Perceived Direction Of Motion Research Articles

Effects of Surface Markings on Judgments of Motion Direction

The effects of surface markings on perceived motion direction were examined for a rotating sphere in a structure-from-motion display. The markings were dot patterns representing separate line segments or intersecting line segments (crosses) covering the surface of the sphere. The orientation of the surface markings and their intersection angles affected the perceived direction of motion, suggesting that the markings were not interpreted as geodesics or planar cuts on the surface. The perceived direction of motion was biased towards the mean orientation of the markings over the visible area of the surface. A similar bias was observed for translating planar stimuli covered with crosses, suggesting that the bias is not specific to curved surfaces or motion in depth. The deviation between the simulated motion direction and the external horizontal and vertical axes also affected the perceived motion direction. These results suggest that the average orientation of surface contours with respect to an external reference frame influences the perceived direction of motion.

Temporal dynamics of visual motion interpretation

To elucidate the mechanism involved in the perception of object motion, we psychophysically studied interaction of temporally distant visual motion signals. As a probe stimulus, we used a motion stimulus that can be perceived as moving horizontally or vertically. Subjects answered perceived motion direction for this ambiguous stimulus. When presented after an unambiguous stimulus for which the direction of motion was unambiguously perceived, the ambiguous stimulus was perceived moving in the same axial direction as that of the preceding one. This effect was very strong when the stimulus interval was less than 1 s, strongly maintained for 1 to 5 s and remained for 10 s. Even when the preceding stimulus was presented at a distant position up to 5.48° from the ambiguous stimulus, perceived motion direction for the ambiguous stimulus was influenced similarly. These results suggest that some mechanism works for reducing ambiguity in the interpretation of object motion by using temporally and spatially distant motion signals.

Localization and motion perception during smooth pursuit eye movements

We investigated the relationship between compensation for the effects of smooth pursuit eye movements in localization and motion perception. Participants had to indicate the perceived motion direction, the starting point and the end point of a vertically moving stimulus dot presented during horizontal smooth pursuit. The presentation duration of the stimulus was varied. From the indicated starting and end points, the motion direction was predicted and compared with the actual indicated directions. Both the directions predicted from localization and the indicated directions deviated from the physical directions, but the errors in the predicted directions were larger than those in the indicated directions. The results of a control experiment, in which the same tasks were performed during fixation, suggest that this difference reflects different transformations from a retinocentric to a head-centric frame of reference. This difference appears to be mainly due to an asymmetry in the effect of retinal image motion direction on localization during smooth pursuit.

Large shifts in perceived motion direction reveal multiple global motion solutions

Moving objects are thought to be decomposed into one-dimensional motion components by early cortical visual processing. Two rules describing how these components might be re-combined to produce coherent object motion are the intersection of constraints and the vector average rules. Using stimuli for which these combination rules predict different directional solutions, we found that adapting one of the solutions through motion adaptation switched perceived direction to the other solution. The effects were symmetrical: shifts from IOC to VA, and from VA to IOC, were observed following adaptation. These large shifts indicate that multiple solutions to global motion processing coexist and compete to determine perceived motion direction.

Perceived motion direction during smooth pursuit eye movements

Although many studies have been devoted to motion perception during smooth pursuit eye movements, relatively little attention has been paid to the question of whether the compensation for the effects of these eye movements is the same across different stimulus directions. The few studies that have addressed this issue provide conflicting conclusions. We measured the perceived motion direction of a stimulus dot during horizontal ocular pursuit for stimulus directions spanning the entire range of 360 degrees. The stimulus moved at either 3 or 8 degrees/s. Constancy of the degree of compensation was assessed by fitting the classical linear model of motion perception during pursuit. According to this model, the perceived velocity is the result of adding an eye movement signal that estimates the eye velocity to the retinal signal that estimates the retinal image velocity for a given stimulus object. The perceived direction depends on the gain ratio of the two signals, which is assumed to be constant across stimulus directions. The model provided a good fit to the data, suggesting that compensation is indeed constant across stimulus direction. Moreover, the gain ratio was lower for the higher stimulus speed, explaining differences in results in the literature.

