Search

Image segmentation is an essential task in computer vision and pattern recognition. There are two key challenges for image segmentation. One is to find the most discriminative image feature set to get high-quality segments. The other is to achieve good performance among various images. In this paper, we firstly propose a selective feature fusion algorithm to choose the best feature set by evaluating the results of presegmentation. Specifically, the proposed method fuses selected features and applies the fused features to region growing segmentation algorithm. To get better segments on different images, we further develop an algorithm to change threshold adaptively for each image by measuring the size of the region. The adaptive threshold can achieve better performance on each image than fixed threshold. Experimental results demonstrate that our method improves the performance of traditional region growing by selective feature fusion and adaptive threshold. Moreover, our proposed algorithm obtains promising results and outperforms some popular approaches. [ABSTRACT FROM AUTHOR]

Abstract: Speech perception involves fusion of multiple sensory inputs, but fusion is not automatic, likely depending on several external and internal factors (e.g., attention, noise, age). In this study, we exploited a specific paradigm in which a short audiovisual context made of coherent or incoherent speech material is displayed before an incongruent audiovisual target likely to provide fusion (McGurk & MacDonald, 1976). We confirmed that incoherent context leads to unbinding, that is, a reduction in the amount of fusion. Importantly, adding acoustic noise in the context though not in the target increases fusion. This suggests that listeners systematically evaluate the reliability of their sensory channels and weight them accordingly in the fusion process. We also showed that older participants display more unbinding than younger participants. We discuss the potential consequences concerning people's ability to understand speech in adverse conditions and relate our findings to a “Binding‐and‐Fusion” model of audiovisual speech perception. [ABSTRACT FROM AUTHOR]

Purpose To assess the effect of elevated core body temperature on temporal and spatial contrast sensitivity and retinal vessel diameters. Methods The study included 13 healthy volunteers aged 20-37 years. Core body temperature elevation (target +1.1°C) was induced by wrapping the participants in cling film, tinfoil and warming blankets. Subsequent cooling was achieved by undressing. Flicker sensitivity (critical flicker fusion frequency) was chosen to assess temporal resolution, while the Freiburg Vision Test was used to determine spatial contrast sensitivity at 1.5 cycles per degree. Scanning laser ophthalmoscopy was used to measure retinal trunk vessel diameters. Assessment was made at baseline, during hyperthermia and after cooling. Results The induction of a mean increase in core body temperature of 1.02°C was associated with a 7.15-mmHg mean reduction in systolic blood pressure (p < 0.01), a 10.6-mmHg mean reduction in diastolic blood pressure (p < 0.01), a mean increase in pulse rate of 36.3 bpm (p < 0.0001), a 2.66% improvement in flicker sensitivity (CI95 1.37-3.94, p < 0.001), a 2.80% increase in retinal artery diameters (CI95 1.09-4.51, p < 0.01) and a 2.95% increase in retinal vein diameters ( CI95 0.96-4.94, p < 0.01). There was no detectable effect of temperature on spatial contrast sensitivity. All ocular test parameters returned to baseline levels after cooling. Conclusion Increased core body temperature was accompanied by improved temporal visual resolution and retinal trunk vessel dilation. The results suggest that hyperthermia is associated with enhanced retinal function and increased retinal metabolism. [ABSTRACT FROM AUTHOR]

Drawing the user's gaze to an important item in an image or a graphical user interface is a common challenge. Usually, some form of highlighting is used, such as a clearly distinct color or a border around the item. Flicker can also be very salient, but is often perceived as annoying. In this paper, we explore high frequency flicker (60 to 72 Hz) to guide the user's attention in an image. At such high frequencies, the critical flicker frequency (CFF) threshold is reached, which makes the flicker appear to fuse into a stable signal. However, the CFF is not uniform across the visual field, but is higher in the peripheral vision at normal lighting conditions. Through experiments, we show that high frequency flicker can be easily detected by observers in the peripheral vision, but the signal is hardly visible in the foveal vision when users directly look at the flickering patch. We demonstrate that this property can be used to draw the user's attention to important image regions using a standard high refresh-rate computer monitor with minimal visible modifications to the image. In an uncalibrated visual search task, users could in a crowded image easily spot the specified search targets flickering with very high frequency. They also reported that high frequency flicker was distracting when they had to attend to another region, while it was hardly noticeable when looking at the flickering region itself. [ABSTRACT FROM AUTHOR]

Background The diagnosis of covert hepatic encephalopathy ( CHE) by means of portosystemic encephalopathy syndrome ( PSE) test is costly and therefore infrequently performed. Aim To determine the ability of critical flicker frequency ( CFF) alone or in combination with laboratory findings, as an initial test to pre-select which patients should undergo further testing for the diagnosis of covert hepatic encephalopathy. Methods This single-centre study included all patients with cirrhosis who underwent PSE and CFF in 2011. CHE was defined by abnormal PSE test. Logistic regression analysis was performed to identify predictors of CHE. ROC curves were used to identify cut-offs of these independent predictors. Results One hundred and seventeen patients were included. Seventy (60%) had CHE with a higher MELD [16 ( IQR 13-21); P = 0.001] and lower CFF [38 Hz ( IQR 36-41) P = 0.0011]. On multivariate analyses, CFF [ OR 0.83 (95% CI 0.74-0.94)] and MELD [ OR 1.13 (95% CI 1.04-1.22)] were identified as independent predictors of CHE. Sensitivity and specificity of a CFF cut-off of 43 Hz was 93.5% and 42.9%, and for a MELD cut-off of 24, it was 97.5% and 32.8% respectively. Most patients with a MELD-Score <24 and a CFF >43 Hz did not have CHE (78%) and with a MELD-Score >24 and CFF <43 Hz most patients had CHE (85%). Therefore, 27% of patients could avoid further testing with a diagnostic accuracy of 81%. Conclusion The combination of MELD-score and critical flicker frequency may be used as a first diagnostic step to filter patients, in whom further covert hepatic encephalopathy testing could be avoided. [ABSTRACT FROM AUTHOR]

