Variability in response criteria affects estimates of conscious identification and unconscious semantic priming

Three experiments examined the role of response criteria in a masked semantic priming paradigm using an exclusion task. Experiment 1 used on-line prime-report ("report the prime if you saw it") and exclusion instructions in which participants were told to avoid completing a word stem (e.g. mo-) with a word related to a prime (e.g. cash) flashed for 0, 38 or 212ms. Semantic priming (i.e. exclusion failure) was significant in the items analysis, but was moderated by peoples' ability to report the prime in the participant analysis. Prime-report thresholds in Experiment 2 were made more liberal by instructing participants to guess on every trial. Prime-report increased from Experiment 1 as exclusion failures were eliminated. Experiment 3 clarified the relationship between awareness and prime identification using an on-line measure of confidence and different liberal prime report instructions. The current findings suggest that the ability to act upon (via exclusion performance) and report information in a masked prime is determined by a variable response criterion, which can be manipulated as an independent variable.

Exploring the temporal dynamics of visual word recognition in the masked repetition priming paradigm using event-related potentials

The present study used event-related potentials (ERPs) to examine the time-course of visual word recognition in a masked repetition priming paradigm. In two experiments, participants monitored a stream of words for occasional animal names, and ERPs were recorded to non-animal critical target items that were either repetitions or were unrelated to the immediately preceding masked prime word. In Experiment 1, the onset interval between the prime and target (stimulus-onset-asynchrony--SOA) was manipulated across four levels (60, 180, 300 and 420 ms) and the duration of primes was held constant at 40 ms. In Experiment 2, the SOA between the prime and target was held constant at 60 ms and the prime duration was manipulated across four levels (10, 20, 30 and 40 ms). Both manipulations were found to have distinct effects on the N250 and N400 ERP components. The results provide converging evidence that the N250 reflects processing at the level of form representations (orthography and phonology) while the N400 reflects processing at the level of meaning.

Subliminal words durably affect neuronal activity

Unconscious mental representations elicited by subliminal stimuli are marked by their fleeting lifetimes, usually below 1 s. Can such evanescent subliminal stimuli, nevertheless, lead to long-lasting learning? To date, evidence suggesting a long-term influence of briefly perceived stimuli on behaviour or brain activity is scarce and questionable. In this study, we used intracranial recordings to provide the first direct demonstration that unconsciously perceived subliminal words could exert long-lasting effects on neuronal signals. When repeating subliminal words over long interstimulus intervals, we observed electrophysiological repetition effects. These unconscious repetition effects suggest that the single presentation of a masked word can durably affect neural architecture.

Exploring consciousness in emotional face decoding: an event-related potential analysis

The author analyzed the role of consciousness in emotional face comprehension. The author recorded psychophysiological measures of event-related potentials (ERPs), elicited by supraliminal and subliminal stimuli when participants viewed emotional facial expressions of 4 emotions or neutral stimuli. The author analyzed an ERP emotion-specific effect (N200 peak variation; temporal interval was 180-300 ms poststimulus) in terms of peak amplitude and latency variables. The results indicated 4 important findings. First, there was an emotional-specific ERP deflection only for emotional stimuli, not for neutral stimuli. Second, the unaware information processing was quite similar to that of aware in terms of peak morphology, but not in terms of latency. In fact, unconscious stimulation produced a more delayed peak variation than did conscious stimulation. Third, valence of facial stimulus (positive or negative) was supraliminally and subliminally decoded because it was showed by differences of peak deflection between negative high arousing (fear and anger) and low arousing (happiness, sadness, and neutral) stimuli. Finally, the author found a more posterior distribution of ERP as a function of emotional content of the stimulus. Cortical lateralization (right or left) was not correlated to conscious or unconscious stimulation. The author discussed the functional significance of her results in terms of supraliminal and subliminal conditions.

Social anxiety predicts unconsciously provoked emotional responses to facial expression

Previous psychometric studies using a visual search task suggested that interpersonal fear in individuals with social anxiety disorder (SAD) may be processed by unconscious preattentive mechanisms. However, little is known about relationships between social anxiety and preattentive emotional responses. We explored whether social anxiety is associated with preattentive emotional responses to facial expression. Groups with high and low social anxiety were selected from 125 healthy volunteers according to scores on the Social Phobia Inventory. Fearful and happy faces were presented subliminally using backward masking, with skin conductance responses (SCRs) being measured as an autonomic index of emotional responses. SCRs to these two facial expressions were compared between groups. The group with high social anxiety showed significantly greater differences in SCRs between masked fearful and happy faces than the group with low social anxiety. Social anxiety was associated with unconscious autonomic responses to fearful faces. A preattentive interpersonal threat evaluation system may be an important factor in SAD.

