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Face evaluation is thought to play a vital role in human social interactions. One prominent aspect is the evaluation of facial signs of trustworthiness, which has been shown to occur reliably, rapidly, and without conscious awareness in adults. Recent developmental work indicates that the sensitivity to facial trustworthiness has early ontogenetic origins as it can already be observed in infancy. However, it is unclear whether infants' sensitivity to facial signs of trustworthiness relies upon conscious processing of a face or, similar to adults, occurs also in response to subliminal faces. To investigate this question, we conducted an event-related brain potential (ERP) study, in which we presented 7-month-old infants with faces varying in trustworthiness. Facial stimuli were presented subliminally (below infants' face visibility threshold) for only 50ms and then masked by presenting a scrambled face image. Our data revealed that infants' ERP responses to subliminally presented faces differed as a function of trustworthiness. Specifically, untrustworthy faces elicited an enhanced negative slow wave (800-1000ms) at frontal and central electrodes. The current findings critically extend prior work by showing that, similar to adults, infants' neural detection of facial signs of trustworthiness occurs also in response to subliminal face. This supports the view that detecting facial trustworthiness is an early developing and automatic process in humans.

BackgroundDeep brain stimulation of the subthalamic nucleus (STN DBS) is known to increase response speed and lower response accuracy in Parkinson's disease (PD) patients. It has been proposed that this speed-accuracy tradeoff is due to enhanced sensitivity of the motor system to sensory information. An alternative possibility is that this effect is due to weakened suppressive processes. The two alternative interpretations can be tested by analyzing the electromyographic activity (EMG) of the response agonists when the patients perform conflict reaction time tasks. In those tasks, fast subthreshold muscle impulses often occur in the agonist of the incorrect response. These impulses are partial errors that are suppressed before being behaviourally committed.Material and methodsHere we analyzed the EMG of the response agonists recorded while sixteen PD patients performed a Simon task that elicits prepotent response tendencies so as to decipher (i) whether STN DBS affects the expression and/or suppression of subthreshold muscle impulses that are critical for action control and (ii) the interaction between dopaminergic treatment and STN DBS. The patients were tested On and Off STN DBS and On and Off dopaminergic medication in a full factorial design.ResultsSTN DBS not only impaired the proficiency to suppress subliminal action impulses (p = 0.01) but also favoured the muscular expression of fast incorrect impulses (p ConclusionContrary to a recent proposal, STN DBS impaired rather than improved action control by weakening erroneous impulse suppression, whether the patients were On or Off their usual medication. These findings are discussed in light of a recent proposal (Servant M, White C, Montagnini A, Burle B, 2015) that reconciles partial errors with accumulation-to-bound models of decision making. Our results suggest that medication specifically lowers the mechanical threshold while STN DBS lowers the mechanical threshold and to a lesser extent the EMG-threshold.

Many cognitive processes operate without consciousness, and exogenous attentional capture seems to be one of them. While endogenously attending to the opposite location of a cue cannot occur without cue awareness, attending the cued location in an exogenous or stimulus driven form can occur even when participants are not aware of the presence of the cue (McCormick, 1997). Orienting attention to a specific location shortens reaction times to supra-threshold stimuli, and increases the likelihood of consciously perceiving near-threshold stimuli in that location. Effects of unconscious cues have mostly been demonstrated in reaction times to supra-threshold targets. In some studies, unconscious cues were perceptually less salient than conscious cues, which introduced a confound between cue awareness and cue saliency. In the present study, we used near-threshold cues and targets, which were titrated to be consciously perceived in ~50% of the trials, therefore eliminating the cue saliency confound. Moreover, we explored for the first time the effects of cue awareness on the conscious perception of subsequently presented near-threshold targets. Our results demonstrate that when cues and targets did not spatially overlap, conscious cues enhanced target localization when they appeared near the target location. In contrast, non-consciously perceived cues impaired target localization when they appeared near the target location, producing a cost in detecting subsequently presented near-threshold targets. This indicates that attentional orienting by unconscious cues cannot be accounted for by the idea that attention modulates perceptual representations, boosting them nearer to the conscious threshold. Rather, the effect of unconscious cues on target localization is qualitatively different to that elicited by conscious cues.

