Scanning visual mental images: A window on the mind.

The process of mental scanning corresponds to the systematic shifting of attention over visualized objects. The first part of this article focuses on the role of mental scanning as an empirical method to assess the structural properties of the representations that underlie visual mental imagery. One theory of imagery posits that the metric properties of the surfaces of objects are made explicit in visual images. If so, then the time to scan across imaged objects should increase linearly with the distance scanned, and such results have been reported in a number of experiments. However, these results proved controversial. Various alternative accounts were proposed, and new studies conducted. The present review shows that the alternative accounts were not compelling, and that results from image scanning studies are best interpreted as reflecting the metric properties of imagery representations and also showing that imagery uses mechanisms that are used to encode and interpret objects during perception. The second part of this article focuses on the use of image scanning to examine whether verbal descriptions may be used to construct images with structural properties similar to those of images of previously seen objects. Newly constructed images have been shown to possess a structure very much like the structure of representations that arise from visual perception. Moreover, the scanning technique has been used to study which properties of descriptions allow them to be converted easily into images. Finally, the article considers the use of the mental scanning paradigm in neuroimaging studies. By examining the neural foundations of mental scanning. researchers are in a good position not only to learn more about imagery. but also to discover more about the roles of particular brain mechanisms.