Event-related potentials during visual selective attention in children of alcoholics

Event-related potentials were recorded from 7- to 18-year-old children of alcoholics (COAs, n = 50) and age- and sex-matched control children (n = 50) while they performed a visual selective attention task. The task was to attend selectively to stimuli with a specified color (red or blue) in an attempt to detect the occurrence of target stimuli. COAs manifested a smaller P3b amplitude to attended-target stimuli over the parietal and occipital scalp than did the controls. A more specific analysis indicated that both the attentional relevance and the target properties of the eliciting stimulus determined the observed P3b amplitude differences between COAs and controls. In contrast, no significant group differences were observed in attention-related earlier occurring event-related potential components, referred to as frontal selection positivity, selection negativity, and N2b. These results represent neurophysiological evidence that COAs suffer from deficits at a late (semantic) level of visual selective information processing that are unlikely a consequence of deficits at earlier (sensory) levels of selective processing. The findings support the notion that a reduced visual P3b amplitude in COAs represents a high-level processing dysfunction indicating their increased vulnerability to alcoholism.     

Development of selective attention during visual search.

Monitored eye movements in 8 2nd graders, 8 6th graders, and 8 college students during a search task in which Ss were given different types of information about target location before trial onset. Whereas color cues facilitated search performance in the 2 older groups, form cues were less successful in facilitating search and significantly interfered with search relative to a control condition for the 2nd graders. Both facilitation and interference effects in overall search times were related to number of fixations rather than to average fixation during a trial. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acupuncture and cortical evoked potentials

Research works for the effects of acupuncture on cortical evoked potentials were reviewed since 1970 in this article. As a result of the acupuncture anesthesia being applied widely in clinical operation, most of the studies were focused on the evoked potential of somatosensory cortex for elucidating the principle of the analgesic effect of acupuncture, while less observations were reported on the aspects of auditory and visual cortex. The amplitude of the evoked potential was often used as an index in assessing the excitability of the cerebral cortex in the studies of the effect of acupuncture in the past. An increase in the amplitude of evoked potential means an excitory process of the cortex and a decrease means depression. Based on their work, the authors consider that whether the change in the amplitude of cortical evoked potential could be served as an optional index in reflecting the excitability of the cortex is still a problem in neurophysiology remained for further investigation.     

An evaluation of the differences in human evoked cortical potentials to visual stimuli

Saccharomyces cerevisiae nuclei possess a polyphosphatase activity which is insensitive to a number of inhibitors of ATPase and pyrophosphatase (PPase) activities of the same organelle. Heparin, an effective inhibitor of the nuclear polyphosphatase activity, does not alter either the ATPase and PPase activity. The nuclear polyphosphatase activity is optimal at pH 7.5. Bivalent metal cations stimulate this activity in the following order: Co2+ > Mg2+ > Zn2+ > Mn2+. However, the magnitude of the stimulating effect is much lower than that for the polyphosphatase activities from other organelles of the same yeast. The polyphosphatase activity is nearly the same for polyphosphates ranging from [symbol: see text] = 9 to [symbol: see text] = 208, but is 1.5 times higher for tripolyphosphate. The K(m) values for the hydrolysis of polyphosphates with chain lengths [symbol: see text] = 3, 15 and 208 are 100, 5 and 4.1 microM, respectively. The polyphosphatase activity differs in some properties from that of the cell envelope, cytosol and vacuoles of the same S. cerevisiae strain.     

Human cortical mechanisms of visual attention during orienting and search

Functional anatomical studies indicate that a set of neural signals in parietal and frontal cortex mediates the covert allocation of attention to visual locations across a wide variety of visual tasks. This frontoparietal network includes areas, such as the frontal eye field and supplementary eye field. This anatomical overlap suggests that shifts of attention to visual locations of objects recruit areas involved in oculomotor programming and execution. Finally, the fronto-parietal network may be the source of spatial attentional modulations in the ventral visual system during object recognition or discrimination.     

