Subliminal perception of others' physical pain induces personal distress rather than empathic concern.

BACKGROUND: What is our immediate reaction when we witness someone experiencing pain? The empathy-altruism hypothesis predicts that observers would display empathy and a tendency to approach the person in pain. Alternatively, the threat value of pain hypothesis (TVPH) argues that others' pain serves as a signal of threat and should induce observers' avoidance response. METHODS: To examine these two hypotheses, three experiments were conducted. The experiments aimed to investigate the impact of subliminal exposure to others' physical pain on participants' emotional and behavioural responses. RESULTS: The results revealed that subliminal pain priming resulted in faster response and attentional bias to fearful faces compared to sad faces (Experiment 1), faster reaction times in recognizing fear-related words compared to anger-related words during a lexical decision task (Experiment 2), and faster avoidance responses towards anger-related words, as opposed to approaching responses towards positive words (Experiment 3). CONCLUSIONS: The consistent findings across all experiments revealed that subliminal perception of pain scenes elicited fear emotion and immediate avoidance responses. Therefore, the outcomes of our study provide supportive evidence for the TVPH.

Implicit bias training can remove bias from subliminal stimuli, restoring choice divergence: A proof-of-concept study.

Subliminal information can influence our conscious life. Subliminal stimuli can influence cognitive tasks, while endogenous subliminal neural information can sway decisions before volition. Are decisions inextricably biased towards subliminal information? Or can they diverge away from subliminal biases via training? We report that implicit bias training can remove biases from subliminal sensory primes. We first show that subliminal stimuli biased an imagery-content decision task. Participants (n = 17) had to choose one of two different patterns to subsequently imagine. Subliminal primes significantly biased decisions towards imagining the primed option. Then, we trained participants (n = 7) to choose the non-primed option, via post choice feedback. This training was successful despite participants being unaware of the purpose or structure of the reward schedule. This implicit bias training persisted up to one week later. Our proof-of-concept study indicates that decisions might not always have to be biased towards non-conscious information, but instead can diverge from subliminal primes through training.

Functional correlates of subliminal stimulation in Posttraumatic Stress Disorder: Systematic review and meta-analysis.

Patients with Post-traumatic stress disorder (PTSD) exposed to traumatic reminders show hyperreactivity in brain areas (e.g., amygdala) belonging or related to the Innate Alarm System (IAS), allowing the rapid processing of salient stimuli. Evidence that IAS is activated by subliminal trauma-reminders could shed a new light on the factors precipitating and perpetuating PTSD symptomatology. Thus, we systematically reviewed studies investigating neuroimaging correlates of subliminal stimulation in PTSD. Twenty-three studies were selected from the MEDLINE and Scopus® databases for a qualitative synthesis, 5 of which allowed a further meta-analysis of fMRI data. The intensity of IAS responses to subliminal trauma-related reminders ranged from a minimum in healthy controls to a maximum in the PTSD patients with the most severe (e.g., dissociative) symptoms or the least responsiveness to treatment. Comparisons with other disorders (e.g., phobias) revealed contrasting results. Our findings demonstrate the hyperactivation of areas belonging or related to IAS in response to unconscious threats that should be integrated in diagnostic as well as in therapeutic protocols.

Perceptual and semantic same-different processing under subliminal conditions.

Although other types of subliminal integrative processing are widely refuted by recent studies, subliminal same-different processing (SSDP) remains unchallenged to this day. Using shapes, categorical images, and Chinese characters as stimuli, the current study assessed whether SSDP can occur on a perceptual and semantic basis. Although some significant results were found, the effects are much weaker than previous studies, with Bayes factors suggesting that these effects are not reliable. It is therefore concluded that substantiating claims of SSDP requires more reliable evidence than currently available.

The contribution of subliminal perceptions, dietary habits, and psychological traits to the perception of oral tingling and burning sensations.

