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At least 757 records · Page 42Linked to original sources
PubMed2005

Differential anterior prefrontal activation during the recognition stage of a spatial working memory task.

Neuroimaging studies commonly show widespread activations in the prefrontal cortex during various forms of working memory and long-term memory tasks. However, the anterior prefrontal cortex (aPFC, Brodmann area 10) has been mainly associated with retrieval in episodic memory, and its role in working memory is less clear. We conducted an event-related functional magnetic resonance imaging study to examine brain activations in relation to recognition in a spatial delayed-recognition task. Similar to the results from previous findings, several frontal areas were strongly activated during the recognition phase of the task, including the aPFC, the lateral PFC and the anterior cingulate cortex. Although the aPFC was more active during the recognition phase, it was also active during the delay phase of the spatial working memory task. In addition, the aPFC showed greater activity in response to negative probes (non-targets) than to positive probes (targets). While our analyses focused on examining signal changes in the aPFC, other prefrontal regions showed similar effects and none of the areas were more active in response to the positive probes than to the negative probes. Our findings support the conclusion that the aPFC is involved in working memory and particularly in processes that distinguish target and non-target stimuli during recognition.

Adult↗
PubMed2003

An attention modulated response to disgust in human ventral anterior insula.

The human brain is expert in analyzing rapidly and precisely facial features, especially emotional expressions representing a powerful communication vector. The involvement of insula in disgust recognition has been reported in behavioral and functional imaging studies. However, we do not know whether specific insular fields are involved in disgust processing nor what the processing time course is. Using depth electrodes implanted during presurgical evaluation of patients with drug-refractory temporal lobe epilepsy, we recorded intracerebral event-related potentials to human facial emotional expressions, that is, fear, disgust, happiness, surprise, and neutral expression. We studied evoked responses in 13 patients with insular contacts to specify the insular fields involved in disgust processing and assess the timing of their activation. We showed that specific potentials to disgust beginning 300 milliseconds after stimulus onset and lasting 200 milliseconds were evoked in the ventral anterior insula in four patients. The occurrence and latency of event-related potentials to disgust in the ventral anterior insula were affected by selective attention. The analysis of spatial and temporal characteristics of insular responses to disgust facial expression lead us to underline the crucial role of ventral anterior insula in the categorization of facial emotional expressions, particularly the disgust.

Attention↗
PubMed2006

Boundary completion is automatic and dissociable from shape discrimination.

Normal visual perception readily overcomes suboptimal or degraded viewing conditions through perceptual filling-in processes, enhancing object recognition and discrimination abilities. This study used visual evoked potential (VEP) recordings in conjunction with electrical neuroimaging analyses to determine the spatiotemporal brain dynamics of boundary completion and shape discrimination processes in healthy humans performing the so-called "thin/fat" discrimination task (Ringach and Shapley, 1996) with stimuli producing illusory contours. First, results suggest that boundary completion processes occur independent of subjects' accuracy on the discrimination task. Modulation of the VEP to the presence versus absence of illusory contours [the IC effect (Murray et al., 2002)] was indistinguishable in terms of response magnitude and scalp topography over the 124-186 ms poststimulus period, regardless of whether task performance was correct. This suggests that failure on this discrimination task is not primarily a consequence of failed boundary completion. Second, the electrophysiological correlates of thin/fat shape discrimination processes are temporally dissociable from those of boundary completion, occurring during a substantially later phase of processing (approximately 330-406 ms). The earlier IC effect was unaffected by whether the perceived contour produced a thin or fat shape. In contrast, later time periods of the VEP modulated according to perceived shape only in the case of stimuli producing illusory contours, but not for control stimuli for which performance was at near-chance levels. Collectively, these data provide further support for a multistage model of object processing under degraded viewing conditions.

Adult↗
PubMed1999

Auditory-visual integration during multimodal object recognition in humans: a behavioral and electrophysiological study.

