Unreliable Signals Research Articles

A Deep Learning–based PPG Quality Assessment Approach for Heart Rate and Heart Rate Variability

Photoplethysmography (PPG) is a non-invasive optical method to acquire various vital signs, including heart rate (HR) and heart rate variability (HRV). The PPG method is highly susceptible to motion artifacts and environmental noise. Unfortunately, such artifacts are inevitable in ubiquitous health monitoring, as the users are involved in various activities in their daily routines. Such low-quality PPG signals negatively impact the accuracy of the extracted health parameters, leading to inaccurate decision-making. PPG-based health monitoring necessitates a quality assessment approach to determine the signal quality according to the accuracy of the health parameters. Different studies have thus far introduced PPG signal quality assessment methods, exploiting various indicators and machine learning algorithms. These methods differentiate reliable and unreliable signals, considering morphological features of the PPG signal and focusing on the cardiac cycles. Therefore, they can be utilized for HR detection applications. However, they do not apply to HRV, as only having an acceptable shape is insufficient, and other signal factors may also affect the accuracy. In this article, we propose a deep learning–based PPG quality assessment method for HR and various HRV parameters. We employ one customized one-dimensional (1D) and three 2D Convolutional Neural Networks (CNN) to train models for each parameter. Reliability of each of these parameters will be evaluated against the corresponding electrocardiogram signal, using 210 hours of data collected from a home-based health monitoring application. Our results show that the proposed 1D CNN method outperforms the other 2D CNN approaches. Our 1D CNN model obtains the accuracy of 95.63%, 96.71%, 91.42%, 94.01%, and 94.81% for the HR, average of normal to normal interbeat (NN) intervals, root mean square of successive NN interval differences, standard deviation of NN intervals, and ratio of absolute power in low frequency to absolute power in high frequency ratios, respectively. Moreover, we compare the performance of our proposed method with state-of-the-art algorithms. We compare our best models for HR-HRV health parameters with six different state-of-the-art PPG signal quality assessment methods. Our results indicate that the proposed method performs better than the other methods. We also provide the open source model implemented in Python for the community to be integrated into their solutions.

A General Degradation Process of Useful Life Analysis Under Unreliable Signals for Accelerated Degradation Testing

In order to achieve fault diagnosis and prognosis, one needs a sufficient and valid life-cycle data. However, this requirement is difficult for current high-reliable manufacturing system. Good thing is that the technique of accelerated degradation testing can be used to address this issue. Bad thing is that, it needs a reliable testing/measuring technique to build an accurate model for accelerated degradation testing. However, in practical applications, data acquisition is obtained by sensors or measurement devices, which cannot guarantee perfect working condition under the influence of external environment and stresses, resulting in unreliable signals. Furthermore, since traditional models require complex differentiation and cannot obtain analytical expressions when considering unreliable signals, traditional models rarely reflect well this situation. Motivated by these facts, an accurate model for the accelerated degradation testing is proposed in this study with considering the unreliable signals. Based on the proposed model, a closed-form expression for the useful life analysis is derived. The M-H sampling method is used to estimate the unknown parameters used in the proposed model. For illustration, the electrical connectors dataset is analyzed with the proposed model and the traditional models. Comparing the obtained results, the proposed model is more accurate in the useful life analysis than the traditional accelerated degradation testing models by considering the unreliable signals.

Trends in Heart Rate and Heart Rate Variability During Pregnancy and the 3-Month Postpartum Period: Continuous Monitoring in a Free-living Context.

