Material perception of a kinetic illusory object with amplitude and frequency changes in oscillated inducer motion

The magnitude of the phase difference between inducers' oscillation of a kinetic illusory surface influences visual material impressions (Masuda et al., 2013). For example, impressions of bending or waving motions on a surface tend to occur at a 30- or 90-deg. phase difference, respectively. Here, we elucidate whether amplitude and frequency changes in an inducer's oscillation influence the visual impressions of an illusory surface's hardness, elasticity, and viscosity. Nine participants were asked to use an analog scale to judge their visual impressions relative to a standard pattern with no damping and no frequency change for each phase difference. Results revealed that hardness ratings were greater when amplitude decayed with time only in the 30-deg. phase difference. Elasticity ratings were greater when the frequency of oscillation had a large increase in the 90-deg. phase difference. In the 30-deg. phase difference, similar tendencies were only observed with no damping and ample damping. Viscosity ratings were greater when the frequency of oscillation decreased in both phase differences and when the amplitude decayed with time in the 30-deg. phase difference. These findings suggest that amplitude and frequency changes in an inducer's oscillation are significant factors for material perception derived from motion.