Perceptual organization of apparent motion in the Ternus display

A typical Ternus display has three sequentially presented frames, in which frame 1 consists of three motion tokens, frame 2 (blank) defines the interstimulus interval, and frame 3 has similar motion tokens with their relative positions shifted to the right. Interestingly, what appears to be a seemingly simple arrangement of stimuli can induce one of two distinct apparent-motion percepts in the observer. The first is an element-motion perception where the left-end token is seen to jump over its two neighboring tokens (inner tokens) to the right end of the display. The second is a group-motion perception where the entire display of the three tokens is seen to move to the right. How does the visual system choose between these two apparent-motion perceptions? It is hypothesized that the choice of motion perception is determined in part by the perceptual organization of the motion tokens. Specifically, a group-motion perception is experienced when a strong grouping tendency exists among the motion tokens belonging to the same frame. Conversely, an element-motion perception is experienced when a strong grouping tendency exists between the inner motion tokens in frames 1 and 3 (i.e. the two tokens that overlap in space between frames). We tested this hypothesis by varying the perceptual organization of the motion tokens. Both spatial (form similarity, 3-D proximity, common surface/common region, and occlusion) and temporal (motion priming) factors of perceptual organization were tested. We found that the apparent-motion perception of the Ternus display can be predictably affected, in a manner consistent with the perceptual organization hypothesis.     

The relationship between visual persistence and event perception in bistable motion display

Observers viewed two alternating frames, each consisting of three rectangular bars displaced laterally by one cycle in one frame with respect to the other. At long interframe intervals (IFIs) observers perceived a group of three bars moving as a whole (group motion), and at short IFIs the overlapping elements in the two frames appeared stationary, while the third element appeared to move from one end of the display to the other (element motion). The upper temporal limit for perceiving element motion was reduced when bars with blurred edges were used and when either frame duration or bar size was increased. However, when inner and outer elements had different sizes, the element motion percept was dominant up to 230 ms IFI. These findings may be interpreted in terms of spatial tuning of motion mechanisms involved in the perception of bistable 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.     

Motion capture by a frame: global or local processing?

The possibility that frames serve to capture lines within them so that they appear on a coplanar surface was investigated, using coherence in direction of rotary motion (Gillam, 1972) as a quantitative measure of the coplanarity of frame and internal lines. It was found that perceptual coherence between a pair of lines was greatly increased by surrounding them with a frame, if the frame was perspectivally consistent with the lines. A second experiment showed that this grouping can be attributed to a global effect of the frame and cannot be accounted for by local grouping of the internal lines with components of the frame.     

Spatio-temporal priority revisited: the role of feature identity and similarity for object correspondence in apparent motion

We live in a dynamic environment in which objects change location over time. To maintain stable object representations the visual system must determine how newly sampled information relates to existing object representations, the correspondence problem. Spatiotemporal information is clearly an important factor that the visual system takes into account when solving the correspondence problem, but is feature information irrelevant as some theories suggest? The Ternus display provides a context in which to investigate solutions to the correspondence problem. Two sets of three horizontally aligned disks, shifted by one position, were presented in alternation. Depending on how correspondence is resolved, these displays are perceived either as one disk "jumping" from one end of the row to the other (element motion) or as a set of three disks shifting back and forth together (group motion). We manipulated a feature (e.g., color) of the disks such that, if features were taken into account by the correspondence process, it would bias the resolution of correspondence toward one version or the other. Features determined correspondence, whether they were luminance-defined or not. Moreover, correspondence could be established on the basis of similarity, when features were not identical between alternations. Finally, the stronger the feature information supported a certain correspondence solution the more it dominated spatiotemporal information.     

A comparison of the effects of spatial separation on apparent motion in the auditory and visual modalities

In the present investigation, the effects of spatial separation on the interstimulus onset intervals (ISOIs) that produce auditory and visual apparent motion were compared. In Experiment 1, subjects were tested on auditory apparent motion. They listened to 50-msec broadband noise pulses that were presented through two speakers separated by one of six different values between 0 degrees and 160 degrees. On each trial, the sounds were temporally separated by 1 of 12 ISOIs from 0 to 500 msec. The subjects were instructed to categorize their perception of the sounds as "single," "simultaneous," "continuous motion," "broken motion," or "succession." They also indicated the proper temporal sequence of each sound pair. In Experiments 2 and 3, subjects were tested on visual apparent motion. Experiment 2 included a range of spatial separations from 6 degrees to 80 degrees; Experiment 3 included separations from .5 degrees to 10 degrees. The same ISOIs were used as in Experiment 1. When the separations were equal, the ISOIs at which auditory apparent motion was perceived were smaller than the values that produced the same experience in vision. Spatial separation affected only visual apparent motion. For separations less than 2 degrees, the ISOIs that produced visual continuous motion were nearly equal to those which produced auditory continuous motion. For larger separations, the ISOIs that produced visual apparent motion increased.     

