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At least 991 records · Page 55Linked to original sources

PubMed1993

Postnatal ontogeny of GABAA and benzodiazepine receptors in individual layers of rat visual cortex and the effect of visual deprivation.

The postnatal development of GABAA and benzodiazepine receptors was studied in the rat visual cortex with [3H]muscimol and [3H]flunitrazepam, respectively. The studies were performed by quantitative receptor autoradiography in the different cortical layers from normally raised rats and from monocularly deprived animals. In all cortical layers of normal rats there was a sharp (approx 3-fold) increase in [3H]muscimol binding from days 1 to 10. Between postnatal days 10 and 20 there was a considerable decrease in GABAA receptors; thereafter this decline continued until adulthood but at a more moderate rate. In all cortical layers, [3H]flunitrazepam binding increased sharply, also from day 1 to 10; at this age the adult values were practically attained. Monocular deprivation, by unilateral eyelid suture at the age of 11 days onwards lead to an increase in [3H]muscimol binding in cortical layers IV-VI. This increase in GABAA receptors was detectable at the age of 25 days onwards. In contrast, monocular deprivation did not alter the density of benzodiazepine receptors in any of the cortical layers, and this lack of effects was regardless of the duration of visual deprivation. The present results suggest that the development of GABAA receptors in the deeper cortical layers, but not that of benzodiazepine receptors, is seemingly regulated by the visual experience at a critical period of brain maturation.

Animals↗

PubMed2006

Visual temporal window of integration as revealed by the visual mismatch negativity event-related potential to stimulus omissions.

We studied whether, similarly to the auditory modality, short-period temporal integration processes occur in vision. Event-related potentials (ERP) were recorded for occasional stimulus omissions from sequences of patterned visual stimuli. A posterior negative component emerged only when the constant stimulus onset asynchrony (SOA) was shorter than 150 ms. This upper limit is comparable with the duration of the temporal window of integration observed in the auditory modality (including experiments studying the effects of stimulus omissions). Parameters of the posterior negativity were highly similar irrespective of whether the stimuli were task-relevant or not (Experiment 1). Thus, we identified this potential as the visual mismatch negativity (vMMN) component, which reflects task-independent detection of violating regularities of the stimulation. vMMN was followed by an anterior positivity (the P3a), indicating attentional shifts induced by the stimulus omissions. In Experiment 2, a posterior negativity similar to that observed in Experiment 1 emerged after the termination of short trains of stimuli, again only when the SOA was shorter than 150 ms. These results support the notion of a temporal integration window in the visual modality, the duration of which is between 150 and 180 ms.

Adult↗

PubMed2004

Early uncorrected visual acuity as a measurement of the visual outcomes of contemporary cataract surgery.

PURPOSE: To determine the uncorrected visual acuity (UCVA) on the first postoperative day and the fifth week after routine slow-motion phacoemulsification with posterior chamber intraocular lens (IOL) implantation. SETTING: Cincinnati Eye Institute, Cincinnati, Ohio, USA. METHODS: This retrospective chart review performed by 3 research fellows analyzed the UCVA 1 day and 5 weeks postoperatively in 100 consecutive best-case scenario eyes of 99 patients who had routine slow-motion phacoemulsification with implantation of an AcrySof single-piece IOL (Alcon). Reasons for UCVAs worse than 20/40 were sought. The stability of the visual result was analyzed. RESULTS: The UCVA was 20/40 or better in 98% of eyes at 1 day. Ninety-seven percent had a UCVA of at least 20/40 by 5 weeks, confirming stability of acuity. The percentage of patients with a UCVA of 20/20 or 20/25 increased from 49% at 1 day to 77% at 5 weeks. CONCLUSIONS: The UCVA 1 day after slow-motion phacoemulsification was 20/40 or better in 98% of eyes and remained stable to the last measurement at 5 weeks. Early UCVA can serve as a more sensitive measurement than best corrected visual acuity for assessing new surgical technologies and techniques.

