Sentences Stuck in Your Head
If you're a learner of German then you may have encountered the term Ohrwurm, or earworm, which describes a piece of music or phrase that repeats itself over and over in your head.
Researchers have done work on individuals to figure out how many sequences of sounds can be remembered, whether understandable or not. Research has shown that sequences of differing sounds are much easier to remember than those with repetitive sounds.
In the case of a string of numbers, it depends on the language. Research has shown that languages with more than one syllable per number have trouble remembering a string of eight numbers they just heard for the first time. However, in languages like Chinese with one syllable each, a string of eight numbers is very easy to recall.
So the phonological loop can handle and recall a limited number of sounds. At first the sounds can mean nothing at all, but after attaching some meaning to the sounds, the length of sounds and length of recall can be stretched out longer and longer.
The idea with building memories with spaced repetition is to get the sounds moved into your semantic memory. If you experience the sounds during interaction with a friend, then they can become episodic memories, if the encounter with that friend was exciting. This is a much stronger memory to have for the long term.
Finally, if you're able to experience and use and live your new language throughout your daily life, it gets ingrained into your routines. In this case, it is passed into your procedural memory. Even if you go through an accident or trauma and lose your memory, you will still have your procedural memory, or the ability to speak your own language. Your native language is programmed into you like an automatic response to the environment. If an acquired language is srong enough and gets passed into procedural memory, you're unlikely to lose it.
The Din in Your Head
As you go through practicing a mass amount of sentences in a spaced repetition format, preferably daily, these sentences are likely to remain in the phonological loop.
When you're not practicing or training your language and go about your daily activities, you'll still hear the sentences bouncing around in your head. This is what Krashen calls the din in your head.
This is an important event because it means that the language is starting to take hold. It's in the phonological loop and you can take advantage of it to pass it into your memory.