The tingling evoked by Sichuan pepper and the burning elicited by chili pepper constitutes the typical flavor of Sichuan cuisine and is a component of leisure food. Although factors affecting the burning sensation have extensively been studied, few studies have examined the factors of individual sensitivity, personality traits, and dietary habits that contribute to the perception of oral tingling sensation, which hinders the formulation of tingling products and the development of new products. In contrast, many studies have examined the factors influencing the burning sensation. In this web-based survey, 68 participants disclosed their dietary habits, liking for tingling and hot foods, and psychological traits. Individual sensitivity to the tingling and burning sensation produced by a range of Sichuan pepper oleoresin and capsaicin solutions was determined using rated differences from control, generalized labeled magnitude scale method and ranking test. The consistency score indicated the accuracy of individual ranking results while also providing an indirect response to the sensitivity of the participant to supra-threshold for burning or tingling. Individual ratings for medium Sichuan pepper oleoresin concentrations significantly correlated with the just noticeable difference (p < 0.01), and ratings for medium and high capsaicin concentrations correlated significantly with 6-n-propylthiouracil ratings (p < 0.01). Notably, the power exponent of burning was significantly correlated with the burning recognition threshold (p < 0.01), and the power exponent of tingling and burning were significantly correlated (r = 0.340, p < 0.05). There was a negative correlation between supra-threshold tingling and burning sensation perceptions and life satisfaction ratings. Further, intensity ratings for oral tingling and burning sensation did not always correspond with individual sensitivity indicators (e.g., recognition threshold, 6-n-propylthiouracil, just noticeable difference, and consistency score). Thus, this study provides new insight into establishing a sensory selection method for chemesthetic sensation panelists and theoretical guidelines for formulation design and in-depth analysis of popular tingling dishes and foods.

Unconscious integration: Current evidence for integrative processing under subliminal conditions.

Integrative processing is traditionally believed to be dependent on consciousness. While earlier studies within the last decade reported many types of integration under subliminal conditions (i.e. without perceptual awareness), these findings are widely challenged recently. This review evaluates the current evidence for 10 types of subliminal integration that are widely studied: arithmetic processing, object-context integration, multi-word processing, same-different processing, multisensory integration and 5 different types of associative learning. Potential methodological issues concerning awareness measures are also taken into account. It is concluded that while there is currently no reliable evidence for subliminal integration, this does not necessarily refute 'unconscious' integration defined through non-subliminal (e.g. implicit) approaches.

Further evidence and theoretical framework for a subliminal sensory buffer store (SSBS).

We recently provided evidence that strongly masked stimuli are not erased or overwritten but are briefly stored in a subliminal sensory buffer store (SSBS), where information can accumulate through repetition and become consciously accessible. SSBS supports a direct prediction made by the global workspace theory of consciousness (GWT) and has implications on discussions about conscious overflow and the problem of the criterion. Here we show that the presentation sequence and the time from the target presentation to evaluation does not significantly impact perception. We suggest that selected information from this subliminal sensory buffer store is transferred into a type of supraliminal short-term memory that keeps stable representations for longer durations with full conscious access. We argue that the level of conscious access of memory storage has a greater impact on subsequent reportability than initial phenomenology and needs to be included more prominently in discussions on perception and consciousness.

The impact of subliminal stimuli on interpersonal trust and team trust.

Although numerous studies related to trust have emerged in recent decades, few studies have explored the impact of subliminal stimuli on trust from an unconscious perspective. This study investigated (a) whether subliminal stimuli could influence interpersonal trust and team trust and (b) whether subjective trust played a mediating role between subliminal stimuli and behavioral trust. It contained two experiments. In Experiment 1, a total of 72 participants took part in a single factor design and completed five tasks. In Experiment 2, a total of 98 participants participated in a single factor design and completed five tasks. Results indicated that subliminal stimuli had a significant impact on interpersonal trust and team trust. Subjective trust played a mediating role between subliminal stimuli and behavioral trust. The results suggest that subliminal priming techniques can influence interpersonal trust and team trust. These techniques first influence subjective trust and then further influence behavioral trust.

