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PubMed2005

Sound-induced flash illusion as an optimal percept.

Recently, it has been shown that visual perception can be radically altered by signals of other modalities. For example, when a single flash is accompanied by multiple auditory beeps, it is often perceived as multiple flashes. This effect is known as the sound-induced flash illusion. In order to investigate the principles underlying this illusion, we developed an ideal observer (derived using Bayes' rule), and compared human judgements with those of the ideal observer for this task. The human observer's performance was highly consistent with that of the ideal observer in all conditions ranging from no interaction, to partial integration, to complete integration, suggesting that the rule used by the nervous system to decide when and how to combine auditory and visual signals is statistically optimal. Our findings show that the sound-induced flash illusion is an epiphenomenon of this general, statistically optimal strategy.

Acoustic Stimulation↗
PubMed2005

The temperature of flash-cooling has dramatic effects on the diffraction quality of nucleosome crystals.

Nucleosome core-particle crystals are routinely flash-cooled in liquid propane at temperatures of approximately 153 K, followed by transfer into a cold nitrogen-gas stream (approximately 93 K). Analysis of diffraction data from crystals flash-cooled at different temperatures shows that the optimal temperature is approximately 153 K. The data quality worsens, with a concomitant reduction in the diffraction limit, at temperatures both higher and lower than 153 K. With some batches of crystals, significant shrinkage of the unit-cell volume is also observed at temperatures of 138 K and lower. The lattice shrinkage is always restricted to the c axis, concurrent with closer packing of two nucleosomes. Direct plunge-cooling of crystals in liquid nitrogen leads to loss of diffraction quality and resolution limit. Thus, in cases where flash-cooling into liquid nitrogen is detrimental to diffraction, optimizing cooling protocols at higher temperatures using liquid propane or other cryogens with similar properties may lead to dramatically improved results. In a related study, it is shown that a nucleosome crystal transported under 'cryocooled' conditions has higher mosaicity and yields inferior data quality in comparison to a crystal cryocooled at the synchrotron. For fragile crystals, transport in mother liquor and/or cryoprotectant followed by subsequent flash-cooling at the synchrotron may be the best procedure.

Crystallography↗
PubMed2004

Object updating and the flash-lag effect.

Flash lag is a misperception of spatial relations between a moving object and a briefly flashed stationary one. This study began with the observation that the illusion occurs when the moving object continues following the flash, but is eliminated if the object's motion path ends with the flash. The data show that disrupting the continuity of the moving object, via a transient change in size or color, also eliminates the illusion. We propose that this is because a large feature change leads to the formation of a second object representation. Direct evidence for this proposal is provided by the results for a corollary perceptual feature of the disruption in object continuity: the perception of two objects, rather than only one, on the motion path.

Analysis of Variance↗
PubMed1989

Laboratory and ambulatory monitoring of menopausal hot flashes.

A large increase in skin conductance activity recorded from the sternum was found during menopausal hot flashes and corresponded well with patient self-reports. The magnitude and time course of this skin conductance change was similar during spontaneous hot flashes recorded in the laboratory, during heat-induced hot flashes, and during those recorded by ambulatory monitoring techniques. This pattern of sternal skin conductance change did not occur in premenopausal women during body heating or ambulatory monitoring. These methods should be useful in research on the etiology and treatment of menopausal hot flashes.

Adult↗
PubMed1978

The double flash ERG during adaptation to the dark.

Electroretinogram (ERG) of albino rabbits and rheusus monkeys were recorded in a dark room applying the double flash stimuli after a sufficient adaptation to light. The stimulus intervals of the flashes were varied. The per cent amplitudes of the ERGs for the first flashes (B1) and those of the second flashes (B2) were plotted against time, as was (B1-B2)/B1 (=K). 1. B1 was independent of the stimulus interval in both species, and increased with lapse of time to reach a plateau. 2. B2 was quite dependent on the stimulus interval, and the ERG dark adaptation curves of the two species were quite different. 3. The time course of (B1-B2)/B1 was specific for the two species. In the rabbit, Ks were almonst equal for three stimulus intervals during states of adaptation to complete darkness, and in the monkey, Ks were different for the three intervals under all conditions.