BackgroundHeart rate variability (HRV) is a noninvasive method that reflects the regulation of the autonomic nervous system. Altered HRV is associated with adverse mental or physical health complications. The autonomic nervous system also has a central role in physiological adaption during pregnancy, causing normal changes in HRV.ObjectiveThe aim of this study was to assess trends in heart rate (HR) and HRV parameters as a noninvasive method for remote maternal health monitoring during pregnancy and 3-month postpartum period.MethodsA total of 58 pregnant women were monitored using an Internet of Things–based remote monitoring system during pregnancy and 3-month postpartum period. Pregnant women were asked to continuously wear Gear Sport smartwatch to monitor their HR and HRV extracted from photoplethysmogram (PPG) signals. In addition, a cross-platform mobile app was used to collect background and delivery-related information. We analyzed PPG signals collected during the night and discarded unreliable signals by applying a PPG quality assessment method to the collected signals. HR, HRV, and normalized HRV parameters were extracted from reliable signals. The normalization removed the effect of HR changes on HRV trends. Finally, we used hierarchical linear mixed models to analyze the trends of HR, HRV, and normalized HRV parameters.ResultsHR increased significantly during the second trimester (P<.001) and decreased significantly during the third trimester (P=.006). Time-domain HRV parameters, average normal interbeat intervals (IBIs; average normal IBIs [AVNN]), SD of normal IBIs (SDNN), root mean square of the successive difference of normal IBIs (RMSSD), normalized SDNN, and normalized RMSSD decreased significantly during the second trimester (P<.001). Then, AVNN, SDNN, RMSSD, and normalized SDNN increased significantly during the third trimester (with P=.002, P<.001, P<.001, and P<.001, respectively). Some of the frequency-domain parameters, low-frequency power (LF), high-frequency power (HF), and normalized HF, decreased significantly during the second trimester (with P<.001, P<.001, and P=.003, respectively), and HF increased significantly during the third trimester (P=.007). In the postpartum period, normalized RMSSD decreased (P=.01), and the LF to HF ratio (LF/HF) increased significantly (P=.004).ConclusionsOur study indicates the physiological changes during pregnancy and the postpartum period. We showed that HR increased and HRV parameters decreased as pregnancy proceeded, and the values returned to normal after delivery. Moreover, our results show that HR started to decrease, whereas time-domain HRV parameters and HF started to increase during the third trimester. The results also indicated that age was significantly associated with HRV parameters during pregnancy and postpartum period, whereas education level was associated with HRV parameters during the third trimester. In addition, our results demonstrate the possibility of continuous HRV monitoring in everyday life settings.

The role of inhibition in the suboptimal choice task.

Given a choice, pigeons prefer an initial-link stimulus that is followed by reliable signals that food will be delivered (S+) or not (S-) after a delay, over an alternative initial-link stimulus that is followed by unreliable signals of food, even when the former yields a lower overall probability of food. This suboptimal preference has been attributed to the combination of a biased attraction to the S+ and ignoring the S-. We evaluated the inhibitory properties of the S- in three experiments to investigate its role in suboptimal choice. In Experiment 1, pigeons were trained in an autoshaping procedure with the four terminal link stimuli of the suboptimal choice task; S+ was continuously reinforced, S3 and S4 were each partially reinforced on a 50% schedule, and S- was never reinforced. Summation tests showed that S- acquired inhibitory properties during training. Experiment 2 replicated the summation tests after training on the full suboptimal choice procedure and found that S- inhibition was not attributable to external inhibition. In Experiment 3, pigeons were trained on the suboptimal choice procedure and the development of inhibition was assessed throughout training. An analysis of individual differences across birds revealed that the response rates to S- were negatively correlated with the strength of suboptimal preference, both within subject as each bird acquired suboptimal preference, and across subjects once all birds had reached asymptotic levels of suboptimal preference. Thus, rather than ignoring the S-, we found evidence that birds attended to S- as an inhibitory stimulus. Future models explaining performance in the suboptimal choice task should consider inhibition to the S- as a factor in suboptimal choice. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Lightweight Photoplethysmography Quality Assessment for Real-time IoT-based Health Monitoring using Unsupervised Anomaly Detection

