SSD Flashcards
Define SSD
A term used to describe individuals with an aidable hearing loss in their better ear and no usable hearing and poor word recognition in the poorer ear.
Define spatial hearing
“A listener’s ability to receive, process, and utilize directionally specific auditory signals from the two ears, working independently and in concert” (Murphy et al., 2011)
Describe spatial hearing for normal hearing individuals
Individuals with normal hearing use interaural time differences (ITDs), interaural level differences (ILDs), and spectral differences as part of spatial hearing. The person utilizes all these cues to determine where the signal is coming from.
What are ITDs?
They are evaluated for low frequency sounds (<1500 Hz)
They compare the time difference of sounds between the two ears.
The sound will arrive first to the ear on the side which it is presented
Envelope of the signal.
What are ILDs?
They are evaluated for higher frequency sounds (>1500 Hz).
They compare the level difference of sounds between the two ears
The sound will be louder in the ear on side which it is presented. This is affected by the head shadow effect.
What is the head shadow effect?
A phenomenon that describes the degradation of a speech signal (particularly the high frequency sounds) by up to 15 dB as they travel from one ear to the other in space. (Staab, 1988)
What frequencies are affected by the head shadow effect? Low frequencies or high frequencies?
High frequency sounds because they have shorter wavelengths
What happens in the presence of noise for normal hearing individuals?
They are able to spatially separate the signal and the noise resulting in binaural unmasking and a louder signal relative to the noise. (Murphy et al., 2011)
What happens with individuals with SSD in terms of spatial hearing?
The individual is unable to use the head shadow effect for localization which is a safety concern.
Speech understanding, especially in the presence of noise, declines due to the inability to take advantage of binaural unmasking (binaural squelch) in the way that normal hearing individuals are able to (Murphy et al., 2011). This binaural squelch, in addition to binaural summation requires two ears.
Define auditory scene analysis (ASA)
“The ability to disentangle the mixture of sound input, integrating sensory inputs that belong together and segregating those inputs that originate from different sources”. (Sussman, 2005)
In other words, it is how we organize the incoming sounds into various streams through integration and segregation.
Why is ASA important?
It allows the listener to identify the sound and either integrate the signal or segregate it into what is important.
Integration is important for music perception as it allows for harmony in a band.
Segregation is important for speech understanding as it involves picking one sound among a variety of inputs.
Why is speech understanding a difficult task?
It requires temporal and spectral cues
How do normal hearing individuals complete ASA?
Inherently and without any difficulty.
They are able to classify input into different streams and integrate or segregate these streams.
What happens with ASA for patients with hearing loss?
As the level of the background noise increases, speech recognition performance deteriorates and a breakdown occurs in separating and integrating the sources of input.
What happens with ASA for patients with SSD?
Binaural unmasking (squelch) does not occur and the patient is unable to complete auditory scene analysis because of their inability to accurately disentangle the sound input.
Why do patients with SSD have poor ASA?
Poor temporal and spectral resolution in these patients may result in the dysfunction in ASA. (Edwards, 2007)
Why are temporal and spectral resolution important?
They affect the envelope and pitch cues.
True or False: Hearing aids restore auditory scene analysis.
FALSE!
Hearing aids do not result in true binaural hearing, especially for patients with SSD.
What are some of the treatment options for SSD?
1) BiCROS
2) Transcranial CROS
3) BAHA
4) CI
What is a BiCROS?
A bilateral contralateral routing of signal amplification system.
How does a BiCROS work?
A microphone in the poorer ear picks up the signal and transmits it wirelessly to the better ear where it is amplified by a hearing aid.
What are the benefits of a BiCROS/CROS system?
Sound awareness
What are the disadvantages of a BiCROS/CROS system?
- Problematic if noise is in the better ear and speech in the poorer ear
- Does not restore binaural processing
Describe use of a CROS/BiCROS for a patient with tinnitus in the poorer ear.
A CROS/BiCROS does not stimulate the poorer cochlea. It is only taking sound delivered on that side of the head and transferring it to the better hearing ear.
If the CROS/BiCROS system is able to provide sound therapy to the poorer ear while simultaneously transferring the signal and amplification to the better ear, then this may provide a reduction in the patient’s perception of tinnitus.
Describe patient satisfaction with a CROS.
Yuen et al., 2009
Compared to other devices, patient satisfaction has remained low for many years with a CROS system
What is a transcranial CROS?
A deep fitting power CIC hearing aid that is maxed out.
How does a transcranial CROS work?
The maxed out CIC hearing aid is placed in the poorer ear and sends the signal transcranially to the other ear
What are the benefits of a transcranial CROS?
Only need 1 device
Cosmetically appealing since it is a deep fitting CIC
What are the disadvantages of a transcranial CROS?
- Uncomfortable b/c needs to be deep fitting
- Signal is affected by interaural attenuation
Describe use of a transcranial CROS for a patient with tinnitus in the poorer ear.
The device is occluding the ear canal, thus it will not result in a reduction in the patient’s perception of their tinnitus
What is a bone anchored hearing aid (BAHA)?
A sound processor implanted in the poorer ear.
How does a BAHA work?
A sound processor implanted in the poorer ear picks up sound vibrations and sends the signal from that side to the better cochlea through bone conduction.
What are the benefits of a BAHA?
- Clearer signal than CROS/transcranial CROS
- Can try in the office on softband before undergoing surgery
What have studies shown between a CROS and a BAHA?
Individuals fit with a CROS and then implanted with a BAHA preferred the BAHA (Lin et al., 2006)
What are the disadvantages of a BAHA?
- Surgery
- Only simulates one cochlea, thus binaural hearing isn’t restored and may experience localization difficulties
- MRI limitations
Describe use of a BAHA for a patient with tinnitus in the poorer ear.
Only the better cochlea is going to be stimulated since the auditory input will lateralize to the better ear.
What is a cochlear implant?
A device that bypasses the damaged auditory system and directly stimulates the auditory nerve.
Good for intensity and timing, but has poor spectral resolution.
Benefit affected by several factors including duration of deafness, age of implantation (critical period for electrical stimulation is 5 years of age), patient’s motivation, age of onset of hearing loss (pre vs. post-lingual)
How does a CI work for someone with SSD?
- Implanted in the poorer ear
- CI users mainly used ILDs which are used for localizing high frequency sounds
What is the limitation of the cochlear implant? (the device limitation)
Poor spectral resolution which requires the fine structure of the signal.
This fine structure is necessary for music appreciation
What are the advantages of a cochlear implant?
- Improved speech understanding in quiet and noise
- Improved sound localization
- Tinnitus relief
What are the disadvantages of a cochlear implant?
- Poor spectral resolution
- Surgery
- MRI limitations
- Not FDA approved indication for implantation
Research of CI vs. Baha and CROS
(Arndt et al., 2011)
Compared to Baha and CROS, SSD patients with a CI have:
- improved localization
- improved speech comprehension
- A positive effect on tinnitus
- Overall benefit on the Speech, Spatial and Qualities (SSQ) of Hearing Scale
- No significant summation and squelch effects
- No negative effects when the noise presented to CI and speech to opposite ear
Recommendations for a child with SSD.
Depends on the child’s age, but need to consider educational and speech/language development implications of hearing loss.
1) BiCROS
2) BAHA on softband or surgery if >5 years of age
3) CI + therapy (AVT which is designed for patients with hearing loss)
4) FM System
5) Preferential seating
