Language learning involves more than acquiring knowledge of the target language; learners must also be able to put their knowledge to use during real-time processing, and in the past twenty years, sophisticated psycholinguistic and neurolinguistic methods have been employed to allow for a deep investigation into these processes. A number of techniques, such as self-paced reading and cross-modal priming rely on speed responses (for instance a button-push) to infer the underlying comprehension processes that are involved in the real-time processing of linguistic material. Specifically, in comparison to a control condition, a slower response indicates difficulty in, for instance, lexical access, or the processing of ambiguous, complex, or ungrammatical input, at certain points in a sentence. Eye-tracking during reading can also be used to examine lexical and sentence processing in a similar way, but this method can add detail to the study of the comprehension processes via the examination of specific eye-movement measures thought to tap early (first fixations) and later comprehension processes (go-past times and regressions).