Parallel search for conjunctions with stimuli in apparent motion

A series of experiments was conducted to determine whether apparent motion tends to follow the similarity rule (i.e. is attribute-specific) and to investigate the underlying mechanism. Stimulus duration thresholds were measured during a two-alternative forced-choice task in which observers detected either the location or the motion direction of target groups defined by the conjunction of size and orientation. Target element positions were randomly chosen within a nominally defined rectangular subregion of the display (target region). The target region was presented either statically (followed by a 250 ms duration mask) or dynamically, displaced by a small distance (18 min of arc) from frame to frame. In the motion display, the position of both target and background elements was changed randomly from frame to frame within the respective areas to abolish spatial correspondence over time. Stimulus duration thresholds were lower in the motion than in the static task, indicating that target detection in the dynamic condition does not rely on the explicit identification of target elements in each static frame. Increasing the distractor-to-target ratio was found to reduce detectability in the static, but not in the motion task. This indicates that the perceptual segregation of the target is effortless and parallel with motion but not with static displays. The pattern of results holds regardless of the task or search paradigm employed. The detectability in the motion condition can be improved by increasing the number of frames and/or by reducing the width of the target area. Furthermore, parallel search in the dynamic condition can be conducted with both short-range and long-range motion stimuli. Finally, apparent motion of conjunctions is insufficient on its own to support location decision and is disrupted by random visual noise. Overall, these findings show that (i) the mechanism underlying apparent motion is attribute-specific; (ii) the motion system mediates temporal integration of feature conjunctions before they are identified by the static system; and (iii) target detectability in these stimuli relies upon a nonattentive, cooperative, directionally selective motion mechanism that responds to high-level attributes (conjunction of size and orientation).     

The reference frame for encoding and retention of motion depends on stimulus set size

The goal of this study was to investigate the reference frames used in perceptual encoding and storage of visual motion information. In our experiments, observers viewed multiple moving objects and reported the direction of motion of a randomly selected item. Using a vector-decomposition technique, we computed performance during smooth pursuit with respect to a spatiotopic (nonretinotopic) and to a retinotopic component and compared them with performance during fixation, which served as the baseline. For the stimulus encoding stage, which precedes memory, we found that the reference frame depends on the stimulus set size. For a single moving target, the spatiotopic reference frame had the most significant contribution with some additional contribution from the retinotopic reference frame. When the number of items increased (Set Sizes 3 to 7), the spatiotopic reference frame was able to account for the performance. Finally, when the number of items became larger than 7, the distinction between reference frames vanished. We interpret this finding as a switch to a more abstract nonmetric encoding of motion direction. We found that the retinotopic reference frame was not used in memory. Taken together with other studies, our results suggest that, whereas a retinotopic reference frame may be employed for controlling eye movements, perception and memory use primarily nonretinotopic reference frames. Furthermore, the use of nonretinotopic reference frames appears to be capacity limited. In the case of complex stimuli, the visual system may use perceptual grouping in order to simplify the complexity of stimuli or resort to a nonmetric abstract coding of motion information.     

When does visual perceptual grouping affect multisensory integration?

Several studies have shown that the direction in which a visual apparent motion stream moves can influence the perceived direction of an auditory apparent motion stream (an effect known as crossmodal dynamic capture). However, little is known about the role that intramodal perceptual grouping processes play in the multisensory integration of motion information. The present study was designed to investigate the time course of any modulation of the cross-modal dynamic capture effect by the nature of the perceptual grouping taking place within vision. Participants were required to judge the direction of an auditory apparent motion stream while trying to ignore visual apparent motion streams presented in a variety of different configurations. Our results demonstrate that the cross-modal dynamic capture effect was influenced more by visual perceptual grouping when the conditions for intramodal perceptual grouping were set up prior to the presentation of the audiovisual apparent motion stimuli. However, no such modulation occurred when the visual perceptual grouping manipulation was established at the same time as or after the presentation of the audiovisual stimuli. These results highlight the importance of the unimodal perceptual organization of sensory information to the manifestation of multisensory integration.     

