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Disgust for contaminating objects (core disgust), immoral behaviors (moral disgust) and unsavory others (interpersonal disgust), have been assumed to be closely related. It is not clear, however, whether different forms of disgust are mediated by overlapping or specific neural substrates. We report that 10 patients with damage to the ventromedial prefrontal cortex (vmPFC) avoided behaviors that normally elicit interpersonal disgust (e.g. using the scarf of a busker) less frequently than healthy and brain-damaged controls, whereas they avoided core and moral disgust elicitors at normal rates. These results indicate that different forms of disgust are dissociated neurally. We propose that the vmPFC is causally (and selectively) involved in mediating interpersonal disgust, shaping patterns of social avoidance and approach.

Moral judgment involves considering not only the outcome of an action but also the intention with which it was pursued. Previous functional magnetic resonance imaging (fMRI) research has shown that integrating outcome and belief information for moral judgment relies on a brain network including temporo-parietal, precuneus, and medial prefrontal regions. Here, we investigated whether the ventromedial prefrontal cortex (vmPFC) plays a crucial role in this process. Patients with lesions in vmPFC (vmPFC patients), and brain-damaged and healthy controls considered scenarios in which the protagonist caused intentional harm (negative-outcome, negative-belief), accidental harm (negative-outcome, neutral-belief), attempted harm (neutral-outcome, negative-belief), or no harm (neutral-outcome, neutral-belief), and rated the moral permissibility of the protagonists' behavior. All groups responded similarly to scenarios involving intentional harm and no harm. vmPFC patients, however, judged attempted harm as more permissible, and accidental harm as less permissible, than the control groups. For vmPFC patients, outcome information, rather than belief information, shaped moral judgment. The results indicate that vmPFC is necessary for integrating outcome and belief information during moral reasoning. During moral judgment vmPFC may mediate intentions' understanding, and overriding of prepotent responses to salient outcomes.

Recent brain imaging studies have implicated the rostral ACC (rACC) in the resolution of conflict between competing response tendencies in emotional task contexts, but not in neutral task contexts. This study tested the hypothesis that the rACC is necessary for such context-specific conflict adaptation. To this end, a group of patients with lesions of the rACC, a group of brain-damaged controls, and a group of normal controls classified the emotional expression (emotional task context) or the gender (neutral task context) of faces while ignoring congruent and incongruent words written across the faces. In all three groups, performance was worse with incongruent as compared with congruent stimuli in both task contexts. In the two control groups, this congruency effect was reduced following incongruent trials in both task contexts. By contrast, the rACC group displayed such conflict adaptation only in the neutral, but not in the emotional, task context. These results show that the rACC is necessary for conflict adaptation in emotional but not in neutral task contexts and suggest that the regulation of behavior is context specific.

The present study investigated whether the error-related negativity, an electrophysiological marker for performance monitoring, reflects (1) the expectancy of errors, or (2) the significance of errors for the current task goal. In the first case, a larger error-related negativity is predicted for less expected errors, whereas in the second case, a larger error-related negativity is predicted for errors with greater significance. To test these predictions, we varied flanker size in a flanker task. With large flankers, more errors occurred by executing the response associated with the flankers (flanker errors) leading to a greater expectancy of flanker errors. As revealed by a multinomial model, these additional flanker errors represented highly significant attention errors, leading to an increased error significance. The error-related negativity was larger for flanker errors with large flankers, which supports the error significance account., (Copyright © 2012 Society for Psychophysiological Research.)

Fundamental to adaptive behaviour is the ability to select environmental objects that best satisfy current needs and preferences. Here we investigated whether temporary changes in food preference influence visual selective attention. To this end, we exploited the fact that when a food is eaten to satiety its motivational value and perceived pleasantness decrease relative to other foods not eaten in the meal, an effect termed sensory-specific satiety. A total of 26 hungry participants were fed until sated with one of two palatable foods. Before and after selective satiation, participants rated the pleasantness of the two foods and then viewed the same as stimuli on a computer screen while attention was assessed by a visual probe task. Results showed that the attentional bias for the food eaten decreased markedly from pre- to postsatiety, along with the subjective pleasantness for that food. By contrast, subjective pleasantness and attentional bias for the food not eaten did not show any such decrease. These findings suggest that the allocation of visual selective attention is flexibly and rapidly adjusted to reflect temporary shift in relative preference for different foods.

People are frequently faced with intertemporal choices, i.e., choices differing in the timing of their consequences, preferring smaller rewards available immediately over larger rewards delivered after a delay. The inability to forgo sooner gratification to favor delayed reward (e.g., impulsivity) has been related to several pathological conditions characterized by poor self-control, including drug addiction and obesity. Comparative and functional human studies have implicated a network of brain areas involved in intertemporal choice, including the medial portion of the orbitofrontal cortex (mOFC). Moreover, damage to this cortical area increases preference for immediate gratification in intertemporal decisions. Here, we review recent neuroscientific studies concerning intertemporal choice, suggesting that the mOFC contributes to preference for delayed rewards, either by computing the value of future outcomes (i.e., valuation), or by enabling people to imagine and represent future rewards and their consequences (e.g., prospection).

