Usami, Keiko. (2013). Experimental research for instruction of the Japanese conjunction de: The effectiveness of input flood, input enhancement, and explicit grammar explanation. Acquisition of Japanese as a Second Language. 16, 196-213. [Article written in Japanese]

宇佐美恵子(2013)「接続詞「で」の指導に関する実験的研究―インプット洪水・インプット強化・明示的な文法説明の効果」『第二言語としての日本語の習得研究』16, 196-213.

This study examined the effects of instruction on the learning of the Japanese conjunction de. Three different treatments were employed: 1) input flood (Flood Group), 2) input flood plus input enhancement by the use of subtitles (Enhancement Group), and input flood, input enhancement plus explicit grammar explanation (Explicit Group). Outcomes of these treatments were compared in a controlled experimental study involving 55 students of Japanese. The effects were measured utilizing a pre-test, post-test, and a delayed post-test using a narrative task. The results indicated that the
explicit grammar explanation had the most significant effect on the learning of the
Japanese conjunction de.