Orientation discrimination in WS 16
those involved in mental rotation. First, neither task has a memory load, which could
confound performance in this population (Jarrold, Baddeley, & Hewes, 1998b).
Second, both tasks involve mental object manipulation, one by enlarging/ reducing
the stimuli, the other by rotating the stimuli (Kosslyn & Koenig, 1992). Third, there is
a linear relationship between response time and the transformation process in both of
these tasks (Bundesen & Larsen, 1975; Shepard & Metzler, 1971), which provides
evidence for mental transformation in both tasks. The similarity between mental
rotation and size transformation tasks is also supported by studies investigating brain
activation. Larsen et al. (2000), using Positron Emission Tomography (PET), found
that dorsal areas were active during a size transformation task, similar to the
activation seen in mental rotation.
This investigation has implications for the dorsal stream deficit hypothesis.
The dorsal visual stream may support information for both mental image
transformation (Alivisatos & Petrides, 1997; Larsen et al., 2001) and actions to
objects (mental and manual; Wohlschlager & Wohlschlager, 1998). If poor mental
rotation ability in WS (Farran et al., 2001) is due to a weak ability to perform image
transformations, one should also observe poor performance on a size transformation
task. However, if performance on the mental rotation task was influenced by the
ability to discriminate between orientations in WS, then performance on the size
transformation task should be comparatively better. This would indicate a
fractionation in dorsal stream processing in WS.
Method
Participants
The testing session for Experiment 2 took place approximately 10 months
after the testing session for Experiment 1. Two participant groups were employed; 21