Relative Changes In Light Intensity Research Articles

Self-calibrated pulse oximetry algorithm based on photon pathlength change and the application in human freedivers.

Pulse oximetry estimates the arterial oxygen saturation of hemoglobin () based on relative changes in light intensity at the cardiac frequency. Commercial pulse oximeters require empirical calibration on healthy volunteers, resulting in limited accuracy at low oxygen levels. An accurate, self-calibrated method for estimating is needed to improve patient monitoring and diagnosis. Given the challenges of calibration at low levels, we pursued the creation of a self-calibrated algorithm that can effectively estimate across its full range. Our primary objective was to design and validate our calibration-free method using data collected from human subjects. We developed an algorithm based on diffuse optical spectroscopy measurements of cardiac pulses and the modified Beer-Lambert law (mBLL). Recognizing that the photon mean pathlength () varies with related absorption changes, our algorithm aligns/fits the normalized (across wavelengths) obtained from optical measurements with its analytical representation. We tested the algorithm with human freedivers performing breath-hold dives. A continuous-wave near-infrared spectroscopy probe was attached to their foreheads, and an arterial cannula was inserted in the radial artery to collect arterial blood samples at different stages of the dive. These samples provided ground-truth via a blood gas analyzer, enabling us to evaluate the accuracy of estimation derived from the NIRS measurement using our self-calibrated algorithm. The self-calibrated algorithm significantly outperformed the conventional method (mBLL with a constant ratio) for estimation through the diving period. Analyzing 23 ground-truth data points ranging from 41% to 100%, the average absolute difference between the estimated and the ground truth is for our algorithm, significantly lower than the observed with the conventional approach. By factoring in the variations in the spectral shape of relative to , our self-calibrated algorithm enables accurate estimation, even in subjects with low levels.

Cooperative and asynchronous stereo vision for dynamic vision sensors

Dynamic vision sensors (DVSs) encode visual input as a stream of events generated upon relative light intensity changes in the scene. These sensors have the advantage of allowing simultaneously high temporal resolution (better than 10 µs) and wide dynamic range (>120 dB) at sparse data representation, which is not possible with clocked vision sensors. In this paper, we focus on the task of stereo reconstruction. The spatiotemporal and asynchronous aspects of data provided by the sensor impose a different stereo reconstruction approach from the one applied for synchronous frame-based cameras. We propose to model the event-driven stereo matching by a cooperative network (Marr and Poggio 1976 Science 194 283–7). The history of the recent activity in the scene is stored in the network, which serves as spatiotemporal context used in disparity calculation for each incoming event. The network constantly evolves in time, as events are generated. In our work, not only the spatiotemporal aspect of the data is preserved but also the matching is performed asynchronously. The results of the experiments prove that the proposed approach is well adapted for DVS data and can be successfully used for disparity calculation.

The Neurospora photoreceptor VIVID exerts negative and positive control on light sensing to achieve adaptation

The light response in Neurospora is mediated by the photoreceptor and circadian transcription factor White Collar Complex (WCC). The expression rate of the WCC target genes adapts in daylight and remains refractory to moonlight, despite the extraordinary light sensitivity of the WCC. To explain this photoadaptation, feedback inhibition by the WCC interaction partner VIVID (VVD) has been invoked. Here we show through data-driven mathematical modeling that VVD allows Neurospora to detect relative changes in light intensity. To achieve this behavior, VVD acts as an inhibitor of WCC-driven gene expression and, at the same time, as a positive regulator that maintains the responsiveness of the photosystem. Our data indicate that this paradoxical function is realized by a futile cycle that involves the light-induced sequestration of active WCC by VVD and the replenishment of the activatable WCC pool through the decay of the photoactivated state. Our quantitative study uncovers a novel network motif for achieving sensory adaptation and defines a core input module of the circadian clock in Neurospora.

Clouds, shadows or twilight? Mayfly nymphs recognise the difference

Summary1. We examined the relative changes in light intensity that initiate night‐time locomotor activity changes in nymphs of the mayfly, Stenonema modestum (Heptageniidae). Tests were carried out in a laboratory stream to examine the hypothesis that nymphs increase their locomotion in response to the large and sustained reductions in relative light intensity that take place during twilight but not to short‐term daytime light fluctuations or a minimum light intensity threshold. Ambient light intensity was reduced over a range of values representative of evening twilight. Light was reduced over the same range of intensities either continuously or in discrete intervals while at the same time nymph activity on unglazed tile substrata was video recorded.2. Nymphs increased their locomotor activity during darkness in response to large, sustained relative light decreases, but not in response to short‐term, interrupted periods of light decrease. Nymphs did not recognise darkness unless an adequate light stimulus, such as large and sustained relative decrease in light intensity, had taken place.3. We show that nymphs perceive light change over time and respond only after a lengthy period of accumulation of light stimulus. The response is much lengthier than reported for other aquatic organisms and is highly adaptive to heterogeneous stream environments.

