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Jamie Ward - One of the best experts on this subject based on the ideXlab platform.
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from mirror touch Synesthesia to models of vicarious experience a reply to commentaries
Cognitive Neuroscience, 2017Co-Authors: Jamie Ward, Michael J. BanissyAbstract:In this reply to the eight commentaries to our article, we discuss three important challenges. First, we discuss the relationship of mirror-touch to other forms of Synesthesia. We note that synesthetic experiences are generally not mistaken as veridical but this does not mean that they lack percept-like qualities. We acknowledge that neither Threshold Theory nor Self-Other Theory offer a direct account of other forms of Synesthesia, although we discuss how the latter could. Second, we discuss alternative explanations. Notably predictive coding offers a different way of framing our current theory, and extending it to related phenomena. Finally, we discuss how mirror-touch Synesthesia may relate to other atypical experiences of body ownership such as the rubber hand illusion, and somatoparaphrenia.
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an extended case study on the phenomenology of sequence space Synesthesia
Frontiers in Human Neuroscience, 2014Co-Authors: Cassandra Gould, Jamie Ward, Tom Froese, Adam B Barrett, Anil K SethAbstract:Investigation of Synesthesia phenomenology in adults is needed to constrain accounts of developmental trajectories of this trait. We report an extended phenomenological investigation of sequence-space Synesthesia in a single case (AB). We used the Elicitation Interview (EI) method to facilitate repeated exploration of AB's synesthetic experience. During an EI the subject's attention is selectively guided by the interviewer in order to reveal precise details about the experience. Detailed analysis of the resulting 9 h of interview transcripts provided a comprehensive description of AB's synesthetic experience, including several novel observations. For example, we describe a specific spatial reference frame (a "mental room") in which AB's concurrents occur, and which overlays his perception of the real world (the "physical room"). AB is able to switch his attention voluntarily between this mental room and the physical room. Exemplifying the EI method, some of our observations were previously unknown even to AB. For example, AB initially reported to experience concurrents following visual presentation, yet we determined that in the majority of cases the concurrent followed an internal verbalization of the inducer, indicating an auditory component to sequence-space Synesthesia. This finding is congruent with typical rehearsal of inducer sequences during development, implicating cross-modal interactions between auditory and visual systems in the genesis of this synesthetic form. To our knowledge, this paper describes the first application of an EI to Synesthesia, and the first systematic longitudinal investigation of the first-person experience of Synesthesia since the re-emergence of interest in this topic in the 1980's. These descriptions move beyond rudimentary graphical or spatial representations of the synesthetic spatial form, thereby providing new targets for neurobehavioral analysis.
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Mechanisms of self-other representations and vicarious experiences of touch in mirror-touch Synesthesia
Frontiers in Human Neuroscience, 2013Co-Authors: Michael J. Banissy, Jamie WardAbstract:In recent years several studies have documented a near-universal tendency to vicariously represent the actions and sensations of others (e.g., see Keysers and Gazzola, 2009 for review). For example, observing another person experiencing pain activates neural regions involved in experiencing pain (e.g., Singer et al., 2004; Avenanti et al., 2005) or observing somebody being touched recruits regions of the somatosensory cortex involved in experiencing touch (e.g., Keysers et al., 2004, 2010; Ebisch et al., 2008; Schaefer et al., 2012). For most of us, these vicarious representations are implicit and do not lead to overt sensations of the observed events (e.g., we do not feel pain when observing pain to others). There are, however, a small number of individuals who do experience overt somatic sensations when observing others' tactile experiences (Ward et al., 2008; Osborn and Derbyshire, 2010; Fitzgibbon et al., 2012; Banissy, 2013). For example, in mirror-touch Synesthesia observing touch or pain to others evokes a conscious tactile sensation on the synesthetes' own body (Banissy and Ward, 2007; Holle et al., 2011). This opinion piece seeks to discuss potential neural mechanisms that contribute to the developmental form of mirror-touch Synesthesia (for descriptions of acquired forms of mirror-touch/pain Synesthesia see Fitzgibbon et al., 2012; Goller et al., 2013), and the important role that self-other representations may have on vicarious experiences of touch in mirror-touch Synesthesia.
