Visualization techniques are becoming more prevalently used as decision support tools for parameter design and engineering optimization. Despite the apparent advantages of visualization techniques, we have found little evidence in the engineering literature that assesses the impact of fast, graphical design interfaces on the efficiency and effectiveness of engineering design decisions or the design optimization process. In this paper, we present experimental results from an I-beam design problem that was used to test the impact of having fast graphical feedback on design efficiency and effectiveness, extending our previous studies. The importance of rapid feedback is investigated by incorporating time delays in the software response to mimic computationally expensive design analyses. Design efficiency is measured by recording the completion time for solving the design problem, and design effectiveness is measured by calculating the error between a submitted design and the known optimum. The impact of graphical feedback is examined by comparing user performance on three different interfaces. The interfaces were constructed based on a richness scale that was motivated from principles of visual attention and object perception to explain the extent to which task demands are compatible with the graphical form of the interface. Response delay appears to have more of an affect on design effectiveness and efficiency, while interface richness appears to have more of an affect on the design search process. Experimental results indicate that response delays of 1.5 seconds significantly impact user performance and that users perform better as the richness of the design interface increases. We also found that the perceived workload of the users increased as delay increased and as the richness of the design interface decreased. Implications for graphical design interface development for engineering design and optimization are explored within the context of our findings.Copyright © 2004 by ASME