Artikel
Sources of ASSR artefacts at high stimulation levels in normal hearing subjects
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Autoren
Veröffentlicht: | 31. Mai 2005 |
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Gliederung
Text
Introduction
To identify non-physiological sources of false-positive ASSRs at high stimulus levels (110 and 120 dB SPL).
Materials and Methods
The ASSR was recorded in normal hearing adults who did not hear the stimulus by using headphones with blocked housing placed behind the ears and adequate masking of the stimulus through insert phones. Tones of 0.5 and 2 kHz were presented simultaneously at both sides at 110 or 120 dB SPL for 4.4 minutes. The tones were 100% amplitude modulated and 20% frequency modulated ("Mixed-Mode" stimulus) or only amplitude modulated but expanded with multiple carriers ("Extended Stürzebecher" stimulus). Both 40 and 90 Hz modulation was tested. The EEG was recorded in six derivations simultaneously. Two electrodes were deliberately altered to produce a medium to high impedance. All recordings were made using two different amplifiers and two different types of headphones.
Results
Preliminary results showed many artefacts, which were caused by a malfunctioning amplifier. After replacement of the amplifier, results from the first subjects showed only a small number of artefacts under all conditions.
Conclusions
The possibility of artefacts is highly disturbing for clinicians, especially testing subjects at risk for large hearing losses. Apart from the specific false-positive rate found with this equipment, the significance of this study is that it proposes a method for each centre to verify the validity of ASSR testing at high stimulus levels as far as non-physiological sources of artefacts are concerned (that is, disregarding potential physiological responses of non-auditory origin).