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Demersal fishes hauled up from depth experience rapid decompression. In physoclists, this can cause overexpansion of the swim bladder and resultant injuries to multiple organs (barotrauma), including severe exophthalmia ("pop-eye"). Before release, fishes can also be subjected to asphyxia and exposure to direct sunlight. Little is known, however, about possible sensory deficits resulting from the events accompanying capture. To address this issue, electroretinography was used to measure the changes in retinal light sensitivity, flicker fusion frequency, and spectral sensitivity in black rockfish (Sebastes melanops) subjected to rapid decompression (from 4 atmospheres absolute [ATA] to 1 ATA) and Pacific halibut (Hippoglossus stenolepis) exposed to 15 minutes of simulated sunlight. Rapid decompression had no measurable influence on retinal function in black rockfish. In contrast, exposure to bright light significantly reduced retinal light sensitivity of Pacific halibut, predominately by affecting the photopigment which absorbs the green wavelengths of light (≈520-580 nm) most strongly. This detriment is likely to have severe consequences for postrelease foraging success in green-wavelength-dominated coastal waters. The visual system of Pacific halibut has characteristics typical of species adapted to low light environments, and these characteristics may underlie their vulnerability to injury from exposure to bright light. [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]

Purpose: To study the quality of the visual field areas that were regained after training. In those areas, we measured some of the elementary visual properties that make up the quality of visual functioning in daily-life. This was to provide information about whether the functional visual field had been enlarged. Methods: Patients with visual field defects after a CVA were trained to detect stimuli presented in the border area of the visual field defect. Then, in the regained areas, we measured visual acuity as a measure for spatial properties. Secondly, to assess for temporal properties we measured critical flicker frequency (CFF). Finally, we studied color vision as a third property of the regained areas. Results: Since we could not predict where restoration of visual fields would occur, we did not present pre-post comparisons. However, despite the fact that training was carried out with simple white light stimuli, we could assess acuity, CFF and color vision in the regained areas. The performance of the patients during testing of the elementary properties appeared to be almost normal when compared to control subjects and comparable to the patient's own ipsilesional visual field. Conclusions: These results support the idea that the regained visual fields that emerged after training are actually used for processing additional visual stimuli other than those used during training. [ABSTRACT FROM AUTHOR]

BACKGROUND AND AIMS: Minimal hepatic encephalopathy (MHE) is associated with poor quality of life and increased work disability in cirrhotic patients. Its prevalence in extrahepatic portal vein obstruction (EHPVO) is not known. We studied the prevalence of MHE in EHPVO patients and utility of critical flicker frequency (CFF) for diagnosing MHE. PATIENTS AND METHODS: Thirty-four EHPVO patients with a history of variceal bleed (age 23.2 ± 11.2 yr, M:F 22:12) diagnosed by either Doppler US or MR angiography, which demonstrated portal vein obstruction and/or portal vein cavernoma, were evaluated by psychometry (number connection tests A, B or figure connection tests A, B) and P300 auditory event-related potential (P300ERP). CFF was also evaluated. MHE was diagnosed by abnormal psychometry (>2 standard deviation [SD]) and/or P300ERP (>2.5 SD). RESULTS: Prevalence of MHE (N = 12) was 35.3%. Of 34 patients, P300ERP was abnormal (380.0 ± 28.9 msec) in 11 (32%), psychometry in 9 (26.4%), both P300ERP and psychometry in 8 (23.5%), and CFF <38 Hz in 7 (21%) patients. Six (67%) patients with abnormal psychometry and 7 (64%) with abnormal P300ERP had CFF below 38 Hz. CFF had sensitivity (75%), specificity (96%), positive predictive value (86%), negative predictive value (93%), and diagnosis accuracy of 91% when compared to patients with both abnormal psychometry and P300ERP. The venous ammonia level was higher in patients with MHE (83.1 ± 29.7 vs 44.7 ± 16.1 μmol/L, P < 0.001) compared to patients without MHE. Spontaneous shunts were present in 67% of patients with MHE compared to 14% of non-MHE patients. MHE was more common in patients with spontaneous shunts (72.7% vs 17.4%, P= 0.001) than without spontaneous shunts. CONCLUSIONS: Prevalence of MHE in EHPVO patients is 35.3%, and CFF alone can reliably diagnose 88% of MHE patients with both abnormal psychometry and P300ERP. However, in view of the relatively low number of patients with MHE, the usefulness of CFF in this setting awaits confirmatory studies. [ABSTRACT FROM AUTHOR]

