A Bayesian observer model reveals a prior for natural daylights in hue perception.

Incorporating statistical characteristics of stimuli in perceptual processing can be highly beneficial for reliable estimation from noisy sensory measurements but may generate perceptual bias. According to Bayesian inference, perceptual biases arise from the integration of internal priors with noisy sensory inputs. In this study, we used a Bayesian observer model to derive biases and priors in hue perception based on discrimination data for hue ensembles with varying levels of chromatic noise. Our results showed that discrimination thresholds for isoluminant stimuli with hue defined by azimuth angle in cone-opponent color space exhibited a bimodal pattern, with lowest thresholds near a non-cardinal blue-yellow axis that aligns closely with the variation of natural daylights. Perceptual biases showed zero crossings around this axis, indicating repulsion away from yellow and attraction towards blue. These biases could be explained by the Bayesian observer model through a non-uniform prior with a preference for blue. Our findings suggest that visual processing takes advantage of knowledge of the distribution of colors in natural environments for hue perception.

Altered mechanisms of adaptation in social anxiety: differences in adapting to positive versus negative emotional faces.

Social anxiety is characterised by fear of negative evaluation and negative perceptual biases; however, the cognitive mechanisms underlying these negative biases are not well understood. We investigated a possible mechanism which could maintain negative biases: altered adaptation to emotional faces. Heightened sensitivity to negative emotions could result from weakened adaptation to negative emotions, strengthened adaptation to positive emotions, or both mechanisms. We measured adaptation from repeated exposure to either positive or negative emotional faces, in individuals high versus low in social anxiety. We quantified adaptation strength by calculating the point of subjective equality (PSE) before and after adaptation for each participant. We hypothesised: (1) weaker adaptation to angry vs happy faces in individuals high in social anxiety, (2) no difference in adaptation to angry vs happy faces in individuals low in social anxiety, and (3) no difference in adaptation to sad vs happy faces in individuals high in social anxiety. Our results revealed a weaker adaptation to angry compared to happy faces in individuals high in social anxiety (Experiment 1), with no such difference in individuals low in social anxiety (Experiment 1), and no difference in adaptation strength to sad vs happy faces in individuals high in social anxiety (Experiment 2).

Does Implicit Racial Bias Affect Auditory-Perceptual Evaluations of Dysphonic Voices?

PURPOSE: The purpose of this study was to understand the role of implicit racial bias in auditory-perceptual evaluations of dysphonic voices by determining if a biasing effect exists for novice listeners in their auditory-perceptual ratings of Black and White speakers. METHOD: Thirty speech-language pathology graduate students at Boston University listened to audio files of 20 Black speakers and 20 White speakers of General American English with voice disorders. Listeners rated the overall severity of dysphonia of each voice heard using a 100-unit visual analog scale and completed the Harvard Implicit Association Test (IAT) to measure their implicit racial bias. RESULTS: Both Black and White speakers were rated as less severely dysphonic when their race was labeled as Black. No significant relationship was found between Harvard IAT scores and differences in severity ratings by race labeling condition. CONCLUSIONS: These findings suggest a minimizing bias in the evaluation of dysphonia for Black patients with voice disorders. These results contribute to the understanding of how a patient's race may impact their visit with a clinician. Further research is needed to determine the most effective interventions for implicit bias retraining and the additional ways that implicit racial bias impacts comprehensive voice evaluations.

Studying perceptual bias in favor of the from-above Necker cube perspective in a goal-directed behavior.

