Wk6a-Bilateral CIs (I) Flashcards
What are binaural cues?
Phase (interaural time difference) and amplitude (ILD) differences between ears, which help us localize sound
Low frequencies diffract ____ (more/less) than high frequencies, so shadow is less
More
Each frequency has a max ILD not at 90 degrees. This maximum is closer to 90 degrees for ___ (higher/lower) frequencies
Higher
NH listeners can detect ILD differences of about ___ dB, which corresponds to about ____ degrees of change in the azimuthal angle
1 dB
2-3 degrees of change
ITD is creased by path-length difference to the two ears. For NH listeners, ITD JND can be as low as ___ ms, or about ___ degree(s) displacement from the midline
10 ms
1 degree
Lower frequencies have ____ (lower/higher) ITDs compared to higher frequencies.
Higher
Which peak is always at 90 degrees azimuth, regardless of frequency: ILDs or ITDs?
ITDs
According to the research of Brughera et al regarding ITD JND, listener performance increased with frequency up to ___ Hz, at which point the threshold ITD was about ___ microseconds or 1 degree.
800
10 microseconds
According to the research by Brughera et al, at what frequency did ITD JNDs become useless?
1400 Hz
According to Brughera et al, in wideband sounds, ITDs in the ___ - ____ Hz bands are the dominant cue for NH listeners
500-1000 Hz
____ frequencies best carry the ILD info.
High
___ frequencies best carry the ITD info
Low
Anatomically, most of the acoustic processing is ____ (ipsi/contra)-lateral
Contralateral
Sound pathway: Ipsilateral cochlea Acoustic Nerve \_\_\_\_\_\_\_ cochlear nucleus \_\_\_\_\_\_\_\_ LSO Ipsilateral \_\_ & \_\_\_
Ipsilateral CN
Contralateral LSO (vis medial nucleus of trapezoidal body)
IC & DNLL
A left side stimulus will trigger a high spike rate in the contralateral ____. When the sound is from the right, we have high inhibition in the right MSO (from ipsi cochlea) and some excitation from left => low spike rate on the ipsi____
MSO
MSO
Describe how research on owls (by Jefferies) was disproven by Brand et al?
There is a lot of variability below and above 0 microseconds, but there was a spike rate increase across all frequencies for contralateral stimuli, thereby disproving the coincidence theory
Besides ITDs and ILDs, how else do we segregate talkers?
Location
In the test by Williges et al, they used one monaural listener and one binaural listener to measure the SRT when noise was presented with the target at the front, and from either side. Describe their findings
They found that the SRT of the was best for the monaural listener when the noise was opposite his good ear, and best for the binaural listener when the noise was separate from the speech signal.
Does binaural summation exist with CIs? Why?
Yes (usually about 1-2 dB in CI users);
- internal noise is reduced
- information may be complementary (good apical in one, good basal in the other)
Describe the head shadow effect, and how it affects binaural hearing.
For a spatially separated signal, one ear may have a better SNR due to head shadow, therefore this will be the ear that gives us a better SRT
- for unilateral listeners, the functioning ear is not always the better SNR ear
How many dB is head shadow (usually)?
Up to 10 dB
What is binaural interaction (or “squelch)?
All benefits beyond head shadow and summation
True/False: When a signal is presented in opposite phase at one ear, compared to the other (NoS(pi)), we get a binaural masking level difference (BMLD) of 15 dB. How do we know this is not due to a better SNR or summation?
There is no better SNR in left or right, and there is no summation b/c the signal is in opposite phase and would = 0 when added.
- when we only add noise in one ear, we only get a BMLD of 9 dB (binaural interaction)
What does squelch rely on?
Interaural temporal disparities
- 2-5 dB in NH
- 0-2 dB in CI users
