Effects of emotional and non-emotional cues on visual search in neglect patients: Evidence for distinct sources of attentional guidance

Perception of emotional facial expressions in aggression and psychopathy

BACKGROUND

Altered affective state recognition is assumed to be a root cause of aggressive behavior, a hallmark of psychopathologies such as psychopathy and antisocial personality disorder. However, the two most influential models make markedly different predictions regarding the underlying mechanism. According to the integrated emotion system theory (IES), aggression reflects impaired processing of social distress cues such as fearful faces. In contrast, the hostile attribution bias (HAB) model explains aggression with a bias to interpret ambiguous expressions as angry.

METHODS

In a set of four experiments, we measured processing of fearful and angry facial expressions (compared to neutral and other expressions) in a sample of 65 male imprisoned violent offenders rated using the Hare Psychopathy Checklist-Revised (PCL-R, Hare, R. D. (1991). The psychopathy checklist-revised. Toronto, ON: Multi-Health Systems) and in 60 age-matched control participants.

RESULTS

There was no evidence for a fear deficit in violent offenders or for an association of psychopathy or aggression with impaired processing of fearful faces. Similarly, there was no evidence for a perceptual bias for angry faces linked to psychopathy or aggression. However, using highly ambiguous stimuli and requiring explicit labeling of emotions, violent offenders showed a categorization bias for anger and this anger bias correlated with self-reported trait aggression (but not with psychopathy).

CONCLUSIONS

These results add to a growing literature casting doubt on the notion that fear processing is impaired in aggressive individuals and in psychopathy and provide support for the idea that aggression is related to a hostile attribution bias that emerges from later cognitive, post-perceptual processing stages.

The impact of attention bias modification training on behavioral and physiological responses

Attention bias modification training aims to alter attentional deployment to symptom-relevant emotionally salient stimuli. Such training has therapeutic applications in the management of disorders including anxiety, depression, addiction and chronic pain. In emotional reactions, attentional biases interact with autonomically-mediated changes in bodily arousal putatively underpinning affective feeling states. Here we examined the impact of attention bias modification training on behavioral and autonomic reactivity. Fifty-eight participants were divided into two groups. A training group (TR) received attention bias modification training to enhance attention to pleasant visual information, while a control group (CT) performed a procedure that did not modify attentional bias. After training, participants performed an evaluation task in which pairs of emotional and neutral images (unpleasant-neutral, pleasant-neutral, neutral-neutral) were presented, while behavioral (eye movements) and autonomic (skin conductance; heart rate) responses were recorded. At the behavioral level, trained participants were faster to orientate attention to pleasant images, and slower to orientate to unpleasant images. At the autonomic level, trained participants showed attenuated skin conductance responses to unpleasant images, while stronger skin conductance responses were generally associated with higher anxiety. These data argue for the use of attentional training to address both the attentional and the physiological sides of emotional responses, appropriate for anxious and depressive symptomatology, characterized by atypical attentional deployment and autonomic reactivity.

Influence of Multimodal Emotional Stimulations on Brain Activity: An Electroencephalographic Study

This study aimed to reveal the influence of emotional valence and sensory modality on neural activity in response to multimodal emotional stimuli using scalp EEG. In this study, 20 healthy participants completed the emotional multimodal stimulation experiment for three stimulus modalities (audio, visual, and audio-visual), all of which are from the same video source with two emotional components (pleasure or unpleasure), and EEG data were collected using six experimental conditions and one resting state. We analyzed power spectral density (PSD) and event-related potential (ERP) components in response to multimodal emotional stimuli, for spectral and temporal analysis. PSD results showed that the single modality (audio only/visual only) emotional stimulation PSD differed from multi-modality (audio-visual) in a wide brain and band range due to the changes in modality and not from the changes in emotional degree. The most pronounced N200-to-P300 potential shifts occurred in monomodal rather than multimodal emotional stimulations. This study suggests that emotional saliency and sensory processing efficiency perform a significant role in shaping neural activity during multimodal emotional stimulation, with the sensory modality being more influential in PSD. These findings contribute to our understanding of the neural mechanisms involved in multimodal emotional stimulation.

