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Re: Question about latency in CI comprehension


Thank you for your comments.

Yes I am aware that the combination of being a CI user and having 
knowledge in acoustics is not precisely common practice.
And I am also convinced that this combination can provide for highly 
valuable information. 

You made the remark:
I thought it might be good to add to this story a cautionary note before 
we draw conclusions about cochlear function or brain function.

Indeed I did that for myself before I composed the sound tracks for my 
experiments. As background information my preliminary considerations 
might be of interest in the discussion.

You stated:
The CI processor transforms the signal into a series of compressed pulse 
trains, and in doing so, discards a number of different properties of 
the acoustic input. So even though we can be clever and design 
experiments where perception of the acoustic signal can differentiate 
various auditory processes, we are in many ways subordinate to the 
prerogative of the CI processor.

Yes and therefore I have observed the CI processor and its software 
content as a grey box.
So aware that I am not knowing all or even most of the internal details 
of this grey box I formulated my consideration that the acoustic stimuli 
I can compose will have the least imaginable chance to interact in an 
undesired or erroneous way with the functional content of the grey box.

And therefore I considered that a beat experiment can be used in which 
the combination of two pure tones is chosen extreme close in frequency, 
which made the duration of the beat period 3000 seconds.
And I used the statement that the total transfer of the external 
acoustic stimulus via the CI processor must give me a perception equal 
to that in my acoustic ear.
Why? Simply because when my brain perceives striking systematic 
differences between both hearing sides, the replacement of the normal 
acoustic hearing by the mechanic-electronically operating CI processor 
does not provide in the mimic of normal hearing.

The logic conclusion I can draw in that case is that not my brain, nor 
my acoustic ear but the CI equipment fails in providing  for the wanted 
hearing disorder correction.

You stated:
In other words, we cannot trust the perceived signal to be what we 
intended it to be. This is especially true in the case of a delicate 
temporal/spectral interaction of the type you described. 

Well, let us look at what delicate temporal/spectral interaction can be 
distinguished in my beat experiment.

The envelope Ep(t) of that beat can be described as:

Ep(t) = A|cos(2pi×t/6000)|

Where A is the starting sound pressure amplitude at t = 0.

>From t = 1485 sec to t = 1500 sec this envelope Ep(t) equals in extreme 
good approximation a linearly decreasing signal from amplitude  0.01×A 
to zero and from t = 1500 to t = 1515 sec a linearly increasing signal 
from amplitude zero to again amplitude  0.01×A.

During that 30 seconds time period the 1000 Hz signal makes 30,000 
complete evolutions.

And my composed sound track only exists of data within that 30 seconds 
time window around the zero crossing.
What is left from the temporal interaction?
A for everybody fairly well acceptable continuous decreasing and 
increasing stimulus of one tone. And no discontinuity, only at t = 1500 
sec a returning from steady decreasing into steady increasing amplitude. 
Hence a composition without any pitfall caused by unexpected 
interactions between the input stimulus and the CI program. 

And this counts for the input of both the CI microphone and the what you 
call acoustic ear. 

The next experiment in which I use the sound energy stimulus calculated 
out of the sound pressure of the beat signal has an envelope Ee(t) given 

	Ee(t) = Ee(0)×[cos(2pi×t/3000) + 1]/2

Where Ee(0) = (2pi×A)^2,  the value of the starting sound energy 
amplitude at t = 0.
The frequency of the sound energy stimulus is 2000 Hz. And this stimulus 
makes 60,000 complete evolutions within the 30 sec time window.

>From t = 1485 sec to t = 1515 sec this envelope equals in extreme close 
approximation the parabolic function:

	Ee(t) = Ee(0)×[(t-1500)/1500]^2

In this parabola Ee(1485) and Ee(1515) have both the value 0.0001×Ee(0)
Between 1492.5 sec and 1507.5 sec the value  is even smaller than 25 
parts per million of Ee(0).

Also here nothing will give rise for a temporal interaction. There only 
exists a smooth quadratic decreasing and increasing amplitude around the 
zero amplitude moment at t = 1500 sec. Nothing else.

