Contrast Effects in Paired Comparisons: Evidence for Both Stimulus-Based and Response-Based Processes

Participants made paired comparisons of square sizes, with blue squares presented on the left side of a computer screen and red squares on the right. Context was manipulated by varying the distributions of blue and red squares separately. In Experiment 1, target squares from low-range distributions were judged larger than the same-size squares from high-range distributions. In Experiment 2, ranges were equated but ranks manipulated between distributions, pairing bell with U-shaped and positively skewed with negatively skewed distributions. Results provided little support for a rank-dependent valuation model. Experiment 3 used distributions that were designed to test between adaptation-level and response-equalization models. Both models received support, with response latencies constituting an important moderating variable. Response patterns for short latency participants were consistent with a stimulus-based adaptation-level process, and those for longer latency participants were consistent with a response-equalization process.