Task relevance and negative reward modulate the disengagement deficit of patients with spatial neglect

Though motivational value is a recognized trigger of approach and avoidance behavior, less is known about the potential of reward to capture attention. We here explored whether positive or negative reward modulates the characteristic deficit of patients with left spatial neglect to disengage attention from an ipsilesional distracter. We built our study on recent observations showing that the disengagement deficit is exaggerated for distracters with target-defining features, indicating that task-relevance captures attention. Patients with left neglect and matched healthy controls were asked to react to lateralized, colored targets preceded by a peripheral cue. Crucially, the cue either possessed the color of the target and was thus task-relevant, or was followed by a positive, negative, or neutral symbolic reward. Neglect patients only exhibited a disengagement deficit when cues were task-relevant or were followed by a negative reward. This finding indicates that attentional selection is driven by task-relevance and negative reward, possibly through interactions between limbic and attention networks.

Amygdala function in emotion, cognition, and behavior

The amygdala is a core structure in the anterior medial temporal lobe, with an important role in several brain functions involving memory, emotion, perception, social cognition, and even awareness. As a key brain structure for saliency detection, it triggers and controls widespread modulatory signals onto multiple areas of the brain, with a great impact on numerous aspects of adaptive behavior. Here we discuss the neural mechanisms underlying these functions, as established by animal and human research, including insights provided in both healthy and pathological conditions.

Emotion-Attention Interaction in the Right Hemisphere

Hemispheric asymmetries in affective and cognitive functions have been extensively studied. While both cerebral hemispheres contribute to most affective and cognitive processes, neuroscientific literature and neuropsychological evidence support an overall right hemispheric dominance for emotion, attention and arousal. Emotional stimuli, especially those with survival value such as threat, tend to be prioritized in attentional resource competition. Arousing unpleasant emotional stimuli have prioritized access, especially to right-lateralized attention networks. Interference of task performance may be observed when limited resources are exhausted by task- and emotion-related processing. Tasks that rely on right hemisphere-dependent processing, like attending to the left visual hemifield or global-level visual features, are especially vulnerable to interference due to attention capture by unpleasant emotional stimuli. The aim of this review is to present literature regarding the special role of the right hemisphere in affective and attentional brain processes and their interaction. Furthermore, clinical and technological implications of this interaction will be presented. Initially, the effects of focal right hemisphere lesion or atrophy on emotional functions will be introduced. Neurological right hemisphere syndromes including aprosodia, anosognosia and neglect, which further point to the predominance of the intact right hemisphere in emotion, attention and arousal will be presented. Then there will be a brief review of electrophysiological evidence, as well as evidence from patients with neglect that support attention capture by emotional stimuli in the right hemisphere. Subsequently, experimental work on the interaction of emotion, attention and cognition in the right hemispheres of healthy subjects will be presented. Finally, clinical implications for better understanding and assessment of alterations in emotion-attention interaction due to brain disorder or treatment, such as neuromodulation, that impact affective brain functions will be discussed. It will be suggested that measuring right hemispheric emotion-attention interactions may provide basis for novel biomarkers of brain health. Such biomarkers allow for improved diagnostics in brain damage and disorders and optimized treatments. To conclude, future technological applications will be outlined regarding brain physiology-based measures that reflect engagement of the right hemisphere in affective and attentional processes.

