The recruitment list elaborated by Professor J.C. LAFON (a word recognition score specific to the recruitment phenomenon) comes together with the cochlear list, as they both provide targeted information about the cochlea.
Indeed, the recruitment list is the logical follow-up of the cochlear list in the particular cases of « distorted spatial perceptions » and « severely distorted spatial perceptions ».
Here is how Professor J.C. LAFON explains the various cochlear distortions that can be encountered and how he came to the elaboration of his recruitment list: “Phonetic testing…highlighted three kinds of distortions: those related to tonal threshold – that I named initial distortions, those that remain although all frequencies can still be perceived – called spatial perception distortions because they are linked to the auditory range – and distortions that increase simultaneously with intensity, named severe spatial perception distortions… Within a few months of use, it became obvious to me that some cases of deafness displayed particular phonetic distortions that could hardly be explained. When supra-threshold pure tone audiometry measurements were possible for these patients, recruitment was detected. Indeed, vowels identification is usually not affected by an impairment of the hearing range occurring above 3000 Hz, but in presence of recruitment and for a same tonal curve, distortion of the “i” would evolve from 5% to 20%. When recruitment also affected slightly deeper tones, /ü/ and /e/ were also strongly impaired, just as /a/ and /o/ among deep tones. I conducted a comparative study of deaf patients suffering from recruitment and I selected, among those word recognition lists, a series of words that were partially distorted and I called it a recruitment list.”(1)
« A distortion observed at 90 dB that does not mainly affects consonants, or an absence of improvement in phonetic intelligibility combined with a measurement curve getting horizontal – or even decreasing – show the necessity of performing recruitment assessment… Using the term “recruitment” to qualify this list is actually wrong here, as we do not measure the recovering of the subjective intensity of a deaf ear. We use it by default, as there is no appropriate term to qualify these distortions. The list gives an analytical overview of pathological cochlear distortions, where recruitment may also be observed. This list is thus of similar interest: positive diagnosis of cochlear impairment, complementary diagnosis of retro-cochlear damage primarily diagnosed based on the integration list”(2).
The recruitment list contributes to hearing devices optimisation: « Data obtained with the recruitment list specify the adjustments to be applied to the response-curve of the device. Recruitment mostly occurs between 3,000 and 4,000 Hz: the response curve should then be strongly attenuated from 2,500 Hz in those cases. We have seen that speech recognition could remain at a satisfactory level if there is no transmission in frequencies ranges over 2,500-3,000 Hz”(3).
Further information on the recruitment list can be found in the previously released “LAFON 9 THE RECRUITMENT LIST (1)” and “LAFON 10 THE RECRUITMENT LIST (2)” articles.
(1) Professor J.C. LAFON « the phonetic test and the measurement of hearing” pp. 115 and 116.
(2) Professor J.C. LAFON « the phonetic test and the measurement of hearing” pp. 144-145.
(3) Professor J.C. LAFON « the phonetic test and the measurement of hearing” page 185.