Differences in early sensory-perceptual processing in synesthesia: a visual evoked potential study.

Institute of Neuroscience (TCIN), Lloyd Building, Trinity College Dublin, Dublin 2, Ireland.
NeuroImage (Impact Factor: 6.25). 08/2008; 43(3):605-13. DOI: 10.1016/j.neuroimage.2008.07.028
Source: PubMed

ABSTRACT Synesthesia is a condition where stimulation of a single sensory modality or processing stream elicits an idiosyncratic, yet reliable perception in one or more other modalities or streams. Various models have been proposed to explain synesthesia, which have in common aberrant cross-activation of one cortical area by another. This has been observed directly in cases of linguistic-color synesthesia as cross-activation of the 'color area', V4, by stimulation of the grapheme area. The underlying neural substrates that mediate cross-activations in synesthesia are not well understood, however. In addition, the overall integrity of the visual system has never been assessed and it is not known whether wider differences in sensory-perceptual processing are associated with the condition. To assess whether fundamental differences in perceptual processing exist in synesthesia, we utilised high-density 128-channel electroencephalography (EEG) to measure sensory-perceptual processing using stimuli that differentially bias activation of the magnocellular and parvocellular pathways of the visual system. High and low spatial frequency gratings and luminance-contrast squares were presented to 15 synesthetes and 15 controls. We report, for the first time, early sensory-perceptual differences in synesthetes relative to non-synesthete controls in response to simple stimuli that do not elicit synesthetic color experiences. The differences are manifested in the early sensory components of the visual evoked potential (VEP) to stimuli that bias both magnocellular and parvocellular responses, but are opposite in direction, suggesting a differential effect on these two pathways. We discuss our results with reference to widespread connectivity differences as a broader phenotype of synesthesia.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Synesthesia, the conscious, idiosyncratic, repeatable, and involuntary sensation of one sensory modality in response to another, is a condition that has puzzled both researchers and philosophers for centuries. Much time has been spent proving the condition's existence as well as investigating its etiology, but what can be learned from synesthesia remains a poorly discussed topic. Here, synaesthesia is presented as a possible answer rather than a question to the current gaps in our understanding of sensory perception. By first appreciating the similarities between normal sensory perception and synesthesia, one can use what is known about synaesthesia, from behavioral and imaging studies, to inform our understanding of "normal" sensory perception. In particular, in considering synesthesia, one can better understand how and where the different sensory modalities interact in the brain, how different sensory modalities can interact without confusion - the binding problem - as well as how sensory perception develops.
    The Yale journal of biology and medicine 06/2013; 86(2):203-16.
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Digestive Diseases and Sciences 01/2012; 57(6):1629-35. · 2.26 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this study we investigated whether synaesthesia is associated with a particular cognitive style. Cognitive style refers to preferred modes of information processing, such as a verbal style or a visual style. We reasoned that related to the enriched world of experiences created by synaesthesia, its association with enhanced verbal and visual memory, higher imagery and creativity, synaesthetes might show enhanced preference for a verbal as well as for a visual cognitive style compared to non-synaesthetes. In Study 1 we tested a large convenience sample of 1046 participants, who classified themselves as grapheme-color, sound-color, lexical-gustatory, sequence-space, or as non-synaesthetes. To assess cognitive style, we used the revised verbalizer-visualizer questionnaire (VVQ), which involves three independent cognitive style dimensions (verbal style, visual-spatial style, and vivid imagery style). The most important result was that those who reported grapheme-color synaesthesia showed higher ratings on the verbal and vivid imagery style dimensions, but not on the visual-spatial style dimension. In Study 2 we replicated this finding in a laboratory study involving 24 grapheme-color synaesthetes with objectively confirmed synaesthesia and a closely matched control group. Our results indicate that grapheme-color synaesthetes prefer both a verbal and a specific visual cognitive style. We suggest that this enhanced preference, probably together with the greater ease to switch between a verbal and a vivid visual imagery style, may be related to cognitive advantages associated with grapheme color synaesthesia such as enhanced memory performance and creativity.
    Frontiers in Psychology 01/2013; 4:632. · 2.80 Impact Factor

Full-text (2 Sources)

Available from
Jun 3, 2014