Conceptual design of a GEM (gas electron multiplier) based gas Cherenkov detector for measurement of 17 MeV gamma rays from T(D, γ)5He in magnetic confinement fusion plasmas

The only method for assessing the fusion power throughput of a deuterium-tritium (DT) reactor presently relies on determining the absolute number of 14 MeV neutrons produced in the DT plasma. An independent method, developed and investigated during the recent DT campaign at the Joint European Torus, is based on the absolute counting of 17 MeV gamma rays produced by the competing T(D, γ)⁵He reaction that features a very weak branching ratio (about 3-6 × 10^-6) when compared to the main T(D, n)⁴He reaction. The state-of-the-art spectrometer used for gamma-ray measurements in magnetic confinement fusion plasmas is LaBr₃(Ce) scintillator detectors, although they require significant neutron shielding to extract a relatively weak gamma-ray signal from a much more abundant neutron field. A better approach relies on a gamma-ray detector that is intrinsically insensitive to neutrons. We have advanced the design of a gamma-ray counter based on the Cherenkov effect for gamma-rays whose energy exceeds 11 MeV, optimized to work in the neutron-rich environment of a steady-state, magnetically confined fusion plasma device. The gamma-rays interact with an aluminum window and extract electrons that move into the radiator emitting photons via the Cherenkov effect. Since the Cherenkov light consists of few photons (25 on average) in the far UV band (100-200 nm), a pre-amplifier is required to transport the photons to the neutron-shielded location, which may be a few meters away, where the readout elements of the detector, either a silicon or standard photomultiplier tube, are placed. The present work focuses on the development of a scintillating GEM (Gas Electron Multiplier) based pre-amplifier that acts as a Cherenkov photon pre-amplifier and wavelength shifter. This paper presents the result of a set of Garfield++ simulations developed to find the optimal GEM working parameters. A photon gain of 100 is obtained by biasing a single GEM foil to 1 kV.

A high-resolution neutron spectroscopic camera for the SPARC tokamak based on the Jet European Torus deuterium-tritium experience

Dedicated nuclear diagnostics have been designed, developed, and built within EUROFUSION enhancement programs in the last ten years for installation at the Joint European Torus and capable of operation in high power Deuterium-Tritium (DT) plasmas. The recent DT Experiment campaign, called DTE2, has been successfully carried out in the second half of 2021 and provides a unique opportunity to evaluate the performance of the new nuclear diagnostics and for an understanding of their behavior in the record high 14 MeV neutron yields (up to 4.7 × 10¹⁸ n/s) and total number of neutrons (up to 2 × 10¹⁹ n) achieved on a tokamak. In this work, we will focus on the 14 MeV high resolution neutron spectrometers based on artificial diamonds which, for the first time, have extensively been used to measure 14 MeV DT neutron spectra with unprecedented energy resolution (Full Width at Half Maximum of ≈1% at 14 MeV). The work will describe their long-term stability and operation over the DTE2 campaign as well as their performance as neutron spectrometers in terms of achieved energy resolution and high rate capability. This important experience will be used to outline the concept of a spectroscopic neutron camera for the SPARC tokamak. The proposed neutron camera will be the first one to feature the dual capability to measure (i) the 2.5 and 14 MeV neutron emissivity profile via the conventional neutron detectors based on liquid or plastics scintillators and (ii) the 14 MeV neutron spectral emission via the use of high-resolution diamond-based spectrometers. The new opportunities opened by the spectroscopic neutron camera to measure plasma parameters will be discussed.

A new dedicated signal processing system for gamma-ray spectrometers in high power deuterium-tritium plasma scenarios in tokamaks

The most performant deuterium-tritium (DT) plasma discharges realized by the Joint European Torus (JET) tokamak in the recent DT campaign have produced neutron yields on the order of 10¹⁸ n/s. At such high neutron yields, gamma-ray spectroscopy measurements with scintillators are challenging as events from the neutron-induced background often dominate over the signal, leading to a significant fraction of pileup events and instability of the photodetector gain along with the consequent degradation of the reconstructed spectrum. Here, we describe the solutions adopted for the tangential lanthanum bromide spectrometer installed at JET. A data acquisition system with free streaming mode digitization capabilities for the entire duration of the discharge has been used to solve dead-time related issues and a data reconstruction code with pileup recovery and photodetector gain drift restoration has been implemented for off-line analysis of the data. This work focuses on the acquired data storage and parsing, with a detailed explanation of the pileup recovery and gain drift restoration algorithms.

