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At least 451 records · Page 25Linked to original sources
PubMed1997

Frequency variation of a pattern-flash visual stimulus during PET differentially activates brain from striate through frontal cortex.

We evaluate regional cerebral blood flow (rCBF) in 19 healthy elderly subjects, mean age 64 +/- 11 (SD, years), during a passive visual stimulus in which pattern-flash frequency was parametrically manipulated. Using goggles with a grid of red lights imbedded into each lens, we performed five positron emission tomography (PET) H2(15)O water scans on each subject at alternating (left to right eye) flash frequencies of 0, 1, 4, 7, and 14 Hz. We found a biphasic rising and falling rCBF response in the striate cortex (7 Hz peak) and left anterior cingulate (4 Hz peak), 1 Hz activation in left middle temporal gyrus (V5), monotonically increasing rCBF in posterior areas (lateral and inferior visual association areas, Brodmann 18 and 19), and monotonically decreasing rCBF in anterior areas (frontal, cingulate, and superior temporal) predominantly in right hemisphere. We suggest the striate rCBF changes at all frequencies primarily reflect lateral geniculate input, the middle temporal activation at 1 Hz reflects perception of apparent motion, and the posterior extrastriate rCBF monotonic increase represents a neural response to increasing luminance intensity and form and color complexity that occur as pattern-flash frequency increases. The anterior monotonic rCBF decrease may represent active cross-modal functional suppression of brain areas irrelevant for processing the passive visual stimulus. Pattern-flash rCBF responses were highly reproducible (no series effect), more so in posterior than in anterior brain regions. The reproducibility and systematically changing rCBF responses to this passive stimulus suggest that it could be successfully used as a disease probe to evaluate neural function and drug effects in cognitively impaired patients.

Aged↗
PubMed1989

Double-flash electroretinography in human eyes.

A tri-color Ganzfeld stimulator with light-emitting diodes as light sources is used to study the suppression of the second electroretinographic response in human eyes to double-flash stimulation. The mechanism suppressing the a- and b-waves of the response to the second (test) flash has a scotopic spectral sensitivity to the first (conditioning) flash. Responses to mild test stimuli are more sensitive to suppression by a conditioning flash than responses to strong test stimuli.

Color Perception↗
PubMed1984

Monitoring demyelination in multiple sclerosis with multi-flash campimetry.

Multi-flash campimetry is a computer-implemented psychophysical technique that allows a rapid and extensive assessment of visual flicker sensitivity. Multi-flash field maps generated from the data typically reveal the presence of 'islands' of degraded temporal resolution in multiple sclerosis (MS) patients, but not in normal control observers. These distinct 'islands' presumably reflect the influence of demyelination as well as a variety of other possible transient factors, such as edema and inflammation of the optic nerve. The question addressed in the present study concerned a means of distinguishing among such influences. The strategy employed was to test MS patients more than once over a period of several months. Under the assumption that there is little or no significant remyelination in the central nervous system, it was argued that 'islands' that remain present over time should be those that principally reflect demyelination. Transient changes that appear in the fields of MS patients probably reflect the influence of other mediating factors. Examples of multi-flash field maps are presented to illustrate this point and to serve as an initial assessment of the reliability of the technique. It is concluded that multi-flash campimetry may prove to be an effective aid in documenting the degree of progressive visual involvement in MS, and provide a means of monitoring the clinical course of demyelination in the visual system.

Adult↗
PubMed1996

The triple flash electroretinogram and its significance in macular diseases. B-wave recovery as a diagnostic tool.

PURPOSE: The purpose of this study was to evaluate recovery data for the b-wave of the electroretinogram (ERG) elicited using multiple flash stimulation with increasing stimulus intervals in normal controls and in patients with macular diseases. The results will describe effects of age and macular disease and define indexes characterizing the recovery process. METHODS: Scotopic Ganzfeld flash ERGs were elicited using interstimulus intervals of 140, 280, and 560 ms. Relative b-waves were calculated as the ratio b140 ms/b560 ms and b280 ms/b560 ms, respectively. Responses obtained in 134 eyes of 134 normal controls served as reference data. Fifty-four patients with different macular diseases were also examined and their data compared to the reference data. RESULTS: Relative b-wave amplitudes correlated with interstimulus interval and with flash luminance, but not with age. All patients had a normal ERG when recorded following the standard of clinical electroretinography. A sigmoidal model was suggested, providing three indexes characterizing the b-wave recovery process. Relative b-waves and recovery indexes varied in age-related macular degeneration, central serous retinopathy, vitelliform macular degeneration, Stargardt's disease, and pattern dystrophy. CONCLUSION: The triple flash ERG reflects energy-yielding and -utilizing mechanisms. It proved to be more sensitive in detecting functional lesions in macular diseases than the standardized explorating procedure. The b-wave recovery model allows differentiation between two independent mechanisms contributing to the b-wave recovery process. One or more of the three characterizing indexes are affected in different macular diseases.