Converging evidence suggests that emotion processing mediated by ventromedial prefrontal cortex (vmPFC) is necessary to prevent personal moral violations. In moral dilemmas, for example, patients with lesions in vmPFC are more willing than normal controls to approve harmful actions that maximize good consequences (e.g., utilitarian moral judgments). Yet, none of the existing studies has measured subjects' emotional responses while they considered moral dilemmas. Therefore, a direct link between emotion processing and moral judgment is still lacking. Here, vmPFC patients and control participants considered moral dilemmas while skin conductance response (SCR) was measured as a somatic index of affective state. Replicating previous evidence, vmPFC patients approved more personal moral violations than did controls. Critically, we found that, unlike control participants, vmPFC patients failed to generate SCRs before endorsing personal moral violations. In addition, such anticipatory SCRs correlated negatively with the frequency of utilitarian judgments in normal participants. These findings provide direct support to the hypothesis that the vmPFC promotes moral behavior by mediating the anticipation of the emotional consequences of personal moral violations.

We report two studies aimed at investigating the effects of distinct negative emotions on pairwise economic interactions. In the ultimatum game, a proposer offers a division of a sum of money to a responder who decides whether to accept the split, or reject and leave both players with nothing. In Experiment 1, we investigated whether induced disgust, as compared to sadness and neutral emotion, specifically influences responders' decisions to reject unfair proposals. In Experiment 2, we assessed whether the effects of disgust were selectively related to social contexts by contrasting interactions with a human partner with those involving a computer. Results showed that relative to being in a sad or neutral mood, induced feelings of disgust significantly increased rejection rates of unfair offers. Moreover, we found that when the partner was not responsible for the fairness violation, such as in the computer-offer condition, the disgust induction failed to affect participants' choices. We conclude by focusing on the hypothesis that disgust and social norm violations may share common computational components, both at a psychological and a neural level., (Copyright 2010 APA, all rights reserved.)

Visual peripersonal space (i.e., the space immediately surrounding the body) is represented by multimodal neurons integrating tactile stimuli applied on a body part with visual stimuli delivered near the same body part, e.g., the hand. Tool use may modify the boundaries of the peri-hand area, where vision and touch are integrated. The neural mechanisms underlying such plasticity have not been yet identified. To this aim, neural network modelling may be integrated with experimental research. In the present work, we pursued two main objectives: (i) using an artificial neural network to postulate some physiological mechanisms for peri-hand space plasticity in order to account for in-vivo data; (ii) validating model predictions with an ad-hoc behavioural experiment on an extinction patient. The model assumes that the modification of peri-hand space arises from a Hebbian growing of visual synapses converging into the multimodal area, which extends the visual receptive field (RF) of the peripersonal bimodal neurons. Under this hypothesis, the model is able to interpret and explain controversial results in the current literature, showing how different tool-use tasks during the learning phase result in different re-sizing effects of the peri-hand space. Importantly, the model also implies that, after tool-use, a far visual stimulus acts as a near one, independently of whether the tool is present or absent in the subject's hand. This prediction has been validated by an in-vivo experiment on a right brain-damaged patient suffering from visual-tactile extinction. This study demonstrates how neural network modelling may integrate with experimental studies, by generating new predictions and suggesting novel experiments to investigate cognitive processes., (2009 Elsevier Ltd. All rights reserved.)

Neurophysiological and behavioral studies suggest that the peripersonal space is represented in a multisensory fashion by integrating stimuli of different modalities. We developed a neural network to simulate the visual-tactile representation of the peripersonal space around the right and left hands. The model is composed of two networks (one per hemisphere), each with three areas of neurons: two are unimodal (visual and tactile) and communicate by synaptic connections with a third downstream multimodal (visual-tactile) area. The hemispheres are interconnected by inhibitory synapses. We applied a combination of analytic and computer simulation techniques. The analytic approach requires some simplifying assumptions and approximations (linearization and a reduced number of neurons) and is used to investigate network stability as a function of parameter values, providing some emergent properties. These are then tested and extended by computer simulations of a more complex nonlinear network that does not rely on the previous simplifications. With basal parameter values, the extended network reproduces several in vivo phenomena: multisensory coding of peripersonal space, reinforcement of unisensory perception by multimodal stimulation, and coexistence of simultaneous right- and left-hand representations in bilateral stimulation. By reducing the strength of the synapses from the right tactile neurons, the network is able to mimic the responses characteristic of right-brain-damaged patients with left tactile extinction: perception of unilateral left tactile stimulation, cross-modal extinction and cross-modal facilitation in bilateral stimulation. Finally, a variety of sensitivity analyses on some key parameters was performed to shed light on the contribution of single-model components in network behaviour. The model may help us understand the neural circuitry underlying peripersonal space representation and identify its alterations explaining neurological deficits. In perspective, it could help in interpreting results of psychophysical and behavioral trials and clarifying the neural correlates of multisensory-based rehabilitation procedures.

