Visual rivalry without spatial conflict

Visual rivalry has been extensively characterized in the literature. It is thought to require spatial conflict between overlapping visual presentations, even in studies that have found nonspatial (i.e., nonretinal) influences on rivalry. Unexpectedly, we identified visual rivalry in the complete absence of spatial conflict. Participants experienced visual rivalry when we placed a nonambiguous motion stimulus in a nonspatial (in our case, object-based) reference frame. Moreover, a stimulus that was displaced within a nonspatial reference frame did not induce rivalry despite the presence of spatial conflict. This finding shows that nonspatial, object-based processing can overrule retinotopic processing and prevent rivalry from occurring when a perceived stimulus exists unambiguously in an object-based reference frame. Our results identify a potent high-level conflict-resolution stage independent of low-level spatial visual conflict. This independence of spatial overlap provides an advantage to the visual system, allowing conflict resolution when an object is nonstationary on the retina (e.g., during frequently occurring eye movements).     

Plaid motion rivalry: correlates with binocular rivalry and positive mood state

Recently Hupé and Rubin (2003, Vision Research 43 531- 548) re-introduced the plaid as a form of perceptual rivalry by using two sets of drifting gratings behind a circular aperture to produce quasi-regular perceptual alternations between a coherent moving plaid of diamond-shaped intersections and the two sets of component 'sliding' gratings. We call this phenomenon plaid motion rivalry (PMR), and have compared its temporal dynamics with those of binocular rivalry in a sample of subjects covering a wide range of perceptual alternation rates. In support of the proposal that all rivalries may be mediated by a common switching mechanism, we found a high correlation between alternation rates induced by PMR and binocular rivalry. In keeping with a link discovered between the phase of rivalry and mood, we also found a link between PMR and an individual's mood state that is consistent with suggestions that each opposing phase of rivalry is associated with one or the other hemisphere, with the 'diamonds' phase of PMR linked with the 'positive' left hemisphere.     

New motion illusion caused by pictorial motion lines

Motion lines (MLs) are a pictorial technique used to represent object movement in a still picture. This study explored how MLs contribute to motion perception. In Experiment 1, we reported the creation of a motion illusion caused by MLs: random displacements of objects with MLs on each frame were perceived as unidirectional global motion along the pictorial motion direction implied by MLs. In Experiment 2, we showed that the illusory global motion in the peripheral visual field captured the perceived motion direction of random displacement of objects without MLs in the central visual field, and confirmed that the results in Experiment 1 did not stem simply from response bias, but resulted from perceptual processing. In Experiment 3, we showed that the spatial arrangement of orientation information rather than ML length is important for the illusory global motion. Our results indicate that the ML effect is based on perceptual processing rather than response bias, and that comparison of neighboring orientation components may underlie the determination of pictorial motion direction with MLs.     

The peripheral drift illusion: a motion illusion in the visual periphery

Circularly repeating patches containing sawtooth luminance gradients produce a sensation of motion when viewed in the periphery. Illusory motion is perceived in a dark-to-light direction, but only when one's gaze is directed to different locations around the stimulus, a point outside the display is fixated and the observer blinks, or when the stimulus is sequentially displayed at different locations whilst the observer fixates one point. We propose that the illusion is produced by the interaction of three factors: (i) introducing transients as a result of eye movements or blinks; (ii) differing latencies in the processing of luminance; and (iii) spatiotemporal integration of the differing luminance signals in the periphery.     

Interactions between apparent motion rivalry in vision and touch

In multistable perception, the brain alternates between several perceptual explanations of ambiguous sensory signals. It is unknown whether multistable processes can interact across the senses. In the study reported here, we presented subjects with unisensory (visual or tactile), spatially congruent visuotactile, and spatially incongruent visuotactile apparent motion quartets. Congruent stimulation induced pronounced visuotactile interactions, as indicated by increased dominance times for both vision and touch, and an increased percentage bias for the percept already dominant under unisensory stimulation. Thus, the joint evidence from vision and touch stabilizes the more likely perceptual interpretation and thereby decelerates the rivalry dynamics. Yet the temporal dynamics depended also on subjects' attentional focus and was generally slower for tactile than for visual reports. Our results support Bayesian approaches to perceptual inference, in which the probability of a perceptual interpretation is determined by combining visual, tactile, or visuotactile evidence with modality-specific priors that depend on subjects' attentional focus. Critically, the specificity of visuotactile interactions for spatially congruent stimulation indicates multisensory rather than cognitive-bias mechanisms.     

