The Effect of Height in the Picture Plane on the Forward Displacement of Ascending and Descending Targets TIMOTHY L. HUBBARD, Texas Christian University Abstract The effect of height in the picture plane on the remembered location of ascending or descending targets was examined. Consistent with previous research, memory was displaced forward in the direc- tion of motion. The magnitude of forward displace- ment was larger for targets low in the picture plane than for targets high in the picture plane, and this was observed with ascending motion and with descending motion. This pattern is consistent with the hypothesis that memo1T for the location of ascending or descend- ing targets is biased by the effects of implied gravita- tional attraction on the velocity of those targets, and some implications of such a bias for issues in mental representation are noted. Resume Nous avons etudie l'effet de la hauteur dans le plan de l'image sur la memorisation du site de cibles ascendantes ou descendantes. Conformement aux recherches anterieures, le site memorise s'est revele decale vers l'avant, dans la direction du mouvement. L'ampleur de ce decalage vers l'avant a ete plus elevee dans le cas des cibles se trouvant dans la pattie inferieure du plan de l'image que dans celui des cibles occupant la pattie superieure; cette difference a ete observee, que le mouvement ait ete descendant ou ascendant. Ce patron est conforme ~ l'hypothese selon laquelle la capacite de memorisation du site de cibles descendantes ou ascendantes est biaisee par les effets de l'attraction gravitationnelle implicite sur la vitesse des cibles; certaines implications d'un tel biais en regard des questions de representation mentale, sont soulignees. The remembered final position of a previously per- ceived moving target is often distorted in ways consis- tent with the operation of implied invariant physical principles. For example, when observers view a hori- zontally moving target, the remembered final position of that target is distorted forward in the direction of motion and downward in the direction of implied grav- itational attraction (Hubbard, 1990), and this pattern is consistent with the operation of the physical principles of momentum and gravity. Distortion forward in the direction of motion has been referred to as representa- tional momentum (e.g., Freyd & Finke, 1984), and dis- tortion downward in the direction of implied gravita- tional attraction has been referred to as representation- algravity (e.g., Hubbard, 1997). However, the magni- tude of forward or downward distortion may be influ- enced by factors other than implied momentum or implied gravity (for review, see Hubbard, 1995), and so the more neutral term displacement is preferred unless the distortion in remembered position is attributable solely to the effects of implied momentum or the effects of implied gravity. The current experiment examines the extent to which displacement along the axis of motion of vertically moving targets is influenced by the height of the target in the picture plane. Hubbard and Motes (2001) reported that memory for horizontally moving targets high in the picture plane of a stimulus display exhibited larger displacement in the direction of motion than did memory for otherwise identical horizontally moving targets low in the picture plane of a stimulus display. They suggested that height in the picture plane functioned as a depth cue, and that subsequent size constancy scaling resulted in targets high in the picture plane being represented as more distant than were targets low in the picture plane. Targets represented as more distant would have to trav- el a larger absolute (allocentric) distance in order to cross the same visual angle than would targets repre- sented as closer, and travelling a larger absolute dis- tance in an equivalent amount of time would require a faster absolute velocity. Faster velocities typically result in larger displacement in the direction of motion (Freyd & Finke, 1985; Hubbard & Bharucha, 1988), and so horizontally moving targets high in the picture plane exhibited larger displacement in the direction of motion than did horizontally moving targets low in the picture plane. Canadian Journal of Experimental Psychology, 2001, 55:4, 325-329