Introduction

When judging the position of a moving object, human observers do not perceive and memorize the moving object's correct position. There are two known phenomena in judged position errors of a moving object, representational momentum (RM) and the flash-lag effect (FLE), both of which we consider here.

RM was originally reported by Freyd and Finke (1984). Freyd and colleagues displayed a series of still frames to imply the rotation of a rectangle (e.g., Freyd & Finke 1984, 1985; Freyd & Johnson 1987). Observers saw three views of a rectangle at different rotations about its center, with 250 msec display duration with 250 msec interstimulus interval. The fourth rectangle was presented as a probe 250 msec after the third frame presentation. The rotation of the probe was selected from possible positions symmetrically distributed around the actual third position of the rectangle. Observers were asked whether the rectangle in the third frame (the last frame of the motion sequence) was the same orientation as the probe. The results showed that their memory for the third orientation tended to be shifted in the direction of rotation. In other words, the orientation of the probe rectangle had to be rotated slightly further to be judged as being in the same position as the third rectangle. To account for the forward shift of the final position of a stimulus undergoing implied motion, some authors postulate that the dynamics of the representational system follow physical laws, such as momentum (representational momentum; Finke & Freyd 1985; Finke et al. 1986; Freyd 1987; Finke & Shyi 1988).