Multichannel, Temporally-Interlaced, Pulsatile Speech Processors

1987 - 1997


Descriptions and Quotes from the Literature:

There was some good news sometime in 1987 or 1988.   A significant section of an RTI progress report detailing the proposed design of RTI's new portable real-time processor (the portable processor was designed by Charlie Finley) indicates significant progress in understanding channel interactions had been made by RTI.  Although there was still more to learn.  This section was also included in the April, 1988 RTI contract proposal described in the next paragraph.

  • Between the end of summer 1987 and April 1988, RTI and Mark White agreed on a set of projects for a sub-contract for NCSU (M White, PI).  The sub-contract was part of an RTI proposal to the Neural Prosthesis Contract Office of NIH.  The first version of the proposal was submitted in April, 1988.  During the initial part of this planning process, RTI's first priority was for NCSU to develop a robust F0 extractor for their cochlear implant processor (using artificial neural network technology).  As before, Mark White indicated that this would not be very interesting to him.  He reminded RTI that there was significant evidence that the CNS could extract f0 cues "on its own" -- if channel pulse-rate were high enough (and, of course, assuming that the envelope-detectors' cutoff frequencies were set higher).  Furthermore, he also reminded them that raising the pulse-rate (far above F0) could communicate to the CNS other important information (e.g., F1) -- that was not currently made available to the CNS by RTI's low-pulse-rate IP processor (i.e., pulse rate = F0 during voiced-speech, 200-300 PPS, at most, during unvoiced speech).

    The different view-points of the two groups were again discussed:  RTI was concerned that pulse-rates above 200-300 pps were above the maximum discharge-rate of auditory nerve fibers.  At the time, RTI felt that it made no sense to drive the nerve at rates above their maximum discharge rate.  M White indicated that fibers may not be driven to such high discharge rates (i.e. many, or all, fibers might be driven stochastically -- i.e., at lower discharge probabilities).  Also, RTI had become concerned about inter-channel interactions that could occur during such high-rate non-simultaneous stimulation.  M White indicated that such interactions were far less substantial than those interactions caused by simultaneous stimuli; and that the "time-constant" and level of non-simultaneous interactions varied widely across patients (with some patients having unmeasurable levels, even at the shortest interpulse intervals), electrode types, and inter-electrode distances.

  • All of the information in the previous 2 paragraphs had been published one or more years before RTI first tested a patient at UCSF: please carefully examine the "basic science" sections of this web site for the research that caused M White to repeatedly suggest and explain the evidence for the proposed processor improvements and related experiments.

  • During the planning and writing of a very large basic science program project proposal (1987-1989) with other scientists, RTI learned a lot about the nerve's stochastic behaviour and how such behaviour might impact stimulus coding and processing for cochlear implant systems.  Once again, science played an extremely important role.   Via the "Road-Map" you can access a larger overview of all of UCSF's and other's work on understanding the auditory nerve's stochastic behaviour.

  • Finally!  During this planning process RTI finally understood the different key research areas, most of the data, and the rationales for testing at much higher pulse rates than 300 PPS.  This broke the logjam.  During a fateful week during this planning period, Charlie and Blake responded with more understanding than in previous years about testing at much higher pulse rates than 300 PPS.  Blake was particularly emotional about it.  The following excerpt and email from Charlie Finley describes just one of the key breakthroughs in RTI's understanding that had "held it back."  

  • In RTI's April 1988 contract proposal listed the new processors they were planning to test.  The 1st new processors that they listed were "promising variations of the existing IP strategy"  (see excerpt 1 and excerpt 2 from that proposal).  The resulting sub-contract for M White continued to support the "development of new signal processing strategies for cochlear implants" but, needless to say, did not mention the "development of a robust F0 extractor!"  See pages B-13 and B-14 in Appendix B of that RTI grant proposal. 

  • The RTI contract proposal to NIH was finally funded after re-submission.  In 1989, RTI tests a relatively low-rate "maximum-rate" IP processor on a subject with a per-cutaneous connector.  This processor is the "maximum-rate" processor described in the patent application: excerpt pp. 11-12 (from RTI QPR N01-DC-9-2401QPR01) of processor description that can be compared with that in the patent application above.  The testing results were somewhat encouraging: excerpt p. 23 and "follow-up studies... to evaluate additional variations of the 'maximum rate' IP processor" were scheduled for the next quarter excerpt p. 33 from RTI QPR N01-DC-9-2401QPR01.

  • The next quarterly progress report from RTI indicates the "maximum-rate" IP processor's (now named the "super-sampler") parameters (i.e., in particular, pulse-rate) were finally adjusted over a wide range and then renamed: excerpt p. 3 (see excerpt p. 33 from previous QPR) and excerpt p. 4 from RTI QPR N01-DC-9-2401QPR02.  Better speech perception was obtained by substantially increasing the pulse-rate of the "max-rate" IP system (i.e., the "super-sampler," and renamed again to the "CIS processor") and making the corresponding change in the low-pass-filter's integration window (excerpt p. 7).  It was postulated that the increased pulse-rate allowed more fine-grain temporal information to be communicated: excerpt p. 8.  The equivalence of the "super-sampler" and the "max-rate" variation of the IP processor class as described in the patent application is made particularly evident in: excerpt 1 p. 6 and excerpt 2 p. 6. Compare this description of the "super-sampler" to the description of the "max-rate" version of the IP processor in the patent application.

  • In the third RTI quarterly progress report (1989-90), the following excerpt again establishes that the "maximum rate IP" processor, the "super-sampler" processor, and the "CIS" processor are identical.   The only difference in RTI's mind, apparently being that they finally tested the processor at relatively high pulse-rates and got better results and renamed the system.

  • It's possible that there were secondary factors that were involved in RTI's delay in testing at higher rates: e.g., Their ability to drive a sufficient number of electrode-channels at high enough rates may have been limited (1) by their laboratory speech/stimulus-delivery system, and (2) by those patients without a "transparent, trans-cutaneous-connection to their intrascalar electrodes."  And (3) in some cases, patient bandwidths were severely limited by several factors (e.g., see this section of an RTI progress Report).  At least in regard to item (1) above, given RTI's significant motivation and technological ability, it is likely that such 'technical problems' would have been quickly circumvented -- and indeed they were!

  • A note about the difficulty in obtaining accurate, historical documentation:  None of RTI's QPRs for Contract # N01-NS-9-2401, covering the period 1988-1992, were available on NIH's web site -- until recently: click-here to see a "snap-shot" of the previous web site's contents.  All other RTI QPRs were available (QPRs before and after this 1988-1992 period) through the web site.  That may be one of the reasons that many investigators have been unaware of the history of IP processor development.  After I made a request, a new staff member at NIH made all of RTI's QPRs available at this website.  I thank him for that.