 Psychologists have studied differentiation in lab environments. In one such study, experimenters took six native Japanese speakers who had lived in the United States from between six months and three years (Logan, Lively, &amp; Pisoni 1991). The subjects were not native English speakers. The experimenters found that they were able to train these subjects to better distinguish between the phonemes /r/ and /l/. This is a case of improved differentiation, where the subjects became better at perceiving the difference between two properties, which they had more trouble telling apart before.