Role of neutron attenuators for gamma-ray measurements in deuterium-tritium magnetic confinement plasmas

The Joint European Torus (JET) is the only tokamak in the world able to operate in Deuterium-Tritium (DT) plasmas. A successful DT experimental campaign, the DTE2, has recently been carried out, providing unique opportunities for studying both physics and technological aspects. In particular, it allowed us to investigate and benchmark the solutions adopted to attenuate the significant 14 MeV neutron flux, needed to enable high-resolution gamma-ray spectroscopy measurements on a tokamak. While in inertial confinement experiments, gamma-rays and neutrons are discriminated through time-of-flight techniques; in magnetic confinement experiments, the neutron attenuators are a key element to allow gamma-ray measurements in order to reestablish the 1 × 10⁵ to 1 background to signal ratio. In this paper, the role of the reference neutron attenuators at JET, based on LiH, has been analyzed and described.

A diagnostic pitfall of a sternal mass

Primary sternal lymphoma represents a rare entity which must be evoked in front of a sternal mass especially as its treatment is different from that of sarcomas, the principal etiology of sternal masses.

Mapping the Featural and Holistic Face Processing of Bad and Good Face Recognizers

Individual abilities in face recognition (good versus bad recognizers) were explored by means of event-related potentials (ERPs). The adaptation response profile of the N170 component to whole faces, eyes and mouths was used in order to highlight the crucial role of individual abilities in identity repetition processes for unfamiliar faces. The main point of this study is to underline the importance of characterizing the performance (bad or good) of the participants and to show that behaviorally selected groups might reveal neural differences. Good recognizers showed selective right hemisphere N170 repetition effects for whole faces and not for features. On the contrary, bad recognizers showed a general repetition effect not specifically related to faces and more pronounced processing for features. These findings suggest a different contribution of holistic and featural analysis in bad and good performers. In conclusion, we propose that the N170 might be used as a tool to tease apart face encoding processes as a function of individual differences.

Fast neutron measurements with solid state detectors at pulsed spallation sources

Fast neutron measurements have been performed with silicon and diamond detectors at nTOF, ChipIr, and CHARM facilities. The detectors have been used in pulse mode; the deposited energy and time stamp is measured event by event for each signal above threshold. The pulsed nature of the spallation sources gives high instantaneous counting rates that dictate the use of a fast electronic chain including a current preamplifier and digital acquisition. The energy-dependent response functions of these detectors to fast neutrons can be extracted from nTOF data using time-of-flight to provide energy tagging. These measured response functions can then be used both to benchmark Monte Carlo simulations of the response functions and to interpret the measurements at ChipIR and CHARM, facilities used for the irradiation of microelectronics, where time-of-flight energy measurement at these neutron energies is not possible.

Reading-related abilities underlying phonological awareness: a cross-sectional study in children with and without dyslexia

PURPOSE

The present cross-sectional study examined the individual role of rapid automatized naming (RAN), verbal short-term memory (VSTM), and phonological verbal fluency (PVF) along with word reading performance in predicting phonological awareness (PA).

MATERIALS AND METHODS

A total of 225 Arabic speaking children from grades 2, 3, 4 and 5 took part in this study, divided into two groups of readers: typical developing readers and dyslexic readers. The participants were tested on word and pseudoword reading, phonological awareness, rapid naming, verbal short-term memory and phonological verbal fluency.

RESULTS

There are different predictive patterns between the two groups. Whereas Raven and Grade contributed directly in predicting PA in typical readers, VSTM and PVF directly predicted PA in children with dyslexia. However, word reading played a dual role in the both groups as direct predictors of PA, mediating the predictive relationships between PA and the other variables.

CONCLUSION

The results suggest the potential existence of an underlying phonological representation processing ability shared between PA, phonological access (RAN and PVF), VSTM, and word reading ability.