The P3 event-related potential has been known for over 50 years, but its function is still a matter of ongoing debate. Current theories interpret P3b either as a correlate of perceptual consciousness, or as reflecting cognitive processes, like working memory and executive functions. Unexpectedly, recent studies indicate that P3b might occur in response to unconsciously presented stimuli which, if further replicated, will be important for defining its functional role. Therefore, in the present study we investigated the P3b component in response to participants' own name - a stimulus which is subjectively extremely salient and known to evoke a robust P3b response. The self-name and control (other) names were presented supra- and subliminally (backward-masked), in a subjective rating task and in a forced-choice identification task. We found that a consciously perceived self-name evoked a P3b of larger amplitude than the other-name in both tasks, which confirms that the self-name was processed preferentially. When the self-name was presented subliminally it was associated with larger P3b amplitude than the other-name in the identification task, but not in the subjective rating task. This indicates that a salient stimulus can in principle modulate the P3b amplitude even when processed outside of awareness, but also that subliminal processing depends on the task-set and top-down factors. Taken as a whole, our results provide evidence against the interpretation of P3b as a correlate of consciousness (and more generally conflict with the Global Workspace Theory) and will allow a more precise description of the relation between P3b and cognitive processes.

The ability to automatically detect changes in the environment is crucial for organisms to survive. In the visual system, changes in visual stimuli may evoke visual mismatch negativity (vMMN), an event-related potential (ERP) component that reflects automatic change detection. Previous studies that used visual masking to examine the effects of consciousness did not yield evidence that vMMN could be elicited by subliminal stimuli. However, these studies used relatively simple visual features. To further examine the role of consciousness in vMMN, the present study used emotional (happy and fearful) faces, which are biologically and socially significant visual stimuli. A passive oddball paradigm was employed, and we found that only fearful faces could evoke vMMN at a low consciousness level. Furthermore, the fear-related vMMN was enhanced by the consciousness level, and localized in regions of the brain associated with emotional face processing and the prefrontal cortex. We also found that the emotional visual mismatch oscillatory responses (vMORs) were associated with the enhancement of the alpha-band oscillation. Moreover, consciousness could weaken the happiness-related vMOR. These results suggested that changes to emotional faces-especially fearful faces-could be unconsciously detected by the brain. More importantly, this automatic change detection mechanism could be modulated by consciousness.

While extinction is most commonly viewed as an attentional disorder and not as a consequence of a failure to process contralesional sensory information, it has been speculated that early sensory processing of contralesional targets in extinction patients might not be fully normal. We used a masked visuo-motor response priming paradigm to study the influence of both contralesional and ipsilesional peripheral subliminal prime stimuli on central target performance, allowing us to compare the strength of the early sensory processing associated with these prime stimuli between right brain damaged patients with and without extinction as well as healthy elderly subjects. We found that the effect of an informative subliminal prime in the left contralesional visual field on central target performance was significantly reduced in both right brain damaged patients with and without extinction. The results suggest that a low-level early sensory deterioration of the neural representation for contralesional prime stimuli is a general consequence of right hemispheric brain damage unrelated to the presence or absence of extinction. This suggests that the presence of a spatial bias against contralesional information is not sufficient to elicit extinction. For extinction to occur, this spatial bias might need to be accompanied by a pathological (non-directional) reduction of attentional capacity.

Stroke of the right cerebral hemisphere often causes deficits in the judgement of the subjective visual vertical (SVV) and subjective tactile vertical (STV) which are related to central vestibular functioning. Clinically, deficits in the SVV/STV are linked to balance problems and poor functional outcome. Galvanic Vestibular Stimulation (GVS) is a non-invasive, save stimulation technique that induces polarity-specific changes in the cortical vestibular systems. Subliminal GVS induces imperceptible vestibular stimulation without unpleasant side effects. Here, we applied bipolar subliminal GVS over the mastoids (mean intensity: 0.7 mA, 20 min duration per session) to investigate its online-influence on constant errors, difference thresholds and range values in the SVV and STV. 24 patients with subacute, single, unilateral right hemisphere stroke were studied and assigned to two patient groups (impaired vs. normal in the SVV and STV) on the basis of cut-off scores from healthy controls. Both groups performed these tasks under three experimental conditions on three different days: a) sham GVS where electric current was applied only for 30s and then turned off, b) left-cathodal GVS and c) right-cathodal GVS, for a period of 20 min per session. Left-cathodal GVS, but not right-cathodal GVS significantly reduced all parameters in the SVV. Concerning STV GVS also reduced constant error and range numerically, though not significantly. These effects occurred selectively in the impaired patient group. In conclusion, we found that GVS rapidly influences poststroke verticality deficits in the visual and tactile modality, thus highlighting the importance of the vestibular system in the multimodal elaboration of the subjective vertical.

