Measuring causal perception: connections to representational momentum?

In a collision between two objects, we can perceive not only low-level properties, such as color and motion, but also the seemingly high-level property of causality. It has proven difficult, however, to measure causal perception in a quantitatively rigorous way which goes beyond perceptual reports. Here we focus on the possibility of measuring perceived causality using the phenomenon of representational momentum (RM). Recent studies suggest a relationship between causal perception and RM, based on the fact that RM appears to be attenuated for causally 'launched' objects. This is explained by appeal to the visual expectation that a 'launched' object is inert and thus should eventually cease its movement after a collision, without a source of self-propulsion. We first replicated these demonstrations, and then evaluated this alleged connection by exploring RM for different types of displays, including the contrast between causal launching and non-causal 'passing'. These experiments suggest that the RM-attenuation effect is not a pure measure of causal perception, but rather may reflect lower-level spatiotemporal correlates of only some causal displays. We conclude by discussing the strengths and pitfalls of various methods of measuring causal perception.     

Perceived physical and social causality in animated motions: spontaneous reports and ratings

Michotte argued that we perceive cause-and-effect, without contributions from reasoning or learning, even in displays of two-dimensional moving shapes. Two studies extend this line of work from perception of mechanical to social causality. We compared verbal reports with structured ratings of causality to gain a better understanding of the extent to which perceptual causality occurs spontaneously or depends on instruction or context. A total of 120 adult observers (72 in the main experiment, 48 in an initial experiment) saw 12 (or 8) different computer animations of shape A moving up to B, which in turn moved away. Animations factorially varied the temporal and spatial relations of the shapes, and whether they moved rigidly or in a non-rigid, animal-like manner. Impressions of social as well as physical causality appeared in both free reports and ratings. Perception of physical causality was stronger than perception of social causality, particularly in free reports. No differences of this nature appear in infants and children, so the asymmetry may reflect learnt knowledge. Physical causality was relatively unspecific initially, but discrimination of causal and delayed control events improved with exposure to multiple events. Experience seems to affect the causal illusion even over a short timeframe; the idea of 'one-trial causality' may be somewhat misleading. Regardless of such effects on the absolute level of responses, the different measures showed similar patterns of variation with the spatio-temporal configuration and type of motion. The good fit of ratings and reports validates much recent work in this area.     

Perceiving causality after the fact: postdiction in the temporal dynamics of causal perception

In simple dynamic events we can easily perceive not only motion, but also higher-level properties such as causality, as when we see one object collide with another. Several researchers have suggested that such causal perception is an automatic and stimulus-driven process, sensitive only to particular sorts of visual information, and a major research project has been to uncover the nature of these visual cues. Here, rather than investigating what information affects causal perception, we instead explore the temporal dynamics of when certain types of information are used. Surprisingly, we find that certain visual events can determine whether we perceive a collision in an ambiguous situation even when those events occur after the moment of potential 'impact' in the putative collision has already passed. This illustrates a type of postdictive perception: our conscious perception of the world is not an instantaneous moment-by-moment construction, but rather is formed by integrating information presented within short temporal windows, so that new information which is obtained can influence the immediate past in our conscious awareness. Such effects have been previously demonstrated for low-level motion phenomena, but the present results demonstrate that postdictive processes can influence higher-level event perception. These findings help to characterize not only the 'rules' of causal perception, but also the temporal dynamics of how and when those rules operate.     

Perceptual causality and animacy

Certain simple visual displays consisting of moving 2-D geometric shapes can give rise to percepts with high-level properties such as causality and animacy. This article reviews recent research on such phenomena, which began with the classic work of Michotte and of Heider and Simmel. The importance of such phenomena stems in part from the fact that these interpretations seem to be largely perceptual in nature - to be fairly fast, automatic, irresistible and highly stimulus driven - despite the fact that they involve impressions typically associated with higher-level cognitive processing. This research suggests that just as the visual system works to recover the physical structure of the world by inferring properties such as 3-D shape, so too does it work to recover the causal and social structure of the world by inferring properties such as causality and animacy.     