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grapheme color and tone color Synesthesia is associated with structural brain changes in visual regions implicated in color form and motion
Cognitive Neuroscience, 2012Co-Authors: Michael J. Banissy, Jamie Ward, Neil G Muggleton, Lauren Stewart, Timothy D Griffiths, Vincent Y Walsh, Ryota KanaiAbstract:Synesthesia is a rare condition in which stimulation in one modality leads to a secondary experience in another sensory modality. Varying accounts attribute the condition to either neuroanatomical differences between the synesthetes and non-synesthetes or functional differences in how sensory brain regions interact. This study employed voxel-based morphometry to examine whether synesthetes who experience both grapheme-color and tone-color Synesthesia as their evoked sensation show neuroanatomical differences in gray matter volume compared to non-synesthetes. We observed that synesthetes showed an increase in gray matter volume in left posterior fusiform gyrus (FG), but a concomitant decrease in anterior regions of left FG and left MT/V5. These findings imply that Synesthesia for color is linked to neuroanatomical changes between adjacent regions of the visual system.
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the development of a scientific understanding of Synesthesia from early case studies 1849 1873
Journal of the History of the Neurosciences, 2011Co-Authors: Jorg Jewanski, Julia Simner, Sean A Day, Jamie WardAbstract:The first case of Synesthesia was reported in 1812 ( Jewanski, Day, & Ward, 2009 ). However, it took almost seven decades before the idea of Synesthesia entered the mainstream of science and, subsequently, art. There are no known new cases described between 1812 and 1848, but in the following three decades there are at least 11 reported cases of Synesthesia and many reviews of these cases. This comes at an important period in the history of the neurosciences, and for sensory physiology in particular. However, the literature that describes Synesthesia during this period is largely unknown to contemporary researchers and historians. The aim of this review is to discuss the reports of Synesthesia during this period, providing translations of some key passages, and to place these reports within the contextual framework of nineteenth-century neuroscience.
Michael J. Banissy - One of the best experts on this subject based on the ideXlab platform.
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from mirror touch Synesthesia to models of vicarious experience a reply to commentaries
Cognitive Neuroscience, 2017Co-Authors: Jamie Ward, Michael J. BanissyAbstract:In this reply to the eight commentaries to our article, we discuss three important challenges. First, we discuss the relationship of mirror-touch to other forms of Synesthesia. We note that synesthetic experiences are generally not mistaken as veridical but this does not mean that they lack percept-like qualities. We acknowledge that neither Threshold Theory nor Self-Other Theory offer a direct account of other forms of Synesthesia, although we discuss how the latter could. Second, we discuss alternative explanations. Notably predictive coding offers a different way of framing our current theory, and extending it to related phenomena. Finally, we discuss how mirror-touch Synesthesia may relate to other atypical experiences of body ownership such as the rubber hand illusion, and somatoparaphrenia.
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social perception in synaesthesia for colour
Cognitive Neuropsychology, 2016Co-Authors: Agnieszka Janik B Mcerlean, Tirta Susilo, Constantin Rezlescu, Amy Bray, Michael J. BanissyAbstract:Synaesthesia is a rare phenomenon in which stimulation in one modality (e.g., audition) evokes a secondary percept not associated with the first (e.g., colour). Prior work has suggested links between synaesthesia and other neurodevelopmental conditions that are linked to altered social perception abilities. With this in mind, here we sought to examine social perception abilities in grapheme–colour synaesthesia (where achromatic graphemes evoke colour experiences) by examining facial identity and facial emotion perception in synaesthetes and controls. Our results indicate that individuals who experience grapheme–colour synaesthesia outperformed controls on tasks involving fine visual discrimination of facial identity and emotion, but not on tasks involving holistic face processing. These findings are discussed in the context of broader perceptual and cognitive traits previously associated with synaesthesia for colour, with the suggestion that performance benefits shown by grapheme–colour synaesthetes may be related to domain-general visual discrimination biases observed in this group.
