Evoked Potential

Understanding the Hearing Aid Candidate

Problems faced by adults with hearing impairment
  • #1 definitive reason was financial
  • The interesting thing that is brought up is that the family receives considerable benefit
    • "you may have a hearing loss but your family has a hearing problem."
    • communication is rendered less rewarding with a family with someone with hearing loss
  • SRTs and UCLs measure the dynamic range of a persons hearing
    • you can do UCL for a tone
  • dynamic range is collected from pure tone assessment
  • example, if have a dynamic range of hearing at 4Khz of 20dB
    • level of hearing is at 80dB and UCL is at 100dB - 20dB dynamic range
    • someone will talk and the person won't hear, will raise voice and still won't hear, will yell and because of the dynamic range will feel like yelling; very limited range
    • a hearing aid will treat soft sounds different in this frequency range and how it's going to treat different levels of sounds; soft sounds a little bit, medium sounds a lot
  • a hearing aid will aid in the clarity for someone who is able to hear but not understand
  • frequency resolution is really important when talking about environments
  • for a vowel, it's partly a first formant but then it's a second formant, which could be missing too, could be more difficult to pick missing information because of frequency loss
Percentage of U.S. Citizens with Hearing Loss by Age
  • not surprisingly, the prevalence of hearing loss increases with increasing age
  • approximately 314 in 1,000 people over the age of 65 have hearing loss
  • 40-50% of people 75 and older have a hearing loss
  • 65% of the 30 million people with hearing loss are under 65
Decreased Audibility
  • Hearing-impaired individuals cannot hear sounds that are below their threshold
  • for speech it can be different depending on the intensity of the speech sounds
  • hearing in the low frequencies
  • hearing the high frequencies
  • distance from the speaker
  • the ear typically identifies the peaks in the spectrum to identify the sound
Decreased Dynamic Range
  • the amount of sound between the threshold of hearing and threshold of discomfort
  • in normal hearing adults it is typically 80-100dB
  • reduced in hearing impaired individuals due to
    • increased threshold
    • abnormal growth of loudness
Frequency Resolution
  • the ability of the system to analyze a sound into its component frequency
    • the more "fine tuned" a system, the greater number of frequencies analyzed, the better its frequency resolution
    • frequency selectivity
  • frequency resolution plays an important role in separating speech from background noise
Decreased Frequency Resolution
  • tonotopic representation of sounds in the auditory system
  • the cochlea has relatively sharp tuning curves
With Cochlear Hearing Loss
  • Flatter tuning curves
  • poor frequency resolution
  • poor speech discrimination
  • poor speech and distracter separation
  • with reduced frequency selectivity
    • intense low frequency components may mask lower intensity high frequency components
    • this is known as upward spread of masking
  • poor frequency resolution at high intensities
  • hearing impaired listeners are listening at high intensities to compensate for poor audibility
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Temporal Resolution
  • temporal resolution refers to the ability to represent information in the time domain
  • envelope
    • envelope is the slower content
  • fine structure
    • relatively fast - reflects spectral components of sounds in the sound waveform, and periodicity
Decreased temporal resolution
  • hearing loss can result in deficiencies in coding the temporal information accurately
  • the temporal fine structure is not preserved
  • temporal cues are distored
  • temporal cues in speech
    • voice onset time
    • formant transitions
    • periodicity
Temporal Masking
  • intense sounds can mask weaker sounds
    • that come after them or that come before them
In Hearing Impaired adults
  • increased temporal masking reduces sensitivity to soft sounds after an intense sound
    • e.g. VC syllable Ash vs As
  • In the presence of background noise
    • normal hearing adults can listen in the gaps
    • hearing impaired adults cannot make use of the gaps 
    • difficulties increase in the presence of background noise
How would we help in the clinic?
  • we can help for audibility
How would we affect speech in noise?
  • directional microphones, whatever we can do to get a better speech in noise performance
Evoked Potential
1640 Stockton Street ​#330071
San Francisco, California 94133
hello@evokedpotential.com