Short-term (or 'working') memory capacity is a strong variable in language development. That is because exposure to language, whether raw or as instruction, may be more or less effective in proportion to memory capacity, through (1) retention of words and (2) holding sets of words together in phrases and sentences, long enough for representations to be established in long term memory. This capacity is not fixed but rather subject to expansion through practice and strategy. Here are two STM instruments with research support that have featured in applied and psycholinguistics studies.
1. Phonological STM v.09 (2020)
In a 'serial recognition task,' learners listen to a string of words or non-words delivered by TTS (text to speech) and try to recall them in the same order. Number and type of items can be varied.
2. Text STM v.0.9 (2020)
(TTS does not work on iPhone) <== NO LONGER TRUE - WORK IN PROGRESS ON THIS...
Users look at a list of words, which then disappears and they try to recall them from a re-ordered lists with distractors. Number and frequency of items can be varied. (A version of Kim's Game)
Service & Kohonen (1995) Phonological memory & vocabulary
Hummel & French (2010) PM & L2 classroom
Hummel & French (2016) PM & L2 proficiency