Priming effect in children with Type 1 Diabetes Mellitus

Previous studies have evidenced cognitive difficulties across various domains in Type 1 Diabetes Mellitus (T1DM) children, but the implicit memory system has not yet been systematically explored.Taking into account that the interplay between memory and perception may be modulated by the semantic category of the stimuli and their salience, we explored explicit and implicit memory using both object and food stimuli to verify whether for T1DM children there is a feebleness in performing the function of memory as a function of the stimuli used.Eighteen T1DM children and 47 healthy children performed an explicit recognition task in which they were requested to judge whether the presented image had already been shown ("old") or not ("new") and an identification priming task in which they were asked to name new and old pictures presented at nine ascending levels of spatial filtering.Results did not reveal any differences between controls and T1DM children in the explicit memory recognition task, whereas some differences between the two groups were found in the identification priming task. In T1DM children, the priming effect was observed only for food images.The dissociation between implicit and explicit memory observed in children with diabetes seems to be modulated by the category of the stimuli, and these results underscore the relevance of taking into account this variable when exploring cognitive functions.

Correction to: Effectiveness of working memory training among children with dyscalculia: evidence for transfer effects on mathematical achievement-a pilot study

The following errors require correction in the article. The authors apologize for these errors.

Design of gamma-ray spectrometers optimized for fast particle studies at ITER

A set of gamma ray spectrometers has been designed for ITER within the Radial Gamma Ray Spectrometer (RGRS) project. The aim of this project is designing a system, integrated with the ITER radial neutron camera, which is able to measure the gamma-rays emitted from the plasma with a good energy resolution (about 1.5% at 4.44 MeV) and at high counting rates (in excess of 1 MHz). The RGRS will be able to operate both in the D phase and in the full-power DT phase and will measure gamma rays from (i) reactions between fast ions, such as α particles, and light impurities and (ii) bremsstrahlung emission generated by runaway electron interactions with both plasma bulk and tokamak walls. The RGRS detectors are arranged in nine lines of sights (able to cover a radial region with r < a/3), each featuring a large LaBr₃ scintillator crystal. Due to the high neutron flux and magnetic field, several solutions have been adopted to guarantee a good signal to background ratio and MHz counting rate capabilities. The RGRS is capable to combine space and energy distribution measurements of α particles and runaway electrons, which will help the study of the fast particle physics in a burning plasma.

Neutron measurements at the ELISE neutral beam test facility and implications for neutron based diagnostics at SPIDER

Along the route to the development of a neutral beam injector for ITER, the Padua based Source for Production of Ion of Deuterium Extracted from Rf plasma (SPIDER) and megavolt ITER injector and concept advancement facilities will make use of neutron diagnostics to quantify the homogeneity of the neutral beam profile by measuring the map of the neutron emission from the beam dump with the close-contact neutron emission surface mapping (CNESM) system. Neutrons are here produced from beam-target reactions between the deuterium beam and the deuterons previously adsorbed in the calorimeter. In order to aid the interpretation of the diagnostic data, a dedicated experiment on neutron emission from beam-target reactions with beam parameters approaching those expected at SPIDER has been performed at the Extraction from a Large Ion Source Experiment (ELISE) neutral beam test facility. The time trace of neutron emission has been measured using a calibrated liquid scintillator detector at increasing power densities on the target. Compared to calculations based on the local mixing model, a systematic discrepancy was observed exceeding the statistical accuracy of the measurements and increasing as a linear function of the power density. The data are used to derive an empirical temperature dependent correction for applications to neutron measurements at SPIDER.

Neutron emission spectroscopy of DT plasmas at enhanced energy resolution with diamond detectors

This work presents measurements done at the Peking University Van de Graaff neutron source of the response of single crystal synthetic diamond (SD) detectors to quasi-monoenergetic neutrons of 14-20 MeV. The results show an energy resolution of 1% for incoming 20 MeV neutrons, which, together with 1% detection efficiency, opens up to new prospects for fast ion physics studies in high performance nuclear fusion devices such as SD neutron spectrometry of deuterium-tritium plasmas heated by neutral beam injection.

