Flicker effect and television compression

Deciphering the Spectrum of Low-Grade Hepatic Encephalopathy in Clinical Practice

critical fusion frequency (CFF), or the flicker fusion threshold, is defined as the critical frequency above which a flickering light source appears steady to the observer (see [Fig. 1][1]). It is known to depend on a number of parameters, namely, intensity of the light source ([5][2], [15][3]),

Text contains a range of different spatial frequencies but the effectiveness of spatial frequencies for normal variations in skilled adult reading ability is unknown. Accordingly, young skilled adult readers showing fast or slow reading ability read sentences displayed as normal or filtered to contain only very low, low, medium, high, or very high spatial frequencies. Reading times and eye movement measures of fixations and saccades assessed the effectiveness of these displays for reading. Reading times showed that, for each reading ability, medium, high, and very high spatial frequencies were all more effective than lower spatial frequencies. Indeed, for each reading ability, reading times for normal text were maintained when text contained only medium, high, or very high spatial frequencies. However, reading times for normal text and for each spatial frequency were all substantially shorter for fast readers than for slow readers, and this advantage for fast readers was similar for normal, medium, high, and very high spatial frequencies but much larger for low and very low spatial frequencies. In addition, fast readers made fewer and shorter fixations, fewer and shorter regressions, and longer forward saccades, than slow readers, and these differences were generally similar in size for normal, medium, high, and very high spatial frequencies, but larger when spatial frequencies were lower. These findings suggest that fast and slow adult readers can each use a range of different spatial frequencies for reading but fast readers make more effective use of these spatial frequencies and especially those that are lower. (PsycINFO Database Record

Critical flicker frequency (CFF) and flicker frequency (FF) are used as indicators for the neurotoxic adverse events of drugs in pharmacology. In this pilot study, we investigated whether patients with epilepsy (PWE) treated with various antiseizure medications (ASM) had significantly different CFFs compared with healthy controls. In addition, we investigated the appropriateness of CFF as an objective measurement tool in PWE who reported adverse events according to the adverse event profile (AEP). Patients receiving regular antiseizure treatment at our center, along with healthy controls, were included in this study. Clinical neurotoxic symptoms, AEP scores, and serum ASM levels were assessed in the PWE group. We used a CFF device that produced a red-black, green-black, blue-black, or white-black flicker. CFF and FF were compared between PWE and healthy controls. In PWE, the correlation of alterations in CFF and FF with AEP results and through ASM serum concentrations was calculated. A total of 33 PWE and 20 healthy controls participated in the study. Except for two light modalities, CFF and FF were significantly reduced in PWE compared with controls. CFF and FF did not differ significantly between PWE with AEP scores >44 points and those with lower scores. CFF and FF levels did not correlate with changes in AEP scores, serum concentrations, or doses. CFF and FF distinguished PWE with ASM from healthy controls. No clinically relevant differentiation was detected in the heterogenous PWE group. To investigate whether CFF and FF may serve as subtle indicators of neurotoxicity or specific modes of action, additional studies are needed in more homogenous PWE groups.

In the present paper, we report two experiments out of series of studies designed to examine various aspects of visual search for icons of differing spatial frequencies. Specifically, the present experiments explore whether there exists a search asymmetry between high and low spatial frequency icons (A amongst B > B amongst A), and whether observers can limit their search to the relevant set of items in a display containing both types of icons. Our results show that a classic search asymmetry does not exist for spatial frequency; that, rather, both types of targets ‘pop out’; that search for a high spatial frequency target amongst high spatial frequency distractors is less efficient than search for a low spatial frequency target amongst low spatial frequency distractors; and that observers are partially able to limit their search to the relevant subset in mixed displays. Implications for the design of touch screen user interfaces are discussed.

The effects of picture manipulations on humans' and pigeons' performance were examined in a go/no-go discrimination of two perceptually similar categories, cat and dog faces. Four types of manipulation were used to modify the images. Mosaicization and scrambling were used to produce degraded versions of the training stimuli, while morphing and cell exchange were used to manipulate the relative contribution of positive and negative training stimuli to test stimuli. Mosaicization mainly removes information at high spatial frequencies, whereas scrambling removes information at low spatial frequencies to a greater degree. Morphing leads to complex transformations of the stimuli that are not concentrated at any particular spatial frequency band. Cell exchange preserves high spatial frequency details, but sometimes moves them into the "wrong" stimulus. The four manipulations also introduce high-frequency noise to differing degrees. Responses to test stimuli indicated that high and low spatial frequency information were both sufficient but not necessary to maintain discrimination performance in both species, but there were also species differences in relative sensitivity to higher and lower spatial frequency information.