This paper proposes a driving method for 240Hz field-sequential-color displays. The proposed method redistributes the image energy in the displayed color fields with the modulation of backlight and liquid crystal signals. Most of the image luminance was concentrated in two multi-color fields, while the luminance of the other mono-color fields was much reduced. The proposed driving method can not only avoid the potential flicker issue but suppress the color breakup phenomenon. [ABSTRACT FROM AUTHOR]

Flicker and image persistence are major issues for low frequency driving. The photo leakage current in an outdoor light environment causes further image quality deterioration. We developed 7.0-inch WUXGA (1200×RGBW×1920) reflective fullcolor LCD, equipped with light-shielding metal layer which suppress photo leakage current, driven by LTPS TFT at 1Hz. [ABSTRACT FROM AUTHOR]

Recently, the driving scheme of a fringe-field switching (FFS) liquid crystal display varies for the best of required performance. Although low-frequency driving can effectively give rise to reduce power consumption in portable displays, proper controlling of liquid crystal director in direct current is challenging. Particularly, under different polarity of applied electric fields, the transmittance difference along the location of electrodes becomes significant, hence giving rise to an image flickering issue. Here, we investigate how physical properties of a bulk liquid crystalline medium are involved to locally modulate the transmitting light, numerically and experimentally. [ABSTRACT FROM AUTHOR]

Background Hepatic encephalopathy ( HE) is a serious complication of liver cirrhosis. Recently, a microsatellite in the promoter region of the phosphate-activated glutaminase ( GLS ) gene was associated with the risk of HE. The aim of the present study was to investigate, using the critical flicker frequency ( CFF) test, whether the described GLS variant increases the risk of developing HE in patients with cirrhosis. Methods We recruited 158 patients (66% men; mean age 59 years, range 23-86) with liver cirrhosis. Mean model for end-stage liver disease score was 13.8 (range 5-35); 48% of patients presented with Child-Pugh score B or C. The presence and severity of HE were determined by the CFF test, with frequencies ≤39 Hz denoting cases. GLS variants were genotyped by sequencing the microsatellite in the promoter region and were classified as short, long or short-long forms (depending on the length of the macrosatellite alleles). Results In total, 53% of patients had abnormal CFF results (i.e. ≤39 Hz; range for entire cohort 26-57). The GLS microsatellite distribution amongst patients was short form (20%), long form (32%) and short-long form (48%) and was consistent with Hardy-Weinberg equilibrium. CFF values differed significantly between groups ( P = 0.043). Carriers of the GLS long microsatellite had a significantly higher risk of HE according to multivariate analyses (odds ratio 3.23, 95% confidence interval 1.46-7.13, P = 0.004). Conclusion CFF results were significantly lower amongst carriers of the GLS long microsatellite. Our findings support the role of the GLS long microsatellite in the development of HE; this could be important for identifying susceptible patients and for the prevention of this condition. [ABSTRACT FROM AUTHOR]

Purpose: To compare the amplitudes and implicit times of the flicker electroretinograms before and after an intravitreal injection of ranibizumab (IVR) in eyes with a central retinal vein occlusion (CRVO). Methods: We reviewed the medical records of 15 consecutive patients who had macular oedema secondary to CRVO and had received an IVR at the Nagoya University Hospital from November 2013 to July 2014. Flicker ERGs were recorded with both the RETeval™ system and a conventional ERG system before the IVR. One month after the IVR, recordings were repeated with only the RETeval™ system. Results: The mean implicit times of the flicker ERGs of the affected eyes recorded with the RETeval™ system were significantly longer than that of the fellow eyes (32.2 ± 2.6 msec versus 28.1 ± 1.2 msec, p < 0.001). One month after the IVR, the implicit times of the flicker ERGs of affected eyes were significantly shortened from 32.2 ± 2.6 to 30.6 ± 2.2 msec (p < 0.001). Conclusions: The shortening of the implicit times of the flicker ERGs after the IVR indicates an improvement of retinal function after anti-VEGF therapy for CRVO eyes. [ABSTRACT FROM AUTHOR]

In this study, a wave park is analysed from the economic and electrical points of view. The system under consideration goes from each wave energy unit up to the point of common connection with the main grid. Time series are obtained from simulation models for a scaled prototype and include data for mild, medium and strong sea states. The simulation models have been validated against the small scale tank testing of a prime mover, a wave rider buoy and a scaled testing of the power take-off in a land-based test rig. The design of the proposed wave park layout aims to minimise its cost and power losses. A life-cycle analysis of the park is performed showing that around 30 €/MWh will be the share of the electricity price required to install and operate the wave park grid. The power quality of the wave park and its compliance with regulations are also analysed. Special emphasis is put in the study of flicker emissions concluding that the proposed wave park is within the grid code limitations and even a reduction of a 66% in the flicker coefficients is reported when considering the aggregation of several units in one model. [ABSTRACT FROM AUTHOR]

Illumination variation is among the several bottlenecks in a practical face recognition system. Extracting illumination-invariant features, such as the gradient-based descriptor, is an effective method to deal with this problem and shows outstanding performance. In this paper, a novel illumination-invariant, histogram-based descriptor, namely local Gradientface XOR and binary pattern (LGXBP), is proposed to enhance the recognition performance of gradient-based method under varying lighting conditions. To this end, first, this approach transforms a face image into the logarithm domain and obtains a pair of illumination-insensitive components. Then the two components are encoded further by local XOR patterns and local binary patterns, respectively, to get compact descriptors and histogram representations, which not only preserve illumination invariance but also gain more discriminating power. Finally, the complementary histograms are integrated for face recognition. Comparative experimental results verify the effectiveness of our approach and show that LGXBP achieves superior recognition rates and a high degree of stability under varying illumination conditions, outperforming most of the state-of-the-art methods. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

