Thresholds For Targets Research Articles

Multi-Task Collaborative Network: Bridge the Supervised and Self-Supervised Learning for EEG Classification in RSVP Tasks.

Electroencephalography (EEG) datasets are characterized by low signal-to-noise signals and unquantifiable noisy labels, which hinder the classification performance in rapid serial visual presentation (RSVP) tasks. Previous approaches primarily relied on supervised learning (SL), which may result in overfitting and reduced generalization performance. In this paper, we propose a novel multi-task collaborative network (MTCN) that integrates both SL and self-supervised learning (SSL) to extract more generalized EEG representations. The original SL task, i.e., the RSVP EEG classification task, is used to capture initial representations and establish classification thresholds for targets and non-targets. Two SSL tasks, including the masked temporal/spatial recognition task, are designed to enhance temporal dynamics extraction and capture the inherent spatial relationships among brain regions, respectively. The MTCN simultaneously learns from multiple tasks to derive a comprehensive representation that captures the essence of all tasks, thus mitigating the risk of overfitting and enhancing generalization performance. Moreover, to facilitate collaboration between SL and SSL, MTCN explicitly decomposes features into task-specific features and task-shared features, leveraging both label information with SL and feature information with SSL. Experiments conducted on THU, CAS, and GIST datasets illustrate the significant advantages of learning more generalized features in RSVP tasks. Our code is publicly accessible at https://github.com/Tammie-Li/MTCN.

Spatial Interactions in Interocular and Monocular "Blur Suppression".

The suppression of blurred images in one eye by clear images in the other eye is thought to contribute to the success of monovision correction. We show that interocular suppression occurs also for low-contrast targets that are not blurred and, to a lesser extent, when clear and low-contrast targets are presented to the same eye. A blurred target presented to one eye may be suppressed when a clear target is presented to the other eye. We sought to determine how this interocular suppression varies according to the separation between the blurred and clear targets and the magnitude of imposed blur. In addition, we examined whether a similar suppression occurs when the clear and blurred targets are imaged in the same eye. Subjects (N = 4) viewed a clear 20/40 Sloan letter surrounded by four 2 × 10 min-arc flanking bars. In different blocks of trials, the gap between the letter and flanking bars varied from 0.5 to 4 bar widths. In addition, the flanking bars were either clear or spatially filtered to simulate 0.5 to 2 D of blur. The contrast required to detect the flanking bars was determined when the letter and flanking bars were presented either dichoptically or monoptically and compared with the thresholds for the bar targets presented alone. In both dichoptic and monoptic viewing conditions, detection thresholds for the blurred flanking bars are highest for the smallest spatial gap and decrease systematically as the gap increases. Thresholds are uniformly higher during dichoptic than monocular viewing, but the proportional change with the bar-to-letter separation is similar in both conditions. Surprisingly, the magnitude of imposed blur has very little influence on the magnitude of threshold elevation in either the dichoptic or monoptic viewing conditions. Because threshold elevation is nearly the same in the presence of 0 to 2 D of blur, we prefer to designate the phenomenon we studied as "contrast suppression." The similar spatial characteristics of suppression during dichoptic and monoptic viewing are consistent with contributions from a common neural mechanism.

Thresholds for Hypertension Definition, Treatment Initiation, and Treatment Targets: Recent Guidelines at a Glance.

Thresholds for Hypertension Definition, Treatment Initiation, and Treatment Targets: Recent Guidelines at a Glance.

Cervical Deformity Correction Fails to Achieve Age-Adjusted Spinopelvic Alignment Targets.

