Over the past few decades, there has been extensive debate as to whether humans represent number abstractly and, if so, whether perceptual features of a set such as cumulative surface area or contour length are extracted more readily than number from the external world. Here we show that 7-month-old infants are sensitive to smaller ratio changes in number than cumulative area when each variable is tested separately and that infants prefer to look at number changes compared with area changes when the 2 variables are pitted directly against each other. Our results provide strong evidence that number is a more salient dimension to young infants than cumulative surface area and that infants' ability to discriminate sets on the basis of number is more finely tuned than their ability to discriminate sets on the basis of cumulative surface area.
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