Six- and ten-month-old infants' intermodal representation of numerical ratios
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The abilities to represent and process quantity information exist across many animal species and are evident early in the life of individuals. Preverbal human infants are able to estimate, discriminate, and perform simple arithmetic over a variety of quantity information (e.g., simple numerosities, durations, and numerical ratios), and their nonverbal quantification suggests that they represent quantities as noisy analog magnitudes (i.e., the Analog Magnitude System, AMS). With magnitude representations, infants discriminate quantities depending on the ratio between quantities but not their absolute difference, and the precision of magnitude representations increases with age. For example, 6-month-old infants require a 2-fold difference in quantity for discrimination, while 10-month-old infants only require a 1.5-fold difference. Importantly, infants can represent quantities presented in different sensory modalities (e.g., vision, audition and tactility) and recognize quantity correspondence across modalities, suggesting that their magnitude representation is amodal. In addition, the precision of infants discriminating intermodal numerosities is the same as that of discriminating unimodal quantities. Existing studies on infants' intermodal quantification, however, have been limited to simple quantities (e.g., simple numerosities such a s 1, 2, 3, and durations), and examined the precision of intermodal quantity representation only in single age groups (e.g., 6-month-olds). These limitations leave two completely open questions: (1) can infants engage amodal magnitudes to quantify complex quantities (i.e., ratios of simple quantities) in addition to simple quantities across modalities, and ( 2) how precise is their intermodal magnitude representation for complex quantities and how does the precision change with age. Research addressing these questions would provide important insights into infants' amodal magnitude representation and greatly extend our understanding of infants' nonverbal quantitative abilities. To
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