Many studies have revealed that attention operates across different sensory modalities, to facilitate the selection of relevant information in the multimodal situations of every-day life. Cross-modal links have been observed either when attention is directed voluntarily (endogenous) or involuntarily (exogenous). The neural basis of cross-modal attention presents a significant challenge to cognitive neuroscience. Here, we used a neural network model to elucidate the neural correlates of visual-tactile interactions in exogenous and endogenous attention. The model includes two unimodal (visual and tactile) areas connected with a bimodal area in each hemisphere and a competition between the two hemispheres. The model is able to explain cross-modal facilitation both in exogenous and endogenous attention, ascribing it to an advantaged activation of the bimodal area on the attended side (via a top-down or bottom-up biasing), with concomitant inhibition towards the opposite side. The model suggests that a competitive/cooperative interaction with biased competition may mediate both forms of cross-modal attention.

Neurons in the superior colliculus (SC) are known to integrate stimuli of different modalities (e.g., visual and auditory) following specific properties. In this work, we present a mathematical model of the integrative response of SC neurons, in order to suggest a possible physiological mechanism underlying multisensory integration in SC. The model includes three distinct neural areas: two unimodal areas (auditory and visual) are devoted to a topological representation of external stimuli, and communicate via synaptic connections with a third downstream area (in the SC) responsible for multisensory integration. The present simulations show that the model, with a single set of parameters, can mimic various responses to different combinations of external stimuli including the inverse effectiveness, both in terms of multisensory enhancement and contrast, the existence of within- and cross-modality suppression between spatially disparate stimuli, a reduction of network settling time in response to cross-modal stimuli compared with individual stimuli. The model suggests that non-linearities in neural responses and synaptic (excitatory and inhibitory) connections can explain several aspects of multisensory integration.

Lesion and imaging studies have implicated the ventromedial prefrontal cortex (vmPFC) in economic decisions and social interactions, yet its exact functions remain unclear. Here, we investigated the hypothesis that the vmPFC represents the subjective value or desirability of future outcomes during social decision-making. Both vmPFC-damaged patients and control participants acted as the responder in a single-round ultimatum game. To test outcome valuation, we contrasted concrete, immediately available gains with abstract, future ones. To test social valuation, we contrasted interactions with a human partner and those involving a computer. We found that, compared to controls, vmPFC patients substantially reduced their acceptance rate of unfair offers from a human partner, but only when financial gains were presented as abstract amounts to be received later. When the gains were visible and readily available, the vmPFC patients' acceptance of unfair offers was normal. Furthermore, unlike controls, vmPFC patients did not distinguish between unfair offers from a human agent and those from a computerized opponent. We conclude that the vmPFC encodes the expected value of abstract, future goals in a common neural currency that takes into account both reward and social signals in order to optimize economic decision-making.

Neurons in the superior colliculus (SC) integrate stimuli of different modalities. In this work, a mathematical model of the integrative response of SC neurons is presented, to gain a deeper insight into the possible mechanisms involved, and on individual differences in integrative abilities. The model includes two unimodal areas (auditory and visual), which communicate via feedforward and feedback synapses with a third multisensory area. Each neuron is represented via a sigmoidal relationship and a first-order dynamic. Neurons in the same area interact via lateral synapses. Simulations show that the model, with a basal parameter set, can mimic various responses described in the literature: (i) multimodal enhancement in response to two cross-modal stimuli within the receptive field, according to the inverse-effectiveness principle; (ii) within-modality suppression and cross-modality suppression by a stimulus (of the same or other modality) placed outside the receptive field. Sensitivity analysis on model parameters demonstrate that different classes of neurons observed in the literature (such as, neurons which exhibit within modality suppression without cross-modality suppression, or neurons with asymmetrical cross-modality suppression) can be reproduced by simply modifying synaptic strengths in the multimodal area. Finally, exempla of the possible role of feedback mechanisms in ambiguous conditions (such as reinforcement of a poor perception by a second cross-modal stimulus, or ventriloquism) are shown and critically discussed. The model may be of value to assess the different mechanisms responsible for multisensory integration in the SC, and, in future, to study neural plasticity in multisensory systems during development or rehabilitation.

Both theoretical and empirical studies suggest that numerical processing is intimately linked to representations of goal-directed hand actions. Further evidence for this possibility is provided here by the results of two experiments, both of which revealed a powerful influence of numerical magnitude on the selection of hand grasping movements. Human participants performed either power or precision grip responses based on the semantic properties (e.g., parity) of visual Arabic numerals, in Experiment 1, or depending on their surface characteristics (e.g., colour), in Experiment 2. In both the experiments, it was found that small numerical values facilitated precision grip (commonly used to grasp small objects), while large numerical value potentiated power grip (commonly used to grasp large objects). These findings reveal that perceiving numbers can automatically prime grasping gestures, in a similar manner to viewing physical objects. This result is coherent with the view that processing of symbolic (numerical) and physical quantitative information converges onto a shared magnitude system representing the coordinates of action.

