Effects of emotional prosody on auditory extinction for voices in patients with spatial neglect

The response of attention systems to emotional stimuli has been intensively investigated in the visual modality. Several findings suggest that neural mechanisms influencing selective attention towards emotional stimuli involve brain systems that are partly independent of cortical networks associated with the control of voluntary attention. To test this hypothesis in the auditory modality, we used a dichotic-listening paradigm in six right-hemisphere patients with left spatial neglect syndrome and left ear extinction during bilateral auditory stimulation. Three different meaningless emotional prosodic utterances (anger, fear, and happiness) were presented to the right or left ear, either alone or paired with another neutral utterance on the other side. Results showed fewer misses for emotional relative to neutral stimuli presented to the left ear, for all emotion categories, including happiness. In addition, we also examined the correlation between the site of brain lesions and the performance of patients for reporting left-ear stimuli. This exploratory anatomical analysis suggested that the relative advantage for emotional over neutral voices may be modulated by the site and extent of brain damage. This modulation consists of reduced influences of emotional prosody in patients with lesions in right ventral prefrontal lobe or right superior temporal cortex. Taken together, our results have provided new evidence that emotional attention mechanisms may be triggered in the auditory modality by negative and positive vocal stimuli.     

Sustained interactions between perception and action in visual extinction and neglect: Evidence from sequential pointing

Interactions between perception and action were examined by assessing the effects of action programming on extinction and neglect. In an extension of prior work, effects of sequential motor programming were assessed under conditions in which attention was first directed to an ipsilesional stimulus. Despite pointing and reporting a stimulus on the ipsilesional side first, programming a second action to the contralesional side reduced the spatial deficit on report, improving the report of contralesional stimuli (relative to when the patient just pointed to the ipsilesional side) while decreasing the report of ipsilesional items. The data suggest that perception and action interact through motor feedback to early visual coding, helping a patient overcome a lack of visual awareness to contralesional stimuli. This is effective even when attention has to be disengaged from the ipsilesional side suggesting that motor programming decreases ipsilesional capture and exerts a sustained influence on perception.     

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

In normal observers, visual search is facilitated for targets with salient attributes. We compared how two different types of cue (expression and colour) may influence search for face targets, in healthy subjects (n = 27) and right brain-damaged patients with left spatial neglect (n = 13). The target faces were defined by their identity (singleton among a crowd of neutral faces) but could either be neutral (like other faces), or have a different emotional expression (fearful or happy), or a different colour (red-tinted). Healthy subjects were the fastest for detecting the colour-cued targets, but also showed a significant facilitation for emotionally cued targets, relative to neutral faces differing from other distracter faces by identity only. Healthy subjects were also faster overall for target faces located on the left, as compared to the right side of the display. In contrast, neglect patients were slower to detect targets on the left (contralesional) relative to the right (ipsilesional) side. However, they showed the same pattern of cueing effects as healthy subjects on both sides of space; while their best performance was also found for faces cued by colour, they showed a significant advantage for faces cued by expression, relative to the neutral condition. These results indicate that despite impaired attention towards the left hemispace, neglect patients may still show an intact influence of both low-level colour cues and emotional expression cues on attention, suggesting that neural mechanisms responsible for these effects are partly separate from fronto-parietal brain systems controlling spatial attention during search.     

Perceived gaze direction in faces and spatial attention: a study in patients with parietal damage and unilateral neglect

Perceived gaze in faces is an important social signal that may influence orienting of attention in normal observers. Would such effects of gaze still occur in patients with right parietal damage and left neglect who usually fail to attend to contralesional space? Two experiments tested for effects of perceived gaze on visual extinction. Face or shape stimuli were presented in the right, left, or both hemifields, with faces looking either straight ahead or toward the opposite field. On bilateral trials, patients extinguished a left shape much less often when a concurrent right face looked leftward rather than straight ahead. This occurred, even though gaze was not relevant to the task and processing of facial signals implied attention to a competing ipsilesional stimulus. By contrast, rightward gaze in faces presented on the left side had no effect on extinction, suggesting that gaze cues are not extracted without attention. Two other experiments examined effects of perceived gaze on the detection of peripheral targets. Targets appeared at one of four possible locations to the right or left of a central face looking either toward the target location, another location on the same side, the opposite side, or straight ahead. Face and gaze were not relevant to the task and not predictive of target location. Patients responded faster when the face looked toward the target on both the contralesional and ipsilesional sides. In contralesional space, gaze allowed shifting of attention in a specific quadrant direction, but only to the first target along the scan path when there were different possible locations on the same side. By contrast, in intact ipsilesional space, attention was selectively directed to one among different eccentric locations. Control experiments showed that symbolic arrow cues did not produce similar effects. These results indicate that even though parietal damage causes spatial neglect and impairs the representation of location on the contralesional side, perceived gaze in faces can still trigger automatic shifts of attention in the contralesional direction, suggesting the existence of specific and anatomically distinct attentional mechanisms.     