When viewing a completely ambiguous image, different interpretations can switch involuntarily due to internal top-down processing. In the case of the Necker cube, an entirely ambiguous stimulus, observers often display a bias in perceptual switching between two interpretations based on their perspectives: one with a from-above perspective (FA) and the other with a from-below perspective (FB). Typically, observers exhibit a priori top-down bias in favor of the FA interpretation, which may stem from a statistical tendency in everyday life where we more frequently observe objects from above. However, it remains unclear whether this perceptual bias persists when individuals voluntarily decide on the Necker cube's interpretation in goal-directed behavior, and the impact of ambiguity in this context is not well-understood. In our study, we instructed observers to voluntarily identify the orientation of a Necker cube while manipulating its ambiguity from low (LA) to high (HA). Our investigation aimed to test two hypotheses: (i) whether the perspective (FA or FB) would result in a bias in response time, and (ii) whether this bias would depend on the level of stimulus ambiguity. Additionally, we analyzed electroencephalogram (EEG) signals to identify potential biomarkers that could explain the observed perceptual bias. The behavioral results confirmed a perceptual bias in favor of the from-above perspective, as indicated by shorter response times. However, this bias diminished for stimuli with high ambiguity. For the LA stimuli, the occipital theta-band power consistently exceeded the frontal theta-band power throughout most of the decision-making time. In contrast, for the HA stimuli, the frontal theta-band power started to exceed the occipital theta-band power during the 0.3-s period preceding the decision. We propose that occipital theta-band power reflects evidence accumulation, while frontal theta-band power reflects its evaluation and decision-making processes. For the FB perspective, occipital theta-band power exhibited higher values and dominated over a longer duration, leading to an overall increase in response time. These results suggest that more information and more time are needed to encode stimuli with a FB perspective, as this template is less common for the observers compared to the template for a cube with a FA perspective.

When less is more: coy display behaviours and the temporal dynamics of animal courtship.

Sexual selection research has been dominated by the notion that mate choice selects for the most vigorous displays that best reflect the quality of the courter. However, courtship displays are often temporally structured, containing different elements with varying degrees of intensity and conspicuousness. For example, highly intense movements are often coupled with more subtle components such as static postures or hiding displays. Here, we refer to such subtle display traits as 'coy', as they involve the withholding of information about maximal display capabilities. We examine the role of intensity variation within temporally dynamic displays, and discuss three hypotheses for the evolution of coy courtship behaviours. We first review the threat reduction hypothesis, which points to sexual coercion and sexual autonomy as important facets of sexual selection. We then suggest that variation in display magnitude exploits pre-existing perceptual biases for temporal contrast. Lastly, we propose that information withholding may leverage receivers' predispositions for filling gaps in information-the 'curiosity bias'. Overall, our goal is to draw attention to temporal variation in display magnitude, and to advocate possible scenarios for the evolution of courtship traits that regularly occur below performance maxima. Throughout, we highlight novel directions for empirical and theoretical investigations.

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.

Chemosensation in anxiety: the trigeminal system matters.

The presence of a perceptual bias due to anxiety is well demonstrated in cognitive and sensory task for the visual and auditory modality. Event-related potentials, by their specific measurement of neural processes, have strongly contributed to this evidence. There is still no consensus as to whether such a bias exists in the chemical senses; chemosensory event-related potentials (CSERPs) are an excellent tool to clarify the heterogeneous results, especially since the Late Positive Component (LPC) may be an indicator of emotional involvement after chemosensory stimulation. This research examined the association between state and trait anxiety and the amplitude and latency of pure olfactory and mixed olfactory-trigeminal LPC. In this study, 20 healthy participants (11 women) with a mean age of 24.6 years (SD = 2.6) completed a validated questionnaire to measure anxiety (STAI), and CSERP was recorded during 40 pure olfactory stimulations (phenyl ethanol) and 40 mixed olfactory-trigeminal stimulations (eucalyptol). LPC latency and amplitude were measured at Cz (electrode located at midline central) for each participant. We observed a significant negative correlation between LPC latencies and the state anxiety scores for the mixed olfactory-trigeminal condition (r(18) = -0.513; P = 0.021), but not for the pure olfactory condition. We did not observe any effect on LPC amplitudes. This study suggests that a higher level of state anxiety is related to a more rapid perceptual electrophysiological response for mixed olfactory-trigeminal stimuli but not for pure odors.

Going forward: perceptual bias for forward-facing motion in chimpanzees.