Automatic texture segmentation in early vision: evidence from priming experiments

Texture segmentation is usually regarded as a fast, early, automatic, preattentive process. Nevertheless, naive participants in texture segmentation tasks are usually not able to perform the task explicitly when the textures are presented rather briefly (49 ms) and subsequently masked. In two experiments it was investigated whether texture stimuli were, nevertheless, automatically segmented under these conditions. By using a priming paradigm, the processing of the texture stimuli was measured indirectly via their influence on a subsequently presented imperative stimulus. Priming effects were found for experienced and naive participants, although novices could not respond overtly to the textures in a subsequent forced-choice task. Although textures influenced subsequent stimulus processing, an analysis of the simultaneously recorded lateralized readiness potential (LRP) showed that they did not cause automatic response activation. The existence of priming effects of textures without participants' ability to overtly respond to them can be regarded as evidence for the automatic segmentation of texture stimuli.

Backward masking: evidence of reduced subcortical amygdala engagement in autism

Recent data suggest that subthreshold presentation of emotional information is relayed to the amygdala along subcortical pathways. We examined the effect of backward masked neutral and anxious faces on the social decisions of a group of high functioning children with autism ages 7-13 years and matched controls. Participants were asked to select the friendliest of two faces, one of which was associated with the subthreshold (33 ms) presentation of an anxious face (A/N) and the other a subthreshold neutral face (N/N). Neutral paired faces were selected more often than A/N paired faces by both groups. However, children with autism selected significantly fewer N/N stimuli and more A/N stimuli than controls. These results suggest that the social choices of children with autism were influenced less by emotional information presented subconsciously and suggest a subcortical contribution to the social/emotional processing deficits observed in autism.

Face processing without awareness in the right fusiform gyrus

We investigated brain activity evoked by faces which were not consciously perceived by subjects. Subdural electrophysiological recordings and functional neuroimaging studies have each demonstrated face-specific processing in the fusiform gyrus (FFG) of humans. Using pattern masks, a stimulus can be presented but not consciously perceived, and thus can be used to assay obligatory or automatic processes. Here, using event-related functional magnetic resonance imaging and pattern masking, we observed that masked faces but not masked objects activated the right FFG. Other regions activated by consciously perceived unmasked faces were not activated when faces were masked. These data provide strong evidence for an automatic face-processing region in the right FFG.

Dissociable effects of bottom-up and top-down factors on the processing of unattended fearful faces

While the role of attention in determining the neural fate of unattended emotional items has been investigated in the past, it remains unclear whether bottom-up and top-down factors have differential effects in shaping responses evoked by such stimuli. To study the effects of bottom-up and top-down factors on the processing of neutral and fearful faces, we employed functional magnetic resonance imaging (fMRI) while participants performed attentional tasks that manipulated these factors. To probe the impact of top-down mechanisms on the processing of face distractors, target letters either had to be found among several distinct nontarget letters (attentional load condition) or among identical nontarget letters (baseline condition). To probe the impact of bottom-up factors, we decreased the salience of the targets by reducing their size and contrast relative to baseline (salience condition). Our findings revealed that bottom-up and top-down manipulations produced dissociable effects on amygdala and fusiform gyrus responses to fearful-face distractors when task difficulty was equated. When the attentional load of the main task was high, weaker responses were evoked by fearful-face distractors relative to baseline during the early trials. By contrast, decreasing target salience resulted in increased responses relative to baseline. The present findings suggest that responses evoked by unattended fearful faces are modulated by several factors, including attention and stimulus salience.

On-line control of pointing is modified by unseen visual shapes

Shapes that are rendered invisible through backward masking are still able to influence motor responses: this is called masked priming. Yet it is unknown whether this influence is on the control of ongoing action, or whether it merely influences the initiation of an already-programmed action. We modified a masked priming procedure (Schmidt, 2002) such that the critical prime-mask sequence was displayed during the execution of an already-initiated goal-directed pointing movement. Psychophysical tests of prime visibility indicated that the identity of the prime shapes were not accessible to participants for conscious report. Yet detailed kinematic analysis of the finger in motion revealed that masked primes had an influence on the pointing trajectories within 277ms of their appearance, 56ms earlier than the trajectory deviations observed in response to the visible masks. These results indicate that subliminal shapes can indeed influence the control of ongoing motor activity.

