In the imagery debate, a key question concerns the inherent spatial nature of mental images. What do we mean by spatial representation? We explore a new idea that suggests that motion is instrumental in the coding of visual space. How is the imagery debate informed by the representation of space being determined by visual motion?

Challenges to visual prediction as an organizing concept come from three main sources: (1) from observations arising from the results of experiments employing unpredictable motion, (2) from the assertions that motor processes compensate for all neural delays, and (3) from multiple interpretations specific to the flash-lag effect. One clarification that has emerged is that visual prediction is a process that either complements or reflects non-visual (e.g., motor) prediction.

Visual percepts are called veridical when a “real” object can be identified as their cause, and illusions otherwise. The perceived position and color of a flashed object may be called veridical or illusory depending on which viewpoint one adopts. Since “reality” is assumed to be fixed (independent of viewpoint) in the definition of veridicality (or illusion), this suggests that “perceived” position and color are not properties of “real” objects.

Over the history of the study of visual perception there has been great success at discovering countless visual illusions. There has been less success in organizing the overwhelming variety of illusions into empirical generalizations (much less explaining them all via a unifying theory). Here, this article shows that it is possible to systematically organize more than 50 kinds of illusion into a 7 × 4 matrix of 28 classes. In particular, this article demonstrates that (1) smaller sizes, (2) slower speeds, (...) (3) greater luminance contrast, (4) farther distance, (5) lower eccentricity, (6) greater proximity to the vanishing point, and (7) greater proximity to the focus of expansion all tend to have similar perceptual effects, namely, to (A) increase perceived size, (B) increase perceived speed, (C) decrease perceived luminance contrast, and (D) decrease perceived distance. The detection of these empirical regularities was motivated by a hypothesis, called “perceiving the present,” that the visual system possesses mechanisms for compensating neural delay during forward motion. This article shows how this hypothesis predicts the empirical regularity. (shrink)

This paper examines the question of why consumers engage in ethical consumption. The authors draw on self-affirmation theory to propose that the choice of an ethical product serves a self-restorative function. Four experiments provide support for this assertion: a self-threat increases consumers’ choice of an ethical option, even when the alternative choice is objectively superior in quantity (Study 1) and product quality (Study 2). Further, restoring self-esteem through positive feedback eliminates this increase in ethical choice (Studies 2 and 3). As (...) an additional test of the robustness of our results, a final study examined the effect of self-threat on choice in a field setting (Study 4). The findings indicate that ethical purchases are not just altruistic. They hold purposeful individual value and can help in the self-restorative process. Implications for managers making decisions regarding investment in ethical product features are discussed. (shrink)

Nijhawan argues that neural compensation is necessary to account for couplings of perception and action. Although perhaps true in some cases, computational tolerance for asynchronously arriving continuous information is of more importance. Moreover, some of the everyday venues Nijhawan uses to argue for the relevance of prediction and compensation can be better ascribed to skill.

Nijhawan's theory rests on the assumption that transient signals compete with predictive signals to generate the visual percept. We describe experiments that show that this assumption is incorrect. Our results are consistent with an alternative theory that proposes that vision is instead postdictive, in that the perception of an event is influenced by occurrences after the event.

Nijhawan redraws our attention to the problem of accurately perceiving an ever-changing visual world via a sensory system that has finite and significant communication times. The quandary is compelling and stark, but the suggestion that the visual system can compensate for these transmission delays by extrapolating the present is not so unequivocal. However, in this current airing of contradictory issues, accounts, and findings, Nijhawan trades spatial extrapolation a far more expansive notion that forces the issue of both the (...) perceived reality and functional significance of compensation. (shrink)

Nijhawan argues convincingly that predictive mechanisms are pervasive in the central nervous system (CNS). However, scientific understanding of visual prediction requires one to formulate empirically testable neurophysiological models. The author's suggestions in this direction are to be evaluated on the basis of more realistic experimental methodologies and more plausible assumptions on the hierarchical character of the human visual cortex.

The visual prediction that Nijhawan proposes cannot explain why the flash-lag effect depends on what happens after the flash. Moreover, using a visual prediction based on retinal image motion to compensate for neuronal time delays will seldom be of any use for motor control, because one normally pursues objects with which one intends to interact with ones eyes.

In the target article Nijhawan speculates that visual perceptual mechanisms compensate for neural delays so that moving objects may be perceived closer to their physical locations. However, the vast majority of published psychophysical data are inconsistent with this speculation.

In the flash-lag effect a non-moving object is quickly flashed directly underneath a moving object, which leads us to perceive the non-moving object as “lagging” the moving object, even though the two objects actually occupy the same horizontal position at the time of the flash. In the example above, for instance, a red square moves across a screen. At the midpoint of the red square’s journey from one side to the other, a green square is quickly presented (flashed) just below. (...) Despite the fact that the two stimuli are presented at the same coordinates along the x axis, the stationary square is perceived as behind the moving square. The perceived lag of the flashed stationary object becomes greater when the speed of the moving object is increased and vice versa (Nijhawan 1994). (shrink)