You need to consider such factors as Noticing, Awareness, Attention, Focusing, immediate and longterm memory.
Do you distinguish between acquisition and learning, as Krashen did?
How much interaction do you believe is necessary?
Do you believe in an innate language device, as Chomsky did/does?
My subjective opinion: In children learning their L1, it is largely unconscious. But learning an L2 by an adult is largely a conscious process.
What do you think?