Communicative ability in an audiological perspective - Theory and application to post-secondary school students

The underlying assumption in the present study is that the individual's spe ech and hearing communicative ability is composed of three components, each corresponding to different functional systems of the brain: afferent, cent ral and efferent. The afferent functions (A) represent the auditory activit y and sound perception largely corresponding to activity in the ascending a uditory pathways. The central functions (C) include cortical auditory and l anguage abilities controlled in parts of the left temporal lobe and subcort ical centres. The efferent functions (E) consist of speech motor processes and articulation. A test battery of 20 tests measuring several aspects of a fferent, central and efferent functions was applied to 11 hearing-impaired post-secondary school students and several control groups. All data were no rmalized with the normal materials as references. Individual communicative profiles were obtained from these primary data, which consisted of audiomet ric tests (tone and speech audiometry, impedance tests, brainstem response audiometry and phase audiometry), sound environmental tests with hearing ai ds (directional speech-in-noise, word localization, sound environment ident ification test), and language tests (reading tests, prosody, auditory memor y and recall, phonology and articulation). Since the central functions cann ot truly and directly be determined in hearing-impaired subjects, they were assessed under optimal listening conditions. Furthermore, central function s were estimated according to three different models: distributive, paralle l model (model 1), multiplicative, serial model (model 2) and compensatory model (model 3). On the basis of these models, a three-component descriptio n of the communicative ability consisting of A,C and E functions was obtain ed. It was found that C and E functions were largely independent of the adu lt afferent functions, but C functions were negatively correlated to hearin g in childhood. A preliminary comparison between the tests and a comparison between the models was performed by predicting benefit of hearing aid. Mod el 3 gave the best prediction. Beyond the three-component A, C, E character ization of the students, a total communicative ability score could be calcu lated giving values from 37% to 79% of the normal mean. On the basis of the conceptual and statistical analyses, the test battery could be reduced to include tone 0-12 years, tone adult, word localization test (afferent); wor d chain, lecture test (central), articulatory test (efferent) and audiovisu al test. The simple algorithm of adding the normalized loss of afferent (pe ripheral) function to the normalized results of the acoustic central tests seems to be promising for isolation for the central auditory capacity even in cases with peripheral impairment. It is concluded that a wider perspecti ve is desirable in the diagnostic evaluation of the hearing-impaired indivi dual in order to understand his communicative abilities and form a cornerst one in the planning of rehabilitation in conjunction with social and psycho logical factors.