The aim of this study was (1) to provide behavioral evidence for multimodal feature integration in an object recognition task in humans and (2) to characterize the processing stages and the neural structures where multisensory interactions take place. Event-related potentials (ERPs) were recorded from 30 scalp electrodes while subjects performed a forced-choice reaction-time categorization task: At each trial, the subjects had to indicate which of two objects was presented by pressing one of two keys. The two objects were defined by auditory features alone, visual features alone, or the combination of auditory and visual features. Subjects were more accurate and rapid at identifying multimodal than unimodal objects. Spatiotemporal analysis of ERPs and scalp current densities revealed several auditory-visual interaction components temporally, spatially, and functionally distinct before 200 msec poststimulus. The effects observed were (1) in visual areas, new neural activities (as early as 40 msec poststimulus) and modulation (amplitude decrease) of the N185 wave to unimodal visual stimulus, (2) in the auditory cortex, modulation (amplitude increase) of subcomponents of the unimodal auditory N1 wave around 90 to 110 msec, and (3) new neural activity over the right fronto-temporal area (140 to 165 msec). Furthermore, when the subjects were separated into two groups according to their dominant modality to perform the task in unimodal conditions (shortest reaction time criteria), the integration effects were found to be similar for the two groups over the nonspecific fronto-temporal areas, but they clearly differed in the sensory-specific cortices, affecting predominantly the sensory areas of the nondominant modality. Taken together, the results indicate that multisensory integration is mediated by flexible, highly adaptive physiological processes that can take place very early in the sensory processing chain and operate in both sensory-specific and nonspecific cortical structures in different ways.

Acoustic Stimulation↗
PubMed1997

Human discrimination of the implicit orientation of simple symmetrical patterns.

Thresholds for detecting the angle of rotation of vertical symmetrical patterns containing few or no explicit vertical or horizontal contours were found to be almost as low as those for an actual vertical line extending approximately the same range. This hyperacuity performance, which we refer to as implicit orientation discrimination, shares most of its properties with the orientation discrimination of explicit lines, suggesting a category of orientation processing whose neural mechanisms are related to those involved in the processing of straight contours and those underlying the detection of axes of symmetry. Strong binding effects between the components of the figures were demonstrated and their temporal interactions were also investigated. Our results have implications for possible neural interactions early in the cortical visual stream.

Humans↗
PubMed1991

The flanker compatibility effect as a function of visual angle, attentional focus, visual transients, and perceptual load: a search for boundary conditions.

When subjects must respond to a relevant center letter and ignore irrelevant flanking letters, the identities of the flankers produce a response compatibility effect, indicating that they are processed semantically at least to some extent. Because this effect decreases as the separation between target and flankers increases, the effect appears to result from imperfect early selection (attenuation). In the present experiments, several features of the focused attention paradigm were examined, in order to determine whether they might produce the flanker compatibility effect by interfering with the operation of an early selective mechanism. Specifically, the effect might be produced because the paradigm requires subjects to (1) attend exclusively to stimuli within a very small visual angle, (2) maintain a long-term attentional focus on a constant display location, (3) focus attention on an empty display location, (4) exclude onset-transient flankers from semantic processing, or (5) ignore some of the few stimuli in an impoverished visual field. The results indicate that none of these task features is required for semantic processing of unattended stimuli to occur. In fact, visual angle is the only one of the task features that clearly has a strong influence on the size of the flanker compatibility effect. The invariance of the flanker compatibility effect across these conditions suggests that the mechanism for early selection rarely, if ever, completely excludes unattended stimuli from semantic analysis. In addition, it shows that selective mechanisms are relatively insensitive to several factors that might be expected to influence them, thereby supporting the view that spatial separation has a special status for visual selective attention.

Attention↗
PubMed1990

Cognitive event-related potential components during continuous recognition memory for pictures.

Event-related brain potentials (ERPs) were recorded from 28 young adult subjects during a continuous recognition memory paradigm, with pictures as stimuli. Subjects were required to determine on each trial if the picture was "new" (never before presented) or "old" (seen previously). To assess differences between primary and secondary memory, old items were presented after lags of 2, 8, and 32 intervening pictures (equiprobable) following their first presentation. The results suggested that a negativity (Cz maximum) at 300 ms was the most likely candidate for the brain event reflecting the retrieval of the item from memory. Old/new effects were modulated by two types of activity, both of which were larger in the ERPs elicited by new items. The earlier of these, possibly similar to the N400, had a duration from about 250-600 ms, began with the N300 deflection, and lasted until "P300" began to decrement. The other was positive, resembled "positive slow wave," onset as P300 began to decrement, and lasted until the end of the recording epoch. There were no consistent effects of item lag on the behavioral data or on any of the ERP components, suggesting that for pictorial stimuli, the distinction between the two types of memory store, primary (i.e., immediate memory) and secondary (newly learned information), may not be relevant. In consonance with the lack of lag effects, it was suggested that the lack of a robust subsequent memory effect on the ERP waveform could have been due to the use of pictures, which may have required less elaborative processing in order to be encoded at input.