Adolescent↗
PubMedDate not supplied

Usefulness of turbo-FLASH dynamic MR imaging of dissecting aneurysms of the thoracic aorta.

PURPOSE: We attempted to determine whether Turbo-FLASH dynamic magnetic resonance imaging is clinically useful for the diagnosis of dissecting aneurysm of the thoracic aorta by differentiating slow flow from thrombus in the false lumen. METHODS: Magnetic resonance imaging (MRI) was performed in ten patients using three different pulse sequences (spin echo, cine and turbo-FLASH dynamic MRI). The three imaging techniques were compared for their ability to demonstrate anatomical and hemodynamic abnormalities by visual assessment. RESULTS: In all patients with thrombus in the false lumen, the thrombus was accurately differentiated from slow flow on contrast enhanced turbo-FLASH dynamic MRI, but only with difficulty on spin echo and cine MRI. Dynamic MRI was also useful for the evaluation of flow dynamics in the false lumen. CONCLUSION: Turbo-FLASH dynamic MRI is recommended for patients with dissecting aneurysm of the thoracic aorta, not definitely diagnosed by spin echo and cine MRI.

Aged↗
PubMed1988

ATP formation onset lag and post-illumination phosphorylation initiated with single-turnover flashes. II. Two modes of post-illumination phosphorylation driven by either delocalized or localized proton gradient coupling.

Two modes of chloroplast membrane post-illumination phosphorylation were detected, using the luciferin-luciferase ATP assay, one of which was not influenced by added permeable buffer (pyridine). That finding provides a powerful new tool for studying proton-membrane interactions during energy coupling. When ADP and Pi were added to the thylakoid suspension after a train of flashes [similar to the traditional post-illumination phosphorylation protocol (termed PIP- here)], the post-illumination ATP yield was influenced by pyridine as expected, in a manner consistent with the ATP formation, in part, being driven by protons present in the bulk inner aqueous phase, i.e., through a delocalized protonmotive force. However, when ADP and Pi were present during the flash train (referred to as PIP+), and ATP formation occurred during the flash train, the post-illumination ATP yield was unaffected by the presence of pyridine, consistent with the hypothesis that localized proton gradients were driving ATP formation. To test this hypothesis further, the pH and flash number dependence of the PIP- and PIP+ ATP yields were measured, the results being consistent with the above hypothesis of dual compartment origins of protons driving post-illumination ATP formation. Measuring proton accumulation during the attainment of the threshold energization level when no delta psi component was allowed to form (+ valinomycin, K+), and testing for pyridine effects on the proton uptake, reveals that the onset of ATP formation requires the accumulation of about 60 nmol H+ (mg Chl)-1. Between that level and about 110-150 nmol H+ (mg Chl)-1, the accumulation appears to be absorbed by localized-domain membrane buffering groups, the protons of which do not equilibrate readily with the inner aqueous (lumen) phase. Post-illumination phosphorylation driven by the dissipation of the domain protons was not affected by pyridine (present in the lumen), even though the effective pH in the domains must have been well into the buffering range of the pyridine. That finding provides additional insight into the localized domains, namely that protons can be absorbed by endogenous low pK buffering groups, and released at a low enough pH (less than or equal to 5.7 when the external pH was 8, less than or equal to 4.7 at pH 7 external) to drive significant ATP formation when no further proton production occurs due to the redox turnovers.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1987

Correlates of menopausal hot flashes.

The purpose of the present study was to examine the relationships of frequency, duration, and intensity of hot flashes with daily stress, ambient temperature, and caffeine, alcohol, and nicotine intake in menopausal women. Ten menopausal women suffering from hot flashes monitored these variables daily for 6 weeks. Intrasubject correlational analyses revealed significant relationships between hot-flash activity and stress for half of the sample; few women exhibited significant relationships between hot-flash activity and other variables. The results are discussed with respect to theoretical implications and treatment strategies.

Arousal↗
PubMed1994

Spatial distribution of local flash electroretinogram by multi-input stimulation.

