Search

The time needed to search for an object in a complex environment increases with the number of distracting stimuli, a phenomenon known as the "set-size effect." This observation has led to the view that, during visual search, several attentional shifts are performed, suggesting that visual information is processed serially. In an attempt to find direct evidence for such attentional shifts, we implemented several dual tasks combining a covert visual search (CVS) task or a cued target detection task with a character reporting task which allowed us to determine, a posteriori, the attentional allocation. We found that, in the cueing task, subjects preferentially reported characters displayed at different locations, demonstrating that the attention spotlight actually shifted in this condition. In contrast, in both feature and conjunction CVS, subjects predominantly reported several characters flashed at the same location, whatever the delay between their presentations, indicating that, despite a clear "set-size effect," attention remained static. These results demonstrate that CVS can be performed without shifting attention and that the "set-size effect" does not necessarily attest that visual information is processed serially. The present study therefore supports the hypothesis that parallel mechanisms are involved in visual information processing during visual search, in agreement with previous theoretical studies.

Several studies have addressed the question of the time it takes for attention to shift from one position in space to another. Here we present a behavioural paradigm which offers a direct access to an estimate of voluntary shift time by comparing, in the same task, a situation in which subjects are required to re-engage their attention at the same spatial location with a situation in which they need to shift their attention to another location, all other sensory, cognitive and motor parameters being equal. We show that spatial attention takes on average 55 ms to voluntarily shift from one hemifield to the other and 38 ms to shift within the same hemifield. In addition, we show that across and within hemifields attentional processes are different. In particular, attentional spotlight division appears to be more difficult to operate within than across hemifields.

The finding that attention can encompass several non-contiguous items at once challenges the current models of visual search based on a winner-take-all mechanism assuming the selection of a single object. It has been proposed instead that attentional guidance involves mechanisms selecting all relevant items simultaneously. In order to test this hypothesis, we studied attentional allocation during various visual search tasks. We confirmed that attention can indeed select several items concurrently but on the basis of their spatial relation, not relevance. This finding corroborates the view that during visual search, attentional guidance is based on a winner-take-all mechanism.

Spotting a prey or a predator is crucial in the natural environment and relies on the ability to extract quickly pertinent visual information. The experimental counterpart of this behavior is visual search (VS) where subjects have to identify a target amongst several distractors. In difficult VS tasks, it has been found that the reaction time (RT) is influenced by salience factors, such as the target-distractor similarity, and this finding is usually regarded as evidence for a guidance of attention by preattentive mechanisms. However, the use of RT measurements, a parameter which depends on multiple factors, allows only very indirect inferences about the underlying attentional mechanisms. The purpose of the present study was to determine the influence of salience factors on attentional guidance during VS, by measuring directly attentional allocation. We studied attention allocation by using a dual covert VS task in subjects who had 1) to detect a target amongst different items and 2) to report letters briefly flashed inside those items at different delays. As predicted, we showed that parallel processes guide attention towards the most relevant item by virtue of both goal-directed and stimulus-driven factors, and we demonstrated that this attentional selection is a prerequisite for target detection. In addition, we show that when the target is characterized by two features (conjunction VS), the goal-directed effects of both features are initially combined into a unique salience value, but at a later stage, grouping phenomena interact with the salience computation, and lead to the selection of a whole group of items. These results, in line with Guided Search Theory, show that efficient and rapid preattentive processes guide attention towards the most salient item, allowing to reduce the number of attentional shifts needed to find the target.

We tested several techniques for decoding the activity of primary motor cortex (M1) neurons during movements of single fingers or pairs of fingers. We report that single finger movements can be decoded with >99% accuracy using as few as 30 neurons randomly selected from populations of task-related neurons recorded from the M1 hand representation. This number was reduced to 20 neurons or less when the neurons were not picked randomly but selected on the basis of their information content. We extended techniques for decoding single finger movements to the problem of decoding the simultaneous movement of two fingers. Movements of pairs of fingers were decoded with 90.9% accuracy from 100 neurons. The techniques we used to obtain these results can be applied, not only to movements of single fingers and pairs of fingers as reported here, but also to movements of arbitrary combinations of fingers. The remarkably small number of neurons needed to decode a relatively large repertoire of movements involving either one or two effectors is encouraging for the development of neural prosthetics that will control hand movements.

