Ego- and Geo-Centered References: A Functional Neuroimagery Study.

INTRODUCTION: The integration of vestibular, visual, and somatosensory cues allows the perception of space through the orientation of our body and surrounding objects with respect to gravity. The main goal of this study was to identify the cortical networks recruited during the representation of body midline and the representation of verticality. METHODS: Thirty right-handed healthy participants were evaluated using fMRI. Brain networks activated during a subjective straight-ahead (SSA) task were compared to those recruited during a subjective vertical (SV) task. RESULTS: Different patterns of cortical activation were observed, with differential increases in the angular gyrus and left cerebellum posterior lobe during the SSA task, in right rolandic operculum and cerebellum anterior lobe during the SV task. DISCUSSION: The activation of these areas involved in visuo-spatial functions suggests that bodily processes of great complexity are engaged in body representation and vertical perception. Interestingly, the common brain networks involved in SSA and SV tasks were comprised of areas of vestibular projection that receive multisensory information (parieto-occipital areas) and the cerebellum, and reveal a predominance of the right cerebral and cerebellar hemispheres. The outcomes of this first fMRI study designed to unmask common and specific neural mechanisms at work in gravity- or body-referenced tasks pave a new way for the exploration of spatial cognitive impairment in patients with vestibular or cortical disorders.

Signs of spatial neglect in unilateral peripheral vestibulopathy.

BACKGROUND AND PURPOSE: In this study, the question of whether egocentric representation of space is impaired in chronic unilateral vestibulopathies was examined. The objective was to test current theories attributing a predominant role to vestibular afferents in spatial cognition and to assess whether representational neglect signs are common in peripheral vestibular loss. METHODS: The subjective straight-ahead (SSA) direction was investigated using a horizontal rod allowing the translation and rotation components of the body midline representation to be dissociated in 21 patients with unilateral vestibular loss (right, 13; left, eight) and in 12 healthy controls. RESULTS: Compared to the controls, the patients with unilateral vestibulopathy showed a translation bias of their SSA, without rotation bias. The translation bias was not lateralized towards the lesioned side as typically found for biases reported after unilateral vestibular loss. Rather, the SSA bias was rightward whatever the side of the vestibular loss. The translation bias correlated with the vestibular loss, as measured by caloric response and vestibulo-ocular reflex gain, but not with the subjective visual vertical or the residual spontaneous nystagmus. CONCLUSION: The present data suggest that the dysfunctions of neural networks involved in egocentred and allocentred representations of space are differentially compensated for in unilateral vestibular defective patients. In particular, they suggest that asymmetrical vestibular inputs to cortical regions lead to representational spatial disturbances as does defective cortical processing of vestibular inputs in spatial neglect after right hemisphere stroke. They also highlight the predominant role of symmetrical and unaltered vestibular inputs in spatial cognition.

Attention orientation to pleasantness and depressive symptomatology predict autonomic reactivity.

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

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

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

Influence of spatial neglect, hemianopia and hemispace on the subjective vertical.

The perception of the vertical is frequently shifted to the contralesional side in patients with hemispheric lesions, and this is amplified by spatial neglect. However, we do not know the specific influence of hemianopia and space of perception on this phenomenon. Here, we analyzed the respective influences of spatial neglect, hemianopia and hemispace on the subjective vertical in patients with right hemispheric stroke. Twelve neglect patients with and 5 without hemianopia were compared to 3 non-neglect patients with and 13 without hemianopia. They had to match a luminous rod to the vertical, either in the mid-sagittal plane or in the right or the left hemispace. Patients showed a counter-clockwise deviation, and this was exaggerated by both neglect and hemianopia. In patients with neglect, the error was greater in the left hemispace. In conclusion, neglect and hemianopia had additive effects on the contralesional bias of the subjective vertical.

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

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

Representation of Body Orientation in Vestibular-Defective Patients Before and After Unilateral Vestibular Loss.