Real-time remote health monitoring is dramatically growing, revolutionizing healthcare delivery and outcome in everyday settings. Such remote services enable monitoring individuals anywhere and anytime, allowing diseases early detection and prevention. Photoplethysmography (PPG) is a non-invasive and convenient technique that enables tracking vital signs such as heart rate, heart rate variability, respiration rate, and blood oxygen saturation. PPG is broadly used in various clinical and commercial wearable devices, as it is easy-to-implement and low-cost. However, the technique is highly susceptible to motion artifacts and environmental noises, which distort the collected signals. Therefore, the signal quality needs to be investigated, and unreliable signals should be discarded. In the literature, rule-based and machine learning-based PPG quality assessment methods have been investigated in several studies. However, the rule-based methods are mostly inaccurate in remote health monitoring, where users engage in different physical activities. The supervised machine learning-based methods –including deep learning–are also infeasible for real-time monitoring applications since they are slow and are dependent on a massive pool of annotated data to train the model. In this paper, we introduce a PPG quality assessment method, enabled by an elliptical envelope, which requires low computational resources. The method clusters the PPG signals into two groups as “reliable” and “unreliable.” We also investigate various features extracted from the PPG signals. Five features with the highest scoring values are selected to be fed to the elliptical envelope model. Moreover, we assess the performance of the proposed method in terms of accuracy and execution time, using data collected in free-living conditions via an Internet-of-Things-based health monitoring system enabled by smart wristbands. The method is evaluated in comparison to a state-of-the-art PPG quality assessment method. We also provide the model implemented in Python for the community to be used in their solutions.

Reliability-Based Signal Detection for Universal Filtered Multicarrier

In this letter, the reliability-based signal detection is proposed for universal filtered multicarrier (UFMC) systems. In the proposed detector, first, the initial subcarrier-wise estimation utilizing the even-component of frequency-domain (FD) received signal is performed, and the reliabilities of the estimated signals are measured by the corresponding FD channel magnitudes. Second, the estimated signals with high reliabilities are accepted and peeled off from the received signal. Third, the signals with low reliabilities are re-estimated by two different methods, symbol-flipping (SF) and joint minimum mean square estimation (MMSE), utilizing the additional odd-component of FD received signal after peeling off. Specifically, one or two of these unreliable signals are flipped simultaneously in turn from the initial estimates to their neighbors in the SF re-estimation, and all the unreliable signals are jointly estimated by MMSE in the joint MMSE re-estimation. Simulation results show that the proposed detection can achieve better performance-complexity tradeoff than conventional UFMC detections.

The Reliability of IoT Networks With Characteristics of Abnormal Induced Signals

The abnormal nodes of the Internet of Things (IoT) are closely related to the reliability of the network, but it is always a difficulty to predict the characteristics of the induced signals that threaten reliability. In this article, a feature analysis method for the abnormal signal inducing the unreliable anomaly in IoT based on chaos attractor is proposed to make phase space reconstruction of the abnormal signal that the nodes of IoT can induce unreliability. The phase space structure is constructed by the sequence of abnormal signals. The chaotic attractor is used to analyze the phase space characteristics and reflect the phase space characteristics of unreliable signals induced by the network from the geometric point of view. The mutual information method is used to solve the time delay of the unreliable abnormal signal of IoT, calculate the embedding dimension, find out the chaotic attractors under different characteristics, and judge the reliability change characteristics by analyzing the chaotic attractors. The experimental results show that the method has a better time slot consumption, throughput, and idle energy indexes. Furthermore, our experiments show that the chaos attractor method can effectively predict the reliability trend of IoT, and better predict the reliability anomalies of IoT.

Audience perceptions of high‐status ties and network advantage: The market for coaching jobs in the National Collegiate Athletic Association (2000–2011)

SummarySocial ties with high‐status others can be a potent signal of an individual's underlying quality and future promise. Individuals in competitive markets, therefore, have an incentive to publicly claim connections to high‐status others. However, cognitive limitations and biases can make social network connections difficult for observers to reliably discern, and claims to high‐status ties can go unrecognized by the audience. Our core contention is that claims to high‐status affiliation are advantageous only when the audience recognizes the claim—unrecognized claims, like unreliable signals, do not deliver advantage and can backfire. Further, we draw on the literature on imprinting and develop arguments for why some people are more likely to make claims to high‐status ties and why some claims to high‐status ties are more likely than others to be recognized by the audience. We test our arguments with data from the market for head coaching jobs in NCAA basketball (2000–2011). Our study contributes to the sparse literature on how social network ties that exist in the minds of third‐party observers influence individual attainment in market settings; and it offers new insights into how imprinting processes shape the perception and use of high‐status network ties.

