Abstract
Until now, phoneme discrimination deficits and central auditory processing disorders could only be diagnosed
by subjective tests. Measurement of event-related-potentials (ERP), especially Mismatch Negativity (MMN),
seems to be a promising tool for objectifing auditory discrimination ability in children. The aim of this study was
to prove the suitability of ERP/MMN measurement in objectifing aspects of central auditory processing in
individual clinical diagnosis of school-age children. Phoneme discrimination (D/G) was tested with ERP`s and
subjective measurements in 82 normal children (2.nd and 3.rd grade). Additional evaluation of phoneme stimuli
was carried out with ten normal adults and five dyslexic children. The ERP´s were evaluated with a
measurement technique developed at the Department of Audiology and Phoniatrics. Cortical responses of
normal children to standard stimuli demonstrate a great interindividual variability for single components. Results
show significant age influences which not only indicate morphological differences between children and adults
but even within the age-range of the tested children. In addition significant gender differences could be found in
the amplitude of some cortical components in school-age children. An assessment of cortical responses should
consider not only age but also gender influences.
MMN reponses in children were much more variable than in adults. The adults and 2/3 of the normal
school-aged children show two negativities (MMN I and MMN II) in their difference waves (deviant response
minus standard response). In 1/3 of children however only an early positivity and a late MMN (MMN II) could be
seen. Early positivity was found more often in younger children, indicating that the typical mismatch response
pattern depends on age. The five dyslexic children demonstrate longer latencies for both MMN I and MMN II. It
seems that preconscious discrimination of phonemes in these children is somewhat prolonged. With the
applied measurement technique individual ability of preconscious processing and phoneme discrimination in
normal school-age children could be objectified. However, a large group of patients must be evaluated before
one can finally decide if this examination procedure is a valuable tool for specific diagnosis of auditory
discrimination deficits. |