Increased sensitivity of insula to supraliminal faces in adults with histories of mood disorders and self-injury.

BACKGROUND: Mood disorders are associated with neurobiological disruptions in subliminal and supraliminal emotion processing. There may be additional variation based on sex and the presence of self-injurious thoughts and behaviors (SITBs). Examining individuals in remission allows us to understand trait-like emotion processing characteristics that persist in the absence of symptoms. This study investigates neural processing in response to supraliminal and subliminal emotional stimuli based upon mood disorder diagnosis, sex, and SITBs. METHODS: Seventy-five participants with a history of any mood disorder (AMD; 52 female) and 27 healthy controls (HC; 14 female) completed a fMRI task presenting subliminal and supraliminal facial stimuli. Within the AMD group, 20 had no history of SITBs, 26 had histories of suicidal ideation only, and 27 had histories of both SI and self-injurious behavior. We examined activation of salience network regions of interest including the amygdala, insula, and subgenual anterior cingulate cortex (sgACC) during the task. RESULTS: AMD showed greater insula activation in response to happy faces relative to sad faces, which was not seen in the HC group. Males exhibited lower insula activation in response to sad faces relative happy faces, a pattern not seen in females. Individuals with SITBs demonstrated a lack of sgACC blunting during supraliminal versus subliminal trials. CONCLUSIONS: We found different patterns of neural responses related to mood disorder status, sex, and SITBs. Findings highlight the importance of considering heterogeneity within diagnoses and examining neurobiological features in the context of remission.

Unconscious information integration: A replication and the role of spatial window in masking experiments.

Consciousness and high-level information integration have commonly been closely related to each other (Baars, 2002; Dehaene & Naccache, 2001; Tononi, 2004). Different results, however, have challenged this assumption by showing that information integration can occur for stimuli presented outside of conscious awareness. More recently, a re-examination of some of the data and different replication attempts questioned these results thereby again suggesting a close link between consciousness and information integration. The current study aimed at (i) replicating another piece of evidence for unconscious information integration and (ii) investigating if the size of the spatial window in which the information to be integrated is presented could explain why unconscious information integration sometimes fails. Results showed a reliable replication so providing further evidence for unconscious information integration in a subliminal priming paradigm. Furthermore, our results revealed that unconscious integration depends on the size of the spatial window in which the information is presented.

A window of subliminal perception.

Under labels such as unconscious processing and subliminal perception, identification of stimuli falling below the subjective threshold (whether truly unconscious or not) has been found remarkably accurate in some experiments while completely at chance in others. Here, we first identify that an apparent window of subliminal perception arises in humans under specific stimulus conditions using different experimental paradigms and analysis methods. We then show that the standard signal detection theory (SDT) model is unable to account for this window and extend it until it is. We finally compare a range of models on empirical data. The models performing best are notable for their absence of hierarchical levels, indicating that the window could be a base property of any phenomenally conscious system. The models explain previously incompatible findings in the literature, and they allow for estimations of peaks in subthreshold perception across the spectrum of stimulus saliency, which may be used in further studies of subliminal perception.

Fast unconscious processing of emotional stimuli in early stages of the visual cortex.

Several cortical and subcortical brain areas have been reported to be sensitive to the emotional content of subliminal stimuli. However, the timing of these activations remains unclear. Our scope was to detect the earliest cortical traces of emotional unconscious processing of visual stimuli by recording event-related potentials (ERPs) from 43 participants. Subliminal spiders (emotional) and wheels (neutral), sharing similar low-level visual parameters, were presented at two different locations (fixation and periphery). The differential (peak-to-peak) amplitude from CP1 (77 ms from stimulus onset) to C2 (100 ms), two early visual ERP components originated in V1/V2 according to source localization analyses, was analyzed via Bayesian and traditional frequentist analyses. Spiders elicited greater CP1-C2 amplitudes than wheels when presented at fixation. This fast effect of subliminal stimulation-not reported previously to the best of our knowledge-has implications in several debates: 1) The amygdala cannot be mediating these effects, 2) latency of other evaluative structures recently proposed, such as the visual thalamus, is compatible with these results, 3) the absence of peripheral stimuli effects points to a relevant role of the parvocellular visual system in unconscious processing.

