Peripheral physiological responses to subliminally presented negative affective stimuli: A systematic review

Serial dependence requires visual awareness: Evidence from continuous flash suppression

The visual system often undergoes a relatively stable perception even in a noisy visual environment. This crucial function was reflected in a visual perception phenomenon-serial dependence, in which recent stimulus history systematically biases current visual decisions. Although serial dependence effects have been revealed in numerous studies, few studies examined whether serial dependence would require visual awareness. By using the continuous flash suppression (CFS) technique to render grating stimuli invisible, we investigated whether serial dependence effects could emerge at the unconscious levels. In an orientation adjustment task, subjects viewed a randomly oriented grating and reported their orientation perception via an adjustment response. Subjects performed a series of three type trial pairs. The first two trial pairs, in which subjects were instructed to make a response or no response toward the first trial of the pairs, respectively, were used to measure serial dependence at the conscious levels; the third trial pair, in which the grating stimulus in the first trial of the pair was masked by a CFS stimulus, was used to measure the serial dependence at the unconscious levels. One-back serial dependence effects for the second trial of the pairs were evaluated. We found significant serial dependence effects at the conscious levels, whether absence (Experiment 1) or presence (Experiment 2) of CFS stimuli, but failed to find the effects at the unconscious levels, corroborating the view that serial dependence requires visual awareness.

Influence of stimulus manipulation on conscious awareness of emotional facial expressions in the match-to-sample paradigm

The conscious perception of emotional facial expressions plays an indispensable role in social interaction. However, previous psychological studies have reported inconsistent findings regarding whether conscious awareness is greater for emotional expressions than for neutral expressions. Furthermore, whether this phenomenon is attributable to emotional or visual factors remains unknown. To investigate these issues, we conducted five psychological experiments to test the conscious perception of emotional and neutral facial expressions using the match-to-sample paradigm. Facial stimuli were momentarily presented in the peripheral visual fields while participants read simultaneously presented letters in the central visual fields. The participants selected a perceived face from nine samples. The results of all experiments demonstrated that emotional expressions were more accurately identified than neutral expressions. Furthermore, Experiment 4 showed that angry expressions were identified more accurately than anti-angry expressions, which expressed neutral emotions with comparable physical changes to angry expressions. Experiment 5, testing the interaction between emotional expression and face direction, showed that angry expressions looking toward participants were more accurately identified than those looking away from participants, even though they were physically identical. These results suggest that the conscious awareness of emotional facial expressions is enhanced by their emotional significance.

Learning emotional dialects: A British population study of cross-cultural communication

The aim of the current research was to explore whether we can improve the recognition of cross-cultural freely-expressed emotional faces in British participants. We tested several methods for improving the recognition of freely-expressed emotional faces, such as different methods for presenting other-culture expressions of emotion from individuals from Chile, New Zealand and Singapore in two experimental stages. In the first experimental stage, in phase one, participants were asked to identify the emotion of cross-cultural freely-expressed faces. In the second phase, different cohorts were presented with interactive side-by-side, back-to-back and dynamic morphing of cross-cultural freely-expressed emotional faces, and control conditions. In the final phase, we repeated phase one using novel stimuli. We found that all non-control conditions led to recognition improvements. Morphing was the most effective condition for improving the recognition of cross-cultural emotional faces. In the second experimental stage, we presented morphing to different cohorts including own-to-other and other-to-own freely-expressed cross-cultural emotional faces and neutral-to-emotional and emotional-to-neutral other-culture freely-expressed emotional faces. All conditions led to recognition improvements and the presentation of freely-expressed own-to-other cultural-emotional faces provided the most effective learning. These findings suggest that training can improve the recognition of cross-cultural freely-expressed emotional expressions.