First neutron spectroscopy measurements with a pixelated diamond detector at JET

A prototype Single crystal Diamond Detector (SDD) was installed at the Joint European Torus (JET) in 2013 along an oblique line of sight and demonstrated the possibility to carry out neutron spectroscopy measurements with good energy resolution and detector stability in discharges heated by neutral beam injection and radio-frequency waves. Starting from these positive results, within the Vertical Neutron Spectrometer project of the Joint European Torus, we have developed a pixelated instrument consisting of a matrix of 12 independent SDDs, called the Diamond Vertical Neutron Spectrometer (DVNS), which boosts the detection efficiency of a single SDD by an order of magnitude. In this paper we describe the main features of the DVNS, including the detector design, energy resolution, and data acquisition system for on-line processing. Preliminary spectroscopy measurements of 2.5 MeV neutrons from the present deuterium plasma at JET are finally presented.

Response function of single crystal synthetic diamond detectors to 1-4 MeV neutrons for spectroscopy of D plasmas

A Single-crystal Diamond (SD) detector prototype was installed at Joint European Torus (JET) in 2013 and the achieved results have shown its spectroscopic capability of measuring 2.5 MeV neutrons from deuterium plasmas. This paper presents measurements of the SD response function to monoenergetic neutrons, which is a key point for the development of a neutron spectrometer based on SDs and compares them with Monte Carlo simulations. The analysis procedure allows for a good reconstruction of the experimental results. The good pulse height energy resolution (equivalent FWHM of 80 keV at 2.5 MeV), gain stability, insensitivity to magnetic field, and compact size make SDs attractive as compact neutron spectrometers of high flux deuterium plasmas, such as for instance those needed for the ITER neutron camera.

Fast ion energy distribution from third harmonic radio frequency heating measured with a single crystal diamond detector at the Joint European Torus

Neutron spectroscopy measurements with a single crystal diamond detector have been carried out at JET, for the first time in an experiment aimed at accelerating deuterons to MeV energies with radio frequency heating at the third harmonic. Data are interpreted by means of the expected response function of the detector and are used to extract parameters of the highly non-Maxwellian distribution function generated in this scenario. A comparison with observations using a time of flight and liquid scintillator neutron spectrometers is also presented. The results demonstrate the capability of diamond detectors to contribute to fast ion physics studies at JET and are of more general relevance in view of the application of such detectors for spectroscopy measurements in the neutron camera of next step tokamak devices.

You are that smiling guy I met at the party! Socially positive signals foster memory for identities and contexts

The emotional influence of facial expressions on memory is well-known whereas the influence of emotional contextual information on memory for emotional faces is yet to be extensively explored. This study investigated the interplay between facial expression and the emotional surrounding context in affecting both memory for identities (item memory) and memory for associative backgrounds (source memory). At the encoding fearful and happy faces were presented embedded in fear or happy scenes (i.e.: fearful faces in fear-scenes, happy faces in happy-scenes, fearful faces in happy-scenes and happy faces in fear-scenes) and participants were asked to judge the emotional congruency of the face-scene compounds (i.e. fearful faces in fear-scenes and happy faces in happy-scenes were congruent compounds). In the recognition phase, the old faces were intermixed with the new ones: all the faces were presented isolated with a neutral expression. Participants were requested to indicate whether each face had been previously presented (item memory). Then, for each old face the memory for the scene originally compounded with the face was tested by a three alternative forced choice recognition task (source memory). The results evidenced that face identity memory is differently modulated by the valence in congruent face-context compounds with better identity recognition (item memory) for happy faces encoded in happy-scenarios. Moreover, also the memory for the surrounding context (source memory) benefits from the association with a smiling face. Our findings highlight that socially positive signals conveyed by smiling faces may prompt memory for identity and context.

Experimental investigation of silicon photomultipliers as compact light readout systems for gamma-ray spectroscopy applications in fusion plasmas

A matrix of Silicon Photo Multipliers has been developed for light readout from a large area 1 in. × 1 in. LaBr3 crystal. The system has been characterized in the laboratory and its performance compared to that of a conventional photo multiplier tube. A pulse duration of 100 ns was achieved, which opens up to spectroscopy applications at high counting rates. The energy resolution measured using radioactive sources extrapolates to 3%-4% in the energy range Eγ = 3-5 MeV, enabling gamma-ray spectroscopy measurements at good energy resolution. The results reported here are of relevance in view of the development of compact gamma-ray detectors with spectroscopy capabilities, such as an enhanced gamma-ray camera for high power fusion plasmas, where the use of photomultiplier is impeded by space limitation and sensitivity to magnetic fields.

