A motion aftereffect from still photographs depicting motion

A photograph of an action can convey a vivid sense of motion. Does the inference of motion from viewing a photograph involve the same neural and psychological representations used when one views physical motion? In this study, we tested whether implied motion is represented by the same direction-selective signals involved in the perception of real motion. We made use of the motion aftereffect, a visual motion illusion. Three experiments showed that viewing a series of static photographs with implied motion in a particular direction produced motion aftereffects in the opposite direction, as assessed with real-motion test probes. The transfer of adaptation from motion depicted in photographs to real motion demonstrates that the perception of implied motion activates direction-selective circuits that are also involved in processing real motion.     

What learning to see arbitrary motion tells us about biological motion perception

In separate studies, observers viewed upright biological motion, inverted biological motion, or arbitrary motion created from systematically randomizing the positions of point-light dots. Results showed that observers (a) could learn to detect the presence of arbitrary motion, (b) could not learn to discriminate the coherence of arbitrary motion, although they could do so for upright biological motion, (c) could apply a detection strategy to learn to detect the presence of inverted biological motion nearly as well as they detected upright biological motion, and (d) performed better discriminating the coherence of upright biological motion compared with inverted biological motion. These results suggest that learning and form information play an important role in perceiving biological motion, although this role may only be apparent in tasks that require processing information from multiple parts of the motion display.     

Effects of element orientation on apparent motion perception

We present an ambiguous motion paradigm that allows us to quantify the influence of aspects of form relevant to the perception of apparent motion. We report on the role of bar element orientation in motion paths. The effect of orientation differences between bar elements in a motion path is small with respect to the crucial role of the orientation of bar elements relative to motion direction. Motion perception between elements oriented along the motion direction dominates motion perception between elements oriented perpendicularly to motion direction. The perception of apparent motion is affected by bar length and width and is anisotropic.     

Cortical dynamics of visual motion perception: short-range and long-range apparent motion.

This article describes further evidence for a new neural network theory of biological motion perception. The theory clarifies why parallel streams V1----V2, V1----MT, and V1----V2----MT exist for static form and motion form processing among the areas V1, V2, and MT of visual cortex. The theory suggests that the static form system (Static BCS) generates emergent boundary segmentations whose outputs are insensitive to direction-of-contrast and to direction-of-motion, whereas the motion form system (Motion BCS) generates emergent boundary segmentations whose outputs are insensitive to direction-of-contrast but sensitive to direction-of-motion. The theory is used to explain classical and recent data about short-range and long-range apparent motion percepts that have not yet been explained by alternative models. These data include beta motion, split motion, gamma motion and reverse-contrast gamma motion, delta motion, and visual inertia. Also included are the transition from group motion to element motion in response to a Ternus display as the interstimulus interval (ISI) decreases; group motion in response to a reverse-contrast Ternus display even at short ISIs; speed-up of motion velocity as interflash distance increases or flash duration decreases; dependence of the transition from element motion to group motion on stimulus duration and size, various classical dependencies between flash duration, spatial separation, ISI, and motion threshold known as Korte's laws; dependence of motion strength on stimulus orientation and spatial frequency; short-range and long-range form-color interactions; and binocular interactions of flashes to different eyes.     

Motion integration during motion aftereffects

The perceived global motion of a stimulus depends on how its different local motion-direction vectors are distributed in space and time. When they are explicitly co-localized, as in the case of locally paired motion, competitive motion integration mechanisms produce a unitary global motion direction determined by their vector average. During motion aftereffects induced by simultaneous adaptation to multiple motion directions, just as in the case of locally paired motion, different directional signals originate simultaneously from exactly the same position in space. Therefore, the perceived global motion direction during motion aftereffects results from local vector averaging of the co-localized motion-direction signals induced by adaptation.     

Visual motion integration for perception and pursuit

To examine the relationship between visual motion processing for perception and pursuit, we measured the pursuit eye-movement and perceptual responses to the same complex-motion stimuli. We show that humans can both perceive and pursue the motion of line-figure objects, even when partial occlusion makes the resulting image motion vastly different from the underlying object motion. Our results show that both perception and pursuit can perform largely accurate motion integration, i.e. the selective combination of local motion signals across the visual field to derive global object motion. Furthermore, because we manipulated perceived motion while keeping image motion identical, the observed parallel changes in perception and pursuit show that the motion signals driving steady-state pursuit and perception are linked. These findings disprove current pursuit models whose control strategy is to minimize retinal image motion, and suggest a new framework for the interplay between visual cortex and cerebellum in visuomotor control.     

