging database consisting of 102 synaesthetic brains using state-of-the-art 3 T MRI protocols from the Human Connectome Project (HCP) which is freely available to researchers. This database consists of structural (T1- and T2-weighted) images together with approximately 24 minutes of resting state data per participant. These protocols are designed to be inter-operable and reproducible so that others can add to the dataset or directly compare it against other normative or special samples. In addition, we provide a 'deep phenotype' of our sample which includes detailed information about each participant's synaesthesia together with associated clinical and cognitive measures. This behavioural dataset, which also includes data from (N = 109) non-synaesthetes, is of importance in its own right and is openly available.

The advantage of being a synesthete: The behavioral benefits of ticker-tape synesthesia.

As first described by Francis Galton, some persons perceive vividly and automatically in their mind's eye the written form of words that they are hearing. This phenomenon, labeled ticker-tape synesthesia (TTS), is thought to reflect an abnormally strong influence of speech processing in language areas on to orthographic representations in the visual cortex. Considering the relevance of TTS for the study of reading acquisition, we looked for objective behavioral advantages or impairments in 22 synesthetes, as compared to 22 matched control participants. In three auditory tasks relying on orthographic working memory (letters counting, backward spelling, and letter shape decision), we predicted and observed better performance in synesthetes than in controls. In two visual tasks (lexical decision and letter decision) with a concurrent auditory stimulation, we predicted that synesthetes should suffer from a larger interference by irrelevant speech than controls, but eventually found no difference between the groups. Those results, which we discuss in relation to orthographic processing, mental imagery, and working memory, promote TTS from pure subjectivity to an experimentally measurable phenomenon.

A single case neuroimaging study of tickertape synesthesia.

Reading acquisition is enabled by deep changes in the brain's visual system and language areas, and in the links subtending their collaboration. Disruption of those plastic processes commonly results in developmental dyslexia. However, atypical development of reading mechanisms may occasionally result in ticker-tape synesthesia (TTS), a condition described by Francis Galton in 1883 wherein individuals "see mentally in print every word that is uttered (…) as from a long imaginary strip of paper". While reading is the bottom-up translation of letters into speech, TTS may be viewed as its opposite, the top-down translation of speech into internally visualized letters. In a series of functional MRI experiments, we studied MK, a man with TTS. We showed that a set of left-hemispheric areas were more active in MK than in controls during the perception of normal than reversed speech, including frontoparietal areas involved in speech processing, and the Visual Word Form Area, an occipitotemporal region subtending orthography. Those areas were identical to those involved in reading, supporting the construal of TTS as upended reading. Using dynamic causal modeling, we further showed that, parallel to reading, TTS induced by spoken words and pseudowords relied on top-down flow of information along distinct lexical and phonological routes, involving the middle temporal and supramarginal gyri, respectively. Future studies of TTS should shed new light on the neurodevelopmental mechanisms of reading acquisition, their variability and their disorders.

A case report of acquired synesthesia and heightened creativity in a musician after traumatic brain injury.

INTRODUCTION: We report on a musician who acquired synesthesia, enhanced sensory experience, and improved creativity following traumatic brain injury (TBI). BACKGROUND: Creativity and synesthesia can be acquired from an injury, though both simultaneously has not been frequently documented. NARRATIVE: This case report details heightened creativity and developing synesthesia in a 66-year-old right-handed man following TBI. He developed a "compulsion" to write music. Synesthesia included "seeing" the notation and being able to name chord structures of music he heard, both of which were novel experiences. The Synesthesia Battery revealed a vision-sound synesthesia with higher than average level of Vividness of Visual Imagery (VVIQ-2), and "Absolute Pitch/Perfect Pitch." PATIENT EXPERIENCE: The patient experienced an approximate four-month history of these changes, including musical compositions, developing perfect pitch, and enhanced sensory experience of typical phenomena. DISCUSSION: Both creativity and synesthesia depend on novel connections in the brain, and both have been reported following insults to the brain, including in degenerative conditions. However, the development of both simultaneously is not frequently reported. Evidence for the etiology of one prompting the other has not been described. Brain injury may result in increased creativity and synesthesia. Our fields would benefit from increased awareness of this possible relationship.

Synesthesia has specific cognitive processing during Go/No-go paradigms.

