Abstract
Over the past decades, abundant evidence has amassed that demonstrates infants’ sensitivity to changes in number. Nonetheless, a prevalent view is that infants are more sensitive to continuous properties of stimulus arrays such as surface area and contour length than they are to numerosity. Very little research, however, has directly addressed infants’ sensitivity to contour. Here we used a change detection paradigm to assess infants’ acuity for the cumulative contour length of an array when the array’s surface area and number were held constant. Seven-month-old infants detected a threefold change in contour length but failed to detect a twofold change. These results, in conjunction with previously published data on numerosity discrimination using the same experimental paradigm, suggest that infants are not more sensitive to changes in contour length compared to changes in numerosity. Consequently, these findings undermine the claim that attention toward contour length is a primary driver of numerical discrimination in infancy.
Highlights
It is well established that infants are sensitive to numerical information in their environment, beginning just hours after birth (Xu and Spelke, 2000; Brannon et al, 2004; Lipton and Spelke, 2004; Xu et al, 2005; Izard et al, 2009; Libertus and Brannon, 2010)
Infants failed to detect a twofold change in cumulative contour length in Condition 1
We compared infants’ change detection preference scores for a threefold change in cumulative contour (Condition 2) to preference scores from previously published data in which infants of the same age were tested in the same paradigm with threefold changes in cumulative area (Libertus et al, 2014) and number (Libertus and Brannon, 2010)
Summary
It is well established that infants are sensitive to numerical information in their environment, beginning just hours after birth (Xu and Spelke, 2000; Brannon et al, 2004; Lipton and Spelke, 2004; Xu et al, 2005; Izard et al, 2009; Libertus and Brannon, 2010) Despite these findings, debate remains as to whether infants’ representations of number are secondary to representations of continuous quantities that covary with number, such as surface area and contour length (Piaget, 1952; Clearfield and Mix, 1999, 2001; Mix et al, 2002; Clearfield, 2005; Cordes and Brannon, 2009; Cantrell and Smith, 2013; Libertus et al, 2014). These findings suggest that number is easier to extract than surface area from arrays containing a large number of elements
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