Serial dependence promotes the stability of perceived emotional expression depending on face similarity

Visual continuum in non-human animals: serial dependence revealed in dogs

Serial dependence is a recently described phenomenon by which the perceptual evaluation of a stimulus is biased by a previously attended one. By integrating stimuli over time, serial dependence is believed to ensure a stable conscious experience. Despite increasing studies in humans, it is unknown if the process occurs also in other species. Here, we assessed whether serial dependence occurs in dogs. To this aim, dogs were trained on a quantity discrimination task before being presented with a discrimination where one of the discriminanda was preceded by a task-irrelevant stimulus. If dogs are susceptible to serial dependence, the task-irrelevant stimulus was hypothesized to influence the perception of the subsequently presented quantity. Our results revealed that dogs perceived the currently presented quantity to be closer to the one presented briefly before, in accordance with serial dependence. The direction and strength of the effect were comparable to those observed in humans. Data regarding dogs' attention during the task suggest that dogs used two different quantity estimation mechanisms, an indication of a higher cognitive mechanism involved in the process. The present results are the first empirical evidence that serial dependence extends beyond humans, suggesting that the mechanism is shared by phylogenetically distant mammals.

Intact Serial Dependence in Schizophrenia: Evidence from an Orientation Adjustment Task

BACKGROUND AND HYPOTHESIS

For a long time, it was proposed that schizophrenia (SCZ) patients rely more on sensory input and less on prior information, potentially leading to reduced serial dependence-ie, a reduced influence of prior stimuli in perceptual tasks. However, existing evidence is constrained to a few paradigms, and whether reduced serial dependence reflects a general characteristic of the disease remains unclear.

STUDY DESIGN

We investigated serial dependence in 26 SCZ patients and 27 healthy controls (CNT) to evaluate the influence of prior stimuli in a classic visual orientation adjustment task, a paradigm not previously tested in this context.

STUDY RESULTS

As expected, the CNT group exhibited clear serial dependence, with systematic biases toward the orientation of stimuli shown in the preceding trials. Serial dependence in SCZ patients was largely comparable to that in the CNT group.

CONCLUSIONS

These findings challenge the prevailing notion of reduced serial dependence in SCZ, suggesting that observed differences between healthy CNT and patients may depend on aspects of perceptual or cognitive processing that are currently not understood.

Opposing serial dependencies revealed for sequences of auditory emotional stimuli

Our percept of the world is not solely determined by what we perceive and process at a given moment in time, but also depends on what we processed recently. In the present study, we investigate whether the perceived emotion of a spoken sentence is contingent upon the emotion of an auditory stimulus on the preceding trial (i.e., serial dependence). Thereto, participants were exposed to spoken sentences that varied in emotional affect by changing the prosody that ranged from 'happy' to 'fearful'. Participants were instructed to rate the emotion. We found a positive serial dependence for emotion processing whereby the perceived emotion was biased towards the emotion on the preceding trial. When we introduced 'no-go' trials (i.e., no rating was required), we found a negative serial dependence when participants knew in advance to withhold their response on a given trial (Experiment 2) and a positive serial dependence when participants received the information to withhold their response after the stimulus presentation (Experiment 3). We therefore established a robust serial dependence for emotion processing in speech and introduce a methodology to disentangle perceptual from post-perceptual processes. This approach can be applied to the vast majority of studies investigating sequential dependencies to separate positive from negative serial dependence.

Interpersonal prior information informs ensemble coding through the co-representation process

Humans have the ability to rapidly extract summary statistics from object groupings through a specific capability known as ensemble coding. Previous literature has reported that this ability can become biased by prior perceptual experiences at the individual level. However, it remains unknown whether interpersonal prior information could also bias ensemble perception through a co-representation process. Experiment 1 found that participants' summary estimations were biased toward their co-actor's stimuli. Experiment 2 confirmed a causal relationship between the bias effect and the co-representation process by showing a reduction in biased estimation after pairing participants with an out-group partner. These findings extend the sources of prior information exploited by humans during perceptual average from individual-level information (i.e., self-tasks) to interpersonal-level information (i.e., co-actor's tasks). More specifically, interpersonal prior information is shown to act in a top-down and implicit manner, biasing ensemble perception.

Frequency-specific contributions to auditory perceptual priors: Testing the predictive-coding hypothesis

Perceptual priors formed by recent stimuli bias our immediate percept. These priors, expressing our implicit expectations, affect both high- and low-level processing stages. Yet, the nature of the inter-level interaction is unknown. Do priors operate top-down and bias low-level features toward recently experienced objects (predictive-coding hypothesis), or are low-level biases bottom-up driven and formed by local memory circuits? To decipher between these options in auditory perception, we used the "missing fundamental illusion", enabling the dissociation of low-level components from the high-level pitch. Surprisingly, in contrast to predictive coding, when the fundamental frequency was missing, pitch contraction across timbre categories was not found to the previously perceived high-level pitch, but to the physically present frequency. This bottom-up contribution of low-level memory components to perceptual priors, operating independently of recent high-level percepts, may stabilize the perceptual organization and underlie continuity between similar low-level features belonging to different object categories in the auditory modality.

Response boosts serial dependence in the numerosity estimation task

Perceptions of current stimuli are sometimes biased toward or away from past perceptions. This phenomenon is called serial dependence. However, the strength of the effect of past responses on serial dependence has not been fully elucidated. We conducted experiments with a task in which participants estimated the number of dot arrays (numerosity estimation task) and directly compared whether the strength of serial dependence changed in the numerosity estimation task when participants responded or did not respond in the immediately preceding trial. We also examined whether the strength of serial dependence affected the accuracy of the numerosity estimation. We found that attractive serial dependence was stronger when participants responded in the immediately preceding trial than when they only saw the stimulus. The results suggest that the information from the previous stimulus must reach the higher-level processes associated with perceptual decisions to influence the estimation of the current stimulus. However, it is possible that the results of this study are specific to tasks in which participants respond with numeric symbols. The magnitude of the serial dependence effect was not observed to affect numerosity estimation performance, and no evidence was found that serial dependence enhances accuracy in the numerosity estimation task.

