The broad aims of this project are to understand normal auditory processing of speech sounds, information that can be used to understand and provide rehabilitation for deficits in hearing and speech comprehension. Responses to speech sounds by the auditory nerve (AN) of an animal model, the chinchilla, demonstrate how information about speech sounds is encoded by the mammalian auditory system. A peripheral auditory system like most mammals and the ability of the chinchilla to demonstrate phoneme perception and categorization make it an excellent animal model. Unique temporal patterns of encoding in the AN will be identified for each phoneme across variable acoustics. Co-articulation with a vowel and the absence of normal voicing in whispered speech both alter the acoustics of a consonant. These temporal patterns will demonstrate the role that the auditory system plays in accurate human perception of one phoneme across acoustic profiles and what information is necessary for hearing-impaired people to understand speech. Responses of single AN fibers to normally-voiced and whispered speech will be recorded and analyzed to demonstrate phoneme-specific patterns of response. The specific questions to be asked for each aim: 1) What temporal patterns are characteristic of the AN response to each phoneme /d/ and /t/ across different acoustic profiles? This will be addressed by using as the stimuli four syllables /da/, /ta/, /dae/, and /tae/, from two speakers produced in both whispered and normal voicing. The AN responses to the eight tokens of each consonant will be compared using a global average peri-stimulus time (PST) histograms and local average PST histograms. 2) Are these temporal patterns unique to /d/ and /t/ or unique to the categories of voiced and unvoiced consonants? Four tokens of /b/ and /p/ will be used as stimuli to compare the AN response to consonants within and between voicing categories.