A method was developed for recording the distribution of the local flash electroretinogram with multi-input stimulation. With the use of a long flash interval, such as 100 ms, the principle and the method are useful for clinicians who know the method for recording the conventional local flash electroretinogram with single-input stimulation. This method results in a long recording time, yet it presents real local flash electroretinogram waveforms at the output.

Electroretinography↗
PubMed2002

[Comparison of MR-sequence in the diagnosis of anal fistula--the clinical value of 3D flash].

To elevate the clinical value of 3D-FLASH in the diagnosis of anal fistula and compare it with convertioned MR sequence, MR sequences, consisting of spin echo T1WI, turbo invertion recovery magnitude (TIRM), fast low-angle shot image (FLASH), mon-enhancement and enhancement substraction and coronary reconstructing, was conducted in 15 cases suspected of anal fistula. Comparison was made among the three sequences in display rate of internal fistula, external fistula, the branch of fistule connulas. Our results showed that 1 patient had perianal abscess. 24 different anal fistulas were identified in 14 patients, and 10 of them was complicated with perianal abscess and 8 of them with complex multi-branch fistula. The display rate of 3D-FLASH sequence was much higher than those of T1WI and TIRM in all cases. It is concluded that 3D-FLASH sequence is an senstive and time-efficient technique for the diagnosis of anal fistula.

Abscess↗
PubMed2002

[Physical and technical elements of short-interval, color-filtered double strobe flash-stroboscopy].

INTRODUCTION: Quantitative measurement of vocal fold movements can be done either with high-speed imaging or with short interval, color-filtered double strobe flash-stroboscopy. The physical and technical elements of this new technique are described. METHODS: Two special strobe units (KAY Elemetrics RLS 9100) are used in a master-slave configuration. In this way an adjustable interval of 0.1-2.0 ms between flashes is introduced. The strobe flashes are color filtered and are separated by a brief interval. By this means a double exposure is created in each video frame.Real-time visualization of opening and closing velocities over the entire length of the vocal fold from anterior to posterior is possible. Quantification is possible off-line after image calibration. CONCLUSION: Short-interval, color-filtered double-strobe flash stroboscopy allows quantitative measurement of the velocity of vocal fold movements during vibration at different pitches and sound pressure levels (SPL). Images gained with this new technique provide information about a dynamic property (velocity) of the vocal fold within a single image.Therefore, its use could be helpful from the aspect of clinical documentation.

Artifacts↗
PubMed2004

Quickly tapping targets that are flashed during smooth pursuit reveals perceptual mislocalisations.

In various studies subjects have been shown to misperceive the positions of targets that are flashed during pursuit eye movements. They mislocalise them in the direction of pursuit. Nevertheless, Hansen (1979) found that subjects accurately hit targets that are flashed during pursuit with a quick hammer blow. We examined whether this is because there is a fundamental difference between the information that determines our perceptual judgements of a target's position and the information that is used to guide our hand to a similar target. Subjects were asked to quickly tap targets that were flashed during pursuit with their index finger. They systematically tapped ahead of the position of the flash, in accordance with the above-mentioned perceptual mislocalisations. Thus the lack of systematic errors in Hansen's study is not a general property of fast motor responses.

Fixation, Ocular↗
PubMed1999

Sigma-optokinetic nystagmus in squirrel monkeys elicited by stationary stripe patterns illuminated by regular and random-interval flash sequences.

Eye position and angular velocity were measured in squirrel monkeys (Saimiri sciureus) by means of the electromagnetic scleral search-coil technique. Horizontal sigma-optokinetic nystagmus (sigma-OKN) was elicited by a stationary, stroboscopically illuminated, periodic, vertical-stripe pattern lining a vertical cylinder. The relationship between the mean slow-phase eye angular velocity, Ve, of sigma-OKN and the product of pattern period, Ps, and flash frequency, f(s), was determined. When Ve approximated k x Ps x f(s) (deg x s(-1)) and k was an integer > or = 1, the sigma-paradigm was fulfilled. Sigma-OKN could be evoked in different "modes", whereby k approximated 1, 2,...n. The sigma-OKN properties of squirrel monkeys were similar to those measured for sigma-OKN in the "stare" mode in man, with the exception of a long-lasting optokinetic afternystagmus (sigma-OKAN) appearing in the monkey. A considerable amount of temporal variability in flash sequence intervals ("temporal noise"), causing retinal error signals that interfered with the sigma-paradigm, was accepted by the visuo-motor system without interruption of sigma-OKN. This observation was explained by the operation of a short memory device for perception of visual motion. The internal gain, g(i), which relates the retinal "error" displacement velocity, Vr, and Ve depended, in turn, on Vr according to a function resembling the known relationship between neuronal activity of NOT (nucleus of the optic tract) nerve cells and Vr. This observation may be taken as direct proof that sigma-OKN can be explained by a centrally preprogrammed relationship between the retinal velocity, Vr, and the OKN slow-phase eye velocity, Ve. It is stipulated that the sum of Vr and efference copy signals generated in cortical or subcortical gaze centers is the essential component controlling the perceived velocity of the sigma-movement, whereby a short-term integrator plays a role for squirrel monkey sigma-OKN. When the flash frequency, f(s), was modulated periodically according to a sinewave or "triangular" function at a rate below 0.5 cycles x s(-1), Ve was found to respond with a corresponding modulation, provided the modulation amplitude did not exceed 50% of the mean flash rate. When the latter occurred, nonlinear responses could be observed. A similar response was found when the speed of "real" optokinetic stimuli was varied sinusoidally. Under these experimental conditions, however, the amplitude of the Ve variation yielded up to 1.0 approximately linear responses.