Introduction: The unilateral vestibular syndrome results in postural, oculomotor, perceptive, and cognitive symptoms. This study was designed to investigate the role of vestibular signals in body orientation representation, which remains poorly considered in vestibular patients. Methods: The subjective straight ahead (SSA) was investigated using a method disentangling translation and rotation components of error. Participants were required to align a rod with their body midline in the horizontal plane. Patients with right vestibular neurotomy (RVN; n =8) or left vestibular neurotomy (LVN; n = 13) or vestibular schwannoma resection were compared with 12 healthy controls. Patients were tested the day before surgery and during the recovery period, 7 days and 2 months after the surgery. Results: Before and after unilateral vestibular neurotomy, i.e., in the chronic phases, patients showed a rightward translation bias of their SSA, without rotation bias, whatever the side of the vestibular loss. However, the data show that the lower the translation error before neurotomy, the greater its increase 2 months after a total unilateral vestibular loss, therefore leading to a rightward translation of similar amplitude in the two groups of patients. In the early phase after surgery, SSA moved toward the operated side both in translation and in rotation, as typically found for biases occurring after unilateral vestibular loss, such as the subjective visual vertical (SVV) bias. Discussion and Conclusion: This study gives the first description of the immediate consequences and of the recovery time course of body orientation representation after a complete unilateral vestibular loss. The overall evolution differed according to the side of the lesion with more extensive changes over time before and after left vestibular loss. It is noteworthy that representational disturbances of self-orientation were highly unusual in the chronic stage after vestibular loss and similar to those reported after hemispheric lesions causing spatial neglect, while classical ipsilesional biases were reported in the acute stage. This study strongly supports the notion that the vestibular system plays a major role in body representation processes and more broadly in spatial cognition. From a clinical point of view, SSA appeared to be a reliable indicator for the presence of a vestibular disorder.

[Computerized method for calculating cervical vertebral maturation]. / Méthode informatisée pour le calcul de l'âge osseux vertébral.

For Helm, "the rhythm of facial growth often governs the course of orthodontic treatment". The moment of treatment is an important dimension for our therapy to last a minimum of time with a greatest chance of success and stability. This notion of processing time is a daily requirement in our practices. The radiographs of the wrists will gradually disappear according to the ALARA principle, since we can in a single irradiation, via the profile radiography, have sufficient information to situate the patient on its growth curve. The vertebral stages are good biological indicators of individual skeletal maturity but their interpretation remains difficult. In this work, a computerized method was used to determine the stage of vertebral maturation in a reliable and reproducible manner. In this study, 15 young boys and 15 young girls (total 30 patients) were included, 12,2 years old on average with a standard deviation of 2,6 years. To determine the skeletal age of these patients, the practitioner made an hand-wrist x-ray and, for diagnostic reasons, he also made a profile radiography the same day. The patients who didn't made an hand-wrist x-ray were excluded. The vertebral computerized method seems to be a reliable method to be used in orthodontic practices. Other studies would allow to use this method for average ages, gender-appropriate.

The influence of facial expression at perceptual threshold on electrodermal activity and social comfort distance.

Interpersonal distance, an essential component of social interaction, is modulated by the emotion conveyed by others and associated physiological response. However, in modern societies with overcrowded and hyperstimulating environments, we can only surreptitiously glimpse the faces of others in order to quickly make behavioral adjustments. How this impacts social interactions is not yet well understood. In the present study, we investigated this issue by testing whether facial expressions that are difficult to identify modify the physiological response (Electrodermal Activity, EDA) and subsequent judgment of interpersonal comfort distance. We recorded participants' EDA while they provided comfort judgments to interpersonal distances with a Point-Light Walker (PLW). The PLW, with an emotionally neutral gait, moved toward and crossed participants at various distances after the latter were exposed to a negative (anger), positive (happiness) or neutral facial expression presented at the perceptual threshold. Bayesian analyses of the data revealed an increase versus decrease of interpersonal comfort distance with the PLW depending on the negative versus positive emotional valence of the facial expression. They also showed an increase in EDA when the approaching PLW violated interpersonal comfort distance after participants were exposed to an angry facial expression. These effects correlated with the subjective assessment of the arousal of facial expressions. Thus, previous exposure to barely visible facial expressions can alter the representation of social comfort space and the physiological response associated with a violation of interpersonal comfort distances, depending on the valence and arousal of the emotional social stimuli.

Depression restricts visual capture and promotes the perception of negative information.

Emotional deficits in major depressive disorder lead to changes in the distribution of attention in the visual field. We investigate the impact of unpleasant and neutral pictures, presented in central (0°) and peripheral vision (12°; 24°), in 15 depression patients (DP) and 15 matched healthy controls (HC). Heart rate, skin conductance responses (SCRs) and electroencephalogram (EEG) were recorded. A spatiotemporal principal component analysis (PCA) was applied to the EEG, and ANCOVAs controlling for participants' state- and trait-anxiety and patients' medication were performed to assess the effects of visual eccentricity and emotion. Unlike HC, DP showed for CV stimulation 1/ greater sensitivity with a response bias toward unpleasant pictures, 2/ larger SCRs, especially to unpleasant pictures, and 3/ deeper cardiac deceleration. Furthermore, eccentricity and emotion modulated cerebral components. Finally, results bring a new vista on visual capture of negative information and support methods to enlarge the attentional span of depressed patients.

