Observed mid-IR visibilities of all the targets, each averaged over 10 to 12 μm in the rest frame of each object, shown as a function of spatial frequency in units of cycles per R_in (log-scale). The data are color-coded in terms of the UV luminosity of the central engine for the corresponding object, which is defined to be 6 νL_ν(5500 Å) (Kishimoto et al. 2007). Each data point is plotted with different symbols for different objects, and is labeled with the PA / length of the baseline. It is quite clear that the radial structure in units of R_in changes from being compact in higher luminosity objects to extended in lower luminosity objects. Dotted curves are visibility functions for power-law brightness distribution with the normalized half-light radius R_1/2/R_in = 3, 10, and 30., which roughly depict the brightness distributions from higher to lower luminosity objects.