CSD 3000 DEAFNESS IN SOCIETY Topic 2 HEARING
Sound System Source Any vibrating object Medium Any gas, liquid or solid Receiver anything designed to detect the vibrations within the medium originating from the source
A Common Sound System Illustration of the distribution of molecules surrounding a source in an instant in time
Condensation and Rarefaction Bands of condensation and rarefaction emanating from a sound source
Propagation of a Disturbance Through a Medium Notice that as time goes on, molecules farther from the source become affected by the disturbance.
Important Physical Characteristics of Sound Frequency Rate of pressure change as a function of time Measured as cycles/sec or Hertz The primary determiner of pitch Intensity Magnitude of the pressure change Measured as the decibel (dB) The primary determiner of loudness
Frequency and Intensity Sounds a and c share the same frequency and sounds b and c share the same intensity
Loudness and Intensity Here are some common sounds and their decibel equivalents
The Hearing System Basic schematic diagram of the entire auditory system
The Outer Ear Major Landmarks: 1. Pinna 2. External Auditory Meatus 3. Tympanic Membrane
Function of the Outer Ear 1. Collect and funnel sound to the eardrum 2. Protection 3. Resonance
The Middle Ear Major Landmarks: 1. Middle Ear Space 2. Eustachian Tube 3. Mastoid 4. Oval and Round Windows 5. Ossicles
Function of the Middle Ear 1. Amplifier and transformer 2. Protection
The Inner Ear Major Landmarks: 1. Bony Labyrinth 2. Membranous Labyrinth 3. Auditory and Vestibular Portions 4. Cochlea
The Organ of Corti
Central Auditory Pathways
Putting It All Together….
Causes of Hearing Loss Ways to Categorize Etiology: 1. By Site of Lesion Conductive Hearing Loss Sensorineural Hearing Loss Central Auditory Processing Disorder 2. By Time of Onset Congenital vs. Adventitious Prelingual vs. Postlingual
Hearing Loss in Children Prelingual Causes 1. Genetic Nonsyndromal Recessive Hearing Losses
Nonsyndromal Recessive Hearing Loss Heredity Pattern Implications: No family history Most members are carriers of the disorder
Hearing Loss in Children Prelingual Causes 1. Genetic Nonsyndromal Recessive Hearing Losses Syndromes
Hearing Loss in Children Prelingual Causes 1. Genetic 2. Premature birth and/or complications during delivery
Hearing Loss in Children Prelingual Causes 1. Genetic 2. Premature birth and/or complications during delivery 3. Prenatal Infections Rubella Cytomegalovirus Herpes Simplex HIV Toxoplasmosis
Hearing Loss in Children Postlingual Causes Viral Infections Otitis Media
Adult Onset Hearing Loss 1. Noise Exposure 2. Presbycusis 3. Ototoxicity 4. Trauma 5. Otologic Disease Otosclerosis Meniere’s Disease Auditory Nerve Tumors
Hearing Assessment Main questions 1. Is hearing normal? 2. What is the degree of hearing loss? 3. What type of hearing loss is it?
Pure Tone Audiometry Measurement of pure tone thresholds between Hz Air conduction Bone conduction
Pure Tone Audiometry The results of PTA tell us 1. Air conduction thresholds across frequency tells us if hearing is normal or not 2. If hearing by air conduction is NOT normal, the thresholds tell us the degree of hearing loss
Average Air Conduction Threshold and the Degree of Hearing Loss
Pure Tone Audiometry The results of PTA tell us 1. Hearing by air conduction across frequency in each ear tells us if hearing is normal or not 2. If hearing by air conduction is NOT normal, the thresholds tell us the degree of hearing loss 3. Differences between hearing by air conduction and hearing by bone conduction tell us the type of hearing loss
Determining the Type of Hearing Loss
Hearing Assessment Speech Audiometry Nonbehavioral measures