Neural correlates of crossmodal visual-tactile extinction and of tactile awareness revealed by fMRI in a right-hemisphere stroke patient

We used fMRI to study the neural correlates of crossmodal, visual-tactile extinction in a single case (patient GK). GK has chronic extinction after a lesion centred on right inferior parietal cortex, and has previously been investigated extensively in purely visual fMRI studies [e.g. Rees, G., Wojciulik, E., Clarke, K., Husain, M., Frith, C., & Driver, J. (2000). Unconscious activation of visual cortex in the damaged right hemisphere of a parietal patient with extinction. Brain, 123(Pt 8), 1624-1633; Rees, G., Kreiman, G., & Koch, C. (2002). Neural correlates of consciousness in humans. Nature Reviews Neuroscience, 3(4), 261-270]. With concurrent stimulation of the right visual field plus left index finger, GK showed crossmodal extinction of left touch on approximately half of such trials here (reflecting impaired sensitivity, i.e. lowered d-prime), albeit becoming aware of left touch on the other half. fMRI revealed activation of contralateral primary somatosensory cortex on crossmodal trials when touch was extinguished from awareness, suggesting unconscious residual processing there. When GK became aware of the left touch, additional activation was found in surviving right parietal cortex, and in frontal regions; moreover, functional coupling was enhanced with a region of frontal cortex implicated in awareness by previous work. Finally, on trials where crossmodal extinction arose, surviving right parietal cortex showed stronger functional coupling with the left visual and right somatosensory regions driven by the competing stimuli, indicating that crossmodal extinction arises when inputs to separate modalities interact competitively via multimodal cortex.     

Spatial and temporal dynamics of visual search tasks distinguish subtypes of unilateral spatial neglect: Comparison of two cases with viewer-centered and stimulus-centered neglect

We developed a computerised test to evaluate unilateral spatial neglect (USN) using a touchscreen display, and estimated the spatial and temporal patterns of visual search in USN patients. The results between a viewer-centered USN patient and a stimulus-centered USN patient were compared. Two right-brain-damaged patients with USN, a patient without USN, and 16 healthy subjects performed a simple cancellation test, the circle test, a visuomotor search test, and a visual search test. According to the results of the circle test, one USN patient had stimulus-centered neglect and a one had viewer-centered neglect. The spatial and temporal patterns of these two USN patients were compared. The spatial and temporal patterns of cancellation were different in the stimulus-centered USN patient and the viewer-centered USN patient. The viewer-centered USN patient completed the simple cancellation task, but paused when transferring from the right side to the left side of the display. Unexpectedly, this patient did not exhibit rightward attention bias on the visuomotor and visual search tests, but the stimulus-centered USN patient did. The computer-based assessment system provided information on the dynamic visual search strategy of patients with USN. The spatial and temporal pattern of cancellation and visual search were different across the two patients with different subtypes of neglect.     

Spatiotemporal dynamics of attention in visual neglect: a case study

Patients with visual neglect are often unaware of contralesional visual stimuli. Recent studies have demonstrated non-spatial as well as spatial deficits in allocating attention in neglect patients. We examined the spatiotemporal dynamics of directing attention in a patient with neglect for visual objects appearing in the left side of space by using a version of the attentional blink paradigm. presenting two visual stimuli in succession. The first target (T1) was presented at fixation. The location of the second target (T2) and time between the two targets was varied. When T2 appeared to the left, the patient required more time between targets to identify both accurately, compared to when T2 appeared at fixation or to the right. Our findings demonstrate a spatial and temporal gradient of attention. The results are discussed with respect to current models of visual processing in visual neglect.     