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Synesthesia an introduction
Frontiers in Psychology, 2014Co-Authors: Michael J. Banissy, Clare N Jonas, Roi Cohen KadoshAbstract:Synesthesia is a rare experience where one property of a stimulus evokes a second experience not associated with the first. For example, in lexical-gustatory Synesthesia words evoke the experience of tastes (Ward and Simner, 2003). There are at least 60 known variants of Synesthesia (Day, 2013), including reports of synesthetic experiences of color (Baron-Cohen et al., 1987), taste (Ward and Simner, 2003), touch (Ward et al., 2008), and sound (Saenz and Koch, 2008). The lower bound prevalence of the condition is considered to be approximately 4% (Simner et al., 2006). While synesthetic experiences have been documented since the 1800s (Jewanski et al., 2009), it is only in the last few decades that the authenticity of synesthetic experiences and mechanisms that contribute to them has been explored in depth (Ward, 2013). This resurgence in research has led to developments in our understanding of mechanisms that contribute to the synesthetic experience and the use of Synesthesia as a unique experimental preparation to inform us about typical models of cognition and perception (e.g., Cohen Kadosh and Henik, 2007; Simner, 2007; Bargary and Mitchell, 2008; Rouw et al., 2011). This has also resulted in many open questions and debates, several of which are touched upon in this research topic. Specifically, this research topic is focused around the following themes: What constitutes Synesthesia and how does it relate to typical cross-modal interactions? What mechanisms contribute to synesthetic experiences? Are there broader cognitive and perceptual traits associated with Synesthesia, and what mechanisms mediate their relationship? In total, there are 20 articles, each addressing at least one of these themes.
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Synesthesia for color is linked to improved color perception but reduced motion perception
Psychological Science, 2013Co-Authors: Michael J. Banissy, Victoria Tester, Neil G Muggleton, Agnieszka Janik, Aimee Davenport, Anna Franklin, Vincent WalshAbstract:Synesthesia is a rare condition in which one property of a stimulus (e.g., shape) triggers a secondary percept (e.g., color) not typically associated with the first. Work on Synesthesia has predominantly focused on confirming the authenticity of synesthetic experience, but much less research has been conducted to examine the extent to which Synesthesia is linked to broader perceptual differences. In the research reported here, we examined whether Synesthesia is associated with differences in color and motion processing by comparing these abilities in synesthetes who experience color as their evoked sensation with nonsynesthetic participants. We show that Synesthesia for color is linked to facilitated color sensitivity but decreased motion sensitivity. These findings are discussed in relation to the neurocognitive mechanisms of Synesthesia and interactions between color and motion processing in typical adults.
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Mechanisms of self-other representations and vicarious experiences of touch in mirror-touch Synesthesia
Frontiers in Human Neuroscience, 2013Co-Authors: Michael J. Banissy, Jamie WardAbstract:In recent years several studies have documented a near-universal tendency to vicariously represent the actions and sensations of others (e.g., see Keysers and Gazzola, 2009 for review). For example, observing another person experiencing pain activates neural regions involved in experiencing pain (e.g., Singer et al., 2004; Avenanti et al., 2005) or observing somebody being touched recruits regions of the somatosensory cortex involved in experiencing touch (e.g., Keysers et al., 2004, 2010; Ebisch et al., 2008; Schaefer et al., 2012). For most of us, these vicarious representations are implicit and do not lead to overt sensations of the observed events (e.g., we do not feel pain when observing pain to others). There are, however, a small number of individuals who do experience overt somatic sensations when observing others' tactile experiences (Ward et al., 2008; Osborn and Derbyshire, 2010; Fitzgibbon et al., 2012; Banissy, 2013). For example, in mirror-touch Synesthesia observing touch or pain to others evokes a conscious tactile sensation on the synesthetes' own body (Banissy and Ward, 2007; Holle et al., 2011). This opinion piece seeks to discuss potential neural mechanisms that contribute to the developmental form of mirror-touch Synesthesia (for descriptions of acquired forms of mirror-touch/pain Synesthesia see Fitzgibbon et al., 2012; Goller et al., 2013), and the important role that self-other representations may have on vicarious experiences of touch in mirror-touch Synesthesia.
