The perceptual stability of visual space becomes fragile in the wake of a saccadic eye movement. Objects flashed shortly before a saccade are mislocalized toward the saccade target. Traditional accounts for this effect have associated the mislocalizations with sluggishness of the efference copy signal, which is important in space perception across eye movements. Recent theories of space perception, however, have emphasized a role for visual memory in the generation of transsaccadic spatial stability. We have investigated the role of visual processes and their interactions with efference copy signals in the perisaccadic compression of space. In our experiments, subjects performed saccades in front of a computer display while visual stimuli were briefly flashed on the screen just before or during the saccade. Subjects had to report the perceived location of the flash. When the saccade target's position was visibly available after the saccade, the perceived location of the flash was compressed toward the target's position. This compression occurred not only along the axis of the saccade but also for parts of visual space along a direction orthogonal to the saccade. When the saccade target was not visibly available after the saccade, the perceived location of the flash showed only a slight shift in saccade direction. In this condition, however, the perceived location of the saccade target was drawn toward the position of the flash. We propose a framework that consists of pre- and postsaccadic processes to explain these findings.

Much work has been described comparing relative timing of different features, mostly motion and color or motion and a flash. Here we study the timing relations of pairs of motion stimuli and pairs of motion and flicker or motion and flashes. In a two-alternative forced choice task we measured thresholds for detecting asynchrony, providing estimates for shifts in subjective simultaneity as well as the window of synchronicity.

Windows of synchronicity varied for different combinations of motion direction. Comparing different velocities or different contrast levels revealed large shifts in subjective synchronicity. Contrast effects were much larger for motion reversals than for luminance flicker, indicating a major influence on motion mechanisms. Our results are compatible with the hypothesis of a flexible, high-level brain program for timing analysis. Temporal resolution of this program is limited. Differences in the processing of separate motion characteristics should be taken into account in cross-feature comparisons involving visual motion information. Results for motion reversals versus luminance flashes did not reveal a clear differential shift in time. Large differences within the motion system and the lack of a differential latency between motion reversals and flashes suggest that the flash-lag effect may be largely caused by instant spatial remapping of positional information for moving objects. We show that spatial extrapolation does not necessarily result in overshoot errors when the motion stops.

In recent years, the study and interpretation of mislocalization phenomena observed with moving objects have caused an intense debate about the processing mechanisms underlying the encoding of position. We use a neurophysiologically plausible recurrent network model to explain visual illusions that occur at the start, midposition, and end of motion trajectories known as the Fröhlich, the flash-lag, and the representational momentum effect, respectively. The model implements the idea that trajectories are internally represented by a traveling activity wave in position space, which is essentially shaped by local feedback loops within pools of neurons. We first use experimentally observed trajectory representations in the primary visual cortex of cat to adjust the spatial ranges of lateral interactions in the model. We then show that the readout of the activity profile at adequate points in time during the build-up, midphase, and decay of the wave qualitatively and quantitatively explain the known dependence of the mislocalization errors on stimulus attributes such as contrast and speed. We conclude that cooperative mechanisms within the network may be responsible for the three illusions, with a possible intervention of top-down influences that modulate the efficacy of the lateral interactions.

Different features of stimuli are processed in the central nervous system at different speeds. However, such neural time differences do not map directly onto perceptual time differences. How the brain accounts for timing disparities to correctly judge the temporal order of events in the world is the temporal binding problem. I weigh physiological data against new psychophysical findings both within and between modalities. The essence of the paradox is that the timing of neural signals appears, at first blush, too variable for the high accuracy of the psychophysical judgments. I marshal data indicating that ∼80 msec is an important duration in perception and make the novel suggestion that this number is directly mirrored in the physiology. In recordings from several areas of the primate visual system, the difference between the slowest and fastest latencies based on luminance contrast is 80 msec. If the rest of the brain wants to time outside stimuli correctly, it must account for the fact that the earliest stages of the visual system spread signals out in time. I suggest that the brain waits for the slowest information to arrive before committing to a percept. This strategy only applies to visual awareness; in contrast, the motor system may form its reactions based on the first incoming spikes.

