Auditory-visual Synesthesia Research Articles

Top-down signal transmission and global hyperconnectivity in auditory-visual synesthesia: Evidence from a functional EEG resting-state study.

Auditory-visual (AV) synesthesia is a rare phenomenon in which an auditory stimulus induces a "concurrent" color sensation. Current neurophysiological models of synesthesia mainly hypothesize "hyperconnected" and "hyperactivated" brains, but differ in the directionality of signal transmission. The two-stage model proposes bottom-up signal transmission from inducer- to concurrent- to higher-order brain areas, whereas the disinhibited feedback model postulates top-down signal transmission from inducer- to higher-order- to concurrent brain areas. To test the different models of synesthesia, we estimated local current density, directed and undirected connectivity patterns in the intracranial space during 2 min of resting-state (RS) EEG in 11 AV synesthetes and 11 nonsynesthetes. AV synesthetes demonstrated increased parietal theta, alpha, and lower beta current density compared to nonsynesthetes. Furthermore, AV synesthetes were characterized by increased top-down signal transmission from the superior parietal lobe to the left color processing area V4 in the upper beta frequency band. Analyses of undirected connectivity revealed a global, synesthesia-specific hyperconnectivity in the alpha frequency band. The involvement of the superior parietal lobe even during rest is a strong indicator for its key role in AV synesthesia. By demonstrating top-down signal transmission in AV synesthetes, we provide direct support for the disinhibited feedback model of synesthesia. Finally, we suggest that synesthesia is a consequence of global hyperconnectivity. Hum Brain Mapp 39:522-531, 2018. © 2017 Wiley Periodicals, Inc.

Seeing sounds after visual loss: a case study of the neural correlates of acquired auditory-visual synesthesia

Seeing sounds after visual loss: a case study of the neural correlates of acquired auditory-visual synesthesia

The color of music: Emotion-mediated associations to Bach’s Well-tempered Clavier.

Associations between music and color, and cross-modal associations in general, have been understood in a variety of ways. One view is that, because we experience the world through multiple sensory modalities simultaneously, integrating these signals provides us with richer and more precise information on which to act (Parise & Spence, 2013; Spence, 2011). Cross-modal associations, for example, between the color of a fruit and whether or not it tastes ripe, are normal and adaptive for integrating information across the senses. Three types of cross-modal associations that have been identified are structural correspondences (originating in the neural processing), statistical correspondences (reflecting regularities in the world), and semantically (primarily verbally) mediated correspondences (Spence, 2011).Walker and colleagues (Walker & Smith, 1984; Walker, Walker, & Francis, 2012) have proposed a system of amodal, conceptual terms that apply across sensory modalities to account for cross-modal associations. These draw on basic features of bodily actions, gestures, and vocalizations. For example, common to hearing and sight are fast versus slow, high versus low, bright versus dark, and small versus large. Such cross-sensory correspondences may be bidirectional and symmetrical, or asymmetrical with the association in one direction being stronger than in the other, or even unidirectional. Hearing a high sound might lead one to expect that a small object is the source, but a small object would not necessarily lead one to expect a high sound. Walker (2016) describes how the theory might apply to music, going beyond associations to simple tones varying in pitch height, loudness, and/or timbre, to possible factors operating at compositional levels of melody and tempo.One issue that arises in the literature on cross-modal associations is what the relationship is between these associations and the phenomenon of synesthesia, in which a trigger stimulus (inducer) causes automatic, perception-like experiences (concurrent) in a different modality. Although cross-modal associations have been found to be consistent across individuals, the focus in research on synesthesia tends to be on individuals under the assumption that the particular correspondences would be idiosyncratic. Hundreds of different types of synesthesia have been identified, with a history of scientific reports going back to the 1800s (Galton, 1883; see Jewanski, 2013; Ward, 2013 for reviews). Recently, it has been suggested that synesthesia may be subject to the same rules that govern normal patterns of cross-modal associations, differing mainly in its automaticity but less in its phenomenology (Marks, 2013; Simner, 2013; but see Spence, 2011).Marks (1975) reviewed >100 reports of auditory-visual synesthesia, many of which involved music. He found that some of the associations are regular, systematic, and consistent across individuals. Specifically, there were correlations between auditory pitch and visual brightness (the higher the brighter, and in some studies more yellow), and pitch and visual size (larger with lower), and loudness and visual size and brightness (larger and brighter with louder). Marks described devices invented to present colors to accompany music, such as an organ built by Scriabin that mapped tones and colors so that, for example, C was accompanied by red, and D accompanied by yellow. Associations between musical notes and/or keys and colors are quite common in synesthetes and a case study demonstrated stability over time (Carroll & Greenberg, 1961). However, as noted by Marks, the specific mappings tend to vary across individuals, so that C might be red to one synesthete and white to another. Other, also idiosyncratic, associations have been reported between color and musical instruments, such as trumpet and scarlet, and flute and blue, and the music of particular composers, such as Chopin and purple, Mozart and green, or specific works by composers. …

