The critical period hypothesis (CPH) states that the first few years of life constitute the time during which language develops readily and after which (sometime between age 5 and puberty) language acquisition is much more difficult and ultimately less successful. The hypothesis that language is acquired during a critical period was first proposed by neurologists Wilder Penfield and Lamar Roberts in 1959 and popularized by linguist Eric Lenneberg in 1967. Lenneberg argued for the hypothesis based on evidence that children who experience brain injury early in life develop far better language skills than adults with similar injuries.