Multisensory Calibration: A Variety of Slow and Fast Brain Processes Throughout the Lifespan

From before we are born, throughout development, adulthood, and aging, we are immersed in a multisensory world. At each of these stages, our sensory cues are constantly changing, due to body, brain, and environmental changes. While integration of information from our different sensory cues improves precision, this only improves accuracy if the underlying cues are unbiased. Thus, multisensory calibration is a vital and ongoing process. To meet this grand challenge, our brains have evolved a variety of mechanisms. First, in response to a systematic discrepancy between sensory cues (without external feedback) the cues calibrate one another (unsupervised calibration). Second, multisensory function is calibrated to external feedback (supervised calibration). These two mechanisms superimpose. While the former likely reflects a lower level mechanism, the latter likely reflects a higher level cognitive mechanism. Indeed, neural correlates of supervised multisensory calibration in monkeys were found in higher level multisensory cortical area VIP, but not in the relatively lower level multisensory area MSTd. In addition, even without a cue discrepancy (e.g., when experiencing stimuli from different sensory cues in series) the brain monitors supra-modal statistics of events in the environment and adapts perception cross-modally. This too comprises a variety of mechanisms, including confirmation bias to prior choices, and lower level cross-sensory adaptation. Further research into the neuronal underpinnings of the broad and diverse functions of multisensory calibration, with improved synthesis of theories is needed to attain a more comprehensive understanding of multisensory brain function.

Hysteresis reveals a happiness bias effect in dynamic emotion recognition from ambiguous biological motion

Considering the nonlinear dynamic nature of emotion recognition, it is believed to be strongly dependent on temporal context. This can be investigated by resorting to the phenomenon of hysteresis, which features a form of serial dependence, entailed by continuous temporal stimulus trajectories. Under positive hysteresis, the percept remains stable in visual memory (persistence) while in negative hysteresis, it shifts earlier (adaptation) to the opposite interpretation. Here, we asked whether positive or negative hysteresis occurs in emotion recognition of inherently ambiguous biological motion, while testing for the controversial debate of a negative versus positive emotional bias. Participants (n = 22) performed a psychophysical experiment in which they were asked to judge stimulus transitions between two emotions, happiness and sadness, from an actor database, and report perceived emotion across time, from one emotion to the opposite as physical cues were continuously changing. Our results reveal perceptual hysteresis in ambiguous emotion recognition, with positive hysteresis (visual persistence) predominating. However, negative hysteresis (adaptation/fatigue) was also observed in particular in the direction from sadness to happiness. This demonstrates a positive (happiness) bias in emotion recognition in ambiguous biological motion recognition. Finally, the interplay between positive and negative hysteresis suggests an underlying competition between visual persistence and adaptation mechanisms during ambiguous emotion recognition.

Spatial correspondence in relative space regulates serial dependence

Our perception is often attracted to what we have seen before, a phenomenon called 'serial dependence.' Serial dependence can help maintain a stable perception of the world, given the statistical regularity in the environment. If serial dependence serves this presumed utility, it should be pronounced when consecutive elements share the same identity when multiple elements spatially shift across successive views. However, such preferential serial dependence between identity-matching elements in dynamic situations has never been empirically tested. Here, we hypothesized that serial dependence between consecutive elements is modulated more effectively by the spatial correspondence in relative space than by that in absolute space because spatial correspondence in relative coordinates can warrant identity matching invariantly to changes in absolute coordinates. To test this hypothesis, we developed a task where two targets change positions in unison between successive views. We found that serial dependence was substantially modulated by the correspondence in relative coordinates, but not by that in absolute coordinates. Moreover, such selective modulation by the correspondence in relative space was also observed even for the serial dependence defined by previous non-target elements. Our findings are consistent with the view that serial dependence subserves object-based perceptual stabilization over time in dynamic situations.

Tuning perception and decisions to temporal context

Recent work suggests that serial dependence, where perceptual decisions are biased toward previous stimuli, arises from the prior that sensory input is temporally correlated. However, existing studies have mostly used random stimulus sequences that do not involve such temporal consistencies. Here, we manipulated the temporal statistics of visual stimuli to examine the role of true temporal correlations in serial dependence. In two experiments, observers reproduced the orientation of the last stimulus in a sequence, while we varied temporal correlations in the stimulus features at two timescales: stimulus history within the trial and decision history across trials. We found a clear dissociation: increasing temporal correlation in the stimulus history led to adaptation-like repulsive biases, whereas increasing temporal correlation in the decision history reduced attractive biases. Thus, we suggest that temporal correlation enhances the discriminative ability of the visual system, revealing the fundamental role of the broader temporal context.

Serial dependence in facial identity perception and visual working memory

Serial dependence (SD) refers to the effect in which a person's current perceptual judgment is attracted toward recent stimulus history. Perceptual and memory processes, as well as response and decisional biases, are thought to contribute to SD effects. The current study examined the processing stages of SD facial identity effects in the context of task-related decision processes and how such effects may differ from visual working memory (VWM) interactions. In two experiments, participants were shown a series of two sequentially presented face images. In Experiment 1, the two faces were separated by an interstimulus interval (ISI) of 1, 3, 6, or 10 s, and participants were instructed to reproduce the second face after a varying response delay of 0, 1, 3, 6, or 10 s. Results showed that SD effects occurred most consistently at ISI of 1 s and response delays of 1 and 6 s consistent with early and late stages of processing. In Experiment 2, the ISI was held constant at 1 s, and to separate SD from VWM interactions participants were post-cued to reproduce either the first or the second face. When the second face was the target, SD effects again occurred at response delays of 1 and 6 s, but not when the first face was the target. Together, the results demonstrates that SD facial identity effects occur independently of task-related processes in a distinct temporal fashion and suggest that SD and VWM interactions may rely on separate underlying mechanisms.