The pusher syndrome reverses the orienting bias caused by spatial neglect.

Spatial neglect can be accompanied by a pusher syndrome (PS) which is characterized by a postural deviation towards the contralesional side. In this study, the representation of the body orientation in the horizontal plane was evaluated in neglect patients with and without PS. The participants had to align a luminous rod with the straight ahead direction, a method allowing the measure of both horizontal components of subjective straight ahead, i.e. lateral shift and yaw rotation. Eighteen patients with a lesion of the right hemisphere were compared with ten healthy participants. Patients had neglect and PS (P+N+; n=3), neglect only (P-N+; n=10), or neither neglect nor PS (P-N-; n=5). P+N+ patients showed a significant leftward shift contrasting with the rightward shift of P-N+. No shift occurred in patients without neglect and controls. No significant yaw error was recorded in any groups. The original result of this study was an inversion of the sign of the bias in neglect patients with PS. This could be related to the postural disorders characterizing this syndrome, and which are opposite to those usually observed in spatial neglect. Thus, these data suggest a link between disorders of spatial representations and disorders of posture.

Functional Neuroanatomy of Vertical Visual Perception in Humans.

Vertical representation is central to posture control, as well as to spatial perception and navigation. This representation has been studied for a long time in patients with vestibular disorders and more recently in patients with hemispheric damage, in particular in those with right lesions causing spatial or postural deficits. The aim of the study was to determine the brain areas involved in the visual perception of the vertical. Sixteen right-handed healthy participants were evaluated using fMRI while they were judging the verticality of lines or, in a control task, the color of the same lines. The brain bases of the vertical perception proved to involve a bilateral temporo-occipital and parieto-occipital cortical network, with a right dominance tendency, associated with cerebellar and brainstem areas. Consistent with the outcomes of neuroanatomical studies in stroke patients, The data of this original fMRI study in healthy subjects provides new insights into brain networks associated with vertical perception which is typically impaired in both vestibular and spatial neglect patients. Interestingly, these networks include not only brain areas associated with postural control but also areas implied in body representation.

Autonomic Reactivity to Arousing Stimuli with Social and Non-social Relevance in Alexithymia.

Emotional difficulties in alexithymia and their social consequences have been linked to alterations in autonomic nervous system. However, most of previous studies did not take into account the distinction between the affective and the cognitive dimensions of the alexithymia, leading to inconsistent results. Aim: In this study, we compared the effects of both dimensions of alexithymia on the autonomic arousal to emotional and social visual stimulations. Methods: Skin conductance responses (SCRs) to items of the International Affective Pictures System characterized by emotional (unpleasant, neutral, and pleasant), social (with humans) or non-social (without humans) content were recorded in non-alexithymic (NA), affective (AA) and cognitive alexithymic (CA) participants, selected on the basis of the Toronto Alexithymia Scale and the Bermond-Vorst Alexithymia Questionnaire. All participants responded to questionnaires of empathy, social phobia, depression, and anxiety before the experiment and evaluated the arousal of the pictures after it. Results: Cognitive alexithymic group showed lower amplitudes of SCRs to pictures with social than without social relevance whereas the opposite pattern was observed for the NA group. Arousal emotional effects of the pictures on SCRs did not differ among groups. In addition, CA participants showed lower scores than NA in the Personal Taking sub-scale of the empathy questionnaire, while AA showed lower scores than NA in the fantasy sub-scale. The CA group showed higher social phobia, depression and anxiety scores, than the other two groups. Conclusion: This work has two original outcomes: first, affective alexithymics expressed lower empathic affective scores than other groups; second, alexithymia modulated the impact of the social relevance of the stimuli on the autonomic reactivity, this impact vanishing in affective alexithymics and reversing in cognitive alexithymics. Thus, though the groups could not be distinguished on the basis of emotional effect on SCRs, they clearly differed when the empathic characteristics and the autonomic impact of social relevance were considered. Finally, the described autonomic signature to social relevant information could contribute to elucidate the difficulty of alexithymics to deal with emotions during social transactions.

Facial thermal variations: A new marker of emotional arousal.