Human visual evoked potentials during the recognition of facial emotional expression

Visual evoked potentials (VEPs) were recorded in 22 right-handed healthy subjects in the occipital, parietal, central, frontal and posterotemporal cortical areas during recognition and passive viewing of positive, negative, and neutral emotional facial expression. Peak latencies of N90, P150, and N180 VEP components appeared to be significantly shorter in response to the negative emotional expression than during administration of other facial stimuli. The differences were observed both during active recognition and passive viewing. Correct recognition was characterized by involvement of both hemispheres and high level of interhemispheric correlation between the peak latencies of P150 in the posterotemporal and of N180 in the frontal areas. It is suggested that the facial expressions are primarily recognized at the subthreshold level with participation of the posterotemporal areas. The role of the frontal areas is discussed in the completion of this process and making the correct decision about the image.     

Feature-specific effects of selective visual attention

Four experiments were conducted to quantify the effect of performing a foveal discrimination task on sensitivity for a peripheral grating. The observer's primary task was to discriminate either the spatial frequency or orientation of successive foveal Gabor patches. On a third of the trials they also performed a secondary task to detect the presence of a near-threshold grating in the periphery. We find that sensitivity for detection of the peripheral grating depends on the similarity of the spatial frequencies and orientations between the foveal and peripheral stimuli. Importantly, sensitivity is also affected by which feature is being discriminated in the central task. Because the detectability of the peripheral grating is different when different features of the central stimuli are discriminated, we suggest that the effects on sensitivity are due to feature-specific attention and not simply to passive interactions between filters with similar tuning properties.     

The cortical representation of somatosensory evoked potentials of the phrenic nerve

Parasitic third-stage larvae of the sheep abomasal nematode Haemonchus contortus develop and molt in vitro to the fourth stage (L4) in 48-72 hr, at which time they begin feeding. Coincident with the third molt, larvae begin to secrete significant amounts of protein into culture fluids, including a zinc metalloproteinase. This culture-derived zinc metalloproteinase differs from a previously described metalloproteinase from infective third-stage larvae (L3[2M]), which mediates the ecdysis process. These differences include time of expression, molecular mass, and substrate specificity. The purified proteinase, from cultures of L4, has a molecular weight of approximately 46 kDa, functions as an endopeptidase, and digests several native proteins of host origin including fibrinogen and fibronectin.     

Perceptual grouping and visual selective attention

The present study demonstrates that incongruent distractor letters at a constant distance from a target letter produce more response competition and negative priming when they share a target's color than when they have a different color. Moreover, perceptual grouping by means of color, attenuated the effects of spatial proximity. For example, when all items were presented in the same color, near distractors produced more response competition and negative priming than far distractors (Experiment 3A). However, when near distractors were presented in a different color and far distractors were presented in the same color as the target, the response competition x distractor proximity interaction was eliminated and the proximity x negative priming interaction was reversed (Experiment 3B). A final experiment demonstrated that distractors appearing on the same object as a selected target produced comparable amounts of response competition and negative priming whether they were near or far from the target. This suggests that the inhibitory mechanisms of visual attention can be directed to perceptual groups/objects in the environment and not only to unsegmented regions of visual space.     

P300 potentials evoked by visual stimulation

INTRODUCTION: The P300 potential is a long-latency endogenous component of the event-related potentials to low-probability target stimuli. The same stimulus delivered without cognitive process does not provoke endogenous components; moreover event-related potentials are not dependent of the sensory pathways used for stimulating the subjects. P300 potential is a biological parameter used in scientific investigations in Clinical Neurophysiology, Neurology, Psychophysiology and Psychiatry. The most frequent methodology for obtaining P300 event-related potential is based on the 'odd-ball' paradigm using auditory stimulation. In this revision we analyzed the difficulties of this methodology and we propose to use the visual stimulation in order to obtain well defined P300 potential, based on a better signal to noise ratio and minor overlapping of exogenous and endogenous components of the evoked potentials. The improvement in the quality of the results obtained when comparing with auditory stimulation, it is supposed to facilitate that the use of P300 potential overflows the field of the investigation and permits their extensive use in the clinical practice.     

