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

Image scanning studies give us another insight into the nature of mental images. In these studies, subjects usually have to mentally scan an imaged map (e.g., Kosslyn, Ball, & Reiser, 1978). Typically, in these experiments subjects are given a fictitious map of an island with landmarks indicated by Xs (see Figure 9.8 for an example). Initially, subjects spend some time memorising the map, until they can reproduce it accurately as a drawing. They are then given the name of an object, and are asked to image the map and focus on that object. Five seconds later, a second object is named and subjects are instructed to scan from the first object to the second object by imaging a flying black dot. As the objects on the map have been placed at different distances from one another, it is possible to determine whether the time taken to scan from one object on the map to another is related to the actual distance on the map between these two points. Using experimental procedures of this type, it has been found repeatedly that the scanning time is related linearly to the actual distance between points on the map; that is, the scanning time increases proportionately with the actual distance between two points. This result lends support to the view that images have special, spatial properties that are analogous to those of objects and activities in the world.

However, there is a worry about these results (see Baddeley, 1986; Intos-Peterson, 1983). It is expressed succinctly by Baddeley (1986) when he says that "I have a nagging concern that implicitly, much of the

A sample of an ambiguous figure from Chambers and Reisberg's (1985) study. It can be seen as either a duck or a rabbit. Copyright © 1985 by the American Psychological Association. Reprinted with permission.

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