Task feedback suggests a post-perceptual component to serial dependence

Decisions across a range of perceptual tasks are biased toward past stimuli. Such serial dependence is thought to be an adaptive low-level mechanism that promotes perceptual stability across time. However, recent studies suggest post-perceptual mechanisms may also contribute to serially biased responses, calling into question a single locus of serial dependence and the nature of integration of past and present sensory inputs. We measured serial dependence in the context of a three-dimensional (3D) motion perception task where uncertainty in the sensory information varied substantially from trial to trial. We found that serial dependence varied with stimulus properties that impact sensory uncertainty on the current trial. Reduced stimulus contrast was associated with an increased bias toward the stimulus direction of the previous trial. Critically, performance feedback, which reduced sensory uncertainty, abolished serial dependence. These results provide clear evidence for a post-perceptual locus of serial dependence in 3D motion perception and support the role of serial dependence as a response strategy in the face of substantial sensory uncertainty.

Stable perceptual phenotype of the magnitude of history biases even in the face of global task complexity

According to a Bayesian framework, visual perception requires active interpretation of noisy sensory signals in light of prior information. One such mechanism, serial dependence, is thought to promote perceptual stability by assimilating current percepts with recent stimulus history. Combining a delayed orientation-adjustment paradigm with predictable (study 1) or unpredictable (study 2) task structure, we test two key predictions of this account in a novel context: first, that serial dependence should persist even in variable environments, and, second, that, within a given observer and context, this behavioral bias should be stable from one occasion to the next. Relying on data of 41 human volunteers and two separate experimental sessions, we confirm both hypotheses. Group-level, attractive serial dependence remained strong even in the face of volatile settings with multiple, unpredictable types of tasks, and, despite considerable interindividual variability, within-subject patterns of attractive and repulsive stimulus-history biases were highly stable from one experimental session to the next. In line with the hypothesized functional role of serial dependence, we propose that, together with previous work, our findings suggest the existence of a more general individual-specific fingerprint with which the past shapes current perception. Congruent with the Bayesian account, interindividual differences may then result from differential weighting of sensory evidence and prior information.

Serial dependence in visual perception: A meta-analysis and review

Positive sequential dependencies are phenomena in which actions, perception, decisions, and memory of features or objects are systematically biased toward visual experiences from the recent past. Among many labels, serial dependencies have been referred to as priming, sequential dependencies, sequential effects, or serial effects. Despite extensive research on the topic, the field still lacks an operational definition of what counts as serial dependence. In this meta-analysis, we review the vast literature on serial dependence and quantitatively assess its key diagnostic characteristics across several different domains of visual perception. The meta-analyses fully characterize serial dependence in orientation, face, and numerosity perception. They show that serial dependence is defined by four main kinds of tuning: serial dependence decays with time (temporal-tuning), it depends on relative spatial location (spatial-tuning), it occurs only between similar features and objects (feature-tuning), and it is modulated by attention (attentional-tuning). We also review studies of serial dependence that report single observer data, highlighting the importance of individual differences in serial dependence. Finally, we discuss a range of outstanding questions and novel research avenues that are prompted by the meta-analyses. Together, the meta-analyses provide a full characterization of serial dependence as an operationally defined family of visual phenomena, and they outline several of the key diagnostic criteria for serial dependence that should serve as guideposts for future research.

The influence of the tested item on serial dependence in perceptual decisions

Serial dependence in vision reflects how perceptual decisions can be biased by what we have recently perceived. Serial dependence studies test single items' effects on perceptual decisions. However, our visual world contains multiple objects at any given moment, so it's important to understand how past experiences affect not only a single object but also perception in a more general sense. Here we asked the question: What effect does a single item have when there is more than one subsequently presented test item? We displayed a single line (inducer) at the screen center, then either a single test-line or two simultaneous test-lines, varying in orientation space to the inducer. Next, participants reported test-line orientation using a left or right located response circle (to indicate which test-line should be reported). The results demonstrated that the inducer influenced subsequent perceptual judgments of a test-line even when two test-lines were presented. Distant items caused repulsive serial dependence, while close items caused attractive serial dependence. This shows how a single inducer can influence test-line judgments, even when two test-lines are presented, and can produce attractive and repulsive serial dependence biases when the item to report is revealed after it has disappeared.

Perceptual history biases in serial ensemble representation

Ensemble perception refers to the visual system's ability to efficiently represent groups of similar objects as a unified percept using their summary statistical information. Most studies focused on extraction of current trial averages, giving little attention to prior experience effects, although a few recent studies found that ensemble mean estimations contract toward previously presented stimuli, with most of these focusing on explicit perceptual averaging of simultaneously presented item ensembles. Yet, the time element is crucial in real dynamic environments, where we encounter ensemble items over time, aggregating information until reaching summary representations. Moreover, statistical information of objects and scenes is learned over time and often implicitly and then used for predictions that shape perception, promoting environmental stability. Therefore, we now focus on temporal aspects of ensemble statistics and test whether prior information, beyond the current trial, biases implicit perceptual decisions. We designed methods to separate current trial biases from those of previously seen trial ensembles. In each trial, six circles of different sizes were presented serially, followed by two test items. Participants were asked to choose which was present in the sequence. Participants unconsciously rely on ensemble statistics, choosing stimuli closer to the ensemble mean. To isolate the influence of earlier trials, the two test items were sometimes equidistant from the current trial mean. Results showed membership judgment biases toward current trial mean, when informative (largest effect). On equidistant trials, judgments were biased toward previously experienced stimulus statistics. Comparison of similar conditions with a shifted stimulus distribution ruled out a bias toward an earlier, presession, prototypical diameter. We conclude that ensemble perception, even for temporally experienced ensembles, is influenced not only by current trial mean but also by means of recently seen ensembles and that these influences are somewhat correlated on a participant-by-participant basis.

Contextualising facial expressions: The effect of temporal context and individual differences on classification

The influence of context on facial expression classification is most often investigated using simple cues in static faces portraying basic expressions with a fixed emotional intensity. We examined (1) whether a perceptually rich, dynamic audiovisual context, presented in the form of movie clips (to achieve closer resemblance to real life), affected the subsequent classification of dynamic basic (happy) and non-basic (sarcastic) facial expressions and (2) whether people's susceptibility to contextual cues was related to their ability to classify facial expressions viewed in isolation. Participants classified facial expressions-gradually progressing from neutral to happy/sarcastic in increasing intensity-that followed movie clips. Classification was relatively more accurate and faster when the preceding context predicted the upcoming expression, compared with when the context did not. Speeded classifications suggested that predictive contexts reduced the emotional intensity required to be accurately classified. More importantly, we show for the first time that participants' accuracy in classifying expressions without an informative context correlated with the magnitude of the contextual effects experienced by them-poor classifiers of isolated expressions were more susceptible to a predictive context. Our findings support the emerging view that contextual cues and individual differences must be considered when explaining mechanisms underlying facial expression classification.

