Representation of the vowel / ε / in normal and impaired auditory nerve fibers: Model predictions of responses in cats

• Published in: The Journal of the Acoustical Society of America 2007-07, Vol.122 (1), p.402-417
• Main Authors: Zilany, Muhammad S. A., Bruce, Ian C.
• Format: Article
• Language: English
• Subjects: Acoustic Stimulation; Animals; Auditory Threshold; Basilar Membrane - innervation; Biological and medical sciences; Cats; Cochlea - innervation; Cochlear Nerve - physiopathology; Computer Simulation; Ear and associated structures. Auditory pathways and centers. Hearing. Vocal organ. Phonation. Sound production. Echolocation; Fundamental and applied biological sciences. Psychology; Hair Cells, Auditory, Inner - physiopathology; Hearing Loss, Sensorineural - physiopathology; Models, Neurological; Phonetics; Pitch Discrimination; Reproducibility of Results; Sound Spectrography; Speech Acoustics; Speech Perception; Synaptic Transmission; Time Factors; Vertebrates: nervous system and sense organs; Vibration
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.2735117

The temporal response of auditory-nerve (AN) fibers to a steady-state vowel is investigated using a computational auditory-periphery model. The model predictions are validated against a wide range of physiological data for both normal and impaired fibers in cats. The model incorporates two parallel filter paths, component 1 (C1) and component 2 (C2), which correspond to the active and passive modes of basilar membrane vibration, respectively, in the cochlea. The outputs of the two filters are subsequently transduced by two separate functions, added together, and then low-pass filtered by the inner hair cell (IHC) membrane, which is followed by the IHC-AN synapse and discharge generator. The C1 response dominates at low and moderate levels and is responsible for synchrony capture and multiformant responses seen in the vowel responses. The C2 response dominates at high levels and contributes to the loss of synchrony capture observed in normal and impaired fibers. The interaction between C1 and C2 responses explains the behavior of AN fibers in the transition region, which is characterized by two important observations in the vowel responses: First, all components of the vowel undergo the C1/C2 transition simultaneously, and second, the responses to the nonformant components of the vowel become substantial.