A computational and perceptual account of motion lines

To indicate motion in a static drawing, artists often include lines trailing a moving object. The use of these motion lines is notable because they do not seem to be related to anything in the optic array. The dynamic behavior of a neural-network model for contour detection is analyzed and it is shown that it generates trails of oriented responses behind moving stimuli. The properties of the oriented response trails are shown to correspond to motion lines. The model generates trails of different orientations depending on the speed and length of the movement, and thereby predicts different uses of two types of motion lines. The model further predicts that motion lines should bias real motion in some situations. An experiment relating motion lines to ambiguous motion percepts demonstrates that motion lines contribute to motion percepts.     

Adaptation in motion perception: Alteration of induced motion

Prolonged exposure to a condition that causes induced motion was found to diminish this effect. The extent of a horizontal induced motion was measured by obtaining estimates of the direction of the apparent oblique path that resulted when a spot was visible on a horizontally moving pattern and was therefore in horizontal induced motion and, at the same time, moved vertically. Because the horizontal component of the perceived motion path represented the induced motion, the slope of the path measured the extent of the induced motion. After a 10-min exposure to induced motion, the apparent motion path was steeper; the mean change corresponded to a 15% smaller extent of the induced motion. Results were obtained that argue that this effect is not due to a diminished horizontal motion of the pattern but amounts to a smaller motion-inducing effect. The experiments were meant to support the view that the perceptual process that underlies induced motion is learned.     

Surface discontinuity is critical in a moving observer's perception of objects' depth order and relative motion from retinal image motion.

The visual system perceptually decomposes retinal image motion into three basic components that are ecologically significant for the human observer: object depth, object motion, and self motion. Using this conceptual framework, we explored the relationship between them by examining perception of objects' depth order and relative motion during self motion. We found that the visual system obeyed what we call the parallax-sign constraint, but in different ways depending on whether the retinal image motion contained velocity discontinuity or not. When velocity discontinuity existed (e.g. in dynamic occlusion, transparent motion), the subject perceptually interpreted image motion as relative motion between surfaces with stable depth order. When velocity discontinuity did not exist, he/she perceived depth-order reversal but no relative motion. The results suggest that the existence of surface discontinuity or of multiple surfaces indexed by velocity discontinuity inhibits the reversal of global depth order.     

The complementarity of apparent and real motion

Summary It is proposed that apparent motion does not parallel real motion. Bather, apparent motion occurs when the off-period is equivalent to angular velocities at which an object in real motion appears blurred. Experimental evidence is reported which supports this view. It suggests that apparent motion serves biologically to extend the range of motion perception beyond that allowed by time-constants early in the visual system.     

The relationship between external thoracopelvic angle and lumbar segmental axial twist angle using an ultrasound imaging technique

The relationship between externally measured and internal spine axial twist motion (rotation about a vertical axis) is not well understood. Ultrasound is a validated technique for measurement of vertebral axial twist motion and has the potential for measuring segmental vertebral axial twist in vivo. The objective of this study was to evaluate lumbar segmental axial twist in relation to external thoracopelvic twist from optical motion capture using an ultrasound imaging technique. Sixteen participants were tested in a custom-built axial twist jig, which isolated motion to the lumbar spine. Participants were moved from neutral to 75% of maximum axial twist range of motion in an upright kneeling posture. Thoracopelvic motion was recorded with a motion capture system and L1 to S1 vertebral axial twist was recorded using ultrasound. From motion capture, maximum thoracopelvic axial twist motion was 41.1 degrees. From ultrasound, the majority of axial twist motion occurred at the L2-L3 (46.8% of lumbar axial twist motion) and L5-S1 (33.5%) intervertebral joints. Linear regression linking axial twist at each vertebral level to thoracopelvic axial twist ranged from 0.43 to 0.79. These findings demonstrate a mathematical relationship between internal and external axial twist motion and the distribution of motion across the lumbar spine suggests that classic use of L4-L5 to represent lumbar spine motion may not be appropriate for axial twist modelling approaches.     

