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Baby Lab

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Infants’ detection of increasing numerical order comes before detection of decreasing number

Or­di­nal­ity is a fun­da­men­tal as­pect of nu­mer­i­cal cog­ni­tion. How­ever, pre­ver­bal in­fants’ abil­ity to rep­re­sent nu­mer­i­cal or­der is poorly un­der­stood. In the pre­sent study we ex­tended the ev­i­dence pro­vided by Mac­chi Cas­sia, Pi­cozzi, Girelli, and de Hevia (2012), show­ing that 4-month-old in­fants de­tect or­di­nal re­la­tion­ships within size-based se­quences, to nu­mer­i­cal se­quences. In three ex­per­i­ments, we showed that at 4 months of age in­fants fail to rep­re­sent in­creas­ing and de­creas­ing nu­mer­i­cal or­der when nu­merosi­ties dif­fer by a 1:2 ra­tio (Ex­per­i­ment 1), but they suc­ceed when nu­merosi­ties dif­fer by a 1:3 ra­tio (Ex­per­i­ments 2 and 3). Crit­i­cally, in­fants showed the same be­hav­ioral sig­na­ture (i.e., asym­me­try) de­scribed by Mac­chi Cas­sia et al. for dis­crim­i­na­tion of or­di­nal changes in area: they suc­ceed at de­tect­ing in­creas­ing but not de­creas­ing or­der (Ex­per­i­ments 2 and 3). These re­sults sup­port the idea of a com­mon (or at least par­al­lel) de­vel­op­ment of or­di­nal rep­re­sen­ta­tion for the two quan­ti­ta­tive di­men­sions of size and num­ber. More­over, the find­ing that the asym­me­try sig­na­ture, pre­vi­ously re­ported for size-based se­quences, ex­tends to nu­meros­ity, points to the ex­is­tence of a com­mon con­straint in or­di­nal mag­ni­tude pro­cess­ing in the first months of life. The pre­sent find­ings are dis­cussed in the con­text of pos­si­ble evo­lu­tion­ary and de­vel­op­men­tal sources of the or­di­nal asym­me­try, as well as their im­pli­ca­tion for other re­lated cog­ni­tive abil­i­ties.



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