Vertical object motion during horizontal ocular pursuit: compensation for eye movements increases with presentation duration

Smooth pursuit eye movements change the retinal image motion of objects in the visual field. To enable an observer to perceive the motion of these objects veridically, the visual system has to compensate for the effects of the eye movements. The occurrence of the Filehne-illusion (illusory motion of a stationary object during smooth pursuit) shows that this compensation is not always perfect. The amplitude of the illusion appears to decrease with increasing presentation durations of the stationary object. In this study we investigated whether presentation duration has the same effect when an observer views a vertically moving object during horizontal pursuit. In this case, the pursuit eye movements cause the perceived motion path to be oblique instead of vertical; this error in perceived motion direction should decrease with higher presentation durations. In Experiment 1, we found that the error in perceived motion direction indeed decreased with increasing presentation duration, especially for higher pursuit velocities. The results of Experiment 2 showed that the error in perceived motion direction did not depend on the moment during pursuit at which the stimulus was presented, suggesting that the degree of compensation for eye movements is constant throughout pursuit. The results suggest that longer presentation durations cause the eye movement signal that is used by the visual system to increase more than the retinal signal.

Perception of motion direction in Glass patterns with opposite contrast polarity dots

Perception of motion direction in Glass patterns with opposite contrast polarity dots

Prior depth information can bias motion perception.

Previous studies of the motion aperture problem have shown that the direction of grating motion can be biased by using binocular disparity to designate borders of the aperture as intrinsic (belonging to the grating) or extrinsic (resulting from occlusion of the grating). Observers report motion in the direction of the extrinsic border, as if the grating was extended and moving underneath an occluding surface. Here we investigate whether prior information about depth ordering, given by structure-from-motion, can bias the perceived motion direction of a subsequent moving grating in a similar manner. We presented an aperture stimulus that rotated about its vertical and horizontal axes, revealing the depth relationships (intrinsic and extrinsic) of the aperture borders. The grating then translated within the aperture and observers reported the direction of perceived motion. The test stimulus contained no information about the depth ordering of the scene. We found that observers' reported motion shifted toward the direction of the occluding edges, consistent with the intrinsic-extrinsic border predictions. These results indicate that prior scene information, not just depth information explicitly defined in the test stimulus, is used to help solve the motion aperture problem.

Pursuit of the ineffable: perceptual and motor reversals during the tracking of apparent motion.

Pursuit can be guided by perceived rather than physical motion, but the temporal relationship between motion perception and pursuit is unknown. We used an apparent motion stimulus consisting of a horizontal row of evenly spaced Kanizsa illusory squares (1.44 deg2): the illusory contours appeared at the midpoints of the illusory squares presented in the previous frame, producing bi-directional apparent motion of the illusory contours (21.5 deg/s) that could be reversed at will. We measured eye movements in five subjects asked to (1) track the motion of the illusory squares, and (2) reverse the perceived direction while continuing to track the squares. We measured the timing of the voluntary perceptual reversals and compared this to the time course of the reversal in tracking direction. We found that subjects could smoothly track the apparent motion of illusory squares and also produce saccade-free reversals in pursuit velocity. The time course of these motor reversals closely followed the measurements of the perceptual reversal and, on average, the perceptual reversals preceded the pursuit reversals by 53 ms, a delay shorter than when the perceptual reversal was visually guided. Smooth pursuit and the perception of motion direction were in temporal register and highly correlated, suggesting that pursuit can provide a real-time readout for the state of motion perception.

Effect of element size on stereoscopic apparent motion.

Spatial displacement limits in stereoscopic (cyclopean) apparent motion were measured from sequentially presented two-frame random-depth configurations. Each depth configuration was defined by stereoscopically near or far elements of various sizes. The limits were compared with those in luminance-defined apparent motion. The subject's task was 2-alternative forced-choice of the perceived motion direction of the sequentially presented two-frame random-dot stereograms. The spatial displacement limit below which correct motion perception arose with stereoscopic configurations was larger in proportion to increases in size of elements. The values were almost consistent with those measured by luminance-defined configurations with the same element sizes. This result suggests that the strategy for discrimination of motion direction of random configurations is similar in both stereoscopic and luminance-defined apparent motion.

The aperture problems in the Pulfrich effect.

The Pulfrich effect yields a perceived depth for horizontally moving objects but not for vertically moving ones. In this study the Pulfrich effect was measured by translating oblique lines seen through a circular window, which made motion direction ambiguous. Overlaying random dots that moved horizontally, vertically, or diagonally controlled the perceptual motion direction of the lines. In experiment 1, when the lines were seen to move horizontally, the effect was strongest in spite of the same physical motion of the lines. Experiment 2 was performed to test the above conditions again, excluding the Pulfrich effect of the dots on the depth of the lines. The overlaid dots were presented to one eye only. The result showed that the Pulfrich effect of the lines was persistently strong in spite of the perceptual changes in motion direction. Experiment 3 also showed that the Pulfrich depth was independent of the perceived horizontal speed in a plaid display. The Pulfrich effect was determined by measuring the horizontal disparity component, independently of the perceived motion direction. These results demonstrate that the aperture problems in motion and stereopsis in the Pulfrich effect are solved independently.

