Orientation discrimination in WS 14
(Farran et al., 2001) suggested that this might be attributable to differential strategies
used during the processes involved in construction. However, the data from the
Squares discrimination task demonstrate that this differential effect of obliqueness in
RT is due to perceptual differences in processing between the groups. This is an
important finding as it suggests that the difficulty in completing Block Construction
tasks in WS is not purely constructional, but also relates to the perceptual processing
of orientation. The group difference could be explained in two ways; the TD controls
could be showing greater problems on oblique trials, or the WS group could be
showing less facilitation for nonoblique relations. As the WS group are responding
faster than the controls on oblique trials, the former explanation seems to best fit the
data. The pattern of performance in the WS group therefore, is not necessarily a
deficit, but it does indicate a deviance from typical development. However, the WS
group were significantly less accurate than the controls in discriminating between
stimuli in both oblique and nonoblique trials. This indicates that, in addition to a
deviant processing style, there is a general impairment in orientation discrimination in
this population.
The Z-score comparison of the performance of the WS group relative to the
controls, across construction and discrimination versions of the Squares task, indicates
that the additional demand of construction does not affect the relative level of
impairment in WS. This direct comparison between the tasks provides evidence
against the hypothesis that visuo-spatial construction/ integration is particularly poor
in WS. However, it is possible that this similarity in the level of impairment reflects
the fact that on the Squares construction task accuracy was only affected by errors at
the local level; global accuracy was constrained as the individuals were given a frame
in which to place the squares. The results of previous investigations (e.g., Bellugi et