In reflective liquid crystal devices that have an asymmetric electrode structure, an internal cell voltage is often present that interferes with the proper functioning of the device. Contrary to transmissive devices, this internal voltage cannot be attributed solely to ionic charges in the liquid crystal. On the basis of extensive measurements, an electro-chemical model is developed and validated, providing a complete explanation for the generation and the dynamic behavior of the internal voltage in asymmetric liquid crystal devices. A possible solution for eliminating the occurrence of the internal voltage is also provided. [ABSTRACT FROM AUTHOR]

Bitemporal hemianopic visual field impairment frequently leads to binocular vision difficulties. Patients with bitemporal hemianopia with pre-existing exophoria complain of horizontal diplopia, sometimes combined with vertical deviation (with pre-existing hyperphoria). The symptoms are a result of the phoria decompensating into a tropia (hemi-slide) due to the lack of retinal correspondence between the remaining nasal fields of both eyes. We measured these effects using a dichoptic perimeter. We showed that aligning the eyes with prisms could prevent diplopia if the bitemporal hemianopia is incomplete. We also describe the successful use of a novel fusion aid - the 'stereo-typoscope' - that utilizes midline stereopsis to prevent diplopia resulting from hemi-sliding in patients with complete bitemporal hemianopia. [ABSTRACT FROM AUTHOR]

Purpose (1) To devise a model-based method for estimating the probabilities of binocular fusion, interocular suppression and diplopia from psychophysical judgements, (2) To map out the way fusion, suppression and diplopia vary with binocular disparity and blur of single edges shown to each eye, (3) To compare the binocular interactions found for edges of the same vs opposite contrast polarity. Methods Test images were single, horizontal, Gaussian-blurred edges, with blur B = 1-32 min arc, and vertical disparity 0-8.B, shown for 200 ms. In the main experiment, observers reported whether they saw one central edge, one offset edge, or two edges. We argue that the relation between these three response categories and the three perceptual states (fusion, suppression, diplopia) is indirect and likely to be distorted by positional noise and criterion effects, and so we developed a descriptive, probabilistic model to estimate both the perceptual states and the noise/criterion parameters from the data. Results (1) Using simulated data, we validated the model-based method by showing that it recovered fairly accurately the disparity ranges for fusion and suppression, (2) The disparity range for fusion (Panum's limit) increased greatly with blur, in line with previous studies. The disparity range for suppression was similar to the fusion limit at large blurs, but two or three times the fusion limit at small blurs. This meant that diplopia was much more prevalent at larger blurs, (3) Diplopia was much more frequent when the two edges had opposite contrast polarity. A formal comparison of models indicated that fusion occurs for same, but not opposite, polarities. Probability of suppression was greater for unequal contrasts, and it was always the lower-contrast edge that was suppressed. Conclusions Our model-based data analysis offers a useful tool for probing binocular fusion and suppression psychophysically. The disparity range for fusion increased with edge blur but fell short of complete scale-invariance. The disparity range for suppression also increased with blur but was not close to scale-invariance. Single vision occurs through fusion, but also beyond the fusion range, through suppression. Thus suppression can serve as a mechanism for extending single vision to larger disparities, but mainly for sharper edges where the fusion range is small (5-10 min arc). For large blurs the fusion range is so much larger that no such extension may be needed. [ABSTRACT FROM AUTHOR]

SUMMARY Wind farms with fixed speed asynchronous generators generate periodic voltage fluctuations and flicker therefore mainly due to the so-called tower shadow effect. An analytical expression of the current supplied by the wind farm (and the voltage at the connection point) can be derived from a simplified model of the farm with a term that quantifies the relative fluctuation of the electrical variable considered. By its very nature, this term is a random variable since it is the result of the fluctuations introduced by each of the generators, and these depend on the angular positions of the individual turbines. In this paper, the authors, based on the aforementioned expression of the total current of the farm, have analyzed the resulting fluctuation phenomenon as a statistical problem by a new theoretical approach. This has allowed the calculation of the distribution and probability density functions as well as the mean values, the variance and the standard deviation, as expressions depending on the number of generators. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Background and Aim: Development of overt hepatic encephalopathy (HE) is associated with poor prognosis in patients with cirrhosis. Lactulose is used for the treatment of HE. There is no study on the prevention of overt HE using lactulose in patients who never had HE earlier. Methods: Consecutive cirrhotic patients who never had an episode of overt HE were randomized to receive lactulose (Gp-L) or no lactulose (Gp-NL). All patients were assessed by psychometry (number connection test [NCT-A and B], figure connection test if illiterate [FCT-A and B], digit symbol test [DST], serial dot test [SDT], line tracing test [LTT]) and critical flicker frequency test (CFF) at inclusion and after 3 months. These patients were followed every month for 12 months for development of overt HE. Results: Of 250 patients screened, 120 (48%) meeting the inclusion criteria were randomized to Gp-L ( n = 60) and Gp-NL ( n = 60). Twenty (19%) of 105 patients followed for 12 months developed an episode of overt HE. Six (11%) of 55 in the lactulose (Gp-L) group and 14 (28%) of 50 in the Gp-NL ( P = 0.02) developed overt HE. Ten (20%) of 50 patients in Gp-NL and five (9%) of 55 patients in the Gp-L group died, P = 0.16. Number of patients with minimal hepatic encephalopathy (MHE) were comparable in two groups at baseline (Gp-L vs Gp-NL, 32:36, P = 0.29). Lactulose improved MHE in 66% of patients in Gp-L. Taking a cutoff < 38 Hz sensitivity and specificity of CFF in predicting HE were 52% and 77% at baseline and 52% and 82% at 3 months of treatment. On multivariate analysis, Child's score and presence of MHE at baseline were significantly associated with development of overt HE. Conclusions: Lactulose is effective for primary prevention of overt hepatic encephalopathy in patients with cirrhosis. [ABSTRACT FROM AUTHOR]

