Re: Question about latency in CI comprehension (Willem Christiaan Heerens )

Subject: Re: Question about latency in CI comprehension
From:    Willem Christiaan Heerens  <heerens1@xxxxxxxx>
Date:    Mon, 15 Dec 2014 15:40:19 -0500

Matt, 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 by: 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 signal. >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 apples. 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

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