An investigation into hemispheric lateralisation of different acoustic rates and its relationship with language ability during infancy

Abstract

Successful language development is dependent on the capacity to process segmental and suprasegmental phonology. Infants have a lateralised right hemisphere response to suprasegmental changes in speech from birth and a bilateral response to segmental changes. A shift occurs by ~12 months old whereby infants become left hemisphere lateralised for segmental changes in real speech. Lateralised processing of segmental and suprasegmental changes have been linked to different rates of change in the speech signal. The aim of this thesis is to investigate the lateralisation of two discrete rates at two stages in infancy. This thesis also aims to investigate how rate lateralisation may be related to concurrent and future language ability.

The studies in this thesis presented two amplitude modulated tones, 4Hz and 16Hz, while measuring brain activity using electroencephalography (EEG) in groups of adults and infants (6 and 12 months). Language ability was measured in infants only. As a measure of future language ability, 12 month olds returned at 18 months. Adult findings were as expected. Infant results were less clear. 6 month olds do not appear to have an adult-like response, whereas 12 month olds do. In addition, the shift found for segmental changes in real speech stimuli, was not found for non-speech stimuli. A shift was found for suprasegmental changes. There was only one significant relationship between lateralisation and language; a positive relationship between lateralisation of slow rate stimuli and vocabulary comprehension in 12 month olds.

By 12 months, infants appear to have adult-like lateralisation of rate which may develop through maturation or language experience. If lateralisation of rate is a result of maturity, it may mean that the relationship between lateralisation of rate and lateralisation of language is minimal and language experience has little impact on the lateralisation of acoustic rate.

Date of Award	Jul 2020
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Tim Fosker (Supervisor)