Attention orientation to pleasantness and depressive symptomatology predict autonomic reactivity

Depression is characterised by attentional bias to emotional information and dysregulated autonomic reactivity. Despite its relevance to understanding depressive mechanisms, the association between attentional bias and autonomic reactivity to emotional information remains poorly characterised. This study compared behavioural and autonomic responses to emotional images in 32 participants in whom subclinical depressive symptomatology was quantified using the Beck Depression Inventory. Pairs of emotional and neutral images (unpleasant-neutral, U-N; pleasant-neutral, P-N; neutral-neutral, N-N) were presented while attentional indices (eye movements) and autonomic activity (skin conductance responses, SCRs; heart rate, HR) were recorded. Results showed that all recorded ocular parameters indicated a preferential orientation and maintenance of attention to emotional images. SCRs were associated with a valence effect on fixation latency: lower fixation latency to pleasant stimuli leads to lower SCRs whereas the opposite was observed for unpleasant stimuli. Finally, stepwise linear regression analysis revealed that latency of fixation to pleasant images and scores of depression predicted SCRs of participants. Thus, our research reveals an association between autonomic reactivity and attentional bias to pleasant information, on the one hand, and depressive symptomatology on the other. Present findings therefore suggest that depressive individuals may benefit from attention training towards pleasant information in association with autonomic biofeedback procedures.

Autonomic reactivity to emotion: A marker of sub-clinical anxiety and depression symptoms?

Anxiety and depression are both characterized by dysregulated autonomic reactivity to emotion. However, most experiments until now have focused on autonomic reactivity to stimuli presented in central vision (CV) even if affective saliency is also observed in peripheral vision (PV). We compared autonomic reactivity to CV and PV emotional stimulation in 58 participants with high anxious (HA) or low anxious (LA) and high depressive (HD) or low depressive (LD) symptomatology, based on STAI-B and BDI scores, respectively. Unpleasant (U), pleasant (P), and neutral (N) pictures from IAPS were presented at three eccentricities (0°: CV; -12 and 12°: PV). Skin conductance (SC), skin temperature, pupillary diameter, and heart rate (HR) were recorded. First, HA participants showed greater pupil dilation to emotional than to neutral stimuli in PV than in CV. Second, in contrast to HD, the valence effect indexed by SC and emotional arousal effect indexed by skin temperature were observed in LD. Third, both anxiety and depression lead to a valence effect indexed by pupillary light reflex and heart rate. These results suggest a hyperreactivity to emotion and hypervigilance to PV in anxiety. Depression is associated with an attenuation of positive effect and a global blunted autonomic reactivity to emotion. Moreover, anxiety mostly modulates the early processes of autonomic reactivity whereas depression mainly affects the later processes. The differential impact of emotional information over the visual field suggests the use of new stimulation strategies in order to attenuate anxious and depressive symptoms.

Keeping an eye on visual search patterns in visuospatial neglect: A systematic review

Patients with visuospatial neglect exhibit a failure to detect, respond, or orient towards information located in the side of space opposite to their brain lesion. To extend our understanding of the underlying cognitive processes involved in neglect, some studies have used eye movement measurements to complement behavioural data. We provide a qualitative synthesis of studies that have used eye-tracking in patients with neglect, with a focus on highlighting the utility of examining eye movements and reporting what eye-tracking has revealed about visual search patterns in these patients. This systematic review includes twenty studies that met the eligibility criteria. We extracted information pertaining to patient characteristics (e.g., age, type of stroke, time since stroke), neglect test(s) used, type of stimuli (e.g., static, dynamic), eye-tracker specifications (e.g., temporal and spatial resolution), and eye movement measurements (e.g., saccade amplitude, fixation duration). Five key themes were identified. First, eye-tracking is a useful tool to complement pen-and-paper neglect tests. Second, the lateral asymmetrical bias in eye movement patterns observed during active exploration also occurred while at rest. Third, the lateral asymmetrical bias was evident not only in the horizontal plane but also in the vertical plane. Fourth, eye movement patterns were modulated by stimulus- and task-related factors (e.g., visual salience, local perceptual features, image content, stimulus duration, presence of distractors). Fifth, measuring eye movements in patients with neglect is useful for determining and understanding other cognitive impairments, such as spatial working memory. To develop a fuller, and a more accurate, picture of neglect, future research would benefit from eye movement measurements.

