I decided to use Portuguese as the second language instead of Spanish for a couple of reasons:
1. It's very hard to find someone who hasn't studied Spanish at some point. While Portuguese is similar to Spanish, the differences are significant enough that, with my counterbalancing methods, there isn't too much of a problem with overlap.
2. I know a native Portuguese speaker. The other common experimental language is German, but I don't know anyone who speaks German.
3. My Spanish knowledge made it easier to find cognates in Portuguese. I know nothing about German, that would've been difficult.
So, I'm using a lexical decision task to measure English vocabulary. It's a really good measure that uses low-frequency English words and pretty convincing non-words (one of everyone's favorites is "boobier"), and asks participants to decide whether or not an item is a word. My hope is that high scores on English vocabulary will correspond to beter Portuguese vocabulary learning.
But my real focus is on the effect of cognates on vocabulary learning. Every participant learns 12 Portuguese words, 4 cognates and 8 not. The Portuguese is the same for everyone, but the English translations are not. This should control for some words being better remembered than others.
I've only tested half of the people I want to, but I'm showing a possible interaction between English vocab and Cognate vs. Not. I hope that when I finish testing this may be significant.