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At least 1,279 records · Page 71Linked to original sources
PubMed2001

Self-images in the video monitor coded by monkey intraparietal neurons.

When playing a video game, or using a teleoperator system, we feel our self-image projected into the video monitor as a part of or an extension of ourselves. Here we show that such a self image is coded by bimodal (somatosensory and visual) neurons in the monkey intraparietal cortex, which have visual receptive fields (RFs) encompassing their somatosensory RFs. We earlier showed these neurons to code the schema of the hand which can be altered in accordance with psychological modification of the body image; that is, when the monkey used a rake as a tool to extend its reach, the visual RFs of these neurons elongated along the axis of the tool, as if the monkey's self image extended to the end of the tool. In the present experiment, we trained monkeys to recognize their image in a video monitor (despite the earlier general belief that monkeys are not capable of doing so), and demonstrated that the visual RF of these bimodal neurons was now projected onto the video screen so as to code the image of the hand as an extension of the self. Further, the coding of the imaged hand could intentionally be altered to match the image artificially modified in the monitor.

Action Potentials↗
PubMed2000

Different scalp topography of brain potentials related to expression and identity matching of faces.

Event-related potentials (ERPs) and behavioral data were recorded while subjects performed two tasks on the same set of faces (presented in pairs). One task was identity matching and the other expression matching. Two groups of subjects participated, one familiar and the other unfamiliar with the faces. Subjects were less accurate in matching expressions than identity. Familiarity facilitated identity but not expression matching. ERPs to mismatches in both tasks elicited a negativity around 400 ms, which was similar in latency and amplitude in the two tasks, but differed in scalp topography. Whereas the mismatch negativity had the same landscape over the left hemisphere for both tasks, the component related to expression had larger amplitudes over the right-temporal regions. Familiarity had no effect on these negativities, although it affected a late positivity (LP). These results support the idea of distinct neural systems subserving face processing, and agree with a role of the right hemisphere for the processing of emotional expressions.

Adult↗
PubMed2003

Neural timing of visual implicit categorization.

Most of the neuroimaging studies that have shown visual category-specific activations or categorization effects have been based on a subtractive approach. In the present study, we investigated, by means of EEG, not only the net result of the categorization but also the dynamics of the process. Subjects had to perform a target detection task throughout an image set of distractors belonging to six categories: letters, geometrical figures, faces, tools, structured textures and Asiatic characters. Multivariate analyses were performed on the responses to the non-target stimuli according to their category. Categorical neural responses were only obtained on P2 latencies and N2 amplitudes. This result suggests that there are no differences in the first stage of the implicit categorization of the distractors (visual analysis and proximal stimulus representation elaboration from 100 to 220 ms) and that differences appear between 220 and 280 ms (matching to structural representations). Over-learned stimuli (e.g. letters) elicited the shortest P2 latency, contrasting with unknown categories (e.g. Asiatic characters) that revealed the longest P2 latencies and flattened N2 waves. Categorical differences indicate that the more a subject knows about an object, the less cognitive resources are used. In conclusion, our results suggest that a reduction in neural activity could reflect an improved accuracy in cognitive and cortical processing.

Adult↗
PubMedDate not supplied

Hierarchical decomposition of dichoptic multifocal visual evoked potentials.

Visual evoked responses to dichoptically presented multifocal stimuli were recorded for 92 eyes. Two stimulus variants were explored: temporally sparse and rapidly contrast reversing. We used hierarchical decomposition (HD) to represent the multifocal responses in terms of a small number of potentially unique component waveforms that are interrelated in a multivariate linear autoregressive (MLAR) relationship. The HD method exploits temporal correlations over a range of delays in the responses to estimate parallel, feedforward and feedback relationships between the HD components. Three HD components having temporal interrelationships constrained (at P < 0.05) to a moving approximately 20 ms window could describe the multifocal responses well (median r2-values up to 90%). HD components were similar for both stimulus types and the component waveforms were temporally correlated, especially the first and third components. The data set was large enough to estimate separate HD components for each multifocal stimulus region. The component waveforms differed somewhat by region but the MLAR relationships were similar. At short delays parallel processing dominated. At longer delays the proportion of response drives that were attributed to feedback and feedforward relationships grew. Overall HD analysis seems to provide an informed summary of multifocal responses and insights into their sources.