Purpose. To describe the characteristics of rod and cone functions in rat models for congenital stationary night blindness (CSNB) and retinal cone dysfunction (RCD). Methods. Rod and cone function were isolated by recording the rod-/cone-driven flicker and blue light flicker electroretinograms (ERGs). Results. During dark adaptation, the amplitudes of flicker ERGs in CSNB rats were lower than those in control rats; the responses of RCD rats were similar to control rats. During light adaptation, the amplitudes of flicker ERGs in CSNB rats were reduced; whereas the responses of RCD rats were not detected. Blue flicker ERGs were not observed in CSNB rats at lower frequencies. The cone driven critical flicker frequencies (CFFs) in control rats were 62 Hz. The rod driven CFF of RCD rats was 20Hz; whereas the rod-/cone-driven CFF of CSNB rats both were about 25Hz. Conclusions. The function of the rod system was damaged completely, the cones were the source of vision in CSNB rats. Rod system function is excellent in RCD rat. The rods of albinism rats are sensitive to frequencies less than 20 Hz; whereas the cones are sensitive to frequencies up to 62 Hz. [ABSTRACT FROM AUTHOR]

Audio-visual integration was studied in children aged 8-17 (N = 30) and adults (N = 22) using the 'flash-beep illusion' paradigm, where the presentation of two beeps causes a single flash to be perceived as two flashes ( fission illusion), and a single beep causes two flashes to be perceived as one flash ( fusion illusion). Children reported significantly more fission illusions than adults, indicating that auditory and visual information was integrated more often, and less selectively, than in adults. Within either group, illusion reports did not correlate with either age or motor coordination measures. The current results show that the form of multisensory integration indexed by the illusion is slow to mature in normally developing children. [ABSTRACT FROM AUTHOR]

In case an LCD panel is driven by a low-frequency fringe field, image flickering phenomenon is detected by the naked human eye. We investigated the dependence on the electrode spacing of the image flickering phenomenon induced by the flexoelectric effect in an FFS LCD panel. We found that the image flicker in an FFS LCD panel under low-frequency driving can be eliminated in a simple manner by optimizing the electrode spacing. [ABSTRACT FROM AUTHOR]

Despite recent active research on vision-based vehicle detection and tracking, its lack of flexibility hindered practical use in real environments. To be practical, adaptation to various illumination conditions is an essential ingredient. We propose a novel adaptation framework that can improve on this current lighting adaptation using a simple road context, feature arbiter, and a proper feature fusion scheme. In real driving environments, self-supervised online learning can efficiently segment the road and nonroad regions in front of the host vehicle. Classification into these regions is very important to generate regions of interest (ROIs) for potential vehicle position, that is, road context. It improves on system efficiency by reducing noise and processing time. In our global and local lighting models, the feature arbiter selects an appropriate daytime or nighttime detector for each ROI. And finally, an adaptive fusion framework method can robustly track by selecting or removing the distinctive visual attributes. This system was successfully tested on real road data obtained with various ambient lighting conditions. © 2008 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 18, 283–295, 2008 [ABSTRACT FROM AUTHOR]

Aim To assess residual psychomotor and cognitive effects of a modified-release formulation of zolpidem (zolpidem-MR), developed to provide sustained hypnotic efficacy during the whole night, compared with placebo and flurazepam. Methods Twenty-four healthy elderly volunteers received four study treatments (zolpidem-MR 6.25 mg and 12.5 mg, placebo and flurazepam 30 mg) using a randomized, cross-over, double-blind design. Residual psychomotor and cognitive effects were assessed with a psychometric test battery. Quality of sleep and residual effects were evaluated subjectively with the Leeds Sleep Evaluation Questionnaire. Results Psychometric performance was significantly impaired with flurazepam but not with zolpidem-MR at either dose. Ease of falling asleep and sleep quality were significantly improved with both doses of zolpidem-MR and with flurazepam. Neither active drug modified perception of well-being on awakening. Conclusion In elderly subjects, zolpidem-MR showed no residual functional impairment in psychometric or cognitive tests sensitive to flurazepam, [ABSTRACT FROM AUTHOR]

Studies of psychopharmacology often use the test of the critical flicker fusion (CFF) threshold as a measure of total information processing. It is true that studies of practice effects have shown that CFF thresholds are remarkably stable within and across multiple days of testing. This study confirms that subjects who undergo CFF testing on sequential days have stable thresholds, but also demonstrates that in subjects who conducted 1 h of motion training per day for 9 days the CFF thresholds increased by an average of 30%. The results show that the perceptual experience of subjects can dramatically alter the CFF thresholds and should be an important consideration in the control of studies employing the CFF as a measure. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Background Critical Flicker Fusion Threshold (CFFT) is a psychophysical threshold and in psychological terms is regarded as a measure of information processing capacity. The test has previously been shown to be a valid and reliable measure of CNS functioning in patients with Alzheimer's disease and may be a useful as a screening measure for the early detection of Alzheimer's disease (AD). Methods Consecutive referrals to the Wakefield Memory Clinic who met DSM-IV criteria for AD or vascular dementia (VaD) were invited to take part in the study. A range of neuropsychological tests and CFFT were administered to the two groups using standardised protocols and the ability of these various tests to distinguish between the two conditions was investigated. Results Forty-six patients were included in the study. Of the various tests, only the descending component of CFFT and word fluency were significantly different in the two groups. In addition, the descending threshold had a sensitivity of 83% and a specificity of 69%. Conclusion CFFT could be useful as a screening instrument for early AD when combined with other measures and could facilitate the decision to commence antidementia treatment at an early stage. Further longitudinal work is needed to establish this. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents a method to fuse measurements from a rigid sensor rig with a stereo vision system and a set of 6 DOF inertial sensors for egomotion estimation and external structure estimation. No assumptions about the sampling rate of the two sensors are made. The basic idea is a common state vector and a common dynamic description which is stored together with the time instant of the estimation. Every time one of the sensor sends new data, the corresponding filter equation is updated and a new estimation is generated. In this paper the filter equations for an extended Kalman filter are derived together with considerations of the tuning. Simulations with real sensor data show the successful implementation of this concept. © 2004 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The possibility of fusion of navigation data obtained by two separate navigation systems (strap-down inertial one and dynamic vision based one) is considered in this paper. The attention is primarily focused on principles of validation of separate estimates before their use in a combined algorithm. The inertial navigation system (INS) based on sensors of medium level quality has been analyzed on one side, while a visual navigation method is based on the analysis of a sequence of images of ground landmarks produced by an on-board TV camera. The accuracy of INS estimations is being improved continuously by optimal estimation of a flying object's angular orientation while the visual navigation system offers discrete corrections during the intervals of presence of landmarks inside the camera's field of view. The concept is illustrated by dynamic simulation of a realistic flight scenario. © 2004 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