Animal studies have shown that the superior colliculus (SC) is important for synthesising information from multiple senses into a unified map of space. Here, we tested whether the SC is a critical neural substrate for multisensory spatial integration in humans. To do so, we took advantage of neurophysiological findings revealing that the SC does not receive direct projections from short-wavelength-sensitive S cones. In a simple reaction-time task, participants responded more quickly to concurrent peripheral (extra-foveal) audiovisual (AV) stimuli than to an auditory or visual stimulus alone, a phenomenon known as the redundant target effect (RTE). We show that the nature of this RTE was dependent on the colour of the visual stimulus. When using purple short-wavelength stimuli, to which the SC is blind, RTE was simply explained by probability summation, indicating that the redundant auditory and visual channels are independent. Conversely, with red long-wavelength stimuli, visible to the SC, the RTE was related to nonlinear neural summation, which constitutes evidence of integration of different sensory information. We also demonstrate that when AV stimuli were presented at fixation, so that the spatial orienting component of the task was reduced, neural summation was possible regardless of stimulus colour. Together, these findings provide support for a pivotal role of the SC in mediating multisensory spatial integration in humans, when behaviour involves spatial orienting responses.

Recent fMRI evidence has detected increased medial prefrontal activation during contemplation of personal moral dilemmas compared to impersonal ones, which suggests that this cortical region plays a role in personal moral judgment. However, functional imaging results cannot definitively establish that a brain area is necessary for a particular cognitive process. This requires evidence from lesion techniques, such as studies of human patients with focal brain damage. Here, we tested 7 patients with lesions in the ventromedial prefrontal cortex and 12 healthy individuals in personal moral dilemmas, impersonal moral dilemmas and non-moral dilemmas. Compared to normal controls, patients were more willing to judge personal moral violations as acceptable behaviors in personal moral dilemmas, and they did so more quickly. In contrast, their performance in impersonal and non-moral dilemmas was comparable to that of controls. These results indicate that the ventromedial prefrontal cortex is necessary to oppose personal moral violations, possibly by mediating anticipatory, self-focused, emotional reactions that may exert strong influence on moral choice and behavior.

The contribution of the medial prefrontal cortex, particularly the anterior cingulate cortex (ACC), to cognitive control remains controversial. Here, we examined whether the rostral ACC is necessary for reactive adjustments in cognitive control following the occurrence of response conflict [Botvinick, M. M., Braver, T. S., Barch, D. M., Carter, C. S., & Cohen, J. D. Conflict monitoring and cognitive control. Psychological Review, 108, 624-652, 2001]. To this end, we assessed 8 patients with focal lesions involving the rostral sector of the ACC (rACC patients), 6 patients with lesions outside the frontal cortex (non-FC patients), and 11 healthy subjects on a variant of the Simon task in which levels of conflict were manipulated on a trial-by-trial basis. More specifically, we compared Simon effects (i.e., the difference in performance between congruent and incongruent trials) on trials that were preceded by high-conflict (i.e., incongruent) trials with those on trials that were preceded by low-conflict (i.e., congruent) trials. Normal controls and non-FC patients showed a reduction of the Simon effect when the preceding trial was incongruent, suggestive of an increase in cognitive control in response to the occurrence of response conflict. In contrast, rACC patients attained comparable Simon effects following congruent and incongruent events, indicating a failure to modulate their performance depending on the conflict level generated by the preceding trial. Furthermore, damage to the rostral ACC impaired the posterror slowing, a further behavioral phenomenon indicating reactive adjustments in cognitive control. These results provide insights into the functional organization of the medial prefrontal cortex in humans and its role in the dynamic regulation of cognitive control.

Two experiments were conducted to examine the Simon effect (i.e., faster responding when irrelevant stimulus location corresponds with response location than when it does not) in visual search tasks. The search items were arranged in a 4 x 4 grid, and grid locations were coded into sets of four, two involving inner columns and two involving outer columns. In experiment 1, three different types of inefficient search tasks were used. The Simon effects were shown to be larger when the target appeared in one of the outer columns than in one of the inner columns ("laterality effect"). This pattern of results was not observed when distractors were absent, suggesting that the laterality effect depends on the operation of selective attention. In experiment 2, a pop-out search task was used, and no significant effect of target location on the Simon effect was found. Interpretations of the results based on the attention-shift account and referential-coding account were discussed.