Adult↗
PubMed2002

Generators of visual evoked potentials for faces and eyes in the human brain as determined by dipole localization.

Human visual evoked potentials were recorded during presentation of photos of human and animal faces and various face features. Negative waves with approximate peak latencies of 165 msec (N170) were bilaterally recorded from the occipito-temporal regions. Mean peak latencies of the N170 were shorter for faces than eyes only. Analyses of amplitudes of evoked potentials indicated that the N170 elicited by faces reflected activity of a specific neural system which was insensitive to detailed differences among individual faces regardless of species, and consequently suggest that this system might function to detect existence of faces in general. On the other hand, the mean amplitude of the N170 elicited by human eyes was significantly larger than those by animal eyes. These differences in response latencies and amplitudes of the N170 suggest existence of at least 2 different visual evoked potentials with similar latencies (i.e., N170) which are sensitive to faces in general and human eyes, respectively. Dipole source localization analysis indicated that dipoles for the N170 elicited by eyes were located in the posterior inferior temporal gyrus, and those for faces, located initially in the same region, but moved toward the fusiform and lingual gyri at the late phase of the N170. The results indicated that information processing of faces and eyes separated at least as early as the latency of the N170 at the posterior inferior temporal gyrus as well as the fusiform and lingual gyri, and might provide neurophysiological and anatomical bases to an initial structural encoding stage of human faces.

Adult↗
PubMed2005

Decoding the visual and subjective contents of the human brain.

The potential for human neuroimaging to read out the detailed contents of a person's mental state has yet to be fully explored. We investigated whether the perception of edge orientation, a fundamental visual feature, can be decoded from human brain activity measured with functional magnetic resonance imaging (fMRI). Using statistical algorithms to classify brain states, we found that ensemble fMRI signals in early visual areas could reliably predict on individual trials which of eight stimulus orientations the subject was seeing. Moreover, when subjects had to attend to one of two overlapping orthogonal gratings, feature-based attention strongly biased ensemble activity toward the attended orientation. These results demonstrate that fMRI activity patterns in early visual areas, including primary visual cortex (V1), contain detailed orientation information that can reliably predict subjective perception. Our approach provides a framework for the readout of fine-tuned representations in the human brain and their subjective contents.

Adult↗
PubMed2006

Attention induces synchronization-based response gain in steady-state visual evoked potentials.

When attention is voluntarily directed to a spatial location, visual sensitivity increases at that location. What causes this improved sensitivity? Studies of single neuron spike rates in monkeys have provided mixed results in regard to whether attending to a stimulus increases its effective contrast (contrast gain) or multiplicatively boosts stimulus-driven neural responses (response or activity gain). We monitored frequency-tagged steady-state visual evoked potentials (SSVEPs) in humans and found that voluntary sustained attention multiplicatively increased stimulus-driven population electrophysiological activity. Analyses of intertrial phase coherence showed that this attentional response gain was at least partially due to the increased synchronization of SSVEPs to stimulus flicker. These results suggest that attention operates in a complementary manner at different levels; attention seems to increase single-neuron spike rates in a variety of ways, including contrast, response and activity gains, while also inducing a multiplicative boost on neural population activity via enhanced response synchronization.

Adult↗
PubMed2005

[Complications and diagnostic limitations of chronic meningitis].

