Flickering Pattern Research Articles

LED警光灯の視認性向上のための感性指標に基づく点滅パターン解析

LED警光灯の視認性向上のための感性指標に基づく点滅パターン解析

Local flicker stimulation evokes local retinal blood velocity changes

We investigated the effect of localized visual stimulation on human retinal blood velocity using an adaptive optics scanning laser ophthalmoscope (AOSLO). To measure the blood velocity response, the AOSLO scanning raster was moved over the target arteries and red blood cell velocity was measured. Localized visual stimuli were delivered by projecting flicker patterns inside or outside the target artery's downstream region. The blood velocity increased in the presence of a flicker stimulus in the downstream region but not when outside the downstream region. The blood velocity increased more with larger area of stimulation. This increase was significant even when the stimulus was smaller than 600 μm × 600 μm. These findings suggest that when the retina regulates its blood flow to metabolic demands, it regulates blood velocity in the vascular system selectively, according to activity of neurons within its field of influence.

Routing of information flow by selective visual attention in LFPs of monkey area V4

Routing of information flow by selective visual attention in LFPs of monkey area V4

Microphotometry of Underwater Shadowing by a Moss from a Niagara Escarpment Waterfall

Microscope and fiber-optic spectrophotometry of transmittance and backscattering both showed moss leaves to be capable of casting strong shadows, with a single leaf blocking approximately 90% of incident light from a point source. In leaves with only one layer of cells, the transmittance through the cytoplasm of single cells was similar to that for whole leaves. Analysis of cell wall birefringence by polarized-light interferometry indicated that cell walls might normally scatter rather than transmit light. Spectra transmitted through, or backscattered from, the upper green layers of moss were dominated by selective absorbance from chlorophyll, but there was also evidence of wavelength-dependent scattering, as detected in the lower layers of brown, dead moss. Specular reflectance from moss leaves was detected by polarimetry and may have contributed to the relatively high macroscopic transmittance of stationary moss in water. Shadowing by moss leaves was confirmed by dynamic measurements of mosses in turbulent water without bubbles. Flicker patterns from leaves were superimposed on the underwater flicker pattern created at the air-water interface, thus flecks of light were reduced in intensity, increased in frequency, and decreased in duration. This was detected with both point source and diffuse illumination of samples.

Highly selective processing of temporal information from attended stimuli in macaque’s visual area V4

Highly selective processing of temporal information from attended stimuli in macaque’s visual area V4

Measurement of layer-like hemodynamic trends in scalp and cortex: implications for physiological baseline suppression in functional near-infrared spectroscopy

A multidetector, continuous wave, near-infrared spectroscopy (NIRS) system is developed to examine whether the hemodynamics of the scalp and brain in adults contain significant layer-like hemodynamic trends. NIRS measurements are made using contrasting geometries, one with four detectors equidistant from a source 33 mm away, and one with detectors collinear with the source (5 to 33 mm away). When NIRS time series are acquired over the prefrontal cortex from resting adults using both geometries, variations among the time series are consistent with a substantially homogeneous two-layer model (p<0.001) and inconsistent with one dominated by heterogeneities. Additionally, when time series measured 5 mm from the source are subtracted from corresponding 33-mm signals via a least-squares algorithm, 60% of the hemoglobin changes are on average removed. These results suggest that hemodynamic trends present in the scalp can contribute significantly to NIRS measurements, and that attempts to reduce this noise by subtracting a simultaneous near-channel measurement using a two-layer model are justified. Such subtractions are then performed on NIRS measurements from two stimulus protocols. For systemic stimulations (Valsalva maneuver), the subtraction cancels the hemodynamic response, as desired. For localized stimulation of the occipital lobe (viewing a flickering pattern), the subtraction isolated a stimulus-correlated hemodynamic feature from background noise.

