Phonetic similarity of /s/ in native and second language: Individual differences in learning curves

Second language learners may merge similar sounds from their native (L1) and second (L2) languages into a single phonetic category, neutralizing subphonemic differences in these similar sounds. This study investigates whether Dutch speakers produce phonetically distinct variants of /s/ in their L1 Dutch and L2 English, and whether and how this phonetic categorization develops over time. Target /s/ sounds in matching words in L1 and L2 were compared in their centre of spectral gravity. Speakers varied in their individual learning curves in the categorization of produced /s/ sounds, both in starting points and in longitudinal trajectories. After 3 years, however, all speakers had converged in producing their /s/ variants in L1 and L2 as two similar but different sounds.