We describe a man with lateral medullary syndrome associated with a long-standing clumsiness of the ipsilateral upper limb. MRI showed that the clinical finding of ipsilateral clumsiness correlated with an extension of the infarction into the dorsal column nuclei but was not reflected in any involvement of the more ventral pyramidal tract. This deficit in movement control that appears superficially like a hemiparesis may result from a combination of lemniscal and spinocerebellar deficits.

A 69-year-old patient with a cortical lesion of the primary sensory area showed a surprising sensorimotor control of the anesthetized arm. This observation suggested the existence of residual capacities of somesthetic information processing. This hypothesis was tested using a forced choice procedure on four tasks involving discrimination between different characteristics of the tactual-kinaesthetic stimulus. Whereas the patient was unable to identify the direction of movement or to discriminate between different letters, she could detect the occurrence of the stimulation or its dynamic quality signficantly well. These results are discussed in reference to an anatomo-functional organization analogous to the one underlying the processing of visual information.

A 34-year-old man experienced a left homonymous hemianopsia due to an occipital infarction, with preservation of the temporal crescent on Goldmann perimetry. The cortical representation of the temporal crescent is discussed with regard to the location of the lesion imaged by magnetic resonance.

Route description was investigated in two patients suffering from left unilateral neglect. Both had evident difficulty with left turns. This finding suggests that the topological correspondence between represented environment and representational mechanisms in the brain is not confined to frozen (picture-like) perspectives.

Head turning and manual pointing to auditory targets have been studied in normal subjects and in subjects with right parietal damage. Important differences were found between these two types of movement. (1) In brain-damaged subjects, audiospatial manual pointing deficit patterns and audiospatial head turning deficit patterns were dissociated. Moreover, head turning deficits tended to appear peripherally in both auditory hemifields, while manual pointing deficits tended to appear unilaterally in the left hemifield. (2) In normal subjects, at all tested eccentricities in both hemifields, head turning performances showed a characteristic undershooting of auditory targets when compared to manual pointing. Results are discussed in terms of differences between the processes underlying audiomotor tasks that involve the head and tasks that involve the hands.

Signs of cerebral disconnection, especially left ear suppression to dichotically presented verbal stimuli, have been reported in multiple sclerosis patients and found to be correlated to morphological atrophy of the corpus callosum on magnetic resonance imaging. To reinvestigate this issue, 26 patients satisfying criteria for definite multiple sclerosis were proposed 3 tasks aimed at evaluating interhemispheric function: a dichotic listening task, a motor finger-tapping task and a sensory transfer task. Performance at these tasks suggested impaired callosal function in MS patients, compared to normal controls. Callosal morphology was assessed on midsagittal MRI sections using a digitalised method of partition of the callosal area into 6 subregions and automatized surface measurements. Results of correlations between task performance and callosal areas showed a significant correlation between total callosal atrophy and severity of interhemispheric impairment on each functional task. Moreover, impaired motor transfer was specifically related to atrophy of the anterior callosal regions. These results suggest that MS patients may constitute a suitable population to studying interhemispheric transfer of information through the callosal commissure and that this approach may be useful in the clinical management of MS patients.

A 37-year-old man experienced cortical blindness following a bilateral stroke in the territory of the posterior cerebral arteries. Four years later, the measurement of visual field defects (Goldmann perimeter) showed persistence of bilateral blindness with a 2-degree preservation of macular vision and a perifoveal sparing between 10 to 30 degrees of eccentricity in the left inferior quadrant. Despite this visual impairment, the subject was able to perform visually-guided locomotion. Moreover he consciously perceived visual motion in the blind parts of his visual field. CT and MRI showed a lesion involving most of the striated cortex. The visual cortex located in the internal occipito-parital regions was relatively spared. The contribution of this structure to extra-striated vision of motion is discussed.

Motion perception was studied in a subject with bilateral lesion of the visual cortex, involving severe damage to cortical areas V1 and V4, but with no apparent damage to visual associative areas situated in occipito-parietal and lateral occipito-temporal (presumably V5) zones. He was able to perceive optical flow motions simulating motion in depth in "blind" parts of his visual field, provided that the stimulus-onset was temporally dissociated from its motion. Moreover, he was able to discriminate between different velocities and directions of motion. The results suggest that perimetrically "blind" parts of the visual field in this patient have true capacities to process visual motion. They are discussed in reference to the subject's ability to move freely in his environment and in reference to the role of extrastriate visual pathways in visual motion processing.

