On the Ontological Status of Visual Mental Images

There has long been considerable controversy over the ontological status of mental images. Most recently, members of the A.I. community have argued for the sufficiency of "propositional representation" and have resisted the notion that other sorts of representations are functional in the human mind. The purpose of this paper is to review what I take to be the best evidence that images are distinct functional representations in human memory. Before reviewing these data, however, I offer a preliminary definition of what I mean by a "visual mental image." This definition arises out of the "cathode ray tube" metaphor originally introduced in Kosslyn (1974, 1975, 1976) and later implemented in a computer simulation by Kosslyn & Shwartz (1977a, in press). On this view, images are spatial representations in active memory generated from more abstract representations in Long-term memory; these spatial representations are able to be interpreted ("inspected") by procedures that classify them into various semantic categories. 1.0 A preliminar 7 definition of a visual mental image I wish to define a "visual mental image" in terms of five basic kinds of properties. Images are often distinguished from more discrete, propositional or linguistic representations because they supposedly have "analogue" properties. Thus, the first two properties noted below describe analogue representations as a class. Goodman (1968), Palmer (in press), Shepard (1975), Sloman (1975), and others have provided informative and detailed discussions of relevance here, and I will draw freely on these sources in the present discussion. 1) Images can capture continuous variations in shape. This continuity