When a row of objects surrounded by a frame suddenly shifts a certain distance so that part of the row is occluded by the frame, humans perceive ambiguous apparent motion either to the left or the right. However, when the objects have "directionality," humans perceive them as moving forward in the direction in which they are pointing, which is termed forward-facing motion bias. In the present study, five experiments were conducted to address whether, and if so how, physical properties or prior knowledge about the objects affected the perception of their apparent motion in two juvenile chimpanzees (Pan troglodytes). In experiment 1, the chimpanzees did not show a clear forward-facing bias in judging the direction of motion when directed triangles were presented, whereas the human participants did. In contrast, when pictures of the lateral view of chimpanzees with quadrupedal postures were shown, there was a clear bias for going "forward" with regards to the side with the head (experiment 2). We presented pictures of dogs looking back to explore what features caused the forward-facing motion bias (experiment 3). Chimpanzees did not show any bias for these stimuli, suggesting that the direction of the head and body interactively affected the perceptual bias. Experiment 4 tested the role of the head and found that only the lateral view of the heads of chimpanzees or humans caused the bias (experiment 4). Additional tests also showed that the chimpanzees could not solve the task based only on the direction of the stimuli without motion (experiment 5). These results indicate that the perception of motion in the chimpanzees was affected by the biological features of the stimuli, suggesting their prior knowledge of the "body" from a biological (morphological and kinetic) perspective.

A key role of orientation in the coding of visual motion direction.

Despite the fundamental importance of visual motion processing, our understanding of how the brain represents basic aspects of motion is incomplete. While it is generally believed that direction is the main representational feature of motion, motion processing is also influenced by nondirectional orientation signals that are present in most motion stimuli. Here, we aimed to test whether this nondirectional motion axis contributes motion perception even when orientation is completely absent from the stimulus. Using stimuli with and without orientation signals, we found that serial dependence in a simple motion direction estimation task was predominantly determined by the orientation of the previous motion stimulus. Moreover, the observed attraction profiles closely matched the characteristic pattern of serial attraction found in orientation perception. Evidently, the sequential integration of motion signals strongly depends on the orientation of motion, indicating a fundamental role of nondirectional orientation in the coding of visual motion direction.

Perceptual bias contextualized in visually ambiguous stimuli.

The visual appearance of an object is a function of stimulus properties as well as perceptual biases imposed by the observer. The context-specific trade-off between both can be measured accurately in a perceptual judgment task, involving grouping by proximity in ambiguous dot lattices. Such grouping depends lawfully on a stimulus parameter of the dot lattices known as their aspect ratio (AR), whose effect is modulated by a perceptual bias representing the preference for a cardinal orientation. In two experiments, we investigated how preceding context can lead to bias modulation, either in a top-down fashion via visual working memory (VWM) or bottom-up via sensory priming. In Experiment 1, we embedded the perceptual judgment task in a change detection paradigm and studied how the factors of VWM load (complexity of the memory array) and content (congruency in orientation to the ensuing dot lattice) affect the prominence of perceptual bias. A robust vertical orientation bias was observed, which was increased by VWM load and modulated by congruent VWM content. In Experiment 2, dot lattices were preceded by oriented primes. Here, primes regardless of orientation elicited a vertical orientation bias in dot lattices compared to a neutral baseline. Taken together, the two experiments demonstrate that top-down context (VWM load and content) effectively controls orientation bias modulation, while bottom-up context (i.e., priming) merely acts as an undifferentiated trigger to perceptual bias. These findings characterize the temporal context sensitivity of Gestalt perception, shed light on the processes responsible for different perceptual outcomes of ambiguous stimuli, and identify some of the mechanisms controlling perceptual bias.

Attractive and repulsive effects of sensory history concurrently shape visual perception.