A diamond based neutron spectrometer for diagnostics of deuterium-tritium fusion plasmas

Single crystal Diamond Detectors (SDD) are being increasingly exploited for neutron diagnostics in high power fusion devices, given their significant radiation hardness and high energy resolution capabilities. The geometrical efficiency of SDDs is limited by the size of commercially available crystals, which is often smaller than the dimension of neutron beams along collimated lines of sight in tokamak devices. In this work, we present the design and fabrication of a 14 MeV neutron spectrometer consisting of 12 diamond pixels arranged in a matrix, so to achieve an improved geometrical efficiency. Each pixel is equipped with an independent high voltage supply and read-out electronics optimized to combine high energy resolution and fast signals (<30 ns), which are essential to enable high counting rate (>1 MHz) spectroscopy. The response function of a prototype SDD to 14 MeV neutrons has been measured at the Frascati Neutron Generator by observation of the 8.3 MeV peak from the (12)C(n, α)(9)Be reaction occurring between neutrons and (12)C nuclei in the detector. The measured energy resolution (2.5% FWHM) meets the requirements for neutron spectroscopy applications in deuterium-tritium plasmas.

Single crystal diamond detector measurements of deuterium-deuterium and deuterium-tritium neutrons in Joint European Torus fusion plasmas

First simultaneous measurements of deuterium-deuterium (DD) and deuterium-tritium neutrons from deuterium plasmas using a Single crystal Diamond Detector are presented in this paper. The measurements were performed at JET with a dedicated electronic chain that combined high count rate capabilities and high energy resolution. The deposited energy spectrum from DD neutrons was successfully reproduced by means of Monte Carlo calculations of the detector response function and simulations of neutron emission from the plasma, including background contributions. The reported results are of relevance for the development of compact neutron detectors with spectroscopy capabilities for installation in camera systems of present and future high power fusion experiments.

A neutron diagnostic for high current deuterium beams

A neutron diagnostic for high current deuterium beams is proposed for installation on the spectral shear interferometry for direct electric field reconstruction (SPIDER, Source for Production of Ion of Deuterium Extracted from RF plasma) test beam facility. The proposed detection system is called Close-contact Neutron Emission Surface Mapping (CNESM). The diagnostic aims at providing the map of the neutron emission on the beam dump surface by placing a detector in close contact, right behind the dump. CNESM uses gas electron multiplier detectors equipped with a cathode that also serves as neutron-proton converter foil. The cathode is made of a thin polythene film and an aluminium film; it is designed for detection of neutrons of energy >2.2 MeV with an incidence angle < 45°. CNESM was designed on the basis of simulations of the different steps from the deuteron beam interaction with the beam dump to the neutron detection in the nGEM. Neutron scattering was simulated with the MCNPX code. CNESM on SPIDER is a first step towards the application of this diagnostic technique to the MITICA beam test facility, where it will be used to resolve the horizontal profile of the beam intensity.

CHRONOMETRY OF VISUAL WORD RECOGNITION DURING PASSIVE AND LEXICAL DECISION TASKS: AN ERP INVESTIGATION

In order to investigate the neuroanatomical chronometry of word processing, two experiments using: Event-Related Potentials (ERPs) have been performed. The first one was designed to test the effects of orthographic, phonologic, and lexical properties of linguistic items on the pre-semantic components of ERPs during a passive reading task and massive repetition used to reduce familiarity effect between words and nonwords. In a second study, the level of familiarity was investigated by varying stimulus repetition and frequency in a lexical decision task. Overall results suggest a functional discrimination between orthographic and nonorthographic stimuli begun as early as 170 ms (N170 component) whereas the next components (N230 and N320) were sensitive to the orthographic nature of the stimuli, but also to their lexical/phonologic proprieties. The N320 associated to phonological processing (Bentin et al., 1999) was modulated by word frequency and massive repetition caused its disappearance. This suggests that this component may reflect a nonobligatory phonologic stage of grapheme-phoneme conversion postulated by the DRC model (Coltheart et al., 2001) or semantic phonologically mediated pathway (Harm & Seidenberg, in press).

