Critical Flicker Frequency Threshold Research Articles

Trichromatic critical flicker frequency as potential visual test in cataract and macula disease patients.

To investigate the capacity of critical flicker frequency (CFF) in discriminating cataract eyes with or without macula disease using trichromatic flickers, and to develop a model to predict postoperative best corrected visual acuity (BCVA). Patients were divided into two groups based on the presence or absence of macular disease. CFF threshold measurements of red (R-CFF), green (G-CFF), and yellow (Y-CFF) flickers were conducted both preoperatively and postoperatively. A generalized estimating equations model (GEE) was employed to examine the relationship between CFF threshold and 3-month postoperative BCVA. A total of 115 eyes were enrolled, with 59 eyes in the cataract alone group and 56 eyes in the cataract with macular disease group completing the follow-up. R-CFF was found to be consistent before and after cataract removal (P = 0.06), even in cases where OCT was not performed successfully (P > 0.05). Y-CFF showed the highest AUC (0.798) for differentiating ocular comorbidities. According to the GEE model, in patients with a CFF threshold below 26Hz, the odds ratios for achieving a postoperative VA of 20/40 or better were 34.8% for R-CFF, 26.0% for G-CFF, and 24.5% for Y-CFF. CFF emerges as a promising tool for predicting postoperative BCVA, providing valuable supplementary insights when fundus examination is obstructed. R-CFF demonstrates the best resistance to cataracts, while Y-CFF exhibits the highest sensitivity both in identifying macular diseases and predicting postoperative BCVA of 20/40 or better.

A camera-based vehicular visible light communication system using modulated taillights in public road scenarios

This paper proposes a camera-based vehicular visible light communication system using modulated LED taillights for vehicle-to-vehicle communication. The taillights are modulated using on-off keying with a carrier frequency above the critical flicker frequency threshold to appear steady to the human eye and only a camera with a short exposure time can perceive the signal. For receiving the signal, a common camera with a recording frame rate of 30 frames per second was used for the experiments. This limits the throughput of the communication system as only one bit per frame and per individually modulated light source can be transmitted, thus the system is not suitable for transmitting time-critical data. However, the main advantage is that the transmitted data as well as the transmitting vehicle are visible in the camera image, hence we can associate the message and its origin.For the communication between two cooperative autonomous vehicles, e.g., members of a platoon, a secure wireless channel with low latency is needed. To establish an encrypted connection in this main channel our system can be used as an out-of-band channel to verify the identity of the vehicle in front by transmitting a verification code.In this paper we evaluate how the communication quality in terms of bit error rate of the raw data transmission without any error correction methods is influenced by various environmental factors, e.g., communication distance, traveling speed, weather, brightness, etc. This is done by testing our system in controlled scenarios as well as on public roads. The results show that our system is capable of transmitting data with a raw bit error rate of 1.59% on average in platooning relevant situations on the highway in dry conditions. Rain affects the system due to raindrops on the windshield, spray thrown up by vehicles in front, and the windshield wipers occluding the modulated taillights of the transmitting car. In light to medium rain conditions the mean bit error rate is between 2.7% and 6.2%, depending on the intensity.

Influence of night vision goggles with white and green phosphor screens on selected parameters of the eye and fatigue

In modern aviation, in particular in the military context, increasingly many aviation tasks are performed at night. To improve the safety of night flights, night vision goggles (NVGs) are commonly used. This study aimed to examine whether changes in ophthalmic parameters during NVGs use vary depending on phosphor screen type (green or white coded as P43 and P45 respectively). Thirteen participants were studied during a 2-h visual task in a night vision laboratory. Before and after NVGs use, we examined visual acuity, pachymetry, critical flicker-frequency thresholds, stereoscopic and contrast vision. During the use of NVGs, visual acuity, intra-ocular pressure and eye refraction were measured. We found no difference in visual performance between NVGs with green and white phosphor screens; however, NVGs use in general may lead to subjective eye fatigue, neck pain and headaches associated with the time of wearing and the weight of the helmet with additional equipment attached. Practitioner summary Night vision goggles (NVGs), widely used to improve the safety of night flights, were examined according to the applied type of the phosphor screen. There was no difference in visual performance between a white and green phosphor screens; however, NVGs and helmet manufacturers should strive to design these devices to be as lightweight as possible. Abbreviations: ANOVA: analysis of variance; CCT: central corneal thickness; CFF: critical flicker frequency; CNS: central nervous system; CS: contrast sensitivity; FOV: field-of-view; I2: image intensifier; IOP: intra-ocular pressure; NVGs: night vision goggles; SV: stereoscopic vision; VA: visual acuity; VAS: visual analog scale