Abstract: How sensitive are viewers to changes in global image properties across saccades during active real-world scene perception? This question was investigated by globally increasing and/or decreasing luminance or contrast in photographs of real-world scenes across saccadic eye movements or during matched brief interruptions in a flicker paradigm. The results from two experiments demonstrated very poor sensitivity to global image changes in both the saccade-contingent and flicker paradigms, suggesting that the specific values of basic sensory properties do not contribute to the perception of stability across saccades during complex scene perception. In addition, overall sensitivity was significantly worse in the saccade-contingent change paradigm than the flicker paradigm, suggesting that the flicker paradigm is an imperfect simulation of transsaccadic vision. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Background/Aims: Minimal hepatic encephalopathy (MHE) is associated with poorer quality of life and increased work disability. Diagnosis requires cumbersome psychometric and neurophysiological tests. We evaluated critical flicker frequency (CFF) to diagnose MHE. Methods: 156 cirrhotic patients (age 41±12.5yr) without overt encephalopathy (Child A 63, Child B 56, Child C 37) were evaluated by psychometric (number connection tests A, B or figure connection tests A, B), P300 auditory event related potential (ERP) and CFF. MHE was diagnosed by abnormal psychometric and/or P300 auditory event related potential. Results: Prevalence of MHE was 53% with 27 (43%) in Child’s A, 33 (59%) in Child’s B and 23 (62%) in Child’s C cirrhosis (p =NS). Of 83 patients, 72 (87%) had abnormal psychometry, 64 (77%) had abnormal P300 auditory event related potential (ERP) (380.6±28.8ms) and in 66 (80%) CFF was below 39Hz. 60 (83%) patients with abnormal psychometry and 51 (80%) with abnormal P300 auditory event related potential had CFF below 39Hz. CFF sensitivity (96%), specificity (77%) and positive predictive value (68%), negative predictive value (98%) and diagnosis accuracy was 83.3% when compared to patients with both abnormal psychometry and P300ERP. Conclusions: Critical flicker frequency is a simple, reliable and accurate test without any age or literacy dependence for the diagnosis of MHE. [Copyright &y& Elsevier]

Aim: To assess the ability of critical flicker frequency (CFF) and optimal reading speed (ORS) to predict the potential vision in patients with cataract with and without ocular comorbidity. Methods: The two novel tests were compared with two well established potential vision tests (PVTs), the potential acuity meter (PAM) and the laser interferometer (LI). Measurements were made preoperatively in 1 eye of 88 subjects using the battery of 4 PVTs. Postoperative measurements were made with the CFF and the ORS. The subjects studied were consecutive cases over a 12-month period who fulfilled the inclusion and exclusion criteria, and agreed to participate in this study. Results: CFF was the PVT most resistant to the presence of cataract. Both CFF and ORS give a similar predictive precision in the presence of cataract and ocular comorbidity, although CFF seems more precise when the cataract is dense. Conclusions: The PAM and the LI showed a limited clinical capability in predicting postoperative visual acuity, particularly with dense opacities. The CFF shows the most promise as a PVT, particularly with dense cataract. Further evaluation is required for both CFF and ORS. [ABSTRACT FROM AUTHOR]

This paper presents a solution to the cloud removal problem, based in a recently developed image fusion methodology consisting in applying a 1-D pseudo-Wigner distribution (PWD) transformation to the source images and on the use of a pixel-wise cloud model. Both features could also be interpreted as a denoising method centered in a pixel-level measure. Such procedure is able to process sequences of multi-temporal registered images affected with spatial-variant noise. The goal consists in providing a 2-D clean image, after removing the spatial-variant noise disturbing the set of multi-temporal registered source images. This is achieved by taking as reference a statistically parameterized model of a cloud prototype. Using this model, a pixel-wise measure of the noise degree of the source images can be calculated through their PWDs. This denoising procedure enables to choose the noise-free pixels from the set of given source images. The applicability of the method to the cloud removal paradigm is illustrated with different sets of artificial and natural cloudy or foggy images, partially occluded by clouds in different regions. Another advantage of the present approach is its reduced computational cost, once the 1-D case has been preferred instead of a full 2-D implementation of the PWD. [Copyright &y& Elsevier]

