Representational Neglect
Of particular relevance to [the case for regarding the sketchpad as a workspace rather than a perceptual gateway] is the phenomenon of representational neglect. Bisiach and Luzzatti (1978) report the case of two patients who were asked to describe from memory the cathedral square in Milan, their native city. In both cases they gave a good description, except that the left side of the square was hardly mentioned. They were then told to imagine walking around the square, turning round, and again giving a description. This time the previously neglected part of the square was on their right, and was now described in detail; the side that was previously well-described was now ignored. Baddeley and Lieberman (1980) suggested that this might represent the impairment of a system for representing information within the visuospatial sketchpad.
(Baddeley, Working Memory, pp 93)

3D Image Rotation
Much of the research on imagery was initially stimulated by the classic demonstration by Shepard and Metzler (1971) who required subjects to judge whether two representations of three-dimensional object were identical or whether one was the mirror image of another. The two were presented in different relative orientations. Response time proved to be a linear function of the difference in orientation between the two, just as if the subjects were mentally rotating one of the objects until it lined up with the other, and then making the judgment…

[Description of Kosslyn’s (1978) computational model of the brain literally rotating a data structure.]

Intons-Peterson (1996) showed that the speed of ‘visual scanning’ varied depending on semantically relevant but non-visual factors such as whether the whether the the subject were imagining herself carrying a weight or not…

Equally problematic for Kosslyn’s interpretation was a study by Hinton and Parsons (1988) who asked their subjects to imagine a wire cube sitting on a shelf in front of them. They were then asked to take hold of the nearest lower right-hand corner, and the furthest [upper] left-hand corner, and then orient the cube such that their left hand was immediately above their right. The task then was to describe the location of the remaining corners. Almost everyone reports that they lay upon a horizontal line, like a cubic equator. In fact, they form a crown shape. Hinton and Parsons suggest that rather than actually manipulating the representation as Shepard or Kosslyn might suggest, subjects attempt to simulate it. When a problem is complex, they simply fail.
(Baddeley, Working Memory, pp 94-95)