Intensive Foreign Language Learning Reveals Effects on Categorical Perception of Sibilant Voicing After Only 3 Weeks

Models of speech learning suggest that adaptations to foreign language sound categories take place within 6 to 12 months of exposure to a foreign language. Results from laboratory language training show effects of very targeted training on nonnative speech contrasts within only 1 to 4 weeks of training. Results from immersion studies are inconclusive, but some suggest continued effects on nonnative speech perception after 6 to 8 years of experience. We investigated this apparent discrepancy in the timing of adaptation to foreign speech sounds in a longitudinal study of foreign language learning. We examined two groups of Danish language officer cadets learning either Arabic (Modern Standard Arabic and Egyptian Arabic) or Dari (Afghan Farsi) through intensive multifaceted language training. We conducted two experiments (identification and discrimination) with the cadets who were tested four times: at the start (T0), after 3 weeks (T1), 6 months (T2), and 19 months (T3). We used a phonemic Arabic contrast (pharyngeal vs. glottal frication) and a phonemic Dari contrast (sibilant voicing) as stimuli. We observed an effect of learning on the Dari learners' identification of the Dari stimuli already after 3 weeks of language training, which was sustained, but not improved, after 6 and 19 months. The changes in the Dari learners' identification functions were positively correlated with their grades after 6 months. We observed no other learning effects at the group level. We discuss the results in the light of predictions from speech learning models.