Stability of memory traces for speech sounds in cochlear implant patients

For this study, we examined the perception and production of vowels by postlingually deafened patients with cochlear implant. Four patients and one normally hearing subject produced typical vowel sounds of Finnish by using a speech synthesizer. Also acoustic analyses of the pronounced vowels were made. The first (F1) and the second (F2) formant frequencies were measured. The mismatch negativity (MMN), a cortical cognitive auditory event related potential, was used to measure objectively the patients' preattentive discrimination of a prototypical /i/ sound from deviants differing in the F2 continuum. In the phonetic tests the hyperspace effect was seen also among the patients. The MMN, which reflects the phonetic discrimination ability, could be identified from the patient with the best vowel perception abilities. The phonetic memory traces once developed for vowels seem to remain quite stable even though they have not been activated by vowel information for years.