Orientation discrimination in WS 6
results showed that the WS group benefited from segmentation to the same extent as
typically developing controls. This suggests that individual with WS do not have a
local bias at perception. Pani et al. (1999) provided further support for this suggestion
using a visual search paradigm. They showed that the relative effects on search
efficiency of the global configuration of the visual array, and the number of local
elements it contained, did not differ between a group of individuals with WS and a
group of typical adults. It appears then, that the poor performance on the Block
Design task reported in WS does not relate to the perceptual stage of segmentation. A
local bias in WS is more evident in production than perception tasks, suggesting that
individuals with WS may suffer more from problems of integration, than of
segmentation. Indeed, the studies by Bellugi and colleagues support this notion; in the
Block Design task, their WS group showed difficulty in integrating the individual
blocks into a coherent whole (e.g., Bellugi et al. 1988b). The impairments in drawing
ability in WS also indicate difficulty with integration (e.g. Bertrand, et al. 1997).
Despite the progress made by considering the processing stages of the Block
Design task in isolation, this task is not a pure measure of local and global processing;
it draws upon a number of cognitive abilities. These include the ability to discriminate
between the block faces (different patterns and different orientations of the same
pattern) and the ability to plan a construction using verbal mediation or mental
imagery. It is therefore possible that poor performance on block construction tasks in
WS reflects these other abilities.
One of the factors above, verbal mediation, was investigated by Farran,
Jarrold, and Gathercole (1999). We examined the possibility that verbal mediation is
used to facilitate task completion in WS by measuring the relative contribution of
verbal and non-verbal intelligence to the level of ability shown by individuals with