Serial dependence in visual perception: A review

How does the visual system represent continuity in the constantly changing visual input? A recent proposal is that vision is serially dependent: Stimuli seen a moment ago influence what we perceive in the present. In line with this, recent frameworks suggest that the visual system anticipates whether an object seen at one moment is the same as the one seen a moment ago, binding visual representations across consecutive perceptual episodes. A growing body of work supports this view, revealing signatures of serial dependence in many diverse visual tasks. Yet, the variety of disparate findings and interpretations calls for a more general picture. Here, we survey the main paradigms and results over the past decade. We also focus on the challenge of finding a relationship between serial dependence and the concept of "object identity," taking centuries-long history of research into account. Among the seemingly contrasting findings on serial dependence, we highlight common patterns that may elucidate the nature of this phenomenon and attempt to identify questions that are unanswered.

Foveal vision determines the perceived emotion of face ensembles

People can extract summary statistical information from groups of similar objects, an ability called ensemble perception. However, not every object in a group is weighted equally. For example, in ensemble emotion perception, faces far from fixation were weighted less than faces close to fixation. Yet the contribution of foveal input in ensemble emotion perception is still unclear. In two experiments, groups of faces with varying emotions were presented for 100 ms at three different eccentricities (0°, 3°, 8°). Observers reported the perceived average emotion of the group. In two conditions, stimuli consisted of a central face flanked by eight faces (flankers) (central-present condition) and eight faces without the central face (central-absent condition). In the central-present condition, the emotion of the central face was either congruent or incongruent with that of the flankers. In Experiment 1, flanker emotions were uniform (identical flankers); in Experiment 2 they were varied. In both experiments, performance in the central-present condition was superior at 3° compared to 0° and 8°. At 0°, performance was superior in the central-absent (i.e., no foveal input) compared to the central-present condition. Poor performance in the central-present condition was driven by the incongruent condition where the foveal face strongly biased responses. At 3° and 8°, performance was comparable between central-present and central-absent conditions. Our results showed how foveal input determined the perceived emotion of face ensembles, suggesting that ensemble perception fails when salient target information is available in central vision.

Serial dependence in estimates of the monetary value of coins

Perceptions of current stimuli are sometimes biased toward or away from past perceptions. This phenomenon is called serial dependence. However, it remains unclear whether serial dependence originates from lower-order perceptual processing, higher-order perceptual processing or cognitive processing. We examined the effects of serial dependence when participants estimated the total number of coins or the monetary value of coins displayed and found attractive effects in both tasks. The attractive effect observed in the value estimation task suggests that serial dependence occurs through higher-order cognitive processes during calculation. We also examined the effect of response history (i.e., the responses of participants on previous trials), with multiple regression analyses that simultaneously evaluated the effects of the previous stimuli and responses. In both number and value estimation tasks, the immediately prior response had an attractive effect on current responses, while the immediately prior stimuli exerted a repulsive effect. This pattern suggests that the attractive serial dependence found in the single regression analysis was due to the correlation between stimulus and response in the previous trials and that the effect of past stimuli per se may be an adaptation that increases sensitivity to current stimuli.

Normal gaze processing in developmental prosopagnosia

Two key functions in human face perception are gaze discrimination and identity recognition. Here we examine whether gaze discrimination can be intact when identity recognition is impaired in developmental prosopagnosia (DP). We ran a large sample of developmental prosopagnosics (DPs) with a series of gaze discrimination tasks that assess various mechanisms in gaze processing. Experiment 1 (N = 101 DP participants) investigates spatial processing using an abnormal eye gaze detection task and a Wollaston illusion task that measures perceptual integration of eye and head direction. Experiment 2 (N = 45 DP participants) investigates temporal processing using an adaptation task and a serial dependence task. Despite their deficits with identity recognition, DPs performed in the normal range across both experiments. These results demonstrate that gaze discrimination can be normal in DP, and that various mechanisms of gaze processing can be spared when identity recognition is impaired. Our findings clarify the highly selective nature of impairments in DP and provide support for neurocognitive models of face perception with distinct mechanisms for gaze and identity processing.

The test-retest reliability and spatial tuning of serial dependence in orientation perception

Humans perceive objects and scenes consistently, even in situations where visual input is noisy and unstable. One of the mechanisms that underlies this perceptual stability is serial dependence, whereby the perception of objects or features at any given moment is pulled toward what was previously seen. Although recent findings from several studies have reported large individual differences in serial dependence, it is not clear how stable the serial dependence is within an individual. Here, we investigated the stability of serial dependence in orientation perception over two different days within the same observers. In addition, we also examined the visual field location specificity of perceptual serial dependence. On each trial, observers viewed a Gabor patch and then reported its apparent orientation by adjusting the orientation of a bar. For each observer, the Gabor was located in the foveal or peripheral (10° right or left eccentricity) visual field on both days or changed location from day to day. The results showed a very high degree of test-retest reliability in serial dependence measured across days within individual observers. Interestingly, this high within-subject consistency was only found when serial dependence was measured at the same visual field location. These results suggest that individual differences in serial dependence are stable across days, and that the spatiotemporal range in which the previous stimulus assimilates the perception of the current stimulus (the continuity field) may vary across different visual field locations in an observer-specific manner.

Illusion of visual stability through active perceptual serial dependence

Despite a noisy and ever-changing visual world, our perceptual experience seems remarkably stable over time. How does our visual system achieve this apparent stability? Here, we introduce a previously unknown visual illusion that shows direct evidence for an online mechanism continuously smoothing our percepts over time. As a result, a continuously seen physically changing object can be misperceived as unchanging. We find that online object appearance is captured by past visual experience up to 15 seconds ago. We propose that, because of an underlying active mechanism of serial dependence, the representation of the object is continuously merged over time, and the consequence is an illusory stability in which object appearance is biased toward the past. Our results provide a direct demonstration of the link between serial dependence in visual representations and perceived visual stability in everyday life.