In this work we analyze the surface roughness of porous silicon films and show that it is possible to quantify some fine differences in the morphology of different samples and even in different points of the surface of one sample using a novel method of Flicker Noise Spectroscopy (FNS). High informative potential of the method is now illustrated by applying it to the analysis of laterally non-uniform porous silicon films produced by the local anodization of silicon using a point cathode placed in the vicinity of the silicon wafer. The possibilities for future explorations are shown. [ABSTRACT FROM AUTHOR]

Experimental participants were asked to make prospective and retrospective time judgements, for both brief and longer periods of time. It was found that when these tasks were performed in hypnosis, prospective estimates became longer than the actual time period, whereas retrospective judgements became shorter than actual. The effects were the same, whether the periods involved were brief or long. It is proposed that this pattern of results is not satisfactorily explained by the 'Busy Beaver' hypothesis (St Jean, McInnes, Campbell-Mayne and Swainson, 1994). These results are better accounted for by assuming that time judgements are derived from an internal clock, which runs slow during hypnosis. An absence of any effect of hypnosis upon critical flicker fusion (CFF) frequency is taken to rule out a simple physiological explanation for the slow clock. Instead, a tentative account is offered that links the timing effects with recent research in the areas of brain mapping, hallucinations and reality monitoring. Experimental participants were asked to make prospective and retrospective time judgements, for both brief and longer periods of time. It was found that when these tasks were performed in hypnosis, prospective estimates became longer than the actual time period, whereas retrospective judgements became shorter than actual. The effects were the same, whether the periods involved were brief or long. It is proposed that this pattern of results is not satisfactorily explained by the 'Busy Beaver' hypothesis (St Jean, McInnes, Campbell-Mayne and Swainson, 1994). These results are better accounted for by assuming that time judgements are derived from an internal clock, which runs slow during hypnosis. An absence of any effect of hypnosis upon critical flicker fusion (CFF) frequency is taken to rule out a simple physiological explanation for the slow clock. Instead, a tentative account is offered that links the timing effects with recent research in the areas of... [ABSTRACT FROM AUTHOR]

Critical Flicker Fusion Threshold (CFFT) is a psychophysical threshold and, in psychological terms, it is regarded as a measure of information processing capacity. CFFT has previously been shown to be a valid and reliable measure in young healthy volunteers and it also has a long history of use as a psychopharmacological measure in this group. Furthermore, the test satisfies many of the requirements of an ‘ideal’ measure for monitoring change, especially in a psychopharmacological context. Despite this, CFFT has been neglected as a research tool in elderly and Alzheimer's disease (AD) populations and was therefore investigated further in this regard. CFFT in community-based healthy elderly subjects was normally distributed, but CFFT and ascending and descending thresholds were not significantly correlated with age. The difference between ascending and descending thresholds was, however, significantly correlated with age and this relationship appeared to be due almost entirely to a change in the descending threshold. In addition, descending thresholds were found to be significantly greater than ascending thresholds in healthy elderly subjects. In contrast, patients with AD were found to have significantly lower CFFT and descending scores compared with healthy elderly subjects. Interestingly, descending thresholds were significantly lower than ascending thresholds in the patient group, a feature that may be a characteristic of AD. Mean CFFT and ascending and descending thresholds were found to have a high test–retest, split-half and inter-rater reliability, in addition to being significantly correlated with a number of psychometric measures, clinical scales and neuropsychological instruments commonly used to assess patients with AD. CFFT is a quick and simple measure to administer and patients had no difficulty completing the test. Because the measure is a psychophysical threshold, it is free from educational and cultural bias and there are no floor or ceiling effects. From the results of this work, CFFT appears to be a useful research tool in AD. It may be a suitable measure for monitoring cognitive change over time, either in community studies of AD or a clinical trial context, but further work is required. The technique might also contribute to the early detection of AD. This application would be particularly important because it would enable effective pharmacotherapies to be started early during the course of the illness before neuronal damage is too advanced and this would have significant benefits for patients. Copyright © 2000 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The pulsating illumination of visual display units is known to induce systematic changes in saccade extent. In two experiments reported in this paper, we further examined this effect, by looking at the location of pulsations relative to saccade onset. Both saccade extent and velocity were shown to increase as a function of the number of 'in-flight' pulsations. This result indicates that part of the so-called 'flicker effect' originates during the saccade itself. From a more general point of view, the present data suggest that saccadic control can be modulated by intra-saccadic visual stimuli. [ABSTRACT FROM AUTHOR]

The PDP (Plasma Display Panel) is a light-emitting matrix display device using the luminescence of a gas discharge. It has such features as thin depth, wide view angle, freedom from geographical distortion, and high brightness. The gray scale is controlled by a subfield driving method using binary weighted pulse width modulation (LSB to MSB sequences). The subfield method essentially has a flicker problem in displaying moving images. When two similar gray values are displayed in a particular interval (field frequency), the flicker phenomenon appears. In this paper, the time-amplitude comodulation subfield method using RBC (Redundant Binary Code) is proposed. This driving method increases the conventional two-level gray scale {0, 1} to a three-level gray scale {0, 1/2, 1}, combining the light-emitting time and amplitude, and selecting the driving waveform so as not to produce flicker. Even if two similar gray values are displayed alternately in field time, the light-emitting frequency is no longer divided into frame frequencies. The proposed driving method improves flicker compared to the conventional subfield method. © 1999 Scripta Technica, Electr Eng Jpn, 129(1): 46–52, 1999 [ABSTRACT FROM AUTHOR]