Matt can you explain in a completely other logic hypothesis to me why 
the in pulse trains transferred stimulus in the CI can mimic so 
perfectly both the amplitude and the sharply in time restricted zero 
crossing of the 1000 Hz sound pressure  tone ? While my other ear 
perceives the sound energy tone of 2000 Hz with an in amplitude smooth 
zero approach in t = 1500 sec?
And why the CI equipment mimics in my brain perfectly well the sound 
energy stimulus, when I evoke in front of the CI microphone the 
artificially calculated corresponding sound energy stimulus?
Exactly equal to the process in my acoustic ear? 

You wrote:
To make a simple analogy, you can imagine the pitfalls of drawing 
conclusions about differences between your right eye and left eye if 
color vision in your right eye were tested using a black & white tube 
monitor from the 40s, and your left eye were tested using an LCD HD 
monitor from 2014. Any conclusions you draw from this test would really 
be a statement about the apparatus, not the visual system itself. In my 
opinion, the same risks apply in the case of comparing a CI ear to an 
acoustic ear. 

I can agree with you to some extend if you would say that in my acoustic 
ear I use for the sound stimulation a high quality BTE hearing aid, the 
Phonak Naida or a high quality headphone . In the CI ear I use a top 
class high quality apparatus of the most recent type, the Advanced 
Bionics Naida CI. And I compare two different apparatuses. Both state of 
the art devices are developed for one task: restoring in the best way 
the capability of hearing and interpreting sound stimuli directed to my 
hearing sense.

And I can clearly draw the conclusion that the Phonak Naida mimics 
perfectly well what the high quality headphone performs. And also what 
other normal hearing subjects perceive from the sound pressure stimulus. 

The AB Naida mimics perfectly well the sound pressure stimulus, but not 
in the format equal to the process in the acoustic ear. 
The AB Naida only does that in case I evoke in front of the CI 
microphone the calculated sound energy stimulus out of the sound 
pressure stimulus. And not the sound pressure stimulus.

Then the conclusion is simple: Apparently the AB CI transfers in 
principle a stimulus linearly proportional to the evoked sound pressure 
>From the Phonak Naida is known that it transfers only a frequency 
related attenuated and/or amplified stimulus to the cochlea. All the 
rest of transfer to the basilar membrane is done by the middle ear and 
cochlear functionality. 
The nerve connection to the brain is still identical in both ears. 
However the electrical signals in both ears differ. And they should be 
equal for normal hearing. 

You wrote:
To your specific experiment: although your acoustic ear heard the 
fundamental in the complex sine tone you created, your CI ear in fact 
never heard the sines at all (just as your right eye never saw the 
color); it heard whatever the processor generated to represent those 
tones. So in my mind, you might not have been comparing apples to 

Here I disagree fundamentally with you. You actually suggest that what I 
observed in the missing fundamental experiments is a pure acoustic 
illusion. Well I can guarantee you that what I did with my mind is 
comparing apples with apples. The cooperating manufacturers  of both 
hearing devices pretend and advertise that to the best of their 
knowledge their goal is the restoration of hearing in their customers.
It isn?t also a kind of ?acoustical? placebo effect. I am not tumbling 
in the pitfall that what I observe is what I want to observe. After a 
scientific lifetime in applied physics research at an academic level I 
characterize myself as a highly qualified observer, who will not easily 
make mistakes like comparing apples with pears ? like it is given in a 
Dutch expression.

You wrote:
What some researchers do is gain control over the CI signal by bypassing 
the clinical processors and instead use research processors (e.g. 
HEINRI, NIC, BEPS+, BEDCS), where each element of stimulation is 
explicitly controlled. Then you can at least be assured of what signal 
is being delivered and be confident about the relationship between 
stimulus and response. Other experimenters have more experience in this 
area and may offer more eloquent descriptions of their approach. 

That is a good suggestion. However being an emeritus associate professor 
without a laboratory or even any other facility in a university setting 
I leave such kind of experiments to others.

Willem Chr. Heerens