Does representational momentum reflect a distortion of the length or the endpoint of a trajectory?

Abstract

Observers viewed a moving target, and after the target vanished, indicated either the initial position or the final position of the target. In Experiment 1, an auditory tone cued observers to indicate either the initial position or the final position; in Experiment 2, different groups of observers indicated the initial position or the final position. Judgments of the initial position were displaced backward in the direction opposite to motion, and judgments of the final position were displaced forward in the direction of motion. The data suggest that the remembered trajectory is longer than the actual trajectory, and the displacement pattern is not consistent with the hypothesis that representational momentum results from a distortion of memory for the location of a trajectory.

Introduction

Memory for the final position of a moving target is often displaced in the direction of implied motion, and this has been referred to as representational momentum (Freyd & Finke, 1984; for review, see Hubbard, 1995). Early theories of representational momentum suggested that this displacement resulted from an internalization of the principles of momentum; much as a moving physical object possessed momentum, so too did the mental representation of that moving physical object possess an analogous form of momentum (e.g. see Finke, Freyd, & Shyi, 1986). A literal momentum metaphor has subsequently been abandoned by researchers, and a number of alternative mechanisms have been proposed including spatiotemporal coherence (Freyd, 1987, Freyd, 1993), implicit knowledge of physical principles (Hubbard, 1998), second-order isomorphism between mental representation and subjective aspects of momentum (Hubbard, 1999), belief in naive impetus (Kozhevnikov & Hegarty, in press), pursuit eye movements (Kerzel, 2000), and properties of image schema (Gibbs & Berg, in press).

Regardless of the mechanism involved, representational momentum is usually considered to reflect bias in memory for the final position of a moving target. In the absence of any discussion regarding memory for prior positions of a target, theories of representational momentum may be read as suggesting that prior positions of the target are represented veridically (or that bias in memory for prior positions is not related to bias in memory for the final position; see top of Fig. 1). However, previous investigators reported that memory for the initial position of a moving target may be displaced forward, and this has been referred to as the Fröhlich Effect (e.g. Kirschfeld and Kammer, 1999, Müsseler and Aschersleben, 1998). Consideration of the Fröhlich Effect raises the possibility that forward displacement in memory for the final position of a moving target might reflect displacement of the entire trajectory rather than displacement of just the final position (see bottom of Fig. 1). Different mechanisms would presumably underlie displacement of the entire trajectory and displacement of just the final position, and so whether a Fröhlich Effect accompanies representational momentum is of interest for theories of representational momentum.

Studies of the Fröhlich Effect usually present faster target velocities than do studies of representational momentum. Within the range of velocities used in studies on the Fröhlich Effect (i.e. typically >20°/s), the magnitude of the Fröhlich Effect decreases with decreases in target velocity (Müsseler and Aschersleben, 1998, Müsseler and Neumann, 1992), and so it is not clear that a Fröhlich Effect would be exhibited within the range of slower velocities used in studies on representational momentum (i.e. typically <20°/s). Indeed, with such slower velocities memory for initial position exhibits a backward displacement (e.g. Actis Grosso, Stucchi, & Vacario, 1996), and this has been referred to as the Onset Repulsion Effect (e.g. Thornton, in press). If an Onset Repulsion Effect were found in memory for the initial position of a target, then a forward displacement in memory for the final position of a target could not result from a forward displacement in memory for the entire trajectory.

Previous investigations of the Fröhlich Effect, Onset Repulsion Effect, and representational momentum usually focused only on memory for either initial position or final position. Therefore, it has not been possible to determine how these displacements might be related to each other or to memory for the entire trajectory. Thornton (in press) recently assessed memory for initial position and final position of a moving target, and although judgments of initial position and judgments of final position were not directly compared, backward displacement for initial position and forward displacement for final position were reported. Such a pattern is not consistent with forward displacement of the entire trajectory or with forward displacement of only the final position. The purpose of the current experiments was to assess and directly compare memory for the initial position and the final position, and to determine whether displacement in memory for the final position reflects a displacement of the entire trajectory or of only the endpoint.