Stimulus uncertainty predicts serial dependence in orientation judgements

How is what you see influenced by what you saw? The visual system may use recent perception to inform responses to current stimuli. This can cause the perception of current stimuli to be attracted toward previous observations, an effect termed serial dependence. This misperception might well be useful in a noisy visual environment, where minor image distortions over time may not actually represent meaningful change. Previous work has suggested that Bayesian perceptual inference may underlie serial dependence. For this to be true, the relative uncertainty associated with both prior and current sensory input should be taken into account. In an experiment manipulating the level of noise present in orientation stimuli, we found an effect of current stimulus uncertainty on serial dependence. We found no good evidence for an effect of previous stimulus uncertainty. Our results provide only partial evidence for the Bayesian interpretation of serial dependence. Non-Bayesian models may provide a better account of the phenomenon.

Experimentally disambiguating models of sensory cue integration

Sensory cue integration is one of the primary areas in which a normative mathematical framework has been used to define the “optimal” way in which to make decisions based upon ambiguous sensory information and compare these predictions to behavior. The conclusion from such studies is that sensory cues are integrated in a statistically optimal fashion. However, numerous alternative computational frameworks exist by which sensory cues could be integrated, many of which could be described as “optimal” based on different criteria. Existing studies rarely assess the evidence relative to different candidate models, resulting in an inability to conclude that sensory cues are integrated according to the experimenter's preferred framework. The aims of the present paper are to summarize and highlight the implicit assumptions rarely acknowledged in testing models of sensory cue integration, as well as to introduce an unbiased and principled method by which to determine, for a given experimental design, the probability with which a population of observers behaving in accordance with one model of sensory integration can be distinguished from the predictions of a set of alternative models.

Positive hysteresis in emotion recognition: Face processing visual regions are involved in perceptual persistence, which mediates interactions between anterior insula and medial prefrontal cortex

Facial emotion perception can be studied from the point of view of dynamic systems whose output may depend not only on current input but also on prior history - a phenomenon known as hysteresis. In cognitive neuroscience, hysteresis has been described as positive (perceptual persistence) or negative (fatigue of current percept) depending on whether perceptual switching occurs later or earlier than actual physical stimulus changes. However, its neural correlates remain elusive. We used dynamic transitions between emotional expressions and combined behavioral assessment with functional magnetic resonance imaging (fMRI) to investigate the underlying circuitry of perceptual hysteresis in facial emotion recognition. Our findings revealed the involvement of face-selective visual areas - fusiform face area (FFA) and superior temporal sulcus (STS) - in perceptual persistence as well as the right anterior insula. Moreover, functional connectivity analyses revealed an interplay between the right anterior insula and medial prefrontal cortex, which showed to be dependent on the presence of positive hysteresis. Our results support the hypothesis that high-order regions are involved in perceptual stabilization and decision during perceptual persistence (positive hysteresis) and add evidence to the role of the anterior insula as a hub of sensory information in perceptual decision-making.

Serial dependence of facial identity for own- and other-race faces

It is well established that individuals are better at recognising faces of their own-race compared with other-races; however, there is ongoing debate regarding the perceptual mechanisms that may be involved and therefore sensitive to face-race. Here, we ask whether serial dependence of facial identity, a bias where the perception of a face's identity is biased towards a previously presented face, shows an other-race effect. Serial dependence is associated with face recognition ability and appears to operate on high-level, face-selective representations, like other candidate mechanisms (e.g., holistic processing). We therefore expected to find an other-race effect for serial dependence for our Caucasian and Asian participants. While participants showed robust effects of serial dependence for all faces, only Caucasian participants showed stronger serial dependence for own-race faces. Intriguingly, we found that individual variation in own-race, but not other-race, serial dependence was significantly associated with face recognition abilities. Preliminary evidence also suggested that other-race contact is associated with other-race serial dependence. In conclusion, though we did not find an overall difference in serial dependence for own- versus other-race faces in both participant groups, our results highlight that this bias may be functionally different for own- versus other-race faces and sensitive to racial experience.

Serial dependence in the perceptual judgments of radiologists

In radiological screening, clinicians scan myriads of radiographs with the intent of recognizing and differentiating lesions. Even though they are trained experts, radiologists’ human search engines are not perfect: average daily error rates are estimated around 3–5%. A main underlying assumption in radiological screening is that visual search on a current radiograph occurs independently of previously seen radiographs. However, recent studies have shown that human perception is biased by previously seen stimuli; the bias in our visual system to misperceive current stimuli towards previous stimuli is called serial dependence. Here, we tested whether serial dependence impacts radiologists’ recognition of simulated lesions embedded in actual radiographs. We found that serial dependence affected radiologists’ recognition of simulated lesions; perception on an average trial was pulled 13% toward the 1-back stimulus. Simulated lesions were perceived as biased towards the those seen in the previous 1 or 2 radiographs. Similar results were found when testing lesion recognition in a group of untrained observers. Taken together, these results suggest that perceptual judgements of radiologists are affected by previous visual experience, and thus some of the diagnostic errors exhibited by radiologists may be caused by serial dependence from previously seen radiographs.

Serial Dependence of Emotion Within and Between Stimulus Sensory Modalities

How we perceive the world is not solely determined by what we sense at a given moment in time, but also by what we processed recently. Here we investigated whether such serial dependencies for emotional stimuli transfer from one modality to another. Participants were presented a random sequence of emotional sounds and images and instructed to rate the valence and arousal of each stimulus (Experiment 1). For both ratings, we conducted an intertrial analysis, based on whether the rating on the previous trial was low or high. We found a positive serial dependence for valence and arousal regardless of the stimulus modality on two consecutive trials. In Experiment 2, we examined whether passively perceiving a stimulus is sufficient to induce a serial dependence. In Experiment 2, participants were instructed to rate the stimuli only on active trials and not on passive trials. The participants were informed that the active and passive trials were presented in alternating order, so that they were able to prepare for the task. We conducted an intertrial analysis on active trials, based on whether the rating on the previous passive trial (determined in Experiment 1) was low or high. For both ratings, we again observed positive serial dependencies regardless of the stimulus modality. We conclude that the emotional experience triggered by one stimulus affects the emotional experience for a subsequent stimulus regardless of their sensory modalities, that this occurs in a bottom-up fashion, and that this can be explained by residual activation in the emotional network in the brain.

