Complex sentence: When reaching an age of 6 months, infants are finally able to control the opening and closing of the vocal tract, and upon obtaining this ability, infants begin to distinguish between the different sounds of vowels and consonants.
Split into simpler sentences: When reaching an age of 6 months, infants are finally able to control the opening and closing of the vocal tract. Upon obtaining this ability, infants begin to distinguish between the different sounds of vowels and consonants.