Jason Kottke brought up the closed captioning topic today:
A few months ago I noticed that several friends (who speak English and aren’t deaf) routinely watch TV and movies with closed captions and subtitles on. I asked about this on Twitter and the resulting thread was fascinating. Turns out many of you watch TV this way for all kinds of different reasons — to follow complex dialog in foreign or otherwise difficult accents, some folks better retain information while reading, keeping the sound down so as not to wake sleeping children in tight living spaces, and lots of people who aren’t deaf find listening difficult for many reasons (some have trouble listening to dialogue when there’s any sort of non-ambient noise in the background).
When I came to U.S. and started watching TVs and movies, as a non-native speak I was very frustrated that there are no closed captioning. I also didn't know there is the option to turn it on. I wouldn't even think that TV technology actually supports separate closed-captioning data.
You see, I grew up in China. All TVs and movies have always-on closed captioning baked into the stream. There is no option to turn it off.
You ask why that's the case in China?
First, there are many varieties of spoken Chinese with many dialects underneath. Most of TVs and movies are spoken in mandarin. Especially in earlier years, many of the population don't or have difficulties to understand it. But for written Chinese, they are the same, mostly. So closed captioning is understood by more people.
Second, more importantly, homophones. Even though there are tens of thousands of Chinese characters, there are only 1327 pronunciations. That means there are just so many homophones. For common phrases, it not a big problem and we can narrow down further from surrounding context. But for things like names, it's just not possible to know what are the Chinese characters they are speaking. So we rely on close captioning.
Of course, there is also the accessibility reason for people who have hearing loss. But it doesn't explain why closed captioning is the default and there is no option to turn off.