An electrophysiological study on the interaction between emotional content and spatial frequency of visual stimuli

Critical flicker frequency fails to disclose brain dysfunction in patients with primary biliary cirrhosis

The precise effect of wavelength on the judgment of critical flicker frequency (CFF) has been a controversial issue for a number of years. Some studies report no effect of wavelength; other studies indicate that wavelength is a basic determiner of the CFF threshold. The purpose of this study was to attempt a resolution of the controversy by means of a systematic and thorough investigation of the problem. The apparatus used was the Fordham calorimeter. By means of monochromators it was possible to deliver various spectral colors with a constant passband of 10 mμ to the subject. The intensity of the light source was controlled by means of neutral tint filters and an optical wedge. Flicker was produced by intercepting the beam of light with a sector disk driven by a Graham variable-speed motor. Eight wavelengths covering most of the range of the visible spectrum were used, and CFF thresholds were obtained at seven different luminance levels in eight experimental sessions for each wavelength. Three subjects with normal color vision were employed.The results showed that the wavelength of the stimulating light changes the slope of the curve relating CFF to log I. The curves at the blue end of the visible spectrum are steeper than those at the red end. Furthermore, the greater the separation between wavelengths, the greater is the probability of a significant difference between slope values. The fact that the slopes of the curves differed with wavelength does not mean that the Ferry–Porter law is invalid, but rather that one should adjust the "constants" of the equation for the particular wavelength being used. Consequently, it can be stated that CFF is a function of the wavelength of the stimulating light. The most explicit interpretation that could be made was that this change reflected some sort of change in the receptor system of the eye.

ABSTRACTCurrent models of visual perception suggest that, during scene categorization, low spatial frequencies (LSF) are rapidly processed and activate plausible interpretations of visual input. This coarse analysis would be used to guide subsequent processing of high spatial frequencies (HSF). The present study aimed to further examine how information from LSF and HSF interact and influence each other during scene categorization. In a first experimental session, participants had to categorize LSF and HSF filtered scenes belonging to two different semantic categories (artificial vs. natural). In a second experimental session, we used hybrid scenes as stimuli made by combining LSF and HSF from two different scenes which were semantically similar or dissimilar. Half of the participants categorized LSF scenes in hybrids, and the other half categorized HSF scenes in hybrids. Stimuli were presented for 30 or 100 ms. Session 1 results showed better performance for LSF than HSF scene categorization. Session 2 scene categorization was faster when participants attended and categorized LSF than HSF scene in hybrids. The semantic interference of a semantically dissimilar HSF scene on LSF scene categorization was greater than the semantic interference of a semantically dissimilar LSF scene on HSF scene categorization, irrespective of exposure duration. These results suggest a LSF advantage for scene categorization, and highlight the prominent role of HSF information when there is uncertainty about the visual stimulus, in order to disentangle between alternative interpretations.

Background and aimsMinimal hepatic encephalopathy (MHE) may impair driving performance and adversely disturbs quality of life. Most drivers with chronic liver disease are not routinely screened for MHE and stay untreated due to the deficiency of standardization of normal values, simple tools, and skills to carry out tests. This study evaluated the usefulness of psychometric tests and critical flicker frequency (CFF) to diagnose MHE among screened drivers with chronic liver disease in Assiut, a city in Upper Egypt.Patients and methodsA total of 100 drivers with chronic liver disease were screened for MHE. Routine investigations were carried out for all. Psychometric tests including number connection tests A, symbol digits test and CFF testing were applied for them. mini mental state examination questionnaires and Beck’s inventory were carried out for those diagnosed as having MHE.ResultsMHE was found among 40%, with 20 (50%) in Child’s A, 11 (27.5%) in Child’s B, and nine (22.5%) in Child’s C cirrhosis (P=0.027), and 45% of those with MHE had bad driving history. Twelve (12%) patients had abnormal psychometric tests. The sensitivity and specificity of receiver operating characteristic curves for CFF in the diagnosis of MHE was 100%, with a cutoff of less than or equal to 38.5 Hz, and the area under the curve was 1.00 (95% confidence interval, 0.964–1.00) (P<0.0001). There was significant reverse correlation between CFF and Child–Pugh score (r=‒0.271, P=0.030).ConclusionOur data revealed a high prevalence of MHE (40%) among drivers with liver cirrhosis. The CFF test is a simple, accurate, and reliable test for diagnosis of MHE, with no age or literacy requirement. Therefore, we suggest to include the CFF test in screening of drivers with chronic liver disease for early discovery and proper management.