The anterior wall of the parieto-occipital sulcus (POs) of the macaque monkey, classically considered as part of Brodmann's area 19, contains two functionally distinct areas: a ventral, purely visual area, V6, and a dorsal area, V6A, containing visual neurons and neurons related to the control of arm movements. The aim of this study was to establish whether areas V6 and V6A, so far identified only on a functional basis, have a cytoarchitectonic counterpart. The cytoarchitectonic analysis of 13 hemispheres from ten macaque brains, cut along different planes of section, showed that the anterior wall of the POs contains three distinct areas. One is located in the ventralmost part of the wall, another in the dorsalmost part of the wall, and the third occupies an intermediate position. The ventralmost region displays architectonic features typical of the occipital cytoarchitectonic domain, whereas the two dorsal areas display architectonic features typical of the posterior parietal cortex. Analysis of myeloarchitecture and of the distribution of SMI-32 immunoreactivity confirmed the cytoarchitectonic parcellation. Correlation of cytoarchitectonic maps with functional and hodological data strongly suggests that the ventral region corresponds to area V6, whereas the other two regions correspond to different subsectors of V6A, here named V6Av and V6Ad, respectively. The present data are in line with electrophysiological and hodological data, which suggest that area V6 is a classic extrastriate area, whereas V6A is an area of the posterior parietal cortex. They also suggest that V6A includes two separate cortical subdivisions, a view supported by preliminary functional and hodological data that needs further confirmation.

West Nile fever (WNF) is a mosquito-borne flavivirus infection. It is epidemic in Africa and Asia. In autumn 1997, a WNF epidemic occurred in the Sfax area (southeastern Tunisia). Fifty-seven patients were hospitalized with aseptic meningitis and/or encephalitis. Search for specific anti-West Nile virus (WNV) antibodies in serum and cerebrospinal fluid (CSF) was performed using an ELISA test. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect the WNV genome in CSF and brain specimens. Recent central nervous system (CNS) infection by WNV was confirmed in 30 patients, probable infection in 17 and it was excluded in 10. In the confirmed subgroup, patients with encephalitis were older than those with meningitis. CSF showed pleocytosis, high protein (47%) and normal glucose levels. Brain computed tomography-scan (CT-scan) and magnetic resonance imaging (MRI) were normal. RT-PCR disclosed WNV genome in the CSF in two cases and in a brain specimen in one. Three patients died rapidly, the remaining cases had favorable prognosis. Autopsy was performed in two cases and showed nonspecific lesions of encephalitis. No viral inclusions were seen with light microscopy. Seropositivity rate in patients' proxies for WNV was 23.4%. Prognosis of CNS involvement during WNF seemed to be poor in older patients. This is the first WNV encephalitis epidemic report in the Sfax area of Tunisia.

We recorded neuronal responses to optic flow stimuli in the ventral intraparietal area (VIP) of two awake macaque monkeys. According to previous studies on optic flow responses in monkey extrastriate cortex we used different stimulus classes: frontoparallel motion, radial stimuli (expansion and contraction) and rotational stimuli (clockwise and counter-clockwise). Seventy-five percent of the cells showed statistically significant responses to one or more of these optic flow stimuli. Shifting the location of the singularity of the optic flow stimuli within the visual field led to a response modulation in almost all cases. For the majority of neurons, this modulatory influence could be approximated in a statistically significant manner by a two-dimensional linear regression. Gradient directions, derived from the regression parameters and indicating the direction of the steepest increase in the responses, were uniformly distributed. At the population level, an unbiased average response for the stimuli with different focus locations was observed. By applying a population code, termed 'isofrequency encoding', we demonstrate the capability of the recorded neuronal ensemble to retrieve the focus location from its population discharge. Responses to expansion and contraction stimuli cannot be predicted based on quantitative data on a neuron's frontoparallel preferred stimulus direction and the location and size of its receptive field. These results, taken together with data on polymodal motion responses in this area, suggest an involvement of area VIP in the analysis and the encoding of heading.

Self-motion detection requires the interaction of a number of sensory systems for correct perceptual interpretation of a given movement and an eventual motor response. Parietal cortical areas are thought to play an important role in this function, and we have thus studied the encoding of multimodal signals and their spatiotemporal interactions in the ventral intraparietal area of macaque monkeys. Thereby, we have identified for the first time the presence of vestibular sensory input to this area and described its interaction with somatosensory and visual signals, via extracellular single-cell recordings in awake head-fixed animals. Visual responses were driven by large field stimuli that simulated either backward or forward self-motion (contraction or expansion stimuli, respectively), or movement in the frontoparallel plane (visual increments moving simultaneously in the same direction). While the dominant sensory modality in most neurons was visual, about one third of all recorded neurons responded to horizontal rotation. These vestibular responses were typically in phase with head velocity, but in some cases they could signal acceleration or even showed integration to position. The associated visual responses were always codirectional with the vestibular on-direction, i.e. noncomplementary. Somatosensory responses were in register with the visual preferred direction, either in the same or in the opposite direction, thus signalling translation or rotation in the horizontal plane. These results, taken together with data on responses to optic flow stimuli obtained in a parallel study, strongly suggest an involvement of area VIP in the analysis and the encoding of self-motion.