Biophysical characterization of Vpu from HIV‐1 suggests a channel‐pore dualism

Vpu from HIV‐1 is an 81 amino acid type I integral membrane protein which consists of a cytoplasmic and a transmembrane (TM) domain. The TM domain is known to alter membrane permeability for ions and substrates when inserted into artificial membranes. Peptides corresponding to the TM domain of Vpu (Vpu1‐32) and mutant peptides (Vpu1‐32‐W23L, Vpu1‐32‐R31V, Vpu1‐32‐S24L) have been synthesized and reconstituted into artificial lipid bilayers. All peptides show channel activity with a main conductance level of around 20 pS. Vpu1‐32‐W23L has a considerable flickering pattern in the recordings and longer open times than Vpu1‐32. Whilst recordings for Vpu1‐32‐R31V are almost indistinguishable from those of the WT peptide, recordings for Vpu1‐32‐S24L do not exhibit any noticeable channel activity. Recordings of WT peptide and Vpu1‐32‐W23L indicate Michaelis–Menten behavior when the salt concentration is increased. Both peptide channels follow the Eisenman series I, indicative for a weak ion channel with almost pore like characteristics. Proteins 2008. © 2007 Wiley‐Liss, Inc.

Concurrent visuo-spatial processing reduces food cravings in prescribed weight-loss dieters

The study investigated the relative effectiveness of thought suppression and the working memory-based method of dynamic visual noise as techniques for reducing food cravings. Twenty dieting women on the weight-loss programme prescribed by weight watchers and 20 non-dieting controls formed images of their most craved food and then suppressed thoughts of the food or watched a flickering pattern of black and white dots (dynamic visual noise). Both thought suppression and dynamic visual noise reduced cravings for weight watchers and non-dieters. However, their relative effectiveness varied according to participant dieting status. Specifically, while both techniques reduced cravings equally well for non-dieters, dynamic visual noise was clearly the more effective technique for weight watchers. Thus, dynamic visual noise may provide a useful tool for controlling problematic cravings in clinically overweight or obese individuals who are actively trying to lose weight.

Space-Time Imaging of Bioluminescence from a Single Colony of Luminous Bacterium

We performed a space-time imaging analysis of a single colony of marine luminous bacterium using a fluorescent microscope connected to a real-color CCD camera. The bioluminescence and bright-field imaging showed that a glowing ring occurred close to the frontline of the growing colony, and that the ring spread out regularly while retaining a concentric ring shape. The glowing ring faded out when the colony terminated its growth. Furthermore, it was found that either aeration or O2-supply triggered a new glowing ring on the dim inside of the colony, and that the newly triggered ring phases out in the absence of aeration or O2-supply. Such a flickering pattern was confirmed to repetitively occur on the same concentric circle, corresponding to the presence and absence of aeration or O2-supply. From these findings, it is postulated that a growing single colony possesses a certain periodic property.

Localizing Sites of Activation in Primary Visual Cortex Using Visual-Evoked Potentials and Functional Magnetic Resonance Imaging

This study compared retinotopic map identification in primary visual cortex (V1) using: (i) functional magnetic resonance imaging (fMRI) and (ii) visual evoked potentials (VEPs) coupled with dipole source localization (DSL). A multielectrode array was used to record VEPs while subjects viewed a flickering dartboard pattern modulated by a 16-bit m-sequence. The stimulus preferentially activates V1. Using a common time function DSL algorithm, the primary source of each stimulus patch was found independent of the fMRI. The VEP/DSL and fMRI localization data for each subject were aligned by a rigid translation and rotation. The average distance between VEP and corresponding fMRI sources was 10.8 mm +/- 3.8 mm. To assess the significance of the results, fMRI and DSL solutions were scrambled so the comparisons were no longer for corresponding patches. The average distance between the noncorresponding data sets was 17.2 mm for 50 million scrambles. The probability of the scrambled data yielding a better fit than the real data was p < 10(-7). The combination of multielectrode recording, multiinput visual stimulation and common time function DSL analysis can provide a detailed retinotopic map of visual cortex that has high correspondence with independent fMRI localization analysis on the same subject.

Quantal Encoding of Information in a Retinal Ganglion Cell

A retinal ganglion cell receives information about a white-noise stimulus as a flickering pattern of glutamate quanta. The ganglion cell reencodes this information as brief bursts of one to six spikes separated by quiescent periods. When the stimulus is repeated, the number of spikes in a burst is highly reproducible (variance < mean) and spike timing is precise to within 10 ms, leading to an estimate that each spike encodes about 2 bits. To understand how the ganglion cell reencodes information, we studied the quantal patterns by repeating a white-noise stimulus and recording excitatory currents from a voltage-clamped, brisk-sustained ganglion cell. Quanta occurred in synchronous bursts of 3 to 65; the resulting postsynaptic currents summed to form excitatory postsynaptic currents (EPSCs). The number of quanta in an EPSC was only moderately reproducible (variance = mean), quantal timing was precise to within 14 ms, and each quantum encoded 0.1-0.4 bit. In conclusion, compared to a spike, a quantum has similar temporal precision, but is less reproducible and encodes less information. Summing multiple quanta into discrete EPSCs improves the reproducibility of the overall quantal pattern and contributes to the reproducibility of the spike train.

