Development of the incorporation of spectral and temporal acoustical features in the perception of the phonemic contrast between [r] and  sounds in the initial prevocalic position was examined for 3 to 6 years old English children. The integration of those features was evaluated in oddity discrimination tasks. It was found that the ability to integrate acoustical cues improves significantly with age. Thus, it may be suggested that the attainment of perceptual distinction between phonemic contrasts (at least for [r] and ) is a gradual and progressive development in the proficiency of categorical perception.
Bibliographic reference. Slawinski, Elzbieta B. (1995): "Development of the perception of initial prevocalic [r] and [l] by English children", In EUROSPEECH-1995, 2293-2296.