Aiming at the quantitative measurement of the fatigue of the television observer, a new practical and simple method of critical flicker frequency (CFF) measurement and analysis is considered. As to the measurement, a method is considered where the CFF at the start of the measurement is used as the initial value and the relative change is measured in a short time with a high accuracy. It is verified experimentally that the measurement by the descending series of the method of limit is suitable. As to the analysis, two methods are compared. One is to normalize the average of measured values of all the observers, and the other is to normalize the measured value of each observer and then to calculate the average. It is shown as a result that the latter can represent more clearly the change of CFF. Then the effectiveness of the proposed method in the measurement of the fatigue of television (TV) observer is examined. CFF of the actual TV image observer is measured, including the binocular three-dimensional (3-D) TV. As a result, it is verified statistically that CFF depends on the observation time and the image display method. The result corresponds well to the subjective evaluation of the fatigue. Thus, it is concluded that CFF can be a useful measure in assessing quantitatively the fatigue of the TV image observer, including the binocular 3-D TV. It is expected that the image quality and the improvement effect of the observation condition can be examined quantitatively. [ABSTRACT FROM AUTHOR]

Previous assessments of spontaneous eyeblink frequency (SEBF) or intertlink intervals (131) have been made over period of 0.5 to 15 mm and average values calculated; the reliability of the methods has not been validated. Video recordings were made of 14 healthy volunteers. aged 20 to 38 years. while silently fixating on a 2 ru distant, 35 mm high target under 350 lux illumination and the traces assessed with an event marker. Significant fluctuations in SEBF or IBI were generally observed, but which did not conform to a minute-by-minute periodicity. Time- dependent trends were uncommon, although uncritical pooling or averaging of data can effectively conceal such fluctuations or trends. Correlation's between SEBF and IBI indicate that eye- blink monitoring over at least 3 mm is required. Simple averaging calculations are not appropriate because of a high chance of non-Gaussian distribution of data. Modal IBI values correlated well with an adjusted modal calculated SEBF which is thus recommended for further use. [ABSTRACT FROM AUTHOR]

Experiments are described in which the steady-state accommodation response versus stimulus curve was measured with an infrared autorefractor for high-contrast stimuli having a 100% square·wave temporal modulation of luminance in the frequency band 1-200 Hz. Slightly more accurate responses were found al frequencies ∼ 50-100 Hz, i.e. above flicker fusion. The relevance of the results to practical situations in which flicker may be experienced is discussed. [ABSTRACT FROM AUTHOR]

If a patternless field is modulated sinusoidally in time so that the luminance change in one eye is in counterphase to that in the other, the resulting flicker appears faster than ii the modulation to both eyes has the same phase. If observers set the frequency and the amplitude or a comparison in-phase field so that it matches a neighbouring counterphase field, modulated at, say. 2.5 × its threshold, they set the frequency to twice the counterphase frequency. and the amplitude to a value that is, for a given frequency, a constant ratio of the modulation of the counterphase field. Counterphase stimulation thus appears to cause an internal second-harmonic signal. However, it is not possible in cancel this by adding a second harmonic component to the stimulus. [ABSTRACT FROM AUTHOR]

Static accommodation responses to sinusoidal grating stimuli that displayed temporal modulations in luminance contrast (i.e. contrast flicker) were measured with a laser speckle optometer. The effects of a variety of temporal waveforms were investigated including square-wave modulations, sinusoidal modulations, and band-pass filtered noise. The effects of altering both the amplitude and the temporal frequency (0.4-30Hz) of the contrast flicker and the spatial frequency of the stimulus (0.77-9.2 c/deg) were also examined. All the flicker waveforms investigated (square wave, sinusoidal and band-pass noise) reduced accommodative accuracy, the effect being most apparent at lower spatial frequencies (0.77-1.15 c/deg). With band-pass filtered noise the effects of flicker were most apparent with frequencies in the range 1-4 Hz, at both lower (0.4 Hz) and higher flicker frequencies (8-32 Hz) accommodation was less affected. It was found that flicker impaired accommodation under conditions where the contrast was at all times suprathreshold. This is incompatible with the proposal that flicker reduces accommodation responses because for part of each flicker cycle the stimulus was below threshold. However, these results are compatible with the alternative hypothesis that flicker impairs the ability of the accommodation system to utilize temporal cues such as those derived from the higher frequency component (1-2 Hz) of accommodative oscillation. [ABSTRACT FROM AUTHOR]

It is well established that a large variety of psychophysical factors influence the critical flicker fusion frequency (CFF). Several recent studies have examined the relationship between CFF and retinal location with confounding and contradictory results. The aim of this study was to determine the CFF for a number of stimulus sizes and luminances in an attempt to evaluate the interactive effects of these parameters and the quadrantic variation in temporal sensitivity. Retinal sensitivity gradients were measured along the two major oblique meridians out to an eccentricity of 50 degrees. CFF profiles for the 1.724 and 0.431 degree targets were shown to decrease with increasing eccentricity more rapidly in the inferior nasal quadrant (superior temporal retina). No significant difference between superior and inferior visual field temporal processing was evident. [ABSTRACT FROM AUTHOR]

Monocular accommodation was measured by a laser optometer while two subjects viewed a letter matrix target illuminated by steady or intermittent (300, 100, 50 and 25 Hz) light and presented at a number of optical distances (0.5, 1.5, 2.5, 3.5 and 4.5 D). At certain rates of intermittent illumination, both above (50 Hz) and below (25 Hz) flicker fusion, an increased accommodation response was found. This increase occurred at all optical distances, except for the distance closest to each subject's dark focus, and resulted in a more accurate accommodation response for one subject, and a less accurate one for the other. Furthermore, for both subjects, evidence of an increase in the amplitude of the fluctuations in accommodation at 50 and 25 Hz was found for the higher stimulus levels. The implications of these findings for the control of accommodation and for practical problems of visual performance in the environment, such as visual discomfort associated with fluorescent lighting and intermittently illuminated visual display units, are discussed. [ABSTRACT FROM AUTHOR]

