The origins of causal perception: Evidence from postdictive processing in infancy

Early-emerging combinatorial thought: Human infants flexibly combine kind and quantity concepts

Combinatorial thought, or the ability to combine a finite set of concepts into a myriad of complex ideas and knowledge structures, is the key to the productivity of the human mind and underlies communication, science, technology, and art. Despite the importance of combinatorial thought for human cognition and culture, its developmental origins remain unknown. To address this, we tested whether 12-mo-old infants (N = 60), who cannot yet speak and only understand a handful of words, can combine quantity and kind concepts activated by verbal input. We proceeded in two steps: first, we taught infants two novel labels denoting quantity (e.g., "mize" for 1 item; "padu" for 2 items, Experiment 1). Then, we assessed whether they could combine quantity and kind concepts upon hearing complex expressions comprising their labels (e.g., "padu duck", Experiments 2-3). At test, infants viewed four different sets of objects (e.g., 1 duck, 2 ducks, 1 ball, 2 balls) while being presented with the target phrase (e.g., "padu duck") naming one of them (e.g., 2 ducks). They successfully retrieved and combined on-line the labeled concepts, as evidenced by increased looking to the named sets but not to distractor sets. Our results suggest that combinatorial processes for building complex representations are available by the end of the first year of life. The infant mind seems geared to integrate concepts in novel productive ways. This ability may be a precondition for deciphering the ambient language(s) and building abstract models of experience that enable fast and flexible learning.

The effect of perceptual history on the interpretation of causality

The ability to interpret spatiotemporal contingencies in terms of causal relationships plays a key role in human understanding of the external world. Indeed, the detection of such simple properties enables us to attribute causal attributes to interactions between objects. Here, we investigated the degree to which this perception of causality depends on recent experience, as has been found for other low-level properties of visual stimuli. Participants were shown launching sequences of colliding circles with varying collision lags and were asked to report their impression of causality. We found short-term attractive and long-term repulsive and attractive effects of perceptual history on the interpretation of causality. Stimuli directly following a causal impression were more likely to be judged as causal and vice versa. However, prior judgments on less recent (>5) trials biased current perception with both positive/attractive and negative/repulsive influences. We interpret these results in terms of two potential mechanisms: adaptive temporal binding windows and updating of internal representations of causality. Overall, these results demonstrate the important role of prior experience even for causality, a fundamental building block of how we understand our world.

Contributions of causal reasoning to early scientific literacy

Although early causal reasoning has been studied extensively, inconsistency in the tasks used to assess it has clouded our understanding of its structure, development, and relevance to broader developmental outcomes. The current research attempted to bring clarity to these questions by exploring patterns of performance across several commonly used measures of causal reasoning, and their relation to scientific literacy, in a sample of 3- to 5-year-old children from diverse backgrounds (N = 153). A longitudinal confirmatory factor analysis revealed that some measures of causal reasoning (counterfactual reasoning, causal learning, and causal inference), but not all of them (tracking cause-effect associations and resolving confounded evidence), assess a unidimensional factor and that this resulting factor was relatively stable across time. A cross-lagged panel model analysis revealed associations between causal reasoning and scientific literacy across each age tested. Causal reasoning and scientific literacy related to each other concurrently, and each predicted the other in subsequent years. These relations could not be accounted for by children's broader cognitive skills. Implications for early STEM (science, technology, engineering, and math) engagement and success are discussed.

The possibility of an impetus heuristic

Evidence consistent with a belief in impetus is drawn from studies of naïve physics, perception of causality, perception of force, and representational momentum, and the possibility of an impetus heuristic is discussed. An impetus heuristic suggests the motion path of an object that was previously constrained or influenced by an external source (e.g., object, force) appears to exhibit the same constraint or influence even after that constraint or influence is removed. Impetus is not a valid physical principle, but use of an impetus heuristic can in some circumstances provide approximately correct predictions regarding future object motion, and such predictions require less cognitive effort and resources than would predictions based upon objective physical principles. The relationship of an impetus heuristic to naïve impetus theory and to objective physical principles is discussed, and use of an impetus heuristic significantly challenges claims that causality or force can be visually perceived. Alternatives to an impetus heuristic are considered, and potential boundary conditions and falsification of the impetus notion are discussed. Overall, use of an impetus heuristic offers a parsimonious explanation for findings across a wide range of perceptual domains and could potentially be extended to more metaphorical types of motion.