Background: The dietary protein restriction that was commonly recommended to hepatic encephalopathy (HE) patients, often leads to malnutrition, whereas malnutrition can deteriorate cirrhosis prognosis. The aims of this study were to find out encephalopathy improvement that was measured by critical flicker frequency (CFF) test and nutritional status by measuring prealbumin level after L-Ornithine L-Aspartate (LOLA) treatment with adequate calories and protein intake in patients with HE. Method: Patients with liver cirrosis who visited Cipto Mangunkusumo hospital on June-October 2009 was evaluated by CFF test using HEPAtonormTM device. Encephalopathy was defined when CFF < 39 Hz. Nutritional status was measured by the mid-arm muscle circumference (MAMC) and was stated as malnutrition when the MAMC was below the 15th percentile. Patients had been treated by 3 x 6 mg LOLA granules for 2 weeks, and adequate calories and protein intake with branched-chain amino acid (BCAAs) substitution. The change of encephalopaty was evaluated by the CFF test and the nutritional status by measuring prealbumin blood level. Results: There were 17 patients with liver cirrhosis who fulfilled the inclusion criteria. The mean CFF Result increased from 34.1 ± 2.5 Hz to 36.5 ± 2.9 Hz after LOLA treatment with the adequate calories and protein intake including BCAAs substitution, which was statistically significant (p < 0.001) compared to before treatment. The prealbumin level also increased significantly compared before treatment, i.e. from 5.4 ± 2.1 mg/dL to 6.4 ± 2.6 mg/dL, p = 0.008. Conclusion: HE patients with malnutrition could be given adequate calorie and protein with BCAAs substitution to improve their nutritional status, and LOLA granules for the improvement of HE. Keywords: minimal hepatic encephalopathy, malnutrition, CFF, LOLA, prealbumin, BCAAs

PurposeThe spatial frequency (SF) characteristics of accommodation in children are not well understood. In this study, we measured accommodative responses to grating targets to investigate the SF dependence of accommodation in children.MethodsThe effects of SF and contrast on the accommodative system were evaluated in two groups of children, including 22 with emmetropia and 20 with myopia. The contrast detection thresholds at five SFs were measured using a near-contrast sensitivity function test. The accommodative responses to grating targets with low (1.5 cycles per degree [cpd]), medium (6 cpd), and high (18 cpd) SFs were measured with a Grand Seiko WAM-5500 in dynamic mode for 30 seconds under standard and detection threshold contrast conditions. The accommodative lag and accommodative microfluctuations (AMFs) were compared between the two groups.ResultsUnder standard contrast conditions, no significant difference was found in the accommodative lag across SFs (F = 2.03, P = 0.14) or between the two groups (F = 3.57, P = 0.07). The AMFs were lowest at 6 cpd in emmetropia group (F = 6.51, P = 0.003) and in total (F = 10.82, P < 0.001). Children in emmetropia group showed greater AMFs at high SFs under detection threshold contrast conditions than under standard contrast conditions (P < 0.05).ConclusionsThis study demonstrated that the instability of accommodation was SF dependent in children. The AMFs in children were smallest at the medium SF for standard contrast grating targets. Myopic children are less sensitive to the low-contrast-induced blur for high SFs than emmetropic children.Translational RelevanceThis study provides a possibility to stabilize accommodative response of children by transforming SF components of fixation targets.