Humans can shift their gazes faster to human faces than to non-face targets during a task in which they are required to choose between face and non-face targets. However, it remains unclear whether a direct projection from the retina to the superior colliculus is specifically involved in this facilitated recognition of faces. To address this question, we presented a pair of face and non-face pictures to participants modulated in greyscale (luminance-defined stimuli) in one condition and modulated in a blue-yellow scale (S-cone-isolating stimuli) in another. The information of the S-cone-isolating stimuli is conveyed through the retino-geniculate pathway rather than the retino-tectal pathway. For the luminance stimuli, the reaction time was shorter towards a face than towards a non-face target. The facilitatory effect while choosing a face disappeared with the S-cone stimuli. Moreover, fearful faces elicited a significantly larger facilitatory effect relative to neutral faces, when the face (with or without emotion) and non-face stimuli were presented in greyscale. The effect of emotional expressions disappeared with the S-cone stimuli. In contrast to the S-cone stimuli, the face facilitatory effect was still observed with negated stimuli that were prepared by reversing the polarity of the original colour pictures and looked as unusual as the S-cone stimuli but still contained luminance information. These results demonstrate that the face facilitatory effect requires the facial and emotional information defined by luminance, suggesting that the luminance information conveyed through the retino-tectal pathway is responsible for the faster recognition of human faces.

Many studies using electroencephalography consistently reported a larger N170 (N1) response in the visual cortices to inverted than upright face images (the face inversion effect in N1, FIE-N1). Here we report this robust effect is diminished and even reversed when face stimuli are processed unconsciously. We measured visual-evoked potentials to neutral faces either visible or rendered invisible by an inter-ocular suppression. In visible condition, we observed a larger N1 to inverted than upright faces, which replicated the traditional FIE-N1. When those faces became invisible, however, neural responses to the inverted faces were greatly reduced compared to visible condition, whereas those to the invisible upright faces were relatively preserved. Consequently, N1 amplitudes were found to be larger in upright, rather than inverted, faces in invisible condition, which was opposite to the traditional FIE-N1 (upright

The localization of harmful stimuli approaching our body is essential for survival. Here we investigated whether the mapping of nociceptive stimuli is based on a spatial representation that is anchored to the stimulated limb. In three experiments, we measured the effect of unilateral visual stimuli on the perceived temporal order of nociceptive stimuli, applied to each hand. Crucially, the position of the hands and the visual stimuli was manipulated, so that visual and nociceptive stimuli occurred in an adjacent or non-adjacent spatial position. Temporal order judgments of nociceptive stimuli were biased in favor of the stimulus applied to the hand most adjacent to the visual stimulus, irrespective to their positions in space. This suggests that the ability to determine the position of a nociceptive stimulus on a specific body area is based on a peripersonal representation of the stimulated limb following it during limb displacement.

The mental-rotation task is a well known research paradigm to examine cognitive processes of mental imaging and mental manipulation ( Shepard & Metzler, 1971 ). So far, research has been focused on stimulus orientation which indicates the necessary amount of mental rotation. But little attention has been paid to stimulus parity, specifically if and how identical and mirror-reversed stimuli are processed differently. We wanted to fill this gap by combining performance, eye-tracking, and neurofunctional measures using pairwise presented three-dimensional Shepard–Metzler stimuli in a self-paced event-related fMRI design. Based on our results we tried to reason at which stage of the mental-rotation process the treatment of mirrored and identical stimuli begins to diverge. As a common finding, response times for tasks with mirrored stimuli were longer compared to tasks with identical stimuli reflecting their higher cognitive demand. Moreover, we observed smaller saccade amplitudes for mirrored than for identical stimuli suggesting a smaller functional field of view during stimulus perception. The eye-movement results were complemented by our neurofunctional findings. Here, the processing of mirrored stimuli led to less activation in parts of the early visual cortex that respond to the visual periphery than the processing of identical figures. This activation difference remained after eye-movement-associated activations had been excluded. We explain our findings by stimulus-parity-induced differences in saliency maps built up to enhance perception. Thus, the treatment of mirrored and identical stimuli begins to diverge very early in the mental-rotation process and is associated with differences in visual processing.