Control Mechanisms of Diel Vertical Migration: Theoretical Assumptions

We explore control mechanisms underlying the vertical migration of zooplankton in the water column under the predator-avoidance hypothesis. Two groups of assumptions in which the organisms are assumed to migrate vertically in order to minimize realized or effective predation pressure (type-I) and to minimize changes in realized or effective predation pressure (type-II), respectively, are investigated. Realized predation pressure is defined as the product of light intensity and relative predation abundance and the part of realized predation pressure that really affects organisms is termed as effective predation pressure. Although both types of assumptions can lead to the migration of zooplankton to avoid the mortality from predators, only the mechanisms based on type-II assumptions permit zooplankton to undergo a normal diel vertical migration (morning descent and evening ascent). The assumption of minimizing changes in realized predation pressure is based on consideration of DVM induction only by light intensity and predators. The assumption of minimizing changes in effective predation pressure takes into account, apart from light and predators also the effects of food and temperature. The latter assumption results in the same expression of migration velocity as the former one when both food and temperature are constant over water depth. A significant characteristic of the two type-II assumptions is that the relative change in light intensity plays a primary role in determining the migration velocity. The photoresponse is modified by other environmental variables: predation pressure, food and temperature. Both light and predation pressure are necessary for organisms to undertake DVM. We analyse the effect of each single variable. The modification of the phototaxis of migratory organisms depends on the vertical distribution of these variables.

The photobehaviour of Daphnia spp. as a model to explain diel vertical migration in zooplankton

ABSTRACTMany pelagic animal species in the marine environment and in lakes migrate to deeper water layers before sunrise and return around sunset. The amplitude of these diel vertical migrations (DVM) varies from several hundreds of metres in the oceans to approx. 5–20 m in lakes. DVM can be studied from a proximate and an ultimate point of view. A proximate analysis is intended to reveal the underlying behavioural mechanism and the factors that cause the daily displacements. The ultimate analysis deals with the adaptive significance of DVM and the driving forces that were responsible for the selection of the traits essential to the behavioural mechanism. The freshwater cladoceran Daphnia is the best studied species and results can be used to model migration behaviour in general. Phototaxis in Daphnia spp., which is defined as a light‐oriented swimming towards (positive phototaxis) or away (negative phototaxis) from a light source, is considered the most important mechanism basic to DVM. A distinction has been made between primary phototaxis which occurs when light intensity is constant, and secondary phototaxis which is caused by changes in light intensity. Both types of reaction are superimposed on normal swimming. This swimming of Daphnia spp. consists of alternating upwards and downwards displacements over small distances. An internal oscillator seems to be at the base of these alternations. Primary phototaxis is the result of a dominance of either the upwards or the downwards oscillator phase, and the direction depends on internal and external factors: for example, fish‐mediated chemicals or kairomones induce a downwards drift. Adverse environmental factors may produce a persistent primary phototaxis. Rare clones of D. magna have been found that show also persistent positive or negative primary phototaxis and interbreeding of the two types produces intermediate progeny: thus a genetic component seems to be involved. Also secondary phototaxis is superimposed on normal swimming: a continuous increase in light intensity amplifies the downwards oscillator phase and decreases the upwards phase. A threshold must be succeeded which depends on the rate and the duration of the relative change in light intensity. The relation between both is given by the stimulus strength versus stimulus duration curve. An absolute threshold or rheobase exists, defined as the minimum rate of change causing a response if continued for an infinitely long time. DVM in a lake takes place during a period of 1‐5‐2 h when light changes are higher than the rheobase threshold. Accelerations in the rate of relative increase in light intensity strongly enhance downwards swimming in Daphnia spp. and this enhancement increases with increasing fish kairomone and food concentration. This phenomenon may represent a ‘decision‐making mechanism’ to realize the adaptive goal of DVM: at high fish predator densities, thus high kairomone concentrations, and sufficiently high food concentrations, DVM is profitable but not so at low concentrations. Body axis orientation in Daphnia spp. is controlled with regard to light‐dark boundaries or contrasts. Under water, contrasts are present at the boundaries of the illuminated circular window which results from the maximum angle of refraction at 48–9° with the normal (Snell's window). Contrasts are fixed by the compound eye and appropriate turning of the body axis orients the daphnid in an upwards or an obliquely downwards direction. A predisposition for a positively or negatively phototactic orientation seems to be the result of a disturbed balance of the two oscillators governing normal swimming.Some investigators have tried to study DVM at a laboratory scale during a 24 h cycle. To imitate nature, properties of a natural water column, such as a large temperature gradient, were compressed into a few cm. With appropriate light intensity changes, vertical distributions looking like DVM were obtained. The results can be explained by phototactic reactions and the artificial nature of the compressed environmental factors but do not compare with DVM in the field.A mechanistic model of DVM based on phototaxis is presented. Both, primary and secondary phototaxis is considered an extension of normal swimming. Using the light intensity changes of dawn and the differential enhancement of kairomones and food concentrations, amplitudes of DVM could be simulated comparable to those in a lake.The most important adaptive significance of DVM is avoidance of visual predators such as juvenile fish. However, in the absence of fish kairomones, small‐scale DVMs are often present, which were probably evolved for UV‐protection, and are realized by not enhanced phototaxis. In addition, the ‘decision‐making mechanism’ was probably evolved as based on the enhanced phototactic reaction to accelerations in the rate of relative changes in light intensity and the presence of fish kairomones.