Abstract: Harper [D.W. Harper, Signal detection analysis of effect of white noise intensity on sensitivity to visual flicker, Percept. Mot. Skills 48 (1979) 791–798] demonstrated that the visual flicker sensitivity was an inverted U-like function of the intensity of different levels of auditory noise from 50 to 90dB (SPL), without concomitant changes in the response bias. The aim of the present study was to extend these observations in the context of the stochastic resonance, a counterintuitive phenomenon in which a particular level of noise enhances the response of a nonlinear system to a weak input signal. We show psychophysical evidence in a yes–no paradigm for the existence of a stochastic resonance-like phenomenon in the auditory–visual interactions. We show that the detection of a weak visual signal was an inverted U-like function of the intensity of different levels of auditory noise. Nevertheless, for a strong visual signal the auditory noise acts in detriment of the ability of visual detection. Our results suggest that auditory noise could be employed in vision rehabilitation interventions in order to improve the detection of weak visual signals. [Copyright &y& Elsevier]

Purpose: To evaluate the clinical features of strabismus that present after cataract surgery and determine the motor and sensory results after surgical correction of the strabismus. Setting: Department of Ophthalmology, the Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. Methods: Thirty-one patients who had strabismus surgery after cataract surgery between January 1996 and June 2004 were included in the study. The clinical features of strabismus and the factors contributing to successful strabismus surgery results were retrospectively analyzed. Sensory functional tests were performed postoperatively. Results: Fifteen patients (48.4%) had exotropia. The types of cataract included traumatic (35.5%), congenital (32.3%), and senile (25.8%). Prolonged deviation was the statistically significant factor contributing to final alignment (P = .023). Fourteen of 31 patients had stereoacuity measurement; all achieved a stereoacuity of 3000 seconds of arc. Five of the 14 patients (35.7%) had better than 200 seconds of arc. Conclusions: The anatomical results and sensory function of the patients were generally good. When appropriate, surgical intervention to treat strabismus after cataract surgery should be offered, and this is important for restoration of fusion. [Copyright &y& Elsevier]

Purpose: To continue developing a potential vision test based on the critical flicker fusion (CFF) phenomenon by using a brighter stimulus and optimizing its size. Setting: Flinders Eye Centre, Flinders Medical Centre, Flinders University, Bedford Park, South Australia, Australia. Methods: In a prospective nonrandomized study, 225 participants were assigned to 1 of 4 groups: normal, media opacity only, retinal/neural disease only, and cataract plus retinal/neural disease. Participants were recruited if they were 20 years or older but were excluded if they had a neurological disorder or medication known to affect CFF. The CFF thresholds were measured for 3 stimulus sizes: 0.5 degree, 1.0 degree, and 1.5 degrees. Discrimination between groups was tested by analysis of variance and receiver operating characteristic analysis. The relationship between visual acuity and CFF in eyes without media opacity was determined by linear regression and used to predict visual outcomes in 23 eyes having cataract surgery. Results: The mean age of the 225 participants was 71.4 years ± 13.2 (SD); 134 (59.8%) were women. The normal group had 41 participants, and the other 3 groups had 61 participants each. Critical flicker fusion thresholds were reduced in retinal/neural disease but resistant to image degradation from media opacity. The 1.5-degree stimulus had 88% sensitivity and 90% specificity for discriminating groups. Visual acuity after cataract surgery was accurately predicted within ±1 line in 43% of eyes, ±2 lines in 83%, and ±3 lines in 100%. All eyes with poor visual acuity (>0.50 logMAR) or dense cataract (>4.0 Lens Opacities Classification System III) were predicted within ±2 lines. Conclusions: The CFF phenomenon effectively discriminated between subjects with and without retinal/neural disease and accurately predicted visual outcome after cataract surgery. The use of a brighter stimulus enhanced performance in cases of dense media opacity. [Copyright &y& Elsevier]

This paper presents an approach to multi-sensory and multi-modal fusion in which computer vision information obtained from calibrated cameras is integrated with a large-scale sentient computing system known as “SPIRIT”. The SPIRIT system employs an ultrasonic location infrastructure to track people and devices in an office building and model their state. Vision techniques include background and object appearance modelling, face detection, segmentation, and tracking modules. Integration is achieved at the system level through the metaphor of shared perceptions, in the sense that the different modalities are guided by and provide updates to a shared world model. This model incorporates aspects of both the static (e.g. positions of office walls and doors) and the dynamic (e.g. location and appearance of devices and people) environment. Fusion and inference are performed by Bayesian networks that model the probabilistic dependencies and reliabilities of different sources of information over time. It is shown that the fusion process significantly enhances the capabilities and robustness of both sensory modalities, thus enabling the system to maintain a richer and more accurate world model. [ABSTRACT FROM AUTHOR]