Object-based warping: an illusory distortion of space within objects

Visual objects are high-level primitives that are fundamental to numerous perceptual functions, such as guidance of attention. We report that objects warp visual perception of space in such a way that spatial distances within objects appear to be larger than spatial distances in ground regions. When two dots were placed inside a rectangular object, they appeared farther apart from one another than two dots with identical spacing outside of the object. To investigate whether this effect was object based, we measured the distortion while manipulating the structure surrounding the dots. Object displays were constructed with a single object, multiple objects, a partially occluded object, and an illusory object. Nonobject displays were constructed to be comparable to object displays in low-level visual attributes. In all cases, the object displays resulted in a more powerful distortion of spatial perception than comparable non-object-based displays. These results suggest that perception of space within objects is warped.     

Perceptual grouping in space and time: Evidence from the Ternus display

We report three experiments investigating the effect of perceptual grouping on the appearance of a bistable apparent-motion (Ternus) display. Subjects viewed a Ternus display embedded in an array of context elements that could potentially group with the Ternus elements. In contrast to several previous findings, we found that grouping influenced apparent motion perception. In Experiment 1, apparent motion perception was significantly affected via grouping by shape similarity, even when the visible persistence of the elements was controlled. In Experiment 2, elements perceived as moving without context were perceived as stationary when grouped with stationary context elements. In Experiment 3, elements perceived as stationary without context were perceived as moving when grouped with moving context elements. We argue that grouping in the spatial and temporal domains interact to yield perceptual experience of apparent-motion displays.     

Load theory of selective attention and the role of perceptual load: Is it time for revision?

Perceptual load hypothesis is proposed as a compromise between early and late theory of selective attention which states that the selection will operate early when the load on perception is high and it will operate late when the load on perception is low. Experimental findings have shown that the perceptual load hypothesis is too simplistic in nature as perceptual load is not the only determinant of selection processes. It is difficult to apply the load hypothesis to explain the occurrence of early selection in low load displays as well as the selection processes that operate on distractor and target stimuli that are a part of the same object. Factors like spatial proximity, cues that manipulate the spatial extent of attentional focus, salience of targets as well as the distractors, and perceptual grouping between the target and the distractors should be taken into account while explaining the selective control of attention. Thus, the perceptual load of the display is one such factor that affects selective attention and goal-directed behaviour, but it is not the only factor to affect the selective control of attention.     

An information integration approach to phenomenal causality

Phenomenal causality was studied by using Michotte's launch event, in which successive motion of two objects evokes an immediate perception that the first motion causes the second. Information integration theory was used to address the complementary issues of invariant perceptual structure and individual differences in phenomenal causality. Three informational cues were varied conjointly: temporal and spatial contiguity of the two motions, and the ratio of their speeds. The dependent measure was a judgment of degree of causality or naturalness. The results showed that individual differences were related to these instruction conditions; the subjects showed five distinctive response patterns. Two were the modal patterns elicited by the instructions, and the others fell in between. The averaging model gave a good account of the data, with meaningful parameter estimates. Individual differences were localized in cueevaluation, whereas theirintegration into a unified judgment followed an invariant averaging rule. The results allow some reconciliation between Michotte and his critics.     

Perceived causality occurs with stroboscopic movement of one or both stimulus elements

It was shown by magnitude estimation that the perception of causality first described by Michotte (1946/1963) also occurs consistently and strongly with stroboscopic, ie apparent or phi, movement. This is so when the 'causal' movement is stroboscopic and the 'caused' movement real, when these movements are reversed, and when both movements are stroboscopic. The effect is not due to prior experience with Michotte-type displays.     

Role of perceptual organization while attending in depth

Seven experiments were conducted in order to explore the conditions under which visual attention can be allocated in depth. In each experiment, observers were cued to the most likely target location in stereoscopic depth displays, and targets could appear in either the cued location or in another location. In Experiments 1 and 2, we show that previous failures to observe effects of cuing in depth may have depended on the specific timing characteristics of the displays. In Experiments 3, 4, and 5, we eliminated the hypothesis, suggested by Experiments 1 and 2, that in order to allocate attention in depth, attention must be allocated to a specific object token. Experiment 6 provides evidence that, in the absence of other organizing information (e.g., color), attention can be allocated in depth on the basis of the surface information available in the display. Finally, in Experiment 7, we demonstrate that, although sufficient, surface information is not necessary for the allocation of attention; color supported the allocation of attention across multiple items that failed to fall on a single coherent surface in depth. Together, these findings suggest that attention in depth, like attention in two-dimensional displays, is determined by the perceptual organization of the display.     