To assess whether surgical cervical deformity (CD) patients meet spinopelvic age-adjusted alignment targets, reciprocal, and lower limb compensation changes. Retrospective review. CD was defined as C2-C7 lordosis >10°, cervical sagittal vertical angle (cSVA) >4 cm, or T1 slope minus cervical lordosis (TS-CL) >20°. Inclusion criteria were age >18 years and undergoing surgical correction with complete baseline and postoperative imaging. Published formulas were used to create age-adjusted alignment target for pelvic tilt (PT), pelvic incidence and lumbar lordosis (PI-LL), sagittal vertical angle (SVA), and lumbar lordosis and thoracic kyphosis (LL-TK). Actual alignment was compared with age-adjusted ideal values. Patients who matched ±10-year thresholds for age-adjusted targets were compared with unmatched cases (under- or overcorrected). A total of 120 CD patients were included (mean age, 55.1 years; 48.4% women; body mass index, 28.8 kg/m2). For PT, only 24.4% of patients matched age-adjusted alignment, 51.1% overcorrected for PT, and 24.4% undercorrected. For PI-LL, only 27.6% of CD patients matched age-adjusted targets, with 49.4% overcorrected and 23% undercorrected postoperatively. Forty percent of patients matched age-adjusted target for SVA, 41.3% overcorrected, and 18.8% undercorrected. CD patients who had worsened in TS-CL or cSVA postoperatively displayed increased TK (-41.1° to -45.3°, P = 1.06). With lower extremity compensation, CD patients decreased in ankle flexion angle postoperatively (6.1°-5.5°, P = 0.036) and trended toward smaller sacrofemoral angle (199.6-195.6 mm, P = 0.286) and knee flexion (2.6° to -1.1°, P = 0.269). In response to worsening CD postoperatively, patients increased in TK and recruited less lower limb compensation. Almost 75% of CD patients did not meet previously established spinopelvic alignment goals, of whom a subset of patients were actually made worse off in these parameters following surgery. This finding raises the question of whether we should be looking at the entire spine when treating CD.

A simple model considering spiking probability during extracellular axon stimulation.

The spiking probability of an electrically stimulated axon as a function of stimulus amplitude increases in a sigmoidal dependency from 0 to 1. However, most computer simulation studies for neuroprosthetic applications calculate thresholds for neural targets with a deterministic model and by reducing the sigmoid curve to a step function, they miss an important information about the control signal, namely how the spiking efficiency increases with stimulus intensity. Here, this spiking efficiency is taken into account in a compartment model of the Hodgkin Huxley type where a noise current is added in every compartment with an active membrane. A key parameter of the model is a common factor knoise which defines the ion current fluctuations across the cell membrane for every compartment by its maximum sodium ion conductance. In the standard model Gaussian signals are changed every 2.5 μs as a compromise of accuracy and computational costs. Additionally, a formula for other noise transmission times is presented and numerically tested. Spiking probability as a function of stimulus intensity can be approximated by the cumulative distribution function of the normal distribution with RS = σ/μ. Relative spread RS, introduced by Verveen, is a measure for the spread (normalized by the threshold intensity μ), that decreases inversely with axon diameter. Dynamic range, a related measure used in neuroprosthetic studies, defines the intensity range between 10% and 90% spiking probability. We show that (i) the dynamic range normalized by threshold is 2.56 times RS, (ii) RS increases with electrode-axon distance and (iii) we present knoise values for myelinated and unmyelinated axon models in agreement with recoded RS data. The presented method is applicable for other membrane models and can be extended to whole neurons that are described by multi-compartment models.

Spatial resolution and sensitivity of the eyes of the stingless bee, Tetragonula iridipennis.

Stingless bees are important pollinators in the tropics. The tremendous variation in body size makes them an excellent group to study how miniaturization affects vision and visual behaviours. Using direct measurements and micro-CT, we reconstructed the eye structure, estimated anatomical spatial resolution and optical sensitivity of the stingless bee Tetragonula iridipennis. T. iridipennis is similar in size to the Australian stingless bee Tetragonula carbonaria and is smaller than honeybees. It has correspondingly small eyes (area = 0.56 mm2), few ommatidia (2451 ± 127), large inter-facet (3.0 ± 0.6°) and acceptance angles (2.8°). Theoretical estimates suggest that T. iridipennis has poorer spatial resolution (0.17 cycles degree-1) than honeybees, bumblebees, and T. carbonaria. Its optical sensitivity (0.08 µm2 sr), though higher than expected, is within the range of diurnal bees. This may provide them with greater contrast sensitivity, which is likely more relevant than the absolute sensitivity in this diurnal bee. Behaviourally determined detection thresholds for single targets using y-maze experiments were 11.5° for targets that provide chromatic contrast alone and 9.1° for targets providing chromatic and achromatic contrast. Further studies into microhabitat preferences and behaviour are required to understand how miniaturization influences its visual ecology.

