The effects of task complexity on performance in constraint satisfaction design

The aim of this thesis is to examine the importance of constraints in design activity, and more specifically, in constraint satisfaction tasks. Constraints are involved in all design tasks and denote criteria on what constitutes a good design outcome. Within the present research, a constraint stipulates a restriction on how a design element may be assimilated into a design. For instance, given a spatial office layout design, the positioning of an employee may be restricted by a constraint stipulating that they should be in close proximity to a particular area. This thesis attempts to address a gap in the design literature by examining the effect of such constraints on design performance using experimental methodology. Two research threads are addressed; the effects of constraints on performance, and how constraint satisfaction performance can be improved by training. In the first research thread, the theoretical framework adopted concerns Newell and Simon’s (1972) problem space theory and more recent suggestions by Halford, Wilson and Phillips (1998) concerning relational complexity. These are used to predict the effects of increasing the number of design constraints (Experiments 1-2) and the number of types of constraint (Experiments 3-4). Both these factors together with a reduction in the degree of cognitive fit (Vessey & Gellata, 1991) between the constraints and the external representation (Experiment 5) were found to reduce design performance. The second research thread examines whether training can improve design performance. Practice only was found to improve performance on a near transfer task relative to a control group but not a dissimilar, far transfer task (Experiment 6). The subsequent Experiments examined the effect of what has been labelled ‘metacognitive’ training on performance. Findings indicated that a training intervention aimed at encouraging either reflective self-explanation (Experiment 7), or aimed at improving planning strategy (Experiment 8) improved performance in comparison to both control and practice only groups. The implications of these results are discussed together with future research directions