One of the most challenging responsibilities of the audiologist is to fit a small child with a hearing aid and adequately determine the gain. The importance of a sufficiently audible signal for the development of hearing and speech is indisputable. However, the methods leading to this goal differ significantly. Few audiologists conduct systematic studies, while many fail to use the most modern technologies. The primary goal in fitting aids for children is to make sure that the patients will hear speech sounds at a safe level. In the fitting process, it is necessary to perform tests, which check the patient´s sound perception and facilitate the choice of adequate acoustic parameters for the aid. Current methods are based either on audiometric test results (ABR, VRA, impedance audiometry, otoacoustic emissions, in situ measurements, matchbox) (4) or on loudness scaling (1). With small children, the latter is of little use as it exceeds the child´s perceptive capacity (5).

The aim of the study was to prepare phonic material for free field testing of the hearing competence of children fitted with hearing aids.

We used a method of hearing aid fitting based on natural sound tests in 20 randomly - chosen children aged between 4 months and 5 years. We evaluated the previously - performed audiometry based on one of the mentioned methods (i.e. ABR, VRA, impedance audiometry or pure tone audiometry) with unaided thresholds obtained by free field testing. Simultaneously, we assessed the discomfort level.

Testing was performed with the use of sounds derived from the child´s natural environment. The concept of using natural sounds for testing has been validated and adopted in several fitting methods, such as HGJ (2). In order to simplify the test and optimise it for children´s needs, we limited our procedure to global audiometry using three bands: low, medium and high frequency. The selected natural sounds were divided into three groups, based on the band of their spectrum: low , medium- and high-frequency sounds. Subsequently, the sounds were processed digitally with the use of high-, low- and bandpass filtering as well as level normalisation. The sound material was recorded on a compact disc (3). Such a recording may serve to evaluate hearing thresholds, comfort threshold values and loudness discomfort levels for low, medium and high frequencies and the determination of electroacoustic parameters for the fitted aids.

Six children had medium hearing loss, 8 had profound hearing loss and 6 had residual hearing. The obtained results were in agreement with the previous audiometric tests. Subsequently, as the children were fitted with a hearing aid, we compared free field natural sound test results with responses to pure tone and in situ measurements. All tested children had a pronounced response to natural sounds, whereas pure tone testing elicited responses in 7 children only. The obtained result may be explained by the fact that children usually respond to familiar sounds only (4). Also, they bore less easily, as they find testing with the use of natural sounds more attractive. The same method was used to determine discomfort levels. After 2-4 weeks all children were re-tested with full test-retest agreement found in 17 children.

Fitting hearing aids with the use of natural sounds makes it possible not only to fit the aid correctly but also to change settings as demanded by the child´s physiological development and the progress of rehabilitation. Thus, the method is a workable test, which may be used in the fitting of hearing aids.

Being recorded on a compact disc, the test may be used widely in audiology labs and rehabilitation clinics as well as being helpful in individual rehabilitation training in the child´s home.