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

The currency of our visual experience consists not only of visual features such as color and motion, but also seemingly higher-level features such as causality--as when we see two billiard balls collide, with one causing the other to move. One of the most important and controversial questions about causal perception involves its origin: do we learn to see causality, or does this ability derive in part from innately specified aspects of our cognitive architecture? Such questions are difficult to answer, but can be indirectly addressed via experiments with infants. Here we explore causal perception in 7-month-old infants, using a different approach from previous work. Recent work in adult visual cognition has demonstrated a postdictive aspect to causal perception: in certain situations, we can perceive a collision between two objects in an ambiguous display even after the moment of potential 'impact' has already passed. This illustrates one way in which our conscious perception of the world is not an instantaneous moment-by-moment construction, but rather is formed by integrating information over short temporal windows. Here we demonstrate analogous postdictive processing in infants' causal perception. This result demonstrates that even infants' visual systems process information in temporally extended chunks. Moreover, this work provides a new way of demonstrating causal perception in infants that differs from previous strategies, and is immune to some previous types of critiques.     

Illusory causal crescents: misperceived spatial relations due to perceived causality

When an object A moves toward an object B until they are adjacent, at which point A stops and B starts moving, we often see a collision--ie we see A as the cause of B's motion. The spatiotemporal parameters which mediate the perception of causality have been explored in many studies, but this work is seldom related to other aspects of perception. Here we report a novel illusion, wherein the perception of causality affects the perceived spatial relations among two objects involved in a collision event: observers systematically underestimate the amount of overlap between two items in an event which is seen as a causal collision. This occurs even when the causal nature of the event is induced by a surrounding context, such that estimates of the amount of overlap in the very same event are much improved when the event is displayed in isolation, without a 'causal' interpretation. This illusion implies that the perception of causality does not proceed completely independently of other visual processes, but can affect the perception of other spatial properties.     

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.     

MORAL PERCEPTION AND THE CAUSAL OBJECTION

One of the primary motivations behind moral anti‐realism is a deep‐rooted scepticism about moral knowledge. Moral realists attempt counter this worry by sketching a plausible moral epistemology. One of the most radical proposals in the recent literature is that we know moral facts by perception – we can literally see that an action is wrong, etc. A serious objection to moral perception is the causal objection. It is widely conceded that perception requires a causal connection between the perceived and the perceiver. But, the objection continues, we are not in appropriate causal contact with moral properties. Therefore, we cannot perceive moral properties. This papers demonstrates that the causal objection is unsound whether moral properties turn out to be secondary, natural properties; non‐secondary, natural properties; or non‐natural properties. 1     

Can you McGurk yourself? Self-face and self-voice in audiovisual speech

We are constantly exposed to our own face and voice, and we identify our own faces and voices as familiar. However, the influence of self-identity upon self-speech perception is still uncertain. Speech perception is a synthesis of both auditory and visual inputs; although we hear our own voice when we speak, we rarely see the dynamic movements of our own face. If visual speech and identity are processed independently, no processing advantage would obtain in viewing one’s own highly familiar face. In the present experiment, the relative contributions of facial and vocal inputs to speech perception were evaluated with an audiovisual illusion. Our results indicate that auditory self-speech conveys a processing advantage, whereas visual self-speech does not. The data thereby support a model of visual speech as dynamic movement processed separately from speaker recognition.     

Audiovisual sentence recognition not predicted by susceptibility to the McGurk effect

In noisy situations, visual information plays a critical role in the success of speech communication: listeners are better able to understand speech when they can see the speaker. Visual influence on auditory speech perception is also observed in the McGurk effect, in which discrepant visual information alters listeners’ auditory perception of a spoken syllable. When hearing /ba/ while seeing a person saying /ga/, for example, listeners may report hearing /da/. Because these two phenomena have been assumed to arise from a common integration mechanism, the McGurk effect has often been used as a measure of audiovisual integration in speech perception. In this study, we test whether this assumed relationship exists within individual listeners. We measured participants’ susceptibility to the McGurk illusion as well as their ability to identify sentences in noise across a range of signal-to-noise ratios in audio-only and audiovisual modalities. Our results do not show a relationship between listeners’ McGurk susceptibility and their ability to use visual cues to understand spoken sentences in noise, suggesting that McGurk susceptibility may not be a valid measure of audiovisual integration in everyday speech processing.     

Effects of grouping and attention on the perception of causality

Beyond perceiving patterns of motion in simple dynamic displays, we can also perceive higher level properties, such as causality, as when we see one object collide with another object. Although causality is a seemingly high-level property, its perception--like the perception of faces or speech--often appears to be automatic, irresistible, and driven by highly constrained and stimulus-driven rules. Here, in an exploration of such rules, we demonstrate that perceptual grouping and attention can influence the both perception of causality in ambiguous displays. We first report several types of grouping effects, based on connectedness, proximity, and common motion. We further suggest that such grouping effects are mediated by the allocation of attention, and we directly demonstrate that causal perception can be strengthened or attenuated on the basis of where observers are attending, independent of fixation. Like Michotte, we find that the perception of causality is mediated by strict visual rules. Beyond Michotte, we find that these rules operate not only over discrete objects, but also over perceptual groups, constrained by the allocation of attention.     

