In this and the next chapter, I attempt to provide a macroscopic analysis of general failure (see also Fig. 1.1). A central argument to be advanced is that adult L2 learners are universally preconditioned to fossilization. Two lines of research – the critical period effects and the NL influence – are brought to bear on the argument. Both lines of inquiry, one being biologically oriented and the other cognitively oriented, have been subject to long-term, substantial investigation over the past 30 years and both by now have mature implications for understanding lack of success in adult SLA.

The focus of this chapter is on examining the critical period effects. I will begin by reviewing the Critical Period Hypothesis (Lenneberg, 1967), and then discuss it in relation to first and second language acquisition. In the section that then follows, I will discuss the modular nature of the critical period, and in the final section, highlight the critical period effects.

The Critical Period Hypothesis

In 1967, Lenneberg, a psycho-biologist, who was inspired by findings from ethological studies and insights from the work of his contemporaries (e.g., Penfield & Roberts, 1959), proposed for human language learning a Critical Period Hypothesis (CPH), suggesting there is a period during the human life span from infancy to puberty (age 2 to 13) that is critical to language learning, during which learning is successful and after which it is marginal. Such a period is thought to be neurobiologically determined in that it is coinceptive and conterminous with a series of neurological processes – lateralization of cognitive, linguistic, and perceptual functions, myelination, the proliferation of neurons in the cerebral cortex, the increase in neurotransmitters, and the variation of amplitudes of certain brain waves, to name a few – that take place during the first years of life and that taper off and plateau by puberty (Scovel, 1988).