Abstract
Increasing psychophysical evidence shows that static images with a specific spatial frequency and orientation spectrum give rise to a feeling of discomfort or unpleasantness. Humans also have unpleasant feeling toward dynamic images such as a movie of swarming worms. However, it is largely unknown how dynamic information affect visual unpleasantness of a spatially patterned image. Here, we examined the unpleasantness rating of static or dynamic visual noises with variable spatial frequencies (0.3 - 5.3 c/deg), temporal frequencies (0 - 15 Hz), temporal frequency bandwidths (1, 2, or infinite deg), and orientation bandwidth (30, 90, infinite deg). The results showed that static noises with narrow spatial frequency bandwidth and with wide orientation bandwidth were rated significantly unpleasant, replicating the previous data (Ogawa & Motoyoshi, 2020, Front. Psych.). Moreover, we found that dynamic noises with relatively low temporal frequencies (0.5 - 2 Hz) appeared even more profound than the static noises regardless of the spatial property. However, translational motion of the noise had no effect on the unpleasantness rating at all. A subsequent experiment with a spatially band-passed global motion display demonstrated that slow motions with variegated directions was a crucial factor for the enhanced unpleasantness in a dynamic stimulus. Given that in the natural environment, image features inside a moving object tend to move in a coherent direction, the present results further support the notion that humans tend to feel unpleasantness toward visual stimuli that deviate from the statistical regularity of natural scenes.