Kinematics of Goal-Directed Arm Movements in Neglect: Control of Hand Velocity

Do patients with unilateral neglect exhibit direction-specific deficits in the control of movement velocity when performing goal-directed arm movements? Five patients with left-sided neglect performed unrestrained three-dimensional pointing movements to visual targets presented at body midline, the left and right hemispace. A group of healthy adults and a group of patients with right-hemispheric brain damage but no neglect served as controls. Pointing was performed under normal room light or in darkness. Time-position data of the hand were recorded with an opto-electronic camera system. We found that compared to healthy controls, movement times were longer in both patient groups due to prolonged acceleration and deceleration phases. Tangential peak hand velocity was lower in both patient groups, but not significantly different from controls. Single peak, bell-shaped velocity profiles of the hand were preserved in all right hemispheric patients and in three out of five neglect patients. Most important, the velocity profiles of neglect patients to leftward targets did not differ significantly from those to targets in the right hemispace. In summary, we found evidence for general bradykinesia in neglect patients, but not for a direction-specific deficit in the control of hand velocity. We conclude that visual neglect induces characteristic changes in exploratory behavior, but not in the kinematics of goal-directed movements to objects in peripersonal space.     

The functional anatomy of a hysterical paralysis

The concept of a conversion disorder (such as hysterical paralysis) has always been controversial (Ron, M.A. (1996). Somatization and conversion disorders. In: B.S. Fogel, R.S. Schiffer & S.M. Rao (Eds.), Neuropsychiatry. Williams and Wilkins, Baltimore, MD). Although the diagnosis is recognised by current psychiatric taxonomies, many physicians still regard such disorders either as feigned or as failure to find the responsible organic cause for the patient's symptoms. We report a woman with left sided paralysis (and without somatosensory loss) in whom no organic disease or structural lesion could be found. By contrast, psychological trauma was associated with the onset and recurrent exacerbation of her hemiparalysis. We recorded brain activity when the patient prepared to move and tried to move her paralysed (left) leg and when she prepared to move and did move her good (right) leg. Preparing to move or moving her good leg, and also preparing to move her paralysed leg, activated motor and/or premotor areas previously described with movement preparation and execution. The attempt to move the paralysed leg failed to activate right primary motor cortex. Instead, the right orbito-frontal and right anterior cingulate cortex were significantly activated. We suggest that these two areas inhibit prefrontal (willed) effects on the right primary motor cortex when the patient tries to move her left leg.     

Lifted-weight difference thresholds as a function of hand

A study was conducted to determine if the two hands of right-handers are differentially sensitive to changes in perceived weight. Using the method of limits, the left and right hands of 20 college students were tested at each of three reference weights: 90, 100, and 110 gm. Results indicated that, over-all, difference thresholds for the two hands were not reliably different, though a trend did emerge toward greater right-handed sensitivity to weight changes at smaller weights and greater left-handed sensitivity at greater weights.     

Perceptual biases in processing facial identity and emotion

Normal observers demonstrate a bias to process the left sides of faces during perceptual judgments about identity or emotion. This effect suggests a right cerebral hemisphere processing bias. To test the role of the right hemisphere and the involvement of configural processing underlying this effect, young and older control observers and patients with right hemisphere damage completed two chimeric faces tasks (emotion judgment and face identity matching) with both upright and inverted faces. For control observers, the emotion judgment task elicited a strong left-sided perceptual bias that was reduced in young controls and eliminated in older controls by face inversion. Right hemisphere damage reversed the bias, suggesting the right hemisphere was dominant for this task, but that the left hemisphere could be flexibly recruited when right hemisphere mechanisms are not available or dominant. In contrast, face identity judgments were associated most clearly with a vertical bias favouring the uppermost stimuli that was eliminated by face inversion and right hemisphere lesions. The results suggest these tasks involve different neurocognitive mechanisms. The role of the right hemisphere and ventral cortical stream involvement with configural processes in face processing is discussed.     

Priming the mental time line

Growing experimental evidence suggests that temporal events are represented on a mental time line, spatially oriented from left to right. Support for the spatial representation of time comes mostly from studies that have used spatially organized responses. Moreover, many of these studies did not avoid possible confounds attributable to target stimuli that simultaneously convey both spatial and temporal dimensions. Here we show that task-irrelevant, lateralized visuospatial primes affect auditory duration judgments. Responses to short durations were faster when the auditory target was paired with left- than with right-sided primes, whereas responses to long durations were faster when paired with right- than with left-sided primes. Thus, when the representations of physical space and time are concurrently activated, physical space may influence time even when a lateralized, spatially encoded response is not required by the task. The time-space interaction reported here cannot be ascribed to any Spatial-Temporal Association of Response Codes effect. It supports the hypothesis that the representation of time is spatially organized, with short durations represented on the left space and longer ones on the right.     

