Semantic analysis of irrelevant speech in dementia

Abstract

This thesis demanded for studies within an interface between semantics, interaction and neuropsychology. The topic for the thesis was irrelevant discourse caused by dementia and foremost so called confabulation. Systematic studies of the semantic aspects of confabulation have previously not been made and it seemed interesting to try to enlighten the psychiatric concept from a different angle.

Interactive discourse includes three principally different cognitive situations defined in the thesis. The speech event is the present situation shared between the speaker and the addressee. The described situation is a situation existing within the speaker as a memory or alike, and it is linked to the cognitive situation by use of linguistic markers called deixis. A resource situation consists of cognitive structures or memories, which are projected on other situations. Projection is the most relevant mean for the speaker to improve communication.

Analyses of the way the situations were used in cognition and of how shifting between cognitive situations took place were central in the project. A semantic analysis was required concerning the cognitive system, ix., the features of stored knowledge, and the cognitive processing for example construction of discourse. The principal aims of the thesis were to explore the occurrence and appearance of the cognitive situations that were used, and to relate the findings to the cognitive system and the cognitive process.

The patients were demented but with various diagnoses, chosen to obtain distinct contrasts between cognitive dysfunction and localisation of brain lesion. Study I searched for semantic features in a case of right hemisphere damage. The work was further developed in Study II, concerning two cases of Fronto-temporal dementia. Two group studies of patients with Alzheimer's disease and of Fronto-temporal lobar degeneration were carried out (Study 111, IV). Finally, in Study V, three contrasting cases were compared (Alzheimer's disease, Fronto-temporal dementia and Primary Progressive Aphasia, nonfluent).

Disease-specific patterns of confabulation were found by semantic analyses of the cognitive system and the cognitive processing. A dissociation was found in the semantic pattern between patients with frontal damage and those with posterior damage. Frontal dysfunction affected the cognitive process the most, while the cognitive system was most disturbed by posterior dysfunction. A dissociation was also indicated between patients with predominantly left hemispheric brain damage and patients with predominantly right hemispheric damage.

The discourse of the demented individuals turned out to be a rich source of information about the demented individuals' self image and cognitive conditions. Their projected resources were closely linked to the individuals' identity and bad an important operative function in interaction.