Abstract
We investigated velocity sensitivity to rotational motion in 2–3-month-olds, using same apparatus and procedure as used by Shirai et al. (2005), who reported rapid increment of the velocity sensitivity to radial motion in that age.
A total of 25 2–3-month-old infants participated in the present study. We presented stimuli composed of one rotational motion pattern (clockwise or counterclockwise: counterbalanced across infants) and one translational motion pattern (up, down, left, or rightward motion: counterbalanced across infants) placed side by side. In each stimulus, the two motion patterns had same velocity value and each dot moved at constant velocity. There were two velocity conditions in the present study: the high and low velocity conditions. For 2 (or 3)-month-olds, the low velocity was 5.31 (or 2.66) deg/s and the high velocity was 10.62 (or 5.31) deg/s. Each infant participated in either of the two conditions. Each velocity condition composed of six stimuli presentations (duration of each = 5 s).
Our progress data have indicated that both the 2- and 3-month-old infants preferred rotations to translations significantly only in the high velocity condition. Because the velocity value for the younger infants was twice as large as that for the older infants, these results suggest the velocity sensitivity to rotational motion may increase between 2 and 3 months of ages. We will discuss a possible model of early development of relative motion sensitivity, based on the results of the present and previous study (Shirai et al., 2005).
This research was financially supported by RISTEX Japan Science and Technology Agency and grants-in-aid for scientific research from Japan Society for the Promotion of Science (15500172 to M.K.Y. and 17-741 to N.S.).