Quantitative effects of fish kairomones and successive light stimuli on downward swimming responses of Daphnia

Swimming in response to light change is considered the proximate mechanism underlying diel vertical migration. This behavioural mechanism is supposed to be tuned to the adaptive needs under natural conditions by the modifying influence of environmental variables, such as predator kairomones. We investigated to what extent fish kairomone level affects downward swimming in response to a continuous relative light intensity increase. At the higher kairomone levels Daphnia had significant higher displacement velocities. Thus, kairomone was perceived quantitatively and behaviour was altered correspondingly. Because the absolute difference in displacement velocity between treatments was small, we assumed that kairomone concentration could not explain much of the seasonal variability in diel vertical migration patterns in Lake Maarsseveen. Therefore, we hypothesised that besides swimming in response to relative changes in light intensity, other aspects of phototaxis were important also. The natural light intensity increase at early morning consists of a continuous increase in the rate of the relative light intensity change, which reach a maximum about 30–45 min before sunrise. After this maximum, the rates of the relative light intensity increase decrease again. Thus far, it was assumed that successive changes in light intensity acted independent on the swimming reaction of the daphnids. In this paper, we present results of experiments with Daphnia swimming in response to a combination of a continuous and an instantaneous increase in light intensity. A continuous relative light increase preceding an instantaneous increase in light intensity (step) enlarged the downward displacement velocity of Daphnia markedly. Hence, successive light stimuli did not act independently. With growing relative light increase rates preceding the step, the displacement velocity increased also. Moreover, the presence of fish kairomone further increased the velocity in response to the light change. Therefore, the rate of the relative change in light intensity is an incomplete description of the stimulus for diel vertical migration behaviour.

Diurnal residence of the larger stages of the calanoid copepod Acartia tonsa in the anoxic monimolimnion of a tropical meromictic lake in New Guinea

We studied diel vertical migration of the calanoid copepod Acartia tonsa in a coastal meromictic lake (Lake Nagada, Papua New Guinea). During the day, the animals migrate several metres below the oxycline to just above or into the sediments, and remain in anoxic water. Vertical migration patterns differ between ontogenetic stages; adults and larger copepodites do not occur in appreciable numbers in the water samples during the day (deepest sample taken at ~0.5 m above the sediment). Around sunset, the larger copepodites gradually appear in the water column, reaching the near-surface food layer (0-2 m) only well after sunset. Our results suggest that the evening ascent of the copepods in this tropical lake is related to relative changes in light intensity, and that there are age- and sex-related differences in the responses to these stimuli.

Changes in Light Intensity and Diel Vertical Migration: a Comparison of Marine and Freshwater Environments

Proximate aspects of diel vertical migration in the freshwater and marine environment are compared using data from the literature. Examples of migrations in both environments are presented, from which it is concluded that relative changes in light intensity before sunrise and after sunset are primary causes of migrations. Experiments have shown that photoreactive behaviour is enhanced in the presence of predators but inhibited by shortage of food. These factors are called secondary causal factors. A hierarchy of causal factors is proposed. In lakes fish exudates suffice but in marine biotopes like bays, it is possible that fish have to be actually present for enhancement to take effect. To what extent the presented stimulus-response mechanism holds for mesopelagic animals in oceans is discussed on the basis of vertical distributions of euphausiids.