Impairments in tactile search following superior parietal damage

The superior parietal cortex is critical for the control of visually guided actions. Research suggests that visual stimuli relevant to actions are preferentially processed when they are in peripersonal space. One recent study demonstrated that visually guided movements towards the body were more impaired in a patient with damage to superior parietal cortex. Whereas past studies have explored disordered movement in optic ataxic patients, there has been less exploration of space perception in terms of search capacity in this population. In addition, there is some debate concerning the relationship between deficits of visuomotor control and impaired attention/perception in optic ataxia. Given that the dorsal stream has been implicated in the spatial processing of stimuli in peripersonal space, and damage to this region is known to cause optic ataxia, we felt that further investigation was warranted. We examined tactile search behavior in the fronto-parallel and radial planes in a patient with right superior parietal damage and optic ataxia. We used a pegboard with removable cylindrical pegs that allowed for the reorganization of targets between trials. To better characterize three-dimensional search behavior, we included both horizontal and vertical search conditions. Results showed that the patient spent more time searching, was more accurate and revisited more targets in right versus left space. Interestingly, the patient spent the majority of her time specifically searching the lower right quadrant of the stimulus array. Further analysis revealed lower target detection rates along the outer borders of the pegboard on all sides. The search pattern observed here is unusual considering that all targets were within arm's reach. The present experiment demonstrates that damage to superior parietal cortex impairs tactile search and biases exploration towards lower right peripersonal space.     

Agency and the Annunciation

Prior research has revealed that when healthy participants, who are not artists, are asked to draw a person who is performing an action, they are more likely to position the agent on the left and the person or object receiving this action, the patient, on the right. Thus, the goal of this study was to learn whether in works of art, such as those portraying the Annunciation of the angel Gabriel to the Blessed Virgin Mary, artists would be more likely to place the angel, who is the agent, on the left of Mary, who is the patient. We found that in our sample of 604 paintings of the Annunciation by different artists that the agent Gabriel is significantly more frequently portrayed to left of Mary. Whereas this result supports the left-agent, right-patient hypothesis, the reason for this spatial bias is not entirely known, but may be related to several factors such as the learned left to right direction of reading/writing in European languages, left-versus right-sided emotional facial expressive asymmetries, a left-sided spatial attentional bias and a spatial motor-action preference of upper extremity for making abductive (left to right) movements when using the right upper extremity. Additionally, biblical explanations and theological principles may have influenced the organization of this scene.     

The role of the left and right thalamus in language asymmetry: dichotic listening in Parkinson patients undergoing stereotactic thalamotomy

Fourteen patients with Parkinson's disease (rigidity and unilateral tremor as main symptoms) were treated with stereotactic thalamotomy. The operation was performed in either the left or right ventrolateral thalamus, depending on which hand (or foot) was most affected with tremor. Nine patients were operated on the left side and four on the right side. All patients were tested for asymmetry of language functioning with dichotic presentations of consonant-vowel (CV) syllables. The patients had to indicate which of the two syllables he/she heard on each trial. Dichotic listening was performed before and after the operation, as well as during electrical stimulation of the VL nucleus just before the lesion was carried out. The results revealed essentially three things: an overall reduced right ear advantage (REA) in the patient group compared to what is known from studies of healthy individuals; an increase in REA during left-sided stimulations; and a marked reduction in REA after left-sided lesions. It is concluded that the present data support the notion put forward by Ojemann (e.g., 1975) of a lateralized activating gating mechanism in the left VL nucleus that gates access for language information to the appropriate cortical areas. The gating mechanism seems to be activated by stimulation, and deactivated after lesions. Dichotic listening may thus be a heuristic instrument in assessment of language functions in Parkinson patients.     

Unilateral neglect: the effect of competing stimuli on estimated line length

Normal subjects and patients with right hemisphere lesions with or without signs of left unilateral neglect judged the length of a horizontal line presented on the left or on the right side of space. In half of the trials, the line was presented with a centrally located square or diamond, and subjects had to identify the central stimulus before performing the judgment of length. The presence of the central stimulus improved accuracy of performance in controls and in patients without neglect; neglect patients, however, produced more overestimations of left-sided lines when these was presented with a central stimulus than when the lines occurred in isolation. This finding underlines the importance of attentional factors in length estimates performed by neglect patients in their neglected space.     