Causality and continuity close the gaps in event representations

Imagine you see a video of someone pulling back their leg to kick a soccer ball, and then a soccer ball soaring toward a goal. You would likely infer that these scenes are two parts of the same event, and this inference would likely cause you to remember having seen the moment the person kicked the soccer ball, even if that information was never actually presented (Strickland & Keil, 2011, Cognition, 121[3], 409-415). What cues trigger people to "fill in" causal events from incomplete information? Is it due to the experience they have had with soccer balls being kicked toward goals? Is it the visual similarity of the object in both halves of the video? Or is it the mere spatiotemporal continuity of the event? In three experiments, we tested these different potential mechanisms underlying the "filling-in" effect. Experiment 1 showed that filling in occurs equally in familiar and unfamiliar contexts, indicating that familiarity with specific event schemas is unnecessary to trigger false memory. Experiment 2 showed that the visible continuation of a launched object's trajectory is all that is required to trigger filling in, regardless of other occurrences in the second half of the scene. Finally, Experiment 3 found that, using naturalistic videos, this filling-in effect is more heavily affected if the object's trajectory is discontinuous in space/time compared with if the object undergoes a noticeable transformation. Together, these findings indicate that the spontaneous formation of causal event representations is driven by object representation systems that prioritize spatiotemporal information over other object features.

Retinotopic adaptation reveals distinct categories of causal perception

We can perceive not only low-level features of events such as color and motion, but also seemingly higher-level properties such as causality. A prototypical example of causal perception is the 'launching effect': one object (A) moves toward a stationary second object (B) until they are adjacent, at which point A stops and B starts moving in the same direction. Beyond these motions themselves - and regardless of any higher-level beliefs - this display induces a vivid visual impression of causality, wherein A is seen to cause B's motion. Do such percepts reflect a unitary category of visual processing, or might there be multiple distinct forms of causal perception? While launching is often simply equated with causal perception, researchers have sometimes described other phenomena such as 'triggering' (in which B moves faster than A) and 'entraining' (in which A continues to move alongside B). We used psychophysical methods to determine whether these labels really carve visual processing at its joints, and how putatively different forms of causal perception relate to each other. Previous research demonstrated retinotopically specific adaptation to causality: exposure to causal launching makes subsequent ambiguous events in that same location more likely to be seen as non-causal 'passing'. Here, after replicating this effect, we show that exposure to triggering also yields retinotopically specific adaptation for subsequent ambiguous launching displays, but that exposure to entraining does not. Collectively, these results reveal that visual processing distinguishes some (but not all) types of causal interactions.

Any way the wind blows: Children's inferences about force and motion events

Göksun, George, Hirsh-Pasek, and Golinkoff (2013) used force dynamics, or the semantic categories defined by spatial arrays of forces, to study the development of preschoolers' predictions about the outcomes of forces working in concert. The current study extends this approach to problems requiring inferences about causal factors. In total, 30 5- and 6-year-old children were asked to identify and coordinate forces to achieve a result. Problems varied in the number and orientation of forces, mirroring spatial arrays characteristic of categories like prevent (i.e., opposing forces). Children successfully inferred causes of single- and dual-force events, performing best when problems reflected the spatial arrays of forces described in language. Results support force dynamics as a valuable framework for the development of force and motion representations.

Causal reports: Context-dependent contributions of intuitive physics and visual impressions of launching

Everyday causal reports appear to be based on a blend of perceptual and cognitive processes. Causality can sometimes be perceived automatically through low-level visual processing of stimuli, but it can also be inferred on the basis of an intuitive understanding of the physical mechanism that underlies an observable event. We investigated how visual impressions of launching and the intuitive physics of collisions contribute to the formation of explicit causal responses. In Experiment 1, participants observed collisions between realistic objects differing in apparent material and hence implied mass, whereas in Experiment 2, participants observed collisions between abstract, non-material objects. The results of Experiment 1 showed that ratings of causality were mainly driven by the intuitive physics of collisions, whereas the results of Experiment 2 provide some support to the hypothesis that ratings of causality were mainly driven by visual impressions of launching. These results suggest that stimulus factors and experimental design factors - such as the realism of the stimuli and the variation in the implied mass of the colliding objects - may determine the relative contributions of perceptual and post-perceptual cognitive processes to explicit causal responses. A revised version of the impetus transmission heuristic provides a satisfactory explanation for these results, whereas the hypothesis that causal responses and intuitive physics are based on the internalization of physical laws does not.

Visual Neuroscience: Seeing Causality with the Motor System?

Understanding how humans perceive cause and effect in visual events has long intrigued philosophers and scientists. A new study in primates reveals the neural correlates of perceived causality at the single-cell level, but in an unexpected place - the motor system.