IMPAIRMENTS IN CONE PIGMENT REGENERATION AND ABSOLUTE THRESHOLD IN MACULAR TELANGIECTASIA TYPE 2.

To test the hypothesis that Müller cell dysfunction in macular telangiectasia type 2 (MacTel) results in delayed cone adaptation kinetics and to assess absolute cone and rod thresholds in this condition. Adaptation after an approximate 63.5% full-field cone photopigment bleach was assessed for Goldmann size V (1.7° diameter) 640 nm (red) and 480 nm (blue) targets presented at a retinal locus corresponding to 2° temporal to fixation. The cone time constant of adaptation and absolute cone and rod thresholds were calculated from exponential functions fitted to the resultant dark adaptation curves. Eighteen eyes with MacTel (from 11 patients) were compared with 19 control eyes (from 16 normal subjects). Cone adaptation kinetics were significantly impaired in MacTel, as was the absolute cone threshold. Final thresholds for blue targets were also significantly elevated in MacTel, consistent with impaired rod absolute threshold. Losses in sensitivity observed in MacTel were consistent with a so-called d1/2 mechanism (i.e., receptoral) site of sensitivity loss. In addition to previously documented impairments in rod dark adaptation, MacTel results in a significant elevation in cone thresholds because of pathology at the level of the photoreceptors. The delays in cone adaptation that we found in eyes with MacTel may reflect impairment of the Müller cell-mediated cone-specific visual cycle.

Visual detection thresholds in the Asian honeybee, Apis cerana.

To understand how insect pollinators find flowers against complex backgrounds in diverse natural habitats, it is required to accurately estimate the thresholds for target detection. Detection thresholds for single targets vary between bee species and have been estimated in the Western honeybee, a species of bumblebee and in a stingless bee species. We estimated the angular range of detection for coloured targets in the Asian honeybee Apis cerana. Using a Y-maze experimental set up, we show that targets that provided both chromatic and green receptor contrast were detected at a minimum visual angle of 7.7°, while targets with only chromatic contrast were detected at a minimum angle of 13.2°. Our results thus provide a robust foundation for future studies on the visual ecology of bees in a comparative interspecific framework.

Current Challenges in the Peripartum Management of Women with von Willebrand Disease.

For many women, pregnancy and childbirth represent their first major hemostatic challenges. Despite advancements in obstetric care, up to 2 to 5% of all deliveries are complicated by postpartum hemorrhage (PPH). To mitigate bleeding risk, physiological changes occur in pregnancy, including increases in plasma von Willebrand factor (VWF) and factor VIII levels. For women with von Willebrand disease (VWD), these physiological alterations are blunted or absent. As a result, women with VWD have a heightened risk of PPH, both primary (in the first 24 hours) and secondary (>24 hours to 6 to 12 weeks postpartum). Pregnancy and delivery management for women with VWD should therefore be carefully coordinated as part of a multidisciplinary team approach. In the absence of large-scale clinical trials, the management of women with VWD during pregnancy is guided by expert consensus guidelines. Clinical practices internationally are not uniform, and areas of considerable clinical uncertainty exist. Traditional peripartum plasma VWF thresholds for hemostatic cover and therapeutic targets are currently under scrutiny, as PPH is not eliminated in women with VWD who receive replacement therapy. The benefit and optimal duration of postpartum tranexamic acid have yet to be defined, and standardized methods of quantification of blood loss at the time of delivery are currently lacking. In this article, we review the evidence base to date and explore the current clinical challenges in the management of pregnant women with VWD.

Detection of occluding targets in natural backgrounds.

