Motion-induced Position Shifts Research Articles

Exploring the extent to which shared mechanisms contribute to motion-position illusions.

Motion-position illusions (MPIs) are visual motion illusions in which motion signals bias the perceived position of an object. Due to phenomenological similarities between these illusions, previous research has assumed that some are caused by common mechanisms. However, this assumption has yet to be directly tested. This study investigates this assumption by exploiting between-participant variations in illusion magnitude. During two sessions, 106 participants viewed the flash-lag effect, luminance flash-lag effect, Fröhlich effect, flash-drag effect, flash-grab effect, motion-induced position shift, twinkle-goes effect, and the flash-jump effect. For each effect, the magnitude of the illusion was reliable within participants, strongly correlating between sessions. When the pairwise correlations of averaged illusions magnitudes were explored, two clusters of statistically significant positively correlated illusions were identified. The first cluster comprised the flash-grab effect, motion-induced position shift, and twinkle-goes effect. The second cluster comprised the Fröhlich and flash-drag effect. The fact that within each of these two clusters, individual differences in illusion magnitude were correlated suggests that these clusters may reflect shared underlying mechanisms. An exploratory factor analysis provided additional evidence that these correlated clusters shared an underlying factor, with each cluster loading onto their own factor. Overall, our results reveal that, contrary to the prevailing perspective in the literature, while some motion-position illusions share processes, most of these illusions are unlikely to reflect any shared processes, instead implicating unique mechanisms.

A motion-induced position shift that depends on motion both before and after the test probe.

Two versions of the flash grab illusion were used to examine the relative contributions of motion before and motion after the test flash to the illusory position shift. The stimulus in the first two experiments was a square pattern that expanded and contracted with an outline square flashed each time the motion reversed producing a dramatic difference in perceived size between the two reversals. Experiment 1 showed a strong illusion when motion was present before and after the flashed tests or just after the flashes, but no significant effect when only the pre-flash motion was present. In Experiment 2, motion always followed the flash, and the duration of the pre-flash motion was varied. The results showed a significant increase in illusion strength with the duration of pre-flash motion and the effect of the pre-flash motion was almost 50% that of the post-flash motion. Finally, Experiment 3 tested the position shifts when the linear motion of a disk before the flash was orthogonal to its motion after the flash. Here, the results again showed that the pre-flash motion made a significant contribution, about 32% that of the post-flash motion. Several models are considered and even though all fail to some degree, they do offer insights into the nature of the illusion. Finally, we show that the empirical measure of the relative contribution of motion before and after the flash can be used to distinguish the mechanisms underlying different illusions.

Exploring the Common Mechanisms of Motion-Based Visual Prediction

Human vision supports prediction for moving stimuli. Here we take an individual differences approach to investigate whether there could be a common processing rate for motion-based visual prediction across diverse motion phenomena. Motion Induced Spatial Conflict (MISC) refers to an incongruity arising from two edges of a combined stimulus, moving rigidly, but with different apparent speeds. This discrepancy induces an illusory jitter that has been attributed to conflict within a motion prediction mechanism. Its apparent frequency has been shown to correlate with the frequency of alpha oscillations in the brain. We asked what other psychophysical measures might correlate positively with MISC frequency. We measured the correlation between MISC jitter frequency and another three measures that might be linked to motion-based spatial prediction. We demonstrate that the illusory jitter frequency in MISC correlates significantly with the accrual rate of the Motion Induced Position Shift (MIPS) effect - the well-established observation that a carrier movement in a static envelope of a Gabor target leads to an apparent position shift of the envelope in the direction of motion. We did not observe significant correlations with the other two measures – the Adaptation Induced Spatial Shift accrual rate (AISS) and the Smooth Motion Threshold (SMT). These results suggest a shared perceptual rate between MISC and MIPS, implying a common periodic mechanism for motion-based visual prediction.