Nice wor_ if you can get the wor_: Subliminal semantic and form priming in fragment completion

Two experiments investigated subliminal semantic and form priming in a word-completion task. Visual gap-words with a dominant and a subordinate solution were preceded by form-related or by semantically related words, which were briefly presented and sandwich-masked. Priming of the subordinate solution was assessed in Experiment 1, relative to a neutral condition. Both solutions were primed in Experiment 2. In the absence of conscious prime recognition, both semantic and form primes reliably increased the probability with which the primed solution was given. With our variant of fragment-completion, response priming can be ruled out as explanation. Moreover, effects were already present at first presentation, excluding an interpretation in terms of partial awareness due to massive repetition. The data demonstrate automatic activation at both form and semantic levels in the absence of conscious awareness.

How the brain translates money into force: a neuroimaging study of subliminal motivation

Unconscious motivation in humans is often inferred but rarely demonstrated empirically. We imaged motivational processes, implemented in a paradigm that varied the amount and reportability of monetary rewards for which subjects exerted physical effort. We show that, even when subjects cannot report how much money is at stake, they nevertheless deploy more force for higher amounts. Such a motivational effect is underpinned by engagement of a specific basal forebrain region. Our findings thus reveal this region as a key node in brain circuitry that enables expected rewards to energize behavior, without the need for the subjects;awareness.

Hypervigilance in patients with borderline personality disorder: Specificity, automaticity, and predictors

According to cognitive theory, an important factor in borderline personality disorder (BPD) is hypervigilance. The aim of the present study was to test whether BPD patients show schema-related biases, and to explore relations with childhood trauma, schemas, and BPD symptoms. Sixteen BPD patients were compared with 18 patients with a cluster C personality disorder, 16 patients with an axis I disorder, and 16 normal controls. An emotional Stroop task was applied with schema-related and unrelated, negative and positive, supra- and subliminal person-related stimuli. BPD patients showed hypervigilance for both negative and positive cues, but were specifically biased towards schema-related negative cues. Predictors were BPD schemas, childhood sexual traumas, and BPD anxiety symptoms. Both BPD and axis I disorder patients showed a trend for a bias for negative schema-related subliminal stimuli. More attention to hypervigilance in BPD is recommended for clinical practice.

Vertical asymmetries in pre-attentive detection of changes in motion direction

Stimulus localization affects visual motion processing. Vertical asymmetries favouring lower visual field have been reported in event-related potentials (ERPs) and behavioural studies under different attention conditions. However, there are no studies examining such asymmetries to non-attended motion changes. The present study investigated whether the asymmetry in processing information from the upper and lower visual fields also affects the automatic detection of motion-direction changes as indexed by visual Mismatch Negativity (vMMN). We recorded vMMN to changes in sinusoidal gratings differing in motion direction presented in the periphery of visual field in three different locations: upper and lower (ULVF), upper (UVF) and lower (LVF) along the vertical meridian. The N2 component elicited to peripheral motion presented lower amplitudes when the UVF was stimulated. The vMMN elicited to infrequent motion-direction changes was present in all stimulation conditions. However, it was reduced to UVF stimulation. These results suggest that the visual system automatically detects motion-direction changes presented at both upper-lower visual fields; however they also indicate that the process is favoured when stimuli are presented in the LVF alone.

Inverse target- and cue-priming effects of masked stimuli

The processing of a visual target that follows a briefly presented prime stimulus can be facilitated if prime and target stimuli are similar. In contrast to these positive priming effects, inverse priming effects (or negative compatibility effects) have been found when a mask follows prime stimuli before the target stimulus is presented: Responses are facilitated after dissimilar primes. Previous studies on inverse priming effects examined target-priming effects, which arise when the prime and the target stimuli share features that are critical for the response decision. In contrast, 3 experiments of the present study demonstrate inverse priming effects in a nonmotor cue-priming paradigm. Inverse cue-priming effects exhibited time courses comparable to inverse target-priming effects. Results suggest that inverse priming effects do not arise from specific processes of the response system but follow from operations that are more general.