Induced rotational motion with nonabutting inducing and induced stimuli: implications regarding two forms of induced motion

Induced motion is the illusory motion of a static stimulus in the opposite direction to a moving stimulus. Two types of induced motion have been distinguished: (a) when the moving stimulus is distant from the static stimulus and undergoes overall displacement, and (b) when the moving stimulus is pattern viewed within fixed boundaries that abut the static stimulus. Explanations of the 1st type of induced motion refer to mediating phenomena, such as vection, whereas the 2nd type is attributed to local processing by motion-sensitive neurons. The present research was directed to a display that elicited induced rotational motion with the characteristics of both types of induced motion: the moving stimulus lay within fixed boundaries, but the inducing and induced stimuli were distant from each other. The author investigated the properties that distinguished the two types of induced motion. In 3 experiments, induced motion persisted indefinitely, interocular transfer of the aftereffect of induced motion was limited to about 20%, and the time-course of the aftereffect of induced motion could not be attributed to vection. Those results were consistent with fixed-boundary induced motion. However, they could not be explained by local processing. Instead, the results might reflect the detection of object motion within a complex flow-field that resulted from the observer's motion.     

Induced Rotational Motion With Nonabutting Inducing and Induced Stimuli: Implications Regarding Two Forms of Induced Motion

Induced motion is the illusory motion of a static stimulus in the opposite direction to a moving stimulus. Two types of induced motion have been distinguished: (a) when the moving stimulus is distant from the static stimulus and undergoes overall displacement, and (b) when the moving stimulus is pattern viewed within fixed boundaries that abut the static stimulus. Explanations of the 1st type of induced motion refer to mediating phenomena, such as vection, whereas the 2nd type is attributed to local processing by motion-sensitive neurons. The present research was directed to a display that elicited induced rotational motion with the characteristics of both types of induced motion: the moving stimulus lay within fixed boundaries, but the inducing and induced stimuli were distant from each other. The author investigated the properties that distinguished the two types of induced motion. In 3 experiments, induced motion persisted indefinitely, inter-ocular transfer of the aftereffect of induced motion was limited to about 20%, and the time-course of the aftereffect of induced motion could not be attributed to vection. Those results were consistent with fixed-boundary induced motion. However, they could not be explained by local processing. Instead, the results might reflect the detection of object motion within a complex flow-field that resulted from the observer's motion.     

Visuotactile apparent motion

This article compares the properties of apparent motion between a light and a touch with apparent motion between either two lights or two touches. Visual and tactile stimulators were attached to the tips of the two index fingers that were held apart at different distances. Subjects rated the quality of apparent motion between each stimulus combination for a range of stimulus onset asynchronies (SOAs). Subjects reported perceiving apparent motion between all three stimulus combinations. For light-light visual apparent motion, the preferred SOA and the direction threshold SOAs increased as the distance between the stimuli increased (consistent with Korte's third law of apparent motion). Touch-touch apparent motion also obeyed Korte's third law, but over a smaller range of distances, showing that proprioceptive information concerning the position of the fingers is integrated into the tactile motion system. The threshold and preferred SOAs for visuotactile apparent motion did not vary with distance, suggesting a different mechanism for multimodal apparent motion.     

Motion adaptation shifts apparent position without the motion aftereffect

Adaptation to motion can produce effects on both the perceived motion (the motion aftereffect) and the position (McGraw, Whitaker, Skillen, & Chung, 2002; Nishida & Johnston, 1999; Snowden, 1998; Whitaker, McGraw, & Pearson, 1999) of a subsequently viewed test stimulus. The position shift can be interpreted as a consequence of the motion aftereffect. For example, as the motion within a stationary aperture creates the impression that the aperture is shifted in position (De Valois & De Valois, 1991; Hayes, 2000; Ramachandran & Anstis, 1990), the motion aftereffect may generate a shift in perceived position of the test pattern simply because of the illusory motion it generates on the pattern. However, here we show a different aftereffect of motion adaptation that causes a shift in the apparent position of an object even when the object appears stationary and is located several degrees from the adapted region. This position aftereffect of motion reveals a new form of motion adaptation--one that does not result in a motion aftereffect--and suggests that motion and position signals are processed independently but then interact at a higher stage of processing.     

