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This study has focused on how assimilation and contrast correlate with the generating processes of various optical illusions. First of all, we defined the meanings of assimilation and contrast from two viewpoints, namely, phenomena and mechanisms. We then examined the characteristic appearances of the Delboeuf illusion as a typical size illusion caused by assimilation and contrast, by referring to major studies on this illusion in Japan. To confirm the different size-judgment processes operating in size illusions of concentric circles, quadrilaterals, lines, and angles, we explored the magnitude of illusion, including peak and conversion from overestimation to underestimation. The consistent occurrences of peak and conversion indicated the antagonistic correlations of assimilation and contrast in the generation of these illusions. Manipulation of figural unification using 1 We are deeply indebted to Professor Tadasu Oyama for his encouragement and support of our research.

When making the glassy water-ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate [DEME][BF(4)] solution, the water molecule existing as a single molecule without self-associated state is preserved even at 77 K and survives not to form the hydrogen bond network among themselves as in pure H(2)O liquid. The water molecule might loosely interact with BF(4)(-) anions. At water-rich concentration, H(2)O ice crystals and the water molecules in the ionic liquid coexist as a mixture, which may result from microheterogeneities in the solid aqueous ionic liquid solution.

By in situ observations using simultaneous X-ray diffraction and the DSC (differential scanning calorimetry) method, the effect of water, methanol, ethanol, and benzene on the crystallization has been observed in an ionic liquid (IL)-rich phase. The IL is a hydrophilic ionic liquid, N, N-diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate, [DEME][BF4]. At a small amount of the above additional molecules in the IL, the conventional preferred orientation on the Debye rings was seen by the X-ray diffraction. At 0.9 mol % H2O, twinlike crystal domains develop extraordinary on the microdomains. By the "crystal-growth enhancement effect" at a slight amount of water, a composite domain structure, which consists of the large domain and the weakly orientated microdomains, is formed without internal strains. Above 2.9 mol % H2O, the domain structure, however, disappears completely. It is remarkable that, in a thermal cycling experiment using pure [DEME][BF4], the similar composite domain structure appeared. This is also caused by an uptake of a slight amount of water.

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