Serial dependence revealed in history-dependent perceptual templates

In any given perceptual task, the visual system selectively weighs or filters incoming information. The particular set of weights or filters form a kind of template, which reveals the regions or types of information that are particularly useful for a given perceptual decision.1,2 Unfortunately, sensory input is noisy and ever changing. To compensate for these fluctuations, the visual system could adopt a strategy of biasing the templates such that they reflect a temporal smoothing of input, which would be a form of serial dependence.3-5 Here, we demonstrate that perceptual templates are, in fact, altered by serial dependence. Using a simple orientation detection task and classification-image technique, we found that perceptual templates are systematically biased toward previously seen, task-irrelevant orientations. The results of an orientation discrimination task suggest that this shift in perceptual template derives from a change in the perceptual appearance of orientation. Our study reveals how serial dependence biases internal templates of orientation and suggests that the sensitivity of classification-image techniques in general could be improved by taking into account history-dependent fluctuations in templates.

A shared mechanism for facial expression in human faces and face pareidolia

Facial expressions are vital for social communication, yet the underlying mechanisms are still being discovered. Illusory faces perceived in objects (face pareidolia) are errors of face detection that share some neural mechanisms with human face processing. However, it is unknown whether expression in illusory faces engages the same mechanisms as human faces. Here, using a serial dependence paradigm, we investigated whether illusory and human faces share a common expression mechanism. First, we found that images of face pareidolia are reliably rated for expression, within and between observers, despite varying greatly in visual features. Second, they exhibit positive serial dependence for perceived facial expression, meaning an illusory face (happy or angry) is perceived as more similar in expression to the preceding one, just as seen for human faces. This suggests illusory and human faces engage similar mechanisms of temporal continuity. Third, we found robust cross-domain serial dependence of perceived expression between illusory and human faces when they were interleaved, with serial effects larger when illusory faces preceded human faces than the reverse. Together, the results support a shared mechanism for facial expression between human faces and illusory faces and suggest that expression processing is not tightly bound to human facial features.

Increased influence of prior choices on perceptual decisions in autism

Autism spectrum disorder (ASD) manifests sensory and perceptual atypicalities. Recent theories suggest that these may reflect a reduced influence of prior information in ASD. Some studies have found reduced adaptation to recent sensory stimuli in ASD. However, the effects of prior stimuli and prior perceptual choices can counteract one-another. Here, we investigated this using two different tasks (in two different cohorts): (i) visual location discrimination and (ii) multisensory (visual-vestibular) heading discrimination. We fit the data using a logistic regression model to dissociate the specific effects of prior stimuli and prior choices. In both tasks, perceptual decisions were biased toward recent choices. Notably, the 'attractive' effect of prior choices was significantly larger in ASD (in both tasks and cohorts), while there was no difference in the influence of prior stimuli. These results challenge theories of reduced priors in ASD, and rather suggest an increased consistency bias for perceptual decisions in ASD.

Serial dependence of facial identity reflects high-level face coding

Serial dependence of facial identity is a type of bias where the perceived identity of a face is biased towards a previously presented face. There are individual differences in serial dependence strength and tuning (how the strength varies depending on stimuli similarity), and previous research has shown that both stronger and more narrowly tuned serial dependence of facial identity is associated with better face recognition abilities. These results are consistent with the idea that this bias plays a functional role in face perception. It is important, therefore, to determine whether serial dependence of facial identity reflects a high-level face-coding mechanism acting on the identity of a face or instead predominantly reflects a bias in low-level features, which are also subject to serial dependence. We first sought evidence that serial dependence of facial identity survived changes in low-level visual features, by varying face viewpoint between successive stimuli. We found that serial dependence persisted across changes in viewpoint, arguing against an entirely low-level locus for this bias. We next tested whether the bias was affected by inversion, as sensitivity to inversion is argued to be a characteristic of high-level face-selective processing. Serial dependence was stronger and more narrowly tuned for upright than inverted faces. Taken together, our results are consistent with the view that serial dependence of facial identity affects high-level visual representations and may reflect a face-coding mechanism that is operating at the level of facial identity.

Perceptual decisions are biased toward relevant prior choices

Perceptual decisions are biased by recent perceptual history-a phenomenon termed 'serial dependence.' Here, we investigated what aspects of perceptual decisions lead to serial dependence, and disambiguated the influences of low-level sensory information, prior choices and motor actions. Participants discriminated whether a brief visual stimulus lay to left/right of the screen center. Following a series of biased 'prior' location discriminations, subsequent 'test' location discriminations were biased toward the prior choices, even when these were reported via different motor actions (using different keys), and when the prior and test stimuli differed in color. By contrast, prior discriminations about an irrelevant stimulus feature (color) did not substantially influence subsequent location discriminations, even though these were reported via the same motor actions. Additionally, when color (not location) was discriminated, a bias in prior stimulus locations no longer influenced subsequent location discriminations. Although low-level stimuli and motor actions did not trigger serial-dependence on their own, similarity of these features across discriminations boosted the effect. These findings suggest that relevance across perceptual decisions is a key factor for serial dependence. Accordingly, serial dependence likely reflects a high-level mechanism by which the brain predicts and interprets new incoming sensory information in accordance with relevant prior choices.

Inferential affective tracking reveals the remarkable speed of context-based emotion perception

Understanding the emotional states of others is important for social functioning. Recent studies show that context plays an essential role in emotion recognition. However, it remains unclear whether emotion inference from visual scene context is as efficient as emotion recognition from faces. Here, we measured the speed of context-based emotion perception, using Inferential Affective Tracking (IAT) with naturalistic and dynamic videos. Using cross-correlation analyses, we found that inferring affect based on visual context alone is just as fast as tracking affect with all available information including face and body. We further demonstrated that this approach has high precision and sensitivity to sub-second lags. Our results suggest that emotion recognition from dynamic contextual information might be automatic and immediate. Seemingly complex context-based emotion perception is far more efficient than previously assumed.