Shifts of visual spatial attention modulate a steady-state visual evoked potential

An uncertain relation between health and angry/hostile behaviour exists in the literature on adolescents. With data from a pilot study, one possible reason for this is explored: health measures such as blood pressure as well as angry/hostile behaviours may change with, or depend upon physical maturity, body size and body fatness. The sample consists of 60 African-, Hispanic-, and Anglo-American adolescents (15 to 16 years of age) drawn from a public school in Houston, TX. Using resting diastolic blood pressure as a model, in a sex stratified analysis, the following conclusions were reached: Physical maturity in girls and body height in boys were related to ethnicity in the sample and were confounders of the blood pressure and anger relationship. In girls secretive anger ('anger-in') and hostility were associated with increased body fat; expressive anger ('anger-out') in boys is associated with increased conicity (central body fat distribution) (p < 0.01). These associations were independent of height and physical maturity. Hostility was not significantly related to diastolic blood pressure in boys after adjusting for height and conicity. 'Anger-in' was significantly and positively related to diastolic blood pressure in girls (p < 0.01). This relationship was strongly mediated by per cent body fat, because the association of 'anger-in' and blood pressure was no longer statistically significant when the model included body fat. The results suggest that measures of physical maturity and more refined measures of body fat and body fat distribution should be considered in studies attempting to link adolescent blood pressure with anger expression.     

Age-related changes in selective attention and perceptual load during visual search.

Three visual search experiments were conducted to test the hypothesis that age differences in selective attention vary as a function of perceptual load (E. A. Maylor & N. Lavie, 1998). Under resource-limited conditions (Experiments 1 and 2), the distraction from irrelevant display items generally decreased as display size (perceptual load) increased. This perceptual load effect was similar for younger and older adults, contrary to the findings of Maylor and Lavie. Distraction at low perceptual loads appeared to reflect both general and specific inhibitory mechanisms. Under more data-limited conditions (Experiment 3), an age-related decline in selective attention was evident, but the age difference was not attributable to capacity limitations as predicted by the perceptual load theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Probability matching in visual selective attention.

J. Jonides (see record 1981-22746-001) suggested a model to account for shifts of spatial attention in visual search tasks with less than 100% cue validity. This 2-stage probability matching model was subsequently tested by Jonides (see record 1984-08558-001). Reaction time (RT) distribution characteristics provided some support for the model. The present author reanalyzes Jonides's data (including that published in 1981). Analysis showed strong support for the probability matching hypothesis. It is concluded that probability matching is an important strategic characteristic of visual spatial attention. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory evoked potentials during multichannel selective listening: role of pitch and localization cues

Auditory evoked potentials were recorded from subjects who listened selectively to tone pips arriving over one of three input channels. Their task was to detect occasional target tones of a slightly longer duration. In different runs the three channels were distinguished from one another by (a) pitch cues alone (800, 1,800, and 2,800 Hz), (b) localization cues alone (right ear, midline, ane left ear), and (c) both of these cues conjointly. In all three conditions the direction of attention was reflected in the amplitude of the N1 wave of the evoked potential, which was selectively enhanced to tones in the attended channel; tones in the central channels in the single-cue conditions, however, produced the least N1 lability and were the least discriminable. The N1 wave was interpreted as a sign of an initial stimulus set or filtering mode of selective attention, whereas a subsequent P3 wave was specifically associated with detections of the target stimuli.     

Pattern-reversal visual evoked potentials in migraineurs with or without visual aura

To determine the possible electrophysiologic changes in migraineurs with or without visual aura, we investigated pattern-reversal visual evoked potentials in 39 patients. We compared the mean P100 latency and amplitude of 16 patients with aura, 23 patients without aura, and 17 age- and sex-matched normal subjects. There were no significant differences between groups. There was no correlation between age and the parameters in any group. However, in 7 of 23 patients without aura, the P100 latency was longer than the mean control value +2 SD. The mean disease duration in this subgroup was significantly longer than the means of the remaining 16 patients without aura or the patients with aura (P < 0.05 for each). This suggests the possibility that P100 latency prolongation is a consequence, but not an entity caused by the pathogenetic mechanism of the disease from the beginning.     

