In the peripheral drift illusion, a static pattern containing asymmetrical spatial luminance gradients can appear to move at its onset and then whenever the viewer moves their eyes or blinks. Recent evidence indicates that the illusion is due to changes in retinal luminance created by pupillary reflexes. Can computational models of human cortical motion sensing account for the illusory motion? An implementation of the Adelson-Bergen motion-energy models was unable to account for the illusion. However, a variant of the model incorporating half-wave rectification (half-squaring) applied to the response of the model's direction-selective sensors can account for the illusion. Half-squaring creates parallel ON and OFF channels. The output of the OFF channel was found to signal motion in the direction of the illusion whereas the ON channel signalled the opposite direction. If the two channels' outputs were combined in a way that is biased in favour of the OFF channel, the net output accounted for the illusion. A bias in favour of OFF responses is supported by evidence from physiological and psychophysical studies of human vision.

The principle of "common fate" tells us that objects that move together, group together. But what happens when physical paths are shared and illusory paths differ? Here, horizontally aligned targets move up and down over columns containing static, oblique gratings. If all columns share the same orientation, the target group appears to drift in that direction, as per the furrow illusion. However, when the two outer "bookend" targets have a different background orientation from the inner "book" targets, group motion is entirely captured by the bookends. This occurs despite the inner books having discriminable features and recoverable relative motion. What is missing is any sense of their opposing illusory path. We suggest that spatial proximity and common vertical motion help create a single grouped object representation. Since rigid objects tend not to move in two directions at once, the salient bookends dominate our perception of where the group is going.

Abstract Volitional intention can bias perception in cases where two or more interpretations of a stimulus are available to us. The neural mechanisms whereby such an intention influences perception are poorly understood. Here we investigated whether intending to see horizontal versus vertical motion in a subsequently presented instantaneous position shift of a quartet apparent motion stimulus establishes decodable sensory representations prior to both the position shift and the perception of motion. Twelve participants underwent fMRI scanning under three conditions: (1) while passively viewing either continuously or (2) discretely moving quartet stimuli, or (3) while actively intending to see a subsequent single-shot apparent motion as either a vertical or horizontal motion. Multivariate decoding analyses revealed that activity patterns during the intention period of (3) generalized to patterns evoked by both (1) physical and (2) ambiguous motion perception. Cross-decoding was strongest within dorsal/lateral visual regions, including hMT+, V3AB, and the intraparietal sulcus (IPS), but was largely absent from ventral visual cortex. Widespread overlap was also observed between intention-related and perceptual motion representations throughout the dorsal/lateral visual cortex. Our findings suggest that volitional intention establishes prospective sensory representations before perceptual experience emerges and that these representations closely resemble those associated with illusory motion perception. The predominance of intention-related representations within dorsal/lateral visual regions is consistent with top-down influences from attentional control systems. More broadly, the results demonstrate that internally generated cognitive states can shape sensory representations, constraining subsequent perceptual experience. Significance Statement How thoughts and intentions influence perception is an important question in the cognitive neuroscience of consciousness. By combining fMRI with multivariate decoding, we demonstrate that volitional intention to see a subsequent instantaneous position shift as either horizontal or vertical motion recruits sensory representations that resemble those evoked during passive perception, with the strongest effects occurring in dorsal visual and parietal cortex. These findings indicate that top-down signals can proactively configure sensory representations and potentially bias the perceived direction of apparent motion, providing new insight into the neural mechanisms through which intention influences conscious visual experience.

In the flash-grab effect, an object flashed on a moving background appears to be shifted in the direction of the motion. The same background motion also distorts the flashed object's perceived shape. An even greater shift in the perceived location is produced by the frame effect, raising the question of whether it also produces a shape distortion. This phenomenon is important because the frame effect has been linked to perceptual stabilization during eye movements where the whole visual field acts as the frame. We found that, unlike the flash-grab case, shape was preserved for the frame effect to a much greater extent than for the flash-grab. Next, we tested the extent to which shape distortions could be predicted from the size of the shifts in position of individual shape elements. We found that observed distortions were weaker than predicted distortions for the frame effect, but stronger for the flash-grab stimulus. Finally, we examined whether the greater shape distortion for the flash-grab was due to the nature of the background motion (rotation vs. translation) or the aperture within which the background motion was presented (circular vs. rectangular). We found that both factors contributed to greater shape distortion. Our findings show that motion-induced shape distortions are not solely based on the individual position shifts of the shape elements when tested in isolation. The shape preservation for the frame effect may be achieved through engaging shape-based mechanisms tuned to the dynamics of saccadic eye movements.