Increased phototaxis in the field leads to enhanced diel vertical migration

Downward and upward displacement velocity of diel vertical migration in Lake Maarsseveen by the hybrid Daphnia galeata × hyalina, was correlated with the relative change in light intensity at dawn and dusk, indicating a phototactic basis for these migrations. The significance of the regression function increased over a period of 4 yr. Changes in environmental factors such as water transparency and food concentration are not responsible.

Diel vertical migration ofEudiaptomus gracilis during a short summer period

Several aspects of a diel vertical migration (DVM) of adultEudiaptomus gracilis in Lake Maarsseveen (The Netherlands) are described. The period of DVM lasted from the end of May until the middle of August. On May 21, 1989, the population was found divided into a deep dwelling part and a part in the upper five meter. Large shoals of juvenile perch were observed in the open water for the first time. On June 7, the whole population was down below 10 m and concentrated in a zone of high chlorphyll-a concentrations. One week later, a regular DVM was performed. The amplitude of this migration gradually decreased towards the end of the migration period. The ascent in the evening and the descent in the morning took place after sunset and before sunrise, respectively. The movements coincided with high relative changes in light intensity. Population size increased rapidly during the period of DVM but decreased again before the end of this period.

Light control of evening vertical migrations by Chaoborus punctipennis larvae

Light control of vertical migration was examined with sonar recordings of the evening migration of Chaoborus punctipennis larvae. Frequently, a slow, upward drift in the afternoon preceded the rapid ascent of larvae. Movement out of the sediments was not consistently related to a fixed light intensity or rate of relative light change. Light intensities were variable at the initiation of and during the upward migration, whereas the beginning of rapid ascent was closely correlated with the timing of a relative light change of 1.7 ×10−1 s−1. The close relationship between the rate of relative change in light intensity and the rate of upward movement including the afternoon drift supports the stimulus‐velocity hypothesis that once larvae leave the sediments the speed and direction of the migration pattern is primarily regulated by relative light changes. Second‐ and third‐instar larvae migrated at higher light intensities than fourth instars, but did not differ in their rate of movement in relation to light change.

Effects of Lighting Program During the Growing Period and Dietary Fat During the Laying Period on Broiler Breeder Performance

In two experiments, broiler breeders were grown in either of two lighting regimens, fed diets without added fat, and then fed diets with or without 5% added poultry fat during the subsequent laying period. In Experiment 1 half the birds were subjected to decreasing daylength using daylight (800 lx) and half were subjected to 9 h of incandescent light (20 lx) to 20 wk of age. In Experiment 2 the lighting regimen was either an 8-h photoperiod supplied by daylight (800 lx) or an 8-h photoperiod supplied by incandescent light (20 lx) to 20 wk of age.Added dietary fat produced significantly higher egg weight (Experiments 1 and 2), egg production (Experiment 2), and significantly lower fertility and hatchability of fertile eggs (Experiments 1 and 2). Short photoperiods (8 or 9 h) provided by incandescent light produced significantly higher fertility (Experiments 1 and 2) and hatchability of fertile eggs (Experiment 2). and significantly lower egg specific gravity, shell percentage (Experiment 1), egg weight, and eggshell weight (Experiment 2). Effects on fertility may be related to higher female body weight during lay due to daylight rearing or added fat, or relative changes in light intensity at photostimulation.

The sensitivity of Daphnia magna straus to changes in light intensity at various adaptation levels and its implication in diurnal vertical migration

1. The threshold value of the absolute change in light intensity ΔI necessary to evoke a phototactic reaction in Daphnia magnaStraus was estimated at various adaptation intensities between 3.4×100 and 3.4×104 erg cm−2sec−1. 2. The results point at the existence of two distinct functions: for I < 40 erg cm−2 sec−1: ΔI = 0.21I0.49; I ≧ 40 erg cm−2 sec−1: ΔI= 0.03I1.06. 3. Starting at 40 erg cm–2 sec−1 the threshold of the relative change in light intensity increases for lower as well as for higher adaptation intensities. 4. Neither Weber's Law nor Hecht's exponential function (Hecht, 1934) seem to cover the results sufficiently. These are, however, highly comparable with those obtained by Heberdey and Kupka (1942) working with Daphnia pulexDe Geer. Our interpretation differs from theirs, however. We think of two different phototactic mechanisms. 5. The significance of the results for diurnal vertical migration of Zooplankton is pointed out.

Stimulus for Diurnal Vertical Migration of Pelagic Animals

RECENTLY I correlated1 the movements of deep scattering layers with the relative decrease in light intensity, using data from Clarke and Backus2 and Kampa and Boden3. In my opinion, this correlation supports my hypothesis that the relative change in light intensity is the stimulus which causes pelagic animals to perform at least part of the diurnal vertical migration.