The Ouchi illusion: An anomaly in the perception of rigid motion for limited spatial frequencies and angles

The spatial parameters underlying a novel illusion of relative motion are characterized. A simple stimulus composed of two sine-wave gratings was sufficient to generate the illusion. We measured the response of subjects to rapid, small-amplitude oscillations of this stimulus behind a fixation point. The effect was clearly strongest for acute angles between the gratings, but only when spatial frequency was between 6 and 11 cpd. We surmise that activity in the grating cells of the primate visual cortex (von der Heydt, Peterhans, & Dursteler, 1992) might be the cause of the illusion. The illusion is potentially an important tool in understanding how higher cortical areas combine disparate motion signals.     

A variant of the anomalous motion illusion based upon contrast and visual latency

We examined a variant of the anomalous motion illusion. In a series of experiments, we ascertained luminance contrast to be the critical factor. Low-contrast random dots showed longer latency than high-contrast ones, irrespective of whether they were dark or light (experiments 1 -3). We conjecture that this illusion may share the same mechanism with the Hess effect, which is characterised by visual delay of a low-contrast, dark stimulus in a moving situation. Since the Hess effect is known as the monocular version of the Pulfrich effect, we examined whether illusory motion in depth could be observed if a high-contrast pattern was projected to one eye and the same pattern of low-contrast was presented to the other eye, and they were binocularly fused and swayed horizontally. Observers then reported illusory motion in depth when the low-contrast pattern was dark, but they did not when it was bright (experiment 4). Possible explanations of this inconsistency are discussed.     

Induced motion considered as a visually induced oculogyral illusion

The possibility that nystagmus suppression contributes to illusory motion was investigated by measuring perceived motion of a stationary stimulus following the removal of an optokinetic stimulus. This was done because optokinetic nystagmus typically outlasts cessation of an optokinetic stimulus. Therefore, it would be expected that a stationary fixated stimulus should appear to move after removal of an optokinetic stimulus if illusory motion results from nystagmus suppression. Illusory motion was reported for a stationary fixation target following optokinetic stimulation. This motion was reported first in the same direction as the preceding induced motion, then in the opposite direction. The two directions of illusory motion following optokinetic stimulation are interpreted as resulting from the use of smooth ocular pursuit to suppress first one phase of optokinetic after nystagmus and then the reverse phase. Implications for the origins of induced motion are discussed.     

内源性空间注意对声音诱发闪光错觉的影响

采用经典的声音诱发闪光错觉范式,通过操纵集中和分散的空间注意的方式,考察内源性空间注意和刺激出现视野位置的交互作用对多感觉整合中听觉主导效应的影响。结果发现：(1)当空间注意处于分散状态时,下视野的裂变错觉量显著大于上视野,而集中条件下则没有差异。(2)闪光出现的位置是否随机不会影响裂变错觉。研究说明了声音诱发闪光错觉中的裂变错觉只会受到内源性空间注意和视野位置交互作用的影响。     

A necessity illusion for modal inferences from conditionals

Three experiments examined how people reason about what is possible or necessary when a conditional is true. Participants were asked to indicate whether it was necessary, possible or impossible for a specific instance to conform to one of the truth-table cases (pq, p¬q, ¬pq and ¬p¬q) (¬ = not), given the truth of the conditional. It was found that most participants, inconsistently, judged the pq case as necessary but the ¬pq or ¬p¬q cases as possible. Logically, these two kinds of judgments are contradictory. Moreover, a true conditional doesn’t imply that a specific instance under the conditional must be pq . Therefore, people demonstrate a necessity illusion for pq cases which contradicts their commitment to the possibility of ¬pq or ¬p¬q cases. Existing accounts of conditionals are unable to explain the contradiction and the necessity illusion. We propose an inference dissociation account and explore the theoretical implications of this necessity illusion.     

Pattern orientation, not motion, determines the two-dimensional tilt illusion

In the usual tilt illusion (TI) configuration, an inducing stimulus which has a single orientation is used psychophysically to explore orientation analysis in the human visual system. Recently, this approach has been extended to the use of inducing stimuli which have two orientations. Such a two-dimensional (2-D) stimulus permits investigation of the low-level analysis of visual patterns. Prior experimentation has left it unclear whether it is the spatial or the motion properties of a moving crossed-grating plaid which determine two-dimensional tilt illusions (2-D TIs) because these two parameters previously were perfectly correlated. In the present experiments pattern orientation and motion were decoupled. It is shown that 2-D TIs are determined by the spatial properties of an inducing annulus and not by its motion properties. The results also support the existence of a mechanism which extracts axes of symmetry, and which is difficult to account for in terms of local cross-orientation domain inhibition.     