Constrained dynamical systems, robust model reference adaptive control, and unreliable reference signals

ABSTRACTIn this paper, we address the robust control design problem for nonlinear dynamical systems tracking unreliable reference signals. Specifically, we present robust model reference adaptive control laws that guarantee uniform ultimate boundedness of the trajectory tracking error for nonlinear plants that are affected by matched, unmatched, and parametric uncertainties, and are subject to constraints on the state space and the measured output. These control laws guarantee satisfactory results even in case the reference trajectory or the reference output signal do not verify the given constraints and hence, may draw the plant's trajectory or measured output outside their constraint sets. A numerical example involving the attitude control of a spacecraft illustrates the feasibility of the theoretical results presented.

Interpopulation Variation in a Condition-Dependent Signal: Predation Regime Affects Signal Intensity and Reliability.

In many models of sexual selection, conspicuous ornaments are preferred by mates because they indicate heritable signaler viability. To function as indicators, ornaments must exhibit a proportional relationship between expression and viability. In cases where the evolutionary interests of signaler and receiver diverge, selection favors exploitative exaggeration by low-viability individuals producing unreliable signals. Theory suggests that the evolutionary stability of such communication systems requires costs that prevent low-viability males from expressing disproportionately intense signals. Therefore, given ecological variation in signaling cost, the reliability of signaling systems will vary concomitantly. In this study, we assess the effect of a variable signal cost, predation, on signal intensity and reliability among 16 populations of Bahamas mosquitofish (Gambusia hubbsi) that use colorful dorsal fins in courtship displays. We found that fin coloration was more intense in low-predation sites and could be used to predict body condition. However, this predictive relationship was apparent only in populations subject to predation risk. We demonstrate an important role for ecological signaling cost in communication and show that ecological heterogeneity drives interpopulation variation in both the intensity and the reliability of a sexual signal.

Building a dishonest signal: the functional basis of unreliable signals of strength in males of the two-toned fiddler crab, Uca vomeris.

Males of many species use signals during aggressive contests to communicate their fighting capacity. These signals are usually reliable indicators of an individual's underlying quality; however, in several crustacean species, displays of weapons do not always accurately reflect the attribute being advertised. Male fiddler crabs possess one enlarged claw that is used to attract females and to intimidate opponents during territorial contests. After the loss of their major claw, males can regenerate a replacement claw that is similar in size but considerably weaker. As this inferior weapon can still be used to successfully intimidate rivals, it represents one of the clearest cases of unreliable signalling of strength during territorial contests. We investigated the functional mechanisms that govern signal reliability in the two-toned fiddler crab, Uca vomeris. Male U. vomeris exhibit both reliable and unreliable signals of strength via the expression of original and regenerated claw morphs. We examined the morphological, biomechanical and biochemical characteristics of original and regenerated claws to establish the best predictors of variation in claw strength. For a given claw size, regenerated claws have less muscle mass than original claws, and for a given muscle mass, regenerated claws were significantly weaker than original claws. The mechanical advantage was also lower in regenerated claws compared with original claws. However, the activity of three catabolic enzymes did not differ between claw types. We conclude that the structural and physiological predictors of force production influence the frequencies of reliable and unreliable signals of strength in U. vomeris. This study furthers our understanding of the proliferation of unreliable signals in natural populations.

Information-content of morphological and behavioural sexual traits in the Palmate newt (Lissotriton helveticus)

The question of why females evaluate more than one sexual trait to choose their mates has received increasing attention in recent years. Here, we investigated the information-content of both morphological and behavioural sexual traits that have been identified as predictors of male reproductive success in the palmate newt, Lissotriton helveticus. We examined the co-variation of multiple traits with one aspect of male quality, the male body condition, using both a correlative study and an experimental diet restriction. We found that the development of the three morphological sexual traits (filament length, hind-foot-web size, and crest size) was positively inter-correlated, and was correlated to body condition. In contrast, courtship activity, an important indicator for male reproductive success, was uncorrelated to male body condition. Our results suggest that females likely obtain redundant information on male condition when evaluating filament length, hind-foot-web size and crest size during mate choice. Contrary to our expectations, display activity was not a reliable indicator of male condition, leaving the information-content of this trait unraveled. Our results further suggest that complex, multiple traits may evolve because redundant message, unreliable signals and, possibly, multiple messages can coexist.