The unconscious mental inhibiting process of human maximal voluntary contraction.

Human maximal voluntary contraction (MVC) is believed to be limited by neural inhibition. Motivational goal priming alters background states of the motor system, leading to enhanced MVC. However, the mechanisms that determine the constant inhibition of force exertion in the motor system remain unclear. The primary behavioural goal of MVC is maximal voluntary force exertion. The final expected or desired state of this behavioural goal is explicitly demonstrated with words related to physical exertion, such as 'maximal', irrespective of the possibility of demand-like properties in participants' minds, such as attainability and/or desirability of the goal. For the primed maximal goal state, most trial results fail to meet expectations, demonstrating negative affect that, without awareness, contributes to the mentioned inhibitory mechanism underlying MVC. We therefore speculated that the behavioural goal of MVC contributes to neural inhibitory mechanisms underlying MVC. In our study, we used a previously developed paradigm (Takarada and Nozaki in Scientific Reports 8: 10135, 2018) in which subliminal visual priming stimuli such as the physical exertion-related words "perform" and "exert" were presented to 12 healthy participants and were followed by supraliminal words that were the word "maximal" or neutral.We found that when combined with the term 'maximal' in the consciously visible form, the effect of this subliminal motor-goal priming in inducing pupil dilation and stronger action preparation/execution was abolished without conscious awareness. This is the first objective evidence of motor inhibitory effect-predicting patterns of pupil-linked noradrenergic activity as a signature of a type of mental inhibition underlying the MVC behavioural goal.

Separating conscious and unconscious perception in animals.

In a new study, Ben-Haim et al. use subliminal stimuli to separate conscious and unconscious perception in macaques. A programme of this type, using a range of cognitive tasks, is a promising way to look for conscious perception in more controversial cases.

The effect of subliminal incentives on goal-directed eye movements.

Over the last decades, several studies have demonstrated that conscious and unconscious reward incentives both affect performance in physical and cognitive tasks, suggesting that goal pursuit can arise from an unconscious will. Whether the planning of goal-directed saccadic eye movements during an effortful task can also be affected by subliminal reward cues has not been systematically investigated. We employed a novel task where participants made several eye movements back and forth between a fixation point and a number of peripheral targets. The total number of targets visited by the eyes in a fixed amount of time determined participants' monetary gain. The magnitude of the reward at stake was briefly shown at the beginning of each trial and masked by pattern images superimposed in time so that at shorter display durations participants perceived reward incentives subliminally. We found a main effect of reward across all display durations as higher reward enhanced participants' oculomotor effort measured as the frequency and peak velocity of saccades. This effect was strongest for consciously perceived rewards but also occurred when rewards were subliminally perceived. Although we did not find a statistically significant dissociation between the reward-related modulation of different saccadic parameters, across two experiments the most robust effect of subliminal rewards was observed for the modulation of the saccadic frequency but not the peak velocity. These results suggest that multiple indices of oculomotor effort can be incentivized by subliminal rewards and that saccadic frequency may provide the most sensitive indicator of subliminal incentivization of eye movements. NEW & NOTEWORTHY Reward incentives motivate humans to exert more effort, and they do so even when rewards are subconsciously perceived. It has been unknown whether these effects also extend to eye movements that have lower energetic demands compared with other movement types. We devised a behavioral task that required fast execution of multiple eye movements. Subliminal rewards enhanced the frequency and peak velocity of saccadic eye movements, with the most reliable effect observed for saccadic frequency.

Regression to the Mean Does Not Explain Away Nonconscious Processing.