Impaired emotional biases in visual attention after bilateral amygdala lesion

It is debated whether the amygdala is critical for the emotional modulation of attention. While some studies show reduced attentional benefits for emotional stimuli in amygdala-damaged patients, others report preserved emotional effects. Various factors may account for these discrepant findings, including the temporal onset of the lesion, the completeness and severity of tissue damage, or the extent of neural plasticity and compensatory mechanisms, among others. Here, we investigated a rare patient with focal acute destruction of bilateral amygdala and adjacent hippocampal structures after late-onset herpetic encephalitis in adulthood. We compared her performance in two classic visual attention paradigms with that of healthy controls. First, we tested for any emotional advantage during an attentional blink task. Whereas controls showed better report of fearful and happy than neutral faces on trials with short lags between targets, the patient showed no emotional advantage, but also globally reduced report rates for all faces. Second, to ensure that memory disturbance due to hippocampal damage would not interfere with report performance, we also used a visual search task with either emotionally or visually salient face targets. Although the patient still exhibited efficient guided search for visually salient, non-emotional faces, her search slopes for emotional versus neutral faces showed no comparable benefit. In both tasks, however, changes in the patient predominated for happy more than fear stimuli, despite her normal explicit recognition of happy expressions. Our results provide new support for a causal role of the amygdala in emotional facilitation of visual attention, especially under conditions of increasing task-demands, and not limited to negative information. In addition, our data suggest that such deficits may not be amenable to plasticity and compensation, perhaps due to sudden and late-onset damage occurring in adulthood.

Impaired visual search with paradoxically increased facilitation by emotional features after unilateral pulvinar damage

Posterior thalamic pulvinar nuclei have been implicated in different aspects of spatial attention, but their exact role in humans remain unclear. Most neuropsychological studies of attention deficits after pulvinar lesion have concerned single patients or small samples. Here we examined a group of 13 patients with focal damage to posterior thalamus on a visual search task with faces, allowing us to test several hypotheses concerning pulvinar function in controlling attention to visually salient or emotionally significant stimuli. Our results identified two subgroups of thalamic patients with distinct patterns of attentional responsiveness to emotional and colour features in face targets. One group with lesions located in anterior and ventral portions of thalamus showed intact performance, with a normal facilitation of visual search for faces with emotional (fearful or happy) expressions on both side of space, similar to healthy controls. By contrast, a second group showed a slower and poorer detection of face targets, most severe for neutral faces, but with a paradoxically enhanced facilitation by both colour and emotional features. This second group had lesions centred on the pulvinar, involving mainly the dorso-medial sectors in patients showing enhanced effects of colour features, but extending to more dorso-lateral sectors in those with enhanced effects of emotional features. These findings reveal that pulvinar nuclei are not critical for orienting attention to emotionally or visually salient features, but instead provide new evidence in support of previous hypotheses suggesting an important role in controlling attention in visual scenes with distracting information.

Value-driven attentional capture in neglect

OBJECTIVE

Recent studies suggest that motivational cues such as rewards may be a powerful determinant of attentional selection, both in healthy subjects and in brain-damaged patients suffering from neglect. However, the exact brain mechanisms underlying these effects and their relation to other well-known attentional systems are still poorly known.

METHODS

We designed a visual search paradigm to examine how value-based attentional priority could modulate spatial orienting in patients with pathological biases due to neglect after right hemispheric stroke. Targets were preceded by exogenous valid or invalid spatial cues, in the presence or absence of distractors that were associated with high reward values subsequent to an initial reinforcement training phase.