Visual-spatial processing in deaf brain-damaged signers

Sign language displays all the complex linguistic structure found in spoken languages, but conveys its syntax in large part by manipulating spatial relations. This study investigated whether deaf signers who rely on a visual-spatial language nonetheless show a principled cortical separation for language and nonlanguage visual-spatial functioning. Four unilaterally brain-damaged deaf signers, fluent in American Sign Language (ASL) before their strokes, served as subjects. Three had damage to the left hemisphere and one had damage to the right hemisphere. They were administered selected tests of nonlanguage visual-spatial processing. The pattern of performance of the four patients across this series of tests suggests that deaf signers show hemispheric specialization for nonlanguage visual-spatial processing that is similar to hearing speaking individuals. The patients with damage to the left hemisphere, in general, appropriately processed visual-spatial relationships, whereas, in contrast, the patient with damage to the right hemisphere showed consistent and severe visual-spatial impairment. The language behavior of these patients was much the opposite, however. Indeed, the most striking separation between linguistic and nonlanguage visual-spatial functions occurred in the left-hemisphere patient who was most severely aphasic for sign language. Her signing was grossly impaired, yet her visual-spatial capacities across the series of tests were surprisingly normal. These data suggest that the two cerebral hemispheres of congenitally deaf signers can develop separate functional specialization for nonlanguage visual-spatial processing and for language processing, even though sign language is conveyed in large part via visual-spatial manipulation.     

Characteristics of recovery of drawing ability in left and right brain-damaged patients

Drawings of a "person" were obtained from 21 patients with left brain damage (LBD) and 13 patients with right brain damage (RBD) at hospital discharge and 1 month postdischarge, corresponding to 2-4 and 6-8 weeks postonset, respectively. Early LBD drawings were simplistic and often incoherent. Most were placed in the upper left quadrant of the page. RBD drawings were scattered, fragmented, and elaborately detailed. Many showed evidence of left-sided neglect. The resolution of drawing disability also differed between the two groups: LBD subjects recovered drawing abilities more rapidly and more completely than RBD subjects. These differences in drawing characteristics and in the resolution of drawing disability were discernable for experienced neuropsychologists.     

Improvement of mental imagery after prism exposure in neglect: a case study

Previous work has shown that various symptoms of unilateral neglect, including the pathological shift of the subjective midline to the right, may be improved by a short adaptation period to a prismatic shift of the visual field to the right. We report here the improvement of imagined neglect after prism exposure in a patient with a left unilateral neglect. Despite a strong neglect observed for mental images as well as for conventional tests, the mental evocation of left-sided information from an internal image of the map of France map was fully recovered following prism adaptation to the right. This improvement could not be explained by the alteration of visuomotor responses induced by the prism adaptation. Prism adaptation may therefore act not only on sensory-motor levels but also on a higher cognitive level of mental space representation and/or exploration.     

Scaling movement amplitude: adaptation of timing and amplitude control in a bimanual task

Participants traced two circles simultaneously and the diameter of one circle was scaled as the diameter of the other circle remained constant. When the scaled circle was larger, amplitude error shifted from overshooting to undershooting, while shifting from undershooting to overshooting when this circle was smaller. Asymmetric coordination was unstable when the left arm traced a circle larger than the right arm, yet stable when the left arm traced a smaller circle. When producing symmetric coordination and the left arm traced the larger circle, relative phase shifted by 30°, but a right arm lead predominated. When the left arm traced the smaller circle and symmetric coordination was required, a 30° shift in relative phase occurred, but hand lead changed from left to right. The modulation of movement amplitude and relative phase emerged simultaneously as a result of neural crosstalk effects linked to initial amplitude conditions and possibly visual feedback of the hands' motion.     

Visual neglect and left-sided context effects

Patients with visual neglect generally fail to respond to an item placed on the left of a target location, even when both stimuli are situated in the right visual field. Little is known, however, about the level of processing for the unattended items. Two patients with left visual neglect served as subjects in several experiments measuring passive contextual effects of a left-sided item on responses to a focal target. The results reveal that a neglected item may influence the speed of responding. The findings are interpreted relative to the loci of context effects in normal subjects.     

The child's experience of Munchhausen syndrome by proxy

This paper examines the emotional impact of Munchhausen syndrome by proxy on a child aged 6 who had been poisoned by her mother. It describes her treatment in child psychotherapy over twenty months at the Cassel Hospital where the family worked towards her successful rehabilitation home. The work with her showed her experience of dangerous relationships in her family that left her distrustful of any new relationship, and doubtful of her capacity to be close without being destructive. Like her parents, she was terrified of facing the murderous feelings in the family, retreating into denial when life was too painful. The paper describes three phases of treatment: fear of separation and preoccupation with the trauma of poisoning, ambivalence about facing the destructiveness in the family and the move into more appropriate latency behaviour as she prepared to go home with her parents. It concludes with an overview of the impact of Munchhausen syndrome by proxy on the developing child, as shown in this treatment: the delay in emotional and cognitive development, the interference with the capacity to relate, the retreat into illness under stress, and the fear of permanent damage caused by the emotional and physical abuse.     