The concurrent validity of critical flicker fusion threshold (CFFT) and flicker threshold measurement was examined in 23 female and three male patients with primary degenerative dementia of the Alzheimer type (PDDAT). Patients had a mean age of 81.7 ± 6.05 years (range 67-89). Diagnosis of PDDAT was based on the DSM-III-R classification. Both the CFFT and flicker thresholds were found to be highly and significantly correlated with standardized clinical assessment (Global Deterioration Scale), cognitive function (Abbreviated Mental Test) and psychomotor performance (Choice Reaction Time). The implications of these two measures for clinical trial research and the longitudinal assessment of patients with Alzheimer's disease are discussed. [ABSTRACT FROM AUTHOR]

Abstract We examined the possibility that neurons or groups of neurons along the retino‐cortical transmission chain have properties of tuned oscillators. To this end, we studied the resonance properties of the retino‐thalamo‐cortical system of anaesthetized cats by entraining responses with flicker stimuli of variable frequency (2–50 Hz). Responses were assessed from multi‐unit activity (MUA) and local field potentials (LFPs) with up to four spatially segregated electrodes placed in areas 17 and 18. MUA and LFP responses were closely related, units discharging with high preference during LFP negativity. About 300 ms after flicker onset, responses stabilized and exhibited a highly regular oscillatory patterning that was surprisingly similar at different recording sites due to precise stimulus locking. Fourier transforms of these steady state oscillations showed maximal power at the inducing frequency and consistently revealed additional peaks at harmonic frequencies. The frequency‐dependent amplitude changes of the fundamental and harmonic response components suggest that the retino‐cortical system is entrainable into steady state oscillations over a broad frequency range and exhibits preferences for distinct frequencies in the θ‐ or slow α‐range, and in the β‐ and γ‐band. Concomitant activation of the mesencephalic reticular formation increased the ability of cortical cells to follow high frequency stimulation, and enhanced dramatically the amplitude of first‐ and second‐order harmonics in the γ‐frequency range between 30 and 50 Hz. Cross‐correlations computed between responses recorded simultaneously from different sites revealed pronounced synchronicity due to precise stimulus locking. These results suggest that the retino‐cortical system contains broadly tuned, strongly damped oscillators which altogether exhibit at... [ABSTRACT FROM AUTHOR]

Twenty female narcoleptic patients treated with central stimulants (CS) were studied during vigilance tests and psychophysiological recordings of autonomic functions, after 3 days off CS, and during CS treatment. Results were compared with healthy female subjects. Narcoleptics were lower in Critical Flicker Fusion (CFF), but did not differ in choice reaction time or continuous vernier visual acuity. CS improved CFF in the narcoleptic group. Narcoleptics had lower skin conductance (SC) level, but did not differ from normals in SC spontaneous fluctuations or heart rate. CS did not affect SC level or heart rate in the narcoleptic group, but counteracted the decrease in SC spontaneous fluctuations normally seen over a monotonous experimental session. CS reduced low frequency tremor and increased high-frequency tremor in the narcoleptic group. Comparison with anxiety and psychosomatic patients was also performed. The results of the vigilance tests suggested a specific disturbance of time resolution of stimulus input in narcoleptics, not related to lowered arousal, but alleviated by CS. The psychophysiological findings suggested that narcoleptic patients have a lowered habitual arousal as well as a marked tendency to decreases in phasic arousal. Central stimulants appear to improve only the latter. [ABSTRACT FROM AUTHOR]

Critical Flicker Fusion Threshold (CFFT) is now a well established measure in psychopharmacological research in both volunteer and patient populations. This paper examines some of the theoretical aspects of CFFT which investigators should be aware of, and the role of CFFT in psychopharmacological research. It also explores the anatomical and neurophysiological basis of CFFT measurement and discusses the possible application of CFFT as a simple means of detecting early Alzheimer's disease. © 1998 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A double-blind, randomized, four-way crossover study was performed to assess the CNS effects of reboxetine, a unique selective noradrenaline reuptake inhibitor (NRI). Eighteen volunteers received reboxetine (1 or 3 mg), imipramine (75 mg) or placebo at weekly intervals. Pharmaco-electroencephalography was recorded under high- and low-vigilance conditions and spectral difference index, total power and alpha slow-wave index (ASI) were calculated. In addition, skilled performance on psychometric tests and well-being were assessed. Absolute and relative power were relatively unaffected by reboxetine but increased by imipramine. Total power and ASI were unaffected or slightly increased by reboxetine, but reduced by imipramine. Reboxetine and imipramine decreased fronto-central θ and fast β power. In pharmaco-electroencephalography, imipramine showed a left shift in the occipito-temporal lead, with an increase in δ and θ and a decrease in α power. Reboxetine increased α power. Following reboxetine administration, the results in performance tests either did not differ from placebo or were better (Pegboard test). After imipramine, a deterioration in the Steadiness and Pauli test occurred. Critical flicker fusion and Vienna test results were unaltered by either drug. In summary, reboxetine, unlike the tricyclic antidepressant imipramine, has no sedative effects of electroencephalography or on any behavioural variable indicative of a decline in vigilance. Furthermore, reboxetine showed a vigilance-enhancing effect. © 1998 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Three doses of citalopram (10, 20 and 40 mg), and placebo were administered to healthy volunteers for periods of 8 days each. Dothiepin 75 mg was given as an acute dose on days 1 and 8 only, with placebo dothiepin on days 2–7. Subjects were tested on days 1 and 8 of the dosing periods on a battery of psychometric tests. The results showed that citalopram at all doses had no detrimental effects on psychomotor performance. The effect of citalopram on critical flicker fusion (CFF) was to raise thresholds. This indicates an improvement in CNS function, i.e. an elevation of cognitive processing ability, with no evidence of an arousing or alerting effect. The effects were apparent after both acute and sub-chronic dosing. These data are in contrast to those collected for dothiepin, which showed significant impairment of cognitive and psychomotor function on most of the measures employed. The most frequent adverse events reported for citalopram were drowsiness, nausea and headache, with the nausea appearing to be dose dependent. The main adverse events reported for dothiepin were drowsiness, sleepiness and dizziness. The rates of adverse events for all active treatments were not statistically significantly different to placebo. It is concluded that citalopram is relatively free from behavioural toxicity and so represents a significant improvement over the older antidepressant agents such as dothiepin. © 1997 by John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The use of psychometrics in psychopharmacology assumes that subjects are trained to ‘plateau’ performance levels prior to experimental data being collected. Fourteen healthy, naive volunteers were tested on CFF and CRT over a 5-day period. On days 1 and 5 subjects carried out the tests six times, with intervals of 10 min between the trials. On days 2, 3 and 4, the subjects were tested once on both CFF and CRT. CFF scores reached a ‘plateau’ after three trials. There was no effect of time on CFF on either day 1 or 5. There was a significant interaction between day, time and CFF thresholds (F = 3 · 71, p < 0·006) which was probably a result of the method of limits technique used in this CFF task, but there were no significant differences in CFF thresholds between test days. The CRT scores reached a ‘plateau’ after six trials on day 1 and this ‘plateau’ was maintained over the following days. The results show performance ‘plateaus’ on CFF and CRT tests are reached after three trials and four sessions of 20 trials respectively. © 1997 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Measures of variability are rarely quoted in drug studies of psychomotor function. Five rectal studies were therefore analysed to calculate the coefficients of variation for different tests of psychomotor function, both during and between study days. Saccadic eye movement analysis and critical flicker fusion threshold were found to have low coefficients of variation (ranging from 2.7 to 7.1 per cent) while visual analogue rating scales and the digit symbol substitution test were found to have much higher coefficients of variation (ranging from 7.9 to 17.6 per cent). It is suggested that measures of test variability be routinely assessed in psychomotor studies as a check on test methodology. [ABSTRACT FROM AUTHOR]

