Yaro and Ward (2007) Yaro, C., & Ward, J. (2007). Searching for Shereshevskii: What is superior about the memory of synaesthetes?Quarterly Journal of Experimental Psychology, 60, 681–695. doi:10.1080/17470210600785208
A study whereby synesthetes performed better on Rey Auditory Verbal Learning Test (Spreen & Strauss, 1998)
Spreen, O., & Strauss, E. (1998). A compendium of neuropsychological tests: Administration, norms, and commentary (2nd ed.). New York, NY: Oxford University Press.