Enhanced Memory in Synaesthesia is Primarily linked to the Familiarity Component of Recognition Memory

People with synaesthesia (e.g. letters evoking colours) have enhanced memory on many standard laboratory tasks, but relatively little is known about the underlying mechanism. In these studies we determined whether the memory advantage of synaesthetes was compromised to the same extent, and in the same way, by manipulations known to adversely affect memory. In Study 1, we employed a continuous recognition memory paradigm in which previously studied items in an early block become lures in a subsequent block, hence requiring careful monitoring of temporal context. In Study 2, we employed a standard levels-of-processing manipulation in which shallow encoded items disrupts memory performance. In both studies, participants indicated their level of confidence from which we estimated separate familiarity and recollection parameters within a dual-process framework (Yonelinas & Parks, 2007). Synaesthetes showed comparable levels of susceptibility to these memory manipulations despite having significantly better performance overall. However, whilst temporal context confusion and shallow processing affected both estimates of recollection and familiarity, the group difference between synaesthetes and controls was carried by the familiarity component alone. This suggests that the mechanisms giving rise to enhanced memory in synaesthesia loads primarily on familiarity-related processes.