Functional infrared thermal imaging (fITI) is considered a promising method to measure emotional autonomic responses through facial cutaneous thermal variations. However, the facial thermal response to emotions still needs to be investigated within the framework of the dimensional approach to emotions. The main aim of this study was to assess how the facial thermal variations index the emotional arousal and valence dimensions of visual stimuli. Twenty-four participants were presented with three groups of standardized emotional pictures (unpleasant, neutral and pleasant) from the International Affective Picture System. Facial temperature was recorded at the nose tip, an important region of interest for facial thermal variations, and compared to electrodermal responses, a robust index of emotional arousal. Both types of responses were also compared to subjective ratings of pictures. An emotional arousal effect was found on the amplitude and latency of thermal responses and on the amplitude and frequency of electrodermal responses. The participants showed greater thermal and dermal responses to emotional than to neutral pictures with no difference between pleasant and unpleasant ones. Thermal responses correlated and the dermal ones tended to correlate with subjective ratings. Finally, in the emotional conditions compared to the neutral one, the frequency of simultaneous thermal and dermal responses increased while both thermal or dermal isolated responses decreased. Overall, this study brings convergent arguments to consider fITI as a promising method reflecting the arousal dimension of emotional stimulation and, consequently, as a credible alternative to the classical recording of electrodermal activity. The present research provides an original way to unveil autonomic implication in emotional processes and opens new perspectives to measure them in touchless conditions.

Subjective visual vertical in pitch and roll in right hemispheric stroke.

BACKGROUND AND PURPOSE: Patients with right hemispheric stroke usually present an anticlockwise deviation of the subjective visual vertical (SVV) in the frontal (roll) plane. However, the occurrence of a similar disorder in the sagittal (pitch) plane has never been assessed. We investigated the subjective visual vertical in both planes in those patients. METHODS: Eight patients, 4 with spatial neglect (N+) and 4 without neglect (N-), were compared with 4 healthy participants (C). They sat facing a luminous bar adjustable in rotation, either in the roll or in the pitch plane, and had to orient it in a vertical position, in the dark. RESULTS: Compared with N- (-0.1 degrees) and C (+1.1 degrees) groups, N+ patients presented with a significant backward deviation (-4.5 degrees) of the SVV in pitch. In accordance with other studies, they also showed a significant anticlockwise deviation (-8.8 degrees) of the SVV in roll, as compared with N- (-1.9 degrees) and C (+0.4 degrees) subjects. This was associated with an opposite trunk deviation in both planes. CONCLUSIONS: While confirming the anticlockwise deviation already reported in the frontal plane, we showed for the first time to our knowledge a backward deviation of the SVV in neglect patients, which has to be put in relation with their balance disorders.

Effect of posture on the perception of verticality in neglect patients.

BACKGROUND AND PURPOSE: The anticlockwise (ACW) deviation of the visual and visuohaptic subjective verticals (SVs), known to occur in patients with right hemisphere lesion, is amplified by spatial neglect (N). These patients have only been assessed when sitting. We investigated the hypothesis that postural changes modulate visuohaptic SV deviation. METHODS: Eight patients presenting with a right hemisphere lesion and spatial N were compared with 6 matched control subjects (C). In the dark, they had to rotate a luminous rod to put it at the vertical in 4 conditions: (1) sitting with plantar sole support; (2) sitting without plantar sole support; (3) sitting with legs extended on a support; and (4) supine position. RESULTS: N patients showed a significant ACW deviation (-4.5 degrees) of the SV compared with C subjects (+0.01 degrees). The effect of body position depended on the group (P=0.022) because changes had definite effects in the N but not in the C group. In fact, the former showed a reduction of the ACW deviation, from the first to the fourth condition. CONCLUSIONS: Although the possible role of plantar and leg somaesthetic inputs remains to be thoroughly investigated, the modulation of gravitational inputs at trunk or vestibular level influences the SV deviation in N patients. This has to be put in relation with the modulation of N signs reported by other authors when passing from the sitting to the supine position.

The egocentric reference deviation of neglect patients is influenced by visuospatial attention.

The right deviation of the subjective straight-ahead (SSA), representing a deviation of the body centered spatial reference frame (egocentric reference), is a frequent phenomenon in spatial neglect. Little is known about the influence of visuo-spatial attention on this SSA shift. The aim of this study was to investigate the influence of eye direction (overt attention) and perception of the visual background (covert attention) on the SSA pointing. We included 12 patients with right hemisphere stroke. Six were classified as neglect (N+) and compared to the six non neglect (N-) patients and 19 normal control subjects (C). They had to point straight-ahead (right hand) on an horizontal board. Pointing was performed in the light or in darkness, first with spontaneous eye direction, then while fixating a visual target (-15 degrees , 0 degrees , +15 degrees ). A first ANOVA of factors group, eye direction (left, center, right fixation) and visual context (light, darkness) showed a right SSA deviation in N+ patients only, which was more severe in the light than in darkness. In this group, the SSA was shifted in the same direction as the target, while that of N- and C groups was mildly shifted in the opposite direction. The comparison of spontaneous and central fixation conditions also showed an eye direction by group interaction, as the spontaneous right SSA deviation was reduced by central fixation in N+ patients only. These results suggest that, in neglect patients, the egocentric reference deviation is not a fixed phenomenon, and that it can be influenced by manipulation of both overt and covert spatial attention.