HISTORY AND ADMISSION FINDINGS: A 37-year-old woman was admitted with total loss of vision of the left eye within 24 hours. Additionally, she complained about fatigue, headache, chills, fever, muscle pain and neck stiffness since 4 days. At admission, the body temperature was 38.7 degrees C. Neurological examination revealed papilledema and meningism. INVESTIGATIONS: Ophthalmologic findings were consistent with a papillitis. The vision was lost, the pattern-shift checkerboard visual evoked potentials were not measurable. MRI of the brain and the optical nerve was without pathological findings, meningeal or cerebral Gadolinium enhancement was not present. The CSF analysis yielded a lymphocytic meningitis with 249 cells/mm (3), the glucose ratio of cerebrospinal fluid and serum was normal. DIAGNOSIS, TREATMENT AND COURSE: The papillitis was treated unsuccessfully with high-dose methylprednisolone, the left eye remained blind. Persistence of the pleocytosis under initial treatment with aciclovir and ceftriaxone, reduction of the glucose ratio of cerebrospinal fluid and serum and intrathecal immunoglobuline A -- synthesis required a change of the diagnostic and therapeutic regimen. Various common and rare differential diagnoses were considered and ruled out, a chronic meningitis of unclear aetiology with the complication of amaurosis was diagnosed. In consideration of the most probable diagnosis, a tuberculostatic therapy was initiated. A prolonged reduction of the pleocytosis and normalization of cerebrospinal fluid parameters could be observed. CONCLUSIONS: A large number of aetiologies can cause chronic meningitis; this case report reviews the most important differential diagnoses and highlights the limitations of the diagnostic work-up although various methods are available. Clinical course and symptoms of chronic meningitis are mild to moderate and may even be absent, but it can cause severe complications.

Adult↗
PubMed1996

[Sensory physiology and biomorphology of the optic papilla: analysis of correlation in normal persons].

BACKGROUND: The aim of the present study was to investigate whether the morphological variability of the optic disc has an influence on sensory test procedures. PATIENTS AND METHODS: In 52 eyes of 52 normal persons psychophysical (perimetry, color vision, contrast sensitivity) and electrophysiological (pattern-ERG and pattern-VEP) tests and planimetric papillometry were performed. A correlation analysis was made between sensory tests and area of optic disc (1.79 to 5.2 mm2) and neuroretinal rim. RESULTS: There was no significant correlation between perimetry, color vision, pattern-ERG, pattern-VEP, spatio-temporal and temporal contrast sensitivity on the one hand and optic disc area or neuroretinal rim area on the other. CONCLUSION: Results of psychophysical and electrophysiological tests do not have to be corrected with respect to the neuroretinal rim area.

Adult↗
PubMed1992

[Discrete media clouding and its effect of contrast transfer coefficients, the pattern ERG and contrast sensitivity].

As a model for our study we selected 11 pseudophacic patients with secondary cataracts who experienced good postoperative visual acuity after extracapsular cataract extraction. Besides best visual acuity and contrast sensitivity Pattern-ERG (PERG) and Contrast-Transfer-Ratio (CTR) were measured before and after YAG-Kapsulotomy was performed. Visual acuity and contrast sensitivity increased in all patients after treatment, whereas CTR increased in eight patients. PERG was measured in five patients, in two cases its amplitudes were higher, the other measurements revealed unchanged or lower amplitudes. Our model shows that in addition to the usual psychophysic tests, with CTR and PERG there are objective methods available to measure discrete opacities of the visual system.

Cataract↗
PubMed2000

Which ocular and neurologic conditions cause disparate results in visual acuity scores recorded with visually evoked potential and teller acuity cards?