Purpose: To investigate whether orthoptic exercises are an effective way to influence the near point of convergence, fusion range and asthenopic symptoms. Methods: Seventy-eight patients met the inclusion criteria of visual acuity 6/9 or better, no history of orthoptic treatment, squint surgery or Meares Irlen syndrome/dyslexia. Information was collected from case records related to diagnosis, near point of convergence, fusion range, prism and cover test measurements and symptoms. Type, duration and frequency of exercises were also recorded. Non-parametric statistics were applied. Results: Patients ranged in age from 5 to 73 years (mean 11.9). Females outnumbered males (46:32). The diagnoses were: decompensating heterophoria (n = 50) or convergence insufficiency (n = 28: primary 27; secondary 1). Exophoria was more common (n = 65), than esophoria (n = 11) or orthophoria (n = 1). Treatments were aimed at improving near point of convergence and/or reduced fusional reserves. The mean treatment period was 8.2 months. Reduced near point of convergence normalized following treatment in 47/55 cases, and mean near point of convergence improved from 16.6 to 8.4 cm (p = 0.0001). Fusional reserves normalized in 29/50. Fusional convergence improved significantly for those with exodeviation (p > 0.0006). Asthenopic symptoms improved in 65 patients. A reduction in deviation of 5 pd or more occurred in 20 patients. Conclusions: Orthoptic exercises are an effective means of reducing symptoms in patients with convergence insufficiency and decompensating exophoria, and appear to target the proximal and fusional components of convergence. Their role in esophoria is unclear and needs further study. [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]

In two experiments we examined the perceived grouping of grids of equidistant dots, which are rapidly modulated over time so that alternate rows or columns are presented out of phase. In Experiment 1, we report that observers were able to group the grids consistent with the temporal modulation reliably, even at contrasts/frequencies for which flicker was not detectable. Moreover, flicker thresholds decreased with stimulus duration, whilst grouping thresholds did not change. In Experiment 2, we examined the impact of visual transients, by measuring performance when, either a mask or a contrast ramp was presented before and after the stimulus. Performance dropped substantially for both conditions, but remained significantly above chance. The results are discussed in relation to the role of temporal correlations in stimulus modulations and visual transients in grouping. [ABSTRACT FROM AUTHOR]

The aim of the study was to verify a hypothesis that critical flicker fusion frequency (CFFF) is season-related because of changes in the intensity and duration of sunlight. CFFF has a wide application in different fields, generally as an indicator of human workload. Therefore, confirmation of previous observations that CFFF is subject to a seasonal rhythm could make theoretical as well as practical sense. The analysis was based on data obtained from 23 male participants, aged 28–60 years. The study lasted 12 months. CFFF was measured with the flicker test. The results of statistical analysis indicate that CFFF changes over time. There are two forms of those changes: a linear trend and oscillations around the trend. Moreover, individual differences in the longitudinal course of CFFF (in trends as well as in oscillations) are observed. The conclusion is that CFFF is subject to longitudinal changes, whose pattern depends on individual differences. Additionally, the individual character of the CFFF changes over time allow the assumption that sunlight is probably not as significant a factor as expected, one that can modify the hypothetical pattern of season-related CFFF fluctuation. The obtained results are important for the methodology of experiments with CFFF and for the interpretation of the results of the flicker test. [ABSTRACT FROM AUTHOR]

Abstract: This paper shows practical examples of the application of a new image fusion paradigm for achieving a 2-D all in-focus image starting from a set of multi-focus images of a 3-D real object. The goal consists in providing an enhanced 2-D image showing the object entirely in focus. The fusion procedure shown here is based on the use of a focusing pixel-level measure. Such measure is defined in the space–frequency domain through a 1-D pseudo-Wigner distribution. The method is illustrated with different sets of images. Evaluation measures applied to artificially blurred cut and pasted regions have shown that the present scheme can provide equally or even better performance than other alternative image fusion algorithms. [Copyright &y& Elsevier]

