Figure

The mean time to decide whether a visual stimulus was in the normal or mirror-image version as a function of orientation. Data from Cooper and Shepard (1973).

rotation. If the imagined object becomes more complex subjects are less able to make correct judgements about its appearance when rotated (Rock, 1973). Such a problem would not arise in the physical rotation of a physical object.

Similarly, people's capacity to imagine rotated objects (even simple cubes) depends crucially on the description of the object they implicitly adopt (Hinton, 1979; Boden, 1988, and later section on reinterpreting images). Hinton (1979) provides a practical demonstration of this proposal. You are asked to imagine a cube placed squarely on a shelf with its base level with your eyes. Imagine taking hold of the bottom corner that is nearest your left hand with your left hand, and the top corner that is furthest away from your left hand with your right hand, taking the cube from the shelf and holding it so that your right hand is vertically above your left. What will be the location of the remaining corners? Most subjects tend to reply that they will form a square along the "equator" of the cube. In fact, the middle edge of the cube is not horizontal but forms a zig zag. This occurs because one does not take the image of the cube (as it is in reality) and rotate it, rather one is working off some less elaborate, structural description.

More recently, the focus of research on mental rotation has tended to concentrate on its relationship to visual processing and neurological correlates (see Gill, O'Boyle, & Hathaway, 1998; Harris, Egan, Paxinos, & Watson, 1998). Mental rotation appears to be important in controlling eye movements (saccades) suggesting the interdependence of visual and imagery-based processing (see later section on Kosslyn's theory). de Sperati (1999) instructed subjects to make saccades in directions different from that of a visual stimulus and found that the saccade latency increased linearly with the amount of directional transformation imposed between the stimulus and the response. Given this evidence, it is not surprising to find that motor processes are also implicated in mental rotation, found using a dual task paradigm in which subjects had to mentally rotate an image while performing a motor rotation (Wexler, Kosslyn, & Berthoz, 1998).

An example of the materials used in mental scanning experiments. Subjects had to image a black dot moving from one point on the map to another (points indicated by the x-ed features). Adapted from Ghosts in the mind's machine: Creating and using images in the brain by Stephen Kosslyn. Reproduced by permission of the author. Copyright© 1983 by Stephen M.Kosslyn.

Image scanning

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