In order to study auditory spatial localization in subjects with posterior damage involving the parietal lobe, we investigated their manual pointing performances to linguistic and white noise signals distributed over six sound sources situated in the anterior auditory field at ear level. The results showed: (1) A striking difference between patterns of deficits associated with right and left damage. In subjects with right damage, auditory localization deficits occurred in the horizontal plane, were manifested as restrictions in the peripheral left auditory hemifield and tended to be related to left visual neglect. In subjects with left damage, auditory localization deficits occurred in the entire auditory field in the horizontal as well as vertical planes, and they were particularly strong in the antero-frontal region. (2) One subject with right damage and visual neglect but no left auditory spatial restriction, showed deficits in the right hemifield where sound source location tended to be overestimated. This subject also showed a better discrimination of the origin of a white noise than of a linguistic signal. Results are discussed in terms of hemispheric asymmetries of function.

In order to test the existence of an hemispheric asymmetry at a basic level of spatial information processing, six right handed and six left handed normal subjects were submitted to a manual pointing task to auditory targets. Results showed a shift in perceived target position according to the hand used for pointing, a striking asymmetry between the two auditory hemispaces reflected in both groups in directional error and dispersion.

The authors report the detection performances of three subjects with unilateral left visual neglect as they were submitted to a closed-loop manual pointing task in the reaching field. Results show, for all three subjects, better detection performances when manual pointing was executed with the left hand—i.e. contralateral to the lesion—than when made with the right hand. Given that, for both hands, signal detection conditions were the same, these results are discussed according to: (a) other studies having showed changes in the expression of neglect as induced by changes in the nature or the strategy of the task; (b) the concept of an indissociable sensorimotor central processing; and (c) one of the models put forward to account for unilateral spatial neglect which includes a motor representation.

The authors report the detection performances of three subjects with unilateral left visual neglect as they were submitted to a closed-loop manual pointing task in the reaching field. Results show, for all three subjects, better detection performances when manual pointing was executed with the left hand--i.e. contralateral to the lesion--than when made with the right hand. Given that, for both hands, signal detection conditions were the same, these results are discussed according to: other studies having showed changes in the expression of neglect as induced by changes in the nature or the strategy of the task; the concept of an indissociable sensorimotor central processing; and one of the models put forward to account for unilateral spatial neglect which includes a motor representation.

The authors of this paper first summarize some of the theoretical frames put forward to account for allesthesia. Then, pointing performances in a case of visual allesthesia is reported; unexpectedly, pointing behavior for identical targets was different according to hand. The most salient feature was that a same visual target elicited relatively short RTs with adequate pointing using the left hand versus much longer reaction times with allesthesic pointing using the right hand. Discussion is focused on the presented theoretical frames. In view of the results, authors are led to hypothesize that, in sensorimotor cerebral organization, some aspects of signal processing are dependent upon some premotor aspects of response elaboration.

The present study was based on the assumption that there are two visual channels which provide separate contributions to visuo-motor recalibration following prismatic displacement of the visual field. The functional properties of the two channels were assumed to conform to predictions from the two motion-analyzing systems models of visual motion perception. The results of the present study confirmed the predictions of the model. Whatever the type of illumination (continuous or stroboscopic) central vision utilizes only cues provided by visual exposure of the arm pointing to a stationary target. Peripheral vision utilizes only cues from visual exposure of the arm freely moving against the homogeneous background but this can be prevented by stroboscopic illumination. In peripheral vision, movement cues provided by exposure of a passively moved arm are not processed. In contrast, the processing of visual cues in central vision is unaffected by whether the movements are active or passive, provided that a stationary target is present. The effects of the two channels may be additive or competitive depending on the conditions. Experimental and theoretical implications are discussed.

(1) The aim of this investigation was to examine if and how proprioceptive information can be encoded in order to locate cues for ballistic reaching in the absence of corrective feedback of exteroceptive origin. Systematic errors in locating the position of the fingertip of the target hand by the reaching hand were observed, according to experimental conditions; but the subjects were unable to make a perceptual evaluation of them.(2) The first set of experiments was designed to determine how different localizing cues (proprioceptive, tactile or visual or combinations thereof) may contribute to the accuracy of ‘open loop’ manual reaching. Five different types of constant error were identified. This led to a search for 5 different kinds of sensory cues about finger target location, which may be encoded to program the reaching movement of the other hand. Such cues are respectively associated with active positioning, passive positioning, stabilized position, vision of the stabilized hand and tactile stimulation during movement of the target hand.The most striking observation was that some proprioceptive information, brought into play by movement and absent during stabilized position of the limb, may contribute to the spatial encoding of sensory cues. In this respect, some specific signal associated with self-induced movement seems to play a role in calibrating the exact location of the final position of the moved limb in external space.(3) The second set of investigations was undertaken in order to assess the nature and origin of the calibrating information produced by active movement. Convergent results were obtained, either by changing the speed of movement of the target hand or by cooling, or ever vibrating, the working muscles; and these results support the hypothesis that a velocity signal incorporated in the dynamic discharge of muscle spindle receptors may be involved in calibrating the final location of an actively-moved segment.