Animals↗
PubMed2001

Dissociating sensory and cognitive contributions to visual persistence II. Photoreceptor integration of flash pairs as a function of interflash interval, intensity, integration site, and candidate code.

Perceived duration can be assessed behaviorally by adjusting the interval between two flashes so that an observer just perceives a certain relation between them. In such studies, the cognitive characteristics of the required relation necessarily interact with the sensory characteristics of the responses evoked by the two flashes. To dissociate the contributions of these two factors, we executed a physiological study which yielded more complete information on the role of each factor in two paradigms which have been used to characterize perceived duration behaviorally, namely the persistence-of-form design and the successive field design. The effect of sensory manipulations have yielded particularly problematic results in these two paradigms because opposite trends were found when intensity was varied. Intracellular recordings were therefore taken from photoreceptor cells exposed to procedural manipulations which match the sensory and cognitive variations employed in behavioral paradigms. The sensory variables of flash intensity, state of adaptation, and flash interval were explored with some completeness. Cognitive factors were assessed in two ways. First, the contribution of the neural site of sensory integration was determined by making a clear distinction between data collected when all stimuli affect the same receptors versus data collected when different stimuli affect different receptors. Second, the consequences of arbitrary choices of candidate code and dependent variable were also explored. When so organized, the physiological data provide a coherent basis for harmonizing apparently contradictory behavioral results because they qualitatively paralleled the behavioral data's complex dependence on intensity and interval. In particular, both direct and inverse dependencies of response duration on intensity exist in both physiology and behavior with the exact nature of the trend depending as much on the cognitive analysis of the neural responses as on their dynamics and energetics. Further, large quantitative differences were found which also were an expression of the different ways in which the two behavioral paradigms affect receptor potentials.

Adaptation, Ocular↗
PubMed2001

Dissociating sensory and cognitive contributions to visual persistence I. Photoreceptor response duration as a function of flash intensity, adaptation state, and candidate code.

Numerous careful behavioral studies of visual persistence have reported a variety of apparently contradictory effects. Variation of flash intensity has particularly been found to have both direct and inverse effects on subjective duration. This conflict has been addressed by theories which contain both sensory and cognitive components. Depending on the weight given to these components, one obtains theories which emphasize intensity dependence or task dependence. Few comparably detailed physiological studies of persistence exist. To clarify the issues raised by these theories, we examined the responses evoked in the model photoreceptor of the Limulus lateral eye. To explore the role of sensory variables, we manipulated adaptation state and flash intensity. To explore cognitive variables, the durations of the photoreceptor potentials (RPs) evoked in this model system were assessed by a mutually complementary and complete set of candidate sensory codes. Accordingly, sharp microelectrodes were used to record RPs intracellularly from single photoreceptor cells in response to 40-ms flashes whose intensity was varied over at least 3.6 log units. Two light adaptation states were used which differed in sensitivity by 3.5 log units. This model system made it possible to employ stringent objective assessments of data quality which ensured that only cells which had remained stable for several hours contributed to the present data. A variety of code-dependent trends were found: direct, inverse, invariant, and U-shaped trends related flash intensity to RP duration, while adaptation state interacted with some of these trends. Only some of the expectations which had generated this research were qualitatively corroborated and numerous quantitative discrepancies were found between data and theory. While caution is necessary when generalizing from neural responses to perception, these data indicate that two major gaps now exist in this field. First, both task and stimulus variables need to be exhaustively explored in more complete behavioral experiments. The present data make it more likely that sensory models and cognitive models simply address different aspects of the same phenomenon. Second, similarly detailed questions need to be posed to more central neural loci, particularly to those in the various visual cortices.