RESULTS

We found that the learned reward value of distractors interfered with spatial reorienting toward the left (neglected) side when neglect patients were invalidly cued to the right side. Moreover, the presence of reward-associated distractors in the contralesional field interfered most with the detection of task-relevant targets on the same side, and this interference was exaggerated with more severe neglect. Voxelwise anatomical lesion analysis indicated that damage to the right angular gyrus, as well as lateral occipital and inferior temporal areas of the right hemisphere, were associated with stronger value-driven attentional effects.

CONCLUSIONS

Visual stimuli previously associated with rewards receive higher attentional priority during visual search despite pathological spatial biases due to neglect, and thus interfere with orienting to contralesional targets, presumably by competing with top-down mechanisms controlling exogenous spatial attention. Reward signals may bias neural activity evoked by visual stimuli, independent of conscious control, through a common priority map integrating several different attentional influences. These results do not only provide novel insights to link spatial orienting and motivational signals within current models of attention, but also open new perspectives that may usefully be exploited for neurological rehabilitation strategies in patients suffering from attentional deficits and neglect.

People look at the object they fear: oculomotor capture by stimuli that signal threat

It is known that people covertly attend to threatening stimuli even when it is not beneficial for the task. In the current study we examined whether overt selection is affected by the presence of an object that signals threat. We demonstrate that stimuli that signal the possibility of receiving an electric shock capture the eyes more often than stimuli signalling no shock. Capture occurred even though the threat-signalling stimulus was neither physically salient nor task relevant at any point during the experiment. Crucially, even though fixating the threat-related stimulus made it more likely to receive a shock, results indicate that participants could not help but doing it. Our findings indicate that the presence of a stimulus merely signalling the possibility of receiving a shock is prioritised in selection, and exogenously captures the eyes even when this ultimately results in the execution of the threat (i.e. receiving a shock). Oculomotor capture was particularly pronounced for the fastest saccades which is consistent with the idea that threat influences visual selection at an early stage of processing, when selection is mainly involuntarily.

Human field of regard, field of view, and attention bias

BACKGROUND AND OBJECTIVE

Human field of regard (FOR) is an important concept that should be considered along with field of view (FOV) for people with/without handicaps, but previous studies have neglected this aspect of human perception. In the current study, we suggest and test a new virtual reality (VR) software with which to evaluate individual's detection abilities in the human FOR.

METHODS

We conducted measurements of human FOV, FOR, and FOR with visual cue (FOR-cue), and we evaluated healthy adults' responses in a first experiment. Participants were asked to detect targets on a head-mounted display (HMD) as quickly as possible in three conditions: (a) FOV: the head rotation doesn't change the view of the screen in the HMD; (b) FOR: the head rotation changes the view of the screen in the HMD; and (c) FOR-cue: same with the FOR condition but an endogenous visual cue indicating the direction of stimulus. To address the need to increase the number of trials in the FOR condition, we also conducted a second experiment with new samples and four times of trial numbers.

RESULTS

The participants' detection time results indicated that the FOV condition was faster than the FOR-cue and FOR conditions, and the FOR-cue was faster than the FOR condition. Interestingly, we found a unique characteristic in the FOR conditions that did not exist in the FOV condition: The target responses were faster for the left side than the right side. The results of the second experiment were consistent with the first, and head motion trajectory analysis showed that participants had more movement toward the left side than the right side in the early parts of each trial.

CONCLUSIONS

In this study, we suggested a new virtual reality (VR) evaluation technique and measured the human searching pattern in the FOR condition. We found a unique left-side attention bias in the FOR condition, and discussed implication of these results and potential attention bias factors. We believe this work is an important foundation for interactive 3D UI design, and we hope it will help people who have FOR handicaps.

