Vowels with extreme articulatory-acoustic properties act as natural referents. Infant perceptual asymmetries point to an underlying bias favoring these referent vowels. However, as language experience is gathered, distributional frequency of speech sounds could modify this initial bias. The perception of the /i/-/e/ contrast was explored in 144 Catalan- and Spanish-learning infants (2 languages with a different distribution of vowel frequency of occurrence) at 4, 6, and 12 months. The results confirmed an acoustic bias at 4 and 6 months in all infants. However, at 12 months, discrimination was not affected by the acoustic bias but by the frequency of occurrence of the vowel.