We have two basic ways of expressing simultaneous actions in Japanese, e.g. “I ate dinner while watching television”. Both translate as “while” in English, but the usage in Japanese is different.
～ながら
| 【Verb: Stem】ながら【Verb】 |
| テレビを |
| Eat dinner while watching television. |
| To go to sleep thinking about work. |
| To work your way through university. |
What about the order? Well, grammatically it doesn’t matter but there the final verb can be considered to be the “main” action.
| テレブを |
| To eat dinner while watching television. |
| To watch television while eating dinner. |
～ている間 に
| 【Verb: Present Participle】 |
The kanji 間 we’ve seen used as a counter for time periods.
| １ |
| One hour. |
| ３ |
| Three weeks. |
In this structure 間 is a noun which the present participle is modifying to express the time period while doing something.
| To refrain from drinking while pregnant. |
The critical difference between ながら and ～ている間に is that in the case of the former both actions will be performed by the speaker. On the other hand, ～ている間に is typically used when something else happens that is outside of your control while you are doing something.
| Yesterday while I was sleeping a burglar crept into my room and stole my wallet. |
| テレビを |
| To get a phone call from a friend while watching television. |