We investigate the subjective experience of space around the visual blind spot area, the cortical representation of which is missing feedforward connectivity from one eye. We performed these experiments as part of an adversarial collaboration to test contrasting theories of consciousness; Integrated Information Theory (IIT), Predictive Processing Active Inference (AI), and Predictive Processing Neurorepresentationalism (NREP) accounts. According to the Integrated Information Theory of consciousness, non-activatable retinotopic cortical regions, such as the blind spot region for the ipsilateral eye, create a different cause-effect structure and therefore should contribute differently to the perceived quality of space of activatable retinotopic regions. The two Predictive Processing accounts, in contrast, posit that internal models will accommodate structural deviations around the blindspot based on the available sensory evidence (particulars of this accommodation differ between the two accounts). We present a series of paradigms in which participants evaluate distances and areas that either include the blind spot or not (without stimulating it directly), as well as illusory motion that is either adjacent to the blind spot or not. We model psychometric functions relating perceived and objective space. These models vary in terms of bias and precision according to the experimental conditions (blind spot involved vs. not involved, ipsilateral vs. contralateral eye), making it possible to quantify the potential disruption of subjective spatial extendedness induced by the blind spot. We present simulated results for each experiment corresponding to the predictions of each account, and conclude by discussing challenges and plans for dissemination.

When two probes are flashed at different times within a moving frame, they can be perceived as dramatically separated from each other even though they are at the same location in the display. This effect suggests that we perceive object position relative to the surrounding frame even when it is moving (Özkan et al., 2021). Here, eight experiments reveal new properties of this frame effect. First, the influence of the frame on the perceived probe positions extends beyond its bounding contours by several degrees of visual angle, both in the direction of the frame's motion and orthogonal to it. It is also undiminished when the probes and the frame are in different depth planes. However, the influence of the frame's motion shows no extension in time-there is no effect on probes presented after the frame is removed and none retroactively before the frame appears either. The frame effect is also driven primarily by the displacement of the frame, not by its motion signals: the effect is stronger for moving bounded frames compared with moving unbounded random dot textures. When the bounded region has an internal texture that moves with or against the frame's motion or remains static, it is the displacement of the frame that produces the perceived position shifts of the probes, and the effect of the internal motion is mostly suppressed. The frame's influence is unaffected by whether the motion is self-initiated or not and does not diminish in strength across 2 hours of testing.

The encoding of locations in world coordinates is often called spatiotopy; it captures how we experience the layout of things around us. The visual system, on the other hand, appears to rely on retinotopic representations. Here we review earlier suggestions that replace spatiotopic maps with the tracking or remapping of a small number of attended targets to keep their positions updated on retinotopic maps, combined with suppression of motion responses to the shift of the retinal image. Importantly, we propose that each attended target’s identity is connected to the locations of its features in early visual cortex through a steerable autoencoder network that shifts the feature activity to the target’s new location with each saccade, explaining the many reports of trans-saccadic integration. This autoencoder process is part of the overall architecture of the visual system, acting to link target properties together, even as the target or the eyes move.

A well-known motion illusion can be seen in stationary patterns that contain repeated asymmetrical luminance gradients, which create a sawtooth-like spatial luminance profile. Such patterns can appear to move episodically, triggered by saccadic eye movements and blinks. The illusion has been known since 1979, but its origin remains unclear. Our hypothesis is that episodes of the illusory movement are caused by transitory changes in the retinal luminance of the pattern that accompany reflexive changes in pupil diameter after eye movements, blinks, and pattern onsets. Changes in retinal luminance are already known to cause illusory impressions of motion in patterns that contain asymmetrical luminance gradients. To test the hypothesis, participants viewed static illusion patterns and made controlled blinks or saccades, after which they pressed a button to indicate cessation of any illusion of movement. We measured changes in pupil diameter up to the point at which the illusion ceased. Results showed that both the amplitude and the duration of pupil dilation correlated well with illusion duration, consistent with the role of retinal luminance in generating in the illusions. This new explanation can account for the importance of eye movements and blinks, and for the effects of age and artificial pupils on the strength of the illusion. A simulation of the illusion in which pattern luminance is modulated with the same time-course as that caused by blinks and saccades creates a marked impression of illusory motion, confirming the causal role of temporal luminance change in generating the illusion.

A moving frame can act as a positional reference for the objects that it surrounds. When a frame moves back and forth on the screen, briefly flashed stimuli appear displaced. This illusory shift can be as large as the distance the frame moves, making it one of the most significant position shift illusions. The frame effect persists under many variations of the frame’s shape and motion trajectories, suggesting a position encoding mechanism that relies on relative location rather than motion. With one exception (the double-drift), motion-induced position shifts produce similar effects on saccadic eye movements and perception. Here, we compare the effect of a moving frame on perception and on saccades across spatial and temporal variations of the frame and the probe. The first experiment showed that saccades targeting the probes were displaced by only about a third of the shift seen for the perception of the probe. A second experiment showed that this difference was constant across a large range of frame speeds. These results add novel evidence in support of dissociable position representations for perception and action.

