Language Acquisiton by Stephen Krashen PhD.

In these youtube videos from the 80's, Stephen Krashen, a well-known linguist and educational researcher talks about the process of Language Acqusition

Stephen Krashen received a PhD. in Linguistics from the University of California, Los Angeles in 1972. Krashen has among papers and books, more than 486 publications, contributing to the fields of second-language acquisition, bilingual education, and reading. He is known for introducing various hypotheses related to second-language acquisition, including the acquisition-learning hypothesis, the input hypothesis, the monitor hypothesis, the affective filter, and the natural order hypothesis. Most recently, Krashen promotes the use of free voluntary reading during second-language acquisition, which he says "is the most powerful tool we have in language education, first and second."

https://en.wikipedia.org/wiki/Stephen_Krashen