The time to decide if a letter is normal or backwards (mirror-reversed) increases as the letter is rotated away from the upright. It is widely accepted that this increase in time reflects the mental rotation of the stimulus to the upright orientation in order to determine the mirror-normal status of the stimulus. Although response times tend to be longer for mirrored stimuli than for normal stimuli, the difference is constant across orientation. Little work has been focused on why mirror-image stimuli produce longer response times than normal stimuli. This study examines the question of whether or not mirrored stimuli are rotated in the picture plane at the same time as normal stimuli, and if so, why response times to mirrored stimuli are longer than that for normal stimuli. Both the behavioural and electrophysiological findings suggest that the mirrored stimuli are not only rotated in the picture plane, but that they are subsequently rotated to the normal view. It is this additional rotation that produces, at least in part, the delayed response times for mirror-image stimuli.

The valence hypothesis and the right hemisphere hypothesis in emotion processing have been alternatively supported. To better disentangle the two accounts, we carried out two studies, presenting healthy participants and an anterior callosotomized patient with 'hybrid faces', stimuli created by superimposing the low spatial frequencies of an emotional face to the high spatial frequencies of the same face in a neutral expression. In both studies we asked participants to judge the friendliness level of stimuli, which is an indirect measure of the processing of emotional information, despite this remaining "invisible". In Experiment 1 we presented hybrid faces in a divided visual field paradigm using different tachistoscopic presentation times; in Experiment 2 we presented hybrid chimeric faces in canonical view and upside-down. In Experiments 3 and 4 we tested a callosotomized patient, with spared splenium, in similar paradigms as those used in Experiments 1 and 2. Results from Experiments 1 and 3 were consistent with the valence hypothesis, whereas results of Experiments 2 and 4 were consistent with the right hemisphere hypothesis. This study confirms that the low spatial frequencies of emotional faces influence the social judgments of observers, even when seen for 28 ms (Experiment 1), possibly by means of configural analysis (Experiment 2). The possible roles of the cortical and subcortical emotional routes in these tasks are discussed in the light of the results obtained in the callosotomized patient. We propose that the right hemisphere and the valence accounts are not mutually exclusive, at least in the case of subliminal emotion processing.

Neglect patients show contralesional deficits in egocentric and object-centred visuospatial tasks. The extent to which these different phenomena are modulated by sensory stimulation remains to be clarified. Subliminal galvanic vestibular stimulation (GVS) induces imperceptible, polarity-specific changes in the cortical vestibular systems without the unpleasant side effects (nystagmus, vertigo) induced by caloric vestibular stimulation. While previous studies showed vestibular stimulation effects on egocentric spatial neglect phenomena, such effects were rarely demonstrated in object-centred neglect. Here, we applied bipolar subsensory GVS over the mastoids (mean intensity: 0.7mA) to investigate its influence on egocentric (digit cancellation, text copying), object-centred (copy of symmetrical figures), or both (line bisection) components of visual neglect in 24 patients with unilateral right hemisphere stroke. Patients were assigned to two patient groups (impaired vs. normal in the respective task) on the basis of cut-off scores derived from the literature or from normal controls. Both groups performed all tasks under three experimental conditions carried out on three separate days: (a) sham/baseline GVS where no electric current was applied, (b) left cathodal/right anodal (CL/AR) GVS and (c) left anodal/right cathodal (AL/CR) GVS, for a period of 20min per session. CL/AR GVS significantly improved line bisection and text copying whereas AL/CR GVS significantly ameliorated figure copying and digit cancellation. These GVS effects were selectively observed in the impaired- but not in the unimpaired patient group. In conclusion, subliminal GVS modulates ego- and object-centred components of visual neglect rapidly. Implications for neurorehabilitation are discussed.