This work describes an original neural network to simulate representation of the peripersonal space around one hand, in basal conditions and after training with a tool used to reach the far space. The model is composed of two unimodal areas (visual and tactile) connected to a third bimodal area (visual-tactile). Neurons in the bimodal area integrate visual and tactile information and are activated only when a stimulus falls inside the peripersonal space. Moreover, the model assumes that synapses linking unimodal to bimodal neurons can be reinforced by an Hebbian rule during training, but this reinforcement is also under the influence of attention mechanisms. Results show that the peripersonal space, which includes just a small visual space around the hand in normal conditions, becomes elongated in the direction of the tool after training. This expansion of the peripersonal space depends on an expansion of the visual receptive field of bimodal neurons, due to a reinforcement of visual synapses, which were just latent before training. The model may be of value to analyze the neural mechanisms responsible for representing and plastically shaping peripersonal space, and in perspective, for interpretation of psychophysical data on patients with brain damage.

It has been proposed that the mental representation of a graspable object involves not only a description of its visual properties but also encodings of the motor programs to act upon it. Thus, observing a handle automatically primes the motor programs responsible for reaching and grasping it. Here, we provide neurological evidence that such action-related object features can bias visual selection. Two patients with visual extinction after right-parietal injury detected cups with left- or right-oriented handles, briefly displayed in either or both visual fields. People with this disorder have deficient awareness for stimuli toward the contralesional, left side of space, especially when competing stimuli appear further to the right. This contralesional extinction was significantly reduced when cups had handles affording a left-hand grasp, even though no hand response was required. No effect was found when handles were replaced with patches equated for position, size, and mean luminance. These data suggest that action-related information may be correctly extracted by the visual system, even though they are unavailable for conscious report. It is proposed that an object affordance for grasping modulates attentional selection by activating specific motor schema that, in turn, enhance the competitive strength of that object representation.

Observing a face with averted eyes results in a reflexive shift of attention to the gazed-at location. Here we present results that show that this effect is weaker in males than in females (Experiment 1). This result is predicted by the 'extreme male brain' theory of autism (Baron-Cohen, 2003), which suggests that males in the normal population should display more autism-like traits than females (e.g., poor joint attention). Indeed, participants' scores on the Autism-Spectrum Quotient (Baron-Cohen, Wheelwright, Stott, Bolton, & Goodyear, 2001) negatively correlated with cueing magnitude. Furthermore, exogenous orienting did not differ between the sexes in two peripheral cueing experiments (Experiments 2a and 2b). However, a final experiment showed that using nonpredictive arrows instead of eyes as a central cue also revealed a large gender difference. This demonstrates that reduced orienting from central cues in males generalizes beyond gaze cues. These results show that while peripheral cueing is equivalent in the male and female brains, the attention systems of the two sexes treat noninformative symbolic cues very differently.

Results obtained with functional magnetic resonance imaging show that both feeling a moderately painful pinprick stimulus to the fingertips and witnessing another person's hand undergo similar stimulation are associated with common activity in a pain-related area in the right dorsal anterior cingulate cortex (ACC). Common activity in response to noxious tactile and visual stimulation was restricted to the right inferior Brodmann's area 24b. These results suggest a shared neural substrate for felt and seen pain for aversive ecological events happening to strangers and in the absence of overt symbolic cues. In contrast to ACC 24b, the primary somatosensory cortex showed significant activations in response to both noxious and innocuous tactile, but not visual, stimuli. The different response patterns in the two areas are consistent with the ACC's role in coding the motivational-affective dimension of pain, which is associated with the preparation of behavioral responses to aversive events.

Neglect dyslexia is a disturbance in the allocation of spatial attention over a letter string following unilateral brain damage. Patients with this condition may fail to read letters on the contralesional side of an orthographic string. In some of these cases, reading is better with words than with non-words. This word superiority effect has received a variety of explanations that differ, among other things, with regard to the spatial distribution of attention across the letter string during reading. The primary goal of the present study was to explore the interaction between attention and lexical processes by recording eye movements in a patient (F.C.) with severe left neglect dyslexia who was required to read isolated word and non-word stimuli of various length. F.C.'s ocular exploration of orthographic stimuli was highly sensitive to the lexical status of the letter string. We found that: (1) the location to which F.C. directed his initial saccade (obtained approximately 230 ms post-stimulus onset) differed between word and non-word stimuli; (2) the patient spent a greater amount of time fixating the contralesional side of word than non-word strings. Moreover, we also found that F.C. failed to identify the left letters of a string despite having fixated them, thus showing a clear dissociation between eye movement responses and conscious access to orthographic stimuli. Our data suggest the existence of multiple interactions between lexical, attentional and eye movement systems that occur from very initial stages of visual word recognition.

