Automaticity in Stimulus-Parity Synaesthesia

Dumbalska, Tsvetomira; White, Rebekah C.; Duta, Mihaela D.; Nation, Kate · 2017 · DOAJ

DOI: 10.1177/2041669517736323

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Summary

This study investigates the automaticity of stimulus-parity synaesthesia, a rare subtype where non-numerical stimuli evoke sensations of oddness or evenness. While automaticity is a defining characteristic of synaesthesia, it had not been objectively demonstrated for this specific subtype, which has been documented in only three prior instances. The research was motivated by an anecdote from Synaesthete R, who reported difficulty using a toy shape-sorter because the parity of certain shapes conflicted with the parity of their corresponding color slots. The authors aimed to verify whether these parity associations are involuntary and automatic, thereby supporting the genuineness of the subtype. To test this, the researchers devised a computerized reaction time task inspired by the shape-sorter anecdote. The study included Synaesthete R, a 33-year-old woman with consistent stimulus-parity associations, and 10 control participants without synaesthesia. In the task, participants viewed a target shape followed by two colored bars, each containing a shape. Participants had to indicate the location (top or bottom) of the shape matching the target. The experimental design manipulated the congruency between the synaesthetic parity of the target shape and the parity of the background color on which it appeared. Two color pairs (blue-red and green-grey) were used to ensure effects were driven by parity rather than direct shape-color links. The study predicted that Synaesthete R would respond faster to congruent trials than incongruent ones, while controls would show no such effect. The results confirmed the hypothesis for Synaesthete R, who exhibited significantly faster reaction times for target-congruent trials (mean = 623 ms) compared to target-incongruent trials (mean = 823.8 ms). This 218 ms difference indicates that incongruent parity associations caused interference, slowing her responses. Statistical analysis revealed a significant main effect for target congruency, with no significant effects for distractor congruency. In contrast, none of the 10 control participants demonstrated significant effects for target or distractor congruency, nor did they show interactions between these factors. The controls’ reaction times varied minimally across trial types, confirming that the observed interference was specific to the synaesthete’s perceptual experience. The findings provide the first objective demonstration of automaticity in stimulus-parity synaesthesia, validating the genuineness of this rare subtype. The study concludes that parity associations are involuntary and interfere with task performance even when parity is irrelevant to the goal. This supports the view that synaesthetic concurrents are automatically generated rather than strategically applied. Furthermore, the authors propose that their spatial matching paradigm offers a novel method for assessing automaticity in other subtypes involving conceptual concurrents, such as personality traits, which lack direct physical representations. This approach expands the toolkit for investigating the cognitive mechanisms underlying diverse forms of synaesthesia.

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• automaticity skill acquisition