“Looks Alike” but “Feels Different”? The Veto Power of Holistic Essence in Design Similarity Assessment

The determination of design patent infringement relies heavily on the visual similarity assessment of the “Ordinary Observer”. However, as the cognitive boundaries of this hypothetical subject have never been quantitatively defined by the legal profession, this standard faces enduring challenges regarding subjectivity and inconsistency. To bridge the gap between legal assumptions and psychological reality, this study operationalizes the abstract concept of the “Ordinary Observer” via psychophysical methods and constructs a quantitative judgment model based on cognitive thresholds. Using vase forms as stimuli, a four-stage experiment was conducted to contrast perceptual differences between novices (representing ordinary observers) and experts. We employed morphological interpolation to measure Just Noticeable Difference (JND) and examined the nonlinear feature-weighting mechanism by integrating the dialectical relationship between “Form” (local details) and “Essence” (global structure) from Chinese aesthetics. Results reveal a significant disparity in perceptual resolution: the experts’ JND (≈3.00%) was significantly finer than that of ordinary observers (≈7.00%), demonstrating that the “Expertise Effect” may introduce systematic bias into judicial assessments. Furthermore, regression models uncovered a “Threshold-Dominant” effect: global topological structure (corresponding to “Essence”) commands a dominant weight (53.74%). Once this global feature fails to reach a specific perceptual threshold (74.24%), the cognitive system triggers a “Veto Mechanism”—regardless of how similar the local details (corresponding to “Form”) are, the overall design tends to be judged as dissimilar. This study challenges traditional assumptions of linear feature weighting, validates the psychological reality of the “Form-Essence” relationship, and provides scientific quantitative tools and evidentiary standards for resolving the “subjectivity dilemma” in intellectual property litigation.