Amygdala reactivity predicts automatic negative evaluations for facial emotions

The amygdala is a key structure in a limbic circuit involved in the rapid and unconscious processing of facial emotions. In the present study, the role of the amygdala in automatic, involuntary appraisal processes, which are believed to be a crucial component of emotion processing, was investigated in 23 healthy subjects. Amygdala activity was recorded in response to masked displays of angry, sad, and happy facial expressions using functional magnetic resonance imaging (fMRI). In a subsequent experiment, the subjects performed a masked affective priming task that characterizes automatic emotion processing by investigating the biasing effect of subliminally presented emotional faces on evaluative ratings to subsequently presented neutral stimuli. In the affective priming task, significant valence-congruent evaluation manipulation was observed. Subjects rated neutral targets more positively if they were primed by happy faces. Significant correlations were found between amygdala responses to masked negative facial expressions and negative evaluation shifts elicited by the corresponding emotion quality in the affective priming task. Spontaneous amygdala reactivity to facial emotions appears to be a determinant of automatic negative evaluative response tendencies. This finding might shed some light on how amygdala hyperresponsivity contributes to negative cognitive biases commonly observed in affective disorders.

Can one suppress subliminal words?

Subliminal words cause behavioral priming, yet the depth of their processing remains debated. Using transcranial magnetic stimulation (TMS), Nakamura et al. demonstrate in this issue of Neuron that this subliminal priming effect can be selectively disrupted. Distinct TMS sites disrupt priming in lexical decision and pronunciation tasks, suggesting that task set influences subliminal processing.

Intact subliminal processing and delayed conscious access in multiple sclerosis

Periventricular white matter damage affecting large bundles connecting distant cortical areas may constitute the main neuronal mechanism for the deficit of controlled information processing observed in patients with early multiple sclerosis (MS). Visual backward masking has been demonstrated to affect late stages of conscious perception involving long-range interactions between visual perceptual areas and higher level integrative cortices while leaving intact early feed-forward visual processing and even complex processing such as object recognition or semantic processing. We therefore hypothesized that patients with early MS would have an elevated masking threshold, because of an impairment of conscious perception whereas subliminal processing of masked stimuli would be preserved. Twenty-two patients with early MS and 22 normal controls performed two backward-masking experiments. We used Arabic digits as stimuli and varied quasi-continuously the temporal interval with a subsequent mask, thus allowing us to progressively "unmask" the stimuli. We finely quantified the visibility of the masked stimuli using both objective and subjective measures, thus obtaining accurate estimates of the threshold duration for access to consciousness. We also studied the priming effect caused by the variably masked numbers on a comparison task performed on a subsequently presented and highly visible target number. The threshold for access to consciousness of masked stimuli was elevated in MS patients compared to controls, whereas non-conscious processing of these stimuli, as measured by priming, was preserved. These findings suggest that conscious access to masked stimuli depends on the integrity of large-scale cortical integrative processes, which involve long-distance white matter projections, and are impaired due to diffuse demyelinating injury in patients with early MS.

The magic spell of language: Linguistic categories and their perceptual consequences

Language is a tool that directs attention to different aspects of reality. Using participants from the same linguistic community, the authors demonstrate in 4 studies that metasemantic features of linguistic categories influence basic perceptual processes. More specifically, the hypothesis that abstract versus concrete language leads to a more global versus local perceptual focus was supported across 4 experiments, in which participants used (Experiment 1) or were primed either supraliminally (Experiments 2 and 3) or subliminally (Experiment 4) with abstract (adjectives) or concrete (verbs) terms. Participants were shown to display a global versus specific perceptual focus (Experiments 1 and 4), more versus less inclusiveness of categorization (Experiments 2 and 3), and incorporation of more rather than less contextual information (Experiment 3). The implications of this new perspective toward the language-perception interface are discussed in the context of the general linguistic relativity debate.

Cancer and the threat of death: The cognitive dynamics of death-thought suppression and its impact on behavioral health intentions

Five studies examined the cognitive association between thoughts of cancer and thoughts of death and their implication for screening intentions. Study 1 found that explicit contemplation of cancer did not increase death-thought accessibility. In support of the hypothesis that this reflects suppression of death-related thoughts, Study 2 found that individuals who thought about cancer exhibited elevated death-thought accessibility under high cognitive load, and Study 3 demonstrated that subliminal primes of the word cancer led to increased death-thought accessibility. Study 4 revealed lower levels of death-thought accessibility when perceived vulnerability to cancer was high, once again suggesting suppression of death-related thoughts in response to conscious threats associated with cancer. Study 5 extended the analysis by finding that after cancer salience, high cognitive load, which presumably disrupts suppression of the association between cancer and death, decreased cancer-related self-exam intentions. Theoretical and practical implications for understanding terror management, priming and suppression, and responses to cancer are discussed.