A dichoptic presentation device and a method for measuring binocular temporal function in the visual system

Recent studies highlight the importance of the temporal domain in visual processing. Critical Flicker Frequency (CFF), the frequency at which a flickering light is perceived as continuous, is a widely used measure for evaluating visual temporal processing. Another important issue to investigate is the cortical interactions arising between the flicker stimuli of both eyes.This paper presents a robust and reliable dichoptic tool for evaluating the CFF threshold in both eyes. This system is based on an analog output device used to independently drive two LEDs through a custom-written MATLAB code (using a laptop PC) for eliciting sinusoidal flickering stimuli and for psychophysically measuring the perceived CFF threshold. The luminance and phases of each LED are individually controlled, enabling the investigation of the effect of phase and luminance differences on binocular summation in subjects with different ocular pathologies. Experiments were designed to evaluate the CFF threshold through a psychophysical test, based on a discrimination task with a stimulus duration of 1 s, based on a temporal alternative forced-choice paradigm. The target stimulus temporal features were modulated using the staircase method. Subjects were requested to discriminate between a target stimulus (a flickering light at various frequencies) and a flickering light at a frequency of 120 Hz, which is significantly higher than the CFF in humans; therefore, it is perceived as constant.One of the main advantages of the introduced dichoptic presentation system is that it enables the visual temporal performance to be measured under both monocular and binocular conditions where phenomena such as temporal binocular summation (BS) can be evaluated. Moreover, the system offers great flexibility by introducing a stimulus phase shift, which enables studying how stimulus timing affects the temporal function at millisecond scale resolution. Our results confirm that no crosstalk exists between the eyes and that the system can reliably separate the stimuli presented to the eyes. Using this set-up, we observed the binocular summation of CFF for low target luminance levels. The CFF was significantly (p = 0.011) higher (5.2%) under binocular compared with monocular viewing conditions. More importantly, introducing an inter - ocular phase shift reduced the binocular CFF in normally sighted subjects. Finally, in amblyopic subjects the amblyopic eye showed a decrease of 3.9 Hz (15%) in CFF, compared with the fellow eye (p = 0.001).The ability to assess binocular temporal performance using a dichoptic display can shed light on visual temporal performance in general, and on binocular temporal summation processes in particular, both for subjects with normal binocular vision and for subjects with impaired binocular vision (e.g., amblyopic subjects). Furthermore, such a presentation set-up may facilitate the development of training paradigms aimed at improving binocular vision performance.In this paper we describe the system and methods in detail and provide all necessary computer code and other details that will enable an easy and quick adaptation of the method by scientists interested in studying the temporal resolution of the visual system in general, and in studying inter-ocular differences or interactions in particular.

Inferior parietal lobule encodes visual temporal resolution processes contributing to the critical flicker frequency threshold in humans.

