Perception, 2013, volume 42, pages 828 – 834 doi:10.1068/p7460 Infants see illusory motion in static figures So Kanazawa 1 , Akiyoshi Kitaoka 2 , Masami K Yamaguchi 3 1 Department of Psychology, Japan Women’s University, 1-1-1 Nishiikuta, Kawasaki City, Kanagawa 214-0037, Japan; e-mail: kanazawas@fc.jwu.ac.jp; 2 Department of Psychology, Ritsumeikan University, 56-1 Toji-in Kitamachi, Kita-ku, Kyoto 603-8577, Japan; 3 Department of Psychology, Chuo University, 742-1 Higashinakano Hachioji-shi, Tokyo 192-0393, Japan Received 2 February 2013, in revised form 21 July 2013 Abstract. We investigated illusory motion perception in 6-to-8-month-old infants using a static figure which produces strong illusory motion. In experiment 1 we prepared a control figure, which was physically similar to the illusory motion figure but which did not produce illusory motion. We presented the illusory figure and the control figure side-by-side, and measured infants’ looking time at the target illusory figure. Results showed that the infants’ looking time at the illusory figure was significantly longer than that for the control. In experiment 2 we made another set of stimuli consisting of the same local pattern used in experiment 1, but which did not produce illusory motion. The results showed that no preferences were observed in experiment 2. These results suggest that 6-to-8-month- old infants perceive illusory motion in static figures. Keywords: infants, visual illusion, illusory motion, preferential looking 1 Introduction A static figure called “rotating snakes” (http://www.ritsumei.ac.jp/~akitaoka/index-e.html) (target area of figure 1a) produces a large amount of illusory motion. This stimulus was invented by Kitaoka (2003) and was recently investigated psychophysically (Backus and Oruc 2005; Beer et al 2008; Hisakata and Murakami 2008; Murakami et al 2006) and neurophysiologically (Conway et al 2005). The illusory motion comes from the local arrangement of yellow, blue, white, and black regions. Kitaoka and Ashida (2003) showed that the illusion depends on the fact that black and white are higher contrast than blue and yellow and produce faster responses. Conway et al (2005) showed that these responses occur in the neurons in V1 and MT of macaque brains. Kuriki et al (2008) found using f MRI that the visual cortex in the human brain also responds to this illusion. Previous research into perceptual development has demonstrated that infants can see illusory patterns such as subjective contour (Ghim 1990; Kavsek 2002; Otsuka and Yamaguchi 2003) or modal and amodal completion behind the occluders (Johnson and Aslin 1995; Kellman and Spelke 1983; Otsuka et al 2006). However, no infant research, especially on illusory motion perception in static figures, has been reported. Here we report studies on the development of local and global motion mechanisms in infants using a static figure called rotating snakes. In order to investigate the development of motion perception, we used this figure because it has much more illusory motion than any other static figure. We observed infants’ preferential looking behavior at this figure on the basis of the hypothesis that infants will prefer to look at illusory motion information. Previous research on infant visual development has shown that a sensitivity to basic relative motion emerges at around 2 to 3 months of age (Shirai et al 2004a, 2004b; Wattam- Bell 1992, 1994). However, a perception of more complex motion such as motion segregation or transparent motion develops from 3 to 5 months (Banton et al 2001; Kanazawa et al 2006, 2007; Wattam-Bell 2010). These results suggest that motion information processed by the dorsal stream—including V1, MT, or MST—develops at 5 months. Compared with motion