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

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

Spatial neglect in a patient with logopenic progressive aphasia

Spatial neglect and extinction are induced by posterior superior temporal and inferior parietal dysfunction. In patients with logopenic progressive aphasia (LPA) these structures are often degenerated, but there are no reports of these disorders being associated. A 53-year-old man with the signs of LPA revealed right-sided spatial neglect on line bisection and drawing tests as well as multimodal extinction. MRI showed left hemispheric posterior temporoparietal atrophy. Since injury to the core structures for these aphasic and attentional syndromes overlaps, patients with LPA should be screened for spatial neglect and extinction.     

LH-RH agonists modulate amygdala response to visual sexual stimulation: A single case fMRI study in pedophilia

Pedophilia is characterized by a persistent sexual attraction to prepubescent children. Treatment with anti-androgen agents, such as luteinizing hormone-releasing hormone (LH-RH) agonists, reduces testosterone levels and thereby sexual drive and arousal. We used functional magnetic resonance imaging (fMRI) to compare visual erotic stimulation pre- and on-treatment with the LH-RH agonist leuprolide acetate in the case of homosexual pedophilia. The pre-treatment contrasts of the erotic pictures against the respective neutral pictures showed an activation of the right amygdala and adjacent parahippocampal gyrus that decreased significantly under treatment with leuprolide acetate. Our single case fMRI study supports the notion that anti-androgens may modify amygdala response to visual erotic stimulation, a hypothesis that should be further examined in larger studies.     

Attention and amygdala activity: an fMRI study with spider pictures in spider phobia

Facilitated detection of threatening visual cues is thought to be adaptive. In theory, detection of threat cues should activate the amygdala independently from allocation of attention. However, previous studies using emotional facial expressions as well as phobic cues yielded contradictory results. We used fMRI to examine whether the allocation of attention to components of superimposed spider and bird displays modulates amygdala activation. Nineteen spider-phobic women were instructed to identify either a moving or a stationary animal in briefly presented double-exposure displays. Amygdala activation followed a dose–response relationship: Compared to congruent neutral displays (two birds), amygdala activation was most pronounced in response to congruent phobic displays (two spiders) and less but still significant in response to mixed displays (spider and bird) when attention was focused on the phobic component. When attention was focused on the neutral component, mixed displays did not result in significant amygdala activation. This was confirmed in a significant parametric graduation of the amygdala activation in the order of congruent phobic displays, mixed displays with attention focus on the spider, mixed displays with focus on the bird and congruent neutral displays. These results challenge the notion that amygdala activation in response to briefly presented phobic cues is independent from attention.

Abnormally speeded saccades to ipsilesional targets in patients with spatial neglect

We mapped the distribution of saccadic reaction times (SRTs) in the visual field of patients with spatial neglect in order to characterise the topography of the bias in spatial orientation peculiar to this disorder. LED-generated stimuli were lit randomly in one of four positions (+/-5 degrees , +/-10 degrees , +/-20 degrees , +/-30 degrees ) along the horizontal meridian in blocks of either ipsilesional or contralesional presentations. Patients were asked to move the gaze as quickly as possible from central fixation to target upon its appearance. Unlike control subjects, patients with neglect showed an asymmetric distribution of visuo-motor performance in the two hemifields with an increasing impairment in target detection and saccadic reaction at increasing eccentricities in the contralesional field. In contrast, in the ipsilesional field they showed abnormally speeded SRTs at 5 degrees and 10 degrees , outperforming even healthy subjects. Latency of saccades increased again at more peripheral ipsilesional locations (20 degrees and 30 degrees ) where there was also a tendency for a higher omission rate as compared to control groups. These results indicate that in neglect patients the spatial orientation bias, as witnessed by saccadic performance, specifically affects an off-centred sector of the ipsilesional space, and this is in keeping with evidence from a previous study using a manual RT paradigm. The generality of this phenomenon across different types of motor response suggests that it depends upon abnormal mechanisms of spatial coding interfering with perceptual processing and orienting behaviour.     

