ISCA Workshop on Plasticity in Speech Perception (PSP2005)
Senate House, London, UK
In the present study we examined the speech processing skills of a child having Landau-Kleffer syndrome (LKS). LKS is a rare childhood epileptic disorder, characterized by an abnormal EEG pattern and the loss of language skill leading to aphasia. The mechanisms behind LKS are not yet fully understood, and questions concern the origin of epileptic activity, the link between epileptic activity and language deficit, as well as the developmental issue, notably the fact that LKS appears exclusively in the developing brain. In our study we assessed two aspects of language processing skills using event related brain potentials (ERPs): discrimination of segmental and that of suprasegmental cues. The segmental task consisted of the discrimination of word initial phonemes, where a two syllable meaningful word was contrasted with its meaningless pair differing only in the initial phoneme ('b' vs. 'p'). The suprasegmental task used differing stress patterns: the obligatory Hungarian trochaic stress pattern (stressed followed by an unstressed syllable) was contrasted with a non-existing iambic pattern (unstressed followed by a stressed syllable). Results indicated that the two cues of spoken language were processed asymmetrically: the mismatch negativity component (MMN) was obtained for the phoneme difference, while the stress pattern difference failed to elicit any MMN. At the same time, a study with normal adults show that both contrasts are processed reliably, resulting in a MMN. Therefore result of the study confirm, that in LKS processing of segmental information is intact, that means phonemes are automatically discriminated, and that of the suprasegmental (stress) information is not. Beside the ERP study several other assessments were carried out so as to obtain a more complex picture on the language deficit, including examination of the source of epileptic activity by using electronic source localization and PET, as well as neuropsychological assessment of cognitive and behavioral skills. As a conclusion we believe that LKS is a childhood language disorder that can be used to study what happens to the language system if in the course of development the essential neural circuits are severely disturbed. We also believe that the tools we use, that is the electrophysiological measurement of pre-attentive language processing is a fruitful approach since it makes possible the assessment of fundamental sub-processes during language comprehension while it does not require the patient / child to be responsive.
Bibliographic reference. Honbolygo, Ferenc / Csépe, Valéria / Sárközy, Gergely / Kálmánchey, Rozália (2005): "Segmental and suprasegmental speech processing in a child with Landau-kleffner syndrome", In PSP2005, 77-80.