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So Kanazawa, Nobu Shirai, Yumiko Otsuka, Masami K. Yamaguchi; Perceptual development of directional transparent motion in infancy. Journal of Vision 2006;6(6):640. https://doi.org/10.1167/6.6.640.
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When the random-dot motion was superimposed on the other random-dots in different direction, we can see two global moving planes. In this study, we used this directional transparent motion as a stimulus and investigated the perceptual development of motion transparency in infants. Our previous study showed that the preference to the transparent motion developed from 3- to 5-month-olds (Kanazawa et al., 2006). Based on this result, we conducted experiments for total 62 3- to 5- month-old infants. In first experiment we controlled the directional difference between two random-dot motions. Stimuli were consisted of 230 dots placed within the 17.1 deg square field. Half of dots moved right and upward direction and remaining half 115 dots moved left and upward. We presented this transparent motion field as a target and the uniform motion as a non-target side by side. We measured the looking time to the target transparent motions and calculated the ratio of the preference to the targets. We prepared four kinds of directional differences; 6 deg, 10 deg, 20 deg and 40 deg. Results showed that the significant preferences to the target transparent motions were observed in 5-month-olds when the directional difference was above 10 deg and in 4-month-olds when that was 40 deg. However there was no significant preference to the target in 3-month-olds. These results suggest that the sensitivity to the directional transparent motion was developed from 4- to 5-month-olds. This result could be explained by the maturation of ventral stream in infants' brain.
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