David Brang - One of the best experts on this subject based on the ideXlab platform.
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how do crossmodal correspondences and multisensory processes relate to Synesthesia
2020Co-Authors: David Brang, Vilayanur S RamachandranAbstract:Abstract Synesthesia is a perceptual phenomenon in which stimulation of one sensory modality evokes additional (usually) sensory experiences in an unrelated modality (e.g., sounds evoking colors). Much has been written about the definition of Synesthesia, but as it remains a behaviorally defined phenomenon, definitional requirements are premature at this early stage (indeed, precision of word use often follows, rather than precedes, conceptual understanding). Synesthesia is thought to arise from either increased connectivity or reduced inhibition between associated sensory areas that usually do not interact. While the condition is typically studied in individuals who experience developmental variants of the condition, nonsynesthetes can experience analogous sensations via hallucinogens or as a result of sensory deprivation,1 raising the possibility that Synesthesia exists as a latent feature in all individuals. Research has long sought to identify the relationship between Synesthesia and more common multisensory interactions, including crossmodal correspondences (commonly agreed upon multisensory associations, such as small, white objects pairing with high-pitched sounds). In this chapter we review evidence both in support of and in opposition to models relating Synesthesia and crossmodal correspondences, and suggest future research to distinguish between them. As a first approximation, we note that idiopathic Synesthesia often involves apparently arbitrary correspondences (e.g., the color blue and the number 5 have nothing in common with one another) whereas multisensory associations usually “make sense” (e.g., an ameboid shape and a jagged shape resemble their auditory counterparts, the pseudowords bouba and kiki, respectively). Yet as we shall see, this distinction is not always true.
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inducing Synesthesia in non synesthetes short term visual deprivation facilitates auditory evoked visual percepts
Consciousness and Cognition, 2019Co-Authors: Anupama Nair, David BrangAbstract:Abstract Sounds can modulate activity in visual cortex, facilitating the detection of visual targets. However, these sound-driven modulations are not thought to evoke conscious visual percepts in the general population. In individuals with Synesthesia, however, multisensory interactions do lead to qualitatively different experiences such as sounds evoking flashes of light. Why, if multisensory interactions are present in all individuals, do only synesthetes experience abnormal qualia? Competing models differ in the time required for synesthetic experiences to emerge. The cross-activation model suggests Synesthesia arises over months or years from the development of abnormal neural connections. Here we demonstrate that after ∼5 min of visual deprivation, sounds can evoke Synesthesia-like percepts (vivid colors and Kluver form-constants) in ∼50% of non-synesthetes. These results challenge aspects of the cross-activation model and suggest that Synesthesia exists as a latent feature in all individuals, manifesting when the balance of activity across the senses has been altered.
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double blind study of visual imagery in grapheme color Synesthesia
Cortex, 2019Co-Authors: David Brang, Eunseon AhnAbstract:Synesthesia is an atypical perceptual phenomenon that has been associated with generalized differences in other cognitive and perceptual domains. Given similarities in the qualitative nature of synesthetic experiences to visual imagery perceptions, several studies have sought to examine whether synesthetes demonstrate increased visual imagery abilities. Using subjective imagery questionnaires, some studies have identified superior imaging abilities in synesthetes, while others have not. However, because most research on Synesthesia uses un-blinded group membership prior to data collection, such methods for studying group differences may be prone to participant and experimenter biases (e.g., a motivated synesthete may rate themselves as having stronger visual imagery abilities due to their own bias and perceived experimenter expectations). To address this issue, we demonstrate the feasibility of double-blind designs in Synesthesia research, applied here to examine differences in subjectively reported levels of imagery usage and intensity. Prior to identifying synesthetes' and non-synesthetes' group membership (in order to eliminate the potential for bias), subjects completed two common measures of visual imagery experiences. Using this approach, we replicated findings of greater visual imagery usage in synesthetes on the Spontaneous Use of Imagery Scale (SUIS) measure, but not of enhanced imagery abilities on the standardized Vividness of Visual Imagery Questionnaire (VVIQ) measure. The present study strengthens prior evidence that Synesthesia is associated with heightened visual imagery and demonstrates the utility of double-blind designs in order to limit biases and promote further replicability of other findings in research on Synesthesia.
