Does immersion experience reduce /r/-/l/ category overlap for Japanese learners of English?

Non-native listeners commonly experience difficulty discriminating foreign speech contrasts, although this may improve over time. This improvement is typically attributed to the establishment of new speech categories that are thought to improve discrimination accuracy. Here, we examined the development of phonetic categories in Japanese listeners, who varied in their degree of immersion in an English environment. Discrimination did not improve following 6 months of immersion, nor did the degree of phonetic category overlap reduce. The findings suggest that more than 6 months of immersion is required to reduce category overlay of /r/ and /l/ in Japanese listeners.