The identification of synthetic vowels by patients using a single-channel cochlear implant

Vowel perception in a /b~:b/-context of patients using a singlechannel extra-cochlear implant developed in Vienna has been studied by means of synthetic speech. Three patients were asked t o adjust the f i r s t and second formant of a synthetic vowel sound so that they perceived the sound as a given long Swedish vowel. To study the effect of training, the experiment was made a t two sessions about a year apart. Normal hearing 1 ist eners ident i f ied the vowel sounds generated by the subjects. The results of the experiment were analyzed i n confusion matrices and as F1-F2 plots. A clear effect of training could be seen. Two years after implanta t ion the best subject could ad just the frequency of F1 and F2 quite close t o the correct values. Int roduct ion It has long been known that stimulation of the auditory nerve with a weak electric current results in auditory sensation. During the la te f i f t ies the f i rs t experiments were made t o use th is effect in an aid for the deaf. Since the beginning of the seventies, muse at the Ear Research Institute in Los Angelses has been implanting deaf subjects with a simple single channel codhlear implant (House, 1983). A t the same time research and development has been going on at several laboratories both on s i ngle-channel and mult i-channel devices. In a s ingle-channel cochlear implant, the electrode is either placed in the middle ear close t o the round window, or inserted a few millimeters into the codhlea. In a multi-channel device, the electrodes are placed i n the cochlea at different posit ions along the basilar membrane. I n a single-channel implant, it seems that only t ime-intensit y informat ion i n a speech signal can be transmitted. In a mult iple-channel device, some frequency selectivity might he obtained by stimulating different nerve endings along the basilar membrane. * This piper was presented at the XIth ICPhS, Tallinn, USSR, Aug. 1987.