Relativistic effects in visual perception of real and apparent motion

Timing in the visual field is regarded as an additive conjoint measurement structure, psychophysical extension of stimulus path as an extensive measurement structure. These two sets of postulates lead to the derivation of an essential maximum for velocity perception. Apparent phi motion perception under strictly stationary stimulus conditions is described as relative motion of the first stimulus' psychophysical mapping with respect to a moving perceptual subsystem. The essential maximum of velocity modifies the relative motion postulate: relativistic dilatation of seen length of path is predicted. Testable properties of the model, comparison with experimental data from "real" motion and apparent phi motion perception are discussed.     

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.     

Object-based apparent motion

The interpretation of a dynamic visual scene requires integrating information within frames (grouping and completion) and across frames (correspondence matching). Fragmentary views of objects were used in five experiments. These views could not be matched with each other by any similarity transformation on the basis of their explicit visual features, but their completed versions were related by a rotational transformation. When the fragmentary images were successively presented to observers, it was found that they produced apparent motion in the picture plane and in depth. Thus, apparent motion is capable of establishing correspondence at the level of perceptually recovered objects in three-dimensional space.     

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.     

The perception of shrinking in apparent motion

Apparent motion was produced using two triangular patterns of different sizes, each exposed for 100 msec, with a 50-msec interstimulus interval and 200-msec recycle interval. The triangles were aligned either on center or on the midpoints of the bases. Experiment 1, filled, outline, and three-dot triangles were viewed over four backgrounds: a blank illuminated field, and texture gradients constructed from horizontal lines, perspective lines, or a combination of these (full texture). In Experiment 2, outline and dot triangles were presented in one of three orientations: base down, base right, and base up over a blank background. Subjects made two forced-choice responses: apparent size was categorized as shrinking or not shrinking, and apparent motion was categorized as motion in depth or motion in a fixed frontal plane. The type of alignment was the major determiner of responses. When the midpoints of the base were aligned, the predominant response described a shrinking object in a fixed-position in depth. When the centers were aligned, the predominant response described an object of constant size moving in depth.     

Theories of apparent motion

Apparent motion is an illusion in which two sequentially presented and spatially separated stimuli give rise to the experience of one moving stimulus. This phenomenon has been deployed in various philosophical arguments for and against various theories of consciousness, time consciousness and the ontology of time. Nevertheless, philosophers have continued working within a framework that does not reflect the current understanding of apparent motion. The main objectives of this paper are to expose the shortcomings of the explanations provided for apparent motion and to offer an alternative explanation for the phenomenon.     

The relationship between apparent motion and object files

Object files (OFs) play an important role in theories of mid-level vision. On some influential views, OFs operate and persist only via spatiotemporal continuity. One open question concerns what occurs when direct spatiotemporal continuity is absent: Do OFs move in accordance with any motion correspondence ultimately resolved? Specifically, do OFs accord with apparent motion (AM) correspondences, which arise despite a lack of continuous spatiotemporal stimulation? In Experiment 1, subjects were presented with an AM display consisting of two circles that, across two frames, were seen as moving between two noncontiguous locations. The two objects were primed with two symbols and were then moved in a single step; a third symbol appeared, and could either match the symbol from the closer or the further object. We found a robust object specific preview benefit (OSPB) for the shorter path, in other words, the path along which AM was perceived. In order to control for the possibility that priming occurs at any nearby object, in Experiment 2, the original two objects never disappeared, but two new objects appeared in the would-be AM locations. No AM was perceived, and no OSPB obtained. In the third experiment the OSPB effect persisted even when motion along the shorter path included an unlikely featural transformation (circles turning into squares). In Experiment 4, which was nearly identical to Experiment 2, no OSPB obtained despite unique featural matches between the initial and new objects, seemingly because no AM was perceived. In Experiment 5, we failed to find an effect of featural priming, even when distance between the objects was equated. Finally, we extended the OSPB effect to two additional kinds of AM—line motion (Experiment 6) and phi motion (Experiment 7), supplying strong evidence that AM correspondences and OF correspondences are controlled by the same basic rules.     

The perception of shrinking in apparent motion.

Apparent motion was produced using two triangular patterns of different sizes, each exposed for 100 msec, with a 50-msec interstimulus interval and 200-msec recycle interval. The triangles were aligned either on center or on the midpoints of the bases. In Experiment 1, filled, outline, and three-dot triangles were viewed over four backgrounds: a blank illuminated field, and texture gradients constructed from horizontal lines, perspective lines, or a combination of these (full texture). In Experiment 2, outline and dot triangles were presented in one of three orientations: base down, base right, and base up over a blank background. Subjects made two forced-choice responses: apparent size was categorized as shrinking or not shrinking, and apparent motion was categorized as motion in depth or motion in a fixed frontal plane. The type of alignment was the major determiner of responses. When the midpoints of the base were aligned, the predominant response described a shrinking object in a fixed position in depth. When the centers were aligned, the predominant response described an object of constant size moving in depth.     

The role of occlusion cues in apparent motion

Classical apparent motion stimuli exhibit an inherent ambiguity with respect to the onsets and offsets of the stimulus elements. Sigman and Rock (1974, Perception 3 9-28) presented evidence suggesting that occlusion cues are used to resolve this ambiguity. We present results from experiments designed to further test predictions of this hypothesis. As expected, we found that the apparent motion of a target stimulus is suppressed when a 'moving' occluder is positioned such that it rationalises the onsets and offsets of the stimulus elements constituting the target. Somewhat unexpectedly, though, we also observed a slight tendency for motion suppression under conditions where the target was only partially occluded. The expected motion suppression occurred both with solid occluders and purely virtual Kanizsa-like occluders, although it was not always observed in the latter case. Motion suppression was found to occur over a wide range of stimulus onset asynchronies. Finally, we used binocular disparity cues to test the occlusion account of the motion suppression phenomenon against an alternative explanation in terms of attentional factors. The results are in clear favour of the occlusion account.     