Acrylic Resins↗

PubMed2004

Convergent and divergent effects of neck proprioceptive and visual motion stimulation on visual space processing in neglect.

Visual motion stimulation as well as neck muscle vibration are known to effectively modulate the subjective body orientation in spatial neglect. However, so far only motion stimulation has been demonstrated to substantially influence size and space distortion in neglect patients. The present study aimed to compare the two stimulation methods with respect to their potentially differential impact on subjective body orientation and on space and size distortion, in five neglect patients showing perceptual distortions. We found comparable beneficial effects during left motion stimulation and left neck vibration for the subjective straight ahead. Additionally, left motion stimulation significantly ameliorated the leftward overextension in size matching, line bisection and distance estimation in all five patients. In contrast, during neck vibration only two patients showed an improvement for line bisection and size estimation and none did so for distance estimation. Since these two patients differed from the others as they had either no visual field defects or a major visual field sparing, we suggest--based on recent anatomical and neuropsychological findings--that neck vibration only tends to improve pure neglect-related visuo-perceptual distortions whereas motion stimulation can additionally improve perceptual distortions in neglect associated with hemianopia.

Adult↗

PubMed2000

Influence of visual experience deprivation on the postnatal development of the microvascular bed in layer IV of the rat visual cortex.

Cerebral vascular density is correlated with metabolic demands, which increase in highly active brain areas. External inputs are an essential requirement in the modeling of the visual cortex. Experience-mediated development is very active during the first postnatal month, when congruous blood supply is needed. We studied the development of visual cortex vascularization in relation to experience, comparing rats raised in darkness with rats reared in normal conditions. Vascular density, vascular area and their ratio vs. neuronal density were calculated. Conventionally stained semi-thin sections were used to measure the vascular area by computer assisted morphometry. Animals from both groups were sampled at 14, 21, and 60 days postnatal (dpn). We found a significantly lower density of vessels and neurons as well as a smaller vascular area in dark-reared adult rats while no differences were founded at the other ages. Our results also show no differences between the ratio of vessels/neuron, and vascular area/neuron, between both groups. The absence of visual experience causes decrease of cortical activity which correlates with lower vessels density and vascular area, without their ratio/neuron being affected.

Age Factors↗

PubMed1997

Visual object priming differs from visual word priming: an ERP study.

Implicit memory is inferred from repetition priming effects in tasks such as word identification, word fragment completion, and perceptual recognition with masking or brief exposures. In this experiment, we explored whether the visual word and object repetition priming effects can be reflected by features of ERP and whether visual word repetition priming differs from visual object repetition priming. We have observed that (1) pre-exposure to recognizable stimuli (both word and object picture) shortened the response time in identifying their repetitions; (2) repetition of unrecognized scrambles of words or object pictures did not show any effects on ERP patterns; (3) ERPs distinguished recognizable from unrecognizable stimuli; and, (4) repetitions of both words and pictures strongly influenced the patterns of ERPs, though the ERPs to word stimuli differed from the ERPs to picture stimuli.

Adult↗

PubMed1978

Normalization of visual fields following bromocriptine treatment in hyperprolactinemic patients with visual field constriction.

Two patients with galactorrhea-amenorrhea and bilateral visual field defects were studied. Routine radiologic examination of each patient revealed a normal sella turcica and no demineralization of the posterior clinoid process. Serum prolactin levels were elevated (patient V. G., 80 ng/ml; patient S. R., 204 ng/ml). Within 2 months of bromocriptine therapy, the serum prolactin levels were normal (patient V. G., 12.21 ng/ml; patient S. R., 8.25 ng/ml) and the bilateral visual field defects were corrected. Bromocriptine has been shown to control prolactin secretion in patients with prolactin-secreting pituitary tumors. Normalization of restricted visual fields following bromocriptine therapy indicates the possibility of an anatomical regression of pituitary hyperplasia or an underlying prolactin-producing microadenoma. It is speculated that the modality of functional galactorrhea reflects hyperplasia of the lactotrophs preceding a nodular and ultimately an adenomatous change. The continuous and prolonged administration of bromocriptine may prevent such a progressive sequence. Further experience is required to validate this possibility.