Fast Responses of the Human Hand to Changes in Target Position

If a target toward which an individual moves his hand suddenly moves, he adjusts the movement of his hand accordingly. Does he use visual information on the target's velocity to anticipate where he will reach the target? These questions were addressed in the present study. Subjects (N = 6 in each of 4 experiments) were instructed to hit a disk with a rod as soon as it appeared on a screen. Trajectories of the hand toward stationary disks were compared with those toward disks that jumped leftward or rightward as soon as the subject's hand started moving toward the screen, and with those in which either the disk or the background started moving leftward or rightward. About 110 ms after the disk was suddenly displaced, the moving hand was diverted in the direction of the perturbation. When the background moved, the disk's perceived position shifted in the direction in which the background was moving, but the disk appeared to be moving in the opposite direction. When hitting such disks, subjects adjusted their movement in accordance with the perceived position, rather than moving their hand in the direction of the perceived motion in anticipation of the disk's future displacement. Thus, subjects did not use the perceived velocity to anticipate where they would reach the target but responded only to the change in position     

Chinese writing system and learning to read

One of the obvious characteristics of the Chinese writing system is its visual complexity. How do children develop their reading and writing ability in such a system? The areas we address in the present study include: (1) The basic unit in character recognition and writing of Chinese children. (2) The role of familiarity of components and the position frequency of components in character recognition and writing. In the first experiment, the subjects were first‐, second‐, fourth‐, and sixth‐graders. Children were asked to delay copy five types of characters: familiar single characters, familiar compound characters, unfamiliar compounds with familiar components, unfamiliar compounds with unfamiliar components, and noncharacters, with the components in impossible positions. The results show that older children were affected more by the familiarity and the position frequency of components in the delayed copy task. In the second experiment, the subjects were from the same grades. Children were asked to carry out lexical decision for five types of characters: real compound characters, pseudocharacters with well‐formed structure and real components, noncharacters with ill‐formed structure but real components, and noncharacters with well‐formed structure but nonreal components. The results show that children can be aware of the ill‐formed structure early, and become aware of well‐formed structure but nonreal components as they grow older. The results suggest that the component of character is the basic unit in children's lexical representation. Familiarity of components and the position frequency of components in characters affect children's character recognition and writing.     

Position uncertainty and the perception of apparent movement

Two experiments compared the perception of apparent movement when the second of two successive stimuli always appeared in the same position and when it varied randomly between two spatial positions. The results of both experiments showed that foreknowledge of the position of the second stimulus does not facilitate the perception of apparent movement. Experiment 2 also clearly showed that the space-time relationships of Korte’s third law of apparent movement does not depend on foreknowledge of the position of the second stimulus. These findings imply that apparent movement in real time occurs after the second stimulus has been registered by the visual system. It suggests that apparent movement involves a delayed decision mechanism that stores the first stimulus, the interstimulus temporal interval, and the second stimulus, and then impletes a motion compatible with the stimulus information.     

The relationship between space and time in the perception of stimuli moving behind a slit

When a shape defined by a set of dots plotted along its contour is presented in a sequence of frames within the boundaries of a slit, and in each frame only one dot (featureless frame) or two dots (feature frame) are displayed, a whole moving dotted shape is perceived. Masking techniques and psychophysical measures have been used to show that a dynamic random-dot mask interferes with shape identification, provided the interframe interval is greater than about 15 ms, and there are no stimulus features for recognition in individual frames. A similar pattern of results was obtained when the observer had only to detect the movement of a single dot or a pair of dots against a dynamic-noise background. It is concluded that the visual system can resolve the correspondence problem in both apparent movement (one moving dot) and aperture viewing (featureless-frame condition) by extracting motion before the extraction of features in each frame. However, the results also show that where feature identification in each frame is possible, it can also be used to identify the moving targets.     

Dynamics of perceptual grouping: Similarities in the organization of visual and auditory groups

In vision, the Gestalt principles of perceptual organization are generally well understood and remain a subject of detailed analysis. However, the possibility for a unified theory of grouping across visual and auditory modalities remains largely unexplored. Here we present examples of auditory and visual Gestalt grouping, which share important organizational properties. In particular, similarities are revealed between grouping processes in apparent motion, auditory streaming, and static 2-D displays. Given the substantial difference in the context, within which the phenomena in question occur (auditory vs. visual, static vs. dynamic), these similarities suggest that the dynamics of perceptual organization could be associated with a common (possibly central) mechanism. If the relevance of supramodal invariants of grouping is granted, the question arises as to whether they can be studied empirically. We propose that a “force-field” theory, based on a differential-geometric interpretation of perceptual space, could provide a suitable starting point for a systematic exploration of the subjective properties of certain classes of auditory and visual grouping phenomena.     

