I am interested in how age, experience and the native language sound system interact with the perception and production of a second language. Adult second language learners approach their second language with a first language already in place. I investigate how experience with a previously acquired language affects the way learners perceive and produce a second (or third) language. I approach these issues by assuming the input signal is a source of rich information that learners may or may not be able to take advantage of when perceiving and producing their non-native language and creating the representations that support further learning.