Hearing and Speech: Comprehensive Lecture Notes

PSYCH 313 Learning Outcomes

  • By the end of this course, students will be able to:
    • Describe and explain the complexity of human communication at a beginning level, and the significance of it to human social, emotional, and cognitive well-being.
    • Gain an understanding of the breadth of disorders which have an impact on communication skills, in the context of the whole person, and those around them.
    • Gain some practical skills in the transcription and analysis of speech and language, and the measurement of hearing and auditory processes.
    • Identify and critically analyze the impact of communication difficulties, in both children and adults.

Course Schedule

  • Week 8 (begins 5 May)
    • Topics:
      • Introduction to hearing & the link between speech and hearing (Welch).
      • Aphasia, TBI, and other acquired language disorders (Friary).
    • No tutorial this week.
  • Week 9 (begins 12 May)
    • Topics:
      • Fluency Disorders (Sultana).
      • Hearing & balance disorders (Purdy).
    • Acquired language impairment in adults (test conditions).
  • Week 10 (begins 19 May)
    • Topics:
      • Hearing loss in adulthood (Welch).
      • Psychosocial aspects of hearing loss in adults (Welch).
    • Tutorials: Anatomy of the ear & the central auditory system.
  • Week 11 (begins 26 May)
    • Topics:
      • Perspectives and experiences of hearing loss (Manuel).
      • Hearing loss in children & supporting families of children with hearing loss (Purdy).
    • Auditory Processing (Assessed content).
  • Week 12 (begins 2 Jun)
    • Topics:
      • Sign language and Deaf culture (Welch).
      • Exam Preparation (Leung).
    • Assessments: Auditory processing lab & Exam. No tutorial this week.

Hearing Loss: A Global Health Concern

  • Hearing loss is ranked as the fifth leading cause of years lived with disability in the Global Burden of Disease Study 2013.
  • It is higher than many other chronic diseases like diabetes, dementia, and chronic obstructive pulmonary disease.
  • However, hearing loss receives limited research funding and public awareness.
  • Global multidisciplinary and collaborative efforts are urgently needed to address the health needs of the child and adult with hearing loss.
  • Hearing loss cannot and must not continue to be a silent epidemic (The Lancet, Vol 387 June 11, 2016).

Sound and Hearing

  • ICF framework:
    • International Classification of Functioning, Disability and Health
  • Hearing and Speech

Sound Waves

  • Sound travels in waves, characterized by high and low pressure areas.
  • Low frequency:
    • Example: 100 Hz
  • High frequency:
    • Example: 10,000 Hz

Anatomy of the Human Auditory System

  • Outer Ear:
    • Pinna
    • External auditory canal
    • Lobule
  • Middle Ear:
    • Malleus
    • Incus
    • Stapes
    • Eardrum (Tympanic Membrane)
    • Eustachian tube
  • Inner Ear:
    • Semicircular canals
    • Vestibular-cochlear nerve
    • Cochlea

Inner Ear Details

  • Cochlea: Contains the cochlear duct, perilymph space, and endolymph.
  • Key Structures:
    • Semicircular canals
    • Ampulla
    • Vestibular nerve
    • Utricle (in vestibule)
    • Saccule (in vestibule)
    • Oval window
    • Round window
    • Cochlear duct
    • Cochlear nerve
    • Modiolus
    • Scala tympani
    • Vestibular (Reissner's) membrane
    • Scala vestibuli
    • Tectorial membrane
    • Basilar membrane
    • Hair cells
    • Supporting cells
    • Organ of Corti

Organ of Corti

  • Contains two populations of sensory hair cells:
    • Inner Hair Cells: Primary role as sensory receptor (Pickles, 1988).
    • Outer Hair Cells: Primary role in cochlear amplifier; electromotility.

Hearing with the Ear

  • Outer Ear: Sound.
  • Middle Ear: Vibration (Tympanic Membrane, Middle-Ear Cavity (air), Bone of Skull, Eustachian Tube; Malleus, Incus, Stapes).
  • Inner Ear: Cochlea, Auditory Nerve.

Inner Ear - Cochlea

  • Vibration:
    • Oval window
    • Round window
    • Cochlear duct
    • Perilymph space
    • Endolymph
    • Cochlear nerve
    • Modiolus
    • Scala tympani
    • Vestibular (Reissner's) membrane
    • Scala vestibuli
    • Tectorial membrane
    • Basilar membrane
    • Hair cells
    • Supporting cells
    • Organ of Corti.

The Traveling Wave

  • Base: High frequency.
  • Apex: Low frequency.

Stereocilia

  • Stereocilia (10 μm).

Shearing Force on Hair Cells

  • Tectorial membrane
  • Hair cells
  • Basilar membrane
    • Shear force
    • Displacement force

Transduction of Sound Energy to Nerve Information

  • Force on hair cells leads to the opening of ion channels (K+, Ca2+) via tip links.
  • Upward movement of the basilar membrane opens channels, causing depolarization.
  • Downward movement closes channels.

Cochlear Hair Cell

  • Endolymph: High K+K^+ concentration.
  • Perilymph: Contains voltage-gated calcium channels.
  • Depolarization leads to calcium influx, causing vesicles filled with neurotransmitters to release their contents into the synaptic cleft.
  • Neurotransmitter binds to receptors on the afferent nerve, transmitting the signal.

Inner Hair Cell

  • Excited hair cell releases neurotransmitter to the auditory nerve.
    • Ribbon
    • Synapse
    • Afferent nerve fiber
    • Auditory nerve
    • Hair bundle
    • Active zone
    • Synaptic vesicles
    • Calcium channels
    • Synaptic cleft
    • Post-synaptic receptors
    • Readily releasable pool of vesicles

Range of Frequencies Humans Can Hear

  • Approximately 2020 Hz to 20,00020,000 Hz.