Commentary: Paternal and maternal influences on offspring phenotype: the same, only different

Commentary: Paternal and maternal influences on offspring phenotype: the same, only different

Multiple achromatic plumage ornaments signal to multiple receivers

We investigated whether achromatic plumage traits can act as multiple ornaments in an Arctic-breeding passerine, the snow bunting (Plectrophenax nivalis). Specifically, we examine whether multiple ornaments are providing multiple differing messages, are redundant, are unreliable signals of male quality, or are aimed at different receivers. We measured plumage reflectance and pigmentation patterns made conspicuous during male inter- and intrasexual displays that advertise different plumage regions. Our results indicate that although several aspects of male plumage may have redundant messages, different body regions appear aimed at different receivers. The wings of males—displayed primarily toward females during courtship—appear to indicate a pair’s future reproductive performance. Conversely, melanin-based plumage reflectance displayed during intrasexual threat displays provides information on territory features and a male’s capacity to defend it (i.e., territory size, territory quality, testosterone levels). Taken together, we suggest that snow buntings have multiple ornaments that provide information of differential importance in inter- versus intrasexual communication. This study demonstrates that achromatic plumage traits can serve in complex communication. Key wor ds: achromatic plumage, individual quality , multiple ornaments, multiple receivers, Plectrophenax nivalis. [Behav Ecol]

Correlations of Condition, Testosterone, and Age with Multiple Ornaments in Male House Sparrows: Patterns and Implications

Abstract. Why many animals display several different kinds of ornaments has been of recent interest in animal-communication research. Three key hypotheses have been suggested: multiple ornaments can function as (1) multiple messages (each ornament provides different information), (2) redundant messages or back-up signals (all ornaments provide the same information), and (3) unreliable signals (no information). Here we tested the signal properties of ornamental traits of male House Sparrows (Passer domesticus) to better resolve the potential information different ornaments reveal. We repeatedly measured badge size, wingbar area and color, bill color, and leg color in 170 captive males over 3 years. We found that (1) badge size and wingbar area were related to condition (to mass, tarsus length, and the interaction of both), (2) badge size, wingbar area, and bill color were related to testosterone levels, (3) all ornaments except bill color were related to age, and (4) origin had only minor effects. We concl...

Evolution of Stress Response in the Face of Unreliable Environmental Signals

Most organisms live in ever-changing environments, and have to cope with a range of different conditions. Often, the set of biological traits that are needed to grow, reproduce, and survive varies between conditions. As a consequence, organisms have evolved sensory systems to detect environmental signals, and to modify the expression of biological traits in response. However, there are limits to the ability of such plastic responses to cope with changing environments. Sometimes, environmental shifts might occur suddenly, and without preceding signals, so that organisms might not have time to react. Other times, signals might be unreliable, causing organisms to prepare themselves for changes that then do not occur. Here, we focus on such unreliable signals that indicate the onset of adverse conditions. We use analytical and individual-based models to investigate the evolution of simple rules that organisms use to decide whether or not to switch to a protective state. We find evolutionary transitions towards organisms that use a combination of random switching and switching in response to the signal. We also observe that, in spatially heterogeneous environments, selection on the switching strategy depends on the composition of the population, and on population size. These results are in line with recent experiments that showed that many unicellular organisms can attain different phenotypic states in a probabilistic manner, and lead to testable predictions about how this could help organisms cope with unreliable signals.