Flicker is one of the artificial distortions of MPEG-2 coded video caused by the display's gamma characteristics and depends on the picture texture. In order to improve the picture quality, we have developed a technique of reducing the flicker by display gamma simulations in the decoded pictures. The effectiveness was confirmed by experiments. The process is less complex, and the implementation of this technique in digital TV receivers is expected to improve the coded picture quality. [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]

Heterochromatic flicker photometry is commonly used to measure macular pigment optical density (MPOD) in the human retina. It has been proposed, and accepted by many, that the MPOD so measured represents the value at a retinal location corresponding to the edge of the flickering, circular stimulus. We have investigated this proposal by using a series of annular stimuli to determine the MPOD distribution in the central 1.5° of the retina for both eyes of 10 subjects. The MPOD obtained using a 1.5° circular stimulus matched the MPOD distribution at a retinal eccentricity that was always less than the stimulus radius, and averaged, for the 10 subjects, 51% of the stimulus radius. Similar results were obtained using a 1° stimulus. Thus the edge hypothesis is inconsistent with our data. We suggest that involuntary eye movements may be responsible for an apparent edge effect. [Copyright &y& Elsevier]

This paper suggests a simple eye-brain model for light flicker studies and examines the response of such a model to voltage flicker. Calculated flicker curves representing the objectionable threshold of voltage fluctuation were found to match reasonably well the experimental IEEE curves. The model may be used to predict flicker curves for diverse voltage flicker waveforms and for lamps with different time constants and gain factors. [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]

The aim of this study was to examine the facilitating effects of moderate physical exercise on the reaction process to gain a better understanding of the interaction between physiological and cognitive processes. Sixteen participants with specific expertise in decision-making sports performed a double task consisting of choice reaction time while cycling. Signal quality, stimulus-response compatibility and time uncertainty were manipulated. Participants were tested at rest and while cycling at 20% and at 50% of their maximal aerobic power. A mood assessment questionnaire and a critical flicker fusion test were administered before and after the choice reaction time task. The results showed that moderate-intensity exercise (50% maximal aerobic power) improves cognitive performance and that low-intensity exercise (20% maximal aerobic power) enables participants to compensate the negative dual-task effect. [ABSTRACT FROM AUTHOR]

A new model for the correction of flicker in archived film sequences is formulated from first principles. The model takes into account the Hurter--Driffield Density versus log Exposure characteristic to estimate image intensity errors caused by exposure inconsistencies. The model is shown to be highly nonlinear and can accommodate typical grayscale manipulations performed during film-to-video transfers. Motivated by the above model, an algorithm for the estimation of a correction profile across the available grayscale is developed. This profile is obtained from histogrammed gray-level differences between a reference and a degraded frame and is robust with respect to intensity changes due to scene and camera motion. Our results show that the proposed algorithm is very effective toward removing flicker for a variety of archived sequences and compares favorably with other state-of-the-art techniques developed for the same purpose. Additionally, the parametric form of the profile makes it particularly suitable for metadata use and allows fast inversion of the restoration process and recovery of the original material. [ABSTRACT FROM AUTHOR]

Sensor fusion for object tracking has become an active research direction during the past few years. But how to do it in a robust and principled way is still an open problem. In this paper, we propose a new fusion framework that combines both the bottom-up and top-down approaches to probabilistically fuse multiple sensing modalities. At the lower level, individual vision and audio trackers are designed to generate effective proposals for the fuser. At the higher level, the fuser performs reliable tracking by verifying hypotheses over multiple likelihood models from multiple cues. Unlike traditional fusion algorithms, the proposed framework is a closed-loop system where the fuser and trackers coordinate their tracking information. Furthermore, to handle nonstationary situations, the proposed framework evaluates the performance of the individual trackers and dynamically updates their object states. We present a real-time speaker tracking system based on the proposed framework by fusing object contour, color and sound source location. We report robust tracking results. [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]

Presents several cases of strabismus patients with obstacles to fusion. Treatment that may restore single vision in primary position; Cases that demonstrate fusion difficulty associated with various types of field defects.