Adult↗

PubMed1998

Auditory and visual event-related potentials and flash visual evoked potentials in Alzheimer's disease: correlations with Mini-Mental State Examination and Raven's Coloured Progressive Matrices.

We investigated possible correlations among neurophysiological examinations [auditory and visual event-related potentials (A-ERPs, V-ERPs), and flash visual evoked potentials (F-VEPs)] and neuropsychological tests [Mini-Mental State Examination (MMSE) and Raven's Coloured Progressive Matrices (RCPM)] in 15 subjects with probable or possible Alzheimer's disease (AD) according to the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria. The P300 latency of A-ERPs was correlated with the scores of MMSE but not with those of RCPM. The P300 latency of V-ERPs was more significantly correlated with the scores of RCPM than with those of MMSE. The P2 latency of F-VEPs was more significantly correlated with the scores of RCPM than with those of MMSE. The P2 latency of F-VEPs was not correlated with the P300 latency of A-ERPs but was correlated with the P300 latency of V-ERPs. The close relationship among V-ERPs, F-VEPs and RCPM suggests that these examinations at least partly reflect the functions of visual association areas in AD. Furthermore, discrepancy between P300 latency by A-ERPs and V-ERPs suggests that the mechanism responsible for P300 generation is not identical between these two stimulus modalities.

Aged↗

PubMed2002

Hemispheric dissociation of visual-pattern processing and visual rotation.

We aimed at investigating whether on-line and delayed visual pattern processing activated different areas in human prefrontal and parietal cortex. For this purpose we measured the regional cerebral blood flow (rCBF) during simultaneous and successive visual matrix processing in 10 right-handed subjects. Delayed matching to sample activated predominantly left hemispheric ventrolateral prefrontal cortex, Broca's area and parts of the parietal cortex. In contrast, visuospatial matrix rotation showed activation of the right dorsolateral prefrontal cortex and parietal lobe. The present results suggest a hemispheric dissociation of fronto-parietal circuits with a left dominance for visual pattern processing like storage and a right dominance for visuospatial processing.

Adult↗

PubMed1999

Visual attention: spotlight on the primary visual cortex.

Visual search tasks appear to involve spatially selective attention to the target, but evidence for attentional modulation in the visual area with the most precise retinotopic organization V1 has been elusive. Recent imaging studies show that spatial attention can indeed enhance visual responses in human V1.

Animals↗

PubMedDate not supplied

AMPA glutamate receptor subunit 2 in normal and visually deprived macaque visual cortex.

Glutamate and its various receptors are known to play an important role in excitatory synaptic transmission throughout the CNS, including the primary visual cortex. Among subunits of the AMPA receptors (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid), subunit 2 (GluR2) is of special significance because it controls their Ca2+ permeability. In the past, this subunit has been studied mostly in conjunction with other AMPA subunits. The present study sought to determine if GluR2 alone has a distinct laminar distribution in the normal macaque visual cortex, and if its pattern correlated with that of cytochrome oxidase (CO) under normal and monocularly deprived conditions. In the normal adult cortex, GluR2 immunoreactivity (ir) had a patchy distribution in layers II/III, in register with CO-rich puffs. GluR2-ir highlighted the upper border of layer II, the lower border of layer IV (previously termed IVC(beta dark)) and, most prominently, layer VI. Labeled neurons were primarily of the pyramidal type present in the upper border and lower half of layer VI, layers II/III, and scattered in layers V and upper IVB. Labeled nonpyramidal cells were large in layer IVB and small in IVC(beta dark). Notably, the bulk of CO-rich layers IVC and IVA had very low levels of GluR2-ir. At fetal day 13, however, GluR2 labeling showed a honeycomb-like pattern in layer IVA not found in the adult. A fragment of GluR2 cDNA was generated from a human cDNA library, and in situ hybridization revealed an expression pattern similar to that of GluR2 proteins. After 1-4 weeks of monocular impulse blockade with tetrodotoxin (TTX), alternating rows of strong and weak GluR2-ir in layers VI and II/III appeared in register with CO-labeled dark and light ocular dominance columns in layer IVC and puffs in II/III, respectively. Our results indicate that various cortical layers are differentially influenced by glutamate. The bulk of the major geniculate-recipient layers IVC and IVA have low levels of GluR2, presumably favoring synaptic transmission via Ca(2+)-permeable glutamate receptors. GluR2 plays a more important role in supragranular and infragranular layers, where the initial geniculate signals are further modified and are transmitted to other cortical and subcortical centers. The maintenance of GluR2 in these output layers is governed by visual input and neuronal activity, as monocular impulse blockade induced a down-regulation of this subunit in deprived ocular dominance columns.