Toddlers infer unobserved causes for spontaneous events

Previous research suggests that children infer the presence of unobserved causes when objects appear to move spontaneously. Are such inferences limited to motion events or do children assume that unexplained physical events have causes more generally? Here we introduce an apparently spontaneous event and ask whether, even in the absence of spatiotemporal and co-variation cues linking the events, toddlers treat a plausible variable as a cause of the event. Toddlers (24 months) saw a toy that appeared to light up either spontaneously or after an experimenter’s action. Toddlers were also introduced to a button but were not shown any predictive relation between the button and the light. Across three different dependent measures of exploration, predictive looking (Study 1), prompted intervention (Study 2), and spontaneous exploration (Study 3), toddlers were more likely to represent the button as a cause of the light when the event appeared to occur spontaneously. In Study 4, we found that even in the absence of a plausible candidate cause, toddlers engaged in selective exploration when the light appeared to activate spontaneously. These results suggest that toddlers’ exploration is guided by the causal explanatory power of events.

Children use temporal cues to learn causal directionality

The ability to learn the direction of causal relations is critical for understanding and acting in the world. We investigated how children learn causal directionality in situations in which the states of variables are temporally dependent (i.e., autocorrelated). In Experiment 1, children learned about causal direction by comparing the states of one variable before versus after an intervention on another variable. In Experiment 2, children reliably inferred causal directionality merely from observing how two variables change over time; they interpreted Y changing without a change in X as evidence that Y does not influence X. Both of these strategies make sense if one believes the variables to be temporally dependent. We discuss the implications of these results for interpreting previous findings. More broadly, given that many real-world environments are characterized by temporal dependency, these results suggest strategies that children may use to learn the causal structure of their environments.

Visual perception of the physical stability of asymmetric three-dimensional objects

Visual estimation of object stability is an ecologically important judgment that allows observers to predict the physical behavior of objects. A natural method that has been used in previous work to measure perceived object stability is the estimation of perceived "critical angle"--the angle at which an object appears equally likely to fall over versus return to its upright stable position. For an asymmetric object, however, the critical angle is not a single value, but varies with the direction in which the object is tilted. The current study addressed two questions: (a) Can observers reliably track the change in critical angle as a function of tilt direction? (b) How do they visually estimate the overall stability of an object, given the different critical angles in various directions? To address these questions, we employed two experimental tasks using simple asymmetric 3D objects (skewed conical frustums): settings of critical angle in different directions relative to the intrinsic skew of the 3D object (Experiment 1), and stability matching across 3D objects with different shapes (Experiments 2 and 3). Our results showed that (a) observers can perceptually track the varying critical angle in different directions quite well; and (b) their estimates of overall object stability are strongly biased toward the minimum critical angle (i.e., the critical angle in the least stable direction). Moreover, the fact that observers can reliably match perceived object stability across 3D objects with different shapes suggests that perceived stability is likely to be represented along a single dimension.

Forces and motion: how young children understand causal events

How do children evaluate complex causal events? This study investigates preschoolers' representation of force dynamics in causal scenes, asking whether (a) children understand how single and dual forces impact an object's movement and (b) this understanding varies across cause types (Cause, Enable, Prevent). Three-and-a half- to 5.5-year-olds (n = 60) played a board game in which they were asked to predict the endpoint of a ball being acted upon by one or two forces. Children mostly understood the interactions of forces underlying each type of cause; only 5.5-year-olds could integrate two contradictory forces. Children perceive force interactions underlying causal events, but some concepts might not be fully understood until later in childhood. This study provides a new way of thinking about causal relations.

Emerging perception of causality in action-and-reaction sequences from 4 to 6 months of age: is it domain-specific?

Two experiments (N=136) studied how 4- to 6-month-olds perceive a simple schematic event, seen as goal-directed action and reaction from 3 years of age. In our causal reaction event, a red square moved toward a blue square, stopping prior to contact. Blue began to move away before red stopped, so that both briefly moved simultaneously at a distance. Primarily, our study sought to determine from what age infants see the causal structure of this reaction event. In addition, we looked at whether this causal percept depends on an animate style of motion and whether it correlates with tasks assessing goal perception and goal-directed action. Infants saw either causal reactions or noncausal delayed control events in which blue started some time after red stopped. These events involved squares that moved either rigidly or nonrigidly in an apparently animate manner. After habituation to one of the four events, infants were tested on reversal of the habituation event. Spatiotemporal features reversed for all events, but causal roles changed only in reversed reactions. The 6-month-olds dishabituated significantly more to reversal of causal reaction events than to noncausal delay events, whereas younger infants reacted similarly to reversal of both. Thus, perceptual causality for reaction events emerges by 6 months of age, a younger age than previously reported but, crucially, the same age at which perceptual causality for launch events has emerged in prior research. On our second question, animate/inanimate motion had no effect at any age, nor did significant correlations emerge with our additional tasks assessing goal perception or goal-directed object retrieval. Available evidence, here and elsewhere, is as compatible with a view that infants initially see A affecting B, without differentiation into physical or psychological causality, as with the standard assumption of distinct physical/psychological causal perception.

