A major difficulty of rhetorical-design analysis is the determination of the actual effects of design artifacts. What defines the effects of a poster, signpost, book cover, or business card? How can the effects of designed objects be described and categorized? Can the effects found in particular objects be generalized? Are there any experts for defining design effects? The determination of effects is crucial for the formulation of design rules and, fundamentally, for a rhetorical understanding of design. There is no straightforward method, given that the visual effects of design objects are manifold and highly context-sensitive.
Materially, the visual impression of an object varies according to perspective, light conditions, or position. Even more obvious are the subjective factors causing an indeterminacy of effect. How a designed object affects a viewer depends on her taste, interests, and values, on her actual disposition and needs as well as on her previous knowledge and experience. Furthermore, the socio-cultural and historical context affects people’s perception and interpretation of such elements as color, textures, and motifs. Visual trends, zeitgeist and technological developments (for example, printing press, photocopy, desktop publishing) lead to changes in visual perception and the impacts design artifacts can have. While some of the design effects are fairly constant over time and cultures, most are informed by fashion and other socio-cultural influences and will, sooner or later, be modified. What used to provoke or even shock people (for example, because it appeared pornographic or brutal) can be attenuated by habituation or a change in moral standards. Images that used to convey severity or heroism might appear awkward or exaggerated now, and what looks modern today is likely to assume an old-fashioned or nostalgic touch in the near future. The more enduring effects are presumably based in the human cognitive system and can perhaps be explained with the physiology and psychology of perception or through evolutionary biology. Darkness and the color black may always and everywhere have had a frightening effect on human beings. This unsettling effect of dark designs could perhaps be traced back to the fact that human beings are not able to orientate in darkness, which–from an evolutionary perspective–is a disadvantage. That neon colors can be used as an eye catcher or in order to warn people could be explained by the fact that the human visual apparatus is particularly sensitive to them and because we were first confronted with their warning function in conjunction with poisonous animals and plants.
The calming effect of a design in panorama format possibly originates in the imitation of an open landscape in which, according to Savanna Theory (Lidwell et al. 2003), human beings feel safe, calm, and comfortable, since here possible dangers can easily be surveyed. The question of why human observers are affected in one way or another by certain visual features is not the object of visual or design rhetoric. For the observer–as well as for the designer as practitioner–it is important to know which stylistic means are required in order to create specific effects, but not to provide explanations for the underlying modes of perception. Design rhetoric is interested in the relation between a design effect and the specific design features related to it–regardless of whether the means-effect relation is universal or context-sensitive. In the section on pinning down design rules, more will be said about the relation between formal means and effect, which can be paired in a design rule.