In studies that use subliminal presentations, participants may become aware of stimuli that are intended to remain subliminal. A common solution to this problem is to analyze the results of the group of participants for whom the stimuli remained subliminal. A recent article (Shanks, 2017) argued that this method leads to a regression to the mean artifact, which may account for many of the observed effects. However, conceptual and statistical characteristics of the original publication lead to overestimation of the influence of the artifact. Using simulations, we demonstrate that this overestimation leads to the mistaken conclusion that regression to the mean accounts for nonconscious effects. We conclude by briefly outlining a new description of the influence of the artifact and how it should be statistically addressed.

Diffusion model-based understanding of subliminal affective priming in continuous flash suppression.

Affective states influence our decisions even when processed unconsciously. Continuous flash suppression (CFS) is a new variant of binocular rivalry that can be used to render the prime subliminal. Nonetheless, how prior information from emotional faces suppressed by CFS influences subsequent decision-making remains unclear. Here, we employed a CFS priming task to examine the effect of the two main types of information conveyed by faces, i.e., facial identity and emotion, on the evaluation of target words as positive or negative. The hierarchical diffusion model was used to investigate the underlying mechanisms. A significant interaction effect on response time was observed following the angry face prime but not the happy or neutral face primes. The results of the diffusion model analyses revealed that the priming effects of facial identity were mapped onto the drift rate and erased the 'positive bias' (the processing advantage of positive over negative stimuli). Meanwhile, the positive emotional faces increased the nondecision time in response to negative target words. The model-based analysis implies that both facial identity and emotion are processed under CFS.

Unconscious processing of subliminal stimuli in panic disorder: A systematic review and meta-analysis.

Attentional biases to threat exist in panic disorder (PD), probably related to altered subliminal processing. We systematically reviewed studies investigating subliminal processing in PD. Studies were retrieved from MEDLINE and Scopus®. We meta-analytically compared PD (n = 167) and healthy controls (HC, n = 165) for processing of masked panic-related and neutral words. We also compared subliminal and supraliminal presentations of panic-related words relative to neutral words within PD subjects and HC. We found a significantly enhanced Stroop interference to masked panic-related words in PD vs HC (Hedges' g = 0.60, p = 0.03; Q = 14.83, I2 = 66.3 %, p = 0.01). While both PD subjects and HC tended to be slower to respond to supraliminal threat words than to neutral words, PD subjects only showed a marginally significant slower response to subliminal panic-related words vs neutral words. Findings remain inconclusive regarding comparison to other mental disorders, neural correlates, and the effect of psychotherapy. Even if possibly flawed by methodological weaknesses, our findings support the existence of a sensitivity to subliminal threat cues in PD, which could be targeted to improve treatment.

Subliminal perception is continuous with conscious vision and can be predicted from prestimulus electroencephalographic activity.

Individuals are able to discriminate visual stimuli they report not consciously seeing. This phenomenon is known as "subliminal perception." Such capacity is often assumed to be relatively automatic in nature and rely on stimulus-driven activity in low-level cortical areas. Instead, here we asked to what extent neural activity before stimulus presentation influences subliminal perception. We asked participants to discriminate the location of a briefly presented low-contrast visual stimulus and then rate how well they saw the stimulus. Consistent with previous studies, participants correctly discriminated with slightly above chance-level accuracy the location of a stimulus they reported not seeing. Signal detection analyses indicated that while subjects categorized their percepts as "unconscious," their capacity to discriminate these stimuli lay on the same continuum as conscious vision. We show that the accuracy of discriminating the location of a subliminal stimulus could be predicted with relatively high accuracy (AUC = 0.70) based on lateralized electroencephalographic (EEG) activity before the stimulus, the hemifield where the stimulus was presented, and the accuracy of previous trial's discrimination response. Altogether, our results suggest that rather than being a separate unconscious capacity, subliminal perception is based on similar processes as conscious vision.