Can native Japanese listeners learn to differentiate/r-l/on the basis of F3 onset frequency?

Many attempts have been made to teach native Japanese listeners to perceptually differentiate English/r-l/(e.g. rock-lock). Though improvement is evident, in no case is final performance native English-like. We focused our training on the third formant onset frequency, shown to be the most reliable indicator of/r-l/category membership. We first presented listeners with instances of synthetic/r-l/stimuli varying only in F3 onset frequency, in a forced-choice identification training task with feedback. Evidence of learning was limited. The second experiment utilized an adaptive paradigm beginning with non-speech stimuli consisting only of/r/and/l/F3 frequency trajectories progressing to synthetic speech instances of/ra-la/; half of the trainees received feedback. Improvement was shown by some listeners, suggesting some enhancement of/r-l/identification is possible following training with only F3 onset frequency. However, only a subset of these listeners showed signs of generalization of the training effect beyond the trained synthetic context.