Auditory-Olfactory Synesthesia Coexisting With Auditory-Visual Synesthesia

Synesthesia is an unusual condition in which stimulation of one sensory modality causes an experience in another sensory modality or when a sensation in one sensory modality causes another sensation within the same modality. We describe a previously unreported association of auditory-olfactory synesthesia coexisting with auditory-visual synesthesia. Given that many types of synesthesias involve vision, it is important that the clinician provide these patients with the necessary information and support that is available.

Neurophysiological investigation of idiopathic acquired auditory–visual synesthesia

We present a case of acquired auditory–visual synesthesia and its neurophysiological investigation in a healthy 42-year-old woman. She started experiencing persistent positive and intermittent negative visual phenomena at age 37 followed by auditory–visual synesthesia. Her neurophysiological investigation included video-EEG, fMRI, and MEG. Auditory stimuli (700 Hz, 50 ms duration, 0.5 s ISI) were presented binaurally at 60 db above the hearing threshold in a dark room. The patient had bilateral symmetrical auditory-evoked neuromagnetic responses followed by an occipital-evoked field 16.3 ms later. The activation of occipital cortex following auditory stimuli may represent recruitment of existing cross-modal sensory pathways.

A Whole-Genome Scan and Fine-Mapping Linkage Study of Auditory-Visual Synesthesia Reveals Evidence of Linkage to Chromosomes 2q24, 5q33, 6p12, and 12p12

Synesthesia, a neurological condition affecting between 0.05%-1% of the population, is characterized by anomalous sensory perception and associated alterations in cognitive function due to interference from synesthetic percepts. A stimulus in one sensory modality triggers an automatic, consistent response in either another modality or a different aspect of the same modality. Familiality studies show evidence of a strong genetic predisposition; whereas initial pedigree analyses supported a single-gene X-linked dominant mode of inheritance with a skewed F:M ratio and a notable absence of male-to-male transmission, subsequent analyses in larger samples indicated that the mode of inheritance was likely to be more complex. Here, we report the results of a whole-genome linkage scan for auditory-visual synesthesia with 410 microsatellite markers at 9.05 cM density in 43 multiplex families (n = 196) with potential candidate regions fine-mapped at 5 cM density. Using NPL and HLOD analysis, we identified four candidate regions. Significant linkage at the genome-wide level was detected to chromosome 2q24 (HLOD = 3.025, empirical genome-wide p = 0.047). Suggestive linkage was found to chromosomes 5q33, 6p12, and 12p12. No support was found for linkage to the X chromosome; furthermore, we have identified two confirmed cases of male-to-male transmission of synesthesia. Our results demonstrate that auditory-visual synesthesia is likely to be an oligogenic disorder subject to multiple modes of inheritance and locus heterogeneity. This study comprises a significant step toward identifying the genetic substrates underlying synesthesia, with important implications for our understanding of the role of genes in human cognition and perception.

