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.