Representation of Vowel-like Spectra by Discharge Rate Responses of Individual Auditory-Nerve Fibers
Glenn LE Prell1, Murray Sachs, Bradford May
1Departments of Biomedical Engineering and Otolaryngology-HNS, Center for Hearing and Balance, The Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Abstract:
Neural representations of complex vowel-like spectra have been extensively characterized by population studies of single fiber responses in the auditory nerve of anesthetized cats. With traditional population measures, neural rate responses to formants (energy peaks) and troughs (energy minima) in a vowel's amplitude spectrum are measured by sampling several fibers, each tuned to one spectral feature. Similar analyses are rarely performed on structures in the central auditory system primarily due to the difficulty of obtaining the samples of neurons that are needed to construct complete population response profiles. As an alternative to population measures, this study introduces a method for estimating population measures from the responses of individual auditory-nerve fibers. With our spectrum manipulation procedure (SMP), a response profile was created by sampling the responses of individual fibers as important spectral features were shifted to the units' best frequency (BF, the frequency to which a neuron is most sensitive). Observed SMP rate profiles showed the same effects of rate saturation, two-tone suppression, and spontaneous rate as population measures. In addition, when analyzed with signal detection methods, changes in rate responses within individual neurons revealed new insights into how the neural representation of vowel stimuli may be influenced by unit threshold and best frequency. SMP sampling techniques should prove useful in future studies of speech encoding in the central auditory system.
Related Concept Videos
The Cochlea
Hearing
Perceiving Loudness, Pitch, and Location
Place theory, or place coding, suggests that different pitches are heard because various sound waves activate specific locations along the cochlea's basilar membrane. The brain determines the pitch of a sound by identifying...
Hair Cells
Perception of Sound Waves
The pitch of a sound depends on the frequency and the pressure amplitude of the source. Two sounds of the same frequency...
Sound Waves: Resonance


