Nguni and Sotho varieties of South African English - distant cousins or twins?

It is well established that accent can have a detrimental effect on the performance of automatic speech recognition (ASR) systems. While accents are usually classified in terms of a speaker’s mother tongue, it remains to be determined if and when this linguistic classification is appropriate for the development of ASR technology. This study focuses on South African English as produced by mother tongue speakers of Nguni and Sotho languages, which account for over 70% of the country’s population. The aim of the investigation is to determine whether these two accent groups should be treated as a single variety, or whether it is better to treat them separately. We begin with a perceptual experiment in which human listeners classify different English accents. Subsequently, speech recognition experiments are conducted to determine whether the acoustic models benefit from the incorporation of Nguni/Sotho accent classifications. The results of the perceptual experiment indicate that most listeners cannot correctly identify a speaker’s mother tongue based on their English accent. This finding is supported by the results of the recognition experiments.