Acquired auditory-visual synesthesia: A window to early cross-modal sensory interactions

Synesthesia is experienced when sensory stimulation of one sensory modality elicits an involuntary sensation in another sensory modality. Auditory-visual synesthesia occurs when auditory stimuli elicit visual sensations. It has developmental, induced and acquired varieties. The acquired variety has been reported in association with deafferentation of the visual system as well as temporal lobe pathology with intact visual pathways. The induced variety has been reported in experimental and post-surgical blindfolding, as well as intake of hallucinogenic or psychedelics. Although in humans there is no known anatomical pathway connecting auditory areas to primary and/or early visual association areas, there is imaging and neurophysiologic evidence to the presence of early cross modal interactions between the auditory and visual sensory pathways. Synesthesia may be a window of opportunity to study these cross modal interactions. Here we review the existing literature in the acquired and induced auditory-visual synesthesias and discuss the possible neural mechanisms.

Do small white balls squeak? Pitch-object correspondences in young children.

Adults with auditory-visual synesthesia agree that higher pitched sounds induce smaller, brighter visual percepts. We have hypothesized that these correspondences are remnants of cross-modal neural connections that are present at birth and that influence the development of perception and language even in adults and children without synesthesia. In this study, we explored these correspondences in preschoolers (30-36 months; n = 12 per experiment). The children were asked to indicate which of two bouncing balls was making a centrally located sound. The balls varied in size and/or surface darkness; the sound varied in pitch. The children reliably matched the higher pitched sound to a smaller and lighter (white) ball (Experiment 1), to a lighter (white) ball (Experiment 2), and in one of two groups, to a smaller ball (Experiment 3). Children's matching of pitch and size cannot be attributed to intensity matching or to learning. These data support the hypothesis that some cross-modal correspondences may be remnants of the neural mechanisms underlying neonatal perception.

Auditory-visual synesthesia: sound-induced photisms.

Nine patients with visual loss due to lesions of the optic nerve or chiasm experienced photisms induced by sound. Descriptions of these varied from simple flashes of white light to complicated colorful hallucinations likened to a flame, a petal of oscillating lines, a kaleidoscope, or an ameba; they always appeared within a defective portion of the visual field as demonstrated by perimetry. The provoking sounds were usually those of normal daily life, ranged from soft to loud, and always seemed to be heard by the ear ipsilateral to the eye in which the photism was seen. Sound-induced photisms occurred under circumstances that would promote a startle reaction to sound, and each patient was startled when the photisms occurred. Visual evoked responses demonstrated partial deafferentation of the eye in which photisms were seen in seven patients tested. The phenomenon may occur when the patient with a partially deafferent anterior visual pathway is startled by sound.

A MULTIVARIATE MODEL OF SYNESTHESIA.

Synesthesia is defined in this paper as a sensory phenomenon in which a stimulus in one sense mode is interpreted in terms appropriate to some other sense mode. The paper deals explicitly with auditory-visual synesthesia or chromesthesia. The model proposes two cognitive spaces for the two sense modes, differing from each other only in terms of what is called a modal axis. Two separate sub-populations of individuals are hypothesized, one made up of persons who can collapse their cognitive space along the modal axis. These people are assumed to be those who regularly experience synesthesia. Persons who do not regularly experience synesthesia axe assumed either (a) to be unable to collapse their cognitive space, or (b) to do so in a different way. Subjeats in the study rated colors and adjectives as to their appropriate- ness in describing musical selections. Estimates of color and adjective spaces were computed by cluster analyses based upon the ratings. The color space closely resembled the three-dimensional color solid, and fit well with the adjective space. Subsamples selected as extreme groups on the basis of synesthesia experience showed identical adjective spaces but different color spaces, as would be predicted from the model.