Dichotic listening with forced attention in patients with temporal lobe epilepsy: significance of left hemisphere cognitive dysfunction

Fifty right-handed patients with focal temporal lobe epilepsy were administered a dichotic listening test with consonant-vowel syllables under non-forced, forced right and forced left attention conditions, and a neuropsychological test battery. Dichotic listening performance was compared in subgroups with and without left hemisphere cognitive dysfunction, measured by the test battery, and in subgroups with left and right temporal epileptic focus. Left hemisphere cognitive dysfunction led to more correct responses to left ear stimuli in all three attention conditions, and fewer correct responses to right ear stimuli in the non-forced attention condition. This was probably caused by basic left hemisphere perceptual dysfunction. Dichotic listening was less affected by a left-sided epileptic focus than by left hemisphere cognitive dysfunction. General cognitive functioning influenced dichotic listening performance stronger in forced than in non-forced attention conditions. Larger cerebral networks were probably involved in the forced attention conditions due to the emphasis on conscious effort.     

Cocaine and food deprivation: effects on food-reinforced fixed-ratio performance in pigeons.

Key pecking by 6 pigeons was maintained by a fixed-ratio 30 schedule of food presentation while body weights were 80% of free-feeding weights. Acute administration of cocaine (0.3 to 13.0 mg/kg, i.m.) dose-dependently decreased response rates. Dose-effect curves were shifted to the right when 3 of the 6 pigeons were maintained at 70% of free-feeding weights and were shifted to the left when the other 3 pigeons were maintained at 90% of free-feeding weights. Then a dose of cocaine that initially decreased response rates by more than 95% of control rates was administered before each daily session. Comparable degrees of tolerance to these rate-decreasing effects developed in the two groups. The rate at which responding recovered was relatively rapid for pigeons in the 70% free-feeding-weight group and was slower for 2 of the 3 pigeons in the 90% free-feeding-weight group. When body weights were then increased from 70% to 80% or were decreased from 90% to 80% of free-feeding weight, performance was disrupted initially only for pigeons whose weight went from 70% to 80% of free feeding. In the present experiment the degree of deprivation may have indirectly influenced the degree of tolerance that developed to cocaine's response rate-decreasing effects because it directly influenced the dose chosen to be administered chronically. The degree of deprivation appeared to have a more direct influence on the rate at which tolerance developed.     

The effect of orthographic uniqueness and deviation points on lexical decisions: evidence from unilateral and bilateral-redundant presentations

Words with an early or late orthographic uniqueness point and nonwords with an early or late orthographic deviation point were presented to the left, right, or both visual fields simultaneously. In Experiment 1, 20 participants made lexical decision judgements to horizontal stimulus presentations. In Experiment 2, a further 20 participants completed the task using vertical presentations to control for attentional biases. Consistent with previous research, words with earlier orthographic uniqueness points prompted faster responses across visual fields, regardless of stimulus orientation. Although research has suggested that the left hemisphere's superiority for language processing stems from a comparatively parallel processing strategy, with the right hemisphere reliant upon a serial mechanism, left and right visual field presentations were not differentially affected by orthographic uniqueness point. This suggests that differential sequential effects previously reported result during processes other than retrieval from the lexicon. The overall right visual field advantage observed using horizontal presentations disappeared when stimuli were presented vertically. Contrary to expectations, there was a facilitatory effect of late orthographic deviation point for horizontal nonword presentations. Overall, the results were interpreted as being consistent with predictions of a cohort model of word recognition, and they highlighted the effect of stimulus orientation on left and right hemisphere word recognition.     

The role of callosal connections in speech prosody

A 39-year-old right-handed woman suffered an aneurysmal hemorrhage damaging the anterior four-fifths of the corpus callosum as shown on MRI. Computer-aided acoustical analyses of fundamental frequency (Fo) contours and durational patterns were performed on emotive and nonemotive utterances at 4 weeks, 4 months, and 1 year postsurgery. The patient read sentences in each of five tones (happy, sad, angry, neutral, questioning) or with emphasis on certain words. She showed little Fo distinction with intended mood at 4 weeks, but her performance improved over time. This improvement in speech production was accompanied by an improvement in perceptual judgments of her intended tone by six normal listeners. Fo patterns characteristic of emphatic stress and question forms were found at all test periods, but again improved with time. Durationally, the patient showed appropriate emotive and nonemotive distinctions on most sentences. These results provide acoustic evidence that interhemispheric connections via the corpus callosum are important to proper Fo programming, especially emotive distinctions. The results suggest that the right hemisphere contributes to Fo programming but, following callosal damage, such programming can later be performed by the left hemisphere.