Grapheme-color synesthesia is a consistent and automatic perception of non-physical color when presented with a grapheme. Many previous studies focused on the synesthetic visual system, but other cognitive functions in grapheme-color synesthetes have remained unclear. Therefore, the objective of the present study was to investigate the characteristics of cognitive processing for motor execution and inhibition during Go/No-go paradigms in grapheme-color synesthesia using event-related potentials (ERPs). Six grapheme-color synesthetes and 24 non-synesthetes performed visual, auditory, and somatosensory Go/No-go paradigms. Omission errors were higher in grapheme-color synesthetes than non-synesthetes. Group-trial interactions (i.e., synesthetes-non-synesthetes × Go-No-go) were observed for the latency of the visual N2 component and amplitude of the somatosensory N2 component. Latencies of auditory and somatosensory P3 components were shorter in grapheme-color synesthetes than non-synesthetes. These findings suggest that grapheme-color synesthetes have specific cognitive processing in motor execution and inhibition as well as synesthetic color perception. Our data advance understanding of cognitive processing in grapheme-color synesthesia.

"I have to translate the colors": Description and implications of a genuine case of phoneme color synaesthesia.

The aim of this paper was to assess the genuineness of a case of phoneme color synesthesia (VA) by evaluating the influence of several psycholinguistic levels with different stimuli (isolated vowels, nonsense syllables, and words). Results demonstrate the robustness of the synesthesia no matter what the type of stimuli. To explore how this form of synesthesia manifested itself in everyday conversation, interviews were also conducted. VA reported that, in the context of conversation, phonemes still evoked colors that she had to translate in order to access the meaning. She also reported that her mental representations were multisensorial and that the verbal dimension was almost non-existent. We address several implications of this phoneme color synesthesia: the atypical speech perception that it implies, the cognitive cost of this stable system, and its relation to a specific cognitive functioning.

What is autonomous sensory meridian response (ASMR)? A narrative review and comparative analysis of related phenomena.

A narrative review of autonomous sensory meridian response (ASMR) was carried out. Definitional factors relevant to ASMR were canvassed. Related, but distinctly unique, sensorial phenomena, including frisson, synaesthesia, and misophonia were considered. Finally, the status of literature with respect to clinical outcomes, individual differences, and current research applications was evaluated. ASMR is a nascent phenomenon that has rapidly progressed in scope and depth of study throughout the past decade; a notable shift from brief-form studies to an increase in formalised trials is noted. Yet, critical questions remain unaddressed, including expectancy and placebo effects, that future research should interrogate.

Subtitled speech: Phenomenology of tickertape synesthesia.

With effort, most literate persons can conjure more or less vague visual mental images of the written form of words they are hearing, an ability afforded by the links between sounds, meaning, and letters. However, as first reported by Francis Galton, persons with ticker-tape synesthesia (TTS) automatically perceive in their mind's eye accurate and vivid images of the written form of all utterances which they are hearing. We propose that TTS results from an atypical setup of the brain reading system, with an increased top-down influence of phonology on orthography. As a first descriptive step towards a deeper understanding of TTS, we identified 26 persons with TTS. Participants had to answer to a questionnaire aiming to describe the phenomenology of TTS along multiple dimensions, including visual and temporal features, triggering stimuli, voluntary control, interference with language processing, etc. We also assessed the synesthetic percepts elicited experimentally by auditory stimuli such as non-speech sounds, pseudowords, and words with various types of correspondence between sounds and letters. We discuss the potential cerebral substrates of those features, argue that TTS may provide a unique window in the mechanisms of written language processing and acquisition, and propose an agenda for future research.

The timing of cortical activation in associator grapheme-colour synaesthetes using MEG.

Grapheme-colour synaesthetes experience an anomalous form of perception in which graphemes systematically induce specific colour concurrents in their mind's eye ("associator" type). Although grapheme-colour synaesthesia has been well characterised behaviourally, its neural mechanisms remain largely unresolved. There are currently several competing models, which can primarily be distinguished according to the anatomical and temporal predictions of synaesthesia-inducing neural activity. The first main model (Cross-Activation/Cascaded Cross-Tuning and its variants) posits early recruitment of occipital colour areas in the initial feed-forward sweep of brain activity. The second (Disinhibited Feedback) posits: (i) later involvement of a multisensory convergence zone (for example, in parietal cortices) after graphemes have been processed in their entirety; and (ii) subsequent feedback to early visual areas (i.e., occipital colour areas). In this study, we examine both the timing and anatomical correlates of associator grapheme-colour synaesthetes (n = 6) using MEG. Using innovative and unbiased analysis methods with little a priori assumptions, we applied Independent Component Analysis (ICA) on a single-subject level to identify the dominant patterns of activity corresponding to the induced, synaesthetic percept. We observed evoked activity that significantly dissociates between synaesthesia-inducing and non-inducing graphemes at approximately 190 ms following grapheme presentation. This effect is present in grapheme-colour synaesthetes, but not in matched controls, and exhibits an occipito-parietal topology localised consistently within individuals to extrastriate visual cortices and superior parietal lobes. Due to the observed timing of this evoked activity and its localization, our results support a model predicting relatively late synaesthesia-inducing activity, more akin to the Disinhibited Feedback model.

synr: An R package for handling synesthesia consistency test data.