The development of voicing categories: A quantitative review of over 40 years of infant speech perception research

Most research on infant speech categories has relied on measures of discrimination. Such work often employs categorical perception as a linking hypothesis to enable inferences about categorization on the basis of discrimination measures. However, a large number of studies with adults challenge the utility of categorical perception in describing adult speech perception, and this in turn calls into question how to interpret measures of infant speech discrimination. We propose here a parallel channels model of discrimination (built on Pisoni and Tash Perception & Psychophysics, 15(2), 285–290, 1974), which posits that both a noncategorical or veridical encoding of speech cues and category representations can simultaneously contribute to discrimination. This can thus produce categorical perception effects without positing any warping of the acoustic signal, but it also reframes how we think about infant discrimination and development. We test this model by conducting a quantitative review of 20 studies examining infants’ discrimination of voice onset time contrasts. This review suggests that within-category discrimination is surprisingly prevalent even in classic studies and that, averaging across studies, discrimination is related to continuous acoustic distance. It also identifies several methodological factors that may mask our ability to see this. Finally, it suggests that infant discrimination may improve over development, contrary to commonly held notion of perceptual narrowing. These results are discussed in terms of theories of speech development that may require such continuous sensitivity.     

Sounds exaggerate visual shape

While perceiving speech, people see mouth shapes that are systematically associated with sounds. In particular, a vertically stretched mouth produces a /woo/ sound, whereas a horizontally stretched mouth produces a /wee/ sound. We demonstrate that hearing these speech sounds alters how we see aspect ratio, a basic visual feature that contributes to perception of 3D space, objects and faces. Hearing a /woo/ sound increases the apparent vertical elongation of a shape, whereas hearing a /wee/ sound increases the apparent horizontal elongation. We further demonstrate that these sounds influence aspect ratio coding. Viewing and adapting to a tall (or flat) shape makes a subsequently presented symmetric shape appear flat (or tall). These aspect ratio aftereffects are enhanced when associated speech sounds are presented during the adaptation period, suggesting that the sounds influence visual population coding of aspect ratio. Taken together, these results extend previous demonstrations that visual information constrains auditory perception by showing the converse - speech sounds influence visual perception of a basic geometric feature.     

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.     

Toward a causal realist account of causal understanding

Within a limited domain, humans can perceive causal relations directly. The term causal realism is used to denote this psychological hypothesis. The domain of causal realism is in actions upon objects and haptic perception of the effects of those actions: When we act upon an object we cannot be mistaken about the fact that we are acting upon it and perceive the causal relation directly through mechanoreceptors. Experiences of actions upon objects give rise to causal knowledge that can be used in the interpretation of perceptual input. Phenomenal causality, the occurrence of causal impressions in visual perception, is a product of the application of acquired causal knowledge in the automatic perceptual interpretation of appropriate stimuli. Causal realism could constitute the foundation on which all causal perception, judgment, inference, attribution, and knowledge develop.     

Modelling relations between sensory processing, speech perception, orthographic and phonological ability, and literacy achievement

The general magnocellular theory postulates that dyslexia is the consequence of a multimodal deficit in the processing of transient and dynamic stimuli. In the auditory modality, this deficit has been hypothesized to interfere with accurate speech perception, and subsequently disrupt the development of phonological and later reading and spelling skills. In the visual modality, an analogous problem might interfere with literacy development by affecting orthographic skills. In this prospective longitudinal study, we tested dynamic auditory and visual processing, speech-in-noise perception, phonological ability and orthographic ability in 62 five-year-old preschool children. Predictive relations towards first grade reading and spelling measures were explored and the validity of the global magnocellular model was evaluated using causal path analysis. In particular, we demonstrated that dynamic auditory processing was related to speech perception, which itself was related to phonological awareness. Similarly, dynamic visual processing was related to orthographic ability. Subsequently, phonological awareness, orthographic ability and verbal short-term memory were unique predictors of reading and spelling development.     

A Puzzle Concerning Time Perception

According to a plausible and influential account of perceptual knowledge, the truth-makers of beliefs that constitute perceptual knowledge must feature in the causal explanation of how we acquire those beliefs. However, this account runs into difficulties when it tries to accommodate time perception – specifically perception of order and duration – since the features we are apparently tracking in such perception are (it is argued) not causal. The central aim of the paper is to solve this epistemological puzzle. Two strategies are examined. The first strategy locates the causal truth-makers within the psychological mechanism underlying time perception, thus treating facts about time order and duration as mind-dependent. This strategy, however, is problematic. The second strategy modifies the causal account of perceptual knowledge to include a non-causal component in the explanation of belief-acquisition, namely chronometric explanation. Applying this much more satisfactory approach to perceptual knowledge of time, we can preserve the mind-independence of order and duration, but not that of time's flow.     