"The many faces of sorrow": An empirical exploration of the psychological plurality of sadness

Sadness has typically been associated with failure, defeat and loss, but it has also been suggested that sadness facilitates positive and restructuring emotional changes. This suggests that sadness is a multi-faceted emotion. This supports the idea that there might in fact be different facets of sadness that can be distinguished psychologically and physiologically. In the current set of studies, we explored this hypothesis. In a first stage, participants were asked to select sad emotional faces and scene stimuli either characterized or not by a key suggested sadness-related characteristic: loneliness or melancholy or misery or bereavement or despair. In a second stage, another set of participants was presented with the selected emotional faces and scene stimuli. They were assessed for differences in emotional, physiological and facial-expressive responses. The results showed that sad faces involving melancholy, misery, bereavement and despair were experienced as conferring dissociable physiological characteristics. Critical findings, in a final exploratory design, in a third stage, showed that a new set of participants could match emotional scenes to emotional faces with the same sadness-related characteristic with close to perfect precision performance. These findings suggest that melancholy, misery, bereavement and despair can be distinguishable emotional states associated with sadness.

Emotional arousal does not modulate stimulus-response binding and retrieval effects

The adaptation-by-binding account and the arousal-biased competition model suggest that emotional arousal increases binding effects for transient links between stimuli and responses. Two highly-powered, pre-registered experiments tested whether transient stimulus-response bindings are stronger for high versus low arousing stimuli. Emotional words were presented in a sequential prime-probe design in which stimulus relation, response relation, and stimulus arousal were orthogonally manipulated. In Experiment 1 (N = 101), words with high and low arousal levels were presented individually in prime and probe displays. In Experiment 2 (N = 170), a high arousing affective word was presented simultaneously with a neutral word during the prime display; in the subsequent probe display, either the arousing or the neutral word repeated or a different high versus low arousal word was shown. Data from both experiments did not demonstrate a modulation of SRBR effects by stimulus arousal and SRBR effects were of equal magnitude for word stimuli of high and low arousal levels. These null results are not in line with binding accounts that hypothesise a modulatory influence of emotional arousal on perception-action binding.

A systematic review of the literature on interpretation bias and its physiological correlates

An important, yet under-explored area of interpretation bias research concerns the examination of potential physiological correlates and sequalae of this bias. Developing a better understanding of the physiological processes that underpin interpretation biases will extend current theoretical frameworks underlying interpretation bias, as well as optimising the efficacy of cognitive bias modification for interpretation (CBM-I) interventions aimed at improving symptoms of emotional disorders. To this end, systematic searches were conducted across the Web of Science, PsycInfo and Pubmed databases to identify physiological markers of interpretation bias. In addition, grey literature database searches were conducted to compliment peer-reviewed research and to counter publication bias. From a combined initial total of 898 records, 15 studies were included in qualitative synthesis (1 of which obtained from the grey literature). Eligible studies were assessed using a quality assessment tool adapted from the Quality Checklist for Healthcare Intervention Studies. The searches revealed seven psychophysiological markers of interpretation bias, namely event-related potentials, heart rate and heart rate variability, respiratory sinus arrythmia, skin conductance response, pupillometry, and electromyography. The respective theoretical and practical implications of the research are discussed, followed by recommendations for future research.

"There Is No (Where a) Face Like Home": Recognition and Appraisal Responses to Masked Facial Dialects of Emotion in Four Different National Cultures

The theory of universal emotions suggests that certain emotions such as fear, anger, disgust, sadness, surprise and happiness can be encountered cross-culturally. These emotions are expressed using specific facial movements that enable human communication. More recently, theoretical and empirical models have been used to propose that universal emotions could be expressed via discretely different facial movements in different cultures due to the non-convergent social evolution that takes place in different geographical areas. This has prompted the consideration that own-culture emotional faces have distinct evolutionary important sociobiological value and can be processed automatically, and without conscious awareness. In this paper, we tested this hypothesis using backward masking. We showed, in two different experiments per country of origin, to participants in Britain, Chile, New Zealand and Singapore, backward masked own and other-culture emotional faces. We assessed detection and recognition performance, and self-reports for emotionality and familiarity. We presented thorough cross-cultural experimental evidence that when using Bayesian assessment of non-parametric receiver operating characteristics and hit-versus-miss detection and recognition response analyses, masked faces showing own cultural dialects of emotion were rated higher for emotionality and familiarity compared to other-culture emotional faces and that this effect involved conscious awareness.

