Some effects of representational friction, target size, and memory averaging on memory for vertically moving targets

Abstract Observers viewed an animated ascending or descending target that varied in size and velocity across trials and appeared either (a) in isolation, (b) to slide along one side of a single larger stationary object, or (c) to slide between two larger stationary objects. Targets vanished without warning, and displacements (i.e., differences between actual and remembered final position) along the axis of motion and orthogonal axis were measured. Forward displacement (a) decreased with increases in implied friction, (b) increased with increases in target size for descending targets, and (c) decreased with increases in target size for ascending targets. When a larger stationary object was to one side of the target, orthogonal displacement was toward that object; when no object or objects on both sides were present, orthogonal displacement was near zero. Results are consistent with previous findings and speculation on the effects of representational friction, memory averaging, and target size on memory. An observer who perceives a target moving in a consistent direction will, when subsequently asked to indicate the remembered final position of that target, usually indicate a position that suggests that the target is remembered as having traveled further than it actually did. In other words, memory for the final position of a target is usually shifted in the direction of anticipated target motion. Early explanations of this shift drew upon parallels between the physical momentum of the target and an analogous momentum within the representational system, and so the shift was referred to as representational momentum (e.g., Finke, Freyd, & Shyi, 1986; Freyd & Finke, 1984). More recent investigations suggest shifts may occur in directions other than the direction of target motion and reflect more than just an internalization of the laws of momentum. For example, memory for horizontally moving targets is also shifted downward slightly in the direction of implied gravitational attraction, a shift referred to as representational gravity. These types of shifts are now referred to by the general term displacement, and the overall displacement for a given target may be influenced by several different factors (for a review, see Hubbard, 1995b).1 Displacement is influenced by whether the target interacts with other stimuli in its surroundings; for example, the forward displacement of a horizontally moving target is decreased if the target slides along the surface of a larger stationary object (Hubbard, 1995a). A physical object that slid along the surface of a larger stationary object would experience friction, and so such decreases in forward displacement are referred to as representational friction. If representational friction results from an internalization of the laws of physical friction, and not from some unspecified factor unique to motion along the horizontal axis, then effects of representational friction should be found whenever there is contact between a moving target and some other object; for example, a vertically moving target that slides along the surface of an adjacent stationary object should exhibit less forward displacement than an equivalent vertically moving target that does not slide along the surface of an adjacent stationary object. However, whether representational friction occurs with vertical (or any other non-horizontal) motion has not been examined. Displacement may be influenced by the size of the target, but effects of target size have previously only been observed along the axis aligned with implied gravitational attraction (Hubbard, 1997). In the terrestrial environment, size, mass, and weight are highly correlated, and differences in mass are usually experienced as differences in weight. Thus, observers may respond to the implied weight, rather than the implied mass, of the target. Indeed, weight is the product of mass and (the acceleration due to) gravity, and so effects of weight should be exhibited only along the axis aligned with implied gravitational attraction. …