In human cognition, most relevant stimuli, such as faces, are processed in central vision. However, it is widely believed that recognition of relevant stimuli (e.g. threatening animal faces) at peripheral locations is also important due to their survival value. Moreover, task instructions have been shown to modulate brain regions involved in threat recognition (e.g. the amygdala). In this respect it is also controversial whether tasks requiring explicit focus on stimulus threat content vs. implicit processing differently engage primitive subcortical structures involved in emotional appraisal. Here we have addressed the role of central vs. peripheral processing in the human amygdala using animal threatening vs. non-threatening face stimuli. First, a simple animal face recognition task with threatening and non-threatening animal faces, as well as non-face control stimuli, was employed in naïve subjects (implicit task). A subsequent task was then performed with the same stimulus categories (but different stimuli) in which subjects were told to explicitly detect threat signals. We found lateralized amygdala responses both to the spatial location of stimuli and to the threatening content of faces depending on the task performed: the right amygdala showed increased responses to central compared to left presented stimuli specifically during the threat detection task, while the left amygdala was better prone to discriminate threatening faces from non-facial displays during the animal face recognition task. Additionally, the right amygdala responded to faces during the threat detection task but only when centrally presented. Moreover, we have found no evidence for superior responses of the amygdala to peripheral stimuli. Importantly, we have found that striatal regions activate differentially depending on peripheral vs. central processing of threatening faces. Accordingly, peripheral processing of these stimuli activated more strongly the putaminal region, while central processing engaged mainly the caudate nucleus. We conclude that the human amygdala has a central bias for face stimuli, and that visual processing recruits different striatal regions, putaminal or caudate based, depending on the task and on whether peripheral or central visual processing is involved. PEst-C/SAU/UI3282/2011 CENTRO-07-ST24-FEDER-00205 FP7-HEALTH-2013-INNOVATION-1 BIAL Foundation

Normal subjects showed costs and benefits of informative auditory spatial cues with auditory targets in RT tasks when stimulus intensity was low, or when the stimuli were presented monaurally through headphones. These findings imply that attention to auditory stimuli, like attention to visual or tactile stimuli, can be shifted spatially in detection tasks, and that covert orienting to auditory stimuli occurs in conditions favoring the intention to orient the head to a sound source. According to this view, orienting of attention to auditory stimuli, as well as to visual and tactile stimuli, is linked functionally to mechanisms controlling overt orienting movements that increase stimulus identification.

Self-related information has been found to be processed more quickly and accurately in studies with supraliminal self-stimuli and traditional paradigms such as masked priming. We conducted two experiments to investigate whether subliminal self-face processing enjoys this advantage and the neural correlates of processing self-faces at both subliminal and supraliminal levels. We found that self-faces were quicker than famous-other faces to gain dominance against dynamic noise patterns during prolonged interocular suppression to enter awareness (Experiment 1). Meanwhile, subliminal contrast of self- and famous-other face processing was reflected in a reduced early vertex positive potential (VPP) component, whereas supraliminal self-other face differentiation was reflected in an enhanced N170, as well as a more positive late component (300-580ms, Experiment 2) to the self-face. The clear dissociations of self- and other-face processing found across our two experiments validate the self advantage. Our findings also contribute to understandings of the mechanisms underlying self-face processing at different levels of awareness.

The self-face is thought to be an especially salient stimulus. Behavioral evidence suggests that self-face processing advantage is associated with enhanced processing of temporally adjacent subliminal stimuli. However, the neural basis of this self-related processing modulation has not been investigated. We studied self-face induced signal amplification through masked priming and repetition suppression (fMRI adaptation). Subjects performed a gender-categorization task on self- and non-self target faces preceded by subliminal (17 ms) prime faces. The relationship between prime and target was varied between task-incongruent (when prime and target belonged to a different gender) and task-congruent (when prime and target belonged to the same gender) pairs. We found that, in the presence of the visible self-face (but not of other non-self faces), a bilateral fronto-parietal network exhibited repetition suppression to subliminal prime faces belonging to the same gender (task-congruent) as the target, consistent with the notion that, in the presence of the self-face, subliminal stimuli access high-level processing systems. These results are in agreement with the notion of self-specific top-down amplification of subliminal task-relevant information, and suggest that the self-face, through its high salience, is particularly efficacious in focusing attention.