Individual conscious and unconscious perception of emotion: Theory, methodology and applications

In this manuscript we review a seminal debate related to subliminality and concerning the relationship of consciousness, unconsciousness, and perception. We present the methodological implementations that contemporary psychology introduced to explore this relationship, such as the application of unbiased self-report metrics and Bayesian analyses for assessing detection and discrimination. We present evidence concerning an unaddressed issue, namely, that different participants and stimulus types require different thresholds for subliminal presentation. We proceed to a step-by-step experimental illustration of a method involving individual thresholds for the presentation of masked emotional faces. We show that individual thresholds provide Bayesian evidence for null responses to the presented faces. Conversely, we show in the same database that when applying established but biased non-individual criteria for subliminality physiological changes occur and relate - correctly, and most importantly incorrectly - to perception concerning the emotional type, and the valence and intensity of a presented masked emotional face.

Degree and Complexity of Non-conscious Emotional Information Processing - A Review of Masked Priming Studies

Whether and to what degree information can be processed non-consciously has been a matter of debate since the emergence of psychology as a science. Emotional information, in particular, has often been assumed to have a privileged status because of its relevance for well-being and survival (e.g., to detect a threat). Indeed, many studies have explored non-conscious processing of evaluative (i.e., "emotional" in a broad sense) or emotional (e.g., facial expressions) features using the "silver bullet" of non-consciousness research - the masked sequential priming paradigm. In its prototypical form, this paradigm involves the categorization of target stimuli according to valence (e.g., is the target positive or negative?). Each target is preceded by a briefly presented prime that is followed by a mask to constrain awareness. Non-conscious processing is inferred from subtle influences of the prime on target processing, that is, whether responses are faster if prime and target are valence-congruent or not. We will review this research with a focus on three questions: first, which methods are used in this area to establish non-conscious processing? Second, is there evidence for non-conscious extraction of evaluative information? Third, is there evidence for non-conscious processing beyond a simple valence (positive/negative) discrimination, for example, processing of emotion-specific information? We will highlight important current debates and potential directions in which the field will move in the future.

Valuing what happens: a biogenic approach to valence and (potentially) affect

Valence is half of the pair of properties that constitute core affect, the foundation of emotion. But what is valence, and where is it found in the natural world? Currently, this question cannot be answered. The idea that emotion is the body's way of driving the organism to secure its survival, thriving and reproduction runs like a leitmotif from the pathfinding work of Antonio Damasio through four book-length neuroscientific accounts of emotion recently published by the field's leading practitioners. Yet while Damasio concluded 20 years ago that the homeostasis-affect linkage is rooted in unicellular life, no agreement exists about whether even non-human animals with brains experience emotions. Simple neural animals-those less brainy than bees, fruit flies and other charismatic invertebrates-are not even on the radar of contemporary affective research, to say nothing of aneural organisms. This near-sightedness has effectively denied the most productive method available for getting a grip on highly complex biological processes to a scientific domain whose importance for understanding biological decision-making cannot be underestimated. Valence arguably is the fulcrum around which the dance of life revolves. Without the ability to discriminate advantage from harm, life very quickly comes to an end. In this paper, we review the concept of valence, where it came from, the work it does in current leading theories of emotion, and some of the odd features revealed via experiment. We present a biologically grounded framework for investigating valence in any organism and sketch a preliminary pathway to a computational model. This article is part of the theme issue 'Basal cognition: conceptual tools and the view from the single cell'.