The measurement of the Critical Flicker Frequency threshold is used to study the visual temporal resolution in healthy subjects and in pathological conditions. To better understand the role played by different cortical areas in the Critical Flicker Frequency threshold perception we used continuous Theta Burst Stimulation (cTBS), an inhibitory plasticity-inducing protocol based on repetitive transcranial magnetic stimulation. The Critical Flicker Frequency threshold was measured in twelve healthy subjects before and after cTBS applied over different cortical areas in separate sessions. cTBS over the left inferior parietal lobule altered the Critical Flicker Frequency threshold, whereas cTBS over the left mediotemporal cortex, primary visual cortex and right inferior parietal lobule left the Critical Flicker Frequency threshold unchanged. No statistical difference was found when the red or blue lights were used. Our findings show that left inferior parietal lobule is causally involved in the conscious perception of Critical Flicker Frequency and that Critical Flicker Frequency threshold can be modulated by plasticity-inducing protocols.

Omega-3 fatty acids improve psychomotor performance via mechanism not related to nitric acid production

Omega-3 fatty acids (ω-3FAs) are essential polyunsaturated fats that protect the brain from cognitive impairment. It increases the activity of endothelial nitric oxide synthetase (eNOS) and thereby increases the nitric acid (NO) production. This study aimed to explore the effect of ω-3FAs on psychomotor performance and to relate this effect to the reactive nitrogen species. This study was conducted in Department of Pharmacology, College of Medicine, Al-Mustansiriya University in Baghdad, Iraq. Twenty healthy subjects, allocated randomly from medical college students, were participated in the single blind clinical trial. Participants were divided into two groups, each of ten subjects to receive either placebo or (ω-3FAs) (750 mg single oral dose daily for 5 days). They were asked to perform psychomotor performance before and after 5 days of treatment, and venous blood was obtained for determination of serum nitric oxide (NO) and peroxynitrite (ONOO). ω-3FAs treated group was significantly different from placebo-treated group in reducing choice and motor reaction times as well as the critical flicker frequency threshold. The serum levels of NO and ONOO in ω-3FAs-treated group did not significantly differ from placebo-treated group. Short term supplementation of ω-3FAs improves the psychomotor performance in young healthy subjects via a mechanism not related to the production of nitric oxide production. Inflorescence is a panicle few flowered and fruit is a capsule. The data of the results obtained were presented and discussed. Key words: Nitrogen species, psychomotor performance, ω-3FAs

Association of SLC6A4 Gene 5-HTTLPR Polymorphism with Parameters of Simple and Complex Reaction Times and Critical Flicker Frequency Threshold in Athletes during Exhaustive Exercise

The incidence of SLC6A4 gene 5HTTLPR polymorphism alleles was evaluated in 223 male athletes engaged in endurance sports, the results were compared with those in 177 male nonathletes. Association between 5-HTTLPR genotypes and the effect of exhaustive treadmill running on simple and complex visual reactions and critical flicker frequency threshold was studied. We found that the incidence of LL genotype was significantly higher in athletes in comparison to nonathletes; after exercise, the velocity of visual reactions and critical flicker frequency increased; exercise did not change the velocity of complex visual reaction in LL-carriers, and increased it in SS-carriers. We conclude that exhausting treadmill running leads to facilitation sensory information processing in athletes and that SS-carriers are more susceptible to the effect of exhaustive treadmill running than LL-carriers.

Critical flicker frequency and related symptoms in mild traumatic brain injury

Primary objective: To determine whether critical flicker frequency (CFF) thresholds are abnormal in individuals with mild traumatic brain injury (TBI) and, if so, if they are correlated with the degree of reported motion and light sensitivity.Methods and procedures: The foveal CFF threshold was assessed in individuals with mild TBI (n = 18) having varying degrees of reported light and motion sensitivity. Mean CFF values were obtained using the ascending and descending psychophysical method of limits with binocular viewing at 40 cm. A 7-item, rating-scale questionnaire was used to assess the degree of light and motion sensitivity. These parameters were also assessed in a large visually-normal, non-TBI cohort.Main outcomes and results: CFF in the mild TBI group was not significantly different across age groups from the visually-normal, non-TBI cohort. However, mean CFF among the mild TBI subjects was significantly higher for the ‘light sensitive’ and ‘motion sensitive’ sub-groups when compared to the ‘not light sensitive’ and ‘not motion sensitive’ sub-groups. The majority of TBI subjects manifested both light and motion sensitivity.Conclusion: CFF was found to be related to the reported degree of light and motion sensitivity in individuals with mild TBI. Neurological disinhibition as a result of brain injury may be causal of the subjective hypersensitivity to light and motion in the presence of normal CFF.