Separating processes in object perception

In this article, I consider research by Needham and colleagues examining the role of object knowledge on infant's segregation of scenes into objects. I suggest that research in this area would benefit from closer connections to computational, psychophysical, and neurophysiological research on adult perceptual segmentation and grouping. I sketch a framework for understanding the components of object perception and apply it to the paradigm and displays used by Needham. This analysis suggests two ideas. First, it would be valuable to demonstrate the role of object knowledge in cases that are less impoverished in terms of perceptual information for segregation and more typical of object arrangements in ordinary scenes. Second, some method is needed to distinguish whether infants' object knowledge affects perceptual organization of new scenes or produces specific beliefs, inferences, or expectations about particular objects and scenes. As a specific example of the benefits of connecting developmental and adult research, some recent research in adult perception is described. The research indicates that in adult object segregation, two types of processes may be distinguished: basic perceptual processes of object segregation and more cognitive processes involving recognition. I suggest that Needham's research may be revealing the developmental origins of the latter processes.     

Launching, Entraining, and Representational Momentum: Evidence Consistent with an Impetus Heuristic in Perception of Causality

Displacements in the remembered location of stimuli in displays based on Michotte’s (1946/1963) launching effect and entraining effect were examined. A moving object contacted an initially stationary target, and the target began moving. After contacting the target, the mover became stationary (launching trials) or continued moving in the same direction and remained adjacent to the target (entraining trials). In launching trials, forward displacement was smaller for targets than for movers; in entraining trials, forward displacement was smaller for movers than for targets. Also, forward displacement was smaller for targets in launching trials than for targets in entraining trials. Data are consistent with a hypothesis that the launching effect involves an attribution that the mover imparted to the target a dissipating impetus that was responsible for target motion. Introspective experience of a perception of physical causality in the launching effect might result because behavior of movers and targets is consistent with that predicted by an impetus heuristic.     

How do humans group non-rigid objects in multiple object tracking?: Evidence from grouping by self-rotation

Previous studies on perceptual grouping found that people can use spatiotemporal and featural information to group spatially separated rigid objects into a unit while tracking moving objects. However, few studies have tested the role of objects’ self-motion information in perceptual grouping, although it is of great significance to the motion perception in the three-dimensional space. In natural environments, objects always move in translation and rotation at the same time. The self-rotation of the objects seriously destroys objects’ rigidity and topology, creates conflicting movement signals and results in crowding effects. Thus, this study sought to examine the specific role played by self-rotation information on grouping spatially separated non-rigid objects through a modified multiple object tracking (MOT) paradigm with self-rotating objects. Experiment 1 found that people could use self-rotation information to group spatially separated non-rigid objects, even though this information was deleterious for attentive tracking and irrelevant to the task requirements, and people seemed to use it strategically rather than automatically. Experiment 2 provided stronger evidence that this grouping advantage did come from the self-rotation per se rather than surface-level cues arising from self-rotation (e.g. similar 2D motion signals and common shapes). Experiment 3 changed the stimuli to more natural 3D cubes to strengthen the impression of self-rotation and again found that self-rotation improved grouping. Finally, Experiment 4 demonstrated that grouping by self-rotation and grouping by changing shape were statistically comparable but additive, suggesting that they were two different sources of the object information. Thus, grouping by self-rotation mainly benefited from the perceptual differences in motion flow fields rather than in deformation. Overall, this study is the first attempt to identify self-motion as a new feature that people can use to group objects in dynamic scenes and shed light on debates about what entities/units we group and what kinds of information about a target we process while tracking objects.     

Multiplicative effects of intention on the perception of bistable apparent motion

When viewing ambiguous displays, observers can, via intentional efforts, affect which perceptual interpretation they perceive. Specifically, observers can increase the probability of seeing the desired percept. Little is known, however, about how intentional efforts interact with sensory inputs in exerting their effects on perception. In two experiments, the current study explored the possibility that intentional efforts might operate by multiplicatively enhancing the stimulus-based activation of the desired perceptual representation. Such a possibility is suggested by recent neurophysiological research on attention. In support of this idea, when we presented bistable apparent motion displays under stimulus conditions differentially favoring one motion percept over the other, observers' intentional efforts to see a particular motion were generally more effective under conditions in which stimulus factors favored the intended motion percept.     

