A colorful advantage in iconic memory.

Synesthesia is a benign neurodevelopmental condition in which stimulation of one sensory modality evokes experiences in a second, unstimulated modality (Simner and Hubbard, 2013). In grapheme-color synesthesia (GCS), which is experienced by 1-2% of adults, synesthetes reliably and involuntarily experience specific colors when viewing blackand-white graphemes. Previous case-studies have identified synesthetes with spectacular memory (Luria, 1968; Smilek, Dixon, Cudahy, & Merikle, 2001) and group studies have found advantages for synesthetes compared to nonsynesthetes in long-term memory (Rothen, Meier, & Ward, 2012). Here, we tested whether similar advantages are also present in earlier stages of memory. We tested visual iconic memory-the sensory store for vision-which has a very large capacity, but decays approximately 1000 ms after stimulus offset (Chow, 1985; Sergent et al., 2013; Sperling, 1960). We tested 20 synesthetes and 20 nonsynesthetes in a direct replication of the Sperling (1960) Partial Report Paradigm using letters (Experiment 1) and non-alphanumeric symbols (Experiment 2) as stimuli. Overall, synesthetes had a greater iconic memory capacity than nonsynesthetes when presented with synesthesia-inducing letter stimuli. This advantage was reduced when they were presented with non-synesthesia inducing symbol stimuli. Critically this advantage was most prominent when memory was stressed by asking participants to remember large arrays. Our results demonstrate that synesthetic memory advantages extend to the earliest stages of memory, and suggest that advantages in later stages of memory may arise from these earlier advantages.