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).

Summary

Introduction

Accurately perceiving where objects are in one's visual field is important for making decisions and interacting with the environment, but the visual system must contend with a significant delay – on the order of 100 msec (Lennie 1981; Maunsell & Gibson 1992; Schmolesky et al. 1998) – between the time of retinal stimulation and the time of the elicited percept. To deal with this delay, it has been hypothesized that the visual system has been selected to attempt to generate a percept that compensates for it, so as to perceive the present (Ramachandran & Anstis 1990; De Valois and De Valois 1991; Nijhawan 1994, 1997, 2001, 2002; Berry et al. 1999; Schlag et al. 2000; Sheth et al. 2000; Khurana et al. 2000; Changizi 2001, 2003, 2009; Changizi & Widders 2002). One circumstance where perceiving the present is crucial is when an observer is moving forward and approaching objects. It has been proposed that the classical geometrical illusion stimuli are due to fixations during forward motion and that the illusions are an expected consequence of perceiving the present mechanisms; that is, the classical geometrical stimuli are perceived not as they actually project but as they would project in the next moment if the observer were moving forward (Changizi 2001, 2003; Changizi & Widders 2002). This theory has been used to explain geometrical illusions such as the Hering, Orbison (Ehrenstein), Ponzo, Muller-Lyer, and Poggendorf.

Since the beginning of sentience, the fabric of reality has been the subject of intense curiosity, and the twin concepts of space and time have figured prominently in the thinking of individuals of various intellectual persuasions. Understanding in science has advanced significantly through the postulates that underpin coherence and precision in the representation, and measurement, of space and time. These advances have formed the bedrock of the development of many disciplines. However, until the latter half of the nineteenth century many properties of space and time were assumed and therefore remained unquestioned. For example, the implicit acceptance of concepts such as absolute space (a coordinate system at rest, relative to which all inertial frames move at constant velocity) and absolute time (a universal time independent of any “clock” or mechanism) made most issues related to space and time impervious to empirical investigation and theoretical debate. This state of affairs was robustly challenged by scientists such as Ernst Mach, who among others imagined observers equipped with measuring devices (rulers and clocks) arriving at concepts at odds with notions of absolute space and absolute time.

Many well-known scientists whose work spanned the latter half of the nineteenth century (Mach included) crossed the disciplinary boundaries of physics, philosophy, and vision science. In Mach's thinking on space and time, the observer's sense perception played a critical role.