PURPOSE: We investigated whether disparity between visually evoked potential (VEP) acuity scores and Teller Acuity Card (TAC) scores varied according to presence of ocular or neurologic conditions. METHODS: Charts from 175 children (mean age, 34.8 months; range, 3 to 158 months) referred for visual acuity testing were examined. All children had been tested with pattern-alternation VEP and TAC and had undergone a complete eye examination. VEP and TAC acuity scores were relative to age-expected acuity scores for each acuity test. The absence and degree of macular abnormality, retinal abnormality, optic nerve hypoplasia, optic nerve atrophy, cortical visual impairment, developmental delay, cerebral palsy, seizures, and nystagmus were noted. Analysis of variance models were used to determine whether differences between VEP and TAC scores varied according to the presence of specific deficits. Logistic regression analysis determined whether degree of specific deficits was associated with a greater chance of inconsistency between VEP and TAC scores (>0.3 log unit difference). RESULTS: Inconsistent scores were found in 48% of children. Developmental delay was associated with relatively poorer TAC than VEP score, and the chance of inconsistency increased with severity of developmental delay. CONCLUSIONS: Diagnosis-dependent variability exists between TAC and VEP scores. Therefore knowledge of the clinical picture is necessary in interpretation of VEP and TAC scores. It is not clear which test is more useful when a disparity exists, either from this or previous studies. When visual acuity is assessed longitudinally in a given child, then consistency in method for acuity assessment is important.

Aging↗
PubMed1990

Event-related potentials to emotional and neutral stimuli.

The present study examined subjects' cognitive processing of pictures of emotional and neutral facial expressions, as measured by Event-Related Potentials (ERPs). In Experiment 1, 10 subjects viewed two slides of a woman modelling angry and happy expressions; in Experiment 2, 10 subjects viewed slides of two women modelling neutral expressions. One face appeared on 20% of the trials and the other on 80% of the trials. Subjects counted the low frequency target face. In both experiments, the area of the P300 component was larger at Pz than Cz. In Experiment 1, P300 area was larger when the target was happy; peak amplitude was greater when the target was angry. No differences between neutral target faces were found for P300 amplitude or area in Experiment 2. These results suggest that emotional versus neutral facial expressions elicit different electrophysiological responses; responses are further differentiated to positive versus negative expressions.

Adult↗
PubMed1994

Learning disability subtypes and the effects of auditory and visual priming on visual event-related potentials to words.

Three learning-disability (LD) subtype groups and a normal control group of children were compared in their visual event-related potentials (ERPs) to primed and unprimed words. The LD subtypes were defined by deficient performance on tests of arithmetic (Group A), reading and spelling (Group RS), or both (Group RSA). The primed words were preceded by pictures or spoken words having a related meaning, while unprimed words were preceded by non-associated pictures or spoken words. For normal controls, N450 amplitude was greater to unprimed words than to words primed by pictures and spoken words. For Group A, N450 amplitude was reduced by spoken-word primes, but not by picture primes, an effect that demonstrates a deficit in processing visual-spatial information. For Group RS and Group RSA, neither picture nor spoken-word primes reduced N450 amplitude. These effects can be understood in terms of deficiencies in processing auditory-verbal information. Normal controls displayed a greater left- than right-hemispheric asymmetry in frontal N450 amplitude to unprimed words, an effect that is consistent with the association of skilled reading with hemispheric specialization. This asymmetry was absent in the ERPs of all the LD subtypes. The distinct ERP effects for the groups endorses the value of defining LD subtypes on the basis of patterns of deficits in arithmetic and reading and spelling.

Adolescent↗
PubMed1994

Visual event-related potentials of dyslexic children to rhyming and nonrhyming stimuli.

In a visual event-related potential (ERP) study, children diagnosed as dyslexic in terms of both age and IQ discrepancy criteria were compared with two contrast groups: poor for age (SLOW) readers and normal reading children with Attention Deficit Disorder (ADD). The children viewed 200 stimulus pairs and judged whether the second stimulus of each pair rhymed with the first. The first stimulus was always a three-letter word, while half of the second stimuli were pronounceable nonsense words and half were real words. Rhyme probability was 50%. The ERP waveforms of the dyslexics were significantly different from those of the ADD group in showing less late negativity. The SLOW group's waveforms more closely paralleled those of the ADD group. The major anomalous feature of the dyslexics' waveform was a pronounced late positive peak (P500), which followed an attenuated N450 peak. Over all groups, the N450 peak was sensitive to the rhyme manipulation, as has been found in adults (Rugg, 1984a, 1984b). Real words and nonsense words produced similar waveforms. Hemispheric effects were found but did not interact with group. Results suggest non-automatic visual cognitive processing of rhyme in dyslexics.