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impaired acquisition of novel grapheme color correspondences in Synesthesia
Frontiers in Human Neuroscience, 2013Co-Authors: David Brang, Michael Ghiam, Vilayanur S RamachandranAbstract:Grapheme-color Synesthesia is a neurological phenomenon in which letters and numbers (graphemes) consistently evoke particular colors (e.g., A may be experienced as red). These sensations are thought to arise through the cross-activation of grapheme processing regions in the fusiform gyrus and color area V4, supported by anatomical and functional imaging. However, the developmental onset of grapheme-color Synesthesia remains elusive as research in this area has largely relied on self-report of these experiences in children. One possible account suggests that Synesthesia is present at or near birth and initially binds basic shapes and forms to colors, which are later refined to grapheme-color associations through experience. Consistent with this view, studies show that similarly shaped letters and numbers tend to elicit similar colors in Synesthesia and that some synesthetes consciously associate basic shapes with colors; research additionally suggests that synesthetic colors can emerge for newly learned characters with repeated presentation. This model further predicts that the initial shape-color correspondences in Synesthesia may persist as implicit associations, driving the acquisition of colors for novel characters. To examine the presence of latent color associations for novel characters, synesthetes and controls were trained on pre-defined associations between colors and complex shapes, on the assumption that the prescribed shape-color correspondences would on average differ from implicit synesthetic associations. Results revealed synesthetes were less accurate than controls to learn novel shape-color associations, consistent with our suggestion that implicit form-color associations conflicted with the learned pairings.
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enhanced mental rotation ability in time space Synesthesia
Cognitive Processing, 2013Co-Authors: David Brang, Vilayanur S Ramachandran, Luke E Miller, Marguerite Mcquire, Seana CoulsonAbstract:Time-space Synesthesia is a variant of sequence–space Synesthesia and involves the involuntary association of months of the year with 2D and 3D spatial forms, such as arcs, circles, and ellipses. Previous studies have revealed conflicting results regarding the association between time-space Synesthesia and enhanced spatial processing ability. Here, we tested 15 time-space synesthetes, and 15 non-synesthetic controls matched for age, education, and gender on standard tests of mental rotation ability, spatial working memory, and verbal working memory. Synesthetes performed better than controls on our test of mental rotation, but similarly to controls on tests of spatial and verbal working memory. Results support a dissociation between visuo-spatial imagery and spatial working memory capacity, and suggest time-space Synesthesia is associated only with enhanced visuo-spatial imagery. These data are consistent with the time-space connectivity thesis that time-space Synesthesia results from enhanced connectivity in the parietal lobe between regions supporting the representation of temporal sequences and those underlying visuo-spatial imagery.
David M Eagleman - One of the best experts on this subject based on the ideXlab platform.
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validating a standardised test battery for Synesthesia does the Synesthesia battery reliably detect Synesthesia
Consciousness and Cognition, 2015Co-Authors: Duncan Carmichael, Matthew Down, Richard Shillcock, David M Eagleman, Julia SimnerAbstract:Synesthesia is a neurological condition that gives rise to unusual secondary sensations (e.g., reading letters might trigger the experience of colour). Testing the consistency of these sensations over long time intervals is the behavioural gold standard assessment for detecting Synesthesia (e.g., Simner, Mulvenna et al., 2006). In 2007 however, Eagleman and colleagues presented an online 'Synesthesia Battery' of tests aimed at identifying Synesthesia by assessing consistency but within a single test session. This battery has been widely used but has never been previously validated against conventional long-term retesting, and with a randomly recruited sample from the general population. We recruited 2847 participants to complete The Synesthesia Battery and found the prevalence of grapheme-colour Synesthesia in the general population to be 1.2%. This prevalence was in line with previous conventional prevalence estimates based on conventional long-term testing (e.g., Simner, Mulvenna et al., 2006). This reproduction of similar prevalence rates suggests that the Synesthesia Battery is indeed a valid methodology for assessing Synesthesia. © 2015 The Authors.