BACKGROUND: Sequential effects of environmental stimuli are ubiquitous in most behavioral tasks involving magnitude estimation, memory, decision making, and emotion. The human visual system exploits continuity in the visual environment, which induces two contrasting perceptual phenomena shaping visual perception. Previous work reported that perceptual estimation of a stimulus may be influenced either by attractive serial dependencies or repulsive aftereffects, with a number of experimental variables suggested as factors determining the direction and magnitude of sequential effects. Recent studies have theorized that these two effects concurrently arise in perceptual processing, but empirical evidence that directly supports this hypothesis is lacking, and it remains unclear whether and how attractive and repulsive sequential effects interact in a trial. Here we show that the two effects concurrently modulate estimation behavior in a typical sequence of perceptual tasks. RESULTS: We first demonstrate that observers' estimation error as a function of both the previous stimulus and response cannot be fully described by either attractive or repulsive bias but is instead well captured by a summation of repulsion from the previous stimulus and attraction toward the previous response. We then reveal that the repulsive bias is centered on the observer's sensory encoding of the previous stimulus, which is again repelled away from its own preceding trial, whereas the attractive bias is centered precisely on the previous response, which is the observer's best prediction about the incoming stimuli. CONCLUSIONS: Our findings provide strong evidence that sensory encoding is shaped by dynamic tuning of the system to the past stimuli, inducing repulsive aftereffects, and followed by inference incorporating the prediction from the past estimation, leading to attractive serial dependence.

Structure of visual biases revealed by individual differences.

Multiple studies have shown that certain visual stimuli are perceived in accordance with strong biases that are both robust within individuals and highly variable from one individual to the next. These biases undergo small changes over time that demonstrate that they constitute latent states of the visual system. The literature to date indicates that the individual biases for different stimulus classes are independent of each other. Here we asked whether some of these biases are nonetheless related to one another. We measured individual biases for five classes of stimuli in 1000 participants. The stimuli were two different versions of two-dimensional apparent motion, smooth motion in Glass patterns, and two different structure-from-motion stimuli. There were pronounced individual biases in all stimuli, and these biases varied in direction and strength across individuals. Some biases were not independent: the two biases for apparent motion direction were most strongly correlated, and they were both correlated, but less strongly, to the bias direction for smooth motion. While all other pairs of biases had unrelated directions, the strengths of all biases were correlated. The correlation of bias strengths may be due to either a common factor across the stimulus types, or an attentional effect. Only a tiny fraction of the between-participant variance can be explained by age and gender. These results show that latent states of the visual system that we measure as individual biases are organized in a structured way, and call out for further study of this under-explored aspect of visual perception.

Cross-fixation interactions of orientations suggest high-to-low-level decoding in visual working memory.

Sensory encoding (how stimuli evoke sensory responses) is known to progress from low- to high-level features. Decoding (how responses lead to perception) is less understood but is often assumed to follow the same hierarchy. Accordingly, orientation decoding must occur in low-level areas such as V1, without cross-fixation interactions. However, a study, Ding, Cueva, Tsodyks, and Qian (2017), provided evidence against the assumption and proposed that visual decoding may often follow a high-to-low-level hierarchy in working memory, where higher-to-lower-level constraints introduce interactions among lower-level features. If two orientations on opposite sides of the fixation are both task relevant and enter working memory, then they should interact with each other. We indeed found the predicted cross-fixation interactions (repulsion and correlation) between orientations. Control experiments and analyses ruled out alternative explanations such as reporting bias and adaptation across trials on the same side of the fixation. Moreover, we explained the data using a retrospective high-to-low-level Bayesian decoding framework.

Testosterone amplifies the negative valence of an agonistic gestural display by exploiting receiver perceptual bias.

Many animals communicate by performing elaborate displays that are incredibly extravagant and wildly bizarre. So, how do these displays evolve? One idea is that innate sensory biases arbitrarily favour the emergence of certain display traits over others, leading to the design of an unusual display. Here, we study how physiological factors associated with signal production influence this process, a topic that has received almost no attention. We focus on a tropical frog, whose males compete for access to females by performing an elaborate waving display. Our results show that sex hormones like testosterone regulate specific display gestures that exploit a highly conserved perceptual system, evolved originally to detect 'dangerous' stimuli in the environment. Accordingly, testosterone makes certain gestures likely to appear more perilous to rivals during combat. This suggests that hormone action can interact with effects of sensory bias to create an evolutionary optimum that guides how display exaggeration unfolds.

Mind's eye: The impact of spider presence and cognitive therapy on size estimation biases in spider phobia.