Brain areas exist that appear to be specialized for the coding of visual space surrounding the body (peripersonal space). In marked contrast to neurons in earlier visual areas, cells have been reported in parietal and frontal lobes that effectively respond only when visual stimuli are located in spatial proximity to a particular body part (for example, face, arm or hand) [1-4]. Despite several single-cell studies, the representation of near visual space has scarcely been investigated in humans. Here we focus on the neuropsychological phenomenon of visual extinction following unilateral brain damage. Patients with this disorder may respond well to a single stimulus in either visual field; however, when two stimuli are presented concurrently, the contralesional stimulus is disregarded or poorly identified. Extinction is commonly thought to reflect a pathological bias in selective vision favoring the ipsilesional side under competitive conditions, as a result of the unilateral brain lesion [5-7]. We examined a parietally damaged patient (D.P.) to determine whether visual extinction is modulated by the position of the hands in peripersonal space. We measured the severity of visual extinction in a task which held constant visual and spatial information about stimuli, while varying the distance between hands and stimuli. We found that selection in the affected visual field was remarkably more efficient when visual events were presented in the space near the contralesional finger than far from it. However, the amelioration of extinction dissolved when hands were covered from view, implying that the effect of hand position was not mediated purely through proprioception. These findings illustrate the importance of the spatial relationship between hand position and object location for the internal construction of visual peripersonal space in humans.

Previous findings have demonstrated the existence of a visual peripersonal space centered on the hand in humans and its modulatory effects on tactile perception. A strong modulatory effect of vision on touch perception was found when a visual stimulus was presented near the hand. In contrast, when the visual stimulus was presented far from the hand, only a weak modulatory effect was found. The aim of the present study was to verify whether such cross-modal links between touch and vision in the peripersonal space centered on the hand could be mediated by proprioceptive signals specifying the current hand positions or if they directly reflect an interaction between two sensory modalities, i.e., vision and touch. To this aim, cross-modal effects were studied in two different experiments: one in which patients could see their hands and one in which vision of their hands was prevented. The results showed strong modulatory effects of vision on touch perception when the visual stimulus was presented near the seen hand and only mild effects when the vision of the hand was prevented. These findings are explained by referring to the activity of bimodal neurons in premotor and parietal cortex of macaque, which have tactile receptive fields on the hand, and corresponding visual receptive fields in the space immediately adjacent to the tactile fields. One important feature of these bimodal neurons is that their responsiveness to visual stimuli delivered near the body part is reduced or even extinguished when the view of the body part is prevented. This implies that, at least for the hand, the vision of the hand is crucial for determining the spatial mapping between vision and touch that takes place in the peripersonal space. In contrast, the proprioceptive signals specifying the current hand position in space do not seem to be relevant in determining the cross-modal interaction between vision and touch.

We describe a patient (P.S.) who, following a right prestriate lesion, reported that objects in the left visual field appeared distorted and smaller than those on the right. Other aspects of visual processing were remarkably unaffected. We carried out a series of size comparison tests using simple or complex stimuli and requiring different types of behavioural responses. We found that P.S. significantly underestimated the size of stimuli presented in her left visual field. When comparison tasks involved stimuli placed along the vertical axis or in the right visual field, P.S. performed well. The vertical and horizontal components of size distortion were found to be differentially affected. We conclude that size processing may be dissociated from other aspects of visual processing, such as form or colour processing, and depends critically on part of the occipital, prestriate areas (Brodmann areas 18-19).

Current interpretations of extinction suggest that the disorder is due to an unbalanced competition between ipsilesional and contralesional representations of space. The question addressed in this study is whether the competition between left and right representations of space in one sensory modality (i.e., touch) can be reduced or exacerbated by the activation of an intact spatial representation in a different modality that is functionally linked to the damaged representation (i.e., vision). This hypothesis was tested in 10 right-hemisphere lesioned patients who suffered from reliable tactile extinction. We found that a visual stimulus presented near the patient"s ipsilesional hand (i.e., visual peripersonal space) inhibited the processing of a tactile stimulus delivered on the contralesional hand (cross-modal visuotactile extinction) to the same extent as did an ipsilesional tactile stimulation (unimodal tactile extinction). It was also found that a visual stimulus presented near the contralesional hand improved the detection of a tactile stimulus applied to the same hand. In striking contrast, less modulatory effects of vision on touch perception were observed when a visual stimulus was presented far from the space immediately around the patient"s hand (i.e., extrapersonal space). This study clearly demonstrates the existence of a visual peripersonal space centered on the hand in humans and its modulatory effects on tactile perception. These findings are explained by referring to the activity of bimodal neurons in premotor and parietal cortex of macaque, which have tactile receptive fields on the hand and corresponding visual receptive fields in the space immediately adjacent to the tactile fields.

Following a trauma causing bilateral posterior brain damage, a patient complained of dyslexia and prosopagnosia, but not object agnosia. On testing she showed intact recognition of object drawings, even when it was assessed with perceptually demanding tasks such as Ghent's overlapping figures and Street completion test. This pattern of deficit is inconsistent with Farah's (1990) prediction that the simultaneous occurrence of alexia and prosopagnosia is invariably associated with object agnosia. The patient's reading performance had the features typically found in letter-by-letter readers. On face tests, she showed a discrepancy between the impairment exhibited in familiarity recognition and famous face naming and the correct (though slow) performance in matching the names of famous persons with their photographs. This apparent contradiction was clarified by showing that the patient had maintained the ability to generate the mental images of famous faces in response to the presentation of their names. We assume that face recognition units were intact, but partially disconnected from the output of perceptual processing.

