Answer to Question 1
Just hearing others converse is not sufficient to promote acquisition. Children whose only exposure to a language is through television, for example, fail to acquire the language. What the evidence does indicate is necessary is some minimal exposure to language through one-on-one conversation with a significant adult. Hearing children of profoundly deaf parents show a normal course of acquisition if they spend five to 10 hours per week in the company of a hearing/speaking adult. The quantity of speech exposed to (over some minimum) is not the critical variable. Opportunity to experience language in the context of jointly attending to an object or event with an adult is predictive of language proficiency. Some characteristics of the language input itself have also been found to influence proficiency, e.g., motherese. Although it is not essential for adults to speak in motherese, it can facilitate the learning process. Motherese does not involve speaking at the child's level, but adjusting input to be slightly more complex than the child's own speech. Adult language that expands, recasts, or otherwise extends the child's speech also has a facilitative effect, particularly on the learning of syntactical principles.
Answer to Question 2
A
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