"Speak of the Devil… and he Shall Appear": Religiosity, Unconsciousness, and the Effects of Explicit Priming in the Misperception of Immorality

Psychological theory and research suggest that religious individuals could have differences in the appraisal of immoral behaviours and cognitions compared to non-religious individuals. This effect could occur due to adherence to prescriptive and inviolate deontic religious-moral rules and socio-evolutionary factors, such as increased autonomic nervous system responsivity to indirect threat. The latter thesis has been used to suggest that immoral elicitors could be processed subliminally by religious individuals. In this manuscript, we employed masking to test this hypothesis. We rated and pre-selected IAPS images for moral impropriety. We presented these images masked with and without negatively manipulating a pre-image moral label. We measured detection, moral appraisal and discrimination, and physiological responses. We found that religious individuals experienced higher responsivity to masked immoral images. Bayesian and hit-versus-miss response analyses revealed that the differences in appraisal and physiological responses were reported only for consciously perceived immoral images. Our analysis showed that when a negative moral label was presented, religious individuals experienced the interval following the label as more physiologically arousing and responded with lower specificity for moral discrimination. We propose that religiosity involves higher conscious perceptual and physiological responsivity for discerning moral impropriety but also higher susceptibility for the misperception of immorality.

Inducing Unconscious Stress

Abstract. Stress-related stimuli may be presented outside of awareness and may ultimately influence health by causing repetitive increases in physiological parameters, such as blood pressure (BP). In this study, we aimed to corroborate previous studies that demonstrated BP effects of subliminally presented stress-related stimuli. This would add evidence to the hypothesis that unconscious manifestations of stress can affect somatic health. Additionally, we suggest that these findings may be extended by measuring affective changes relating to these physiological changes, using measures for self-reported and implicit positive and negative affectivity. Using a repeated measures between-subject design, we presented either the prime word “angry” ( n = 26) or “relax” ( n = 28) subliminally (17 ms) for 100 trials to a student sample and measured systolic and diastolic BP, heart rate (HR), and affect. The “angry” prime, compared to the “relax” prime, did not affect any of the outcome variables. During the priming task, a higher level of implicit negative affect (INA) was associated with a lower systolic BP and diastolic BP. No association was found with HR. Self-reported affect and implicit positive affect were not related to the cardiovascular (CV) activity. In sum, anger and relax primes elicited similar CV activity patterns, but implicit measures of affect may provide a new method to examine the relationship between (unconscious) stress and health.

"The Harder One Tries …": Findings and Insights From the Application of Covert Response Pressure Assessment Technology in Three Studies of Visual Perception

In this article, we present a force measuring method for assessing participant responses in studies of visual perception. We present a device disguised as a mouse pad and designed to measure mouse-click-pressure and click-press-to-release-time responses by unaware, as regards to the physiological assessment, participants. The aim of the current technology, in the current studies, was to provide a physiological assessment of confidence and task difficulty. We tested the device in three experiments. The studies comprised of a gender-recognition study using morphed male and female faces, a visual suppression study using backwards masking, and a target-search study that included deciding whether a letter was repeated in a subsequently presented letter string. Across all studies, higher task difficulty was associated with higher click-release-time responses. Higher task difficulty was, intriguingly, also associated with lower click pressure. Higher confidence ratings were consistently associated with higher click pressure and shorter click-release time across all experiments. These findings suggest that the current technology can be used to assess responses relating to task difficulty and participant confidence in studies of visual perception. We suggest that the assessment of release times can also be implemented using standard equipment, and we provide manual and easy-to-use code for the implementation.

The mere physical presence of another person reduces human autonomic responses to aversive sounds

Social animals show reduced physiological responses to aversive events if a conspecific is physically present. Although humans are innately social, it is unclear whether the mere physical presence of another person is sufficient to reduce human autonomic responses to aversive events. In our study, participants experienced aversive and neutral sounds alone (alone treatment) or with an unknown person that was physically present without providing active support. The present person was a member of the participants' ethnical group (ingroup treatment) or a different ethnical group (outgroup treatment), inspired by studies that have found an impact of similarity on social modulation effects. We measured skin conductance responses (SCRs) and collected subjective similarity and affect ratings. The mere presence of an ingroup or outgroup person significantly reduced SCRs to the aversive sounds compared with the alone condition, in particular in participants with high situational anxiety. Moreover, the effect was stronger if participants perceived the ingroup or outgroup person as dissimilar to themselves. Our results indicate that the mere presence of another person was sufficient to diminish autonomic responses to aversive events in humans, and thus verify the translational validity of basic social modulation effects across different species.