Can spatio-temporal energy models of motion predict feature motion?

Current “spatio-temporal energy” models of how we perceive pattern motion have been very successful in helping us to understand the mechanisms of motion perception. Although they have been supported by a large number of physiological and psychological studies, they have so far not provided a complete explanation for a number of results. These results emerge from experiments concerned with predicting perceived motion direction from patterns comprising two or more components. It has been suggested that these results are more consistent with an earlier type of model based on the motion of two-dimensional features. This paper briefly describes how three generic spatio-temporal energy models have been extended to predict motion derived from two-component stimuli. A new model is then presented that utilises similar architecture to the two-stage spatial-temporal energy model proposed by Adelson and Movshon (Nature 300 (1982) 523). The first stage is a spatial temporal filtering stage and the second stage computes the intersection of constraints (IOC), an important constraint used in combining motion information across two or more components. In the model presented here the second stage is different. A directional spatial second derivative is used to extract zero-crossings at the component level, i.e. gratings. If any zero-crossing falls in the same spatial position for two or more components its displacement is tracked using a nearest neighbour match. Tracking these `intersecting zero-crossings' essentially computes the IOC but also provides other properties that predict non-IOC motion, and second-order component motion. Surprising new insights are described into how current spatio-temporal energy models may also account for these results. However, unlike the model presented here, they rely on operations carried out on the two-dimensional pattern.

MEG alpha activity decrease reflects destabilization of multistable percepts

Multistable stimuli offer the possibility to investigate visual awareness, since they evoke spontaneous alternations between different perceptual interpretations of the same stimulus and, therefore, allow to dissociate perceptual from stimulus-driven mechanisms. In the present study, we used an ambiguous motion paradigm and compared endogenous reversals of perceived motion direction which occur spontaneously during constant ambiguous stimulation with exogenous reversals that were induced externally by changes of stimulation. Contrasting the two conditions allowed to investigate processes that trigger endogenous reversals, since the related activity should be absent in the exogenous reversal condition. We employed ambiguous dot patterns which can easily be transformed to present two stable motion directions in order to induce exogenous pattern reversals. Whole-head MEG was recorded from 10 subjects. We analyzed event-related fields (ERFs) and oscillatory activity in the alpha and gamma ranges. The results showed P300-like slow waves in response to both endogenous and exogenous reversals reflecting the conscious recognition of pattern reversals. Analyses in the gamma-band did not reveal any significant modulations. The alpha activity showed different time courses for endogenous and exogenous reversals. While the exogenous alpha activity decreased in temporal relation to the pattern reversal, the endogenous alpha activity displayed a continuous decrease starting in the time interval preceding the reversal. This time course of the endogenous alpha activity is consistent with a bottom-up approach to figure reversals, since it reflects a process of destabilization of the actual percept until a switch of visual awareness occurs.

The interaction between element orientation and perceived direction of motion

The interaction between element orientation and perceived direction of motion

Prior monocular information can bias motion perception

Previous studies of the motion aperture problem have shown that the direction of grating motion can be biased by using binocular disparity to designate borders of the aperture as intrinsic (belonging to the grating) or extrinsic (resilting from occlusion of the grating). Observers report motion in the direction of the intrinsic border, as if the grating was extended and moving underneath an occluding surface. Here we investigate whether prior information about depth ordering, given by structure-from-motion, can bias the perceived motion direction of a subsequent moving grating in a similar manner. We presented an aperture stimulus that rotated about its vertical and horizontal axes, revealing the depth relationships (intrinsic and extrinsic) of the aperture borders. The grating then translated within the aperture and observers reported the direction of perceived motion. The test stimulus contained no information about the depth ordering of the scene. We found that observers' reported motion shifted toward the direction of the occluding edges, consistent with the intrinsic-extrinsic border predictions. These results indicate that prior scene information, not just depth information explicitely defined in the test stimulus, is used to help solve the motion aperture problem.

A new variant of the barberpole effect: Psychophysical data and computer simulations

The classic barberpole effect shows that perceived direction of motion of parallel line segments depends on the orientation of the frame defined by segment end points. A stimulus configuration was created by crossing two oblique barberpoles. Perceived motion in the crossed portion of the configuration is bi-stable, alternating between two oblique directions defined by the two component barberpoles. Ratings of dominance of perceived motion direction in the crossed portion of two barberpoles of different width and orientation revealed a strong preference for the wider component barberpole and a weak preference for the nearer-to-vertical component barberpole. A network model is presented in which each unit inhibits units with different direction sensitivity and co-extensive receptive fields, and excites units with equal direction sensitivity and neighboring receptive fields. Simulations of the temporal evolution of the spatial activity profile exhibit the effect of barberpole width and the bi-stability of percepts. Fatigue of highly adapted units enables the gradual emergence of non-adapted units. Small initial variations can lead to profound differences in the final state of the system, explaining the quasi-random fluctuation between the two perceptual variants.

