Sensory Neuroscience: Hearing and speech

Though Neuroscience is listed as a prerequisite, it will not prepare you adequately for this text until it is finished (and perhaps not even then).

This covers some introductory aspects of the mechanisms of human hearing, sound localization, speech perception and speech production. The reader should have a partial undergraduate education (2nd or 3rd year) in either neuroscience (or psychology, provided the focus is on human biological psychology). This book explains only jargon which is unlikely to have been encountered previously - a working vocabulary of neuroscience terms is expected and required for understanding.

It explores many of the processes which occur between the occurrence of a sound in the world and the perception of that sound. In particular, there is a focus on speech as a distinct type of sound which occurs often in the environment of humans.

The processes involved operate on several levels:

• Mechanical (transmission of sound from its source to the outer and middle ears)
• Biophysical (transduction in the cochlea)
• Neurophysiological (representation of the sound in the nervous system and sound localization)
• Perceptive (detecting the sound and discrimination)
• Cognitive (identifying the sound)

The text is laid out such that an interested reader can follow it from start to end to learn the subject matter covered - it is not a reference text.

Table of contents

• Sound
  • The nature and properties of sound
  • Key terms: frequency, amplitude, phase, period, wavelength, diffraction, interference, standing waves, filtering, brick-wall, cutoff slope, impedance
  • Fourier analysis, fundamental frequency, harmonics
  • Measuring sound: dB scales, short-term/long-term spectra & rise time

• Outer & middle ear
  • Structure and "funneling" function of the pinna
  • Anatomy of the middle ear
  • The impedance mismatch problem
  • Conductive hearing loss

• Inner ear
  • Gross anatomy of the cochlea
  • Basilar membrane mechanics
  • Passive and active components
  • Fine structure of the Organ of Corti
  • Transduction: hair cell receptor potentials
  • Innervation patterns of the two types of hair cells
  • Genesis of auditory nerve fiber tuning and the roles of the two hair cell populations
  • Cochlear hearing loss

• Auditory nerve
  • Two types of auditory nerve fibers
  • Phase-locking
  • Spatial & temporal neural coding
  • Rationale for Cochlear Implant programs

• Central auditory nervous system
  • Structural and functional organization
  • Brainstem-evoked potentials in audiological & neurological diagnosis

• Sound localization
  • Nature of binaural sound localization cues: effects of sound frequency and azimuth
  • Neural coding of binaural sound localization cues, interaural phase and intensity differences
  • Behavior-lesion studies of sound localization

• Speech
  • Distinguishing speech and language
  • Nature of speech sounds

• Speech production
  • Generation of speech sounds: the source-filter theory
  • The problem of invariance in speech perception
    • Solution: Liberman's motor theory
    • Testing the motor theory: Linguistic feature detectors
    • Testing linguistic feature detectors: Problem of invariance again

• Speech perception
  • The acoustic account of speech recognition
  • The auditory cortex and "pure word deafness"