Learning the speech sounds of a foreign language is difficult for adults, and often requires significant training and attention. For example, native Japanese speakers are usually unable to differentiate between the "l" and "r" sounds in English
thus, words like "light" and "right" are hardly discriminated. We previously showed that the discrimination ability for similar pure tones can be improved unconsciously using neurofeedback (NF) training with mismatch negativity (MMN), but it is not clear whether it can improve discrimination of the speech sounds of words. We examined whether MMN Neurofeedback is effective in helping native Japanese speakers discriminate 'light' and 'right' in English. Participants seemed to unconsciously improve significantly in speech sound discrimination through NF training without attention to the auditory stimuli or awareness of what was to be learnt. Individual word sound recognition also improved significantly. Furthermore, our results indicate a lasting effect of NF training.