Sensory extinction is frequent and often persistent after brain damage. Previous studies have shown the transient influence of sensory stimulation on tactile extinction. In the present two case studies we investigated whether subliminal galvanic vestibular stimulation (GVS) modulates tactile extinction. GVS induces polarity-specific changes in cerebral excitability in the vestibular cortices and adjacent cortical areas in the temporo-parietal cortex via polarization of the vestibular nerves. Two patients (DL, CJ) with left-sided tactile extinction due to chronic (5 vs. 6 (1/2) years lesion age) right-hemisphere lesions (right fronto-parietal in DL, right frontal and discrete parietal in CJ) were examined. Both showed normal tactile sensitivity to light touch and yielded 90-100% correct identifications in unilateral tactile stimulations for both hands. In Baseline investigations without GVS and Sham-GVS both showed stable left-sided tactile extinction rates of 40-55% (DL) and 49-72% (CJ). In contrast, one session of right-cathodal GVS (intensity: 0.6 mA, duration: 20 min) permanently improved tactile identification of identical stimuli, while a second session with left-cathodal GVS significantly reduced left-sided extinction rates for different stimuli in DL. Patient CJ's left-sided tactile extinction was significantly improved by left-cathodal GVS (0.5 mA, 20 min) for different stimuli, while right-cathodal GVS induced a significant reduction for identical materials. In contrast, Sham-stimulation was ineffective. Improvements remained stable for at least 1 year (DL) resp. 3 weeks (CJ). Control experiments ruled out improvements in tactile extinction merely by retesting. In conclusion, chronic tactile extinction may be permanently improved by GVS in a polarity-specific way.

Ignoring irrelevant information becomes more difficult with increasing age. The present cross-sectional study addressed this issue by investigating age-related differences in the ability to withhold a response to non-target stimuli. Fourteen young (20-34 years) and 14 elderly (60-80 years) participants performed two go/nogo tasks (simple vs. complex). In the simple task the subjects responded to red O and blue X (target go stimuli) while withholding responses to the blue O and red X (conflict nogo stimuli) and to numbers of either color (irrelevant nogo stimuli). In the complex version, 4 vowels and 4 consonants were used instead of O and X. Accuracy, response times (RTs) and event-related potentials (ERPs) were recorded. Both young and elderly groups made more commission errors to conflict nogo stimuli (mean 5% and 8% in the simple and complex tasks, respectively, age differences not significant) than to irrelevant nogo stimuli (mean

Task-irrelevant visual cues with near zero visibility proved apt to retard reaction time for the detection of supraliminal visual targets presented at the cued location. The time course of the effect was similar to that of the so-called inhibition-of return (IOR), which is assumed to be due to the withdrawal of attention from the inhibited location. However the present subliminal cues consistently failed to induce an RT facilitation prior to the RT inhibition, contrary to what would be expected if the cue were able to attract attention to the cued location. Since the RT inhibition from subliminal cues could not be attributed to the withdrawal of attention from the cued location, it can be argued that such cues acted both outside of consciousness and without the influence of attention. Therefore, the RT inhibitory effect seems best accounted for by an automatic, unconscious and attention-independent self-inhibition of response tendencies instructed by irrelevant information, akin to that postulated by (Eimer, M., & Schlaghecken, F. (1998). Effects of masked stimuli on motor activation: behavioural and electrophysiological evidence. Journal of Experimental Psychology Human Perception and Performance, 24, 1737-1747.) to explain the negative compatibility effect.

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.

To cast light on the possible neural substrate of visual imagery we tested normal participants and one hemianopic patient on simple reaction time (RT) to real and imagined visual stimuli. In one experiment participants were to detect as quickly as possible a luminous square presented at one out of two different retinal eccentricities. A well known effect with visual stimuli is that RT is slower for peripheral versus central stimuli. We found that imagined stimuli showed an eccentricity effect similar to that obtained with real stimuli. However, this was not the case in a patient with a hemianopic visual field loss (quadrantanopia) as a result of damage to the optic radiation. Even though the patient showed no difficulty in imaging stimuli in the affected hemifield she did not show an eccentricity effect as was the case in her intact side. In a second experiment, normal participants showed faster RT to stimuli of larger size with either real or imagined stimuli. Overall, these results show that visual perception and imagination share a similar visuotopic organisation that is disrupted following deafferentation of the visual cortex.

