Hz Refresh Rate Research Articles

Temporal Encoding of Spatial Information during Active Visual Fixation

Humans and other species continually perform microscopic eye movements, even when attending to a single point. These movements, which include drifts and microsaccades, are under oculomotor control, elicit strong neural responses, and have been thought to serve important functions. The influence of these fixational eye movements on the acquisition and neural processing of visual information remains unclear. Here, we show that during viewing of natural scenes, microscopic eye movements carry out a crucial information-processing step: they remove predictable correlations in natural scenes by equalizing the spatial power of the retinal image within the frequency range of ganglion cells' peak sensitivity. This transformation, which had been attributed to center-surround receptive field organization, occurs prior to any neural processing and reveals a form of matching between the statistics of natural images and those of normal eye movements. We further show that the combined effect of microscopic eye movements and retinal receptive field organization is to convert spatial luminance discontinuities into synchronous firing events, beginning the process of edge detection. Thus, microscopic eye movements are fundamental to two goals of early visual processing: redundancy reduction and feature extraction.

Nonretinotopic Exogenous Attention

Attention is crucial for visual perception because it allows the visual system to effectively use its limited resources by selecting behaviorally and cognitively relevant stimuli from the large amount of information impinging on the eyes. Reflexive, stimulus-driven attention is essential for successful interactions with the environment because it can, for example, speed up responses to life-threatening events. It is commonly believed that exogenous attention operates in the retinotopic coordinates of the early visual system. Here, using a novel experimental paradigm [1], we show that a nonretinotopic cue improves both accuracy and reaction times in a visual search task. Furthermore, the influence of the cue is limited both in space and time, a characteristic typical of exogenous cueing. These and other recent findings show that many more aspects of vision are processed nonretinotopically than previously thought.

A simple technique to improve fixation performance in naive observers

Maintenance of stable central eye fixation is crucial for a variety of behavioral, electrophysiological, and neuroimaging experiments. Naïve observers in these experiments are not typically accustomed to fixating and are often unable to reliably maintain fixation and this may produce confounds in experimental results. Verifying fixation requires the use of cumbersome and costly eye-tracking and results in loss of participants when they are unable to reliably fixate. We devised a simple flicker display consisting of a random-dot pattern (single pixels [.047 deg], 50% black, 50% white) rapidly alternating (37.5 Hz; 75 Hz refresh rate) with its video reversed complement (i.e. white dots became black and black dots became white). This display appeared as a uniform gray patch when the eyes were stable (due to temporal luminance summation), but produced an easily detectable momentarily static noise pattern (due to disrupted temporal summation of luminance) whenever the eyes moved or blinked. A few minutes of training using this display dramatically improved the accuracy of eye fixation when observers later performed a demanding peripheral attention-cueing task. Observers reliably detected their own eye-movements when their eyes deviated by as little as 0.5 degrees. In contrast, the same amount of training using control displays that were uninformative about fixation performance did not produce significant fixation improvements, and some observers consistently made eye movements towards the attention cue, contaminating the observed attention-cueing effect. Our results indicate that (1) eye fixation can be rapidly improved in naïve observers by providing contingent feedback about eye movements, and (2) our simple flicker technique provides an easy and effective method for providing this feedback.

Analytic solution to remove flickers on a liquid crystal display television

Flickers have been critical issues on liquid crystal displays (LCDs) which use a backlight unit (BLU) under a panel. The luminance modulation of the backlight and the transmittance of the panel are independently investigated in frequency domain to look for an analytic solution to remove flickers on the LCD panel. The transmittance of the panel depends on how to drive the LC molecules and how the LC molecules respond. We shows there are three frequency components caused by only the panel driving. It is shown that the flicker can be generated by the inter-modulation effect between two different frequency groups from the BLU and the panel. To remove flickers on LCD TV panels, the frequency of the PWM backlight signal should be carefully chosen so that the inter-modulation frequencies may be higher than 60 Hz. It is shown that it is impossible to perceive flickers on an LCDTV operating at 120 Hz refresh rate if the frequency of the PWM signal is 120 Hz or 180 Hz.

Zinc tin oxide based driver for highly transparent active matrix OLED displays

Zinc tin oxide (ZTO) is a promising active material for transparent electronics. We have realized the first transparent active matrix OLED pixel drivers with ZTO channels. The devices are highly transparent (>80%) in the visible part of the spectrum and suitable for see-through AM OLED displays with brightness levels of 2000 cd/m 2 at 100 Hz refresh rate and full-HD resolution.

High throughput diffractive multi-beam femtosecond laser processing using a spatial light modulator

High throughput femtosecond laser processing is demonstrated by creating multiple beams using a spatial light modulator (SLM). The diffractive multi-beam patterns are modulated in real time by computer generated holograms (CGHs), which can be calculated by appropriate algorithms. An interactive LabVIEW program is adopted to generate the relevant CGHs. Optical efficiency at this stage is shown to be ∼50% into first order beams and real time processing has been carried out at 50 Hz refresh rate. Results obtained demonstrate high precision surface micro-structuring on silicon and Ti6Al4V with throughput gain >1 order of magnitude.