In the flash-lag effect (FLE) a stationary flash is usually mislocalized as lagging behind a moving object in spatiotemporal alignment. Nijhawan, who postulated a mechanism of perceptual extrapolation of motion to explain the phenomenon, rediscovered this perceptual effect. The first challenge to the motion extrapolation hypothesis included an attentional shift mechanism as the alternative, which implicitly relied on the spotlight metaphor for visual attention. Other explanations have been forwarded since then, such as those based on differential latencies or perceptual postdiction. In this chapter we aim to scrutinize the role of attention in either modulating or engendering the FLE.

When observers are asked to localize the initial position of a moving target, they often indicate a position displaced in the direction of motion relative to the true onset position. In this review, the debate between Fröhlich, who discovered this phenomenon, and his contemporaries in the 1920s and 1930s is summarized. Striking misinterpretations of Fröhlich's findings and the anticipation of recent research on the flash-lag effect will be presented. In the second part, current accounts of the Fröhlich effect in terms of attention and metacontrast are evaluated. In the final section, reconciliation between research on the Fröhlich effect and recent reports of an error opposite the direction of motion (the onset repulsion effect) is offered.

This chapter is concerned with the temporal aspects of visual binding. In particular, it concentrates on findings from studies of perceptual asynchrony between stimulus features and the temporal resolution of feature binding. I review the circumstances in which perceptual asynchronies are apparent versus those in which they are not. I argue that the existing data cannot be accounted for simply by a characteristic latency difference in the processing of different visual attributes (Moutoussis & Zeki 1997a,b) or by a scheme of temporal markers at salient stimulus transitions (Nishida & Johnston 2002). Instead, I outline a potential mechanism based on feedback from higher visual areas to primary visual cortex to account for the dynamics of binding color with orientation and direction of motion.

The dual-channel differential latency hypothesis (Öğmen et al. 2004) successfully accounts for many aspects of the flash-lag effect (FLE). Here we use the dual-channel differential latency hypothesis to explain an illusion of perceived line length that can be viewed as one component of an illusion reported by Cai and Schlag (2001a). In the phenomenon studied here, a flash is presented collinear with a moving line that is simultaneously changing in length. The moving line is perceived to be misaligned with the flash (the FLE) and the length of the moving line is perceived to differ from its physical length at the instant of the flash. We designate this phenomenon the Cai line-Length Effect (CLE). Our analysis treats a horizontally moving line that also changes its vertical length as composed of two simultaneous motion components: (1) horizontal motion, and (2) vertical expansion or contraction. We measured perceived position misalignment and length misperception in the CLE paradigm, as well as separately for stimuli with the individual motion components of the CLE, as a function of target luminance. Perceived position misalignment and length misperception varied similarly with target luminance, both in the CLE paradigm and when the individual motion components were tested separately. The misperception of stimulus position and length in the CLE reflects an additional processing delay that may be caused by an interaction between the motion components in two directions. […]

Some basic versions of the flash-lag effect have been known since the early decades of the twentieth century. Intriguingly, neural delays were as central in the early attempts at explaining the effect, as they are in the more recent investigations into its cause. For a changing visual stimulus a delayed registration of the stimulus by the central nervous system (CNS) constitutes an “error” between the instantaneously registered state of the stimulus on the one hand and its physical state on the other. Therefore, for animals to acquire food, mate, and avoid predators, compensation of sensory delays is essential. One may ask which component(s) of the CNS compensate for visual delays. Logically compensation could be carried out either by visual or motor mechanisms, or both. The motion extrapolation account of the flash-lag effect challenged the dominant view that only motor mechanisms compensate for visual delays, suggesting instead that visual mechanisms also contribute. Controversy fueled by empirical observations with unpredictable motion, in particular the flash-initiated and flashterminated conditions of the flash-lag effect, soon followed; prima facie motion extrapolation could not accommodate these results. Armed with these challenging findings (primarily) several alternative accounts of flash-lag were proposed. In light of new developments, this chapter evaluates the motion extrapolation, motion sampling, motion integration, postdiction, differential latency, and attentional cuing accounts of flash-lag.

