Automaticity and localisation of concurrents predicts colour area activity in grapheme-colour synaesthesia

Gould van Praag, Cassandra D, Garfinkel, Sarah, Ward, Jamie, Bor, Daniel and Seth, Anil K (2016) Automaticity and localisation of concurrents predicts colour area activity in grapheme-colour synaesthesia. Neuropsychologia, 88. pp. 5-14. ISSN 0028-3932

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Abstract

In grapheme-colour synaesthesia(GCS), the presentation of letters or numbers induces an additional ‘concurrent’ experience of colour. Early functional MRI (fMRI) investigations of GCS reported activation in colour-selective area V4 during the concurrent experience. However, others have failed to replicate this key finding. We reasoned that individual differences in synaesthetic phenomenology might explain this inconsistency in the literature. To test this hypothesis, we examined fMRI BOLD responses in a group of grapheme-colour synaesthetes (n¼20) and matched controls(n¼20) while characterising the individual phenomenology of the synaesthetes along dimensions of ‘automaticity’ and ‘localisation'. We used an independent functional localiser to identify colour-selective areas in both groups. Activations in these areas were then assessed during achromatic synaesthesia-inducing, and non-inducing conditions; we also explored whole brain activations, where we sought to replicate the existing literature regarding synaesthesia effects. Controls showed no significant activations in the contrast of inducing > non-inducing synaesthetic stimuli, in colour-selective ROIs or at the whole brain level. In the synaesthete group, we correlated activation within colour-selective ROIs with individual differences in phenomenology using the Coloured Letters and Numbers (CLaN) questionnaire which measures,amongst other attributes, the subjective automaticity/attention in synaesthetic concurrents, and their spatial localisation. Supporting our hypothesis, we found significant correlations between individual measures of synaesthetic phenomenology and BOLD responses in colour-selective areas, when contrasting inducing- against non-inducing stimuli. Specifically, left-hemisphere colour area responses were stronger for synaesthetes scoring high on phenomenological localisation and automaticity/attention, while right-hemisphere colour area responses showed a relationship with localisation only. In exploratory whole brain analyses, the BOLD response within several other areas was also correlated with these phenomenological factors, including the intra parietalsulcus, insula, precentral and supplementary motor areas. Our findings reveal a network of regions underlying synaesthetic phenomenology and they help reconcile the diversity of previous results regarding colour-selective BOLD responses during synaesthesia, by establishing a bridge between neural responses and individual synaesthetic phenomenology.

Item Type: Article
Schools and Departments: Brighton and Sussex Medical School > Neuroscience
School of Engineering and Informatics > Informatics
School of Psychology > Psychology
Subjects: B Philosophy. Psychology. Religion > BF Psychology > BF0231 Sensation. Aesthesiology > BF0241 Special senses. Vision. Visual perception
B Philosophy. Psychology. Religion > BF Psychology > BF0309 Consciousness. Cognition Including learning, attention, comprehension, memory, imagination, genius, intelligence, thought and thinking, psycholinguistics, mental fatigue
Depositing User: Marianne Cole
Date Deposited: 03 May 2016 12:30
Last Modified: 26 Jul 2017 23:51
URI: http://sro.sussex.ac.uk/id/eprint/60730

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