Matched-accent processing: Bulgarian-English bilinguals do not have a processing advantage with Bulgarian-accented English over native English speech

The Interlanguage Speech Intelligibility Benefit (ISIB) hypothesis for Talkers suggests that there is a potential benefit when listening to one's second language when it is produced in the accent of one's first language (matched-accent processing). This study explores ISIB, considering listener proficiency. According to second language learning theories, the listener's second language proficiency determines the extent to which they rely on their first language phonetics, hence the magnitude of ISIB may be affected by listener proficiency. The accuracy and reaction times of Bulgarian-English bilinguals living in the UK were recorded in a lexical decision task. The English stimuli were produced by native English speakers and Bulgarian-English bilinguals. Listeners responded more slowly and less accurately to the matched-accent stimuli than the native English stimuli. In addition, they adapted their reaction times faster to new speakers with a native English accent compared to a Bulgarian accent. However, the listeners with the lowest English proficiency had no advantage in reaction times and accuracy for either accent. The results offer mixed support for ISIB for Talkers, and are consistent with second language learning theories according to which listeners rely less on their native language phonology when their proficiency in the second language has increased.