High frequency oscillations in early cortical somatosensory evoked potentials

OBJECTIVE: To evaluate the characteristics of high frequency (HF) components of the early cortical somatosensory evoked potentials (SEPs). METHODS: We recorded 8-channel SEPs from the frontal and left centro-parietal scalp after right median nerve stimulation with a wide band-pass (0.5-2000 Hz) and digitized at 40 kHz sampling rate in 12 healthy subjects. HF components were analyzed after digital band-pass filtering (300-1000 Hz). The power spectrum was obtained by a maximum entropy method. RESULTS: HF oscillations (maximum power at 600-800 Hz) consisting of 5 to 8 peaks were discriminated from the preceding P14 far-field in all cases and their phases were reversed between the frontal and contralateral parietal regions. In addition, in subjects with a high amplitude central P22 potential in original wide-band recordings, a single HF oscillation with a maximum at the central region was present. Furthermore, this component showed no phase reversal over the centro-parietal area. CONCLUSION: We therefore conclude that HF oscillations are superimposed not only on the tangential N20-P20 but on the radial P22 potential, and are generated from both tangential (area 3b) and radial (area 1) current sources.     

Processing of auditory stimuli during auditory and visual attention as revealed by event-related potentials

Auditory event-related brain potentials (ERPs) were recorded during auditory and visual selective attention tasks. Auditory stimuli consisted of frequent standard tones (1000 Hz) and infrequent deviant tones (1050 Hz and 1300 Hz) delivered randomly to the left and right ears. Visual stimuli were vertical line gratings randomly presented on a video monitor at mean intervals of 6 s. During auditory attention, the subject attended to the stimuli in a designated ear and responded to the 1300-Hz deviants occurring among the attended tones. During visual attention, the subject responded to the occasional visual stimuli. ERPs for tones delivered to the attended ear were negatively displaced relative to ERPs elicited by tones delivered to the unattended ear and to ERPs elicited by auditory stimuli during visual attention. This attention effect consisted of negative difference waves with early and late components. Mismatch negativities (MMNs) were elicited by 1300-Hz and 1050-Hz deviants irrespective of whether they occurred among attended or unattended tones. MMN amplitudes were unaffected by attention, supporting the proposal that the MMN is generated by an automatic cerebral discrimination process.     

Macular pigment and the colour-specificity of visual evoked potentials

A modified Moreland anomaloscope was used to examine two subjects, one with dense macular pigment, the other with relatively light pigmentation. Chromatic visual evoked potentials (VEPs) were elicited from these two subjects using coarse, isoluminant gratings of different sizes. Colour-specificity was verified by comparing chromatic onset VEPs (reflecting sustained activity) with chromatic reversal VEPs (reflecting mainly transient activity) and also by Fourier analysis (colour-specific responses are dominated by the fundamental, transient activity by the second harmonic). Achromatic (transient-type) intrusions, produced by large blue-green gratings could be related to the extent of subject-specific macular pigmentation.     

Topographic distribution of visual evoked potentials in optic neuropathy

INTRODUCTION: Digital treatment of electrical signals coming from the central nervous system on stimulation of the optic nerve path offers an objective method for evaluation of visual evoked potentials (VEP) shown graphically on a cerebral map. OBJECTIVE: To evaluate the topographical distribution of VEP in cases of optic neuropathy adding this parameter to the usual parameters of latency and amplitude. MATERIAL AND METHODS: We studied 35 patients with suspected optic neuropathy and normal findings on basic ophthalmological examination, in whom VEP and VEP mapping (VEPM) was done. RESULTS: In 26% of the cases there was no response for evaluation with the usual VEP recording techniques, whilst in those with VEPM this percentage was reduced to 11.5%. In the other cases there was a potential with characteristic distribution in the occipital areas and a maximally positive dipole posteriorly. CONCLUSION: VEPM is an objective method for evaluation of the visual pathway offering better discrimination than the usual VEP in more severe cases of neuropathy.