Asymmetric contextual effects in age perception

Perception is context dependent. For example, the perceived orientation of a bar changes depending on the presence of oriented bars around it. Contextual effects have also been demonstrated for more complex judgements, such as facial attractiveness or expression, although it remains unclear how these contextual facial effects depend on the types of faces surrounding the target face. To examine this, we measured the perceived age (a quantifiable measure) of a target face in the presence of differently aged faces in the surround. Using a unique database of standardized passport photos, participants were asked to estimate the age of a target face which was viewed either on its own or surrounded by two different identity flanker faces. The flanker faces were either both younger or both older than the target face, with different age offsets between flankers and targets of ±5, ±10, ±15, ±20 years. We find that when a target face is surrounded by younger faces, it systematically appears younger than when viewed on its own, and when it is surrounded by older faces, it systematically appears older than when viewed on its own. Surprisingly, we find that the magnitude of the flanker effects on perceived age of the target is asymmetric with younger flankers having a greater influence than older flankers, a result that may reflect the participants' own-age bias, since all participants were young. This result holds irrespective of gender or race of the faces and is consistent with averaging.

The influence of spatial location on same-different judgments of facial identity and expression

The "spatial congruency bias" is a behavioral phenomenon where 2 objects presented sequentially are more likely to be judged as being the same object if they are presented in the same location (Golomb, Kupitz, & Thiemann, 2014), suggesting that irrelevant spatial location information may be bound to object representations. Here, we examine whether the spatial congruency bias extends to higher-level object judgments of facial identity and expression. On each trial, 2 real-world faces were sequentially presented in variable screen locations, and subjects were asked to make same-different judgments on the facial expression (Experiments 1-2) or facial identity (Experiment 3) of the stimuli. We observed a robust spatial congruency bias for judgments of facial identity, yet a more fragile one for judgments of facial expression. Subjects were more likely to judge 2 faces as displaying the same expression if they were presented in the same location (compared to in different locations), but only when the faces shared the same identity. On the other hand, a spatial congruency bias was found when subjects made judgments on facial identity, even across faces displaying different facial expressions. These findings suggest a possible difference between the binding of facial identity and facial expression to spatial location. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

How positive emotional content overrules perceptual history effects: Hysteresis in emotion recognition

The human visual system is constantly processing multiple and often conflicting sensory cues to make perceptual decisions. Given the nonlinear nature of emotion recognition, this often leads to different percepts of the same physical facial expression. Moreover, the state of the emotion recognition system might depend on the trajectory of temporal context, potentially leading to a phenomenon known as perceptual hysteresis. Here, we aimed to explore temporal context-related mechanisms underlying perceptual hysteresis during emotion recognition. We hypothesized that dependence on recent perceptual experience might reveal important clues about the role of short-term memory on the perception of emotional stimuli. Behavioral data were acquired using reality-based, changing emotion expressions morphed from a source to a target emotion with different valences, always passing through a neutral expression. Participants identified the onset and offset of what they perceived as the neutral expression interval. Our results showed that current perception of emotional expression is affected by recent temporal context, thus revealing perceptual hysteresis. We also found a relation between recent perceptual history effects and stimulus emotional Content: The positive valence of the stimulus emotional content appeared to abolish perceptual history effects, whereas negatively loaded stimuli induced clear short-term memory effects and positive hysteresis. Our findings show direct competition between recent perceptual experience and stimulus emotional content during decision making, which affects the formation of current percepts in emotion recognition.

Context information supports serial dependence of multiple visual objects across memory episodes

Serial dependence is thought to promote perceptual stability by compensating for small changes of an object’s appearance across memory episodes. So far, it has been studied in situations that comprised only a single object. The question of how we selectively create temporal stability of several objects remains unsolved. In a memory task, objects can be differentiated by their to-be-memorized feature (content) as well as accompanying discriminative features (context). We test whether congruent context features, in addition to content similarity, support serial dependence. In four experiments, we observe a stronger serial dependence between objects that share the same context features across trials. Apparently, the binding of content and context features is not erased but rather carried over to the subsequent memory episode. As this reflects temporal dependencies in natural settings, our findings reveal a mechanism that integrates corresponding content and context features to support stable representations of individualized objects over time.

Visual cognition compensates for small changes in an object’s appearance to ensure its perceived continuity. We show that in situations with multiple objects, context features like color, temporal or spatial position are used as anchors to selectively integrate corresponding objects over time.

Attraction to the recent past in aesthetic judgments: A positive serial dependence for rating artwork

Visual perception can be systematically biased towards the recent past. Many stimulus attributes-including orientation, numerosity, facial expression and attractiveness, and perceived slimness-are systematically biased towards recent past experience. This phenomenon has been termed serial dependence. In the current study, we tested whether serial dependence occurs for aesthetic ratings of artworks. A set of 100 paintings depicting scenery and still life was collected from online archives. For each participant, 40 paintings were randomly selected from the set, and presented sequentially 20 times in random order. Serial dependence was quantified for each observer by measuring how their rating response on each trial depended on the attractiveness of the previous trial. The data were pooled across participants and fitted with a Bayesian model of serial dependence. Results showed that the current painting earned significantly higher aesthetic ratings when participants viewed a more attractive painting on the previous trial, compared to when they viewed a less attractive one. The magnitude of serial dependence was greatest when the attractiveness distance between consecutive paintings was relatively close. The effect held both for 1 s exposure times, and for brief 250 ms exposures (followed by a mask). These findings show that aesthetic judgments are not sequentially independent, showing that positive serial dependencies are not limited to low-level perceptual judgments.

