Figure 1.

Visual and Left Primary Motor Cortex Thresholds in Controls and Grapheme-Color Synesthetes

A 4 (stimulation area) × 2 (group) mixed-model analysis of variance (ANOVA) revealed that motor thresholds were higher than phosphene thresholds [F(3, 27) = 11.87, p < 0.001, η_p² = 0.57], and synesthetes displayed lower thresholds than controls [F(1, 9) = 105.15, p < 0.001, η_p² = 0.92]. These effects were qualified by a stimulation area × group interaction [F(3, 27) = 21.80, p < 0.001, η_p² = 0.71], reflecting reduced phosphene, but not motor, thresholds in synesthetes than controls. See also Table S1.

Data represent mean ± 1 SEM. ^∗p < 0.001.