Critical Flicker Frequency Threshold Increment after an Exhausting Exercise

The purpose of this study was to assess the effect of an incremental test to exhaustion on sensory sensitivity using critical flicker fusion (CFF) frequency. The CFF threshold, tympanic temperature, and heart rate were measured before and immediately after an incremental cycling test of maximal oxygen uptake. Deterioration in perceptual processes linked to fatigue were not observed in the present study. On the contrary, results indicated that incremental exhausting exercise increases the sensory sensitivity threshold, thereby suggesting an exercise-induced increase in cortical arousal. Furthermore, the absence of change in subjective judgment threshold suggests that change observed immediately after exercise was not linked to a change of strategy (more cautious or more risky). The CFF threshold protocols appear to be relevant for assessing the effect of exercise on sensory sensitivity and cortical arousal.

Critical Flicker Frequency as a Potential Vision Technique in the Presence of Cataracts

Potential vision testing attempts to predict the visual outcome that might be expected as a result of a cataract operation. This report details the clinical utility of critical flicker frequency (CFF) as a potential vision test (PVT). CFF thresholds were determined in 31 subjects with age-related idiopathic cataract and no other eye disease, 19 subjects with macular disease (MD) and clear ocular media, and 24 age-matched control subjects. In addition, the CFF technique was administered before cataract surgery in 52 patients and compared with the information provided by presurgical case history and ocular examination alone (ophthalmological judgment [OJ]) and results from two commonly used PVTs (the retroilluminated pinhole and the potential acuity meter). CFF thresholds obtained in the nonsurgical cataract group were unrelated to cataract severity and were similar to those in the control group. In contrast, CFF scores were significantly related to visual acuity (VA) in the MD group. In the pre- and postsurgical studies, OJ predicted postoperative VA very well in patients with moderate cataract and normal fundi and better than all the PVTs. OJ performed less well in patients with comorbid eye disease and dense cataracts, when information from the PVTs would probably have been useful. CFF provided the most accurate predictions of postoperative VA in the small sample of patients with dense cataracts. CFF was unaffected by cataract, yet sensitive to MD, and provided useful information about the postoperative visual outcome beyond that obtained through history and ocular examination in patients with dense cataracts.

The use of critical flicker frequency (CFF) as a potential vision test prior to cataract surgery: a pilot study

Background: To determine whether a patient would benefit from cataract surgery, a pre‐operative evaluation of retinal visual function is required. Age‐related macular disease has been reported as the most important factor leading to poor outcome after cataract surgery. The critical flicker frequency (CFF) is a psychophysical test that measures temporal resolution properties in the visual system.Purpose: (1) To evaluate if CFF can be used as a tool to predict visual outcome after cataract surgery. (2) To assess if lens opacities and/or retinal damage affects CFF values. (3) To assess the optimal configuration for the CFF target in relation to stimulus size.Methods: Thirty‐two patients have been included in the pilot study. Subjects were divided into the following categories: cataract, central retinal disease, pseudophakes and cataract after pupil dilatation. CFF threshold measurements were obtained after optimal refraction and visual acuity measurement using a Bailey–Lovie logMAR chart. A staircase method was used to find the CFF threshold. For each subject, three different stimulus sizes were analysed.Results: Critical flicker frequency measurements were unaffected by the presence of cataract (p > 0.05). Pupil dilatation gave slight higher results in patients with cataracts, although this difference was not statistically significant (anovaF = 3.6, p = 0.07). A significant difference for the three targets sizes was found (anovaF = 41.94, p < 0.05). Retinal disease produced an insignificant decrease in CFF (p > 0.05, n = 5).Conclusions: Critical flicker frequency appears to be independent of the image degrading effects of cataract. Comparison of the means for the different conditions studied show a slight decrease in CFF measurement for retinal disease in comparison to the cataract group. However, more subjects are needed to determine the usefulness of CFF as a potential vision test.

