Semantics, Syntax, and Pragmatics of Graphics

dimensions, notably, causality. Semantics, Syntax and Pragmatics of Graphics 149 To understand the role of arrows in mechanical diagrams, Heiser and I (2002) asked participants to write descriptions of diagrams. Each participant described a single diagram, either of a bicycle pump or a car brake or a pulley system, either with arrows indicating the operation of the device or without. When participants saw diagrams without arrows, they wrote primarily structural descriptions, providing details of the spatial relations among the parts of the system. When participants saw diagrams with arrows, they wrote causal, functional descriptions. The arrows provided the temporal order of the operation of the device. The inference from temporal to causal was apparently immediate. As in the previous examples, routes and graphs, we ran the mirror-image experiment, asking participants to produce diagrams from descriptions of the devices. As expected, more participants produced diagrams without arrows for structural descriptions and more participants produced diagrams with arrows for functional descriptions. Arrows, then, allow mental animation of systems; they promote understanding of a system’s dynamics and function. Actual animations are computationally expensive and not easily transported. What’s more, animated and static graphics have been compared in a multitude of contexts, concrete and abstract. When the content of animated and static graphics is equated, and when interactivity is equated, there is no evidence to support the superiority of animations (Tversky, Morrison, and Betrancourt, in press). Geoglyphs, such as lines, arrows, crosses, and blobs, appear in a wide range of diagrams. They have interpretations that are readily understood in context from their geometric or Gestalt properties. They can be combined in a multitude of rule-bound ways to create different graphical ideas. Thus, they have many properties in common with semantic elements, words, in spoken or written language. Geoglyphs parallel language also in meaning; the meanings of words like relation, intersection, and field, spatial concepts all,