The contribution of each hemisphere to the generation of number representations was investigated by two lateralized priming experiments in which participants had to compare Arabic digits to a fixed standard of four. In Experiment 1, unmasked primes (Arabic digits or word numerals) were used. In Experiment 2, masked primes were presented consciously or subconsciously. In both experiments similar priming effects were found in the left (LH) and the right hemisphere (RH) when the prime was presented consciously. However, asymmetries emerged when the primes were presented subconsciously: while the priming effects of digits and word numbers were equally large in the right visual half field (RVF-LH), the influence of the word prime on the semantic and the response stage of the left visual half field (LVF-RH) was absent, indicating that a word prime was no longer processed when it was presented subconsciously in LVF-RH. We believe that the origin of the latter effect can be attributed to a failure to transfer word number primes from the RH to the LH when attentional resources are restricted.

Previous research has shown that negative stimuli elicit more attention than do positive stimuli. However, this research has relied on response-based measures to assess attention. The current research uses the P1 component of the event-related brain potential (ERP) as a proximal index of attention allocation to valenced stimuli. In two studies, P1 amplitude was measured while participants evaluated positive and negative pictures. In both studies, principal components analysis showed that P1 amplitudes to frequent stimuli and to rare negative stimuli were larger than P1 amplitudes to rare positive stimuli. This is (a) evidence for the extremely rapid (

We examined a patient with left spatial neglect and visual extinction due to right parietal damage in tasks where identical stimuli were presented before and after they were primed so as to be perceived as the eyes of schematic faces. In a first block, we presented alphanumeric stimuli (+, o, T, 6) on the right, left, or both sides of fixation on a blank background, and established that the patient could perceive unilateral stimuli on either side but extinguished most of the left-sided ones in the bilateral trials. In a second block, some of these stimuli (+, o) were presented again, but now in the position of eyes within the context of an oval frame which created the impression of a schematic face. Other stimuli (T, 6) were presented as previously on a blank background for an equal number of trials. In the third critical block, all stimuli were presented once again on a blank background, as in the first block. Now the patient extinguished very few of those left-sided stimuli primed to be seen as a pair of eyes in face configuration (+, o), but still extinguished most of the other stimuli (T, 6). A second control experiment showed no effect of repeatedly exposing stimuli in a common region of space defined by meaningless shape boundaries. These results suggest that facial organization can group eye features before the level where attentional selection or extinction occurs, and that such grouping may be influenced by rapid perceptual learning.

Event-related potentials (ERPs) are recordings of the electric field which the brain produces in fixed time-relation to an event. ERPs open a time and space window onto covert steps of brain information processing which need not be accompanied by overt behavior or private experiences. ERPs are the only noninvasive method which resolves the dynamic pattern of events in the human brain down to the millisecond range. Early ERP components are valuable tools in clinical testing of the afferent sensory systems in the absence of anamnestic or clinical pathology. Later components (e.g. the 'P300') index intermediate, covert steps of information processing and have clarified the time course and the contingencies of processes in attention, decisions and language. ERP waveshapes show electric potential differences between two recording points. Conventional analysis often ignores the fact that there is no unique voltage amplitude or signal latency for a single point, and interprets ambiguous results. Although important insights have emerged with such strategies, full utilization of ERP data requires unambiguous ERP assessment and converging evidence from neuropsychological and cognitive experimentation. Sequences of field distribution maps offer an unbiased display of ERP data. Spatial analysis yields unambiguous values for further comprehensive assessment, and should precede analysis over time. Examples of spatial analysis have shown that different ERP field configurations follow the presentation of noun and verb meaning of homophone words; that the ERP effects to subjective contours resemble those to attention in time course and topography; that the 'cognitive' P300 component reflects the specific stimulus location; and that subliminal information influences the configuration of late ERP fields.

In a study of simple reaction time to visual stimuli it was found that the offset (or termination) of stimuli presented in the right visual field elicits significantly later responses than does the offset of stimuli presented in the left visual field. No such differences was observed for the responses to stimulus onset. A similar effect has been reported for responses to tonal stimuli. The results do not support the view that hemispheric asymmetries arise at higher stages of information processing than those which mediate simple reaction time.

The difference favoring the right ear, in vocal reaction time to speech stimuli, does not appear to be smaller for stimuli presented strictly monaurally than for stimuli opposed by contralateral noise.

Pairs of auditory and visual stimuli were presented to brain-damaged and non-brain-damaged subjects who were asked to indicate which member of the stimulus pair came first. The interstimulus interval between members of the stimulus pair was varied. Results demonstrated that performance depends upon sensory modality, spatial location of stimuli, features by which the stimuli differ, and type of aphasia present.