Decreased electrodermal activity in patients with epilepsy

OBJECTIVE

Biofeedback therapy using electrodermal activity (EDA) is a new noninvasive therapy for intractable epilepsy. However, the characteristics of EDA in patients with epilepsy are little known; therefore, we assessed the EDA characteristics in patients with epilepsy.

METHODS

A cross-sectional observational study was conducted in 22 patients with epilepsy and 24 healthy individuals. We collected information on demographic characteristics, EDA, and state anxiety from both groups, and epilepsy diagnosis, seizure number per month, disease duration, and number of antiepileptic drugs (AED) from the epilepsy group. A wristband device was used to measure resting EDA from both wrists for 10 min under controlled temperature and humidity. We compared the EDA levels between the epilepsy group and the control group and examined correlations between EDA and epilepsy-associated factors in the epilepsy group.

RESULTS

A decreasing trend in EDA was observed during the first 1 min from the start of the measurement in 22 patients with epilepsy (with or without seizures) compared with healthy controls (P = 0.12). However, a significant decrease in EDA was found in 18 patients with epilepsy with seizures compared with healthy controls (-0.48 versus -0.26; P = 0.036). Furthermore, seizure frequency showed a significant inverse correlation with EDA in the epilepsy group (ρ = -0.50, P = 0.016). However, neither disease duration nor the number of drugs prescribed correlated with EDA in the epilepsy group .

SIGNIFICANCE

Marginally decreased EDA was observed in patients with epilepsy, and significantly decreased EDA was found in patients with a higher seizure frequency. The present findings shed light on the appropriateness of EDA-biofeedback therapy in epilepsy.

Increased blood pressure during the suggested immobilization test in Restless Legs Syndrome

Objective

To investigate the relationship between sensory discomfort/motor component and cardiovascular autonomic response by continuous beat-to-beat blood pressure monitoring (CBPM) during the suggested immobilization test (SIT) in patients with restless legs syndrome (RLS).

Methods

Thirty-two drug-free patients with primary RLS (10 men; mean age 60.29 ± 10.81 years) and 17 healthy controls (2 men; mean age 58.82 ± 11.86 years) underwent a 1-hour SIT starting at 8 pm with concomitant CBPM to measure the heart rate (HR) and systolic/diastolic blood pressure (SBP, DBP). In all subjects, the presence of sensory discomfort and motor component during the SIT (S-SIT+ and M-SIT+, respectively) was quantified. Mixed regression models were used to compare the SBP, DBP, and HR profiles during the SIT by taking into account the repeated measures (6 time periods of 10 minutes).

Results

In patients with S-SIT+ (n = 17), SBP (p < 0.0001), DBP (p = 0.0007), and HR (p = 0.03) increased during the SIT compared with other patients and controls. Seventeen patients had M-SIT+ (none among healthy controls). Classifying patients in 4 groups in function of the presence/absence of the SIT sensory and motor components revealed that SDB and DBP increased throughout the SIT in patients with S-SIT+, independently of the motor component (p < 0.0001 and p = 0.0008 for SBD; p < 0.0001 and p = 0.01 for DBP in the S-SIT+/M-SIT− and S-SIT+/M-SIT+ groups, respectively).

Conclusion

During the SIT, BP concomitantly increased only in patients with RLS and sensory discomfort, with or without motor component. This highlights the link between evening sensory RLS symptoms, autonomic activation, and potential long-term cardiovascular consequences.

Beauty Is in the Eye of the Beholder: The Appraisal of Facial Attractiveness and Its Relation to Conscious Awareness

Previous research suggests that facial attractiveness relies on features such as symmetry, averageness and above-average sexual dimorphic characteristics. Due to the evolutionary and sociobiological value of these characteristics, it has been suggested that attractiveness can be processed in the absence of conscious awareness. This raises the possibility that attractiveness can also be appraised without conscious awareness. In this study, we addressed this hypothesis. We presented neutral and emotional faces that were rated high, medium and low for attractiveness during a pilot experimental stage. We presented these faces for 33.33 ms with backwards masking to a black and white pattern for 116.67 ms and measured face-detection and emotion-discrimination performance, and attractiveness ratings. We found that high-attractiveness faces were detected and discriminated more accurately and rated higher for attractiveness compared with other appearance types. A Bayesian analysis of signal detection performance indicated that faces were not processed significantly at-chance. Further assessment revealed that correct detection (hits) of a presented face was a necessary condition for reporting higher ratings for high-attractiveness faces. These findings suggest that the appraisal of attractiveness requires conscious awareness.