Crossed aphasia with left spatial neglect and visual imperception: a case report

A 64-year-old right-handed woman with no left-handers in the family developed aphasia associated with moderate left hemiparesis and dense left homonymous hemianopia following rupture of a right middle cerebral artery aneurysm and subsequent selective surgery confined to the right hemisphere. Severe left spatial neglect and constructional apraxia were also present. The patient was an achondroplasic dwarf whose previous medical and neurological history was otherwise unremarkable. Computed tomography of the brain showed a large right temporo-insulofrontoparietal lesion. Language and nonverbal cognitive functions were assessed after 2 and 6 months, and then four years later. A reportedly overall language disruption in the acute period evolved into Wernicke's aphasia and then into a mild form of conduction aphasia. The associated left spatial neglect eventually shrank to a minimum. The patient never had clinically detectable visual agnosia, but on specific tests of visual recognition and perception some impairment was found four years after onset. The left hemiparesis disappeared in time while the left hemianopia persisted. This case is a convincing example of an entirely righthanded person in whom both linguistic and visuospatial functions are represented in the right hemisphere. Received: 12 May 2002 / Accepted in revised form: 18 November 2002 Correspondence to L.A. Vignolo     

Manual responses and saccades in chronic and recovered hemispatial neglect: a study using visual search

Hemispatial neglect affects both the ability to respond to targets on the contralesional side of space and to programme saccades to such targets. In the current study, we looked in detail at saccade programming and manual reaction times (RTs) in a range of visual search tasks, in which task difficulty was systematically increased by changing the nature of the distractors. In condition 1, the target was presented with no distractors. In the other conditions, displays contained three distractors that were changed across conditions to manipulate similarity to the target and so task difficulty.We tested two neglect patients, one chronic, one recovered along with two RCVA control patients and 12 age-matched controls. Both neglect patients studied could successfully execute saccades into the neglected field when the target was presented alone. However, a dissociation emerged between the two patients when the target was presented with distractor items. Patient ERs first saccade to target performance in the three search conditions revealed clear effects of distractor type. In contrast for the recovered patient AF, the left/right difference was present for all search displays and appeared to be constant regardless of distractor type. This differential pattern of behaviour may reflect the different underlying neural causes of the neglect in these patients. In the current study, the measurement of saccades allowed the task to be fractionated, and thus, reveal the action of multiple mechanisms controlling saccades in search.     

Individual differences in alexithymia and brain response to masked emotion faces

Alexithymia is considered a dimensional personality trait that refers to a cluster of deficits in the recognition, differentiation, and verbalization of emotions. Research on the neurobiology of alexithymia has focused hitherto on impairments in the controlled processing of emotional information. In the present study automatic brain reactivity to facial emotion was investigated as a function of alexithymia (as assessed by the 20-Item Toronto Alexithymia Scale - TAS-20). During 3 T fMRI scanning, pictures of sad, happy, and neutral facial expression masked by neutral faces were presented to 33 healthy women. A priori regions of interest in the whole brain analysis were cerebral structures that are known to be crucially involved in the emotion perception from the face. Independently from trait anxiety and depression TAS-20 alexithymia was negatively correlated with activation to masked sad and happy faces in several regions of interest (in particular, insula, superior temporal gyrus, middle occipital and parahippocampal gyrus). In addition, the TAS-20 score was negatively correlated with response of the left amygdala to masked sad faces. A reduced automatic reactivity of the amygdala and visual occipito-temporal areas could implicate less automated engagement in the encoding of emotional stimuli in high alexithymia. In addition, a low spontaneous insular and amygdalar responsivity in high alexithymia individuals could be related to an attenuation of basic emotional experiences which may contribute to problems in identifying and differentiating one's feelings.     

Acceleration perception and spatial distortion in a left unilateral neglect patient

To explain relative leftward overextension in a line extension task by left unilateral neglect subjects, Bisiach et al. (1998) suggested that the representation of space is distorted--i.e., dilated towards the left side. If perception of the velocity of a moving stimulus is due to a calculation of the distance covered per unit time in representational space, then a stimulus with uniform linear motion should be perceived as decelerating when moving leftwards in the visual field of a subject with left unilateral neglect. We investigated the perception of acceleration in a patient with left unilateral neglect and spatial distortion (revealed as relative left overextension in a line extension task) using a task in which the stimuli were right and left moving targets with variable acceleration. The patient's ability to perceive acceleration was much lower (higher acceleration threshold) for leftward movements than rightward movements. Fourteen months later unilateral neglect had improved, and the relative left overextension and decreasing acceleration threshold for leftward movements were reduced. By contrast, alterations in the perception of acceleration for leftward movements were not found in a patient with left unilateral neglect and left underextension and in a patient with right brain damage and left hemianopia. These findings in one patient with left spatial unilateral neglect and a relative left overextension in a line extension task are consistent with the hypothesis that representational space is distorted, with a disproportionate leftward expansion, that affects perception of movement.     

