Experiment 1 provides evidence that 6-month-old infants discriminate 8 from 16 sounds when the potentially confounding continuous variables of element duration, sequence duration, sequence rate, ISI, and amount of total acoustic energy are controlled. This finding accords with previous evidence that infants of this age discriminate nu-
merosities in a 2.0 ratio in visual-spatial arrays (Xu & Spelke, 2000), and it raises the question whether numerosity discrimination has the same ratio limit for the two types of displays. Because 6-month-old infants failed to discriminate arrays of dots that differed in numerosity by a 1.5 ratio, we tested discrimination at this ratio in Experiment 2