Arousal↗
PubMed1987

Pathology of the optic nerve and visual association areas. Information given by the flash and pattern visual evoked potential, and the temporal and spatial contrast sensitivity function.

Spatial and temporal contrast sensitivity functions (CSF) were compared with visual evoked potentials (VEP) in two groups of patients with pathology selectively affecting different parts of the visual pathway. These consisted of 10 patients with a selective delay of the pattern VEP due to demyelination of one optic nerve (unilateral optic neuritis) and 11 patients with a selective delay of the flash VEP due to pathology of the visual association areas (primary presenile dementia, or Alzheimer's disease). The results led to the following conclusions. Comparison of the VEP and CSF results indicated that VEP latency was more closely associated with the temporal CSF than the spatial CSF. Pathology of the visual association areas which selectively increased the latency of the flash P2 component also reduced sensitivity at low and medium temporal frequencies. In demyelination of the optic nerve, a highly significant correlation was found between the delay of the pattern reversal VEP and sensitivity at high temporal frequencies. Comparison of the results in these two types of pathology suggests that the pattern VEP and flash P1 component, the spatial CSF, and temporal CSF at high temporal frequencies are all processed in the geniculostriate pathway. The flash P2 component and temporal CSF at low and medium frequencies were affected differently from the other measures. The possibility that these processes are transmitted by nongeniculate pathways is discussed.

Adult↗
PubMed1999

Visual evoked potentials in migraine patients: alterations depend on pattern spatial frequency.

Visual information is conducted by two parallel pathways (luminance- and contour-processing pathways) which are thought to be differentially affected in migraine and can be investigated by means of pattern-reversal visual evoked potentials (VEPs). Components and habituation of VEPs at four spatial frequencies were compared between 26 migraineurs (13 without aura, MO; 13 with aura, MA) and 28 healthy volunteers. Migraineurs were recorded in the headache-free interval (at least 72 h before and after an attack). Five blocks of 50 responses to chequerboards of 0.5, 1, 2 and 4 cycles per degree (c.p.d.) were sequentially averaged and analysed for latency and amplitude. Differences in VEPs were dependent on spatial frequency. Only when small checks were presented, i.e. at high spatial frequency (2 and 4 c.p.d.), was the latency of N2 significantly prolonged in MA and did it tend to be delayed in MO subjects. Habituation behaviour was not significantly different between groups under the stimulating conditions employed. Prolonged N2 latency might be explained by the lack or attenuation of a contour-specific component N130 in migraineurs, indicating an imbalance of the two visual pathways with relative predominance of the luminance-processing Y system. These results reflect an interictally persisting dysfunction of precortical visual processing which might be relevant in the pathophysiology of migraine.

Adult↗
PubMed1996

VEP in neglect patients have longer latencies for luminance but not for chromatic patterns.

In patients with unilateral neglect, visual evoked potentials (VEP) to stimuli displayed in the left visual field are delayed compared with responses to right visual field stimuli. In the present study, 10 patients with right brain damage and neglect were tested with contrast-reversed sinusoidal gratings, modulated either in luminance or in chromaticity. For gratings of luminance contrast modulated over relatively high temporal frequencies (4-10.5 Hz), latencies of VEP were about 30 ms longer for stimuli presented to the contralesional (left) visual field than to the field ipsilateral to the lesion. For equiluminant stimuli modulated at relatively low temporal frequencies (1-4 Hz), however, latency was the same for both hemifields. As this condition activates predominately the parvocellular pathway the results are consistent with our previous suggestion that the delay observed with luminance stimuli in neglect patients results from selective disruption of the faster response of the magnocellular pathway.

Cognition Disorders↗