This paper reports on a small-scale pilot study further investigating the perceptual development in the acquisition of durational contrasts by different levels of adult English-speakers of Japanese. Four kinds of naturally spoken word-tokens were edited by a synthesizer to generate word-stimuli varying the duration of a certain consonant/vowel (originally contained in each word-token) along a durational continuum. These synthetic word-stimuli were randomized and presented to both native speakers and English-speaking learners of Japanese, in four forced-choice word identification tasks. The overall identification data in all tasks, indicated that the second language learners' levels of language experience or proficiency correlated positively with the closeness of their perceptual categories of the durational continua, to the perceptual categorization of the native speaker group. This seems to imply that the second language learners' initial perceptual categories or perceptual targets, may be possibly modified/developed towards the "categorical perception" model shown by the native speakers in the course of adult second language acquisition. (Contains 24 references.) (Author)