Exploring the benefit of synaesthetic colours: Testing for “pop-out” in individuals with grapheme–colour synaesthesia

Abstract

In grapheme–colour synaesthesia, letters, numbers, and words elicit involuntary colour experiences. Recently, there has been much emphasis on individual differences and possible subcategories of synaesthetes with different underlying mechanisms. In particular, there are claims that for some, synaesthesia occurs prior to attention and awareness of the inducing stimulus. We first characterized our sample using two versions of the “Synaesthetic Congruency Task” to distinguish “projector” and “associator” synaesthetes who may differ in the extent to which their synaesthesia depends on attention and awareness. We then used a novel modification of the “Embedded Figures Task” that included a set-size manipulation to look for evidence of preattentive “pop-out” from synaesthetic colours, at both a group and an individual level. We replicate an advantage for synaesthetes over nonsynaesthetic controls on the Embedded Figures Task in accuracy, but find no support for pop-out of synaesthetic colours. We conclude that grapheme–colour synaesthetes are fundamentally similar in their visual processing to the general population, with the source of their unusual conscious colour experiences occurring late in the cognitive hierarchy.

Keywords:

• Grapheme–colour synaesthesia
• Pop-out
• Projector/associator
• Individual differences

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Corrigendum

Acknowledgments

We thank Chris Hammond and David Fencsik for programming assistance, and Rocco Chiou and Margery Pardey for comments on the manuscript. A.N.R. is supported by the Australian Research Council (DP0984494) and the Menzies Foundation. Conflict of interest: Nil.

Notes

¹It is difficult to directly analyse the comparison of interest—namely, the magnitude of the difference between incongruent and congruent trials in the two tasks—at an individual level. Here, we look for an interaction in Task × Congruency using an independent-measures ANOVA. As the data come from a single individual, we checked for autocorrelation of RTs. In all but four cases (out of 96 performed correlations) the assumption of independence was valid.

²It is of course possible that this reflects a need for more trials per participant (i.e., a lack of power to detect interactions). There were no hints in the statistics, however, even for a trend (F < 1 for all analyses of the interaction terms), despite most synaesthetes showing a significant congruency effect across the two tasks (i.e., a main effect of congruency).