Influence of Colour Lightness Differences in Patients With Left Unilateral Spatial Neglect

We used desk-based tasks to evaluate and clarify the effects of colour lightness differences (Liebmann effect) in patients with left unilateral spatial neglect (USN) following stroke. Participants were 30 adults with USN (16 men and 14 women; mean age = 72.3 years, SD = 8.9 years). They took the ‘Letter Cancellation Test’ of the Japanese version of the Behavioral Inattention Test using two types of paper: black letters with a yellow background (‘black on yellow’) and red letters with a green background (‘red on green’). They also took the Line Bisection Test and their laterality index (LI) was also determined. Paired t-tests were computed comparing the LI by colour displays. LI was higher for ‘black on yellow’ than for ‘red on green’ in patients with mild left USN. However, LI for ‘red on green’ was higher in patients with severe left USN. Colour lightness differences are likely on the left side in patients with relatively mild left USN, but not in those with severe left USN.

Effects of lateralized light flash and color on unilateral neglect

PURPOSE

Bottom-up-based sensory stimulation has been useful in promoting recovery from post-stroke neglect. Light and color are salient stimuli for guiding our orienting behaviors and influence the degree of spatial bias. This study evaluated the effects of lateralized light flash and color on spatial bias in unilateral neglect (UN).

METHOD

We enrolled 15 individuals with UN as a consequence of a right hemispheric stroke of less than 65 d. This was a 3 × 3 design study with three conditions of lens color (colorless, red, and blue) and three conditions of flash light locations (no flash, left, and right).

RESULTS

All participants showed a decrease in ipsilesional spatial bias under left-side light flash and a red lens. Right-side light flash and a blue lens induced more rightward bias than other conditions.

CONCLUSIONS

This evidence confirms the use of sensory stimulation to complement post-stroke UN remediation. Lateralized light flash to the contralesional space and red-colored lenses have beneficial effects on amelioration of UN, whereas ipsilesional light flash and the color blue may exacerbate ipsilesional spatial bias in stroke survivors with UN. Implications for Rehabilitation Contralesional light flash and the color red may ameliorate ipsilesional spatial bias in stroke survivors with unilateral neglect (UN). Ipsilesional flash of light and the color blue may worsen ipsilesional spatial bias in stroke survivors with UN.

Immediate effects of exposure to positive and negative emotional stimuli on visual search characteristics in patients with unilateral neglect

The performance of patients with unilateral neglect (UN) in tasks demanding visual attention is characterized by contralesional disadvantage which is markedly unstable in magnitude. Such instability of the attentional system is seen very clearly in clinical practice and thus far has no satisfying explanation. Here we examined the immediate effect of exposure to non-lateralized emotional stimuli on UN patients' attentional bias and performance variability. We tested eight right-hemisphere damaged stroke patients with left-sided neglect and eight age-matched healthy subjects in a visual conjunction-search task, each trial performed immediately after viewing a centrally-presented picture, which was emotionally negative, positive or neutral. Both performance bias and variability in performing the search task was analyzed as a function of the valence of the picture, and a method for analyzing reaction time (RT) variance in a small sample is introduced. Overall, UN subjects, but not controls, were slower and more variable in their RT for left- compared to right-sided targets. In the UN group, detecting left-sided targets was significantly slower in trials that followed presentation of negative pictures as compared to positive pictures, regardless of the fact that both picture types were judged as equally arousing by the patients. Moreover, UN patients exhibited larger performance variance on the left then on the right, and negative emotional stimuli were associated with larger variance asymmetry than positive emotional stimuli. Examining the coefficient of variation pointed to a possible dissociation between the effects of emotional stimuli on the lateralized RT mean (reflecting attentional bias) and on the lateralized RT variance (reflecting system instability). We conclude that emotional stimuli affect the spatial imbalance of both performance speed and stability in UN patients.

Pleasant music improves visual attention in patients with unilateral neglect after stroke

OBJECTIVE

To investigate whether listening to pleasant music improves visual attention to and awareness of contralesional stimuli in patients with unilateral neglect after stroke.