Physiology of human photosensitivity.

Human epileptic photosensitivity has been studied in several ways. (a) Visual stimulation that resembles the stimulation normally responsible for seizures, such as that from televisions or videogames, both of which typically use cathode ray tubes in which the display is created in a flickering pattern. Such stimulation is often rendered yet more epileptogenic by programmes with content that also involves flashing or patterned material. (b) Elementary visual stimuli that enable inferences to be drawn concerning the physiological trigger mechanisms. The topographic distribution of epileptiform EEG activity in response to such stimuli has complemented this approach, leading to the inference that the trigger is cortical and requires sychronised mass action of neurons. (c) Stimuli that avoid paroxysmal EEG activity and permit an investigation of the subepileptic response to visual stimuli, using the evoked potential. This has revealed abnormalities in the cortical mechanisms that control the response to strong visual stimulation.

Illusory jitter in a static stimulus surrounded by a synchronously flickering pattern

The eyes are always moving even during fixation, making the retinal image move concomitantly. While these motions activate early visual stages, they are excluded from one’s perception. A striking illusion reported here renders them visible: a static pattern surrounded by a synchronously flickering pattern appears to move coherently in random directions. There was a positive correlation between the illusion and fixational eye movements. A simulation revealed that motion computation artificially creates a motion difference between center and surround, which is usually a cue to object motion but now a wrong cue to seeing eye movements of oneself on-line. Therefore, this novel illusion indicates that the visual system normally counteracts shaky visual inputs due to small eye movements by using retinal, as opposed to extraretinal, motion signals. As long as they comprise common image motions over space, they are interpreted as coming from a static outer world viewed through moving eyes. Such visual stability fails in the condition of artificial flicker, because common image motions due to eye movements are registered differently between flickering and non-flickering regions.

Modification of the Heidelberg retinal flowmeter to record pattern and flicker induced blood flow changes.

We tested a prototype stimulator interfaced with a commercially available scanning laser ophthalmoscope designed to measure retinal capillary perfusion (Heidelberg Retina Flowmeter (HRF)). The add-on stimulator optically superimposed the image of a monitor display on to the subject's retina coaxially with the imaging optics of the HRF. The purpose of the study was to determine if flicker and pattern stimulation presented in this manner could evoke changes in retinal perfusion that could be measured by the HRF. The prototype stimulator projected 55 degrees visual angle circular fields of homogeneous flicker, alternating checkerboard, and multi-focal m-sequence hexagonal patterns on the retina of 10 human subjects during acquisition of images by the HRF. Images were successfully acquired and processed. HRF perfusion values during flicker and pattern stimulation were not significantly different from control values. Results of the present study and a previously published study showing a flicker-induced increase in the HRF perfusion values are contradictory. Retinal perfusion measured by the HRF were not affected by flicker and pattern stimulation delivered through the prototype device. These data are not consistent with a large flicker or pattern induced increase in retinal perfusion. The instrumental modification appears promising. However, the raster scan stimulation technique or some other aspect of stimulation or image acquisition may account for the different results in the present study and previous studies in our laboratory and in the laboratories of other investigators.

The impact of fixation on the multifocal electroretinogram.

There are a number of variables which can influence the quality of multifocal ERG waveforms. In common with visual field measurements, fixation quality may be an important parameter on the integrity of the acquired data. A low cost, fixation-monitoring device was used to assess fixation quality on a group of normal volunteers. Data was successfully acquired while five subjects viewed a fixation target for a period of time equal to that of a single multifocal recording segment. The target was presented on a stationary grey background and as the central fixation mark on a 61-element multifocal flicker stimulus. The results show no significant difference with or without the flickering pattern. The percentage of samples falling within 1.2 degrees of the point of fixation was 51%. This suggests that fixation quality is adequate for scaled stimuli where the central element subtends 2.4 degrees. High resolution stimuli of less than 2.4 degrees may be more susceptible to fixation fluctuations during the recording process.

