Synesthesia Affects Verification of Simple Arithmetic Equations

ABSTRACT

To investigate the effects of color–digit synesthesia on numerical representation, we presented a synesthete, called SE, in the present study, and controls with mathematical equations for verification. In Experiment 1, SE verified addition equations made up of digits that either matched or mismatched her color–digit photisms or were in black. In Experiment 2A, the addends were presented in the different color conditions and the solution was presented in black, whereas in Experiment 2B the addends were presented in black and the solutions were presented in the different color conditions. In Experiment 3, multiplication and division equations were presented in the same color conditions as in Experiment 1. SE responded significantly faster to equations that matched her photisms than to those that did not; controls did not show this effect. These results suggest that photisms influence the processing of digits in arithmetic verification, replicating and extending previous findings.

Keywords:

• arithmetic verification
• numerical representation
• synesthesia

Acknowledgments

Portions of this work have been presented at the 47th Annual Meeting of the Psychonomic Society and the 78th and 79th Annual Meetings of the Eastern Psychological Association. We would like to thank Mallory Clark and Meridith Hurd for contributing to this work and Mouna Attarha and Melissa Talleda for help with data collection.

Notes

1. We used black as a standard condition encountered in real life. However, because SE's photism for 9 is black, the black digit condition may not be entirely neutral.

2. We also ran the same ANOVA that we ran on SE's data with Block as a random factor on data from the control participants and found no effect of color condition on RT or accuracy in any experiments.