Sounds that are not included in one's native language first begin to disappear from use during the stage of language development.

Babbling

At around 3-4 months, children start the babbling period, which is characterized by the production of sounds that approach the sounds of adult speech and whose frequency is maximum between 9 and 12 months. During this period, the sounds produced already have an upward and downward intonation pattern, however they are not intelligible until seven or eight months, when parents begin to identify babbling with requests, hunger, surprise, etc.

The role of this period in the acquisition process is not clear; according to Menyuk (1970, p.79) the purposes of babbling are "to explore the possibilities of the vocal mechanism, to feel pleasure in the vocal performance, to learn to control the output of the mechanism and thus, to repeat certain sequences. In a later stage, babbling has the function of drawing the parents' attention and communicating the child's emotional state.

answer:

d. because dr. laguardia selected a widely used measure, his study generalizes to has strong external validity. external validity has limited external validity. other applications of this measure.

the widely used measure that he applied to his experiment was the benton facial recognition test. it employed on to football players and as result, only players who suffered brain concussions did not pas this test. and although it has an external validity, it is limited because it isn't general to apply to other population.