This chapter is a critical review and discussion of psychophysical studies on perisaccadic visual mislocalization. In particular, it focuses on factors influencing the mislocalization curves. The chapter is organized as follows: first some findings on perisaccadic mislocalization observed in complete darkness are reviewed, followed by empirical and theoretical considerations on eye position signals estimated psychophysically from the mislocalization curves. Next, issues on mislocalization in a lit environment are discussed. Finally, findings on perisaccadic perceptual effects of flickering stimulus are reviewed. Although our understanding of how saccadic eye movements affect visual localization has advanced dramatically in recent years, we probably have only a crude outline of the phenomena and, therefore, further research is needed.

People shift their gaze more frequently than they realize, sometimes smoothly to track objects in motion, more often abruptly with a saccade to bring a new part of the visual field under closer visual examination. Saccades are typically made three times a second throughout most of our waking life, but they are rarely noticed. Yet they are accompanied by substantial changes in visual function, most notably suppression of visual sensitivity, mislocalization of spatial position, and misjudgments of temporal duration and order of stimuli presented around the time. Here we review briefly these effects and expound a novel theory of their cause. To preserve visual stability, receptive fields undergo a fast but not instantaneous remapping at the time of saccades. If the speed of remapping approaches the physical limit of neural information transfer, it may lead to relativistic-like effects observed psychophysically, namely a compression of spatial relationships and a dilation of time.

Visual information is crucial for goal-directed reaching. Recently a number of studies have shown that motion in particular is an important source of information for the visuomotor system. For example, when reaching for a stationary object, nearby visual movement, even when irrelevant to the object or task, can influence the trajectory of the hand. Although it is clear that various kinds of visual motion can influence goal-directed reaching movements, it is less clear how or why they do so. In this chapter, we consider whether the influence of motion on reaching is unique compared to its influence on other forms of visually guided behavior. We also address how motion is coded by the visuomotor system and whether there is one motion processing system that underlies both perception and visually guided reaching. Ultimately, visual motion may operate on a number of levels, influencing goal-directed reaching through more than one mechanism, some of which may actually be beneficial for accurate behavior.

The human sensory system, at least in its early stages, consists of multiple channels for different modalities (e.g., vision, audition) and for different attributes in each modality (color, motion). Temporal congruency is a critical factor in the binding of signals across channels, but little is known about what representations and algorithms are used for matching. We first analyze this mechanism from a general theoretical point of view and then address the specific mechanisms underlying the perception of color–motion synchrony and audiovisual simultaneity. We hypothesize that judgments about cross-channel temporal relations are based on the comparison of time markers by a mid-level perceptual process. The time markers are amodal tokens that reference salient, figural features extracted from early-level sensory signals. A temporal marker should reference the time a specific event occurs in the world rather than the time the processing of the event completes in the brain.

How do human observers determine the relative timings of different events? One perspective, which I shall refer to as the brain–time theory of perception, suggests that apparent timing is related to when specific analyses are concluded within distinct and relatively independent regions of the brain. This proposal is controversial, not least because it suggests that temporal perception is error prone and subject to the rates at which analyses are concluded in different parts of the brain. One observation that may favor this perspective is that physically coincident changes in color and direction can appear asynchronous – a perceptual asynchrony. In this chapter I will review the theoretical interpretations and empirical evidence that relate to this phenomenon. I will argue that this timing illusion provides good evidence for a relationship between the time courses of sensory processing in the brain and perceived timing.