Adult↗
PubMed1989

[Cerebral evoked potentials and conscious and unconscious recognition of faces: application to the study of prosopagnosia].

Twelve normal subjects and a prosopagnosic patient were tested in a classification task of a random display of well-known among unknown faces. Each face was presented several times. Event-related potentials (ERP) and reaction time (RT) were studied as a function of face repetition and familiarity. For normal subjects, the greater the repetition level, the more positive ERPs were on both hemispheres: between 250 and 600 msec. Moreover, the familiarity of faces modified ERPs between 350 and 600 msec. In contrast for the patient, the greater the repetition, the more negative the ERPs were. This "negative effect" was maximum on right parieto-temporal leads and was longer for unrecognized well-known than for unknown faces. These results support a differential processing of faces as a function of their memory representations for both normal subjects and patients. They further demonstrate the existence of covert face recognition processes in prosopagnosia.

Adult↗
PubMed1987

Hemispheric asymmetries for complex visual patterns.

Three tachistoscopic studies examined the laterality of spatial-form perception in normal adults using randomly generated eight-point and 12-point patterns (Vanderplas & Garvin, 1959) as the lateralized stimuli. In the first study of recognition accuracy, 36 subjects were tested in a partial replication of Fontenot. No laterality effects were found, and over-all recognition was better for the more complex 12-point patterns. In a second similar study with 20 subjects, the lateralized stimulus was followed by a central masking pattern. A left-hemisphere superiority for recognition and better over-all recognition for more complex patterns was obtained. These data do not support Fontenot's report of right-hemisphere superiority in complex visuospatial processing. Given these diverse findings, a reaction time study using mental rotation was conducted using the same patterns to determine whether latency would reflect accuracy of recognition. Twenty-six subjects judged whether a rotated lateralized test pattern was the same or different from a central target pattern. Measures of both latency and accuracy were separately assessed. No main effect of visual field was obtained on either measure. These studies suggest that the nature of hemispheric involvement in spatial form perception is far from resolved.

Adult↗
PubMed2005

Visual shape recognition with contour propagation.

A neural architecture is presented that encodes the visual space inside and outside of a shape. The contours of a shape are propagated across an excitable neuronal map and fed through a set of orientation columns, thus creating a pattern which can be viewed as a vector field. This vector field is then burned as synaptic, directional connections into a propagation map, which will serve as a "shape map". The shape map identifies its own, preferred input when it is translated, deformed, scaled and fragmented, and discriminates other shapes very distinctively. Encoding visual space is much more efficient for shape recognition than determining contour geometry only.

Form Perception↗
PubMed1992

Retinocalcarine function in Alzheimer's disease. A clinical and electrophysiological study.

Impaired visual function in Alzheimer's disease (AD) could result from either precortical or cortical lesions, or both. In a parallel psychophysical study of visual function in AD, we found that contrast sensitivity function, color vision, stereoacuity, and backward masking were impaired relative to the performance of age-matched control subjects, whereas performance on a critical flicker fusion test was normal. The intent of the present study was to determine whether abnormalities of the retinocalcarine pathway contribute to visual dysfunction. We performed neuro-ophthalmological examinations on 38 patients with AD; from this group, 25 received additional psychophysical testing and 13 underwent electrophysiological testing. Clinical neuro-ophthalmological examinations, full-field electroretinograms, focal electroretinograms, and pattern visual evoked potentials were normal in all patients tested. There was no evidence of retinocalcarine abnormality specific to AD. We conclude that the visual impairment experienced by some patients with AD primarily results from involvement of the visual association cortices rather than from precortical damage, at least before the end stage of the disease.

