Inspired by previous findings that manipulating sound frequency alters perceived crispness and freshness in potato chips (Zampini and Spence, 2004), this study investigated how the frequency components of the sound produced when cracking an eggshell influence multisensory (audiovisual) shitsukan perception. In Experiment 1, we shifted the frequency spectrum upward or downward while preserving its spectral shape. This manipulation did not produce substantial changes in perceived crispness. In Experiment 2, we examined the effects of amplifying or attenuating high-frequency components, as well as selectively removing specific frequency bands, on perceived crispness and freshness. The results showed that amplifying high-frequency components increased perceived crispness, whereas attenuating or removing them decreased both crispness and freshness. In contrast, removing low-frequency components had no clear effect. These findings suggest that perceived crispness depends not on the absolute presence of high frequencies, but rather on the relative prominence of high-frequency components within the overall spectral structure.

Human perception of three-dimensional (3D) shape from two-dimensional images is strongly influenced by illumination. Previous studies have shown that changes in lighting direction can cause observers to misjudge identical 3D shapes as different under monocular and static viewing conditions. Such misperception may lead to practical problems when 3D computer graphics are used to present design proposals or final products in professional practice. This study investigates whether surface properties can reduce illumination-induced misperception of 3D shape. Focusing on specular reflection and shading strength, we conducted the shape re-identification task using a two-alternative forced-choice paradigm under multiple surface conditions. The results showed improved performance with specular reflection and weaker shading. In addition, to examine whether observers relied on subjective image similarity rather than perceived shape and the involvement of higher-level visual mechanisms, we performed a supplementary experiment and algorithmic simulations based on objective image quality metrics.