Hearing Ranges of Animals

  • Hearing ranges of various animals (Red Ear Turtle, Bullfrog, Pigeon, Mouse, Rat, Hamster, Rabbit, Guinea Pig, Dog, Cat, Pig, Japanese Macaque, Human) compared; differing frequency sensitivities.

Range of Sound Levels in Decibels

  • Sound Level (dB Leq) - Example:
    • 140140 - Jet aircraft taking off
    • 120120 - Loud concert
    • 100100 - Petrol lawnmower
    • 8080 - Busy street
    • 6060 - Normal conversation
    • 4040 - Quiet room in a house
    • 2020 - Whisper
    • 00 - Threshold of hearing
    • NB: These values are generic and do not account for the proximity of the sound source to the ears.

Measuring Sound Level

  • Sound level meter.
  • Decibels (dB).
  • Logarithmic scale.
  • Sound level meters use dB(A) Leq.
    • dB(A): sound is filtered to include only sounds relevant to human hearing.
    • Leq: Level is averaged over time.
  • Hearing tests use dB hearing level (dB HL).
    • Relative to normal hearing.
    • Zero dB HL is the threshold of a person with averagely good hearing.

Pure-tone Audiogram

  • "Speech banana"
  • A graphical representation of hearing thresholds at different frequencies.
    • dB HL scale: Loud to Soft.
    • Frequency (Hz): Low Pitched to High Pitched.
  • Hearing Loss Categories:
    • Normal Hearing: Up to 2525 dB HL.
    • Mild Hearing Loss: 2626 to 4040 dB HL.
    • Moderate Hearing Loss: 4141 to 7070 dB HL.
    • Severe Hearing Loss: 7171 to 9090 dB HL.
    • Profound Hearing Loss including deafness: +9191 dB HL.

Typical Age-Related Hearing Loss (Presbyacusis)

  • Age-related permanent threshold shift in decibels (dB).
  • Median audiograms for males and females based on data in International Standard ISO 1999 shown.

ICF Framework

  • Health Condition (disorder/disease) impacts on:
    • Body function & structure (Impairment).
    • Activities (Limitation).
    • Participation (Restriction).
    • Influenced by Environmental Factors and Personal Factors.

ICF Framework Details

  • Two Parts: Functioning and Disability.
    • Body functions and structures: Anatomy, physiology, pathology, etc.
    • Activity and participation: Ability to take part in activities of daily life.
  • Contextual:
    • Environmental: Factors outside personal control (e.g., family, laws, cultural beliefs).
    • Personal: Not specifically coded in the ICF because of the wide variability among cultures but influences a person's functioning.

Hearing Loss Impacts

  • Hearing loss affects:
    • Sound detection.
    • Sound discrimination.
    • Speech discrimination.
    • Attention functions.
  • Influenced by:
    • Age, gender, SES etc.
    • Sound (intensity & quality).
    • Technology to assist communication.
    • Listening environment.
    • Discussion.
    • Complex interpersonal interactions.
    • Learning to read.
    • School education.

Acoustic Characteristics of Speech

  • Level: Measured in decibels (dB).
  • Pitch: Fundamental frequency (F0) measured in Hertz (Hz).
  • Spectral energy distribution: Measured in level (dB) at each frequency (Hz).
  • Timing – rate, pauses, voice onset time: Measured in milliseconds (ms).

Effects of Hearing Loss on Speech

  • Cannot detect speech sounds below the level of hearing at each frequency.
  • Impact on speech perception depends on the type of hearing loss.
  • Even when the level of speech is high enough for detection, ability to identify speech sounds may be poor due to:
    • Loss of frequency resolution.
    • Loss of temporal precision.
    • Greater ambiguity in speech sounds due to loss of redundancies.

Listening Environment

  • Poor listening conditions have a stronger impact on speech intelligibility for people with hearing loss:
    • Background noise is harder to cope with because of reduced frequency specificity.
    • Reverberation causes confusion between speech sounds because of poorer temporal discrimination.
    • Fast speech is harder to follow because longer processing time is required.

Understanding Spoken Language with Hearing Loss

  • Most hearing loss is in high frequencies, while many speech sounds are in low frequencies, so a lot of speech is still available.
  • Strategies for understanding:
    • Auditory streaming.
    • Auditory Attention.
    • Redundancy in speech.
    • Visual cues.
    • Hearing aids or cochlear implants.
    • Sign language.
  • Involves:
    • Auditory processing.
    • Auditory-visual processing.
    • Electronics.
    • Visual language processing.

Auditory Feedback and Speech Production

  • Accurate production of speech sounds is influenced by auditory feedback (hearing our own speech).
  • Hearing loss also affects speech production.

Effect of Loss of Auditory Feedback on Speech

  • Measured peaks of energy (formants) in vowel sounds in normally-hearing vs. postlingually deafened adults.

Vowel Production

  • Expiration: Airflow from lungs.
  • Source: Vibration of vocal folds.
  • Filter: Vocal tract resonances (Frequency -> Amplitude).
    • Peaks of acoustic energy (formant frequencies) depend on the position of articulators.
      • F1 relates to jaw position.
      • F2 relates to tongue shape.

Effect of Loss of Auditory Feedback on Speech

  • Reduced vowel frequency range.

Summary

  • The auditory system is complex.
    • Different parts of the auditory pathway can be affected in people with hearing loss.
  • The ICF framework provides a good model for thinking about the effects on body function and everyday life activities and participation.
  • Hearing loss can have a significant impact on activities and participation.
  • The listening environment is very important for people with hearing loss.
  • Speech production and perception (hearing) are closely linked.
    • Loss of auditory feedback due to hearing loss in adults has a significant impact on speech production.