Small subitizing range in people with Williams syndrome

Recent evidence suggests that the rapid apprehension of small numbers of objects—often called subitizing—engages a system which allows representation of up to 4 objects but is distinct from other aspects of numerical processing. We examined subitizing by studying people with Williams syndrome (WS), a genetic deficit characterized by severe visuospatial impairments, and normally developing children (4–6.5 years old). In Experiment 1, participants first explicitly counted displays of 1 to 8 squares that appeared for 5 s and reported “how many”. They then reported “how many” for the same displays shown for 250 ms, a duration too brief to allow explicit counting, but sufficient for subitizing. All groups were highly accurate up to 8 objects when they explicitly counted. With the brief duration, people with WS showed almost perfect accuracy up to a limit of 3 objects, comparable to 4-year-olds but fewer than either 5- or 6.5-year-old children. In Experiment 2, participants were asked to report “how many” for displays that were presented for an unlimited duration, as rapidly as possible while remaining accurate. Individuals with WS responded as rapidly as 6.5-year-olds, and more rapidly than 4-year-olds. However, their accuracy was as in Experiment 1, comparable to 4-year-olds and lower than older children. These results are consistent with previous findings, indicating that people with WS can simultaneously represent multiple objects, but that they have a smaller capacity than older children, on par with 4-year-olds. This pattern is discussed in the context of normal and abnormal development of visuospatial skills, in particular those linked to the representation of numerosity.     

Cohésion–non-cohésion des scores composites : valeurs seuils et interprétabilité. L’exemple du WISC-IV

When interpreting the composite scores of the Wechsler Intelligence scales, some authors recommended to determine whether the composite scores are unitary or not. It has been suggested that when variability among scores is too large, then the composite score does not provide a good estimate of the psychological attribute, and is not interpretable. The first objective of the paper is to demonstrate that the cut-off threshold values (23 points and 5 points) proposed by some authors are inadequate. Other cut-off threshold values should be used. Most importantly, the second goal of this paper is to demonstrate that the notion of unitary abilities that was guiding principle of interpretation is also inadequate. Indeed, nonunitary index still provides relevant information.