Wk5a - Other Speech Processing Strategies Flashcards
Name two variations of CIS
SPEAK (Spectral Peak; obsolete)
ACE/n-of-m
What does SPEAK stand for? How does it work?
Spectral Peak
- it stimulates a variable number of electrodes at a low pulse rate (~250 pps) compared to CIS (~1000 pps)
- the electrodes corresponding to the 6-10 highest amplitude channels are stimulated
With the SPEAK speech processing strategy, the number of channels is adaptive. What 2 things determine the number of channels used?
Input level
Spectrum
What speech processing strategy superseded SPEAK?
ACE
Describe how the SPEAK processing strategy processes an acoustic signal?
- The waveform is passed through a 22 channel bandpass filter bank
- At a single moment in time, the filter-bank output envelopes are evaluated and the 6 channels with the largest output results in stimulation of the corresponding electrodes
- On another cycle, other channels might be selected
What does ACE stand for?
Advanced Combination Encoder
How does ACE differ from SPEAK?
- combines high pulse rate (like CIS) with channel selection
- only stimulates the electrodes corresponding to the highest n filter bank channel levels (e.g. 8 out of 16) on each cycle
- the number of active electrodes is NON-ADAPTIVE (can be changed in the CI program by the audiologist, not changing with each cycle)
What is the name of the strategy of which ACE is a proprietary name of?
n-of-m
Describe the n-of-m strategy?
- on each cycle, the n largest filter bank outputs will results in the stimulation of the corresponding n electrodes, out of the total m electrodes of the implant
- n is a variable programming parameter, but does not vary c/ the incoming signal (non-adaptive)
What are 2 benefits of n-of-m?
- maintaining fine structure
- noise reduction?
CIS mostly eliminates fine structure info, focussing mainly on the _______
Envelope
What 3 strategies did Med-EL use to attempt to maintain fine structure information?
- FSP (fine structure processing)
- FS4
- FS4-p
How did Med-EL’s fine structure processing strategies work?
- high frequency channels use CIS variants CIS+ or HDCIS (overlapping band-pass filters and Hilbert envelope extractor)
- the fine structure was maintained in the 2-4 low frequency channels, where pulses were only emitted when the waveform crossed zero in a positive direction
- supposedly gives listener access to additional low-freq fine structure info, helpful for pitch perception and SIN
With Med-EL’s FSP strategy, pulse trains were generated at each ascending zero crossing of the acoustic signal. What might determine which electrodes were programmed to receive this signal?
Depth of insertion - we have a rate-limit for AM sensitive of 250-300 hz
- deeper insertion = more fine structure electrodes can be employed (up to 4 c/ FSP)
FS4 was programmed to deliver fine structure stimulation to the 4 most ____ electrodes up to ____ Hz
Apical; 1000 Hz
Between HDCIS and FS4, which demonstrates more fine structure in the first 4 electrodes/channels?
FS4
Which of Med-El’s 4 strategies used sharp filter banks and a bandwidth b/w 250-8500 Hz?
CIS+
What was CIS+ upgraded to?
HDCIS - the same as CIS+, but with a bell-shaped filter bank
Which Med-El strategy included fine structure in the 2-4 apical electrodes up to 470 Hz and extended bandwidth down to 100 Hz
FSP
How is FS4 different from FSP?
- 4 apical electrodes always stimulated to provide fine structure (vs 2-4)
- fine structure bandwidth increased to up to 1000 Hz
How is FS4p different from FS4?
- it’s FS4 with parallel stimulation
How does a sharp filter bank differ from overlapping?
- sharp filter banks have small amount of info being carried by neighbouring electrodes (sharply tuned)
- bell-shaped will overlap info b/w diff channels (e.g. 1kHz info carried mostly by one filter, but also a little by each on either side
- trend is to overlapping filters (so sound “fades” b/w electrodes, instead of “jumping”)
What is current steering?
Activation of multiple electrodes simultaneously
- can stimulate diff (but maybe overlapping) populations of neurons than those from activating any single electrode
- on-purpose channel interaction
What changes can we expect to see to the typical bell-shaped electric field by simultaneously stimulating adjacent electrodes with the same bipolar stimulus with half the current/amplitude?
We would see a wider, flatter stimulus
(whereas if one electrode were stimulated with the same current and electrode 2 with half amplitude and reversed polarity, we would see the same bell shape, but with sharper/ more precise stimulation)
