Subitizing reflects visuo-spatial object individuation capacity.

Center for Mind/Brain Sciences, University of Trento, Italy.
Cognition (Impact Factor: 3.16). 06/2011; 121(1):147-53. DOI: 10.1016/j.cognition.2011.05.007
Source: PubMed

ABSTRACT Subitizing is the immediate apprehension of the exact number of items in small sets. Despite more than a 100years of research around this phenomenon, its nature and origin are still unknown. One view posits that it reflects a number estimation process common for small and large sets, which precision decreases as the number of items increases, according to Weber's law. Another view proposes that it reflects a non-numerical mechanism of visual indexing of multiple objects in parallel that is limited in capacity. In a previous research we have gathered evidence against the Weberian estimation hypothesis. Here we provide first direct evidence for the alternative object indexing hypothesis, and show that subitizing reflects a domain general mechanism shared with other tasks that require multiple object individuation.

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    ABSTRACT: Enumeration can be accomplished by subitizing, counting, estimation, and combinations of these processes. We investigated whether the dissociation between subitizing and counting can be observed in 4-to 6-year-olds and studied whether the maximum number of elements that can be subitized changes with age. To detect a dissociation between subitizing and counting, it is tested whether task manipulations have different effects in the subitizing than in the counting range. Task manipulations concerned duration of presentation of elements (limited, unlimited) and configuration of elements (random, line, dice). In Study 1, forty-nine 4-and 5-year-olds were tested with a computerized enumeration task. Study 2 concerned data from 4-, 5-, and 6-year-olds, collected with Math Garden, a computer-adaptive application to practice math. Both task manipulations affected performance in the counting, but not the subitizing range, supporting the conclusion that children use two distinct enumeration processes in the two ranges. In all age groups, the maximum number of elements that could be subitized was three. The strong effect of configuration of elements suggests that subitizing might be based on a general ability of pattern recognition. Subitizing, the ability to rapidly and accurately enumerate a small set of elements (Kaufman, Lord, Reese, & Volkmann, 1949), is a component of number sense, which is essential for proficient math performance (Jordan, Kaplan, Locuniak, & Ramineni, 2007; Kroesbergen, van Luit, van Lieshout, van Loosbroek, & van de Rijt, 2009). Deficient subitizing is suggested to underlie lagging math skills of children with dyscalculia (Schleifer & Landerl, 2011). Despite extensive work on subitizing (starting with Kaufman et al., 1949), the question whether subitizing is a separate process, dissociable from estimation and counting is still actively investigated in various domains, such as neuropsychology (e.g.
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