Individual variability for the strength of synesthetic associations.

<p><i>Left</i>: Interference for the Color Naming task (x-axis) is negatively correlated with the speed to name synesthetic colors relative to real colors (y-axis). <i>Right</i>: The distribution of the index of photism strengh is unimodal, with a few subjects with extreme values. The subject with the largest photism strength could be unambigously characterized as a “projector” based on questionnaires and phenomenological reports, while the subject with the second largest value was characterized as an associator. Several other subjects, with lower values, were tentatively categorized as projectors based on questionnaires. The average effect size of the congruency effect in the color naming task (x-axis of the left panel) is 65 ms (CI = [34 96] ms). If excluding the two large values (above 3 standard deviations), it is 46 ms (CI = [34 59] ms).