The present study assessed the circumstances under which size estimation biases in spider phobia occur, and whether such biases are modifiable by treatment. Women with (n = 67) and without (n = 33) spider phobia approached a spider during a behavioral approach test (BAT). They provided size estimates of the spider both during and shortly after the BAT (with the spider in view, or not in view, respectively). Phobic women then received cognitive therapy or a placebo treatment and one week later they underwent a second BAT and provided size estimates of the same spider during and after the BAT. Phobic women reported larger size estimates than non-phobic women after, but not during, the BAT. Size estimates after, but not during, the BAT correlated with self-reported fear but not avoidance. Size estimates after, but not during, the BAT reduced from the first to second BAT in phobic women; an effect evident in both the cognitive therapy and placebo treatment conditions. Changes in size estimates were not associated with treatment-induced reductions in fear or avoidance. These results suggest that estimation biases in spider phobia are likely driven by non-perceptual processes. The clinical utility of size estimation measures is discussed.

Do Primary Care Physicians Contribute to the Immunization Status of Their Adult Patients? A Story of Patients' Overconfidence Coupled With Physicians' Passivity.

Context: Immunization coverage counts among the priorities of public health services. To identify factors that motivate or fail to motivate patients to update their vaccination status would help to design future strategies and awareness campaigns. Objective: Our aim was to assess the impact of primary care physicians on the immunization status of their adult patients, and to explore possible explanations. Methods: We invited students and collaborators of Geneva University to bring their paper vaccination records to receive an assessment of their immunization status and personalized vaccination recommendations. Participants completed a first questionnaire at the recruitment phase, and a second 2-3 months later. We assessed their immunization status with the viavac algorithms based on the Swiss national immunization plan. Results: Having a primary care physician did not correlate with better immunization status: only 22.5% patients who reported having a physician and 20% who reported having no physician were up-to-date (n = 432; p > 0.5). A linear regression indicates that the frequency of medical consultations did not affect patients' immunization status either. Even the participants who recently showed their vaccination record to their primary care physician did not have a better vaccination status. We explored possible explanatory factors and found evidence for the patients' overconfidence about their own immunization status: 71.2% of the participants who predicted that they were up-to-date were wrong about their actual status, and 2-3 months after having received their immunization assessment, 52.8% of the participants who "remembered" having received the assessment that they were up-to-date were wrong: they had in fact received the opposite information that they were not up-to-date. This substantial proportion of wrong beliefs suggests that adult patients are unworried and overconfident about their own immunization status, which is likely to induce a passive resistance toward vaccination updating. Conclusions: This study indicates that the vaccination coverage and beliefs of adults about their immunization status is suboptimal, and that primary care physicians need further support to improve their health-protection mandate through routine immunization check-ups. We highlight that the current covid vaccination campaigns offer a rare opportunity to update patients' immunization status and urge physicians to do so.

Higher-Order Musical Temporal Structure in Bird Song.

Bird songs often display musical acoustic features such as tonal pitch selection, rhythmicity, and melodic contouring. We investigated higher-order musical temporal structure in bird song using an experimental method called "music scrambling" with human subjects. Recorded songs from a phylogenetically diverse group of 20 avian taxa were split into constituent elements ("notes" or "syllables") and recombined in original and random order. Human subjects were asked to evaluate which version sounded more "musical" on a per-species basis. Species identity and stimulus treatment were concealed from subjects, and stimulus presentation order was randomized within and between taxa. Two recordings of human music were included as a control for attentiveness. Participants varied in their assessments of individual species musicality, but overall they were significantly more likely to rate bird songs with original temporal sequence as more musical than those with randomized temporal sequence. We discuss alternative hypotheses for the origins of avian musicality, including honest signaling, perceptual bias, and arbitrary aesthetic coevolution.

Overly Strong Priors for Socially Meaningful Visual Signals Are Linked to Psychosis Proneness in Healthy Individuals.

