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Assessing Lateral Interaction in the Synesthetic Visual Brain

Department of Psychology, Université du Québec à Montréal, Montréal, QC H2X 3P2, Canada
Cognitive Neurosciences Research Center, Université du Québec à Montréal, Montréal, QC H2X 3P2, Canada
Research Center of the Sainte-Justine University Hospital, Montréal, QC H3T 1C5, Canada
Author to whom correspondence should be addressed.
Received: 10 August 2018 / Revised: 14 January 2019 / Accepted: 6 February 2019 / Published: 8 February 2019
(This article belongs to the Special Issue Visual Perception and Its Neural Mechanisms)
In grapheme-color synesthesia, letters and numbers evoke abnormal colored perceptions. Although the underlying mechanisms are not known, it is largely thought that the synesthetic brain is characterized by atypical connectivity throughout various brain regions, including the visual areas. To study the putative impact of synesthesia on the visual brain, we assessed lateral interactions (i.e., local functional connectivity between neighboring neurons in the visual cortex) by recording steady-state visual evoked potentials (ssVEPs) over the occipital region in color-grapheme synesthetes (n = 6) and controls (n = 21) using the windmill/dartboard paradigm. Discrete Fourier Transform analysis was conducted to extract the fundamental frequency and the second harmonics of ssVEP responses from contrast-reversing stimuli presented at 4.27 Hz. Lateral interactions were assessed using two amplitude-based indices: Short-range and long-range lateral interactions. Results indicated that synesthetes had a statistically weaker signal coherence of the fundamental frequency component compared to the controls, but no group differences were observed on lateral interaction indices. However, a significant correlation was found between long-range lateral interactions and the type of synesthesia experience (projector versus associator). We conclude that the occipital activity related to lateral interactions in synesthetes does not substantially differ from that observed in controls. Further investigation is needed to understand the impact of synesthesia on visual processing, specifically in relation to subjective experiences of synesthete individuals. View Full-Text
Keywords: synesthesia; visual evoked potentials; EEG; occipital cortex; lateral interaction synesthesia; visual evoked potentials; EEG; occipital cortex; lateral interaction
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Jimena Arias, D.; Hosein, A.; Saint-Amour, D. Assessing Lateral Interaction in the Synesthetic Visual Brain. Vision 2019, 3, 7.

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