This thesis embarks from the idea that aesthetic appreciation of product designs is determined by simultaneously perceiving the two partially opposing dimensions of unity and variety. People actively avoid boredom by searching for variety because it challenges the senses and offers the potential of learning new information. Hence, people browse through thick catalogues, are attracted to colourful bouquets and let their eyes and hands explore a novel car interior. In doing so, these products offer stimulation to the senses. However, too much variety leads to confusion, as people fail to make sense of what they perceive. It is therefore that they appreciate perceiving unity at the same time, as it brings structure to variety; items in a catalogue are precisely ordered, flowers are neatly arranged and components of a car interior are carefully picked and organized. The above idea is captured in an age-old aesthetic principle, aptly named Unity-in-Variety (UiV). The principle states that perceiving a balance between the opposing forces of unity and variety is aesthetically preferred. While this principle has been argued to explain aesthetic appreciation for works of art, music and landscapes, little empirical research existed on this principle and, to our knowledge, none for product designs. By performing twelve studies and multiple pilot studies, mostly quantitative in nature, we empirically investigated the principle of UiV to determine whether it can explain how and why we aesthetically appreciate perceiving product designs by vision and touch.
To demonstrate how unity and variety relate to each other and to aesthetic appreciation, we first separately researched the visual and tactile modality using a range of products readily found on the market. We continued with experimental investigations of the principle by systematically manipulating unity and variety in product designs through various design factors (e.g. the Gestalt laws of symmetry and similarity). For the visual modality, these manipulations were performed in newly designed sets of webpages. For the tactile modality, we designed and produced 3-D printed models of car key remotes to systematically manipulate materials and shapes. The investigations within vision and touch were followed by a study combining both senses to assess how unity and variety relate to visual-tactile aesthetic appreciation, and an additional study exploring how unity and variety may interact across the senses. Furthermore, to build a broader understanding of what influences our appreciation for unity and variety, we investigated individual differences in motivational drives and design expertise. Lastly, we explored the possibility of extending the principle’s applicability from individual products to product-service systems.
Our main finding is that unity and variety, despite being negatively correlated, positively influence aesthetic appreciation of product designs. As a result of their partial opposition, there is a trade-off between unity and variety leading to a balance where aesthetic appreciation is highest. Additionally, we found that unity is the dominant factor of the two; its influence is on average twice the size of variety, and its presence is a condition for an appreciation of variety. These results were obtained with a range of products from different product categories and replicated in the visual, tactile and visual-tactile product experience.
Having demonstrated how unity and variety together determine aesthetic appreciation, we investigated how several factors underlie the degree of unity and variety and their respective appreciation. Several commonly used design factors were experimentally shown to influence unity and variety in vision (through symmetry, contrast, similarity and colourfulness), and in touch (through continuity, emergence and similarity). Besides these design factors, we identified how individual differences in motivational drives and expertise can influence the preferred balance between unity and variety. Individuals with safety needs preferred visual or tactile unity to individuals with accomplishment needs. As a result, the preferred balance between unity and variety shifts towards unity for safety seekers. A similar shift towards a preference for unity occurred for (design) experts. Experts rate the same products differently on unity and variety compared to laymen, possibly as a result of their explicit and implicit training in applying unifying design factors. Yet, they also appreciate an optimum balance between unity and variety and the principle therefore equally holds for design experts.
The combined results of our studies demonstrate that the UiV principle can consistently explain visual, tactile and visual-tactile aesthetic appreciation for product designs. It does so by showing that aesthetic appreciation is highest when the two partially opposing dimensions of unity and variety are increased until they arrive at an optimum balance. We furthermore demonstrated how various design factors and individual differences underlie this preferred unity and variety balance. In doing so, the principle offers a holistic understanding of how the smallest perceptual properties of a design are combined to form the unified experience of the product and its aesthetic appreciation. The knowledge generated through our research contributes to current theories and models of aesthetic appreciation by explaining how and why people find aesthetic pleasure in perceiving product designs. Furthermore, UiV is possibly the first principle to account for tactile aesthetic appreciation, as we illustrated how the Gestalt laws play an important role in creating tactile unity within the variety of shapes and materials of a physical product. Next to this, our methodological approach demonstrates how novel 3-D printing technologies can aid in accurately studying realistic stimuli. Lastly, the results from our research can act as a guideline for designers and provides a promising basis for researching the principle in other modalities (such as auditory and gustatory), as well as for other domains (such as for product-service systems, architecture and the arts).