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neural networks of colored sequence Synesthesia
The Journal of Neuroscience, 2013Co-Authors: Steffie N Tomson, Manjari Narayan, Genevera I Allen, David M EaglemanAbstract:Synesthesia is a condition in which normal stimuli can trigger anomalous associations. In this study, we exploit Synesthesia to understand how the synesthetic experience can be explained by subtle changes in network properties. Of the many forms of Synesthesia, we focus on colored sequence Synesthesia, a form in which colors are associated with overlearned sequences, such as numbers and letters (graphemes). Previous studies have characterized Synesthesia using resting-state connectivity or stimulus-driven analyses, but it remains unclear how network properties change as synesthetes move from one condition to another. To address this gap, we used functional MRI in humans to identify grapheme-specific brain regions, thereby constructing a functional “synesthetic” network. We then explored functional connectivity of color and grapheme regions during a Synesthesia-inducing fMRI paradigm involving rest, auditory grapheme stimulation, and audiovisual grapheme stimulation. Using Markov networks to represent direct relationships between regions, we found that synesthetes had more connections during rest and auditory conditions. We then expanded the network space to include 90 anatomical regions, revealing that synesthetes tightly cluster in visual regions, whereas controls cluster in parietal and frontal regions. Together, these results suggest that synesthetes have increased connectivity between grapheme and color regions, and that synesthetes use visual regions to a greater extent than controls when presented with dynamic grapheme stimulation. These data suggest that Synesthesia is better characterized by studying global network dynamics than by individual properties of a single brain region.
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pathways to seeing music enhanced structural connectivity in colored music Synesthesia
NeuroImage, 2013Co-Authors: Anna Zamm, David M Eagleman, Gottfried Schlaug, Psyche LouiAbstract:article i nfo Synesthesia, a condition in which a stimulus in one sensory modality consistently and automatically triggers concur- rent percepts in another modality, provides a window into the neural correlates of cross-modal associations. While research on grapheme-color Synesthesia has provided evidence for both hyperconnectivity-hyperbinding and disinhibited feedback as potential underlying mechanisms, less research has explored the neuroanatomical basis of other forms of Synesthesia. In the current study we investigated the white matter correlates of colored-music syn- esthesia. As these synesthetes report seeing colors upon hearing musical sounds, we hypothesized that they might show unique patterns of connectivity between visual and auditory association areas. We used diffusion tensor im- aging to trace the white matter tracts in temporal and occipital lobe regions in 10 synesthetes and 10 matched non-synesthete controls. Results showed that synesthetes possessed hemispheric patterns of fractional anisotropy, an index of white matter integrity, in the inferior fronto-occipital fasciculus (IFOF), a major white matter pathway that connects visual and auditory association areas to frontal regions. Specifically, white matter integrity within the right IFOF was significantly greater in synesthetes than controls. Furthermore, white matter integrity in synesthetes was correlated with scores on audiovisual tests of the Synesthesia Battery, especially in white matter un- derlying the right fusiform gyrus. Our findings provide the first evidence of a white matter substrate of colored-music Synesthesia, and suggest that enhanced white matter connectivity is involved in enhanced cross-modal associations.