Reduced flash lag illusion in early deaf individuals

When a brief flash is quickly presented aligned with a moving target, the flash typically appears to lag behind the moving stimulus. This effect is widely known in the literature as a flash-lag illusion (FLI). The flash-lag is an example of a motion-induced position shift. Since auditory deprivation leads to both enhanced visual skills and impaired temporal abilities, both crucial for the perception of the flash-lag effect, here we hypothesized that lack of audition could influence the FLI. 13 early deaf and 18 hearing individuals were tested in a visual FLI paradigm to investigate this hypothesis. As expected, results demonstrated a reduction of the flash-lag effect following early deafness, both in the central and peripheral visual fields. Moreover, only for deaf individuals, there is a positive correlation between the flash-lag effect in the peripheral and central visual field, suggesting that the mechanisms underlying the effect in the center of the visual field expand to the periphery following deafness. Overall, these findings reveal that lack of audition early in life profoundly impacts early visual processing underlying the flash-lag effect.

Paradoxical stabilization of relative position in moving frames

To capture where things are and what they are doing, the visual system may extract the position and motion of each object relative to its surrounding frame of reference [K. Duncker, Routledge and Kegan Paul, London 161-172 (1929) and G. Johansson, Acta Psychol (Amst.) 7, 25-79 (1950)]. Here we report a particularly powerful example where a paradoxical stabilization is produced by a moving frame. We first take a frame that moves left and right and we flash its right edge before, and its left edge after, the frame's motion. For all frame displacements tested, the two edges are perceived as stabilized, with the left edge on the left and right edge on the right, separated by the frame's width as if the frame were not moving. This stabilization is paradoxical because the motion of the frame itself remains visible, albeit much reduced. A second experiment demonstrated that unlike other motion-induced position shifts (e.g., flash lag, flash grab, flash drag, or Fröhlich), the illusory shift here is independent of speed and is set instead by the distance of the frame's travel. In this experiment, two probes are flashed inside the frame at the same physical location before and after the frame moves. Despite being physically superimposed, the probes are perceived widely separated, again as if they were seen in the frame's coordinates and the frame were stationary. This paradoxical stabilization suggests a link to visual stability across eye movements where the displacement of the entire visual scene may act as a frame to stabilize the perception of relative locations.

Integration of Position and Predictive Motion Signals in Aging Vision

We examined the effect of aging on the integration of position and motion signals, which is essential for tracking visual objects, using the motion-induced position shift (MIPS) phenomenon. We first measured the MIPS and bias in speed perception at three eccentricities. Both young and older adults showed the increasing MIPS and decreasing perceived speed as the eccentricity increased, which is consistent with previous literature. More importantly, we found that the mean MIPS was 2.87 times larger in older adults, and the response variability in position tasks showed a larger difference between age groups compared with the difference in speed tasks. We then measured the MIPS across stimulus durations. Temporal changes in the MIPS showed similar patterns in young and older adults in that the MIPS initially peaked at around 60 ms and approached an asymptote. We further analyzed the changes in response variability across stimulus durations to estimate sensory noise and propagation noise separately and found that only sensory noise was significantly larger in older adults. The overall results suggest that the increased MIPS in older adults is due to the increased dependency on predictive motion signals to compensate for the relatively imprecise position signals, which in turn implies that older adults would depend more on the motion signals to track objects.

Neural Correlates of the Conscious Perception of Visual Location Lie Outside Visual Cortex.

When perception differs from the physical stimulus, as it does for visual illusions and binocular rivalry, the opportunity arises to localize where perception emerges in the visual processing hierarchy. Representations prior to that stage differ from the eventual conscious percept even though they provide input to it. Here, we investigate where and how a remarkable misperception of position emerges in the brain. This "double-drift" illusion causes a dramatic mismatch between retinal and perceived location, producing a perceived motion path that can differ from its physical path by 45° or more. The deviations in the perceived trajectory can accumulate over at least a second, whereas other motion-induced position shifts accumulate over 80-100ms before saturating. Using fMRI and multivariate pattern analysis, we find that the illusory path does not share activity patterns with a matched physical path in any early visual areas. In contrast, a whole-brain searchlight analysis reveals a shared representation in anterior regions of the brain. These higher-order areas would have the longer time constants required to accumulate the small moment-to-moment position offsets that presumably originate in early visual cortical areas and then transform these sensory inputs into a finalconscious percept. The dissociation between perception and the activity in early sensory cortex suggests that consciously perceived position does not emerge in what is traditionally regarded as the visual system but instead emerges at a higher level.