A target that differs in orientation from neighboring lines and “pops out” has been found to evoke larger responses in cortical V1 cells than lines in the uniform texture surround which do not popout (e.g., Journal of Neurophysiology 67 (1992) 961). If this is more than a coincidence of observations, physiological properties of contextual modulation should be reflected in the perception of salience. In particular, as the differential suppression from texture surround has been reported to be delayed, target salience may be affected by the history of surrounding lines, i.e. by their orientation before the target was presented. This was tested using a feature flicker paradigm in which target and background lines changed their orientations (Experiment 2). All subjects (N=4) indicated a benefit in target detection when target orientation was not previously present in the surround. A control experiment showed that this effect was not caused by the purely temporal aspects of asynchronous stimulus presentation (Experiment 3). To distinguish this effect from other sources of delayed processing, Experiment 1 compared the performance in target detection and target identification tasks, for single-lines and popout targets. All subjects required longer stimulus presentation time to identify the orientation of a single line than to detect the line itself, indicating that orientation coding needs longer processing than encoding stimulus onset. However, most subjects needed even longer presentations to detect popout, suggesting that the processing of orientation contrast adds to this delay. In an appendix, putative response variations of V1 cells to asynchronous flicker are computed. [Copyright &y& Elsevier]

The final stage of the Adelson–Bergen model [J. Opt. Soc. Am. A 2 (1985) 284] computes net motion as the difference between directionally opposite energies EL and ER. However, Georgeson and Scott-Samuel [Vis. Res. 39 (1999) 4393] found that human direction discrimination is better described by motion contrast (Cm)––a metric where opponent energy (EL−ER) is divided by flicker energy (EL+ER). In the present paper, we used a lateral masking paradigm to investigate the spatial properties of flicker energy involved in the normalization of opponent energy. Observers discriminated between left and right motion while viewing a checkerboard in which half of the checks contained a drifting sinusoid and the other half contained flicker (i.e. a counterphasing sinusoid). The relative luminance contrasts of flicker and motion checks determined the checkerboard''s overall motion contrast Cm. We obtained selectivity functions for opponent-motion normalization by measuring Cm thresholds whilst varying the orientation, spatial frequency, or size of flicker checks. In all conditions, performance (percent correct) decayed lawfully as we decreased motion contrast, validating the Cm metric for our stimuli. Thresholds decreased with check size and also improved as we increased either the orientation or spatial-frequency difference between motion and flicker checks. Our data are inconsistent with Heeger-type normalization models [Vis. Neurosci. 9 (1992) 181] in which excitatory inputs are normalized by a non-selective pooling of inhibitory inputs, but data are consistent with the implicit assumption in Georgeson and Scott-Samuel''s model that flicker normalization is localized in orientation, scale, and space. However, our lateral masking paradigm leaves open the possibility that the spatial properties of flicker normalization would be different if opponent and flicker energies spatially overlapped. Further characterization of motion contrast will require models of the spatial, temporal, and joint space–time properties of mechanisms mediating opponent-motion and flicker normalization. [Copyright &y& Elsevier]

While some lower vertebrates, such as zebrafish, do not appear to possess anatomically separate pathways of processing visual information (such as M-pathways and P-pathways), it is believed that separate processing of the visual stimulus (such as luminance and chromatic processing) is a basic requirement of vertebrate vision. In this study, spectral sensitivity functions were obtained from electroretinogram responses to heterochromatic flicker photometry stimuli at several flicker rates, including a low flicker rate (2 Hz), in an attempt to predominately stimulate chromatic processes and a high flicker rate (16 Hz), in an attempt to predominately stimulate luminance processes. In addition, chromatic adaptation was used to isolate and examine the temporal properties of the different cone-type contributions to the electroretinogram response. Spectral sensitivity functions based on responses to heterochromatic stimuli of a low flicker rate appeared to receive both opponent and nonopponent contributions; however, when the stimulus flicker rate was high, spectral sensitivity appeared to be a function of only nonopponent mechanisms. Also, the differences in cone contributions to the spectral sensitivity functions across the different flicker rates appear to be related to the temporal properties of the cone contributions to the electroretinogram response. [ABSTRACT FROM AUTHOR]

Rationale: Serotonin reuptake inhibitors (SSRIs) have been attributed CNS-activating properties based on their ability to elevate the Critical Flicker Fusion (CFF) threshold. However, such an interpretation may be questioned since CFF elevations may also be due to SSRI-induced increases in pupil diameter. Objectives: The effect of pupillary changes on CFF assessment following SSRI administration was investigated in a double blind, crossover study. Methods: During three periods of 15 days, 21 healthy men and women (30–50 years) received sertraline (50 mg on days 1–8, 100 mg on days 9–15), citalopram (20 mg on days 1–8, 40 mg on days 9–15) and placebo. Assessments were done on days 1, 8 and 15 and consisted of pupillary measurements and CFF assessments with and without pupillary control (a 2-mm artificial pupil) using the Leeds Psychomotor Tester. Results: Both SSRIs induced an acute and steady increase in pupil diameters. CFF thresholds were depressed following acute administration of sertraline and citalopram, but this was only apparent when a control was made for the pupillary changes. No CFF effects were seen at day 8, but CFF was again reduced at day 15, with and without control for pupil size. Conclusions: Mydriasis masked the detrimental effects of both SSRIs on CFF during the acute assessments. Our results raise questions regarding the validity of the assessment of the behavioural toxicity of SSRIs based on CFF measurements without ample control for pupil size, especially when these concern acute measurements. [ABSTRACT FROM AUTHOR]