Animals↗
PubMed1993

Measurement of visual readaptation time after flash exposure using optokinetic nystagmus.

It is concluded that measurement of visual readaptation time (RAT) using optokinetic nystagmus (OKN) is a repeatable measure of visual recovery after flash exposure. The semi-automatic method for measurement of RAT used here requires further development, but it is anticipated that the improved method will provide an efficient tool for increased understanding of the physiology of flash blindness. In this study on humans, it was found that if RAT is recorded twice on the same occasion, the second RAT is shorter. However, there was no systematic difference between RAT recordings on consecutive occasions. The newly developed semi-automatic method was found to provide RATs comparable to those obtained by manual measurement on a paper print out of EOG recordings. In RAT estimation, the variability between subjects shadows other sources of random variability. The least number of subjects needed in each group to detect a 20% alteration of RAT due to an experimental factor (alpha = 0.05, beta = 0.05) was estimated to 13 with independent groups design. For paired design < 10 are needed. OKN was elicited with a horizontally moving vertical grating. The eye movement was recorded by DC EOG. A sudden flash of green light temporarily abolished the OKN. The internal between the flash and the reappearance of OKN was measured as the RAT.

Adaptation, Ocular↗
PubMed1975

Rhodopsin flash photolysis in man.

1. Human rhodopsin in vivo was flash bleached by a 600 musec xenon flash which could deliver to the retina up to 15 rod-equivalent quanta per rhodopsin molecule, and the fraction bleached measured by fundus reflexion densitometry. 2. The curve relating fraction rhodopsin bleached to intensity of flash saturates at 0.5 to 0.6. Thus, 40-50% of the rhodopsin is left photo-regenerated by the brightest flashes. 3. Three types of densitometry experiments confirm the saturation of the bleaching curve. 4. The kinetic constants required to account for the observed photo-regeneration were somewhat discrepant with in vitro and in situ estimates from infrahuman species. Specifically, (i) the quantum efficiency of the back reaction, metarhodopsin I hv leads to rhodopsin, was inferred to be nearly as high as that of the forward reaction; and (ii) the rate of the metarhodopsin I leads to metarhodopsin II dark reaction was inferred to be less than 500 sec(-1).

Densitometry↗
PubMed1993

Saccade-vestibulo-ocular reflex co-operation and eye-head uncoupling during orientation to flashed target.

1. Eye-head co-ordination in the horizontal plane was studied in four human subjects using two successive flashes in the same direction, either increasing in eccentricity (IE), or decreasing in eccentricity (DE). 2. Results showed that for both conditions, head movements preceded eye movements and were typically longer or followed by a slow gaze movement. This slow movement was due to a vestibulo-ocular reflex gain of less than one. Gaze accuracy was achieved by small head movement adjustments. 3. Gaze movement to an IE stimulus had a staircase pattern, and to a DE stimulus, a pulse-step pattern or one gaze saccade to the final flash eccentricity. 4. In some cases, however, in response to a DE stimulus, the eye and head movements were directed to different displacements (dissociation); i.e. the head movement started towards the first flash eccentricity with a concomitant eye saccade to the second flash eccentricity. When this occurred, gaze movement did not resemble a pulse-step pattern. 5. It is suggested that non-visually orienting gaze is driven mainly by head movement. Eye and head movements can be either tightly coupled or dissociated, depending on the stimulus pattern.

Eye Movements↗
PubMedDate not supplied

Flash lamp-excited time-resolved fluorescence microscope suppresses autofluorescence in water concentrates to deliver an 11-fold increase in signal-to-noise ratio.

