Hexanal (C6) and octanal (C8) exhibit two different odor qualities at all concentrations: C6 is perceived as green, while C8 is perceived as citrus. This paper examines the odor perception (quality + intensity) of C6-C8 binary mixtures by varying the concentration ratios within the mixtures and using an odor reference-matching task to estimate perceived intensity. Three perceptible concentrations of C6 and C8, low (L), medium (M), and high (H), were prepared. Subjects were trained to match the quality and intensity of blind samples of these standards with their appropriate reference. Mixtures were composed of a focal or "figure” odorant (indicated below in bold) of the same odor quality as the references and a second odorant defined as the "ground” odorant. In subsequent sessions, subjects were asked to evaluate their perception of the quality of the focal odorant in a C6-C8 mixture. Stimuli for C6 matching tasks, where C6 was both the reference and the figure, were: 6L-8M, 6M-8L, 6M-8M, 6M-8H, and 6H-8M. The C8 matching tasks were the same, except that the roles of C6 and C8 were reversed. When the figure odorant was stronger than or iso-intense to the ground odorant, mixtures were often matched to a less intense reference, indicating suppression (compensation) of the figure by the ground odoran