How to detect an electrocutaneous shock which is not delivered? Overt spatial attention influences decision.

Lateral shifts in overt attention have been previously shown to modulate reaction times to lateral electrocutaneous stimuli, as well as perception or unpleasantness thresholds. A response bias can play a role in the elicitation of these lateral differences. Therefore, the present experiment aimed at investigating whether eye orientation induces a decision bias in favour of the ipsilateral hemispace. Participants were asked whether or not they suspected subliminal electrocutaneous shocks, whereas no subliminal stimulation was actually delivered. A secondary visual task led participants to direct their eyes ipsi- or contralateral to the stimulated area. Differences between experimental conditions in the amount of subliminal shocks participants acknowledge to receive (number of positive responses) are thought to reflect decision biases. Low and high trait anxiety participants were involved. Results showed an interaction between the eye orientation and the tested hand. The number of positive responses was smaller in right-hand tests with contralateral eye orienting. This effect fits those described previously with real electrocutaneous stimuli. This interaction is related to hemispheric differences in spatial attention. In contrast to thresholds studies, this study failed to replicate that a lateral difference arises in the low but not in the high trait anxiety individuals, suggesting that this interaction was mostly due to the neurosensory processing of the electrocutaneous stimuli.

The visual vertical in the pusher syndrome: influence of hemispace and body position.

The subjective visual vertical (SVV) was investigated in right brain-damaged (RBD) patients with pusher syndrome (PS) which is thought to stem from an erroneous perception of body orientation. The participants, sitting or lying, had to align a luminous rod with gravity. The task was performed in darkness with the rod centred to the body, or placed in the left (neglected) or in the right hemispace. The error, negligible in the control group (+0.3 degrees; n = 6) and mild in the nonneglect non-pusher patients (-1.8 degrees; n = 6), was clearly clockwise in the pusher neglect patients (N+P+; +7.2 degrees; n = 4), but anticlockwise in the non-pusher neglect patients (-6.6 degrees; n = 6). In both neglect groups, error was greater when the rod was in the left space. In N+P+ patients, the performance was strongly affected by posture (lying: +5.2 degrees ; sitting: +9.2 degrees ). Intra-individual variability was also much greater in this group. This study confirms the contralesional deviation of SVV in RBD patients without PS and suggests the presence of an opposite bias in RBD patients affected by PS.

An anatomical and psychophysical comparison of subjective verticals in patients with right brain damage.

INTRODUCTION: Brain hemisphere lesions often cause a contralesional tilt of the subjective vertical (SV) a phenomenon related to spatial neglect and postural disorders. Depending on the method employed, different perceptual systems come into play when this gravitational vertical is assessed. Here, we compared the anatomical and psychophysical characteristics of modality-dependent SV biases in patients with right hemisphere stroke. METHODS: The SV was measured with visual, haptic and visual-haptic modalities (SV, SVV, SVHV) in 46 patients with a relatively recent stroke. Voxel-based lesion-symptom mapping (performed with NPM(®)) was used to highlight brain areas in which lesions best explained the severity of task biases (p < .05). RESULTS: Lesions explaining the SVV tilt (TSVV) were centered on the posterior part of the middle temporal gyrus, those explaining the TSHV were more limited and anterior, without convergence with the former. Lesions explaining the TSVHV were centered on the superior temporal gyrus and more anterior those explaining the TSVV, with convergence with lesions explaining both the TSVV and the TSHV. Patients showed counterclockwise deviations in the SVs. Constant and variable errors were greater for the SHV than for the SVV and for the SVHV. The TSVV and TVHV were closely related to the presence of left spatial neglect and hemianopia. CONCLUSIONS: Errors in the SVV and (at a lesser degree) SVHV were preferentially related to lesions in visual associative cortex. The SVV and especially the SVHV provide valuable estimates of patient difficulties, in view of the lower associated variable errors (i.e., greater precision) and closer relationships with clinical disorders.