Designers use various representations to externalize their ideas, physical models being an important one. Physical models are widely used by designers and their use is promoted as an effective design tool by industry and government agencies. However, very little is known about the cognitive effects of physical models in the design process; the available guidelines are conflicting. Some researchers argue for the frequent implementation of physical models, while others observe that the use of physical models fixates designers. In light of these conflicts, the research discussed in this dissertation focuses on understanding the cognitive effects of physical models and developing guidelines for aiding designers in their implementation. A combination of controlled lab studies and qualitative studies is adopted to achieve said goal. The results from the controlled studies show that physical models supplement designers’ erroneous mental models and help them to come up with more ideas satisfying the problem requirements. These studies also demonstrate that design fixation is not inherent in physical modeling, but it is caused by the Sunk Cost Effect. According to Sunk Cost Effect, as designers spend more time building physical models of their initial ideas, they tend to fixate more to the variations of those ideas. A qualitative study on industry-sponsored projects and development cases of award-winning products further supports these results in more realistic situations. Further, the studies reported in this dissertation show that physical models can be effective tools for the mitigation of fixation to undesirable design features in a flawed example; however, these results can also depend upon the experience level of a designer in solving open-ended design problems. With these insights from the series of studies, a set of guidelines and a Model Error Reeducation Method (MERM) are formulated and tested with novice designers. MERM helps designers in identifying critical loads and interface designs they miss in their original designs, before prototyping. The results from the testing of this method show that this method is very useful in avoiding said errors in physical modeling.

In today’s competitive market, it is essential to be innovative and creative for an industry to sustain. Industry need to introduce new products to the market. Engineering idea generation plays a vital role in the development of new products. This research study is focused on the engineering idea generation. The representations of ideas have an important impact on the idea generation process. Design concepts may be represented in a variety of forms like sketches, physical models or computer based models. The goal of this research is to understand how these various representations affect design cognition. In this thesis, three studies showing the effects of two different representations in the idea generation process are presented. The first study focuses on the effects of physical models in engineers’ design cognition. This preliminary study investigates two different hypotheses: (1) Physical models supplement and improve designer’s mental models and (2) Physical models induce design fixation. The results show that physical models supplement the designer’s mental models but fail to enhance them. No evidence of design fixation is observed. The second and third studies investigate the effects of computer-based idea generation software on design cognition. The research questions investigated in this study are: (1) How does the use of this software tool assist design cognition? (2) How can the software interface be improved so that designers can generate ideas more easily? To answer these questions, a between-subjects idea generation experiment is conducted. In the experiment, the participants are asked to generate ideas to solve a design problem with and without the software. The results show that participants who generated ideas with the help of the software tool have less quantity of ideas compared to the control group. This may be due to the design fixation induced by the concepts presented. In the third study, the opinions of the participants for the improvements of the software interface are collected. Results show that participants do not have any preference of one way of clustering the concepts over the other. The results of this study also provide creative input for the future improvement of the software.