Whether learning is driven consciously or unconsciously has been a controversial topic for second language (L2) researchers. The first researcher that introduced the research findings of psychology into the studies of second language acquisition (SLA) is Schmidt (1990), who claims that what is noticed becomes intake which is necessary for L2 learning. He hypothesizes that noticing is a necessary condition for L2 learning. Although noticing is generally considered to be a necessary component for L2 learning, opinions differ as to whether it is indispensable for L2 learning or not. There are quite a few researchers who believe that conscious understanding of the target language (TL) system is necessary if learners are to use linguistic forms correctly and appropriately. For example, Peters (1998) has proposed that in every domain of language learning, learners must attend to and notice any source of variation that matters. On the other hand, however, there are also quite a few researchers who believe that language learning is essentially unconscious. Krashen (1985) is one of the researchers who belong to this group and has asserted that conscious learning is of little use in actual language production and comprehension. Gregg (1984) also assumes that most L2 learning is unconscious.
It is plausible that both conscious learning and unconscious learning surely exist and that they both contribute to L2 learning respectively. Although the existence of unconscious learning cannot be denied completely, conscious learning, or attended learning, is assumed to have a role of greater consequence in L2 learning. It should be noted that paying attention to form is facilitative and necessary if learners are to learn redundant grammatical forms and to acquire the ability to produce them correctly.
This paper will first review attention, consciousness and noticing to elucidate the relationship between them. It will then review the Noticing Hypothesis. Although it is a fascinating hypothesis for L2 researchers and teachers, it has also drawn criticism from some researchers (for example, Tomlin & Villa, 1994; Truscott, 1998).It is necessary to review the details of their criticism and to confirm the validity of the hypothesis. Then, focusonform activities, in which attention-drawing devices are employed to facilitate L2 learning, will be reviewed. It is finally suggested that L2 learning is mainly driven by what learners pay attention to and notice in TL input.