Visual search in divided areas: Dividers initially interfere with and later facilitate visual search

A common search paradigm requires observers to search for a target among undivided spatial arrays of many items. Yet our visual environment is populated with items that are typically arranged within smaller (subdivided) spatial areas outlined by dividers (e.g., frames). It remains unclear how dividers impact visual search performance. In this study, we manipulated the presence and absence of frames and the number of frames subdividing search displays. Observers searched for a target O among Cs, a typically inefficient search task, and for a target C among Os, a typically efficient search. The results indicated that the presence of divider frames in a search display initially interferes with visual search tasks when targets are quickly detected (i.e., efficient search), leading to early interference; conversely, frames later facilitate visual search in tasks in which targets take longer to detect (i.e., inefficient search), leading to late facilitation. Such interference and facilitation appear only for conditions with a specific number of frames. Relative to previous studies of grouping (due to item proximity or similarity), these findings suggest that frame enclosures of multiple items may induce a grouping effect that influences search performance.     

Object-centered representations support flexible exogenous visual attention across translation and reflection

Visual attention can be deployed to stimuli based on our willful, top-down goal (endogenous attention) or on their intrinsic saliency against the background (exogenous attention). Flexibility is thought to be a hallmark of endogenous attention, whereas decades of research show that exogenous attention is attracted to the retinotopic locations of the salient stimuli. However, to the extent that salient stimuli in the natural environment usually form specific spatial relations with the surrounding context and are dynamic, exogenous attention, to be adaptive, should embrace these structural regularities. Here we test a non-retinotopic, object-centered mechanism in exogenous attention, in which exogenous attention is dynamically attracted to a relative, object-centered location. Using a moving frame configuration, we presented two frames in succession, forming either apparent translational motion or in mirror reflection, with a completely uninformative, transient cue presented at one of the item locations in the first frame. Despite that the cue is presented in a spatially separate frame, in both translation and mirror reflection, behavioralperformance in visual search is enhanced when the target in the second frame appears at the same relative location as the cue location than at other locations. These results provide unambiguous evidence for non-retinotopic exogenous attention and further reveal an object-centered mechanism supporting flexible exogenous attention. Moreover, attentional generalization across mirror reflection may constitute an attentional correlate of perceptual generalization across lateral mirror images, supporting an adaptive, functional account of mirror images confusion.     

Fixation and the stereokinetic phenomenon

One of two circles on a rotating disk appears to execute a planetary motion about the other circle. It is shown that the fixated circle serves as the center of rotation for the nonfixated circle. The effect of fixation is absent when polygons replace the circles. However, when one corner of an isolated square is fixated, the remaining corners rotated about the fixated corner. These planetary effects are consistent with the retinal paths followed by the elements of a display during fixation. This is not unlike the failure of position constancy associated with smooth pursuit of linearly moving targets in environments lacking a stationary visual frame of reference. In the present instance, however, the “retinal” responses occur during tracking of circularly moving targets, even in the presence of a visual frame of reference. These results are discussed in relation to the stereokinetic phenomenon. It is also shown that there is a strong interaction between the effects of fixation and the configurational features of the display. When a circle and a square are overlapping on a rotating disk, fixation of the square does not produce the perception of planetary motion. However, when the circle is fixated, the square is readily perceived as executing a planetary path about the circle. The possibility that position constancy in general is attributable to the geometry of the scene rather than to a “discounting” of information about eye movements is mentioned.     

The adjacency principle and induced movement

The apparent movement of a stationary point of light was investigated as a function of the apparent distance of the point of light with respect to the inducing frame of frames. When two frames were presented simultaneously, they were at different distances and physically moved at opposite phase in frontoparallel planes. When one frame was presented alone, it was positioned at different times at each of the two distances. The point of light was presented stereoscopically at the distance of either the near or far frame or midway in depth between these distances. With the single frame, it was found that the magnitude of the induced movement decreassed as the point of light was increasingly far in front of a frame but decreased less or remained approximately constant for distances be hind a frame. With the two frames presented simultaneously, it was found that as the depth between a particular frame and the point of light decreased, the contribution of that frame to the induced movement increased. The results illustrate the interaction of perceptions, in this case perceived depth and perceived motion, and are consistent with the adjacency principle.     

Visual texture as a factor in the apparent velocity of objective motion and motion aftereffects

The apparent velocity of an objectively rotating visually textured disk is an increasing monotonic function of the coarseness (size) of visual texture. The apparent velocity of a negative motion aftereffect increases with coarseness of moving induction texture but decreases with coarseness of stationary test texture, and there is an interaction between induction and test textures. An explanation of these effects is based principally on the assumption of greater lateral inhibition between neighboring elements in finer textures.