Sabine,

I think that there are a lot of RP studies on learning vocabulary words in a
new language. Here's one:

http://www.sciencemag.org/content/319/5865/966.abstract

Jim Sibley's link, earlier in this thread, also mentioned vocabulary
acquisition:

http://bjorklab.psych.ucla.edu/research.html

It appears that this field could be ripe for more research.

Mike