The ubiquity of naturally fluorescing components (autofluorophores) encountered in most biological samples hinders the detection and identification of labeled targets through fluorescence-based techniques. Time-resolved fluorescence (TRF) is a technique by which the effects of autofluorescence are reduced by using specific fluorescent labels with long fluorescence lifetimes (compared with autofluorophores) in conjunction with time-gated detection. A time-resolved fluorescence microscope (TRFM) is described that is based on a standard epifluorescence microscope modified by the addition of a pulsed excitation source and an image-intensified time-gateable CCD camera. The choice of pulsed excitation source for TRFM has a large impact on the price and performance of the instrument. A flash lamp with rapid discharge characteristics was selected for our instrument because of the high spectral energy in the UV region and short pulse length. However, the flash output decayed with an approximate lifetime of 18 micros and the TRFM required a long-lived lanthanide chelate label to ensure that probe fluorescence was visible after decay of the flash plasma. We synthesized a recently reported fluorescent chelate (BHHCT) and conjugated it to a monoclonal antibody directed against the waterborne parasite Giardia lamblia. For a 600-nm bandpass filter set and a gate delay of 60 micros, the TRFM provided an 11.3-fold improvement in the signal-to-noise ratio (S/N) of labeled Giardia over background. A smaller gain in an SNR of 9.69-fold was achieved with a 420-nm longpass filter set; however, the final contrast ratio between labeled cyst and background was higher (11.3 versus 8.5). Despite the decay characteristics of the light pulse, flash lamps have many practical advantages compared with optical chopper wheels and modulated lasers for applications in TRFM.

Animals↗
PubMed2003

Left ventricular mass: manual and automatic segmentation of true FISP and FLASH cine MR images in dogs and pigs.

PURPOSE: To evaluate the accuracy of manually and automatically segmented true fast imaging with steady-state precession (FISP) and fast low-angle shot (FLASH) cine magnetic resonance (MR) imaging in the determination of left ventricular (LV) mass. MATERIALS AND METHODS: Nine dogs and five pigs underwent cine MR imaging of the entire LV from base to apex. Manual and automatic segmentation times were recorded, and LV masses determined with each were compared with each other and with the true LV mass at autopsy. Estimated mass and true mass at autopsy were compared by calculating the correlation coefficient and the mean difference between the two for each MR sequence and segmentation method. RESULTS: True LV mass at autopsy correlated well with masses determined with manual and automatic contours on true FISP MR images. Mean differences between true LV mass and masses determined from manual contours on true FISP and FLASH images were -0.8 g +/- 2.6 and 3.7 g +/- 6.8, respectively. When manually drawn end-diastolic contours were automatically propagated to end systole, mean differences were 2.0 g +/- 3.6 (P =.05) and 9.1 g +/- 6.5 (P <.05) for true FISP and FLASH images, respectively. For automatic contours, mean differences were 10.6 g +/- 8.5 (P <.05) and 27.7 g +/- 13.4 (P <.05) for true FISP and FLASH images, respectively. Mean automatic segmentation time was six times less than mean manual segmentation time. CONCLUSION: LV mass was determined most accurately by using manual contours on true FISP images. In these animal models, fully automatic segmentation of true FISP images was performed in one-sixth of the time of manual segmentation and yielded LV masses with a mean error of approximately 5% of true LV mass.

Animals↗
PubMed1987

Cartilage disorders: comparison of spin-echo, CHESS, and FLASH sequence MR images.

Magnetic resonance (MR) imaging is known to be a suitable modality for the visualization of the hyaline cartilage and the fibrocartilage joint structures. To compare standard spin-echo (SE) images with water images obtained with the chemical shift selective (CHESS) sequence and with the fast low angle shot (FLASH) sequence, examinations were performed with all three sequences in eight volunteers and 28 patients with inflammatory degenerative and traumatic alterations of the knee, hip, and sacroiliac joints. Arthroscopic and/or surgical correlation were available in 16 patients; bone scanning and computed tomography of the sacroiliac joints were performed in four patients. CHESS-water and FLASH images proved superior to SE images in demonstrating hyaline cartilage disorders. There was no difference between SE, CHESS, and FLASH in the detection of fibrocartilage disorders. Short imaging times and satisfactory depiction of cartilage alterations make FLASH a promising method.

Adult↗
PubMed1996

Accuracy of fat-suppressed three-dimensional spoiled gradient-echo FLASH MR imaging in the detection of patellofemoral articular cartilage abnormalities.