Ocular torsion is related to perceived motion-induced position shifts.

Ocular torsion (i.e., rotations of the eye about the line of sight) can be induced by visual rotational motion. It remains unclear whether and how such visually induced torsion is related to perception. By using the flash-grab effect, an illusory position shift of a briefly flashed stationary target superimposed on a rotating pattern, we examined the relationship between torsion and perception. In two experiments, 25 observers reported the perceived location of a flash while their three-dimensional eye movements were recorded. In Experiment 1, the flash coincided with a direction reversal of a large, centrally displayed, rotating grating. The grating triggered visually induced torsion in the direction of stimulus rotation. The magnitude of torsional eye rotation correlated with the illusory perceptual position shift. To test whether torsion caused the illusion, in Experiment 2, the flash was superimposed on two peripheral gratings rotating in opposite directions. Even though torsion was eliminated, the illusory position shift persisted. Despite the lack of a causal relationship, the torsion-perception correlations indicate a close link between both systems, either through similar visual-input processing or a boost of visual rotational signal strength via oculomotor feedback.

Adaptation to an illusory aspect ratio distorted by motion induced position shift

Adaptation to an illusory aspect ratio distorted by motion induced position shift

Dynamics of Motion Induced Position Shifts Revealed by Continuous Tracking

Dynamics of Motion Induced Position Shifts Revealed by Continuous Tracking

Continuous Tracking of Motion Induced Position Shifts

Continuous Tracking of Motion Induced Position Shifts

Motion-induced position mis-localization predicts the severity of Alzheimer's disease.

Patients with Alzheimer's disease (AD) often exhibit motion processing deficits. It is unclear whether the localization of moving objects - a perceptual process tightly linked to motion - is impaired or intact in AD. In this study, we used the phenomenon of illusory shift of position induced by motion as a behavioural paradigm to probe how the spatial representation differs between AD patients and healthy elderly controls. We measured the magnitudes of motion-induced position shift in a group of AD participants (N=24) and age-matched elderly observers (N=24). We found that AD patients showed weakened position mis-localization, but only for motion stimuli of slow speeds. For fast motion, the position mis-localization did not differ significantly between groups. Furthermore, we showed that the magnitudes of position mis-localization can predict the severity of AD; that is, patients with more severe symptoms had less preserved position mis-localization. Our results suggest that AD pathology impacts not only motion processing per se, but also the perceptual process related to motion such as the localization of moving objects.

When predictions fail: Correction for extrapolation in the flash-grab effect.

Motion-induced position shifts constitute a broad class of visual illusions in which motion and position signals interact in the human visual pathway. In such illusions, the presence of visual motion distorts the perceived positions of objects in nearby space. Predictive mechanisms, which could contribute to compensating for processing delays due to neural transmission, have been given as an explanation. However, such mechanisms have struggled to explain why we do not usually perceive objects extrapolated beyond the end of their trajectory. Advocates of this interpretation have proposed a "correction-for-extrapolation" mechanism to explain this: When the object motion ends abruptly, this mechanism corrects the overextrapolation by shifting the perceived object location backwards to its actual location. However, such a mechanism has so far not been empirically demonstrated. Here, we use a novel version of the flash-grab illusion to demonstrate this mechanism. In the flash-grab effect, a target is flashed on a moving background that abruptly changes direction, leading to the mislocalization of the target. Here, we manipulate the angle of the direction change to dissociate the contributions of the background motion before and after the flash. Consistent with previous reports, we observe that perceptual mislocalization in the flash-grab illusion is mainly driven by motion after the flash. Importantly, however, we reveal a small but consistent mislocalization component in the direction opposite to the direction of the first motion sequence. This provides empirical support for the proposed correction-for-extrapolation mechanism, and therefore corroborates the interpretation that motion-induced position shifts might result from predictive interactions between motion and position signals.

Is the perceived present a predictive model of the objective present?

