  Thus, in the case of phonological learning, there does seem to be an  inborn predisposition to segment vocal sounds into language-relevant  units, or   phonemes.[25]  However, there is also evidence that learning plays a role in shaping phonological knowledge — and not just by ‘pruning  away’ unwanted ‘phonological representations,’ as  Eimas (1975) hypothesized, but also by shaping the precise boundaries of adult phonemic categories. For example, caregivers reliably speak  a special ‘language’ (“Motherese” or  “Parentese”) to young babies, raising pitch, shortening  sentences, emphasizing stressed morphemes and word boundaries and  — most relevant here — exaggerating the acoustical  differences between certain crucial vowels (in English, /i/, /a/ and  /u/) . This ‘stretching’ of the distance between vowels  (demonstrated in Finnish and Russian as well as English by Kuhl et  al. 1997a) facilitates the infant's representation of clearly  distinguishable vowel prototypes. Kuhl 2000 argues that these  prototypes subsequently function as ‘magnets’ around  which subsequent linguistic experiences are organized, and form the  set points of the language-specific phonological ‘map’  that emerges by the end of the first year.