The difficulty of tracking multiple moving objects among identical distractors increases with the number of tracked targets. Previous research has shown that the number of targets tracked (i.e., load) modulates activity in brain areas related to visuospatial attention, giving rise to so-called attention response functions (ARFs). While the hemifield/hemispheric effects of spatial attention (e.g., hemispatial neglect, hemifield capacity limits) are well described, it had not previously been tested whether a hemispheric or hemifield imbalance exists among ARFs. By recording blood oxygenation level-dependent activity from human brains (n =19, female and male) in a multiple-object tracking paradigm, we show that the number of tracked objects modulates activity in a large network of areas bilaterally. A significant effect of contralateral load was found in earlier areas throughout the dorsal and ventral visual streams, while the effects of ipsilateral load emerged in later areas. Both contra-and ipsilateral load significantly influenced activity in the parietal and frontal lobes, specifically the dorsal attention network. In addition, some brain regions in the occipital lobe were significantly more sensitive to contralateral than ipsilateral load. Our results are consistent with findings showing that a diverse set of brain areas contributes to tracking multiple targets. In particular, we extend the canonical view of load-based ARFs to include hemifield bias. Given the hemifield-specific nature of speed and capacity limits to multiple-object tracking, we conjecture that areas that show a strong hemifield preference may impose a bottleneck on processing that results in limits on the capacity and speed of tracking.

In 1992, Randolph Blake, in collaboration with Robert Cormack and Eric Hiris, reported a strong deviation in perceived direction for a target moving over an oblique, static grating. Here we follow up on this effect, subsequently called the furrow illusion, to determine its origin. We find, unlike Cormack et al., that it is influenced by the luminance of the target and that it does not survive smooth pursuit of a moving fixation that stabilizes the target on the retina. We also introduce an inverted version of the furrow stimulus with the static grating visible only within the moving target rather than only around it. This "peep-hole" furrow stimulus shows a similar deviation in its direction and is quite similar to the well-known double-drift stimulus (Lisi & Cavanagh, 2015). Like the double-drift but unlike the furrow stimulus, its illusory direction persists when tracking a fixation that moves in tandem with the target. The main source for the illusion in both cases appears to be the terminators where the grating's bars meet the target contour. These terminators move laterally along the target's contour as the target moves vertically and the combination of these two directions creates the illusory oblique motion. However, the loss of the illusion for the tracked furrow stimulus suggests either a contribution from negative afterimages within the target or from induced motion in this case.

Moving frames produce large displacements in the perceived location of flashed and continuously moving probes. In a series of experiments, we test the contributions of the probe's displacement and the frame's displacement on the strength of the frame's effect. In the first experiment, we find a dramatic position shift of flashed probes whereas the effect on a continuously moving probe is only one-third as strong. In Experiment 2, we show that the absence of an effect for the static probe is a consequence of its perceptual grouping with the static background. As long as the continuously present probe has some motion, it appears to group to some extent with the frame and show an illusory shift of intermediate magnitude. Finally, we informally explored the illusory shifts seen for a continuously moving probe when the frame itself has a more complex path. In this case, the probe appears to group more strongly with the frame. Overall, the effects of the frame on the probe demonstrate the outcome of a competition between the frame and the static background in determining the frame of reference for the probe's perceived position.

The perception of an object's location is profoundly influenced by the surrounding dynamics. This is dramatically demonstrated by the frame effect, where a moving frame induces substantial shifts in the perceived location of objects that flash within it. In this study, we examined the elements contributing to the large magnitude of this effect. Across three experiments, we manipulated the number of probes, the dynamics of the frame, and the spatiotemporal relationships between probes and the frame. We found that the presence of multiple probes amplified the position shift, whereas the accumulation of the frame effect over repeated motion cycles was minimal. Notably, an oscillating frame generated more pronounced effects compared to a unidirectional moving frame. Furthermore, the spatiotemporal distance between the frame and the probe played pivotal roles, with larger shifts observed near the leading edge of the frame. Interestingly, although larger frames produced stronger position shifts, the maximum shift occurred almost at the same distance relative to the frame's center across all tested sizes. Our findings suggest that the number of probes, frame size, relative probe-frame distance, and frame dynamics collectively contribute to the magnitude of the position shift.

The ability to accurately perceive and track moving objects is crucial for many everyday activities. In this study, we use a "double -drift stimulus" to explore the processing of visual motion signals that underlie perception, pursuit, and saccade responses to a moving object. Participants were presented with peripheral moving apertures filled with noise that either drifted orthogonally to the aperture's direction or had no net motion. Participants were asked to saccade to and track these targets with their gaze as soon as they appeared and then to report their direction. In the trials with internal motion, the target disappeared at saccade onset so that the first 100 ms of the postsaccadic pursuit response was driven uniquely by peripheral information gathered before saccade onset. This provided independent measures of perceptual, pursuit, and saccadic responses to the double -drift stimulus on a trial -by -trial basis. Our analysis revealed systematic differences between saccadic responses, on one hand, and perceptual and pursuit responses, on the other. These differences are unlikely to be caused by differences in the processing of motion signals because both saccades and pursuits seem to rely on shared target position and velocity information. We conclude that our results are instead due to a difference in how the processing mechanisms underlying perception, pursuit, and saccades combine motor signals with target position. These findings advance our understanding of the mechanisms underlying dissociation in visual processing between perception and eye movements.