Why then, for this patient, is this prognosis wrong in terms of speech understanding in quiet and noisy situations ?
Professor J.C. LAFON answers that question in his explanation of how the auditory integration list was developed: « … having young children among my patients, I encountered severe cases of spatial distortions that could only originate from speech identification difficulties, as tonal was normal and no damage had been detected in the ear. Incidentally, I then noticed that those distortions would come up more easily and to a higher extend in noisy situations. That fact sounded interested to me, as it could help distinguish between what should be assigned to cochlea and what should be interpreted as speech discrimination impairment. Allthere was to do was to perform a comparative measurement of two elements from a wordlist, in silence, and of two others, with a noisy background. Noise intensities were selected so that noise was almost as loud as speech, both measurements being performed at a same intensity: similar acoustic intensities would overcome the effects of cochlea impairments, since this was a comparative measurement. I had chosen a high level, 90 dB, in order to set the message at a higher level than the hearing treshold in cases of heraing loss. This measurement could thus be performed on deaf as well as hearing patients. »(1)
The open-set word recognition list established by Professor J.C. LAFON indicates whether the patient’s auditory integration is efficient. That is an important point to know, as the expected effect of the hearing aids will vary accordingly.
Indeed, that list allows to « … quickly detect whether we are facing a case of damaged cochlea or an auditory processing disorder… That list containing only 34 words, it tell us whether further examination is required and whether a cochlear or an auditory integration list should be used. »(2)
Out of these 34 words, 17 are articulated in a silent background (« A » item), then the next 17 words are pronounced with a non-masking noise (« B » item). By subtracting the number of pjonetical mistakes in both lists (A-B), we obtain what is specifically due to an auditory processing disorder, and only to it. An abacus – based on the patient’s age and on the number of phonetic mistakes on the « A » and « A-B » elements – provides a better understanding of the cochlear damage and or the auditory processing disorder. Further information on the open-set word recognition list can be found in the previously released LAFON 12 and LAFON 13 articles.
An open-set word recognition test only takes 3 minutes to be performed! Little time, big results. I personally perform it straight after pure tone audiometry (air conduction treshold, intolerance and, if neccesary, bone conduction treshold).
Let’s say, for example, that this open-set word recognition test detects that a deaf patient about to be equipped with hearing aids is suffering from auditory integration disorder: it thus means that he or she can hardly understand the auditory message he/she gets, on neuro-physiological to physio-psycjological points of view. As a result, the list helps the audioprothetist decide what hearing aids to use: the pratitioner now knows there is no point in going for the top range devices, as in this situation, even the best noise cancelling systems will be useless. The list thus helps the audioprothetist select the most suitable hearing aids for each patient.
(1) Professor J.C. LAFON « the phonetic test and the measurement of hearing » pp 116-117.
(2) Professor J.C. LAFON « the phonetic test and the measurement of hearing » page 132.
(translated from french by O.B.)