Wk6b-Bilateral CI's (II) Flashcards
When testing sound localization in NH individuals, Kerber and Seeber found that as SNR decreases, performance ______ (decreases/increases)
Decreases - anything more lateral than 40 degrees was still estimated to be at 40 degrees
When the localization experiment by Kerber and Seeber was repeated with Unilateral CI users, they found that CI users nearly always perceive sounds as coming from ______ and showed ____ (better/worse) discrimination with decreased SNR
0 degrees, or the front
Worse
How did bilateral CI users do in good SNR conditions compared to NH listeners and unilateral CI users?
Bilat CI users did well - better than unilateral CI users and almost as well as NH listeners - in good SNRs, but very poor in poor SNR environments.
Why do bilateral CI users experience difficulty localizing sound?
Automatic Gain Control, Adaptive Sound Window, and n-of-m operate independently in L and R CI
- the CI outputs will even out the inputs, even though the inputs were originally very different (cannot use ILD cues)
What does binaural technology in hearing aids include? How does it help with localization?
- Identical program selection
- Identical compression (which helps maintain ILDs)
- Identical directionality (polar plots)
In bilateral CIs, we should have more than identical program selection and compression to help with localization. What else should be included?
- Identical Adaptive Sound Window
- Identical n-of-m selection
- Let the sound processor exploit the binaural squelch
- ITD enhancement (if possible)
- Manipulate the ILD to make it as linear as possible (e.g. 90 degrees)
When was the first binaural CI (by advanced bionics) put on the market? What binaural processing did it have?
2018
- identical program selection
- identical compression (helps with ILDs)
- Identical Adaptive Sound Window
- > let the sound processor exploit the binaural squelch
Describe a binaural implant
A device with one internal component that has 2 electrode arrays (a short ipsi one, and a longer contra one)
- one speech processor on ipsi side processes the acoustic information from the same side AND from the remote mic on the other side
- by using one speech processor, this device can synchronously stimulate the electrodes on both sides
- surgery is difficult
What does “FAST” stand for?
Fundamental Asynchronous Stimulus Timing
- it is a strategy that presents a pulse at each envelope maximum at each channel (usually at ~100-200 pps)
- the interaural timing difference is visible in the final output, so can now be exploited by the LSO
HA users can use their binaural system, including their cochlear amplifier, to help with sound localization. CI users cannot, and so must rely on their ___ _____.
Sound Processor
What is a fixed minimum variance distortionless response (as seen in the Baumgartel paper comparing NH, HI, and CI user performance using technology in different listening situations)?
A beam former; It is a spatial filtering technique aimed at minimizing the noise power output while preserving target speech components
Baumgartel et al found that ______ (NH/HI/CI users) benefited most from binaural pre-processing
CI users
What does the “cone of confusion” refer to?
The fact that ITDs and ILDs only provide us with spatial cues related to the lateral angle
- e.g. a sound in the lower front and upper front generate the same ITDs and ILDs
How does the pinna affect sound localization?
The pinna alters sounds differently by frequency depending on if they are coming from the front, back, above, etc.
- helps localize the sound source in the vertical plane
- mostly visible with high frequencies (above 4000 Hz)
The ____, torso, and ____ act as directionally-dependent acoustical filters, characterized as ____-_____ ____ _____ or ______ ______ _______
Head; pinna
Head-related transfer functions (HRTFs)
Directional Transfer Functions (DTFs)