Critical flicker frequency responses in visual cortex.

Critical flicker frequency (CFF) threshold is defined as the frequency at which a flickering light is indistinguishable from a steady, non-flickering light. CFF is useful for assessing the temporal characteristics of the visual system. While CFF responses are believed to reflect activity in the central visual system, little is known about how these temporal frequencies are processed in the visual cortex. The current paper estimated the CFF threshold for cells in the rat visual cortex by recording single unit responses to flickering stimuli. Results showed that: (1) there was a broad range of temporal tuning, (2) CFF threshold was lower in simple cells than in complex and hypercomplex cells, and (3) there was no significant difference in CFF threshold between areas 17 and 18.

Temporal processing in deaf signers

The auditory and visual modalities differ in their capacities for temporal analysis, and speech relies on more rapid temporal contrasts than does sign language. We examined whether congenitally deaf signers show enhanced or diminished capacities for processing rapidly varying visual signals in light of the differences in sensory and language experience of deaf and hearing individuals. Four experiments compared rapid temporal analysis in deaf signers and hearing subjects at three different levels: sensation, perception, and memory. Experiment 1 measured critical flicker frequency thresholds and Experiment 2, two-point thresholds to a flashing light. Experiments 3–4 investigated perception and memory for the temporal order of rapidly varying nonlinguistic visual forms. In contrast to certain previous studies, specifically those investigating the effects of short-term sensory deprivation, no significant differences between deaf and hearing subjects were found at any level. Deaf signers do not show diminished capacities for rapid temporal analysis, in comparison to hearing individuals. The data also suggest that the deficits in rapid temporal analysis reported previously for children with developmental language delay cannot be attributed to lack of experience with speech processing and production.

Emergence of a biological rhythm when certain psychological tests are repeated at regular intervals in mentally retarded children

Abstract A heterogenous group of mentally retarded children with I.Q. c. 50 and aged up to 18 years was compared with a group of similarly aged “bright normal” children. Two test procedures were carried out: the Critical Flicker Frequency threshold (CFF) and a maximal speed 15 sec Tapping test. Each test was repeated serially on a minute by minute basis. While significant differences between the groups were found in the maximal speed tapping test average scores, graphing the minute by minute serial test scores against time fore each individual revealed the emergence of a continuously changing series of scores which formed spontaneous cycles of recurrence. The rough graphed plots with their approximately best fit lines were confirmed by auto‐correlation tests, the statistical significance of which was found to be statisfactory. This finding applied equally to the CFF, its deviation about the means and to the tapping test when the combined scores for the right and left hands were considered and the deviatio...

The effect of iris color on critical flicker frequency (CFF).

Summary The purpose of this investigation was to determine the effect of iris color on critical flicker frequency (CFF). CFF thresholds were obtained on 56 male subjects between the ages of 18 and 25 divided into three groups on the basis of iris color (blue, green, and brown). The results indicate that iris color is a statistically significant factor in the determination of CFF (p < .05), though it was emphasized that the effect may have been due to the correlation between iris color and other ocular pigmentation. The blue-eyed group received the highest mean CFF and the brown-eyed group the lowest mean CFF with the mean CFF threshold of the green-eyed group falling between these values.

Effect of Wavelength on the Relationship between Critical Flicker Frequency and Intensity in Foveal Vision*

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.

Critical flicker frequency and EEG alpha: A reliability study

Correlations between resting per-cent time alpha activity and critical flicker frequency threshold (CFF) were sought in psychiatric and volunteer subjects. Test-retest correlations for each test were high, but intercorrelations were insignificant. The lack of relationship is seen as an example of the general failure to relate resting EEG variables with psychological measures; and a more fruitful area of inquiry, that of the relations of brain reactivity (change) with behavioral measures is suggested.