Research has demonstrated that focused perceptual training facilitates L2 learners' segmental perception and spoken word identification. Hardison (2003) and Motohashi-Saigo and Hardison (2009) found benefits of visual cues in the training for acquisition of L2 contrasts. The present study examined factors affecting perception and production of vowel duration (i.e., long versus short) in Japanese and benefits of waveform displays as visual cues on the acquisition of vowel duration in L2 Japanese by native speakers of L1 English, and transfer to production. Vowel length in Japanese is a contrastive feature, important for communication, and a challenge for many L2 learners. A pretest-posttest design with controls was used. A between-subject variable was training type: auditory visual (AV), auditory-only (A-only), and no training (controls). Within-subject variables were vowel type, preceding consonant, and pitch pattern. Participants were 64 learners of Japanese whose L1 was American English. Testing and training materials were 40 bisyllabic-words containing long and short vowels. To create the stimuli, two Japanese vowels (/a, u/), two consonants (/k, s/), and 10 pitch patterns were selected. The stimuli, produced by six NSs of Japanese, were recorded. Production and perception pre- and post-tests were administered to assess the effects of training on perception accuracy and reaction time (RT). During production testing, participants produced 16 bisyllabic words in isolation. For perception testing, they completed a forced-choice, four-alternative identification task for 18 stimuli, the bisyllabic words. Perception training, conducted between the pre- and post-tests, involved eight sessions, each 25 minutes; the participants also completed the same identification task, using a computer. During training, feedback was provided on both correct and incorrect responses; immediately after the choice, correct words appeared on the screen. Results indicated significant improvement on identification accuracy for both groups, but the rate of improvement of the AV group was greater. On the other hand, RTs of the two groups became slower after the training. In addition, it was found that vowel type, preceding consonant, and pitch patterns in addition to the talker's voice in the training together affected L2 learners' perception of vowel duration. The results suggested that the learners' stages of L2 perceptual development involve the evaluation of input based on context- and talker-dependent perceptual categories. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]