Binocular Coordination of the Eyes during Reading

Saccadic eye movements and fixations are the behavioral means by which we visually sample text during reading. Human oculomotor control is governed by a complex neurophysiological system involving the brain stem, superior colliculus, and several cortical areas. A very widely held belief among researchers investigating primate vision is that the oculomotor system serves to orient the visual axes of both eyes to fixate the same target point in space. It is argued that such precise positioning of the eyes is necessary to place images on corresponding retinal locations, such that on each fixation a single, nondiplopic, visual representation is perceived. Vision works actively through a continual sampling process involving saccades and fixations. Here we report that during normal reading, the eyes do not always fixate the same letter within a word. We also demonstrate that saccadic targeting is yoked and based on a unified cyclopean percept of a whole word since it is unaffected if different word parts are delivered exclusively to each eye via a dichoptic presentation technique. These two findings together suggest that the visual signal from each eye is fused at a very early stage in the visual pathway, even when the fixation disparity is greater than one character (0.29 deg), and that saccade metrics for each eye are computed on the basis of that fused signal.

Vt-Shift Compensating Amorphous Silicon Pixel Circuits for Flexible OLED Displays

ABSTRACTIn this paper, we present design considerations pertinent to amorphous silicon pixel circuits for mechanically flexible active matrix display applications. We describe both circuit topologies and pixel architectures that are amenable to surface emissive pixels in a-Si:H technology. Metastable shifts in the a-Si:H material characteristics after prolonged gate bias or mechanical stress are manifested in the form of increasing TFT threshold voltages and varying mobilities. As a result, the TFT drive current and consequently the OLED brightness decrease, and the pixel eventually turns off. The circuits presented here compensate for this decrease in current through the use of current programming and feedback, and allow for stable OLED brightness over longer time periods. They also enable the implementation of high aperture ratio (close to 100%), low leakage current, surface emissive OLED pixels. Results show that the circuits provide higher linearity and dynamic range than currently available pixel circuits while minimizing the pixel area. Charge injection effects at the gate of the drive TFT have been reduced by using smaller switching TFTs, along with circuit topologies that provide in-pixel current gain. All circuits meet the speed requirements of a QVGA 60 Hz refresh rate display, and occupy less than 300um x 300um area.

Direct video-microscopic observation of the dynamic effects of medical ultrasound on ultrasound contrast microspheres.

Ultrasound can cause destruction of microbubble contrast agents used to enhance medical ultrasound imaging. This study sought to characterize the dynamics of this interaction by direct visual observation of microbubbles during insonification in vitro by a medical ultrasound imaging system. Video microscopy was used to observe air-filled sonicated albumin microspheres adsorbed to a solid support during insonation. Deflation was not observed at lowest transmit power settings. At higher intensities, gas left the microparticle gradually, apparently dissolving into the surrounding medium. Deflation was slower for higher microsphere surface densities. Intermittent ultrasound imaging (0.5 Hz refresh rate) caused slower deflation than continuous imaging (33 Hz). Higher concentrations of microbubbles, lower ultrasound transmit power settings, and intermittent imaging each can reduce the rate of destruction of microspheres resulting from medical ultrasound insonation.

Steady-state visual evoked potentials to computer monitor flicker

In the present study, steady-state visual evoked potentials (S-VEP) in response to amplitude-modulated light from a computer monitor (colour sVGA, 15-inch tube) have been examined. S-VEPs to computer monitors with different refresh rates (60 Hz or 72 Hz) and screen brightness (65 cd/m 2 or 6 cd/m 2) were recorded in 13 subjects with normal or corrected-to-normal vision. EEG samples were amplified, averaged and stored using Cadwell Excel EMG-EP recorder and a regression model was applied for the amplitude analysis. The mean values of S-VEP amplitude at 60 Hz were found to be significantly higher at 60 Hz refresh rate vs. 72 Hz ( F 1,12=14.1; P=0.003). Effect of screen brightness ( F 2,24=6.5; e=0.62; P=0.00075) as well as the interaction effect of refresh rate and screen brightness ( F 2,24=11.6; P=0.0003) were also found to be significant. Data obtained show that the characteristics of amplitude-modulated light from a computer monitor (frequency, brightness, waveform) are sufficient to elicit S-VEP, and the influence is not only restricted to the peripheral divisions of the visual system as it was shown earlier, but also extends to the central brain structures.

Microprocessor-based monitoring system for the Orsay MP-9 injector

The data acquisition system of the MP-9 injector monitors about 90 analog and digital parameters, which are displayed on a console with 2.5 Hz refresh rate. Automatic data logging and alarm monitoring are implemented. The system permits oscilloscope display of any channel with a 300 Hz bandwidth.