Module 4: CSD 232

  • Audiology and Hearing Loss

    • Sound Consists of vibrations through a medium

    • The vibrations are periodic motion of molecules from a state of rest

      • Ex: Pendulum

  • Two types of vibrations

  • Longitudinal (linear) sound

    • Longitudinal (ears) and Transverse (eyes) waves

    • Longitudinal waves move linear and produce compressions and rarefactions which change the pressure (or density) passes through a medium\

    • Waves can go through solids, liquids as well as gasses (ex: air)

    • Sound is a type of longitudinal wave that is perceived by the ears

      • When particles come together it is a compression

      • When particles move apart is a rarefaction

    • Transverse Waves (perpendicular) vision

      • Transverse waves consist of crests and troughs as they propagate through solids with no variation in pressure (or density) in the medium

      • Movement of particles is at a right angle or perpendicular

      • Light is a type of transverse wave that is perceived by the eyes

  • Frequency is the number of cycles of oscillation per second

    • The unit for f is Hz

  • Intensity

    • Loudness is the amplitude or the intensity of vibration (measured in dB and varied units

    • How much movement for individual molecules

      • Determines the intensity

  • Audiogram

    • X-axis frequency in Hz

    • Y-axis intensity in dB, note axis is reversed

    • Air Conduction Thresholds (AC)

    • Bone conduction Thresholds (BC)

    • For left ear and right ear each

    • Right ear thresholds are plotted as Red Rounds

    • Left ear thresholds are plotted as Blue Crosses

    • Higher the number louder the sound, lower the number quieter the sound on sound chart

  • Threshold-Intensity at a particular frequency that one can detect 50% of the time

  • Pitch

    • Pitch is frequency of vibration

  • Degrees of hearing loss

  • Several levels to hearing loss

    • Difficulty with distant or faint speech

    • Difficulty following conversational level speech

    • Can hear only loud speech

    • Difficulty understanding even loud speech: may require alternative communication system

    • Usually considered deaf: cannot depend on auditory system alone to obtain information, no amount of loudness can help at this point

  • Degrees of hearing loss

    • Normal hearing

    • Mild hearing

    • Moderate hearing

    • Moderately severe

    • Severe hearing loss

    • Profound hearing loss (cannot use hearing to communicate at all, deaf)

  • Conductive hearing loss

    • Problem in the outer or middle ear (you can experience this type of hearing loss without harm) 

    • Causes

      • Microtia or small malformed pinna or ear canal

      • Atresia or complete of canal at pinna or beyond

      • Cerumen (wax) 

      • Otitis media (middle ear inflammation/infections)

    • Early identification and treatment helps control the hearing loss, usually treatable

  • Sensorineural hearing loss 

    • Problem in the inner ear or beyond

    • Causes could be congenital or acquired

    • Usually permanent, not medically treatable

    • Classification

    • IT can be genetic (hereditary) or acquired (non-hereditary)

    • Congenital or adventitious (age of onset perspective)

    • Prelingual (before child has acquired language) or postlingual (after the child has acquired language) (sp & lg dev perspective)

    • Causes

      • Aplasia-inner ear developmental problems

      • Atresia-Outer ear developmental problems

      • Several syndromes and infections (rubella, meningitis)

      • Ototoxicity (penicillin)

      • Noise induced hearing loss

      • Presbycusis (hearing loss because of normal aging)

  • (1+2) Mixed hearing loss, has to be present in the same ear

    • Combinations of conductive and sensorineural hearing loss

      • Why might this not be treatable?

      • The conductive hearing loss is all we can treat to mixed hearing loss in not fully treatable

  • Central Auditory Processing Disorders

    • CAPD problems typically affect brainstem pathways/auditory cortex (auditory nervous system)

    • Hearing thresholds may be normal, but ability to use and interrupt auditory information is lost

    • Assessment of CAPD is by a certified Audiologist

  • Noise Induced Hearing Loss (NIHL)

  • Types of Threshold Shifts

    • Hearing loss results from exposure to intense noise

    • Hg loss is measurable in terms of threshold shifts

    • If the hearing recovers, the shifts are temporary (aka Temporary Threshold shift or TTS)

    • If the hearing fails to recover, the shifts are permanent (Permanent Threshold Shift or PTS)

  • Risks

    • Aspirin may increase TTS
      Men are more likely to end up with NIHL

    • Children exposed to loud toys are at risk of HL- 

    • The individual size of the cars can vary the sound level by up to 25 dB

  • Types of Changes in Cochlea

    • Biological changes in the hair cells

    • Physical dislodging of hair cells

    • Changes in blood supply to the Cochlea

    • Rupture of Reissner’s membrane

    • Detachment of the organ of Corti from the basilar membrane

  • Acoustic Trauma

    • Acoustic trauma is NIHL from impulsive sounds

    • Typical acoustic notch on audiogram (from 4k-6k Hz)

      • Truck drivers in Canada, left ear affected (due to wind noise), Hunters

  • Noise Standards

    • NIOSH standards for max exposure, 85 dBA for 8 hours

      • If you turn up loudness by 3 dB or “double intensity”

      • Down the time by half

    • Dosimeters (measure the amount or intensity of sounds in noisy areas

    • Recreational audiology (noise exposure due to hobbies)

  • Noise Control

    • Control at source

      • Modify equipment

        • Maintain machines

        • Develop quieter machines

        • Use different processes

        • Reduce vibrations

        • Reduce structure-borne sounds

    • Control transmission

      • Absorb sound (carpets, curtain, acoustic tiles_

      • Create a barrier (close doors, windows, add partitions

      • Gasket (seal air leaks)

      • Dampen (reduce intensity)

      • Isolate

    • Protect at ear level

      • Ear plugs

      • Earmuffs

      • Helmets with plugs

      • Turn down the volume

  • Presbycusis

  • Age Induced Hearing Loss

    • Deterioration begins at birth 

      • In men by early 60s in women by late 50s

    • Significant difficulty in speech recognition

    • Cause is aging

      • Parts of auditory system affected include TM, Ossicular chain, cochlear windows, and CANS

  • Gender difference

    • Men have poorer sensitivity above 1kHz

    • Women have poorer sensitivity below 1kHz

  • Treatment

    • Speak slower rather than louder

    • When talking to people who have presbycusis

      • Use hearing Aid

        • Body aid, BTE (BEHIND THE EAR), ITC(IN THE CANAL), ITE (IN THE EAR), CIC Eyeglass   BC

        • Left is blue right is red