Detection of target objects in the surrounding environment is a common visual task. There is a vast psychophysical and modeling literature concerning the detection of targets in artificial and natural backgrounds. Most studies involve detection of additive targets or of some form of image distortion. Although much has been learned from these studies, the targets that most often occur under natural conditions are neither additive nor distorting; rather, they are opaque targets that occlude the backgrounds behind them. Here, we describe our efforts to measure and model detection of occluding targets in natural backgrounds. To systematically vary the properties of the backgrounds, we used the constrained sampling approach of Sebastian, Abrams, and Geisler (2017). Specifically, millions of calibrated gray-scale natural-image patches were sorted into a 3D histogram along the dimensions of luminance, contrast, and phase-invariant similarity to the target. Eccentricity psychometric functions (accuracy as a function of retinal eccentricity) were measured for four different occluding targets and 15 different combinations of background luminance, contrast, and similarity, with a different randomly sampled background on each trial. The complex pattern of results was consistent across the three subjects, and was largely explained by a principled model observer (with only a single efficiency parameter) that combines three image cues (pattern, silhouette, and edge) and four well-known properties of the human visual system (optical blur, blurring and downsampling by the ganglion cells, divisive normalization, intrinsic position uncertainty). The model also explains the thresholds for additive foveal targets in natural backgrounds reported in Sebastian et al. (2017).

Prevention, Diagnosis, and Management of Hypertensive Disorders of Pregnancy: a Comparison of International Guidelines

Hypertensive disorders of pregnancy (HDP)-gestational hypertension, preeclampsia, and eclampsia-are a leading cause of adverse maternal and perinatal outcomes internationally. Prevention, timely diagnosis, and prompt management can reduce associated morbidity. The purpose of this review is to compare international guidelines pertaining to HDP. Fourteen HDP guidelines were compared relative to guidelines for the United States (US) where the authors practice. Aspirin is universally recommended for high-risk women to reduce preeclampsia risk. Recommended dose and gestational age at initiation vary. Diagnoses of chronic hypertension, gestational hypertension, and preeclampsia in pregnant women are similar, although blood pressure (BP) thresholds for antihypertensive medication initiation and treatment targets vary due to the limitations in high-quality evidence. There are differences among international HDP guidelines related to dose and timing of aspirin initiation, thresholds for antihypertensive medication initiation, and BP targets. However, all guidelines acknowledge the significant morbidity associated with HDP and advocate for timely diagnosis and management to reduce associated morbidity and mortality. More research is needed to understand optimal BP thresholds at which to initiate antihypertensive medication regimens and BP targets in pregnancy.

The influence of rhythm on detection of auditory and vibrotactile asynchrony

The perception of an event is strongly influenced by the context in which it occurs. Here, we examined the effect of a rhythmic context on detection of asynchrony in both the auditory and vibrotactile modalities. Using the method of constant stimuli and a two-alternative forced choice (2AFC), participants were presented with pairs of pure tones played either simultaneously or with various levels of stimulus onset asynchrony (SOA). Target stimuli in both modalities were nested within either: (i) a regularly occurring, predictable rhythm (ii) an irregular, unpredictable rhythm, or (iii) no rhythm at all. Vibrotactile asynchrony detection had higher thresholds and showed greater variability than auditory asynchrony detection in general. Asynchrony detection thresholds for auditory targets but not vibrotactile targets were significantly reduced when the target stimulus was embedded in a regular rhythm as compared to no rhythm. Embedding within an irregular rhythm produced no such improvement. The observed modality asymmetries are interpreted with regard to the superior temporal resolution of the auditory system and specialized brain circuitry supporting auditory–motor coupling.

The history of proprotein convertase subtilisin kexin-9 inhibitors and their role in the treatment of cardiovascular disease.

A consensus has formed based on epidemiological studies and clinical trials that intervention to reduce low density lipoprotein cholesterol (LDL-C) will reduce cardiovascular disease (CVD) events. This has progressively reduced the thresholds for intervention and targets for treatment. Whist statins are sufficient for many people in primary prevention, they only partially achieve the newer targets of secondary prevention for established CVD. Increasing use of statins has highlighted that 1–2% cannot tolerate these drugs. Other cholesterol-lowering drugs such as ezetimibe add to the benefits of statins but have limited efficacy. The discovery of activating mutations in proprotein convertase subtilisin kexin-9 (PCSK9) as a cause of familial hypercholesterolaemia while inactivating mutations lower LDL-C led to the idea to develop PCSK9 inhibitors as drugs. This article reviews the history of lipid-lowering therapies, the discovery of PCSK9 and the development of PCSK9 inhibitors. It reviews the key trials of the current antibody-based drugs and how these have influenced new guidelines. It also reviews the controversy caused by their cost and the increasing application of health economics to determine the optimum strategy for implementation of novel therapeutic pathways and surveys other options for targeting PCSK9 as well as other LDL-C lowering compounds in late development.

