Consistency and strength of grapheme-color associations are separable aspects of synesthetic experience

•Synesthetic status is usually determined by testing consistency of associations.•Consistency may not be entirely reliable: associations can change with age or mood.•We compared consistency to strength of association in grapheme-color synesthetes.•Strength identified synesthetes but was unrelated to consistency.•Synesthetes may be under-detected by tests that rely on consistency. Consistency of synesthetic associations over time is a widely used test of synesthesia. Since many studies suggest that consistency is not a completely reliable feature, we compared the consistency and strength of synesthetes’ grapheme-color associations. Consistency was measured by scores on the Synesthesia Battery and by the Euclidean distance in color space for the specific graphemes tested for each participant. Strength was measured by congruency magnitudes on the Implicit Association Test. The strength of associations was substantially greater for synesthetes than non-synesthetes, suggesting that this is a novel, objective marker of synesthesia. Although, intuitively, strong associations should also be consistent, consistency and strength were uncorrelated, indicating that they are likely independent, at least for grapheme-color synesthesia. These findings have implications for our understanding of synesthesia and for estimates of its prevalence since synesthetes who experience strong, but inconsistent, associations may not be identified by tests that focus solely on consistency.