The dependence of monocular rivalry on spatial frequency: some interaction variables

The effect of spatial frequency upon the rate of monocular rivalry has been investigated on several occasions, with conflicting results. With increases in spatial frequency the rivalry rate has been variously reported as declining monotonically, increasing slightly and briefly before declining sharply, or showing a sharp increase before a sharp decrease. Experiments are reported which show that all three functions may be obtained depending on whether the number of cycles of the gratings is held constant across spatial frequency, or the field size is held constant (and, if the latter, what field size is used). The point at which any high-frequency decline occurs is also shown to increase with increasing luminance. All functions obtained correspond to visual sensitivity functions obtained under comparable conditions.     

The spoke brightness illusion originates at an early motion processing stage

When a bright white disk revolves around a fixation point on a gray background, observers perceive a "spoke": a dark gray region that connects the disk with the fixation point. Our first experiment suggests that motion across the retina is both necessary and sufficient for spokes: The illusion occurs when a disk moves across the retina even though it is perceived to be stationary, but the illusion does not occur when the disk appears to move while remaining stationary on the retina. A second experiment shows that the strength of the illusion decreases with decreasing luminance contrast until subjective equiluminance, where little or no spoke is perceived. These results suggest that spokes originate at an early, predominantly luminance-based stage of motion processing, before the visual system discounts retinal motion caused by smooth pursuit.     

Vection can be induced without explicit motion signal using backscroll illusion

We demonstrated that vection is induced by a motion stimuli that does not have an explicit, bottom‐up motion component. The stimulus motion used in this experiment was animation movie clips of walking people, with no positional changes within the stimulus field. There were no low‐level motion signals in the direction of gait. The results indicate that strong vection was observed under optimal stimuli conditions, that is, large visual field and multiple walkers. These results suggest that vection can be elicited solely by motion signals extracted at relatively higher levels within the visual system. This is the first report that a pure high‐level motion related to “implied motion” induces vection.     

A static geometrical illusion contributes largely to the footsteps illusion

When a black and a white rectangle drifts across a stationary striped background with constant velocity, the rectangles appear to alternately speed up and slow down. Anstis (2001, Perception 30 785-794; 2004, Vision Research 44 2171-2178) suggested that this 'footsteps' illusion is due to confusion between contrast and velocity signaling in the motion detectors of the human visual system. To test this explanation, three experiments were carried out. In experiment 1, the magnitudes of the footsteps illusion in dynamic and static conditions was compared. If motion detectors play an important role in causing the illusion, it should be reduced in the static condition. Remarkably, however, we found that the illusory misalignment between the black and the white rectangle was even more prominent in the static condition than in the dynamic condition. In experiment 2, we measured the temporal-frequency properties of the footsteps illusion. The results showed that the footsteps illusion was tuned to low temporal frequencies. This suggests that the static illusory misalignment can contribute sufficiently to the dynamic illusory misalignment. In experiment 3, the magnitude of the illusion was measured with the rectangles drifting on a temporally modulated background instead of a spatially modulated background. If contrast affects the apparent velocity of the rectangles, temporal modulation of a uniform background should also cause the footsteps illusion. However, the results showed that the magnitude of the illusion was much reduced in this condition. Taken together, the results indicate that the footsteps illusion can be regarded as a static geometrical illusion induced by the striped background and that motion detectors play a minor role at best.     

A new optical-geometrical illusion

We describe and attempt to explain a new and unusual optical-geometrical illusion with three levels of distortion. The illusory figure is made up of three juxtaposed bands of the same width, which, when appropriately juxtaposed, appear to be of different widths. We hypothesised that the effect would depend on the combined action of various factors: (i) the band shapes and their reciprocal spatial position; (ii) the degree of coincidence of the sides of the juxtaposed bands; and (iii) the inability of the perceptual system to account for all the projective transformations. An experiment was conducted in which the shape of three stimuli was manipulated through affine transformation as well as variation of side lengths. The participants' task was to evaluate the width of the bands. The results revealed a robust and stable illusory effect; the factors that seem to influence the illusion most are band shape and conjoining side lengths.