The number and coloration of white flank spots predict the strength of a cutaneous immune response in female Diamond Firetails, Stagonopleura guttata

Colour variation in birds is often used to signal functional differences between individuals and sexes, though white plumage has usually been disregarded because white feathers were thought to be cheap to produce and hence unreliable signals. Here, we provide evidence for sex-specific morphological and colour differences in the strikingly patterned but apparently monomorphic Dia- mond Firetail (Stagonopleura guttata). We found that males had longer and darker tails, wider lores and a darker bill, while females had significantly more white flank spots. These gender-specific trait differences could be used to signal individual quality in sexual or social interactions, and hence we examined the correlation between these traits and the cell-mediated immune response (phytohaemag- glutinin, PHA test). During both the breeding and non- breeding seasons, we found a positive correlation between PHA response and white flank spot number as well as their ultra-violet reflectance in females, and a negative correla- tion with white chroma and hue. In males, there was a positive correlation between PHA response and red rump reflectance (hue, red-chroma). There was no association between PHA response and either tail length or lore depth in either sex. These results add to a growing body of evidence that female spot number and white plumage reflectance signal quality.

Cryptic asymmetry: unreliable signals mask asymmetric performance of crayfish weapons

Animals commonly use their limbs as signals and weapons during territorial aggression. Asymmetries of limb performance that do not relate to asymmetries of limb size (cryptic asymmetry) could substantially affect disputes, but this phenomenon has not been considered beyond primates. We investigated cryptic asymmetry in male crayfish (Cherax dispar), which commonly use unreliable signals of strength during aggression. Although the strength of a chela can vary by an order of magnitude for a given size, we found repeatable asymmetries of strength that were only weakly related to asymmetries of size. Size-adjusted strength of chelae and the asymmetry of strength between chelae were highly repeatable between environmental conditions, suggesting that asymmetries of strength stemmed from variation in capacity rather than motivation. Cryptic asymmetry adds another dimension of uncertainty during conflict between animals, which could influence the evolution of unreliable signals and morphological asymmetry.

Social control of unreliable signals of strength in male but not female crayfish,Cherax destructor

The maintenance of unreliable signals within animal populations remains a highly controversial subject in studies of animal communication. Crustaceans are an ideal group for studying unreliable signals of strength because their chela muscles are cryptically concealed beneath an exoskeleton, making it difficult for competitors to visually assess an opponent's strength. In this study, we examined the importance of social avenues for mediating the possible advantages gained by unreliable signals of strength in crustaceans. To do this, we investigated the factors that determine social dominance and the relative importance of signalling and fighting during aggressive encounters in male and female freshwater crayfish, Cherax destructor. Like other species of crayfish, we expected substantial variation in weapon force for a given weapon size, making the assessment of actual fighting ability of an opponent difficult from signalling alone. In addition, we expected fighting would be used to ensure that individuals that are weak for their signal (i.e. chela) size would not achieve higher than expected dominance. For both male and female C. destructor, we found large variation in the actual force of their chela for any given weapon size, indicating that it is difficult for competitors to accurately assess an opponent's force on signal size alone. For males, these unreliable signals of strength were controlled socially through increased levels of fighting and a decreased reliance on signalling, thus directly limiting the benefits accrued to individuals employing high-quality signals (large chelae) with only low resource holding potential. However, in contrast to our predictions, we found that females primarily relied on signalling to settle disputes, resulting in unreliable signals of strength being routinely used to establish dominance. The reliance by females on unreliable signals to determine dominance highlights our poor current understanding of the prevalence and distribution of dishonesty in animal communication.

Relatedness influences signal reliability in evolving robots

Communication is an indispensable component of animal societies, yet many open questions remain regarding the factors affecting the evolution and reliability of signalling systems. A potentially important factor is the level of genetic relatedness between signallers and receivers. To quantitatively explore the role of relatedness in the evolution of reliable signals, we conducted artificial evolution over 500 generations in a system of foraging robots that can emit and perceive light signals. By devising a quantitative measure of signal reliability, and comparing independently evolving populations differing in within-group relatedness, we show a strong positive correlation between relatedness and reliability. Unrelated robots produced unreliable signals, whereas highly related robots produced signals that reliably indicated the location of the food source and thereby increased performance. Comparisons across populations also revealed that the frequency for signal production-which is often used as a proxy of signal reliability in empirical studies on animal communication-is a poor predictor of signal reliability and, accordingly, is not consistently correlated with group performance. This has important implications for our understanding of signal evolution and the empirical tools that are used to investigate communication.