[The cutaneous leishmaniasis of the face in Gafsa area, Tunisia]

The cutaneous leishmaniasis is a frequent affection in Tunisia. In the Gafsa region it is a endemoepidemic infection. Our prospective study was carried out on 225 cases of cutaneous leishmaniasis of the face collected over two years in the outpatients' department of dermatology at Gafsa hospital. The aim of our study was to know more about the evolutive epidemio-clinical particularities of the cutaneous leishmaniasis of the face. The relative frequency of the cutaneous leishmaniasis of the face for the new patients reached 5%. An equal distribution between the two sexes was noted. The average age of our patients was 24 years old and 6 months old with extremes ranging from 3 months to 77 years. The nodular and ulcerated forms were the most frequent (35.3%), followed by impetiginoid forms (23%), then the lupoid forms (15%). The papular form was quite frequent (13%). Impetiginoid lesions occurred frequently in the child. Lupoid lesions appeared particularly on the nose. The complicated forms: the cutaneuos necrosis or erysipelas of the face appeared after intralesional injections of meglumine antimoniate (Glucantime). The intramuscular meglumine antimoniate was used in 172 patients, among them 47 needed two treatments or more because of a particular resistance of the lesions of the face. The pimple of Gafsa, term initially used for ulcerated skin nodules, was actually characterised by a lesional polymorphism. The prognosis was good however the risk of in aesthetic scar of the face was important.

ERPs associated with familiarity and degree of familiarity during face recognition

Event-related potentials (ERPs) triggered by three different faces (unfamiliar, famous, and the subject's own) were analyzed during passive viewing. A familiarity effect was defined as a significant difference between the two familiar faces as opposed to the unfamiliar face. A degree of familiarity effect was defined as a significant difference between all three conditions. The results show a familiarity effect 170 ms after stimulus onset (N170), with larger amplitudes seen for both familiar faces. Conversely, a degree of familiarity effect arose approximately 250 ms after stimulus onset (P2) in the form of progressively smaller amplitudes as a function of familiarity (subject's face < famous face < unfamiliar). These results demonstrate that the structural encoding of faces, as reflected by N170 activities, can be modulated by familiarity and that facial representations acquire specific properties as a result of experience. Moreover, these results confirm the hypothesis that N170 is sensitive to face versus, object discriminations and to the discrimination among faces.

Event-related potentials for category-specific information during passive viewing of faces and objects

Normal subjects passively viewed an upright or inverted face or objects during recording of event-related potentials. Face inversion augmented N170 amplitude and latency in the temporal region, but only the latency in the parietal region. The same manipulation slowed down the onset of the P220 and caused disappearance of the N300, whereas none of these effects was seen after object inversion. Item-specific processing of objects was observed, namely disappearance of the N190 and the appearance of a P170 wave in the left posterior hemisphere to one object but not the other. These results are concordant with the hypothesis of category-specific processing during the recognition of faces and objects.

Electrophysiological correlates of the visual after effect by means of visual evoked potentials

An attempt was made to determine whether changes of electrical activity could be seen in the posterior cortex during an after image of high frequency luminance gratings. Steady state visual evoked potentials were recorded (midoccipital, right and left temporo-occipital sites) immediately after a period of visual adaptation (15 min) to the stimulus, while the subjects experienced the after image. During this illusion, frequencies of the fast Fourier transform spectra linked to the stimulation differed from the noise and were larger at temporo-occipital sites than at the midoccipital one. In view of these results, the hypothesis that the after effect represents a short term storage of the temporal characteristics of the stimulus is evoked.

[Pseudarthrosis and non-union of disjunctive talar fractures]

PURPOSE OF THE STUDY

Neck fractures of the talus are rare. Necrosis is the complication most often observed. Mal union or non union are rarely reported: 11 cases of such complications have been treated and are presented with results of surgical treatment.

MATERIAL

Seven non unions and 4 mal unions after separation fracture of the talus, presenting with pain and deformity of the hindfoot were treated. The treatment included removal of the fibrous tissue, heel reaxation, bone grafting, peritalar joints arthrodesis.

RESULTS

Bone healing was observed in 5 of 7 non unions, and the correction of the hindfoot deformity in 9 of the 11 cases.