See an object,hear an object file: Object correspondence transcends sensory modality

An important task of perceptual processing is to parse incoming information into distinct units and to keep track of those units over time as the same, persisting representations. Within the study of visual perception, maintaining such persisting object representations is helped by “object files”—episodic representations that store (and update) information about objects' properties and track objects over time and motion via spatiotemporal information. Although object files are typically discussed as visual, here we demonstrate that object–file correspondence can be computed across sensory modalities. An object file can be initially formed with visual input and later accessed with corresponding auditory information, suggesting that object files may be able to operate at a multimodal level of perceptual processing.     

Active versus passive processing of biological motion

Johansson's point-light walker figures remain one of the most powerful and convincing examples of the role that motion can play in the perception of form (Johansson, 1973 Perception & Psychophysics 14 201 - 211; 1975 Scientific American 232(6) 76 - 88). In the current work, we use a dual-task paradigm to explore the role of attention in the processing of such stimuli. In two experiments we find striking differences in the degree to which direction-discrimination performance in point-light walker displays appears to rely on attention. Specifically, we find that performance in displays thought to involve top-down processing, either in time (experiment 1) or space (experiment 2) is adversely affected by dividing attention. In contrast, dividing attention has little effect on performance in displays that allow low-level, bottom-up computations to be carried out. We interpret these results using the active/passive motion distinction introduced by Cavanagh (1991 Spatial Vision 5 303-309).     

Perceptual Grouping and Motion Coherence in Visual Search

Search for a conjunction of form and motion is greatly affected by manipulations of phase in the target and nontarget motion sets. To test whether this finding can be best explained by perceptual grouping, we moved a random set of dots in phase or counterphase with target or nontarget motion. Perceptual grouping was found to have a dramatic effect on search performance. We propose that this interaction between perceptual grouping and visual search is governed by three general rules. Our data also provide convincing evidence of the preattentive organization of a visual display into surfaces defined by common motion.     

Perceiving Stability in a Changing World: Combining Shots and Intergrating Views in Motion Pictures and the Real World

One of the central debates in the study of media concerns the relationship between our perception of real-world events and mediated events such as motion pictures. A number of authors have argued convincingly that both rely on similar natural perceptual processes. Here we extend this argument by reviewing research on scene perception showing that the similarity between film and natural perception includes a common tendency to perceive events as continuous in the face of large view-to-view inconsistencies. This research shows that observers are frequently unable to detect large unexpected changes that occur between views, even in objects within their focus of attention. This is true both in mediated stimuli such as motion pictures and during staged real-world interactions. Thus, perception of continuity may be an inference that proceeds in spite of impossible between-view changes, both in motion pictures and real-world scenes.     

On the perception of shape from shading

The extraction of three-dimensional shape from shading is one of the most perceptually compelling, yet poorly understood, aspects of visual perception. In this paper, we report several new experiments on the manner in which the perception of shape from shading interacts with other visual processes such as perceptual grouping, preattentive search (“pop-out”), and motion perception. Our specific findings are as follows: (1) The extraction of shape from shading information incorporates at least two “assumptions” or constraints—first,that there is a single light source illuminating the whole scene, and second, that the light is shining from “above” in relation to retinal coordinates. (2) Tokens defined by shading can serve as a basis for perceptual grouping and segregation. (3) Reaction time for detecting a single convex shape does not increase with the number of items in the display. This “pop-out” effect must be based on shading rather than on differences in luminance polarity, since neither left-right differences nor step changes in luminance resulted in pop-out. (4) When the subjects were experienced, there were no search asymmetries for convex as opposed to concave tokens, but when the subjects were naive, cavities were much easier to detect than convex shapes. (5) The extraction of shape from shading can also provide an input to motion perception. And finally, (6) the assumption of “overhead illumination” that leads to perceptual grouping depends primarily on retinal rather than on “phenomenal” or gravitational coordinates. Taken collectively, these findings imply that the extraction of shape from shading is an “early” visual process that occurs prior to perceptual grouping, motion perception, and vestibular (as well as “cognitive”) correction for head tilt. Hence, there may be neural elements very early in visual processing that are specialized for the extraction of shape from shading.