Is there a direct neural correlate for memory-trace formation in audition?

Recently, Haenschel et al. (2005) suggested that a positive event-related potential wave called 'repetition positivity' (RP) is a direct neural correlate of the formation of sensory memory traces. We investigated whether RP is elicited by familiar vowels that have previously been suggested to form accurate memory representations faster than unfamiliar sounds. No evidence for RP elicitation was found, however, even though memory representations for the vowels were formed. Instead of finding an increasing positive response along with stimulus repetition predicted by the RP hypothesis, we found that N1 and sustained potential were enhanced in amplitude for the familiar vowels as compared with unfamiliar sounds, indicating stronger activation at the auditory cortex.