Color logic of apparent motion

Two shapes of either the same or different color will seem to be in smooth apparent motion with like-colored mates, at proper conditions of flash timing and spacing. An experiment is reported in which the condition was tested for unlike-colored pairs, for example red-green alternated with green-red. The question of interest was how the visual system would resolve the disparity of color. An 'intelligent' solution would rotate the shapes in three dimensions. Like-colored and unlike-colored parts were found to move and transform similarly, however, the resolution being dependent more upon timing than upon color. The motion of intelligence as it might be applied to vision is discussed in light of these results.     

Fixation and attention in apparent motion

The likelihood of reporting a figure in motion was measured when the point of fixation was systematically separated from the point of attention. More reports of optimal motion were made when the two points were separated than when they were close together. Control tests showed that the reduction in the probability of seeing motion through the center of fixation was more likely due to the structure of the eye than to the conflict of fixation point and object in illusory motion. The notion of attention as a perceptual event contributes little to these results.     

The role of apparent motion cues in orientation masking

It has been reported that the tuning function relating masking of a vertical line to the orientation of a masking line differs in form depending upon whether the mask is presented with the target (simultaneous masking) or before it (forward masking). From such evidence, it might be concluded that different mechanisms are implicated. Lovegrove (1976) suggested that lateral inhibition mediates the simultaneous effect, whereas postexcitatory suppression (adaptation) mediates the successive effect. The six experiments reported here show that apparent motion cues reduce the effectiveness of successive masking when single-line stimuli are used, but that when such motion cues are eliminated, the two tuning functions are similar in form. It is, thus, unnecessary to invoke separate mechanisms in the two cases.     

A motion aftereffect for long-range troboscopic apparent motion

The existence of a directional motion aftereffect (MAE) for long-range (LR) stroboscopic apparent motion (SAM) was examined with the use of a directionally ambiguous test stimulus. The spatial and temporal parameters were such that the LR, rather than the short-range, mechanism was likely to be implicated. MAEs were found for SAM, which were in the same direction, but somewhat weaker than those for a comparable stimulus in real motion. The MAEs for SAM were present only when good apparent motion was perceived, and could be shown also when only the unstimulated area between the two stroboscopic flashes was tested. The LR mechanism was further implicated, since the MAEs were also obtained under dichoptic adaptation conditions. It is concluded that the LR-motion mechanism does show a usual MAE under proper testing conditions.     

Color correspondence in apparent motion

To maintain figural identity during motion perception, the visual system must match images over space and time. Correct matching requires a metric for identifying "corresponding" images, those representing the same physical object. To test whether matching is based on achromatic (black/white) polarity and chromatic (red/green) color, observers viewed an ambiguous motion display and judged the path of apparent motion. Matching preserved black/white identity regardless of whether frames were viewed binocularly or dichoptically. Red/green identity was also preserved, but coherence of motion depended in part on the number of frames in the motion sequence and on the background luminance. These results suggest that correspondence is computed by a weighted metric containing terms for image features coded early in visual processing.     

Topological aspects of apparent visual motion

Summary and Conclusions Linke's pioneer observations made just fifty years ago on apparent visual motion conditioned by pairs of stimulus objects which differ in form, has been here experimentally elaborated and brought into relation with topology. Both deformations and connectivities have been studied. Topological limits of t-motion have been encountered in this investigation. Linke's concept of identity, which he regarded as the psychological key to seen movement, should now be replaced by the modern, powerful concept of invariance. Topology, with its biunique point-order structure, is inevitably brought into relation with the phenomena of apparent movement. There appears to be a substantial isomorphic relation between topological deformation in the stimulus objects and seen movement, although there are some topological inhibitors of motion. The perceptual contents of apparent motion do not evidence positional and form properties as separated parts: The contents are funded as an integrated kinematic whole.     

Neural correlates of transformational apparent motion

Transformational apparent motion (TAM) arises when a shape that is abruptly flashed on and off next to a static shape of similar color or texture appears as a protrusion that extends and retracts smoothly from the static object. Here we report that the strength of the TAM percept can be predicted from the waveform of visual evoked potentials (VEPs) measured while observers rated their percepts. The VEPs at pattern onset and offset are maximally symmetric when the static inducer and the flashing patches of the display are of the same contrast. VEP symmetry is affected by how the two patches can be matched as a single surface and may reflect the relative contribution of different motion and object detection systems in visual cortex.     

Primed and unprimed rebounding illusory apparent motion

Although sequences of uncorrelated random dots can yield a wide range of illusorily coherent motion percepts (including translation, rotation, contraction, expansion, shear, and rebounding motion), past priming studies have relied on two-alternative forced choice tasks that only measure unidirectional (positive or negative) priming effects. In Experiment 1 we showed that when participants are primed with unidirectional motion and given an additional option to report bidirectional (rebounding) motion, they do so frequently, suggesting that unidirectional motion can “default” to a rebounding percept. Furthermore, rebounding percepts are more prevalent during trials with long frame durations, suggesting a role for attention in forming and maintaining these illusory percepts. In Experiment 2 we compared rebounding percepts that followed unidirectional, drifting primes with rebounding percepts that followed bidirectional, rebounding primes, and found that these two types of illusory rebounding motion percepts differ systematically in their temporal structures. We argue that rebounding percepts following drifting primes can be understood as a breakdown of positive priming into an underlying oscillatory state, whereas rebounding percepts following rebounding primes may be understood either as (1) the initialization of the same oscillatory process, or (2) the entrainment of a two-step motion pattern by a higher-order mechanism.