Effects of variable input in the acquisition of plural in two dialects of Spanish

In Mexico City Spanish, plural morphology is always overtly realized but in Chilean Spanish, due to a lenition process that targets syllable-final [s], plural morphology is not always realized, and the conditions of overt realization of plural morphology are subject to both linguistic and extra-linguistic factors. In this paper we show that variability in the input for grammatical morphology causes the performance of Chilean and Mexican children to differ from each other and from the adult control groups in production and comprehension tasks in ways that correlate with the reliability of plural marking in the input. Our results support Yang (2002)'s proposal that variability in the input does cause some children to assume a different grammar from the adult.