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Mariko Yamaguchi, Arin S. Tuerk, Lisa Feigenson; Heterogeneous object arrays increase working memory capacity in 7-month old infants. Journal of Vision 2008;8(6):202. doi: 10.1167/8.6.202.
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Previous studies have shown that whereas 6.5 month-olds can represent only 1 object at a time (Kaldy & Leslie, 2003), 12 month-old infants, just like adults, can represent up to 3 or 4 identical objects within working memory (Feigenson & Carey, 2003; 2005, Luck & Vogel, 1997). However, nearly all studies measuring infants' memory capacity have used identical objects. Evidence from adults suggests that visual working memory capacity may decrease as item complexity and similarity increase (Alvarez & Cavanagh, 2004), but capacity returns to 3–4 when using cross-category items (Awh, Barton & Vogel, 2007). Can infants, too, store more objects in memory when those objects have distinct features? Recent work suggests that array heterogeneity can affect infants' memory once they have already attained the adult-like capacity of 3 items (Zosh & Feigenson, submitted). However, it remains unknown whether array heterogeneity affects memory earlier in life, when capacity is still undergoing developmental change. Here, we asked how heterogeneity affects memory capacity in younger infants. Seven-month-olds infants were shown 3 objects hidden sequentially behind 2 opaque screens (2 behind one screen and 1 behind the other). The screens were then lifted to reveal either the correct outcome of 3 total objects, or the incorrect outcome of 2. In Experiment 1, when the 3 objects were all identical, infants looked equally to both outcomes, thus failing to represent all 3 objects. However, in Experiment 2 when the 3 objects contained contrasting features, infants looked longer to the unexpected 2-object outcome, indicating an increased capacity limit that matches that of 12 month-olds. These results serve as the first demonstration of infants younger than 12 months representing an array of 3 total objects. Additionally, the heterogeneity of features plays an important role in establishing infants' memory representations for object arrays.
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