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Michelle Jarick, Colin Hawco, Todd Ferretti, Mike Dixon; Electrophysiological evidence of shifts in spatial attention corresponding to a synaesthetes mental calendar. Journal of Vision 2009;9(8):98. doi: https://doi.org/10.1167/9.8.98.
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© ARVO (1962-2015); The Authors (2016-present)
For individuals with Time-Space Synaesthesia, months of the year occupy very specific and highly consistent spatial locations. For example, L experiences the months of the year in the form of a “scoreboard 7”, where January is experienced on her left side, July on her right side, with the rest of the months curving behind her. Using a spatial cueing paradigm, we were able to empirically confirm L's subjective reports of her mental calendar. Month names were centrally presented followed by a target square appearing on the left or right of the display. L was reliably faster at detecting targets in validly cued relative to invalidly cued locations, whereas controls showed no response time differences. Furthermore, L demonstrated cueing effects even at short stimulus onset asynchronies (150 ms SOAs) between cue and target, suggesting her attention was automatically shifted to the cued location. Here, we used event-related brain potentials (ERP's) to provide converging evidence for these rapid shifts of attention. Compared to non-synaesthetes, at approximately 100 ms following the onset of the targets, L's brain potentials were more positive in frontal sites for valid than invalid targets, reflecting an early enhancement in attention to validly cued locations. Moreover, L exhibited a later posterior positivity occurring about 300 ms to 600 ms in response to invalidly cued targets, possibly reflecting a re-directing of attention to the uncued location. Importantly, non-synaesthetes showed neither the early or later deflections in response to validly and invalidly cued targets. Overall, we were able to substantiate L's behavioural cueing effects at short SOAs with electrophysiological evidence revealing the emergence of early evoked potentials to validly cued locations. These findings further strengthen our claim that for some synaesthetes months automatically trigger shifts in spatial attention.
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