METHODS

A within-subject design was used with 19 participants with unilateral neglect following a right hemisphere stroke. Participants were tested in three conditions (pleasant music, unpleasant music and white noise) within 1 week. All musical pieces were chosen by the participants. In each condition, participants were asked to complete three sub-tests of the Behavioural Inattention Test (the Star Cancellation Test, the Line Bisection Test and the Picture Scanning test) and a visual exploration task with everyday scenes. Eye movements in the visual exploration task were recorded simultaneously. Mood and arousal induced by different auditory stimuli were assessed using visual analogue scales, heart rate and galvanic skin response.

RESULTS

Compared with unpleasant music and white noise, participants rated their moods as more positive and arousal as higher with pleasant music, but also showed significant improvement on all tasks and eye movement data, except the Line Bisection Test.

CONCLUSION

The findings suggest that pleasant music can improve visual attention in patients with unilateral neglect after stroke. Additional research using randomized controlled trials is required to validate these findings.

Trait anxiety and perceptual load as determinants of emotion processing in a fear conditioning paradigm

The impact of trait anxiety and perceptual load on selective attention was examined in a fear conditioning paradigm. A fear-conditioned angry face (CS+), an unconditioned angry face (CS-), or an unconditioned face with a neutral or happy expression were used in distractor interference and attentional probe tasks. In Experiments 1 and 2, participants classified centrally presented letters under two conditions of perceptual load. When perceptual load was high, distractors had no effect on selective attention, even with aversive conditioning. However, when perceptual load was low, strong response interference effects for CS+ face distractors were found for low trait-anxious participants. Across both experiments, this enhanced distractor interference reversed to strong facilitation effects for those reporting high trait anxiety. Thus, high trait-anxious participants were faster, rather than slower, when ignoring CS+ distractors. Using an attentional probe task in Experiment 3, it was found that fear conditioning resulted in strong attentional avoidance in a high trait-anxious group, which contrasted with enhanced vigilance in a low trait-anxious group. These results demonstrate that the impact of fear conditioning on attention is modulated by individual variation in trait anxiety when perceptual load is low. Fear conditioning elicits an avoidance of threat-relevant stimuli in high trait-anxious participants.

Brain mechanisms for emotional influences on perception and attention: what is magic and what is not

The rapid and efficient selection of emotionally salient or goal-relevant stimuli in the environment is crucial for flexible and adaptive behaviors. Converging data from neuroscience and psychology have accrued during the last decade to identify brain systems involved in emotion processing, selective attention, and their interaction, which together act to extract the emotional or motivational value of sensory events and respond appropriately. An important hub in these systems is the amygdala, which may not only monitor the emotional value of stimuli, but also readily project to several other areas and send feedback to sensory pathways (including striate and extrastriate visual cortex). This system generates saliency signals that modulate perceptual, motor, as well as memory processes, and thus in turn regulate behavior appropriately. Here, we review our current views on the function and properties of these brain systems, with an emphasis on their involvement in the rapid and/or preferential processing of threat-relevant stimuli. We suggest that emotion signals may enhance processing efficiency and competitive strength of emotionally significant events through gain control mechanisms similar to those of other (e.g. endogenous) attentional systems, but mediated by distinct neural mechanisms in amygdala and interconnected prefrontal areas. Alterations in these brain mechanisms might be associated with psychopathological conditions, such as anxiety or phobia. We conclude that attention selection and awareness are determined by multiple attention gain control systems that may operate in parallel and use different sensory cues but act on a common perceptual pathway.

A tale of two negatives: differential memory modulation by threat-related facial expressions

