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

Abstract

The underlying assumption in the present study is that the individual's speech and hearing communicative ability is composed of three components, each corresponding to different functional systems of the brain: afferent functions (A) represent the auditory activity and sound perception largely corresponding to activity in the ascending auditory pathways. The central functions (C) include cortical auditory and language abilities controlled in parts of the left temporal lobe and subcortical centres. The efferent functions (E) consist of speech motor processes and articulation. A test battery of 20 tests measuring several aspects of afferent, central and efferent functions was applied to 11 hearing-impaired post-secondary school students and several control groups. All data were normalized with the normal materials as references. Individual communicative profiles were obtained from these primary data, which consisted of audiometric tests (tone and speech audiometry, impedance tests, brainstem response audiometry and phase audiometry), sound environmental tests with hearing aids (directional speech-in-noise, word localization, sound environment identification test), and language tests (reading tests, prosody, auditory memory and recall, phonology and articulation). Since the central functions cannot truly and directly be determined in hearing-imparied subjects, they were assessed under optimal listening conditions. Furthermore, central functions were estimated according to three different models: distributive, parallel model (model 1), multiplicative, serial model (model 2) and compensatory model (model 3). On the basis of these models, a three-component description of the communicative ability consisting of A,C and E functions was obtained. It was found that C and E functions were largely independent of the adult afferent functions, but C functions were negatively correctly to hearing in childhood. A preliminary comparison between the tests and a comparison between the models was performed by predicting benefit of hearing aid. Model 3 gave the best prediction. Beyond the three-component A,C, and E characterization of the students, a total communicative ability score could be calculated 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 adults, word localization test (afferent); word chain, lecture test (central), articulatory test (efferent) and audiovisual test. The simple algorithm of adding the normalized loss of afferent (peripheral) 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 perspective is desirable in the diagnostic evaluation of the hearing-impaired individual in order to understand his communicative abilities and form a cornerstone in the planning of rehabilitation in conjunction with social and psychological factors.