Synesthesia is a phenomenon where sensory stimuli or cognitive concepts elicit additional perceptual experiences. For instance, in a commonly studied type of synesthesia, stimuli such as words written in black font elicit experiences of other colors, e.g., red. In order to objectively verify synesthesia, participants are asked to choose colors for repeatedly presented stimuli and the consistency of their choices is evaluated (consistency test). Previously, there has been no publicly available and easy-to-use tool for analyzing consistency test results. Here, the R package synr is introduced, which provides an efficient interface for exploring consistency test data and applying common procedures for analyzing them. Importantly, synr also implements a novel method enabling identification of participants whose scores cannot be interpreted, e.g., who only give black or red color responses. To this end, density-based spatial clustering of applications with noise (DBSCAN) is applied in conjunction with a measure of spread in 3D space. An application of synr with pre-existing openly accessible data illustrating how synr is used in practice is presented. Also included is a comparison of synr's data validation procedure and human ratings, which found that synr had high correspondence with human ratings and outperformed human raters in situations where human raters were easily mislead. Challenges for widespread adoption of synr as well as suggestions for using synr within the field of synesthesia and other areas of psychological research are discussed.

Everyone Inside. Transformation of an Inaccessible Heterotopy. The Case of Buoncammino's Prison.

The specific architectural typology of the prison, congenitally inaccessible to the urban morphological and cultural context in which it sets, as heterotopia carries in itself physical and cognitive barriers. The day after their abandonment, as happened for the former prison of Buoncammino in Cagliari, it's interesting to understand what new relationships should be put in place to make it accessible to all of the city users, in both material and immaterial terms.

Perceptual Dissimilarity Analysis Distinguishes Grapheme-Color Synesthetes from Nonsynesthetes.

Synesthetes can be distinguished from nonsynesthetes on a variety of experimental tasks because their concurrent synesthetic experiences can affect task performance if these experiences match or conflict with some aspect of the stimulus. Here, we tested grapheme-color synesthetes and nonsynesthetic control participants using a novel perceptual similarity task to assess whether synesthetes' concurrent color experiences influence perceived grapheme similarity. Participants iteratively arranged graphemes and, separately, their associated synesthetic colors in a display, such that similar items were placed close together and dissimilar items further apart. The resulting relative inter-item distances were used to calculate the pair-wise (dis)similarity between items in the set, and thence to create separate perceptual representational dissimilarity matrices (RDMs) for graphemes and colors, on an individual basis. On the assumption that synesthetes' similarity judgments for graphemes would be influenced by their concurrent color experiences, we predicted that grapheme and color RDMs would be more strongly correlated for synesthetes than nonsynesthetes. We found that the mean grapheme-color RDM correlation was indeed significantly higher in synesthetes than nonsynesthetes; in addition, synesthetes' grapheme-color RDM correlations were more likely to be individually statistically significant, even after correction for multiple tests, than those of nonsynesthetes. Importantly, synesthetes' grapheme-color RDM correlations were scaled with the consistency of their grapheme-color associations as measured by their Synesthesia Battery (SB) scores. By contrast, the relationship between SB scores and grapheme-color RDM correlations for nonsynesthetes was not significant. Thus, dissimilarity analysis quantitatively distinguished synesthetes from nonsynesthetes, in a way that meaningfully reflects a key aspect of synesthetic experience.

Touching you, touching me: Higher incidence of mirror-touch synaesthesia and positive (but not negative) reactions to social touch in Autonomous Sensory Meridian Response.

The characterisation of autonomous sensory meridian response (ASMR) as an audio-visual phenomenon overlooks how tactile experiences are not just perceptual concurrents of ASMR (i.e., tingling) but also commonly strong ASMR inducers. Here we systematically investigated whether ASMR-responders show altered tactile processing compared to controls. Using a screening measure of vicarious touch with a predefined cut-off for mirror-touch synaesthesia (MTS; a condition where tactile sensations are experienced when viewing, but not receiving, touch), we found that ASMR-responders had more frequent and intense vicarious touch experiences, as well as a strikingly higher incidence of MTS, than non-responders. ASMR-responders also reported greater reactivity to positive, but not negative, interpersonal touch. Correlations further showed these patterns to be more prevalent in those responders with stronger ASMR. We discuss the implications of our findings in terms of heightened sensory sensitivity, bodily awareness, and the underlying neuro-cognitive mechanisms driving vicarious tactile perception in ASMR and MTS.