Glare visual acuity and contrast sensitivity are important indicators of visual quality. Studies have shown that the glare visual acuity and contrast sensitivity in dry eye patients tend to degenerate, further affecting their quality of life. The objective of this study was to investigate the effect of notch filters on glare VA and contrast sensitivity in patients with dry eye or with dry eye syndrome. 36 subjects in the 20‒65 age group were diagnosed as having dry eye disease or perceived dry eye syndromes themselves who were included after the initial screening with the OSDI questionnaire, and one was subsequently excluded as they had undergone retinal detachment surgery. Finally, 35 subjects (14 male and 21 female) with a mean age of 40.66 ± 15.62years participated in this study. All subjects wore their habitual prescriptions and four different filter lenses (namely 480, 620, dual 480 & 620 notch filter, and FL-41 tinted lens), and measured the parameters of glare visual acuity and contrast sensitivity using CSV-1000 and sine wave contrast test (SWCT), respectively. Student t-test and Repeated measurement analysis (R-ANOVA) were utilized by using SPSS 26.0 software. A dual-wavelength 480 & 620nm optical notch filter had a significant anti-glare effect decreasing glare disabilities or discomfort, and leading to better visual quality, the same effect was also shown on a 480nm notch filter lens. All participants showed a significant difference among the baseline, three notch filters (480nm, 620nm, dual-wavelength 480 & 620nm), and FL-41 tinted lens were used on SWCT_A (1.5cpd, F = 3.054, p = 0.019) and SWCT_E (18cpd, F = 2.840, p = 0.049); but did not show statistical different on SWCT_B (3cpd, F = 0.333, p = 0.771), SWCT_C (6cpd, F = 1.779, p = 0.159), and SWCT_D (12cpd, F = 1.447, p = 0.228). The baseline showed the best visual performance on CS at a low spatial frequency (SWCT_A, 1.5cpd), any filter might reduce the contrast sensitivity at low spatial frequencies in the clinical trial, whereas 480nm notch filter showed the best effectiveness on CS at a high spatial frequency (SWCT_E, 18cpd), the FL-41 lens that also filters out the 480nm band does not achieve the same effect. Moreover, patients with dry eye or those older than 40years old preferred optical multilayer notch filters to FL-41 tinted lenses. The 480- & 620-nm dual-wavelength and 480-nm single-wavelength notch filters have the best effect on the glare visual acuity and contrast sensitivity (CS) at high spatial frequencies in dry eye patients. The 620-nm notch filter performs better in CS at low and mid-low spatial frequencies; the FL-41 tinted lens performs poorly for glare VA and CS spatial frequencies examination. Patients with glare disabilities or CS disturbance at high spatial frequencies may choose a 480-nm notch filter lens, and patients who have CS disturbance at low spatial frequencies may consider a 620-nm notch filter for the prescription.

BACKGROUND: In daily clinical practice, the detection of HE is still less represented but strongly required. Therefore, we assessed the EncephalApp (Stroop-Test) in a German population by standard diagnostic procedures such as the Critical Flicker Frequency (CFF) and the PHES-Test (Psychometric Hepatic Encephalopathy Score). One of the purposes of the trial was finding a Cut-Off value for the EncephalApp in the German population. METHODS: 81 patients with liver cirrhosis underwent the testing of the CFF, the PHES-Test and the EncephalApp. A control group of 25 healthy subjects were examined in the same manner. The CFF was considered pathological with &lt;39 Hz and the PHES-Test with &lt; - 4 value points. The On-plus-Off Time of the EncephalApp was compared to the results of the CFF and the PHES-Test. Different Cut-Offs of the On-plus-Off Time were analyzed. Within these HE groups, the mean values of the PHES-Test, the CFF and the On-plus-Off Time of the EncephalApp were compared and the ROC Analysis (receiver operating characteristic) was conducted. Laboratory parameters, clinical data, and further imaging techniques were also included and compared. RESULTS: The study group (n = 81) included 52 men and 29 women (62.8 years ± 12.5). For the evaluation of the EncephalApp, different Cut-Off values were determined and their specificity and sensitivity were calculated. The comparative parameter was the result of the PHES-Test. Through the creation of a ROC curve, the AUC (area under the curve) showed that the Cut-Off time of &gt;224 sec with 0.803 is the most efficient with better sensitivity (79%) and specificity (82%). Other Cut-Off values showed lower sensitivities and higher false negative values. CONCLUSIONS: After evaluating the specificity, sensitivity and AUC the most efficient Cut-Off value for the On-plus-Off Time in the EncephalApp is &gt;224 sec. In comparison with the CFF and the PHES testing, most of the patient withdrawals (especially in higher grade HE) within the study were registered by the EncephalApp. The EncephalApp is a valid and quick method to diagnose minimal HE but has its limitations in the grading between HE grade 1 and 2.