Synchronous period-doubling in flicker vision of salamander and man.

Periodic flashes of light have long served to probe the temporal properties of the visual system. Here we show that during rapid flicker of high contrast and intensity the eye reports to the brain only every other flash of light. In this regime, retinal ganglion cells of the salamander fire spikes on alternating flashes. Neurons across the entire retina are locked to the same flashes. The effect depends sharply on contrast and flash frequency. It results from a period-doubling bifurcation in retinal processing, and a simple model of nonlinear feedback reproduces the phenomenon. Pharmacological studies indicate that the critical feedback interactions require only cone photoreceptors and bipolar cells. Analogous period-doubling is observed in the human visual system. Under bright full-field flicker, the electroretinogram (ERG) shows a regime of period-doubling between 30 and 70 Hz. In visual evoked potentials from the occiput, the subharmonic component is even stronger. By analyzing the accompanying perceptual effects, we find that retinal period-doubling begins in the periphery of the visual field, and that it is the cause of a long mysterious illusory flicker pattern.

Reaction of diphtheria toxin channels with sulfhydryl-specific reagents: observation of chemical reactions at the single molecule level.

The diphtheria toxin channel is believed to be a homooligomer of its T domain in which each subunit consists of two alpha-helices, lying within the membrane, connected by a short interhelical loop of four amino acids (residues 349-352). To investigate the validity and implications of this model, we singly mutated each of these amino acids to cysteines, formed channels with the mutant T-domain proteins in planar lipid bilayers, and added to the trans compartment sulfhydryl-specific reagents [methanethiosulfonate derivatives (MTS-ER)] that introduce a positive or negative charge to reacted cysteines. The introduction of a positive charge at residue 351 or 352 (through the MTS-ER reactions) resulted in a step decrease in single-channel conductance, whereas the introduction of a negative charge resulted in a step increase. The opposite sign of these effects indicates the predominantly electrostatic nature of the phenomenon and implies that residues 351 and 352 lie close to the channel entrance. The same reactions at residue 350 resulted in very little change in channel conductance but instead changed the character of the natural rapid flickering of the channel between open and closed states to one in which the channel spent more time in the closed state; this may have resulted from the group introduced at position 350 acting as a tethered channel blocker. The MTS derivatives had no effect on channels containing a cysteine at position 349, suggesting that this residue faces away from the channel entrance. We propose that the step changes in conductance or flickering pattern result from the chemical reaction of one MTS-ER molecule with one cysteine, and thus a bimolecular chemical reaction is being witnessed at the single molecule level. From the distribution of waiting times between the appearance (i.e., the opening) of a channel and the step change in its conductance or flickering pattern, we can calculate a pseudo-first-order rate constant, which can then be converted to a second-order rate constant, for the chemical reaction.

Intracellular picrotoxin blocks pentobarbital-gated Cl − conductance

Using the ‘inside-out’ configuration of frog sensory neurons, we studied the effect of intracellular picrotoxin on the pentobarbital-gated single channel response of Cl −-current ( i Cl). The pentobarbital-induced i Cl showed no voltage-dependency and the single channel conductance ( γ Cl) was 16±3.1 pS ( n = 6). Picrotoxin caused the pentobarbital-gated Cl − channels to react in a flickering pattern and then finally caused them to cease their opening altogether. This inhibitory action of picrotoxin was reversible.

Mechanisms of human motion perception revealed by a new cyclopean illusion.

A new cyclopean illusion of motion may bear on neural mechanisms of direction selectivity. Stationary flickering patterns were presented to each eye, and the resulting fused pattern was perceived to be moving. To determine direction of motion, the visual system seems to integrate image components differing by 90 degrees in spatial and temporal phase. On the other hand, image speed seems to be derived from displacement of features over time. A model of neural direction selectivity is discussed in light of these results.

Letter: Binocularly induced motion of flicker patterns.

A new apparent motion phenomenon is described. It occurs when two flashing screens are observed binocularly, one screen for each eye, and the temporal phase between the flashes is suddenly changed. It appears as a low-contrast pattern of vertical stripes that move either to the left or right, depending on the phase of the lights. Changing the relative intensity of the screens alters the effect in a manner consistent with previous measurements on visual time delays.