The role of feature-based attention in visual serial dependence

Perceptual decisions about current sensory input are biased toward input of the recent past-a phenomenon termed serial dependence. Serial dependence may serve to stabilize neural representations in the face of external and internal noise. However, it is unclear under which circumstances previous input attracts subsequent perceptual decisions, and thus whether serial dependence reflects a broad smoothing or selective stabilization operation. Here we investigated whether focusing attention on particular features of the previous stimulus modulates serial dependence. We found an attractive bias in orientation estimations when previous and current stimuli had similar orientations, and a repulsive bias when they had dissimilar orientations. The attractive bias was markedly reduced-to less than half of its original magnitude-when observers attended to the size, rather than the orientation, of the previous stimulus. Conversely, the repulsive bias for stimuli with large orientation differences was not modulated by feature-based attention. This suggests separate sources of these positive and negative perceptual biases.

Neural Dynamics of Serial Dependence in Numerosity Perception

Serial dependence—an attractive perceptual bias whereby a current stimulus is perceived to be similar to previously seen ones—is thought to represent the process that facilitates the stability and continuity of visual perception. Recent results demonstrate a neural signature of serial dependence in numerosity perception, emerging very early in the time course during perceptual processing. However, whether such a perceptual signature is retained after the initial processing remains unknown. Here, we address this question by investigating the neural dynamics of serial dependence using a recently developed technique that allowed a reactivation of hidden memory states. Participants performed a numerosity discrimination task during EEG recording, with task-relevant dot array stimuli preceded by a task-irrelevant stimulus inducing serial dependence. Importantly, the neural network storing the representation of the numerosity stimulus was perturbed (or pinged) so that the hidden states of that representation can be explicitly quantified. The results first show that a neural signature of serial dependence emerges early in the brain signals, starting soon after stimulus onset. Critical to the central question, the pings at a later latency could successfully reactivate the biased representation of the initial stimulus carrying the signature of serial dependence. These results provide one of the first pieces of empirical evidence that the biased neural representation of a stimulus initially induced by serial dependence is preserved throughout a relatively long period.

The roles of preceding stimuli and preceding responses on assimilative and contrastive sequential effects during facial expression perception

In contrast to the classic view that facial expressions convey specific emotional states, recent theories have postulated that perception is a highly contextualised phenomenon. The present study utilised sequential effects as a probe to examine how the preceding context informs current facial expression perception, while participants performed a binary categorisation task on a sequence of expressions morphed from fearful to disgusted prototypes. We found that preceding stimuli/responses played differential roles in expression-based sequential effects. When preceding responses were analytically controlled for, the participants were biased to categorise the current targets as being either away from or close to the category of preceding expressions, yielding stimulus-related contrast or assimilation effects, depending on whether the stimulus similarity between the preceding and current expressions was small or large. When the stimulus similarity between successive expressions was analytically controlled for, preceding responses slanted current categorisation judgments toward response-related assimilative consequences. Distinct from stimulus-related contrast, both stimulus-related and response-related assimilations were robust since they could persist for expressions presented up to two trials back and when the perceptual quality of the stimuli was poor. We suggest that the criterion-shift account is generally compatible with the overall findings, revealing how facial expression perception is temporally contextualised.

Visual serial dependence in an audiovisual stimulus

Serial dependence is a phenomenon that biases the perception of features or objects systematically toward sensory input from the recent past (Fischer & Whitney, 2014). There is an active debate whether this effect is rooted directly in perception or reflects biases in decision making. We investigated serial dependence across three experiments by manipulating the decision made on each trial. A multimodal audiovisual stimulus comprising a Gabor and a vowel sound was presented repeatedly. On each trial, participants reported either the Gabor orientation or the vowel sound. Participants either ignored one modality (Experiment 1) or attended to both modalities (Experiments 2 and 3). In Experiments 2 and 3, the response task was randomized to prevent anticipating which modality to respond to until the response phase. In Experiment 3, no-response trials were additionally interleaved. Results across the three experiments demonstrated serial dependence only when participants reported the visual modality. Serial dependence was also present in visual reports when participants completed auditory reports or made no reports on previous trials. The previous stimulus alone was enough to elicit an effect. Serial dependence is unlikely to be an effect of the previous decision on the stimulus, but rather an effect of perceiving the previous stimulus.

Working Memory Maintenance Modulates Serial Dependence Effects of Perceived Emotional Expression

The stability of face perception is vital in interpersonal interactions. Recent studies have revealed the mechanism of the stability in the perception of stable attributes of faces (such as facial identity) by serial dependence, a phenomenon in which perception of current stimuli is pulled toward recently viewed stimuli. However, whether serial dependence of perceived emotional expression (a changeable attribute of faces) exists remains controversial, and its exact nature has not been examined yet. To address these issues, we used the methods of constant stimuli and two-interval forced choice tasks in three psychophysical experiments. Participants compared two successive facial expressions selected from a continuum with 50 morphed faces ranging from sad to happy. Experiment 1a and 1b showed that a perceived facial expression pulled toward previously seen facial expressions (i.e., a significant serial dependence effect), independent of response instructions. Furthermore, a stronger serial dependence effect was found when the first facial expression was retained in working memory for a longer delay duration (Experiment 2), and yet a weaker serial dependence effect was observed when a longer delay between decision and response was performed (Experiment 3). These findings indicate that serial dependence facilitates the stability of facial expression perception and is modulated by working memory representations.

Laws of concatenated perception: Vision goes for novelty, decisions for perseverance

Every instant of perception depends on a cascade of brain processes calibrated to the history of sensory and decisional events. In the present work, we show that human visual perception is constantly shaped by two contrasting forces exerted by sensory adaptation and past decisions. In a series of experiments, we used multilevel modeling and cross-validation approaches to investigate the impact of previous stimuli and decisions on behavioral reports during adjustment and forced-choice tasks. Our results revealed that each perceptual report is permeated by opposite biases from a hierarchy of serially dependent processes: Low-level adaptation repels perception away from previous stimuli, whereas decisional traces attract perceptual reports toward the recent past. In this hierarchy of serial dependence, "continuity fields" arise from the inertia of decisional templates and not from low-level sensory processes. This finding is consistent with a Two-process model of serial dependence in which the persistence of readout weights in a decision unit compensates for sensory adaptation, leading to attractive biases in sequential perception. We propose a unified account of serial dependence in which functionally distinct mechanisms, operating at different stages, promote the differentiation and integration of visual information over time.