PURPOSE: To determine the accuracy of T1-weighted fat-suppressed (FS) three-dimensional (3D) fast low-angle shot (FLASH) magnetic resonance (MR) imaging for the detection of articular cartilage abnormalities of the patellofemoral joint. MATERIALS AND METHODS: Forty-one patients with suspected internal derangement of the knee were examined with a T1-weighted FS 3D FLASH sequence and subsequently underwent arthroscopy. The patellofemoral articular cartilage was graded blindly on both the MR and arthroscopic images with a modification of the Noyes classification scheme. RESULTS: For the detection of abnormal articular cartilage of the patellofemoral joint with the FS 3D FLASH sequence, sensitivity was 81%, specificity was 97%, and accuracy was 97%. Of the lesions detected on MR images, 77% were graded identically on MR and arthroscopic images. For the remaining 23%, MR imaging and arthroscopic ratings were within one grade of each other. CONCLUSION: T1-weighted FS 3D FLASH imaging is accurate for the detection and grading of articular cartilage abnormalities of the patellofemoral joint.

Adolescent↗
PubMed2001

Adrenal masses: quantification of fat content with double-echo chemical shift in-phase and opposed-phase FLASH MR images for differentiation of adrenal adenomas.

PURPOSE: To quantify fat content in adrenal lesions with double-echo chemical shift magnetic resonance (MR) imaging in a phantom study and to differentiate adrenal adenomas from other adrenal masses by assessing fat content in a clinical study. MATERIALS AND METHODS: The study consisted of two parts: a phantom study and a clinical study. To explore the effect of the T1 value on in- and opposed-phase MR images of fat-containing tissues, phantom models with various proportions of fat and gadopentetate dimeglumine concentrations were implemented. Signal intensity (SI) indexes ([SI in-phase - SI opposed-phase]/SI in-phase) were calculated with double-echo fast low-angle shot (FLASH) MR imaging. In the clinical study, 23 patients with 28 adrenal masses (16 adrenal adenomas, nine adrenal metastases, and three pheochromocytomas) underwent double-echo FLASH MR imaging, and SI indexes were calculated. RESULTS: SI index reached a maximum of 0.87 at 53% fat fraction for gadopentetate dimeglumine concentration at 0.5 mmol/L as the simulated T1 of the adrenal mass. The SI indexes of the adrenal adenomas, adrenal metastases, and pheochromocytomas, respectively, were 0.36, -0.15, and -0.07, and estimated fat fraction from the phantom study was 26.5%, 0%, and 0%. All adrenal adenomas contained fat on double-echo FLASH images. There was no overlap in SI index between adenomas and other tumors. CONCLUSION: Preliminary experience indicates that quantitative measurement of the fat fraction of adrenal masses is possible with the double-echo chemical shift FLASH technique and allows for differentiating adrenal adenomas from other adrenal masses.

Adenoma↗
PubMed1987

Double-flash responses in different retinal layers.

Stimulating the isolated arterially perfused cat eye with two consecutive flashes (double flashes) we have studied the reduction of the 2nd response recorded from outer (isolated PIII component of the ERG), middle (b-wave) and inner (optic nerve response, ONR) retinal layers. The spectral sensitivity of the mechanism that reduces the amplitude of the 2nd response, determined by a constant threshold of 20% amplitude reduction of the b-wave, could be matched by a 500 nm pigment absorption function. For a given stimulus irradiance the response reduction was largest in the b-wave and smaller in the PIII and ONR. The injection of the dopamine antagonist fluphenazine, which presumably does not influence rod receptor function, changes the ratio between the two b-wave double-flash responses. These data indicate that the reduction of the 2nd response is produced by a rod driven mechanism that has a receptoral as well as a postreceptoral component. The ONR data indicate that mechanisms in the inner retina counteract the amplitude reduction of the 2nd flash, thereby stabilizing the retinal output.

Animals↗
PubMed2006

Glaucoma detection is facilitated by luminance modulation of the global flash multifocal electroretinogram.

