Weakening of stop articulation in Japanese voiced plosives was analyzed using the phonetically annotated part of the Corpus of Spontaneous Japanese (CSJ). It turned out that the weakening of/b/ and /d/ into [ß] and [ð] could be best described as a function of TACA (time allotted for consonant articulation) as was the case in the affricate-fricative variation of Japanese /z/. The location of the voiced plosive phonemes in a linguistic unit showed secondary importance as the factor of the variation, but it was the location in a higher-level unit like accentual phrase or utterance that played a crucial role. The weakening of /g/ into [ϒ] or [η], on the other hand, is somewhat different in that it should be treated differently depending on whether the phoneme was immediately preceded by a moraic nasal /N/. When it was preceded by an /N/, the TACA-RSA (rate of stop articulation) relationship reached a plateau much earlier (at around 70%) than in /b/, /d/, and /g/ not preceded by an /N/ (where the RSA values reaches the level of 90%). It also turned out that the curve of TACA-RSA relationship changed systematically reflecting the complexity of phonological contrast at the point of articulation of the phoneme in question. The more complex the contrast is, the earlier the curve reaches a plateau. Statistical modeling by means of logistic regression analysis revealed it was possible to predict the variation with 68-76% accuracy (closed data) using only the TACA information. The accuracy reached 72-81% when TACA and all other linguistic and extra-linguistic variables were used.
