Still there are some interesting critical period phenomena in human devel. Any later and there will always be lack of binocularly driven cells necessary to binocular vision. There is considerable reason to believe that there is a critical period for learning human language that does not extend beyond age 10 or so. The primary data come from case histories but there are some data too from second language learning among immigrants that imply a real change in facility of language learning some time at or before adolescence. Still, the bottom line is that the concept of critical periods that developed from embryological studies has limited applicability to behavioral, emotional, linguistic, intellectual, and social development in humans and other animals that manifest these.
Critical periods are no threat to the general rule of plasticity. .
That Indicate Stability and Predictability Data that are given as measures of stability and predictability are frequently inadequate for a number of reasons. One is that they can fail to capture the practical importance of the data. Cohen likes to point out that the correlation between taking aspirin and fatal heart disease is nearly zero yet the clinical efficacy of taking aspirin is so great that the Framingham study in which this issue was addressed was terminated early so that all of the controls could be placed on aspirin. A second reason that the data can be inadequate is that they focus attention on a single conditional relationship rather than on the big picture. Even with a doubled risk, the overall risk for fatal heart disease will still be quite small.