PURPOSE: To investigate the variation of retinal electrophysiological function in glaucoma by using the global flash multifocal electroretinogram (mfERG) stimulation with altered differences in the stimulus luminance of the multifocal flashes, in an attempt to alter the levels of inner retinal contributions. METHODS: The mfERG was assessed with a visual stimulus in steps of four video frames, which consisted of 103 scaled hexagonal elements followed by a dark frame, global flash, and dark frame. The localized luminance difference was set at 96%, 65%, 49%, or 29% stimulus contrast. Thirty subjects with glaucoma and 30 age-matched normal subjects were recruited for visual field and mfERG measurements. RESULTS: This stimulus induces complex local first-order responses with an early direct component (DC) and a later induced component (IC). The luminance-modulated response functions of the DC and IC responses showed markedly different behavior. The peripheral IC showed a linear dependence on luminance difference, whereas the peripheral DC was saturated for higher luminance differences. This saturation became less obvious in subjects with glaucoma, mostly because of greater reduction of the response amplitude in the mid luminance-difference level. An "adaptive index" was calculated from the luminance-difference dependence of the peripheral DC, and it showed a sensitivity of 93%, with a specificity of 95% for differentiating normal from glaucomatous eyes, and also had a significant correlation (r = 0.58) with the glaucomatous visual field defect. CONCLUSIONS: The peripheral DC luminance-modulated response function is altered by the adaptive mechanism that is induced by the global flash; the reduction of the adaptive index may thus relate to an abnormal adaptive mechanism, presumably due to inner retinal damage. Glaucoma appears to produce large reductions of the adaptive index which correlate with field defects.

Adult↗
PubMed1992

The effects of temperature on the circadian rhythms of flashing and glow in Gonyaulax polyedra: are the two rhythms controlled by two oscillators?

Circadian rhythms of flashing and glow were recorded simultaneously in Gonyaulax polyedra by determining maximum and minimum light emission at each measured interval of 28 sec. In constant light, the two rhythms in some cases showed different period lengths (tau), the glow rhythm being up to 1 hr shorter than the flashing rhythm. Lower temperatures shortened the tau of the glow rhythm more than that of the flashing rhythm. The amplitude of the flashing rhythm decreased when the temperature was increased from 15 degrees C to 25 degrees C, whereas that of the glow rhythm was increased. These results may indicate that the two rhythms are controlled by two separate oscillators.

Animals↗
PubMed1993

Use of clonidine to treat hot flashes secondary to leuprolide or goserelin.

OBJECTIVE: To determine the effects of clonidine, a centrally acting adrenergic agonist, in abating symptoms of hot flashes in men receiving either leuprolide or goserelin for prostate cancer. DESIGN: Patients were administered transdermal or oral clonidine 0.1-0.2 mg/d. Dosages were increased in increments of 0.1-0.3 mg/d every two to four weeks if symptoms persisted or until adverse effects developed. SETTING: Medical oncology clinic at the University of Illinois and the hypertension clinic at the Veterans Affairs West Side Medical Center. PARTICIPANTS: Consenting male patients were eligible for the study if they were receiving leuprolide or goserelin for prostate cancer and were experiencing hot flashes. Exclusion criteria included diastolic blood pressure of 75 mm Hg or below or a history of adverse reactions to clonidine. MAIN OUTCOME MEASURES: Effectiveness of clonidine was determined by questioning patients about frequency, severity, and duration of hot flashes at baseline and at two- to four-week intervals. RESULTS: All four patients receiving clonidine experienced a partial response within two weeks of starting treatment. No dose-dependent response was observed. Adverse effects were noted in one patient but did not result in discontinuation. CONCLUSIONS: Our results document the first report of the use of clonidine to treat hot flashes secondary to leuprolide or goserelin therapy. Symptomatic improvement was noted in all four patients. Further evaluation of clonidine as well as other centrally acting adrenergic agonists is needed.

Climacteric↗
PubMed1979

LH, FSH and skin temperaure during the menopausal hot flash.

Six postmenopausal women, who were experiencing frequent hot flashes, had an 8 h continuous recording of skin temperature over the dorsum of the finger as an objective index of hot flashes. Frequent blood samples were obtained during the time of the recording for the measurement of serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels. During the 48 h of recording 34 significant temperature elevations were recorded and 32 were associated with a subjective hot flash. 3l pulses of LH release were also observed with 26 occurring simultaneously with the temperature rises. Correlation analysis of simultaneous skin temperature and circulating LH levels showed a significant positive correlation (p less than 0.01). FSH levels showed no consistent relationship with skin temperature. These data suggest that LH or the factors that trigger its pulsatile release are related to the mechanism responsible for the initiation of hot flashes.

Climacteric↗