Memory for the final location of a moving target is often displaced in the direction of target motion, and this has been referred to as representational momentum. Characteristics of the target (e.g., velocity, size, direction, and identity), display (e.g., target format, retention interval, and response method), context (landmarks, expectations, and attribution of motion source), and observer (e.g., allocation of attention, eye movements, and psychopathology) that influence the direction and magnitude of displacement are reviewed. Specific conclusions regarding numerous variables that influence displacement (e.g., presence of landmarks or surrounding context), as well as broad-based conclusions regarding displacement in general (e.g., displacement does not reflect objective physical principles, may reflect aspects of naive physics, does not solely reflect eye movements, may involve some modular processing, and reflects high-level processes) are drawn. A possible computational theory of displacement is suggested in which displacement (1) helps bridge the gap between perception and action and (2) plays a critical part in localizing stimuli in the environment. DISPLACEMENT IN SPATIAL MEMORY 823Given the issues associated with the term representational momentum, Hubbard (1995c) has suggested that the broader term displacement should be used to refer to general mislocalizations in memory for the final position of a target, and the more specific term representational momentum should be used only to refer to that component of displacement that is attributed to the implied momentum of the target. The momentum of a physical object is defined as the product of that object's mass and velocity (i.e., momentum ϭ mass ϫ velocity), but neurons representing the motion of a physical object would not themselves actually be in motion (just as neurons representing a mental rotation would not themselves actually be rotating), and so mental representations would not be expected to possess physical momentum per se. In the following discussion, the term representational momentum is used to describe that component of displacement consistent with how physical momentum would influence a physical object, but such a use is necessarily more abstract and metaphorical than concrete and literal (i.e., more consistent with second-order isomorphism than with first-order isomorphism; Hubbard, in press-b). Similarly, the terms representational gravity, representational friction, and representational centripetal force abstractly and meta- 824HUBBARD phorically describe components of displacement consistent with how physical gravity, friction, and centripetal force would influence a physical object. Displacement in the Direction of Motion (Representational Momentum)The initial demonstration of a forward displacement in memory for the final position of a previously viewed moving target was provided by Freyd and Finke (1984; see panel A in Figure 1), who presented observers with computer-animated displays consisting of three concentric sequential pr...

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Memory for the final position of a moving target is often shifted or displaced from the true final position of that target. Early studies of this memory shift focused on parallels between the momentum of the target and the momentum of the representation of the target and called this displacement representational momentum, but many factors other than momentum contribute to the memory shift. A consideration of the empirical literature on representational momentum and related types of displacement suggests there are at least four different types of factors influencing the direction and magnitude of such memory shifts: stimulus characteristics (e.g., target direction, target velocity), implied dynamics and environmental invariants (e.g., implied momentum, gravity,friction, centripetal force), memory averaging of target and nontarget context (e.g., biases toward previous target locations or nontarget context), and observers' expectations (both tacit and conscious) regarding future target motion and target/context interactions. Several theories purporting to account for representational momentum and related types of displacement are also considered. An observer's memory regarding the final position of a previously perceived target is often distorted in ways consistent with the operation of invariant physical principles. For example, an observer indicating the remembered final orientation of a previously perceived rotating target will often indicate an orientation that is shifted slightly forward in the direction of target rotation from the actual final orientation ofthe target. One early theory to explain this forward shift drew upon an analogy between the momentum of the physical target and the momentum of the mental representation ofthe target, and referred to this forward shift as representational momentum (Freyd & Finke, 1984). Momentum is just one of several environmentally invariant factors that distort memory, however; in this discussion, therefore, the term representational momentum will be restricted to discussions of the influence of target momentum. The more general terms displacement and shift will be used to describe the distortions produced by other environmentally invariant factors or by noninvariant factors and the interaction of those other factors with each other and with representational momentum.The discussion presents a roughly chronological exposition of how our understanding of displacement has grown beyond a concern with momentum and the concrete momentum metaphor and into a broader investigation of the physical principles that have been invariant within human evolutionary experience (e.g., gravity, fricThe author thanks two anonymous reviewers for helpful comments. Correspondence should be addressed to T. Hubbard, who is now at the Department of Psychology, Texas Christian University, Fort Worth, TX 76129. tion, centripetal force) and that appear to influence our representation of physical systems in systematic ways. Influences of individual experience and expectation on displacement will also...

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The empirical literature on auditory imagery is reviewed. Data on (a) imagery for auditory features (pitch, timbre, loudness), (b) imagery for complex nonverbal auditory stimuli (musical contour, melody, harmony, tempo, notational audiation, environmental sounds), (c) imagery for verbal stimuli (speech, text, in dreams, interior monologue), (d) auditory imagery's relationship to perception and memory (detection, encoding, recall, mnemonic properties, phonological loop), and (e) individual differences in auditory imagery (in vividness, musical ability and experience, synesthesia, musical hallucinosis, schizophrenia, amusia) are considered. It is concluded that auditory imagery (a) preserves many structural and temporal properties of auditory stimuli, (b) can facilitate auditory discrimination but interfere with auditory detection, (c) involves many of the same brain areas as auditory perception, (d) is often but not necessarily influenced by subvocalization, (e) involves semantically interpreted information and expectancies, (f) involves depictive components and descriptive components, (g) can function as a mnemonic but is distinct from rehearsal, and (h) is related to musical ability and experience (although the mechanisms of that relationship are not clear).