We report a case of Candida glabrata perinephric abscess in a patient with diabetes mellitus who recently underwent ureteropelvic surgery for lithiasic urinary tract obstruction. Surgical drainage and amphotericin B treatment led to resolution of the infection. C. glabrata urinary infection has become more prevalent over the last decade in immunocompromised patients. Drainage is indicated for development of a fungal abscess in the perinephric area. Most authors recommend administration of an antifungal adjuvant treatment.

Many neurons in area VIP encode the location of visual stimuli in a non-retinocentric frame of reference. In this context the question needed to be addressed whether the underlying coordinate transformation of the incoming visual signals could be generated within area VIP or whether this information would have to arrive from other areas. We tested 74 neurons in area VIP of two awake monkeys for an influence of eye position while animals performed a fixation task. More than half of the neurons (40/74) revealed an eye position effect. At the population level, however, this effect was balanced out. We suggest that local connections within area VIP could be used to generate an encoding of visual information in a non-retinocentric frame of reference.

Spatial information is conveyed to the primary visual cortex in retinal coordinates. Movement trajectory programming, however, requires a transformation from this sensory frame of reference into a frame appropriate for the selected part of the body, such as the eye, head or arms. To achieve this transformation, visual information must be combined with information from other sources: for instance, the location of an object of interest can be defined with respect to the observer's head if the position of the eyes in the orbit is known and is added to the object's retinal coordinates. Here we show that in a subdivision of the monkey parietal lobe, the ventral intraparietal area (VIP), the activity of visual neurons is modulated by eye-position signals, as in many other areas of the cortical visual system. We find that individual receptive fields of a population of VIP neurons are organized along a continuum, from eye to head coordinates. In the latter case, neurons encode the azimuth and/or elevation of a visual stimulus, independently of the direction in which the eyes are looking, thus representing spatial locations explicitly in at least a head-centred frame of reference.

A 14-year-old girl developed skin rash, fever and dyspnea. The chest roentgenogram showed diffuse reticulonodular infiltration. Pulmonary function tests revealed mild restrictive defect and blood oxygen pressure at 71 mm Hg. BAL showed increased cell counts with lymphocytosis at 15% and neutrophilia at 3%. Outcome was good after carbamazepine withdrawal and without corticosteroid therapy. Relapse was observed after patient-induced rechallenge.

The authors report the case of a 22 year old patient with brucella endocarditis on a Starr-Edwards aortic valve prosthesis implanted 5 years previously. Six blood cultures were positive for Brucella melitensis biovar I. Antibiotic therapy associating Rifampicin and Tetracycline and then Rifampicin and Ofloxacine did not prevent abscess formation and valve dehiscence. The poor haemodynamic status and persistent infection led to replacement of the valve prosthesis. Culture of the infected prosthesis grew a colony of brucella melitensis resistant to fluoro-quinolones. Valve replacement and antibiotic therapy led to clinical improvement and constant apyrexia with a 12 month follow-up. Brucella endocarditis on a valve prosthesis is a very rare occurrence. The combination of valve replacement and antibiotic therapy is usually required.

In this study, the authors have attempted to collect files of jaundice in pregnant women. 65 cases were included in this study, over a period of 4 years. Several etiologies of jaundice have been reported but viral hepatitis especially the non A, non B viral hepatitis remain the most frequent. The epidemiology, and the clinical and evolutive criteria of each disease are briefly summarized.

From 1982 to 1986, 122 strains of non-typhoid Salmonellae were isolated at the University Hospital of Sfax (Tunisia). Both tests: serotype classification and sensitivity have demonstrated that the most frequent serotypes: S. wien and S. typhimurium have the highest degree of multiresistance. Ampicillin, cotrimoxazole and chloramphenicol are the most affected while cefotaxime, amikacin and colistin are still saved. Facing these facts, the authors insist on the seriousness of the excessive use of antibiotherapy which leads to the selection of such strains.