Visual impressions of pushing and pulling: the object perceived as causal is not always the one that moves first

Stimuli were presented in which a moving object (A) contacted a stationary object (B), whereupon both objects moved back in the direction from which object A had come. When object B rapidly decelerated to a standstill, so that the two objects did not remain in contact, object B was perceived as pushing object A. Thus, even though object B only moved when contacted by object A, it was perceived as the causal object, as making something happen to object A. This is contrary to the hypothesis that the object perceived as causal is always the object that moves first. It is, however, consistent with a theoretical account, in which visual causal impressions occur through a process in which visually picked-up kinematic information is matched to stored representations, based on experiences of actions on objects, which specify forces and causality as part of the perceptual interpretation of the event.

Causation From Perception

Beginning with the research of Albert Michotte, investigators have identified simple perceptual events that observers report as causal. For example, suppose a square moves across a screen and comes to a halt when it makes contact with a second square. If the second square then begins moving in the same direction, observers sometimes report that the first square “pushed” the second or “caused it to move.” Based on such reports, Michotte claimed that people perceive causality, and a number of psychologists and philosophers have followed his lead. This article examines Michotte’s hypothesis by comparing it with its chief rival: Observers possess representations of pushings, pullings, and other events in long-term memory. A Michottean display triggers one of these representations, and the representation classifies the display as an instance of pushing (or pulling, etc.). According to this second explanation, recognizing an event as a pushing is similar to classifying an object as a cup or a dog. Data relevant to this debate come from infant and animal studies, cognitive and neuropsychological dissociation experiments, and studies of context effects and individual differences. However, a review of research in these paradigms finds no reason to prefer Michotte’s theory over its competitor.

The property transmission hypothesis: a possible explanation for visual impressions of pulling and other kinds of phenomenal causality

Under certain circumstances, stimuli involving two moving objects that do not come into contact reliably give rise to the illusory perceptual impression that one of the objects is pulling the other, as if there is an unseen connection between them. It is proposed that the conditions determining the occurrence of this impression can be explained as cases of application of the property-transmission hypothesis. This is a general hypothesis that causal objects operate in part by transmitting some of their own properties to effect objects under conditions where the causal object is active, where there are cues to the occurrence of generative transmission between the causal object and an effect object, and where there is a time-ordered relation of resemblance between properties of the causal object and those of the effect object. This hypothesis predicts that the pulling impression should occur only when the effect object adopts kinematic properties (speed and direction) that resemble those of the causal object. An experiment is reported that supports this prediction.

Amodal Causal Capture in the Tunnel Effect

In addition to identifying individual objects in the world, the visual system must also characterize the relationships between objects, for instance when objects occlude one another or cause one another to move. Here we explored the relationship between perceived causality and occlusion. Can one perceive causality in an occluded location? In several experiments, observers judged whether a centrally presented event involved a single object passing behind an occluder, or one object causally launching another (out of view and behind the occluder). With no additional context, the centrally presented event was typically judged as a non-causal pass, even when the occluding and disoccluding objects were different colors—an illusion known as the ‘tunnel effect’ that results from spatiotemporal continuity. However, when a synchronized context event involved an unambiguous causal launch, participants perceived a causal launch behind the occluder. This percept of an occluded causal interaction could also be driven by grouping and synchrony cues in the absence of any explicitly causal interaction. These results reinforce the hypothesis that causality is an aspect of perception. It is among the interpretations of the world that are independently available to vision when resolving ambiguity, and that the visual system can ‘fill in’ amodally.

Infants' causal representations of state change events

Five experiments extended studies of infants' causal representations of Michottian launching events to 8-month-olds' causal representations of physical state changes. Infants were habituated to events in which a potential causal agent moved behind a screen, after which a box partially visible on the other side of the screen underwent some change (motion or state change). After habituation the screen was removed, and infants observed full events in which the potential agent either did or did not contact the box (contact vs. gap events). Infants were credited with causal representations of the events if their attention was drawn both to gap events in which the effect nonetheless occurred and to events with contact in which the effect did not happen. The experiments varied the nature of the effect (motion vs. state change) and the nature of the possible causal agent (train, hand, novel intentional agent). Both the nature of the effect and the nature of the possible agent influenced the likelihood of causal attribution. The events involving motion of the patient replicated previous studies of infants' representations of Michottian launching events: the toy train was taken as the source of the boxes motion. In contrast, infants attributed the cause of the box's physical state change to a hand and novel self-moving entity with eyes, but not to a toy train. These data address early developing causal schemata, and bring new information to bear on theories of the origin of human causal cognition.