Using baseline target moderation to guide decisions on adapting prevention programs.

Tom Dishion, a pioneer in prevention science, was one of the first to recognize the importance of adapting interventions to the needs of individual families. Building towards this goal, we suggest that prevention trials be used to assess baseline target moderated mediation (BTMM), where preventive intervention effects are mediated through change in specific targets, and the resulting effect varies across baseline levels of the target. Four forms of BTMM found in recent trials are discussed including compensatory, rich-get-richer, crossover, and differential iatrogenic effects. A strategy for evaluating meaningful preventive effects is presented based on preventive thresholds for diagnostic conditions, midpoint targets and proximal risk or protective mechanisms. Methods are described for using the results from BTMM analyses of these thresholds to estimate indices of intervention risk reduction or increase as they vary over baseline target levels, and potential cut points are presented for identifying subgroups that would benefit from program adaptation because of weak or potentially iatrogenic program effects. Simulated data are used to illustrate curves for the four forms of BTMM effects and how implications for adaptation change when untreated control group outcomes also vary over baseline target levels.

Length summation in noise.

To investigate the effect of background noise on visual summation, we measured the contrast detection thresholds for targets with or without a white noise mask in luminance contrast. The targets were Gabor patterns placed at 3° eccentricity to either the left or right of the fixation and elongated along an arc of the same radius to ensure equidistance from fixation for every point along the long axis. The task was a spatial two-alternative forced-choice (2AFC) paradigm in which the observer had to indicate whether the target was on the left or the right of the fixation. The threshold was measured at 75% accuracy with a staircase procedure. The detection threshold decreased with target length with slope -1/2 on log-log coordinates for target lengths between 30' and 300' half-height full-width (HHFW), defining a range of ideal matched-filter summation extending up to about 200' (or about 16× the center width of the Gabor targets). The summation curves for different noise contrasts were shifted copies of each other. For the threshold versus mask contrast (TvN) functions, the target threshold was constant for noise levels up to about -22 dB, then increased with noise contrast to a linear asymptote on log-log coordinates. Since the "elbow" of the target threshold versus noise function is an index of the level of the equivalent noise experienced by the visual system during target detection, our results suggest that the signal-to-noise ratio was invariant with target length. We further show that a linear-nonlinear-linear gain-control model can fully account for these results with far fewer parameters than a matched-filter model.

The Effect of Optical Blur on Central and Peripheral Word Visual Acuity

We investigated how dioptric blur affected word acuity thresholds for targets presented at different retinal eccentricities. Word thresholds were measured at 0, 5, and 10 degrees and for different Weber contrast levels of 4, 10, 45, and 90%. We find that increasing optical blur increased word acuity thresholds, but the extent of change was dependent on retinal eccentricity and stimulus contrast. In particular, the resolution reduction per diopter of blur (as indicated by the slope of lines fitted to data) was significantly less at peripheral locations (0 degrees vs. 5 and 10 degrees) and for low-contrast targets. These findings provide useful guidelines to predict how patients with contrast loss and/or those that rely upon an eccentric retinal location for reading respond to the introduction of optical blur in a clinical setting.

Can spatial resolution reveal individual differences in the L:M cone ratio?

We measured spatial resolution in the parafovea for targets designed to isolate either the long-wavelength (L) or the middle-wavelength (M) cones. Landolt C optotypes were presented for 100ms on a calibrated monitor at an eccentricity of 5° to the left or right of fixation. There were large individual differences in the ratio of the resolution obtained with L targets to that obtained with M targets, and we suggest that these differences reflect variations in the relative sampling densities of L and M cones in the parafovea. In Experiment 1, we measured contrast thresholds for targets of varying size. Among 10 unselected observers, there was a threefold variation in the ratio of the contrast thresholds for the smallest targets. In Experiments 2 and 3, we held contrast constant and we varied size, in order to establish the minimal target that could be discriminated for each of the two classes of cone. In Experiment 2, two groups of observers, selected on the basis of their settings on a flicker-photometric test, showed a highly significant difference in the ratio of the M and L acuities on the spatial task. In Experiment 3, female carriers of protan or deutan deficiencies, classified only on the basis of their sons’ phenotypes, also showed a large difference in the ratio of their acuities for M and L targets. In all three experiments, there was a strong correlation between the ratio of M and L spatial acuities and a flicker-photometric measure of relative sensitivity to long- and middle-wavelength light.