In this placebo and verum (lorazepam 2 mg) controlled double-blind crossover study the acute effects of Remoxipride 50 mg and 100 mg; Haloperidol 2.5 mg and Thioridazine 50 mg were examined in 18 healthy volunteers. CNS function was assessed using a battery of psychometric measures, viz: Critical Flicker Fusion Threshold (CFFT); Choice Reaction Time (CRT); Tracking Accuracy (RMS) and Peripheral Reaction Time (PRT); Sternberg Memory Scanning (SMS); Word Memory (WM) as well as Line Analogue Ratings of subjective sedation (LARS) and the Leeds Sleep Evaluation Questionnaire (LSEQ). Both doses of remoxipride were associated with a reduction of CFFT: 0.9 Hz for 50 mg and 1.3 Hz for 100 mg. The 100 mg dose caused an increase (impairment) in CRT total time of 38 msec. Haloperidol reduced CFFT, while thioridazine and lorazepam impaired performance on the majority of objective measures, as expected for known sedative drugs. Thioridazine led to hypotension in three subjects, and to subjective sedation (LARS), but no treatment affected responses on the LSEQ administered the morning of the day following treatment. These results show that remoxipride has some depressant effects on CNS function, but that these are less prominent than those of sedative neuroleptics such as thioridazine. [ABSTRACT FROM AUTHOR]

This was a double-blind, placebo-controlled crossover study in 15 healthy female volunteers, it consisted of live sessions. separated by I week wash-out between sessions. The purpose of the trial was to study the potential amnesic and sedative activity of clobazam and lorazepam, and the potential antagonism between these effects under the joint influence of a high noise level and intense intermittent light stimulation (ILS). aimed at increasing the level of alertness. The study drugs were administered as a single daily oral dose. The amnesic and sedative effects were evaluated by objective measurements (digit span. Buschke selective reminding test, critical flicker fusion. reaction time, tapping. mental arithmetic test) and subjective measurements (visual analogue scale and adverse effect questionnaire) before each administration, then I Ft. 2 h. 25 h. 3 h. 4 h and 7 h post-dosing. An analysis of variance according to a balanced Latin square design was performance Clobazam. at a dosage of 10 mg. was devoided of sedative and amnesic effects: at a dosage of 30 mg ii induced only moderate memory disturbances. In contrast. Iorazepam, administered at doses of 1 and 3 mg. produced marked and dose-dependent disturbances of memory, alertness and cognitive functions. The use of visual and sound stimuli, designed to increase the level of alertness, did not counteract the sedative effects induced by lorazepam. [ABSTRACT FROM AUTHOR]

The effects of clobazam on critical flicker fusion threshold (CEFT) and menstrual cycle-related symptomatology were examined in a double-blind placebo-controlled study of 11 normally cycling women. Clobazam 10 mg or placebo was administered in two doses, the evening before and the morning of testing at four points in the menstrual cycle (days 7, 14. 21 and 26). Subjects were tested on CEFT and completed the Menstrual Distress Questionnaire (MDQ) and the Premenstrual Mood Index (PMI). Results showed that clobazam did not disrupt the menstrual cycle rhythm in CFFT. which accords with the non-sedative nature of this drug. The lack of effect of clobazam on subjective indices. Impaired Concentration and Behaviour Change of the MDQ confirms the tack of sedative effects, A general tendency. however, was observed For clobazam to reduce symptom reports on some other MDQ PMI scales in the first half of the cycle and to produce a subsequent exacerbation of symptoms in the second half of the cycle. [ABSTRACT FROM AUTHOR]

The article measures the usefulness of critical flicker-fusion (CFF). Recently it has been suggested that critical flicker-fusion frequency may have prognostic significance for the recovery of mental patients. Since it appeared that lower critical flicker-fusion (CFF) thresholds were more characteristic of recovered than of chronically ill mental patients, it might be expected that those patients whose thresholds were lower at the time of admission would show a better recovery. The investigation revealed that the severely ill patients needed more information, were less cooperative and were more cautious than the less severely ill patients.