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the genetics of colored sequence Synesthesia suggestive evidence of linkage to 16q and genetic heterogeneity for the condition
Behavioural Brain Research, 2011Co-Authors: Steffie N Tomson, Anand K Sarma, Nili Avidan, Kwanghyuk Lee, Rejnal Tushe, Dianna M Milewicz, Molly S Bray, Suzanne M Leal, David M EaglemanAbstract:Synesthesia is a perceptual condition in which sensory stimulation triggers anomalous sensory experiences. In colored sequence Synesthesia (CSS), color experiences are triggered by sequences such as letters or numbers. We performed a family based linkage analysis to identify genetic loci responsible for the increased neural crosstalk underlying CSS. Our results implicate a 23 MB region at 16q12.2-23.1, providing the first step in understanding the molecular basis of CSS.
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why color Synesthesia involves more than color
Trends in Cognitive Sciences, 2009Co-Authors: David M Eagleman, Melvyn A GoodaleAbstract:Synesthesia is a perceptual phenomenon in which stimuli can trigger experiences in non-stimulated sensory dimensions. The literature has focused on forms of Synesthesia in which stimuli (e.g. music, touch or numbers) trigger experiences of color. Generally missing, however, is the observation that synesthetic colors are often accompanied by the experience of other surface properties such as texture (e.g. a visual experience of linen, metal, marble, velvet, etc). Current frameworks for Synesthesia focus only upon the involvement of brain regions such as the V4 color complex. Here, we propose an expanded framework that includes brain regions involved in the encoding of material properties – specifically, larger regions of the medial ventral stream. The overlap of visual texture and color processing within ventral regions might explain why many experiences of Synesthesia extend beyond color to other material properties.
Vilayanur S Ramachandran - One of the best experts on this subject based on the ideXlab platform.
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how do crossmodal correspondences and multisensory processes relate to Synesthesia
2020Co-Authors: David Brang, Vilayanur S RamachandranAbstract:Abstract Synesthesia is a perceptual phenomenon in which stimulation of one sensory modality evokes additional (usually) sensory experiences in an unrelated modality (e.g., sounds evoking colors). Much has been written about the definition of Synesthesia, but as it remains a behaviorally defined phenomenon, definitional requirements are premature at this early stage (indeed, precision of word use often follows, rather than precedes, conceptual understanding). Synesthesia is thought to arise from either increased connectivity or reduced inhibition between associated sensory areas that usually do not interact. While the condition is typically studied in individuals who experience developmental variants of the condition, nonsynesthetes can experience analogous sensations via hallucinogens or as a result of sensory deprivation,1 raising the possibility that Synesthesia exists as a latent feature in all individuals. Research has long sought to identify the relationship between Synesthesia and more common multisensory interactions, including crossmodal correspondences (commonly agreed upon multisensory associations, such as small, white objects pairing with high-pitched sounds). In this chapter we review evidence both in support of and in opposition to models relating Synesthesia and crossmodal correspondences, and suggest future research to distinguish between them. As a first approximation, we note that idiopathic Synesthesia often involves apparently arbitrary correspondences (e.g., the color blue and the number 5 have nothing in common with one another) whereas multisensory associations usually “make sense” (e.g., an ameboid shape and a jagged shape resemble their auditory counterparts, the pseudowords bouba and kiki, respectively). Yet as we shall see, this distinction is not always true.
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impaired acquisition of novel grapheme color correspondences in Synesthesia
Frontiers in Human Neuroscience, 2013Co-Authors: David Brang, Michael Ghiam, Vilayanur S RamachandranAbstract:Grapheme-color Synesthesia is a neurological phenomenon in which letters and numbers (graphemes) consistently evoke particular colors (e.g., A may be experienced as red). These sensations are thought to arise through the cross-activation of grapheme processing regions in the fusiform gyrus and color area V4, supported by anatomical and functional imaging. However, the developmental onset of grapheme-color Synesthesia remains elusive as research in this area has largely relied on self-report of these experiences in children. One possible account suggests that Synesthesia is present at or near birth and initially binds basic shapes and forms to colors, which are later refined to grapheme-color associations through experience. Consistent with this view, studies show that similarly shaped letters and numbers tend to elicit similar colors in Synesthesia and that some synesthetes consciously associate basic shapes with colors; research additionally suggests that synesthetic colors can emerge for newly learned characters with repeated presentation. This model further predicts that the initial shape-color correspondences in Synesthesia may persist as implicit associations, driving the acquisition of colors for novel characters. To examine the presence of latent color associations for novel characters, synesthetes and controls were trained on pre-defined associations between colors and complex shapes, on the assumption that the prescribed shape-color correspondences would on average differ from implicit synesthetic associations. Results revealed synesthetes were less accurate than controls to learn novel shape-color associations, consistent with our suggestion that implicit form-color associations conflicted with the learned pairings.
