Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
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One of the few "deficiencies" of brainstem evoked potentials has been the determination of frequency specific thresholds in order to establish an objective audiometric valuation, especially as regards low frequencies (Purdy et al, 1989; Eggermont and Schmidt , 1990; Gersdoff et al, 1991).

Another problem is the concerning the morphology and characteristics of the frequency stimulus, which arises when trying to match an appropriate stimulus and a synchronised answer of the auditory fibres. From a theoretical point of view, the best matching or mixture between an abrupt rectangular wave with precision in time and a perfectly defined continuous pure tone in frequency is the "logon". This is a pure tone whose amplitude is modulated by a gaussian distribution curve, described in detail by Gabor in 1947 (Davis, 1994).

To avoid the problem of frequency specificity in the diagnosis, it has been designed through the years different techniques such as the "answer derived" one (for example: Laukli and Mair, 1986) or different stimuli: click filtered (for example: Conjin et al, 1993) tone-pip with ipsilateral masking (for example: Hyde, 1985; Stapells et al, 1990; Munnerley et al, 1991) tone-burst (for example: Beattie and Kennedy, 1992) or different types of tone-pip (for example: Maurizi et al, 1984; Ito et al, 1988; Telian and Kileny, 1989; Gorga et al,1991; Robier et al, 1992; Gorga et al, 1992).

All these techniques and methods, described among others by the above said authors, have advantages and disadvantages and therefore detractors and defenders.

The purpose of this study is to bring forward new experiences in the objective tonal measuring by means of brainstem auditory evoked potentials with a frequency specific stimulus ("logon" type, described further on). Moreover, to compare them with those obtained by other authors, so that it can be considered when choosing a specific frequency valuation.

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