Velocity not acceleration of self-motion mediates vestibular-visual interaction.

We investigated the influence of vestibular stimulation with different angular accelerations and velocities on the perception of visual motion direction. Constant accelerations resulting in different angular velocities and constant angular velocities obtained at different accelerations were combined in twenty healthy subjects. Random-dot kinematograms with coherently moving pixels and randomly moving pixels were used as visual stimuli during whole-body rotations. The smallest percentage of coherently moving pixels leading to a clear perception of motion direction was taken as the perception threshold. Perception thresholds significantly increased with increasing angular velocity. Increased acceleration, however, had no significant effect on the perception thresholds. We conclude that the achieved angular velocity, and not acceleration, is the predominant factor in the processing of vestibular-visual interaction.

Allocation of Attention Affects Perceived Heading Direction with Transparent Flow Fields

Transparent motion occurs whenever dynamic HUD or HMD symbology is overlaid on the scene available through the windscreen. Psychophysical research has shown that two-dimensional transparent motion can produce systematic errors in perceived motion direction. In two experiments, we examined: a) whether transparent radial expansion patterns that accompany observer motion and specify heading direction are subject to such errors, b) whether attentional allocation to different motion components affects these errors, and c) whether these errors can result in inappropriate control input. We found that significant errors in perception of heading direction do occur for transparent radial expansion patterns, that attentional allocation influences these errors, and that these errors result in inappropriate control input.

Differences between motion-direction perception and unspecific motion perception in the human knee joint.

Perception has commonly been seen as a conscious performance. Thus, regarding proprioception in some publications, it has been proposed that the term is properly used only when subjects are able to report on the direction as well as presence of imposed movements. Consequently, detections of movements without movement-direction perception have not been accepted as perceived, since these detections were regarded as unspecific. Unspecific sensation has been suggested to precede perception. From this "two-state model", it follows that threshold values should be lower for unconscious unspecific perception than for conscious specific perception. The aim of the present study was to test this suggested dichotomy. Proprioception was compared in unspecific detection trials (only the occurrence of a movement had to be detected, not its direction) and direction-specific detection trials (the occurrence of a movement of a specific direction had to be detected). Two types of specific detection trials and two types of unspecific detection trials were studied. Pairs of threshold values were determined, regarding amplitude detection using different angular velocities and regarding velocity detection using different angular displacements, for flexion and extension. Our results showed that, independent of each other, both threshold paradigms (amplitude detection and velocity detection) revealed the same perception characteristics. In specific detection paradigms, the proprioceptive thresholds were two times lower than in unspecific detection paradigms. Thus, movements of a particular type could be detected more easily than movement per se. The suggested "two-state model" might, therefore, not be appropriate in describing proprioceptive perception.

Neural model of first-order and second-order motion perception and magnocellular dynamics.

A neural model of motion perception simulates psychophysical data concerning first-order and second-order motion stimuli, including the reversal of perceived motion direction with distance from the stimulus (gamma display), and data about directional judgments as a function of relative spatial phase or spatial and temporal frequency. Many other second-order motion percepts that have ascribed to a second non-Fourier processing stream can also be explained in the model by interactions between ON and OFF cells within a single, neurobiologically interpreted magnocellular processing stream. Yet other percepts may be traced to interactions between form and motion processing streams, rather than to processing within multiple motion processing streams. The model hereby explains why monkeys with lesions of the parvocellular layers, but not of the magnocellular layers, of the lateral geniculate nucleus (LGN) are capable of detecting the correct direction of second-order motion, why most cells in area MT are sensitive to both first-order and second-order motion, and why after 2-amino-4-phosphonobutyrate injection selectively blocks retinal ON bipolar cells, cortical cells are sensitive only to the motion of a moving bright bar's trailing edge. Magnocellular LGN cells show relatively transient responses, whereas parvocellular LGN cells show relatively sustained responses. Correspondingly, the model bases its directional estimates on the outputs of model ON and OFF transient cells that are organized in opponent circuits wherein antagonistic rebounds occur in response to stimulus offset. Center-surround interactions convert these ON and OFF outputs into responses of lightening and darkening cells that are sensitive both to direct inputs and to rebound responses in their receptive field centers and surrounds. The total pattern of activity increments and decrements is used by subsequent processing stages (spatially short-range filters, competitive interactions, spatially long-range filters, and directional grouping cells) to determine the perceived direction of motion.