Adaptation, Ocular↗
PubMed2005

Photoinactivation of photosystem II by flashing light.

Inhibition of Photosystem II (PS II) activity by single turnover visible light flashes was studied in thylakoid membranes isolated form spinach. Flash illumination results in decreased oxygen evolving activity of PS II, which effect is most pronounced when the water-oxidizing complex is in the S2 and S3 states, and increases with increasing time delay between the subsequent flashes. By applying the fluorescent spin-trap DanePy, we detected the production of singlet oxygen, whose amount was increasing with increasing flash spacing. These findings were explained in the framework of a model, which assumes that recombination of the S2QB - and S3QB - states generate the triplet state of the reaction center chlorophyll and lead to the production of singlet oxygen.

Light↗
PubMed1985

Safety evaluation of flashing amber operation at signalized intersections.

The safety of a flashing amber signal for all directions at off-peak hours as a replacement for regular traffic signal operations was evaluated. The proposed control strategy was motivated by the need for energy conservation through reduced amounts of acceleration and of idling time of vehicles. The methodology of the study employed as a measure a broadened definition of "conflict" that freed observers from the need to detect only emergency evasive manoeuvres and decreased their subjective interpretations. Observations were carried out by trained observers at a sample of intersections, using two control strategies: full signal operation and flashing amber phase. Stationed at each leg of an intersection, the observers noted the travel direction of any two vehicles involved in a conflict. The results showed that the most frequent type of conflict under full signal operation was of the rear-end type; during the flashing amber operation, crossing and merging conflicts were dominant. It was concluded that up to a volume of 600 vehicles per hour, flashing operation does not increase the number of conflicts.

Accidents, Traffic↗
PubMed1990

Car driver behavior at flashing light railroad grade crossings.

The behavior of car drivers at two Dutch railroad grade crossings with automatic flashing warning lights was analyzed. Car drivers were videotaped while approaching either the red flashing lights or the white flashing "safe"-signal. Approach speeds, positions, and time intervals were semiautomatically measured from videos of more than 900 drivers: 660 while confronted with the red lights and 272 while passing the white light. Of the latter group, head movements during the approach to the crossing were also registered. Red light compliance was relatively good, as no driver was observed to cross later than 6 seconds after the onset of the red lights, despite train-arrival times of well over 60 seconds. The level of red light compliance was further quantified in terms of both the deceleration and time-to-stopping-line as accepted by drivers. From a comparison with earlier research on red light compliance at signalized road intersections it appeared that red light compliance was better at railroad crossings than at road crossings. It is concluded that faulty red light compliance is not a major cause for car-train accidents and that emphasis should be placed on the ability of the present device to attract attention and to signal unambiguously. The high degree of compliance also causes unexpected driver actions, such as emergency braking and hesitations. A yellow phase may reduce these problems. Some drivers tended to proceed immediately after a train had cleared the road instead of waiting for the end of the red signal (typically some 3 to 5 seconds after the train had passed). This tendency might reveal a major cause of dramatic errors when a second train is approaching. Immediate extinction of the red signal is suggested, or even better, a separate signal to announce the arrival of the second train. Behavior during the white signal phase also showed indications of uncertainty. In some 10% of cases drivers tended to decelerate more strongly than necessary and to make extra head movements. It is recommended that the present white flashing signal be reconsidered.

Accidents, Traffic↗
PubMed1987

Treatment of menopausal hot flashes with transdermal administration of clonidine.

A randomized prospective double-blind study was performed to evaluate the efficacy of a transdermal therapeutic system delivering clonidine in the treatment of menopausal hot flashes. Frequency, severity and duration of the flushing attacks before and during the 8-week treatment period were evaluated. The reduction in the number of hot flashes was highly significant in patients receiving the clonidine transdermal therapeutic system. On subjective comparison of flushing attacks before and during treatment, of the 15 patients who received the clonidine transdermal therapeutic system, 80% reported fewer hot flashes; 73% a decrease in severity; and 67% a decrease in duration. Among the 14 patients who were treated with placebo only, 36% reported fewer hot flashes; 29% a decrease in severity; and 21%, shorter duration (frequency, p less than 0.04; severity, p less than 0.04; and duration, p less than 0.03). Reported side effects were minimal, and no significant effect was observed on blood pressure or pulse rate. Transdermal clonidine therapy had no effect on the pulsatile luteinizing hormone secretion.

Administration, Cutaneous↗