Briefly put .. A résumé of the case I explain in detail in the Main Argument section of this site
Frequently, even profoundly deaf people can understand speech and enter into conversations if their hearing is amplified by hearing aids. “Profound” deafness is defined as a loss across the three main speech frequencies of 90dB or more, and since hearing aids cannot provide amplification of any more than about 50dB, it is clear that normal hearing has not been restored, so how do they do it?
Visual clues play a large part, from the general demeanour of the speaker, to the more particular movement of their lips. Over time, some deaf people develop great skill in lip-reading, to such an extent that they can sometimes get by without hearing any of the sound coming from the speaker. It is a popular misconception, however, that a lip-reader can infallibly understand any speech without sound. He or she depends on contextual clues to do so, both in the sense of needing to know the topic being discussed, and in the sense that he relies on correctly interpreting at least a proportion of the words, so that other less clear ones can be guessed in the context of the sentences they appear in.
Alongside the mentally challenging activity of striving to seize upon every available visual clue, there is an equally challenging one devoted to wringing everything possible from whatever sound is available. Many, if not most, of the sound elements that make up the pattern of sound for any given word are probably missing, so, just as with lip-reading, contextual clues are required to make sense of the limited sound. Having enough sound to interpret correctly just one word in a sentence immediately provides a strong contextual clue to help interpret the rest. This is a process of applying intelligent guesswork, but because this site is devoted to changing the approach of audiologists, I have given it the more respectable title “supplementary sound interpretation” — interpretation that supplements whatever sound is available.
Both supplementary sound interpretation and lip-reading are skills that take time to develop, and deaf people master them with varied success. In the “Main Argument” section of this site, I demonstrate that supplementary sound interpretation can contribute anything from nil to 74% towards a sound-only sentence test score. (A test in which arbitrarily selected, and unconnected, sentences are played, usually from a pre-recorded DVD, and the candidate repeats them) Put another way, a sentence test score could over-state how well someone hears by a factor of four. The closest one can get to measuring their ability to hear speech is a sound-only test comprising single words, so that the influence of context, and the application of supplementary sound interpretation, is minimised.
So, when it comes to deciding if a profoundly deaf person might benefit from implantation, one would expect the key measurement to be a word test score. In stead, throughout the international Cochlear Implant community, the cut-off for eligibility is a score in a sentence test. Until recently, the level in the UK was a score of 30%, while that in the USA was set by the US Food and Drugs Administration at 40%. Both have now been relaxed, so clinical trials are taking place in the UK applying a level of 50%, while in the States a new Medicare limit of 60% has just been introduced for certain candidates. As I understand it, similar levels apply wherever Cochlear Implants are used.
The over-dependence of audiologists on the inaccurate sentence test has an insidious effect, because, not only are large numbers of profoundly deaf people denied the benefits of implantation, but the results from those who are implanted conceal the true impact on hearing of the implant. If the test can over-state hearing by anything up to a factor of four, how can one judge the impact of the implant on hearing , when one has measured neither post, nor pre-implant hearing?
If this has whetted your appetite for more information, please go to the Main Argument section of this site, where I explain my approach in greater detail by way of a commentary upon a paper by Jay Rubinstein.