Studies of normal behaviour have shown that the process of selection takes a finite time, one measure of which is the attentional dwell time, that is the period of interference produced by one attended stimulus on a subsequent one. Here we investigated the time for selection in FB, a neurological patient suffering from a visuospatial disorder of attention (unilateral extinction). FB was asked to identify two letters displayed in rapid succession either to the left (damaged), or to the right (intact) visual hemifield. By varying the interval between stimuli, we measured how long the first letter continued to interfere with accuracy on the second- that is the first letter's attentional demand over time. The results showed that the process of selection has an abnormal duration in the affected visual field, being at least twice as long as in the intact field. We suggest that the slowed visual processing for the contralesional object may contribute to the competitive bias against that object which is the hallmark of unilateral extinction.

A fully recurrent neural network model was optimized to perform a spatial delayed matching-to-sample task (DMS). In DMS, a stimulus is presented at a sample location, and a match is reported when a subsequent stimulus appears at that location. Stimuli elsewhere are ignored. Computationally, a DMS system could consist of memory and comparison components. The model, although not constrained to do so, worked by using two corresponding classes of neurons in the hidden layer: storage and comparator units. Storage units form a dynamical system with one fixed point attractor for each sample location. Comparator units constitute a system receiving input from these storage units as well as from current input stimuli. Both unit types were tuned directionally. These two sources of information combine to create unique patterns of activity that determine whether a match has occurred. In networks with abundant hidden units, the storage and comparator functions were distributed so that individual units took part in both. We compared the model with single-neuron recordings from premotor (PM) and prefrontal (PF) cortex. As shown previously, many PM and PF neurons behaved like storage units. In addition, both regions contain neurons that behave like the comparator units of the model and appear to have dual functionality similar to that observed in the model units. No neuron in either area had properties identical to those of the match output neuron of the model. However, four PF neurons and one PM neuron resembled the output signal more closely than any of the hidden units of the model.

Despite the fact that visual extinction is widely considered a space-based disturbance of selective attention, there has been little theoretical consensus about the nature of its pathogenic mechanism. A specific disruption in the ability to disengage attention from ipsilesional stimuli, or a loss of weight with which contralesional objects compete for visual selection, have been hypothesized to account for the disorder. We tested the merits of these two explanations in a right-hemisphere-lesioned patient, FB, who failed to recognize a contralesional target only when it was shown concurrently to an ipsilesional target (i.e. visual extinction). His task was to report two target letters presented in rapid succession to the left and right of the fixation point. The order of stimulus presentation (Left-First vs Right-First), and the intertarget interval (stimulus onset asynchrony) were varied systematically. We showed that contralesional extinction may occur for successively presented targets, not just for stimuli displayed at the same time. Of most importance, FB was seriously and equally impaired in dealing with a contralesional stimulus when this either preceded the ipsilesional stimulus or followed it by an interval less than about 600 msec. The data appear to contradict the disengagement hypothesis, which predicted a substantial reduction of extinction when a stimulus was displayed first into the lesioned side of space. We suggest that a competitive model of visual selective attention fits the data quite well.

We have studied the distortion of perceived time in a patient with left neglect. This patient consistently over-estimated the duration of stimuli in the neglected space. Overestimation was observed both with an interval comparison (300/700 ms) and with a time production (1 s) paradigm. We suggest that encoding duration in the hundreds of milliseconds range is a process based on an internal clock mechanism. The functioning of that clock varies as a function of the processing load.

In the typical course of daily events, we often gaze at an object, attend to its features and its place, reach toward it and grasp it, all with an awareness of what we are doing at the time. But behavior is not always thus. Gaze, attention, limb movement direction and awareness can be behaviorally dissociated from each other, and this review focuses on one such dissociation: that between the perception of an object and the use of that object's inherent spatial and nonspatial information for mediating visuomotor control. We review evidence that partially different neuronal systems underlie these two aspects of visual information processing. In neurophysiological studies of the primate frontal lobe, it has been possible to demonstrate that neural signals appearing to be visual responses reflect, at least in part, the motor significance of a stimulus. This finding has been confirmed, in separate studies, for both spatial and nonspatial visual information and supports the hypothesis that some frontal cortex activity reflects the selection and guidance of action rather than the properties of visual stimuli, per se. These findings are discussed in the context of neuropsychological studies indicating that accurate and appropriate movements are possible without perceptual awareness of the information guiding those movements.

