Abstract
Aversion to clusters of holes or warts is called as trypophobia. Previous studies have suggested that trypophobic discomfort can be explained by high-contrast energy at midrange spatial frequencies (Cole & Wilkins, 2013; Le et al., 2015; Sasaki et al., 2017). Their spectral analyses, however, were based on an image-dependent unit (cycles per image: cpi). Therefore, the spatial properties perceived by our visual system (e.g., cycles per degree: cpd) should vary depending on the size and the viewing distance of images. To clarify the relationship between spatial properties and discomfort, we manipulated spatial frequencies within the range of two octaves in both units separately by resizing and cropping images while maintaining their appearances. Participants viewed an image which was filled with holes (e.g., lotus, barnacles, sponge) and rated aversion by a 7-point scale. The eye movement including the pupil response was also recorded. In the first experiment, aversion ratings varied regardless of keeping frequencies in cpi or cpd constant individually. Next, we changed the size and the viewing distance while keeping the retinal image identical. The result depended not on the spatial frequency but on the size of images. When the size was kept constant while manipulating the spatial frequencies and the viewing distance, aversion ratings were almost constant with the moderate tendency that the discomfort response to strong trypophobic images was increased as shortening the distance. Our findings suggest that the apparent size of trypophobic images affects aversion greatly and the influence of the spatial frequencies may be overestimated. In addition, the effect of the viewing distance supports the recent idea that trypophobic discomfort is triggered by involuntary avoidance of skin diseases (Imaizumi et al., 2016; Yamada & Sasaki, 2017). The relationship between the subjective rating and the eye movement will be also discussed.