Aged↗
PubMed1995

Selectively distributed processing of visual object recognition in the temporal and frontal lobes of the human brain.

Evoked potentials to visually driven cognitive tasks were recorded through depth electrodes placed bilaterally within the amygdala, hippocampus, midtemporal and inferotemporal cortex, and lateral frontal cortex of 6 epileptic patients. Task-related differential response patterns were used to identify the recording sites engaged by specific aspects of visual encoding. In this group of 6 patients, the amygdala was most frequently engaged in encoding the familiarity of faces; midtemporal and inferotemporal cortex, in encoding perceptual identity and object categorization; and lateral frontal cortex, in holding visual object information in working memory. The two aspects of encoding that most frequently engaged the hippocampal region were related to working memory and object categorization. The processing of complex visual knowledge is thus anatomically distributed but regionally specialized. These experiments also showed that identical input and output parameters can engage different areas of the brain depending on the nature of the instructional set.

Adult↗
PubMed1990

The effects of levodopa and haloperidol on flash and pattern ERGs and VEPs in normal humans.

We investigated the effects of single doses of the dopamine agonist levodopa and the dopamine antagonist haloperidol on pattern and flash electroretinograms (ERGs) and visual evoked potentials (VEPs) in normal subjects. A placebo and two treatment regimens were administered in a randomized double-masked design. No significant intertreatment differences in the pattern ERGs and VEPs were noted. Although not statistically significant, a clearly discernible tendency was found for increased flash ERG b-wave amplitudes after levodopa administration compared with placebo. In comparison with placebo and levodopa, haloperidol was associated with significantly prolonged flash ERG b-wave implicit times, including each oscillatory potential, which also showed increased duration, particularly in the O1-O3 interpeak implicit time. The failure of pattern ERGs and VEPs to show changes after haloperidol may have been related to the timing of the recordings, which took place during the presumed phase of rising blood levels and before the flash ERG and VEP recordings. Our findings further demonstrated the reliability of the flash ERG in revealing changes in dopaminergic status in the visual system and suggest that steady-state (flicker) ERGs, cone ERGs, and oscillatory potentials have particular use in this regard.

Adult↗
PubMed1991

Visual evoked potentials in macular hole.

Pattern reversal visual evoked potentials (VEPs) with checks of 50' and 12' were recorded in 15 patients with idiopathic unilateral macular hole. VEPs from the affected eyes were reduced in amplitude compared with those from the fellow eyes, especially with checks of 12' (percentage of the amplitude in the affected eye to that in the fellow eye was 86% +/- 19% with checks of 50' and 61% +/- 35% with checks of 12'). The latencies showed no statistically significant difference between the affected and the fellow eyes, although a marked interocular delay was found in a few patients. The degree of amplitude reduction and interocular delay had no relation to the size of the macular hole or visual acuity. The effects of experimental scotomata of various sizes on the VEPs, which were evaluated in nine normal subjects, were also variable among the subjects. We conclude that although the macula predominantly participates in the pattern VEP, an estimation of the extent of macular pathology from the VEP changes may be difficult because the VEP changes induced by a macular hole have wide individual variation and have no relation to the size of the hole.

Adult↗
PubMed1990

Evoked responses in patients with macular holes.

Thirty-two eyes with idiopathic macular holes and one eye with a traumatic macular hole were assessed by pattern-reversal electroretinography, ganzfeld electroretinography and pattern-reversal visual evoked potentials. Results were inspected for qualitative abnormalities and then measured in comparison with fellow eyes and 41 control eyes of similar age. Qualitative abnormalities occurred in some eyes with macular holes, most commonly a reduction in pattern-reversal electroretinogram or pattern-reversal visual evoked potential amplitude; 15' check amplitudes were significantly lower in eyes with macular holes than in control eyes, but no significant difference in latency was found. Control pattern-reversal electroretinogram and pattern-reversal visual evoked potential amplitudes were noted to decline with age, and paired t-tests on an age-matched subgroup of eyes with macular holes and control eyes showed appreciable differences only in the pattern-reversal electroretinogram q-r (N95) amplitude.

Aged↗