Orientation discrimination in WS 2

Orientation discrimination in WS 23

to individuals with WS, and that the poor level of mental rotation ability in WS can be
accounted for by the orientation perception requirements of this task. The orientation
requirements of mental and manual rotation tasks are thought to be properties of the
dorsal visual stream, (Wohlschlager & Wohlschlager, 1998), as is the ability to
transform mental images (Cohen et al., 1986; Larsen et al., 2000). These results
suggest that dorsal stream functioning is fractionated in WS; there is a relative deficit
in some, but not all, aspects of dorsal stream functioning.

General Discussion

The present study provides a more precise illustration of the deficits in visuo-
spatial ability in the WS population. It is well known that performance on block
construction tasks in WS is particularly poor (Mervis et al., 1999). Until now, the
main focus of investigation into this deficit has been on the local and global
processing requirements of the task. Although fruitful, this approach has ignored
many other factors involved in block construction. Experiment 1 elaborated on the
hypothesis that there is a local bias in production tasks in WS (Bellugi et al., 1988;
Farran & Jarrold, 2003). The results indicated that poor block construction
performance in WS is not necessarily due to weak constructional abilities, but also
due to atypical perception, in particular unusual orientation processing.

Experiment 2 examined the dorsal stream deficit hypothesis (Atkinson et al.,
1997) by investigating whether size transformation was equally impaired as mental
rotation among individuals with WS. The level of performance of the WS group on
the size transformation task did not differ from that of TD controls. This in turn
suggests that the weak mental rotation ability previously reported was due to a
difficulty in processing orientation, rather than performing mental transformation.
Both mental rotation and the dorsal stream version of the post box task employed by

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