According to the predictive coding theory of psychosis, hallucinations and delusions are explained by an overweighing of high-level prior expectations relative to sensory information that leads to false perceptions of meaningful signals. However, it is currently unclear whether the hypothesized overweighing of priors (1) represents a pervasive alteration that extends to the visual modality and (2) takes already effect at early automatic processing stages. Here, we addressed these questions by studying visual perception of socially meaningful stimuli in healthy individuals with varying degrees of psychosis proneness (n = 39). In a first task, we quantified participants' prior for detecting faces in visual noise using a Bayesian decision model. In a second task, we measured participants' prior for detecting direct gaze stimuli that were rendered invisible by continuous flash suppression. We found that the prior for detecting faces in noise correlated with hallucination proneness (r = 0.50, p = 0.001, Bayes factor 1/20.1) as well as delusion proneness (r = 0.46, p = 0.003, BF 1/9.4). The prior for detecting invisible direct gaze was significantly associated with hallucination proneness (r = 0.43, p = 0.009, BF 1/3.8) but not conclusively with delusion proneness (r = 0.30, p = 0.079, BF 1.7). Our results provide evidence for the idea that overly strong high-level priors for automatically detecting socially meaningful stimuli might constitute a processing alteration in psychosis.

Updating facial emotional expressions in working memory: Differentiating trait anxiety and depressiveness.

Individual differences in updating emotional facial expressions in working memory are not fully understood. Here we focused on the effects of high trait anxiety and high depressiveness in men and women on updating schematic emotional facial expressions (sad, angry, scheming, happy, neutral). A population representative sample of young adults was divided into four emotional disposition groups based on STAI-T and MADRS cut-offs: high anxiety (HA, n = 41), high depressiveness (HD, n = 31), high depressiveness & high anxiety (HAHD, n = 65) and control (CT, n = 155). Participants completed a 2-back task with schematic emotional faces, and valence/arousal ratings and verbal recognition tasks. A novel approach was used to separate encoding from retrieval. We found an interaction of emotional dispositions and emotional faces in updating accuracy. HD group made more errors than HA when encoding happy schematic faces. Other differences between emotional dispositions on updating measures were found but they were not specific to any emotional facial expression. Our findings suggest that there is a minor happy disadvantage in HD in contrast to HA which can be seen in lower accuracy for visual encoding of happy faces, but not in retrieval accuracy, the speed of updating, nor perception of emotional content in happy faces. These findings help to explain differences and similarities between high trait anxiety and high depressiveness in working memory and processing of facial expressions. The results are discussed in relation to prevalent theories of information processing in anxiety and depression.

Identifying pain perceptual biases related to fear of pain and threat in a pain-free sample.

BACKGROUND: The association between fear of pain (FOP) and pain intensity has remained unclear. This study aimed to examine whether highly pain-fearful participants showed pain perceptual biases to general painful stimulus or to specific threatening painful stimulus. METHODS: Fifty-nine undergraduates were recruited into low (n = 30) and high (n = 29) FOP groups and completed a threatening pain perception task with two tasks. Task 1 assessed pain perceptual biases by calculating the percentage of near-threshold pain stimulus judged as painful and assessing the average pain intensity ratings to those painful stimuli. Task 2 assessed pain perceptual biases by measuring pain ratings to each single threshold (low intensity) and twice-threshold (high intensity) pain stimulus. RESULTS: Results from task 1 indicated that higher FOP levels were associated with higher pain sensitivity when pain was appraised as a threat, reflected as high FOP group reporting higher pain intensity to those stimuli judged as painful in high threat condition than in low threat condition. Consistently, results from task 2 observed that when noxious stimulus intensity increased to threshold pain and twice threshold pain levels, high FOP group also generally reported higher pain intensity in high threat condition than in low threat condition. However, for both tasks, no such threat level differences were observed in low FOP group. CONCLUSIONS: The current research emphasized that participants with higher FOP level showed pain perceptual biases to specific threatening painful stimulus. Threat appraisal of pain played a key role in the positive association between pain-related fear and pain perceptual biases. SIGNIFICANCE: The findings highlight the modulatory influence of threat appraisal of pain in the positive association between pain-related fear and pain perceptual biases.