Correspondence matching in long-range apparent motion precedes featural analysis

It has been suggested that correspondence matching in long-range motion is mediated by a perceptually high-level, 'intelligent' system. This suggestion is based on findings that long-range motion can be perceived between stimuli that could not be detected by lower-level motion mechanisms acting on Fourier motion energy, and that correspondence matching is affected by featural similarities between motion tokens that would be invisible to low-level (Fourier) motion detectors. Here, the effects of spatial-frequency content, color, and binocular disparity on correspondence matching are investigated. It is shown that the effects of featural matches between motion tokens develop only over time and lag behind the effects of the relative proximity between motion tokens in the retinal projection. This suggests that correspondence matching in long-range apparent motion is mediated by a mechanism which acts initially on the retinal coordinates of the motion tokens only, but may be biased to favor matching tokens that are featurally similar through a slower top-down influence by higher-level processes.     

Stance Width Influences Postural Stability and Motion Sickness

We examined the influence of stance width (the distance between the feet) on postural sway and visually induced motion sickness. Stance width influences the magnitude of body sway, and changes in sway precede the subjective symptoms of motion sickness. Thus, manipulation of stance width may influence motion sickness incidence. Participants (healthy young adults) were exposed to complex, low-frequency oscillation of a moving room. Participants stood with their feet 5 cm, 17 cm, or 30 cm apart. During exposure to visual motion, the widest stance (30 cm) was associated with reduced incidence of motion sickness. For all stance widths, motion sickness was preceded by significant changes in motion of the head and torso. The results support the postural instability theory of motion sickness and suggest practical implications for the prevention of motion sickness. Adoption of wider stance may decrease the risk of motion sickness in operational situations.     

The cognitive representation of an event involving human motion

Human motion is analyzed as a function of the temporal pattern of relative stability and instability of the body in relation to its supporting ground. The cognitive representation of an event unit involving human motion is described as some small number of relatively stable, preparatory motions, followed by an unstable, completing motion. Two experiments tested the coherence of the preparatory motion (s)-completing motion structure, and the visual conditions under which an unstable motion is encoded as the completing motion of an event unit. Preparatory-completing structures were recognized more easily than completing-preparatory structures. The offset of contour motion at the center of an unstable motion was found to be an important variable in the encoding of a completing motion.     

Neural dynamics of motion perception: Direction fields,apertures, and resonant grouping

A neural network model of global motion segmentation by visual cortex is described. Called the motion boundary contour system (BCS), the model clarifies how ambiguous local movements on a complex moving shape are actively reorganized into a coherent global motion signal, Unlike many previous researchers, we analyze how a coherent motion signal is imparted to all regions of a moving figure, not only to regions at which unambiguous motion signals exist. The model hereby suggests a solution to the global aperture problem. The motion BCS describes how preprocessing of motion signals by a motion oriented contrast (MOC) filter is joined to long-range cooperative grouping mechanisms in a motion cooperative-competitive (MOCC) loop to control phenomena such as motion capture. The motion BCS is computed in parallel with the static BCS of Grossberg and Mingolla (1985a, 1985b, 1987). Homologous properties of the motion BCS and the static BCS, specialized to process motion directions and static orientations, respectively, support a unified explanation of many data about static form perception and motion form perception that have heretofore been unexplained or treated separately. Predictions about microscopic computational differences of the parallel cortical streams V1 → MT and V1 → V2 → MT are made— notably, the magnocellular thick stripe and parvocellular interstripe streams. It is shown how the motion BCS can compute motion directions that may be synthesized from multiple orientations with opposite directions of contrast. Interactions of model simple cells, complex cells, hyper-complex cells, and bipole cells are described, with special emphasis given to new functional roles in direction disambiguation for endstopping at multiple processing stages and to the dynamic interplay of spatially short-range and long-range interactions.     

Visuotactile apparent motion

This article compares the properties of apparent motion between a light and a touch with apparent motion between either two lights or two touches. Visual and tactile stimulators were attached to the tips of the two index fingers that were held apart at different distances. Subjects rated the quality of apparent motion between each stimulus combination for a range of stimulus onset asynchronies (SOAs). Subjects reported perceiving apparent motion between all three stimulus combinations. For light—light visual apparent motion, the preferred SOA and the direction threshold SOAs increased as the distance between the stimuli increased (consistent with Korte’s third law of apparent motion). Touch—touch apparent motion also obeyed Korte’s third law, but over a smaller range of distances, showing that proprioceptive information concerning the position of the fingers is integrated into the tactile motion system. The threshold and preferred SOAs for visuotactile apparent motion did not vary with distance, suggesting a different mechanism for multimodal apparent motion.