Purpose. In the retina there is general agreement that blood flow adapts in response to different conditions of light and darkness including diffuse luminance flicker. By contrast, regulation of choroidal blood flow in response to different light conditions is still a matter of controversy. Thus, we investigated the effect of diffuse luminance flicker on choroidal and optic nerve head blood flow. Methods. In a group of 14 healthy volunteers, choroidal blood flow and ocular fundus pulsation amplitude were assessed with laser Doppler flowmetry and laser interferometry, respectively. Measurements were done before, during and after stimulation with diffuse luminance flicker. Furthermore, the response of optic nerve head blood flow (ONHBF) to flicker stimulation was measured. Flicker stimuli were generated by a Grass® PS2 photostimulator, stimulating at a frequency of 8 Hz. Flicker light consisted of light flashes at a wavelength below 550nm and produced a retinal irradiance of 140 µW/cm². Blood pressure and pulse rate were measured non-invasively. Paired t-test was used for statistical analysis. Results. ONHBF increased immediately after onset of flicker stimulation. The maximum increase in ONHBF was 30% ± 10% (mean ± SEM, p < 0.008). Both choroidal perfusion parameters were only slightly increased during flicker stimulation, by 2 ± 2% (laser Doppler flowmetry, p < 0.5) and by 4 ± 1% (laser interferometry, p < 0.12). After the end of stimulation all values returned to baseline levels. Conclusion. Our study clearly demonstrates that diffuse luminance flicker increases optic nerve head blood flow. In contrast, increased neural activity in the retina has no effect on choroidal blood flow. Thus, choroidal blood flow appears to be largely independent of alterations in retinal metabolism. [ABSTRACT FROM AUTHOR]

The photopic flicker sensitivity of the chicken was determined using an operant conditioning psychophysical technique. The results show both high- and low-frequency fall-off in the sensitivity response, which peaked around 15 Hz. Flicker sensitivity was determined for a range of stimulus luminance levels, and directly compared to human flicker response measured under similar stimulus conditions. At five luminance levels (10, 100, 200, 500 and 1000 cd/m2), the overall chicken flicker sensitivity was found to be considerably lower than for humans, except at high frequencies. A greater degree of frequency tuning was also found in the chicken response. The critical flicker fusion values were either similar or slightly higher for chickens compared to humans (40.8, 50.4, 53.3, 58.2 and 57.4 Hz vs 39.2, 54.0, 54.0, 57.4 and 71.5 Hz respectively for humans and chickens for increasing stimulus luminance level). A recently proposed model for flicker sensitivity [Vision Research 39 (1999) 533], which incorporates low- and high-pass temporal filters in cascade, was found to be applicable to the chicken response. From this model, deductions were made concerning mechanisms controlling the transfer of temporal information. [Copyright &y& Elsevier]

Describes two cases of unilateral optic neuritis in which relative afferent pupillary defect and decreased critical flicker fusion frequency (CFF) could be detected before visual acuity worsened. Data showing that a dissociation between visual acuity and light reflex or between visual acuity and CFF may occur during the early onset of optic neuritis.

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. [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]

The results are given of an experimental investigation of fluctuation phenomena under conditions of electric arc discharge. Fluctuations are observed whose spectral density is inversely proportional to frequency (1/f noise). Power dependences are revealed of the fluctuation distribution functions. The behavior of spectral density and of distribution functions is associated with the simultaneous occurrence of various nonequilibrium phase transitions. Within the framework of the mean field theory, a mathematical model is suggested of interacting nonequilibrium phase transitions in a distributed system, which predicts the self-organization of the critical state and the generation of fluctuations with diverging spectral characteristics. An adequate agreement is observed between the suggested model and experimental data. © 2001 MAIK “Nauka / Interperiodica”. [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]

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