Unconscious priming eliminates automatic binding of colour and alphanumeric form in synaesthesia

Abstract

Synaesthesia is an unusual perceptual phenomenon in which events in one sensory modality induce vivid sensations in another1,2. Individuals may ‘taste’ shapes3, ‘hear’ colours4, or ‘feel’ sounds5. Synaesthesia was first described over a century ago6, but little is known about its underlying causes or its effects on cognition. Most reports have been anecdotal or have focused on isolated unusual cases3,7,8,9. Here we report an investigation of 15 individuals with colour-graphemic synaesthesia, each of whom experiences idiosyncratic but highly consistent colours for letters and digits. Using a colour–form interference paradigm, we show that induced synaesthetic experiences cannot be consciously suppressed even when detrimental to task performance. In contrast, if letters and digits are presented briefly and masked, so that they are processed but unavailable for overt report, the synaesthesia is eliminated. These results show that synaesthetic experiences can be prevented despite substantial processing of the sensory stimuli that otherwise trigger them. We conclude that automatic binding of colour and alphanumeric form in synaesthesia arises after initial processes of letter and digit recognition are complete.

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Figure 1: Mean (+1 s.e.) consistency of colour associations for 150 items (letters, arabic numerals and words), plotted separately for each of 11 categories tested.
Figure 2: Mean voice-onset times (±1 s.e.) for colour naming in the standard and synaesthetic Stroop tasks, plotted as a function of congruency condition.
Figure 3: Mean percentage correct prime identification (+1 s.e.) for the priming experiments.
Figure 4: Mean voice-onset times (±1 s.e.) for colour naming in the visible priming (500 ms) and masked priming (56 and 28 ms) experiments, plotted as a function of synaesthetic congruency condition.

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Acknowledgements

We wish to thank A. Kritikos, M. O'Boyle, P. Wilken and M. Williams for their comments on the manuscript. This work was supported by a grant from the Australian Research Council to J.B.M.

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Correspondence to Jason B. Mattingley.

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Mattingley, J., Rich, A., Yelland, G. et al. Unconscious priming eliminates automatic binding of colour and alphanumeric form in synaesthesia. Nature 410, 580–582 (2001). https://doi.org/10.1038/35069062

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