Effects of prismatic adaptation on spatial gradients in unilateral neglect: A comparison of visual and auditory target detection with central attentional load

Prismatic adaptation is increasingly recognised as an effective procedure for rehabilitating symptoms of unilateral spatial neglect - producing relatively long-lasting improvements on a variety of spatial attention tasks. The mechanisms by which the aftereffects of adaptation change neglect patients’ performance on these tasks remain controversial. It is not clear, for example, whether adaptation directly influences the pathological ipsilesional attention bias that underlies neglect, or whether it simply changes exploratory motor behaviour. Here we used visual and auditory versions of a target detection task with a secondary task at fixation. Under these conditions, patients with neglect demonstrated a spatial gradient in their ability to orient to the brief, peripheral visual or auditory targets. Following prism adaptation, we found that overall performance on both the auditory and visual task improved, however, most patients in our sample did not show changes in their visual or auditory spatial gradient of attention, despite adequate aftereffects of adaptation and significant improvement in neglect on visual cancellation. Although there were individual cases that suggested prism-induced changes in visual target detection, and even reversal of the visual spatial gradient, such cases were not evident for the auditory modality. The findings indicate that spatial gradients in stimulus-driven attention may be less responsive to the effects of prism adaptation than neglect symptoms in voluntary orienting and exploratory behaviour. Individual factors such as lesion site and symptom severity may also determine the expression of prism effects on spatial neglect.     

Preattentive surface and contour grouping in Kanizsa figures: Evidence from parietal extinction

Visual extinction commonly occurs after unilateral, parietal brain damage and manifests in a failure to identify contralesional stimuli when presented simultaneously with other, ipsilesional stimuli - but full awareness for single stimulus presentations. However, extinction can be substantially reduced when preattentive grouping operations link fragmentary items across hemifields into a coherent object. For instance, one study demonstrated preserved access to bilateral stimulus segments when these could be grouped to form a Kanizsa square [Mattingley, J. B., Davis, G., & Driver, J. (1997). Preattentive filling-in of visual surfaces in parietal extinction. Science, 275, 671-674]. Here, we investigated the relative contributions of distinct object attributes to the spared access in Kanizsa figure completion in extinction, by systematically varying the degree to which bilateral surface filling-in and contour interpolations group disparate items. We demonstrate that surface information can substantially reduce extinction, whereas contour completions showed comparably smaller influences. In summary, such graded influences of object attributes support recurrent models of grouping, first, linking fragmentary parts into coherent surfaces and, second, interpolating the precise boundaries.     

When the brain remembers, but the patient doesn’t: Converging fMRI and EEG evidence for covert recognition in a case of prosopagnosia

The role of the occipito-temporal cortex in visual awareness remains an open question and with respect to faces in particular, it is unclear to what extent the fusiform face area (FFA) may be involved in conscious identification. An answer may be gleaned from prosopagnosia, a disorder in which familiar faces are no longer recognized. This impairment has sometimes been reported to be associated with implicit processing of facial identity, although the neural substrates responsible for unconscious processing remain unknown. In this study, we addressed these issues by investigating the functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) responses to familiar and unfamiliar faces in a well-known prosopagnosic patient (P.S.). Our fMRI results show that faces known prior to the onset of prosopagnosia produce an increase in activation in the lateral fusiform gyrus encompassing the FFA, as well as the right middle frontal gyrus, when compared to unknown faces. This effect is not observed with photographs of celebrities dating after the onset of prosopagnosia. Furthermore, electrophysiological responses show that previously familiar faces differ from unfamiliar ones at around 550 msec.Since covert processing of familiarity is associated with activation in FFA, this structure does not appear to be sufficient to produce awareness of identity. Furthermore, the results support the view that FFA participates in face individuation.     

Evidence for dissociable representations for body image and body schema from a patient with visual neglect

The existence of independent and dissociable representations of the body within the brain for perception (body image) and action (body schema) is currently under debate. Although demonstrations in which fake limbs are incorporated into the body image but not body schema are commonplace, such findings can be explained due to the strength of the illusion rather than autonomous representations. The current study, however, offers striking evidence in favor of a clear dissociation in a patient with visual neglect, such that different fake limbs were incorporated into the body image and body schema simultaneously.