Facial expressions serve as cues that encourage viewers to learn about their immediate environment. In studies assessing the influence of emotional cues on behavior, fearful and angry faces are often combined into one category, such as "threat-related," because they share similar emotional valence and arousal properties. However, these expressions convey different information to the viewer. Fearful faces indicate the increased probability of a threat, whereas angry expressions embody a certain and direct threat. This conceptualization predicts that a fearful face should facilitate processing of the environment to gather information to disambiguate the threat. Here, we tested whether fearful faces facilitated processing of neutral information presented in close temporal proximity to the faces. In Experiment 1, we demonstrated that, compared with neutral faces, fearful faces enhanced memory for neutral words presented in the experimental context, whereas angry faces did not. In Experiment 2, we directly compared the effects of fearful and angry faces on subsequent memory for emotional faces versus neutral words. We replicated the findings of Experiment 1 and extended them by showing that participants remembered more faces from the angry face condition relative to the fear condition, consistent with the notion that anger differs from fear in that it directs attention toward the angry individual. Because these effects cannot be attributed to differences in arousal or valence processing, we suggest they are best understood in terms of differences in the predictive information conveyed by fearful and angry facial expressions.

Additive effects of emotional, endogenous, and exogenous attention: behavioral and electrophysiological evidence

Selective attention is not a unitary construct, but is composed of several processes. Attention selection may be guided by low-level stimulus properties, by the emotional value of the stimulus, or more voluntarily by the goals and plans of the observer. Whether these three systems operate independently during attention selection or not remains a debated question. We report results from two studies investigating the extent to which these different attention mechanisms may interact with one another. Using a standard dot probe paradigm wherein effects of exogenous, emotional, and endogenous attention were orthogonally manipulated, we found attentional facilitation effects for each component, indicated by faster decision times for validly, as opposed to invalidly cued targets. Moreover, results confirmed that these three attentional effects added up in a linear fashion. Complementing ERP results allowed us to disentangle the respective contributions of the two reflexive, bottom-up attention processes (exogenous vs. emotional) by showing non-overlapping temporal loci for attentional effects related either to low-level physical properties or the emotional content of the stimulus. These findings suggest that multiple separate attention mechanisms can operate simultaneously to yield a rapid and efficient visual processing of various classes of potentially relevant stimuli.

[Functional neuroimaging of neglect]

Though the neglect syndrome is often observed in clinical practice, there are few studies investigating its mechanisms or developing new therapeutic approaches. Most studies on attention were conducted in healthy subjects. In this paper I provide functional neuroimaging data about functional networks for stimuli perception independently from their modality. Additionally, the restoration of stimulus perception and its modulation through emotion are discussed.

Does emotion processing require attention? The effects of fear conditioning and perceptual load

This study examined the impact of perceptual load on the processing of unattended threat-relevant faces. Participants performed a central letter-classification task while ignoring irrelevant face distractors, which appeared above or below the central task. The face distractors were graded for affective salience by means of aversive fear conditioning, with a conditioned angry face (CS+), an unconditioned angry face (CS-), and a neutral control face. The letter-classification task was presented under conditions of both low and high perceptual load. Results showed that fear conditioned (i.e., CS+) angry face distractors interfered with task performance more than CS- angry or neutral face distractors but that this interference was completely eliminated by high perceptual load. These findings demonstrate that aversively conditioned face distractors capture attention only under conditions of low perceptual load.

Emotional attention in acquired prosopagnosia

The present study investigated whether emotionally expressive faces guide attention and modulate fMRI activity in fusiform gyrus in acquired prosopagnosia. Patient PS, a pure case of acquired prosopagnosia with intact right middle fusiform gyrus, performed two behavioral experiments and a functional imaging experiment to address these questions. In a visual search task involving face stimuli, PS was faster to select the target face when it was expressing fear or happiness as compared to when it was emotionally neutral. In a change detection task, PS detected significantly more changes when the changed face was fearful as compared to when it was neutral. Finally, an fMRI experiment showed enhanced activation to emotionally expressive faces and bodies in right fusiform gyrus. In addition, PS showed normal body-selective activation in right fusiform gyrus, partially overlapping the fusiform face area. Together these behavioral and neuroimaging results show that attention was preferentially allocated to emotional faces in patient PS, as observed in healthy subjects. We conclude that systems involved in the emotional guidance of attention by facial expression can function normally in acquired prosopagnosia, and can thus be dissociated from systems involved in face identification.