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enhanced mental rotation ability in time space Synesthesia
Cognitive Processing, 2013Co-Authors: David Brang, Vilayanur S Ramachandran, Luke E Miller, Marguerite Mcquire, Seana CoulsonAbstract:Time-space Synesthesia is a variant of sequence–space Synesthesia and involves the involuntary association of months of the year with 2D and 3D spatial forms, such as arcs, circles, and ellipses. Previous studies have revealed conflicting results regarding the association between time-space Synesthesia and enhanced spatial processing ability. Here, we tested 15 time-space synesthetes, and 15 non-synesthetic controls matched for age, education, and gender on standard tests of mental rotation ability, spatial working memory, and verbal working memory. Synesthetes performed better than controls on our test of mental rotation, but similarly to controls on tests of spatial and verbal working memory. Results support a dissociation between visuo-spatial imagery and spatial working memory capacity, and suggest time-space Synesthesia is associated only with enhanced visuo-spatial imagery. These data are consistent with the time-space connectivity thesis that time-space Synesthesia results from enhanced connectivity in the parietal lobe between regions supporting the representation of temporal sequences and those underlying visuo-spatial imagery.
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survival of the Synesthesia gene why do people hear colors and taste words
PLOS Biology, 2011Co-Authors: David Brang, Vilayanur S RamachandranAbstract:Synesthesia is a perceptual experience in which stimuli presented through one modality will spontaneously evoke sensations in an unrelated modality. The condition occurs from increased communication between sensory regions and is involuntary, automatic, and stable over time. While Synesthesia can occur in response to drugs, sensory deprivation, or brain damage, research has largely focused on heritable variants comprising roughly 4% of the general population. Genetic research on Synesthesia suggests the phenomenon is heterogeneous and polygenetic, yet it remains unclear whether Synesthesia ever provided a selective advantage or is merely a byproduct of some other useful selected trait. Progress in uncovering the genetic basis of Synesthesia will help us understand why Synesthesia has been conserved in the population.
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similarly shaped letters evoke similar colors in grapheme color Synesthesia
Neuropsychologia, 2011Co-Authors: David Brang, Romke Rouw, Vilayanur S Ramachandran, Seana CoulsonAbstract:Grapheme-color Synesthesia is a neurological condition in which viewing numbers or letters (graphemes) results in the concurrent sensation of color. While the anatomical substrates underlying this experience are well understood, little research to date has investigated factors influencing the particular colors associated with particular graphemes or how Synesthesia occurs developmentally. A recent suggestion of such an interaction has been proposed in the cascaded cross-tuning (CCT) model of Synesthesia, which posits that in synesthetes connections between grapheme regions and color area V4 participate in a competitive activation process, with synesthetic colors arising during the component-stage of grapheme processing. This model more directly suggests that graphemes sharing similar component features (lines, curves, etc.) should accordingly activate more similar synesthetic colors. To test this proposal, we created and regressed synesthetic color-similarity matrices for each of 52 synesthetes against a letter-confusability matrix, an unbiased measure of visual similarity among graphemes. Results of synesthetes' grapheme-color correspondences indeed revealed that more similarly shaped graphemes corresponded with more similar synesthetic colors, with stronger effects observed in individuals with more intense synesthetic experiences (projector synesthetes). These results support the CCT model of Synesthesia, implicate early perceptual mechanisms as driving factors in the elicitation of synesthetic hues, and further highlight the relationship between conceptual and perceptual factors in this phenomenon.
