Neural Resolution of Formant Frequencies in the Primary Auditory Cortex of Rats.

Christian Honey,Jan Schnupp

doi:10.1371/journal.pone.0134078

Abstract

Pulse-resonance sounds play an important role in animal communication and auditory object recognition, yet very little is known about the cortical representation of this class of sounds. In this study we shine light on one simple aspect: how well does the firing rate of cortical neurons resolve resonant (“formant”) frequencies of vowel-like pulse-resonance sounds. We recorded neural responses in the primary auditory cortex (A1) of anesthetized rats to two-formant pulse-resonance sounds, and estimated their formant resolving power using a statistical kernel smoothing method which takes into account the natural variability of cortical responses. While formant-tuning functions were diverse in structure across different penetrations, most were sensitive to changes in formant frequency, with a frequency resolution comparable to that reported for rat cochlear filters.

Highlights

Pulse-resonance sounds (PRSs) are the backbone of most animals vocalization [1] and vowels in human speech are a prominent member of this sound class
Most mammalian vocal sounds, including vowels in human speech, are examples of PRSs, in which the fundamental frequency of the harmonics is determined by the glottal pulse rate emanating from the larynx, and the formant frequencies depend on the size of resonant cavities in the vocal tract
We examined whether cortical depth or location had a systematic influence on formant frequency resolution of two-formant PRSs

Summary

Introduction

Pulse-resonance sounds (PRSs) are the backbone of most animals vocalization [1] and vowels in human speech are a prominent member of this sound class. They are richer and more ecologically relevant than the pure tones or noise bursts more commonly used in physiological studies, but they remain simple enough to be described by a relatively small number of parameters. Most mammalian vocal sounds, including vowels in human speech, are examples of PRSs, in which the fundamental frequency of the harmonics is determined by the glottal pulse rate emanating from the larynx, and the formant frequencies depend on the size of resonant cavities in the vocal tract. The pitch of such vocal sounds depends on their fundamental frequency, but the “identity” of the sound is mostly recognized from its formant frequencies [2]

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