Accessory stimuli modulate effects of nonconscious priming

In a recent study, it was shown that subliminal priming (SP) effects are affected by the temporal predictability of a stimulus onset. If predictability is not given, SP effects are eliminated (Naccache, Blandin, & Dehaene, 2002). In two experiments, we investigated how different levels of preparation for target processing affect SP effects. For this purpose, an accessory tone stimulus was presented at different times prior to a subliminal priming task. The results demonstrate a clear modulation of the SP effects at different foreperiod intervals. Relative to conditions without an accessory stimulus, SP effects were smaller for short foreperiod intervals of the accessory stimulus, and larger for long foreperiod intervals. The results suggest that the presentation of an accessory stimulus facilitates response activation processes because of the participants' enhanced level of preparation for stimulus processing.

No difference between conscious and nonconscious visuomotor control: evidence from perceptual learning in the masked prime task

Negative compatibility effects (NCEs) in the masked-prime paradigm are usually obtained when primes are masked effectively. With ineffective masks-and primes above the perceptual threshold-positive compatibility effects (PCEs) occur. We investigated whether this pattern reflects a causal relationship between conscious awareness and low-level motor control, or whether it reflects the fact that both are affected in the same way by changes in physical stimulus attributes. In a 5-session perceptual learning task, participants learned to consciously identify masked primes. However, they showed unaltered NCEs that were not different from those produced by participants in a control group without equivalent perceptual learning. A control experiment demonstrated that no NCEs occur when prime identification is made possible by ineffective masking. The results suggest that perceptual awareness and low-level motor control are affected by the same factors, but are fundamentally independent of each other.

Critique of Sohlberg and Birgegard's (2003) report of persistent complex effects of subliminal psychodynamic activation messages

Silverman in 1983 held that the unconscious encoding of MOMMY AND I ARE ONE triggers a fantasy of symbiotic union with the good mother of early childhood. In contrast, later Sohlberg and Birgegard contended that MOMMY AND I triggers associations to similarity issues with mother, associations that may be influenced by the words following MOMMY AND I. Although their messages produce, lmost invariably, no reportable sensation, Sohlberg and Birgegard claimed strong evidence for the influence of such messages on perception, motivation, and memory, 10 ays poststimulation and suggestive evidence 4 mo. later. Their findings are not compelling evidence for these claims; and there is no evidence that any result was associated with the unconscious encoding of the psychodynamic meaning of a multiword message.

Preserved subliminal processing and impaired conscious access in schizophrenia

BACKGROUND

Studies of visual backward masking have frequently revealed an elevated masking threshold in schizophrenia. This finding has frequently been interpreted as indicating a low-level visual deficit. However, more recent models suggest that masking may also involve late and higher-level integrative processes, while leaving intact early bottom-up visual processing.

OBJECTIVE

To test the hypothesis that the backward-masking deficit in schizophrenia corresponds to a deficit in the late stages of conscious perception, whereas the subliminal processing of masked stimuli is fully preserved.

DESIGN

Twenty-eight patients with schizophrenia and 28 normal control subjects performed 2 backward-masking experiments. We used Arabic digits as stimuli and varied quasi-continuously the interval with a subsequent mask, thus allowing us to progressively unmask the stimuli. We finely quantified their degree of visibility using objective and subjective measures to evaluate the threshold duration for access to consciousness. We also studied the priming effect caused by the variably masked numbers in a comparison task performed on a subsequently presented and highly visible target number.

RESULTS

The threshold delay between the digit and mask necessary for the conscious perception of the masked stimulus was longer in patients compared with controls. This higher consciousness threshold in patients was confirmed by an objective and a subjective measure, and both measures were highly correlated for the patients and controls. However, subliminal priming of masked numbers was effective and identical in patients and controls.

CONCLUSIONS

Access to conscious report of masked stimuli is impaired in schizophrenia, whereas fast bottom-up processing of the same stimuli, as assessed by subliminal priming, is preserved. These findings suggest a high-level origin of the masking deficit in schizophrenia, although they leave open for further research its exact relation to previously identified bottom-up visual processing abnormalities.