PSYCHOACOUSTICS: Impact of hearing impairment on auditory perception

Question 1

what is the impact of hearing impairment on loudness perception?

Answer 1

-Reduced dynamic range because of elevated absolute threshold

-Loudness increases very rapidly for hearing impaired listeners

-Cochlear hearing loss isassociated with abnormal loudness perception. Detection thresholds are elevated, but the level of sound that is found uncomfortably loud is elevated by a smaller amount

-Could be a contributor to poor speech in noise due to the discomfort caused by the abnormal loudness growth

Question 2

what is the impact of hearing impairment on frequency selectivity and how do we measure it?

Answer 2

• Measured with psychoacoustic tuning curves
  *for impaired ears
  more flattened, and higher threshold
  *For normal ears
  Sharper, and lower threshold.
• Impact of hearing impairment on frequency selectivity
  *Measured with auditory filter width (in ERB)
  *Figure: ERB width relative to normal ERB as a function of audiometric threshold
  *The larger the ERB value, the broader the auditory filter / the worse the frequency selectivity

Question 3

what is meant by excitation pattern?

Answer 3

Excitation pattern is considered to describe the displacement on the basilar membrane.

Question 4

what is the Impact of cochlear hearing loss on pitch perception?

Answer 4

Excitation pattern will be much more smoothed out for CHL than normal hearing, leading to pitch perception difficulties.

Question 5

what is the Impact of hearing loss (auditory neuropathy) on intensity, frequency, and temporal processing

Answer 5

• Auditory neuropathy can have significant effects on auditory perception across different domains:
• Intensity discrimination threshold (left panel): Individuals with auditory neuropathy may experience difficulties in accurately discriminating between different levels of sound intensity.
• Frequency discrimination threshold (middle panel): Auditory neuropathy can also impair the ability to discriminate between different frequencies of sound, leading to challenges in perceiving pitch differences.
• Gap detection threshold (right panel): Gap detection threshold refers to the ability to detect silent gaps between two sounds. Auditory neuropathy can affect temporal processing, impacting gap detection abilities. Individuals with auditory neuropathy may have poorer temporal integration, characterized by a longer temporal integration window, which can result in difficulties in detecting gaps. Conversely, those with finer temporal resolution, indicated by a shorter temporal integration window, may also experience challenges in gap detection.

Question 6

what is the Impact of hearing loss on temporal processing and how is it measured?

Answer 6

• Measured using gap detection thresholds
• Figure: gap threshold as a function of absolute threshold
• The larger the gap, the worse the temporal processing

Question 7

How does dip listening impact speech perception in individuals with hearing loss compared to those with normal hearing?

Answer 7

• Dip listening, the ability to benefit from dips in background noise for improved speech perception, is reduced in individuals with hearing loss compared to those with normal hearing.

Normal hearing individuals typically experience significant masking release, around -10 dB, indicating their ability to benefit from dip listening.

However, individuals with hearing loss, whether characterized by sloped or flat audiograms, show diminished masking release and require higher presentation levels due to their hearing impairment, impacting their ability to benefit from dip listening.

Question 8

what is the Impact of hearing loss on sound localization?

Answer 8

• Monaural sound localization: listening on the vertical plane (elevation)

*Spectral cues: head-related transfer function (HRTF)
*Hence, if spectral resolution is worse because of hearing loss, it should impact the person’s ability to use the spectral cues in the HRTFs

• Binaural sound localization: ITD & ILD

*ITD: interaural timing difference. It requires the auditory system especially the auditory nerves to fire in phase with the signal. If cochlea or the auditory nerves are damaged, then these fine timing information will not be encoded properly or faithfully, causing ITD to become worse and leading to poor sound localization ability and any further auditory perception that needs sound localization (e.g. cocktail party listening)

• ILD: interaural level difference. It requires the auditory system especially the auditory nerves to fire in group to encode the level difference between the ears. Any parts in the auditory system that relate to level transmission or encoding may impact the encoding of ILD more or less.

Question 9

what is speech discrimination?

Answer 9

• This is the brain’s ability to organise and make sense of the phonology* of speech sounds. This includes the ability to:

*Compare and contrast speech sounds
*Separate and blend phonemes**
*Identify phonemes within spoken words
*Combine phonemes into spoken words

Question 10

what is meant by phoneme?

Answer 10

a component of a word

Question 10

what is phonology?

Answer 10

study of sound patterns and their meanings

Question 11

how does a conductive loss impact speech discrimination?

Answer 11

• Generally patients with conductive losses still maintain good speech discrimination and may even report that they actually hear speech better in background noise
• This is because they mainly have a loss in transmission of sound energy (remember the function of the outer and middle to collect, amplify and transmit sound), therefore if people raise their voices to overcome the background noise then the energy is increased and the signal to noise ratio improves
• Once the sound hits the cochlea and nerve it is coded for and processed as normal

Question 12

how does a sensorineural hearing loss impact speech discrimination?