ABSTRACTProcessing latencies for coherent, high level percepts in vision are at least 100 ms and possibly as much as 500 ms. Processing latencies are less in other modalities, but still significant. This seems to imply that perception lags behind reality by an amount equal to the processing latency. It has been proposed that the brain can compensate for perceptual processing latencies by using the most recent available information to extrapolate forward, thereby constructing a model of what the world beyond the senses is like now. The present paper reviews several lines of evidence relating to this hypothesis, including the flash-lag effect, motion-induced position shifts, representational momentum, static visual illusions, and motion extrapolation at the retina. There are alternative explanations for most of the results but there are some findings for which no competing explanation has yet been proposed. Collectively, the evidence for extrapolation to the present is suggestive but not yet conclusive. An alternative account of compensation for processing latencies, based on the hypothesis of rapid emergence of percepts, is proposed.

Motion Extrapolation for Eye Movements Predicts Perceived Motion-Induced Position Shifts.

Transmission delays in the nervous system pose challenges for the accurate localization of moving objects as the brain must rely on outdated information to determine their position in space. Acting effectively in the present requires that the brain compensates not only for the time lost in the transmission and processing of sensory information, but also for the expected time that will be spent preparing and executing motor programs. Failure to account for these delays will result in the mislocalization and mistargeting of moving objects. In the visuomotor system, where sensory and motor processes are tightly coupled, this predicts that the perceived position of an object should be related to the latency of saccadic eye movements aimed at it. Here we use the flash-grab effect, a mislocalization of briefly flashed stimuli in the direction of a reversing moving background, to induce shifts of perceived visual position in human observers (male and female). We find a linear relationship between saccade latency and perceived position shift, challenging the classic dissociation between "vision for action" and "vision for perception" for tasks of this kind and showing that oculomotor position representations are either shared with or tightly coupled to perceptual position representations. Altogether, we show that the visual system uses both the spatial and temporal characteristics of an upcoming saccade to localize visual objects for both action and perception.SIGNIFICANCE STATEMENT Accurately localizing moving objects is a computational challenge for the brain due to the inevitable delays that result from neural transmission. To solve this, the brain might implement motion extrapolation, predicting where an object ought to be at the present moment. Here, we use the flash-grab effect to induce perceptual position shifts and show that the latency of imminent saccades predicts the perceived position of the objects they target. This counterintuitive finding is important because it not only shows that motion extrapolation mechanisms indeed work to reduce the behavioral impact of neural transmission delays in the human brain, but also that these mechanisms are closely matched in the perceptual and oculomotor systems.

The faster you decide, the more accurate localization is possible: Position representation of "curveball illusion" in perception and eye movements.

When the inside texture of a moving object moves, the perceived motion of the object is often distorted toward the direction of the texture’s motion (motion-induced position shift), and such perceptual distortion accumulates while the object is watched, causing what is known as the curveball illusion. In a recent study, however, the accumulation of the position error was not observed in saccadic eye movements. Here, we examined whether the position of the illusory object is represented independently in the perceptual and saccadic systems. In the experiments, the stimulus of the curveball illusion was adopted to examine the temporal change in the position representation for saccadic eye movements and for perception by varying the elapsed time from the input of visual information to saccade onset and perceptual judgment, respectively. The results showed that the temporal accumulation of the motion-induced position shift is observed not only in perception but also in saccadic eye movements. In the saccade tasks, the landing positions of saccades gradually shifted to the illusory perceived position as the elapsed time from the target offset to the saccade “go” signal increased. Furthermore, in the perception task, shortening the time between the target offset and the perceptual judgment reduced the size of the illusion effect. Therefore, these results argue against the idea of dissociation between saccadic and perceptual localization of a moving object suggested in the previous study, in which saccades were measured in a rushed way while perceptual responses were measured without time constraint. Instead, the similar temporal trends of these effects imply a common or similar target representation for perception and eye movements which dynamically changes over the course of evidence accumulation.