Multi-Target Regulation by Small RNAs Synchronizes Gene Expression Thresholds and May Enhance Ultrasensitive Behavior

Cells respond to external cues by precisely coordinating multiple molecular events. Co-regulation may be established by the so-called single-input module (SIM), where a common regulator controls multiple targets. Using mathematical modeling, we compared the ability of SIM architectures to precisely coordinate protein levels despite environmental fluctuations and uncertainties in parameter values. We find that post-transcriptional co-regulation as exemplified by bacterial small RNAs (sRNAs) is particularly robust: sRNA-mediated regulation establishes highly synchronous gene expression thresholds for all mRNA targets without a need for fine-tuning of kinetic parameters. Our analyses reveal that the non-catalytic nature of sRNA action is essential for robust gene expression synchronization, and that sRNA sequestration effects underlie coupling of multiple mRNA pools. This principle also operates in the temporal regime, implying that sRNAs could robustly coordinate the kinetics of mRNA induction as well. Moreover, we observe that multi-target regulation by a small RNA can strongly enhance ultrasensitivity in mRNA expression when compared to the single-target case. Our findings may explain why bacterial small RNAs frequently coordinate all-or-none responses to cellular stress.

Detection Thresholds for Rare, Spectrally Unique Targets within Semiarid Rangelands

Many factors influence classification accuracy, and this study assessed detection thresholds for various sub-pixel targets using QuickBird multispectral imagery. Six iterations of maximum-likelihood classification were used to determine classification accuracy for 100 spectrally unique targets randomly placed over a semiarid rangeland site. Error matrices were calculated using independent validation sites and producer’s, user’s, and overall accuracy, Kappa Index of Agreement, and transformed divergence were analyzed to compare the performance of each classification and determine detection thresholds. Results indicate a strong relationship between target size and classification accuracy (R 2 0.94) as well as an increasingly prominent role played by training site selection as target size decreased. Strong spectral separability and good classification accuracies were achieved for targets 25 percent cover. Sub-pixel targets 25 percent in size were not detectable. This study highlights the effect of target size upon classification accuracy and has direct implications for invasive plant research and rare target detection.

A Novel Psychophysical Method for Estimating the Time Course of Olfactory Rapid Adaptation in Humans

In this presentation, we describe a novel method for estimating the onset time course of psychophysical odor adaptation in human observers. The method employs stimulus conditions derived from an analogous stimulus paradigm in audition. To test this procedure, we used liquid-dilution olfactometry to estimate 2-bottle discrimination thresholds for brief (600 ms) presentations of vanilla odor; 17 volunteers (14 females; ages 18-24) served as participants. The adapting odorant concentration for each participant was set relative to baseline threshold for the 600-ms target alone (i.e., the same level relative to each participant's threshold). To characterize the adaptation-onset time course, we compared thresholds for targets presented simultaneously with the adapting stimulus as a function of the relative delay between the onset of the adapting stimulus and onset of the target. As predicted from the analogous auditory studies, thresholds for the target stimulus increased in an orderly manner with increases in adaptation-to-target onset delay (i.e., as the adaptation process progressively decreased sensitivity). Initial increases in threshold were consistently observed for the briefest onset delays of 50-100 ms. An onset time constant was estimated at 319 ms by fitting a 2-component exponential to the mean group function. Adaptation magnitude was dependent on the level of adapting odorant, relative to threshold. When thresholds were measured in one participant with a different, unrelated target odorant, cineole, there was no effect of the vanilla-adapting stimulus on threshold. The results suggest that olfactory rapid adaptation is measurable psychophysically within 50-200 ms after odor onset, values consistent with physiological measures of adaptation in olfactory receptor neurons. This novel stimulus paradigm offers a powerful psychophysical tool to study both odor adaptation and stimulus interactions at the olfactory periphery.