Amino Acid Sequence↗

PubMed2002

A longitudinal study of visual acuity and visual rehabilitation needs in an urban Swedish population followed from the ages of 70 to 97 years of age.

PURPOSE: To investigate the longitudinal change in visual acuity (VA) in the oldest members of the elderly population, to estimate future numbers of people with visual impairments, and to estimate needs for and the effects of visual rehabilitation. METHODS: In the Gerontological and Geriatric Population Studies in Gothenburg, Sweden (H 70), subjects underwent repeated eye examinations at the ages of 70, 82, 88, 95 and 97 years. Logistic regression analysis was used to estimate the probability of independent living as a function of distance VA at different ages. RESULTS: Rates of normal VA (>or= 0.8) declined from 86% of the study group at age 70 to 7% of the study group at age 95 (0% at age 97). The incidence of VA <or= 0.1 increased from 1.4% at age 70 to 27% (all women) at age 97. The deterioration was faster at higher ages. No statistically significant difference in best-corrected distance VA between genders was found. A substantial improvement was achieved by correcting refractive errors. There was a statistically significant correlation between distance VA and the probability of independent living at all ages except age 97. At ages 95 and 97, about 50% of the study group were able to read newspaper print with best-corrected glasses. CONCLUSIONS: The number of old people with impaired vision will increase. People aged 80 years and older should have regular eye-screening in order to preserve vision and present conditions of living. Cataract surgery and low vision rehabilitation should be offered when the subject can still benefit from it, preferably during their 80s at the latest.

Activities of Daily Living↗

PubMed1984

Abrupt visual onsets and selective attention: evidence from visual search.

The effect of temporal discontinuity on visual search was assessed by presenting a display in which one item had an abrupt onset, while other items were introduced by gradually removing line segments that camouflaged them. We hypothesized that an abrupt onset in a visual display would capture visual attention, giving this item a processing advantage over items lacking an abrupt leading edge. This prediction was confirmed in Experiment 1. We designed a second experiment to ensure that this finding was due to attentional factors rather than to sensory or perceptual ones. Experiment 3 replicated Experiment 1 and demonstrated that the procedure used to avoid abrupt onset--camouflage removal--did not require a gradual waveform. Implications of these findings for theories of attention are discussed.

Adult↗

PubMed1991

Parallel versus serial processing in visual search: further evidence from subadditive effects of visual quality.

The authors propose a diagnostic for distinguishing between serial and parallel processing in visual search; it is based on testing for subadditive effects of a within-trial visual quality manipulation on target-absent trials. It was evaluated in 2 experiments wherein parallel and serial processing might be expected on the basis of previous work and was then applied to a more uncertain situation in a third experiment. The diagnostic indicates parallel processing of stimuli that differ from each other on a featural basis (Xs and Os) and canonical letters that differ in line arrangement (Ts and Ls) but serial processing when Ts and Ls are randomly rotated. These results form a coherent pattern that is understandable in terms of the literature on visual search, and thus they suggest that the diagnostic may be a useful addition to the methodology used to distinguish between serial and parallel processes.

Adult↗

PubMed2005

Resolving visual interference during covert spatial orienting: online attentional control through static records of prior visual experience.

