Red, green, blue equals 1, 2, 3: Digit-color synesthetes can use structured digit information to boost recall of color sequences

Abstract

Digit-color synesthetes report experiencing colors when perceiving letters and digits. The conscious experience is typically unidirectional (e.g., digits elicit colors but not vice versa) but recent evidence shows subtle bidirectional effects. We examined whether short-term memory for colors could be affected by the order of presentation reflecting more or less structure in the associated digits. We presented a stream of colored squares and asked participants to report the colors in order. The colors matched each synesthete’s colors for digits 1–9 and the order of the colors corresponded either to a sequence of numbers (e.g., [red, green, blue] if 1 = red, 2 = green, 3 = blue) or no systematic sequence. The results showed that synesthetes recalled sequential color sequences more accurately than pseudo-randomized colors, whereas no such effect was found for the non-synesthetic controls. Synesthetes did not differ from non-synesthetic controls in recall of color sequences overall, providing no evidence of a general advantage in memory for serial recall of colors.

Keywords:

• Synesthesia
• Digits
• Color memory
• Short-term memory
• Bidirectional
• Sequences
• Serial recall

Notes

¹ We also calculated Bayes Factors (BF; Love et al., 2015) for the key contrasts. 200 ms Structured 5 vs. Baseline: Synesthetes BF₁₀ = 1.14, Controls BF₁₀ = 0.41; 500 ms Synesthetes BF₁₀ = 21.79, Controls BF₁₀ = 0.57. A BF of ~1 is an indication that we do not have enough power to differentiate whether there is evidence for the null or alternative hypothesis (Dienes, 2011) for synesthetes in the 200 ms case. We therefore only have clear evidence that there is no effect for controls in either condition, and that structure affects synesthetes in the 500 ms condition.

² We were unable to calculate false alarms in this way for synesthetes S7 and S12 and their corresponding controls because they had two identical color associations that corresponded to two different numbers.

³ It is worth noting that the lack of a significant structure effect in the fast presentation condition is unlikely to be due to an inability to perceive a rapid sequence of ascending or descending digits in the correct order. Research has shown that participants have little difficulty in perceiving and remembering other types of structured sequences, such as sentences presented word by word at rates of up to 10 words per second (e.g., Potter, Nieuwenstein, & Strohminger, 2008).

Additional information

Funding

ALT was supported by a Marco Polo scholarship and the Groningen University Fund. ANR acknowledges the support of the Menzies Foundation.