DISCUSSION

Non union or mal union after separation fracture of the neck of the talus are poorly tolerated, the patients walking with the foot in internal rotation, bearing most of the weight on the lateral border of the foot. Such poor course results from: the less mechanical stiffness of the medial part of the talus, the severity and the comminution of the fracture, insufficienct reduction and fixation, too early weight bearing, and is associated with degenerative changes of peritalar joints. Functional and antomical good results can be obtained with bone healing, hindfoot reaxation and peritalar arthrodesis. We emphasize the interest of X Rays in the examination and the adequacy of a good initial treatment.

The Stroop's test evokes a negative brain potential, the N400

The Event Related Potential (ERP) of 8 french right handed subjects were recorded with 5 active electrodes located in frontal (Fz), central (Cz), occipital (Oz) and right/left parietal (RH, LH) sites while they were performing a modified version of the test of Stroop. They had either to read the names of basic colors (yellow, green, blue, red) written in the same colors (red written in red: concordant stimuli) or in a different color (red written in blue: discordant stimuli) or to name mentally the color in which was written the name of a color, both colors being concordant or discordant. The ERPs for reading were similar for concordant and discordant stimuli and showed no sign of a N400 wave, this was also the case for the mental naming of a color associated to the written name of the same color. A N400 wave with a Cz location was evident for the mental naming of a color when it was associated to the written name of another color. In this last case, the automatic reading of the name of a color would correspond to a priming which interferes with the access to the target word: the name of another color that the subject is required to evoke mentally.

Hemispheric asymmetry in transient visual evoked potentials induced by the spatial factor of the stimulation

In order to enhance the effect of spatial frequency on the hemispheric asymmetry of visual evoked potentials (VEP), the response amplitudes to ON-OFF modulated gratings were compared with the responses to pattern reversal stimulation. Sinusoidal gratings of different spatial frequencies were presented to six righthanders. VEPs were recorded from temporal leads on each hemisphere. In the left hemisphere, the amplitude was constant for the two modes of presentation and independent of spatial frequency. In the right hemisphere, the response amplitude was larger to the ONSET stage of ON-OFF stimulation than to reversal and presented the characteristic spatial frequency tuning curve. This asymmetry is assumed to reflect a difference in sensitivity of the two hemispheres to the spatiotemporal characteristics of the stimulus. The relevance of these findings is discussed in relation to the other hemispheric specialization models.

Influence of spatial frequency and handedness on hemispheric asymmetry in visually steady-state evoked potentials

Recent suggestions on the involvement of the spatial frequency of visual stimuli in the hemispheric lateralization were investigated by recording steady-state evoked potentials in two groups of subjects: five right-handers and five left-handers. Sinusoidal gratings at spatial frequency of 0.5, 1, 3, 4, 6, 8, 10, 12 or 16 cpd were phase reversed at 4 Hz or 12 Hz. Evoked potentials recorded from temporal leads over each hemisphere were submitted to a FFT analysis. Results concern the amplitude of the fundamental component. In right-handers, the temporal frequency was the deciding factor of the lateralization: the evoked activities were greatest in the RH at 4 Hz and in the LH at 12 Hz. This effect was obvious for the range of spatial frequencies from 3-12 cpd. Results, discussed in terms of global/local information, suggested the existence of two transient and sustained systems. In left-handers, both the spatial and temporal parameters were relevant to the lateralization. A spatio-temporal interaction was observed which was reversed at 6 cpd.

Hemispheric asymmetries in the visual evoked potentials to temporal frequency: preliminary evidence

Steady-state evoked potentials were recorded in eight adult subjects from occipital and temporal leads of both hemispheres to investigate the effect of temporal frequency on the hemispheric specialization for basic visual information. A 3 cycles deg-1 grating was phase-reversed at different temporal frequencies (from 4 to 18 Hz), and the frequency spectrum of evoked potentials was computed by means of a fast Fourier transform program. Significant results were obtained for the component at twice the temporal frequency of stimulation. Occipital evoked potentials did not show hemispheric asymmetry, whereas temporal evoked potentials showed an interaction between hemisphere and temporal frequency: right and left hemispheres were respectively prominent for low (4 and 6 Hz) and for high (8-18 Hz) temporal frequencies. The results are discussed in the context of current research on hemispheric specialization for basic spatiotemporal parameters of visual information processing.