Models of attentional control usually describe online shifts in control settings that accommodate changing task demands. The current studies suggest that online control over distractor exclusion--a core component of visual selection--can be accomplished without online shifts in top-down settings. Measurements of target discrimination accuracy suggested that the degree of distractor exclusion was guided by retinotopic maps of the prior probability of distractor interference at the attended locations. These probability maps can be retrieved via object-based cues, and they interact with shifts of attention to elicit increased levels of distractor exclusion when it is most needed. Thus, static probability maps can provide an internal template that guides the resolution of visual interference as spatial attention traverses the visual field.

Attention↗

PubMed1982

Auditory, visual, and auditory-visual perception of vowels by hearing-impaired children.

The vowels (foreign letters in text) were presented through auditory, visual, and combined auditory-visual modalities to hearing-impaired children having good, intermediate, and poor auditory work-recognition skills. When they received acoustic information only, children with good word-recognition skills confused neighboring vowels (i.e., those having similar formant frequencies). Children with intermediate work-recognition skills demonstrated this same difficulty and confused front and back vowels. Children with poor word-recognition skills identified vowels mainly on the basis of temporal and intensity cues. Through lipreading alone, all three groups distinguished spread from rounded vowels but could not reliably identify vowels within the categories. The first two groups exhibited only moderate difficulty in identifying vowels audiovisually. The third group, although showing a small amount of improvement over lipreading alone, still experienced difficulty in identifying vowels through combined auditory and visual modes.

Adolescent↗

PubMed2003

Exploratory eye movements during the Benton Visual Retention Test: characteristics of visual behavior in schizophrenia.

In order to investigate the relationship between the behavioral patterns and clinical symptomatology in schizophrenia, exploratory eye movements of schizophrenic subjects and healthy controls during the Benton Visual Retention Test were examined using an eye-mark recorder. The results were as follows: (i) with card 1, the number of eye fixations of schizophrenic subjects was fewer, and the total and mean eye scanning lengths of schizophrenic subjects were shorter than those of healthy controls; (ii) with card 3, almost none of the schizophrenic subjects looked at the blank area opposite the peripheral figure on the right; (iii) with cards 3, 5, 6 and 9 there were some schizophrenic subjects who did not look at the peripheral figures; (iv) with card 6, many of the schizophrenic subjects made stereotypical movements; (v) with card 9, schizophrenic subjects used a narrow vertical gaze to look at the large figure on the right. Based on these characteristics among the schizophrenic subjects themselves, factors such as longer eye scanning length, looking at peripheral figures without fail, and not making stereotypical movements were reflected directly in the results of the Benton test, while there was no relationship between the width of the vertical gaze and the Benton results. Correlations between visual behavior and some psychiatric symptoms were observed. The visual behavioral patterns of schizophrenic subjects were various according to the characteristics of the Benton figures, while those of normal subjects were always almost the same. It was suggested that these results were caused by disturbances of the mental attitude of schizophrenic subjects toward objects or environments.

Adult↗

PubMed2000

Visual contrast gain control in migraine: measures of visual cortical excitability and inhibition.

The present study examined the extent to which migraineurs demonstrate interictal visual cortical hyperexcitability as a result of poor inhibitory control in the visual system. We employed a well-established psychophysical measure of inhibition, visual contrast gain control. The task involved detecting a briefly presented target that was superimposed on a highly excitable high contrast masking pattern. The strength of inhibition was assessed by comparing target detection thresholds with and without the operation of gain controls. Migraineurs with and without aura (n=25, n=22, respectively) were compared with those with no history of migraine (n=25). Our results do not indicate a loss of inhibition in migraine; the strength of inhibitory feedback contrast gain controls was similar between migraineurs and controls. We did however, find a statistically greater masking effect in migraineurs compared with controls in the zero delay condition, suggesting cortical hyperexcitability in migraine. Possible mechanisms of cortical hyperexcitability are discussed in light of the results.

Adolescent↗