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: 6.13). 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.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Synesthesia based in visual modalities has been associated with reports of vivid visual imagery. We extend this finding to consider whether other forms of synesthesia are also associated with enhanced imagery, and whether this enhancement reflects the modality of synesthesia. We used self-report imagery measures across multiple sensory modalities, comparing synesthetes’ responses (with a variety of forms of synesthesia) to those of non-synesthete matched controls. Synesthetes reported higher levels of visual, auditory, gustatory, olfactory and tactile imagery and a greater level of imagery use. Furthermore, their reported enhanced imagery is restricted to the modalities involved in the individual’s synesthesia. There was also a relationship between the number of forms of synesthesia an individual has, and the reported vividness of their imagery, highlighting the need for future research to consider the impact of multiple forms of synesthesia. We also recommend the use of behavioral measures to validate these self-report findings.
    Consciousness and Cognition 01/2015; 31:73-85. · 2.31 Impact Factor
  • Rendiconti Lincei. Scienze Fisiche e Naturali 09/2014; 25(3):309-316. · 0.76 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Synesthesia is a condition in which a particular sensory stimulus (or even the thought of that stimulus) — the inducer — reliably elicits not only the normal perceptual experience but also some additional, inappropriate sensation—the concurrent. In the earliest known reference to this phenomenon, John Locke (1690) described a blind man who, when asked to describe the color scarlet, replied that it is " like the sound of a trumpet. " Indeed, the commonest forms of synesthesia involve seeing colors when listening to sounds or words, or reading letters or numbers. Like schizophrenia and dementia, synesthesia is oft en described as a singular phenotype. Th e implication is that this extraordinary condition is a well-defi ned " pathological " form of perception with a distinct neurological basis. However, like schizophrenia and dementia, convenient terminology and minimal defi nition might hide a variety of conditions, with diff erent etiologies and manifestations. In this chapter we question the defi nition of synesthesia, its proposed causes and neurological underpinnings; whether it takes one or many forms, and whether it is a highly aberrant condition or merely the extreme end of a continuum of perceptual function. Despite the fl urry of research on synesthesia in the past 20 years, aided by the advent of neuroimaging, many of these fundamental issues remain unresolved. We are left with more certainty about what synesthesia is not, than about what it is. Problems With the Definition of Synesthesia Any serious study of an unusual phenotype depends on the clarity of its description: but there is still ambivalence and debate about the essential criteria that defi ne synesthesia. Early descriptions of the phenomenon, which was then usually called " hyperchromat-opsia " (" hyperchromatopsie " in French), emphasized the vivid nature of the concurrent experiences, which were oft en described as illusions or hallucinations (see Jewanski et al. 2011). It was not until the late nineteenth century that Heinrich Kaiser (1872) described OUP UNCORRECTED PROOF – FIRSTPROOFS, Wed May 29 2013, NEWGEN
    The Oxford Handbook of Synaesthesia, Edited by J Simner, E Hubbard, 01/2013: pages 959-988; Oxford University Press.

Full-text (2 Sources)

Available from
Jun 3, 2014