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.     

I—Moral Perception and Moral Knowledge

This paper presents a theory of how perception provides a basis for moral knowledge. To do this, the paper sketches a theory of perception, explores the sense in which moral perception may deserve that name, and explains how certain moral properties may be perceptible. It does not presuppose a causal account of moral properties. If, however, they are not causal, how can we perceive, say, injustice? Can it be observable even if injustice is not a causal property? The paper answers these and other questions by developing an account of how moral properties, even if not causal, can figure in perception in a way that grounds moral knowledge.     

Characterizing the influence of native language experience on adult speech perception.

Previous cross-language research has indicated that some speech contrasts present greater perceptual difficulty for adult non-native listeners than others do. It has been hypothesized that phonemic, phonetic, and acoustic factors contribute to this variability. Two experiments were conducted to evaluate systematically the role of phonemic status and phonetic familiarity in the perception of non-native speech contrasts and to test predictions derived from a model proposed by Best, McRoberts, and Sithole (1988). Experiment 1 showed that perception of an unfamiliar phonetic contrast was not less difficult for subjects who had experience with an analogous phonemic distinction in their native language than for subjects without such analogous experience. These results suggest that substantive phonetic experience influences the perception of non-native contrasts, and thus should contribute to a conceptualization of native language-processing skills. In Experiment 2, English listeners' perception of two related nonphonemic place contrasts was not consistently different as had been expected on the basis of phonetic familiarity. A clear order effect in the perceptual data suggests that interactions between different perceptual assimilation patterns or acoustic properties of the two contrasts, or interactions involving both of these factors, underlie the perception of the two contrasts in this experiment. It was concluded that both phonetic familiarity and acoustic factors are potentially important to the explanation of variability in perception of nonphonemic contrasts. The explanation of how linguistic experience shapes speech perception will require characterizing the relative contribution of these factors, as well as other factors, including individual differences and variables that influence a listener's orientation to speech stimuli.     

Duplex perception: a comparison of monosyllables and slamming doors

Duplex perception has been interpreted as revealing distinct systems for general auditory perception and speech perception. The systems yield distinct experiences of the same acoustic signal, the one conforming to the acoustic structure itself and the other to its source in vocal-tract activity. However, this interpretation has not been tested by examining whether duplex perception can be obtained for nonspeech sounds that are not plausibly perceived by a specialized system. In five experiments, we replicate some of the phenomena associated with duplex perception of speech using the sound of a slamming door. Similarities between subjects' responses to syllables and door sounds are striking enough to suggest that some conclusions in the speech literature should be tempered that (a) duplex perception is special to sounds for which there are perceptual modules and (b) duplex perception occurs because distinct systems have rendered different percepts of the same acoustic signal.     

Perceptuomotor compatibility effects in speech

Kerzel and Bekkering (2000) found perceptuomotor compatibility effects between spoken syllables and visible speech gestures and interpreted them as evidence in favor of the distinctive claim of the motor theory of speech perception that the motor system is recruited for perceiving speech. We present three experiments aimed at testing this interpretation. In Experiment 1, we replicated the original findings by Kerzel and Bekkering but with audible syllables. In Experiments 2 and 3, we tested the results of Experiment 1 under more stringent conditions, with different materials and different experimental designs. In all of our experiments, we found the same result: Perceiving syllables affects uttering syllables. The result is consistent both with the results of a number of other behavioral and neural studies related to speech and with more general findings of perceptuomotor interactions. Taken together, these studies provide evidence in support of the motor theory claim that the motor system is recruited for perceiving speech.     

Characterizing the influence of native language experience on adult speech perception

Previous cross-language research has indicated that some speech contrasts present greater perceptual difficulty for adult non-native listeners than others do. It has been hypothesized that phonemic, phonetic, and acoustic factors contribute to this variability. Two experiments were conducted to evaluate systematically the role of phonemic status and phonetic familiarity in the perception of non-native speech contrasts and to test predictions derived from a model proposed by Best, McRoberts, and Sithole (1988). Experiment 1 showed that perception of an unfamiliar phonetic contrast was not less difficult for subjects who had experience with an analogous phonemic distinction in their native language than for subjects without such analogous experience. These results suggest that substantive phonetic experience influences the perception of non-native contrasts, and thus should contribute to a conceptualization of native language-processing skills. In Experiment 2, English listeners’ perception of two related nonphonemic place contrasts was not consistently different as had been expected on the basis of phonetic familiarity. A clear order effect in the perceptual data suggests that interactions between different perceptual assimilation patterns or acoustic properties of the two contrasts, or interactions involving both of these factors, underlie the perception of the two contrasts in this experiment. It was concluded that both phonetic familiarity and acoustic factors are potentially important to the explanation of variability in perception of nonphonemic contrasts. The explanation of how linguistic experience shapes speech perception will require characterizing the relative contribution of these factors, as well as other factors, including individual differences and variables that influence a listener’s orientation to speech stimuli.