We report a patient who, following a left fronto-temporal lesion, showed a complete sparing of the semantic store and a deficit of word production characterized by two types of dissociations. First, oral and written output was severely disrupted in naming and partially impaired in repetition, writing to dictation and oral spelling, with the exception of verbs, which were normally produced in every modality and condition of stimulation. Second, reading was normal for all type of words as well as non-words. This pattern of deficits suggests two functional lesions, one affecting the connections between the semantic store and the phonological lexicon and the other damaging the sublexical route that converts sound to sound and sound to print. It also implies that words are independently organized in the phonological lexicon, based on their grammatical class and have discrete connections with the semantic store. However, CT scan evidence does not support the hypothesis that this functional dissociation finds its anatomical correlate in the specialization of the frontal premotor cortex for verbs and the antero-medial temporal cortex for nouns. In spite of his normal reading performance, both in terms of comprehension and of accuracy and speed in word production, the patient complained that he met with great difficulty in reading newspapers and books, to the point that he had to renounce to this previously favourite activity. It was found that it took him time and effort to grasp the meaning of complex sentences and passages and it was speculated that, contrary to single words and elementary sentences, comprehension of this type of material cannot be achieved by the mere access of orthographic stimuli to semantics, but requires the retrieval of word-forms. It would appear that a patient, whose lexical route is blocked, can only read passages, by first converting print to sound via the sublexical route and then re-entering the semantic store with oral input.

A persistent line of inquiry for the students of visuo-spatial neglect has involved the perceptual frame of reference respect to which the neglected region of space is defined. On standard testing conditions viewer-centered and object-centered systems of coordinates are confounded. In order to disambiguate these two reference frames FB, a patient with severe left visual neglect consequent upon a right parieto-temporal haemorrhage, was asked to identify chimeric figures presented at different orientations. FB continued to recognize poorly the left side of chimeric figures even when the display was rotated 90 degrees clockwise or anticlockwise so that the 'left' of the chimeric fell on the patient's egocentric up or down, respectively. The result suggests that, at least under the present testing conditions, unilateral neglect is tied to the principal (top-bottom) axis of the object. Object-centered vs. (viewer-centered) representational accounts of this finding are discussed.

A patient (C.B.) with severe left visuo-spatial neglect and hemianopia after right hemisphere stroke was tested on three conditions of a clock-drawing task. Either on spontaneous drawing or when the number sequence was provided by the experimenter, C.B. drew a clockface with left-sided numbers transposed to the right side of the dial. By contrast, when each number was drawn on a separate dial, its location was correct and there was no transposition. Directional hypokinesia or a representational deficit cannot explain these effects. It is proposed that a deficit in disengaging attention from right-sided visual stimuli plays a critical role in some forms of number transpositions.

We examined neuronal activity in the primate premotor (PM) and prefrontal (PF) areas during a demanding spatial matching task. On each behavioral trial, a rhesus monkey moved its forelimb when a visual stimulus, called the "prime stimulus," reappeared at a previously cued location. Because it triggered a movement, the part of space cued by the prime stimulus had to be either remembered or attended during the time between prime stimulus presentations. Between the first and second appearances of the prime stimulus, behaviorally irrelevant visual stimuli could appear at one or several locations other than that of the prime stimulus. We could thereby examine the activity that followed a stimulus when it was attended versus when it was irrelevant and presumably unattended. We found that visuospatial attention affected neuronal activity in both the motor and "nonmotor" parts of the frontal cortex. The magnitude of attention effects exceeded that previously reported--a finding that probably resulted from the intensive attentional demands of the present task.

We examined whether reported physiological distinctions between prefrontal (PF) and premotor (PM) areas reflect true dissimilarity or instead result from technical considerations such as differences among species, individuals, or behavioural, physiological and anatomical techniques. A Rhesus monkey performed a task involving 2 stimulus events on each trial: the first stimulus appeared briefly, then after a delay period, 2 peripheral stimuli appeared simultaneously. The monkey had to delay responding for an additional, self-timed instructed delay period, then contact a touch pad beneath the peripheral stimulus of the colour matching the first stimulus. PM and PF cortex differ in several respects. More PF than PM neurons discharge during the presentation of the first stimulus, and only PF neurons show phasic bursts of activity shortly after that stimulus disappears. During the instructed delay period, cells in PF begin activity earlier than PM neurons, whereas PM neurons continue their activity longer. Similarly, PF cells show greater discharge modulation early in the instructed delay period compared with PM cells, which discharge more intensely later. Cells with apparent selectivity for stimulus characteristics appear only in PF. Thus our results support the view that PM and PF have distinctive physiological properties that cannot be accounted for by technical considerations alone. In addition, we describe the activity cells in a cortical region, here termed the dorsomedial frontal cortex, which has a distinctive dysgranular cytoarchitecture and has physiological properties that ally it with PF.

This report describes an 18-year-old woman who, after a febrile illness, developed opsoclonus, truncal ataxia and mild body tremulousness. The oculomotor disorder was documented by electro-oculography. The results of extensive neurological investigations, including CT scan, visual, auditory and somesthetic evoked potentials, nuclear magnetic resonance and complete cerebrospinal fluid evaluation, were negative. The patient recovered completely within about 1 month. After having thoroughly analyzed the pertinent literature, we conclude that the pathogenetic hypothesis of direct encephalitic damage is unproved, and that these peculiar unwanted ocular movements can be explained by assuming an abnormality of "pause" cell control over saccadic "burst" neurons.