Motion-induced position shift in early Alzheimer\u2019s disease

The localization of object position in space is one of the most important visual abilities in humans. Motion-induced position shift is a perceptual illusion in which the position of a moving object is perceived to be shifted in the direction of motion. In this study, we wanted to explore whether and how Alzheimer’s disease (AD) affects this illusion. We recruited a group of patients with early AD and a group of age-matched healthy controls. In our experiments, two drifting Gabor patches moving in opposite directions were presented and participants were asked to report whether the upper Gabor appeared rightwards or leftwards of the lower one. We measured the psychometric functions, of which the point of subjective alignment was taken as the magnitude of motion-induced position shift. We compared the position shift across the two groups at three different retinal eccentricities. We found that position shifts were systematically smaller in the AD group as comparing to the elderly control group. Our data demonstrated that AD patients were less prone to motion-induced position shift. The results add to the existing knowledge of perceptual deficits in AD patients. We suggest that motion induced position shift may be effective as a new behavioral indicator for AD identification.

Visual crowding is unaffected by adaptation-induced spatial compression.

It has recently been shown that adapting to a densely textured stimulus alters the perception of visual space, such that the distance between two points subsequently presented in the adapted region appears reduced (Hisakata, Nishida, & Johnston, 2016). We asked whether this form of adaptation-induced spatial compression alters visual crowding. To address this question, we first adapted observers to a dynamic dot texture presented within an annular region surrounding the test location. Following adaptation, observers perceived a test array comprised of multiple oriented dot dipoles as spatially compressed, resulting in an overall reduction in perceived size. We then tested to what extent this spatial compression influences crowding by measuring orientation discrimination of a single dipole flanked by randomly oriented dipoles across a range of separations. Following adaptation, we found that the magnitude of crowding was predicted by the physical rather than perceptual separation between center and flanking dipoles. These findings contrast with previous studies in which crowding has been shown to increase when motion-induced position shifts act to reduce apparent separation (Dakin, Greenwood, Carlson, & Bex, 2011; Maus, Fischer, & Whitney, 2011).

Meridian interference reveals neural locus of motion-induced position shifts.

When a Gabor patch moves along a path in one direction while its internal texture drifts orthogonally to this path, it can appear to deviate from its physical path by 45° or more. This double-drift illusion is different from other motion-induced position shift effects in several ways: it has an integration period of over a second; the illusory displacement that accumulates over a second or more is orthogonal to rather than along the motion path; the perceptual deviations are much larger; and they have little or no effect on eye movements to the target. In this study we investigated the underlying neural mechanisms of the motion integration and position processing for this double-drift stimulus by testing possible anatomical constraints on its magnitude. We found that the illusion was reduced at the vertical and horizontal meridians when the perceptual path would cross or be driven toward the meridian, but not at other locations or other motion directions. The disruption of the accumulation of the position error at both the horizontal and vertical meridians suggests a central role of quadrantic areas in the generation of this type of motion-induced position shift. NEW & NOTEWORTHY The remarkably strong double-drift illusion is disrupted at both the vertical and horizontal meridians. We propose that this finding is the behavioral consequence of the anatomical gaps at both meridians, suggesting that neural areas with quadrantic representations (e.g., V2, V3) are the initial locus of this motion-induced position shift. This result rules out V1 as the source of the illusion because it has an anatomical break only at the vertical meridian.

Motion-Induced Position Shifts Activate Early Visual Cortex.

The ability to correctly determine the position of objects in space is a fundamental task of the visual system. The perceived position of briefly presented static objects can be influenced by nearby moving contours, as demonstrated by various illusions collectively known as motion-induced position shifts. Here we use a stimulus that produces a particularly strong effect of motion on perceived position. We test whether several regions-of-interest (ROIs), at different stages of visual processing, encode the perceived rather than retinotopically veridical position. Specifically, we collect functional MRI data while participants experience motion-induced position shifts and use a multivariate pattern analysis approach to compare the activation patterns evoked by illusory position shifts with those evoked by matched physical shifts. We find that the illusory perceived position is represented at the earliest stages of the visual processing stream, including primary visual cortex. Surprisingly, we found no evidence of percept-based encoding of position in visual areas beyond area V3. This result suggests that while it is likely that higher-level visual areas are involved in position encoding, early visual cortex also plays an important role.