Answer 12

• If an individual has a sensori-neural hearing loss it is often associated with poor speech discrimination
• Remember, this could be attributed to different things:
  1) cochlea hair cell damage leading to reduced frequency selectivity

2) cochlea nerve fibre or auditory nerve damage causing the message to be distorted, interrupted or blocked
Or
A combination of both 1 and 2!

Question 13

why is it that some people with normal PTAs will have issues with speech discrimination?

Answer 13

• This can be due to early auditory nerve damage or due to processing disorders occurring higher in the pathway.
• Often these patients may have a social history which you would expect more from a person with a high frequency loss i.e. significant difficulty in group conversation/meetings, social situations, background noise etc. so it can be confusing to you and them when they present as normal in a PTA.

Question 14

what do patients with processing disorders normally experience?

Answer 14

• Patients with these disorders have difficulty in filtering out sounds i.e. they hear everything all at once and at a similar level, and the brain attributes the same (or similar) importance to every sound they hear
• This lack of discrimination means listening requires very high levels of concentration which can result in over-exertion, fatigue, stress and avoidance of social situations

Question 15

why do we do speech discrimination tests or auditory discrimination tests?

Answer 15

We can do speech discrimination tests (auditory discrimination tests ADT) to check how well a person can discriminate speech.

Question 16

what environment are speech discrimination tests or auditory discrimination tests done in?

Answer 16

These can be done under quiet conditions or with controlled/calibrated levels of background noise.

Question 17

how do we do speech tests or ADTs?

Answer 17

We can use word lists or sentences to check if they can perceive differences in word length (number of syllables) and sentence length and recognise segmentals/suprasegmentals

Question 17

what are suprasegmental?

Answer 17

-special characteristics of segmental including:

duration, rhythm
intensity, rate
pitch, emotion
intonation, male/ female
stress, own name

Question 18

what are segmental?

Answer 18

-individual speech sounds or phonemes including:

place: where sound is produced

voice: are vocal chords involved or not

manner: how sound is produced e.g. ff, ss, t, g, l, m

Question 19

what are some examples of auditory discrimination tests (ADT)?

Answer 19

• QuickSin – commonly used now in UK adult audiology
• AB word lists – mainly for adults
• Manchester Junior Word Lists - paediatrics
• McCormick Toy Test - paediatrics
• Wepman’s Auditory Discrimination Test (WADT)
• Goldman-Fristoe-
  Woodcock Test of Auditory Discrimination

Question 20

explain the McCormick toy test?
-who uses it?
- how its carried out?

Answer 20

-used in paediatric testing.

• Uses phonetically paired words (vowels the same, consonants different)
• Child is instructed to “Show me the house/cow, also plate/plane, tree/key, man/lamb, duck/cup, spoon/shoe etc.” These words are either spoken by the audiologist (difficult to calibrate) or produced through a calibrated loudspeaker/handheld speaker device at controlled intensity levels which are reduced throughout the test.
• Toys that relate to the items are arranged carefully on a surface with items with similar sounding names well separated. The child points to the toys related to the word they heard to demonstrate they have discriminated the word correctly. For example, they will point to the key not the tree if they have discriminated correctly.

Question 21

What role does central processing play in discrimination of auditory signals?

Answer 21

• Discrimination of auditory signals relies on effective processing by the auditory cortex and auditory association areas in the brain.
• While the outer and middle ear may transmit the message accurately and the cochlea may code it correctly, any disruptions in the transmission of the message by cochlear nerve fibers or its delivery by the auditory nerve to the brain can lead to misinterpretation of the signal.
• Central processing, therefore, plays a crucial role in ensuring accurate discrimination of auditory information.

Question 22

what is the standard method for discrimination tests?

Answer 22

• Many discrimination tests follow the method described below:
• Words or sentences are played to the subject.
• The test can be conducted unaided, or aided by a hearing aid
• The subject should repeat the word or sentence exactly as they hear it.
• If they are not sure of the word or parts of the sentence they should guess them, and if only part of a word/sentence is heard, then they should say that part.
• Present all the words in the list at the same sound level, and then reduce the intensity for the next test set.
• Make a note of the result of each presentation on the results sheet to achieve a speech discrimination score (SDS) or Word Recognition (WR) score

Question 23

What are the components of central auditory processing skills besides auditory discrimination?

Answer 23

• Auditory memory : the ability to store and later recall the impression perceived by the ears
• Auditory blending : the ability to synthesize the individual sounds (phonemes) of a word so that the whole word can be comprehended or understood.
• Auditory comprehension : the ability to understand the content of the speech
• Auditory localisation : the ability to determine the source of a sound using only the sense of hearing
• Auditory discrimination : the ability to interpret information relating to the differences between sounds, which facilitates understanding spoken words and spelling skills
• Auditory closure : The ability to complete indistinct or inaudible words to create a clear auditory image
• Auditory conceptualising : the ability to interpret and form a clear impression of a sound or combination of sounds.
• Auditory sequential memory : the ability to store a series of information in the order it was heard and later recall it