Heart rate variability response to affective pictures processed in and outside of conscious awareness: Three consecutive studies on emotional regulation

Previous research has increased understanding of the neurobiological basis of emotional regulation. However, less is known concerning the unconscious processing of affective information. Three experiments were performed to investigate the extent to which complex affective stimuli can be processed outside of consciousness and demonstrate possible mechanisms for regulation of resulting emotional responses. In Experiment 1, participants were either instructed to passively observe blocked-picture cues (neutral and negative) or to downregulate their emotions by distancing. Resulting emotional regulation activity was assessed with 0.1-Hz heart rate variability (HRV) indices. In Experiment 2, participants were presented with affective pictures that were rendered consciously invisible by means of continuous flash suppression (CFS). In Experiment 3, two equivalent sets of negative affective pictures were covertly presented and the effect of a cognitive task on emotional regulation was evaluated. Our findings revealed that 0.1-Hz HRV indices exhibited greater change over baseline in response to negative compared to neutral stimuli for both presentation conditions (consciously perceived or not). The implementation of distancing and the cognitive task were both associated with higher 0.1-Hz HRV change scores. These results indicate that even complex affective stimuli can be processed without awareness, resulting in a congruent emotional response that is physiologically detectable. Cognitive strategies can help more effectively regulate this response, implying that conscious perception of a triggering stimulus may not be essential for cognitive regulation.

Generalized Unsafety Theory of Stress: Unsafe Environments and Conditions, and the Default Stress Response

Prolonged physiological stress responses form an important risk factor for disease. According to neurobiological and evolution-theoretical insights the stress response is a default response that is always "on" but inhibited by the prefrontal cortex when safety is perceived. Based on these insights the Generalized Unsafety Theory of Stress (GUTS) states that prolonged stress responses are due to generalized and largely unconsciously perceived unsafety rather than stressors. This novel perspective necessitates a reconstruction of current stress theory, which we address in this paper. We discuss a variety of very common situations without stressors but with prolonged stress responses, that are not, or not likely to be caused by stressors, including loneliness, low social status, adult life after prenatal or early life adversity, lack of a natural environment, and less fit bodily states such as obesity or fatigue. We argue that in these situations the default stress response may be chronically disinhibited due to unconsciously perceived generalized unsafety. Also, in chronic stress situations such as work stress, the prolonged stress response may be mainly caused by perceived unsafety in stressor-free contexts. Thus, GUTS identifies and explains far more stress-related physiological activity that is responsible for disease and mortality than current stress theories.

Skin Conductance Responses to Masked Emotional Faces Are Modulated by Hit Rate but Not Signal Detection Theory Adjustments for Subjective Differences in the Detection Threshold

The biological preparedness model suggests that survival-related visual cues elicit physiological changes without awareness to enable us to respond to our environment. Previous studies have reported some evidence for this effect. In the current article, we argue that this evidence is subject to methodological confounds. These include the use of a universal masked presentation threshold, the employment of hit rates (HRs) to measure meta-awareness, and the assertion of overall guess-level target detection using nonsignificance. In the current report, we address these issues and test whether masked emotional faces can elicit changes in physiology. We present participants with subjectively adjusted masked angry, fearful, happy, and neutral faces using HRs and signal detection theory. We assess detection performance using a strict Bayesian criterion for meta-awareness. Our findings reveal that HR adjustments in the detection threshold allow higher skin conductance responses to happy, fearful, and angry faces, but that this effect could not be reported by the same participants when the adjustments were made using signal detection measures. Combined these findings suggest that very brief biologically relevant stimuli can elicit physiological changes but cast doubt to the extent that this effect can occur in response to truly unconscious emotional faces.