From a diary study of his own acquisition of Portuguese in Brazil, leading second language psychologist Richard Schmidt developed the following insight:
SLA is largely driven by what learners pay attention to and notice in target language input and what they understand the significance of noticed input to be.
Traditional information processing models explain acquisition as the conversion of declarative knowledge, obtained through explicit instruction, into procedural knowledge through processing practice which involves the automatisation of controlled processing (see Dual Processing).
The Noticing hypothesis reverses this process: implicit knowledge is acquired through focusing attention on a form which becomes procedural knowledge; declarative knowledge may develop later with practice.
Schmidt defines noticing in a special sense, meaning apperception as opposed to conscious attention. Conscious attention is a metalinguistic process which leads to metalinguistic knowledge; noticing is a more subtle phenomenon.
Doughty claims that:
People learn about the structure of a complex system without necessarily intending to do so, and in such a way that the resulting knowledge is difficult to express.
Classroom illustration: Noticing