[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Influence of amplitude on place pitch in cochlear implants (CIs)
When we do single-channel electrode discrimination, even a small rove will cause wild variations in the results. "Pitch" -- or whatever sound quality the CI listeners are listening to -- changes with loudness substantially: it's not like normal hearing. With multi-channel stimuli, this loudness-dependent change may be different on different channels, so your listener may not be using the same cue at the different roving levels.
It's a problem.
>>> "Ward R. Drennan" <drennan@xxxxxxxxxxxxxxxx> 12/7/2007 11:15 AM >>>
I have experience roving level with CI subjects. I've tried profile analysis (spectral shape discrimination) with both-back end (current level rove on the electrodes) and front-end (acoustic rove through the sound processor). In the back-end case, it was an profile of current levels on multiple electrodes using CIS. For acoustic profiles, it was the standard Dave Green inspired tone complexes. Die hard profile analysis folks will tell you that it's not REALLY profile analysis if you can't control for level i.e. level rove the stimuli within a trial and subjects are able to hear a spectral change in a single component that's LESS THAN the amount of the rove (see Green "Profile Analysis 1988).
Getting to the pitch thing, roving level in CI patients WITH THE SAME SPECTRAL STIMULI, sends pitch all over creation. Place of stimulation is constant, only level changes, whether done at the front or back end. As a result, CI users can't do "true" profile analysis at all (with one exception out of 9, who was a violin major). This is a bit of a problem in music. Take Bolero for example at a loud level and a soft level. It could sound COMPLETELY DIFFERENT to a CI user, depending on the level.
If you do a complex pitch study and rove level too much, it will be hard to get a systematic result, because every person will respond differently to the level changes. If we could solve the problem-- and keep pitch constant with level changes for CI users, certainly I would expect it to help them appreciate dynamic changes in music. It is, I believe possible to turn off the AGC. I think that will help but not solve the problem.
We do an acoustic test of pitch direction discrimination with complex tones. The level rove is +/- 4 dB. CI users seem to be pretty good at this task. Many can discriminate a semitone direction change. With larger roves, I'm sure they would not do as well.
Nimmons GL, Kang RS, Drennan WR, Longnion J, Ruffin C, Worman T, Yueh B, Rubinstein JT.
Clinical Assessment of Music Perception in Cochlear Implant Listeners.
Otol Neurotol. 2007 Aug 2;Publish Ahead of Print [Epub ahead of print]
On Fri, 7 Dec 2007, Matthias Milczynski wrote:
> Dear list,
> I am testing pitch ranking in CI subjects. In general, I work with a research
> processor and I stream pre-processed stimuli directly to a subject's implant.
> To get rid of loudness cues I want to apply amplitude roving. However, when
> applying the roving at the front-end (i.e. manipulating the amplitude of
> wav-files to be processed by a particular strategy) I observe the following
> Let's assume a complex tone (e.g. piano) at a frequency of 164.8 Hz (E3), with
> a duration of 500 ms. Thereby the rms of the sound is relative small (e.g. -30
> dB re full scale). Then, let's assume a tone at 130.8 Hz (C3) from the same
> instrument and at the same duration but at a higher rms (e.g. 10 dB higher in
> rms than the first tone). Due to the non-linear loudness growth function
> implemented in these days' CIs (assuming e.g. the ACE strategy with default
> adjustments) the stimulation pattern corresponding to the first tone will show
> activity on a few apical electrodes (up to about 900 Hz). However the
> stimulation pattern corresponding to the second tone (which is higher in
> amplitude but lower in pitch) will also show activity at electrodes
> corresponding to much higher frequencies (up to approx. 1700 Hz). As a
> consequence a subject that mainly relies on place pitch cues could falsely rank
> the second tone as the higher one in pitch. That means that amplitude roving at
> the front-end can introduce a misleading place pitch cue. Of course the
> stimulation patterns for E3 and C3 will differ in temporal pitch cues (i.e. the
> frequency of the envelope fluctuations in the E3-pattern will be higher than
> for the C3-pattern), however the effectivity of this cue will be
> Another possibility to amplitude-rove the stimuli would be to apply the roving
> at the back-end, i.e. manipulating the electrode current (i.e. multiplication
> by a scaling factor) but this type of roving does not necessarily correspond to
> a real-life situation and is difficult to implement when working with the
> subject's own device.
> I would very much appreciate any comments and/or suggestions.
> Many thanks!!
> Matthias Milczynski
> PhD Student
> ExpORL, Dept. Neurosciences, K.U.Leuven
> O.& N2, Herestraat 49 bus 721
> B-3000 Leuven
> +32 16 330476
Ward R. Drennan, Ph. D.
VM Bloedel Hearing Research Center
Department of Otolaryngology
University of Washington Box 357923
Seattle, WA 98195
Office: (206) 897-1848
Fax: (206) 616-1828