A paradigm for characterizing motion misperception in people with typical vision and low vision.

PURPOSE: We aimed to develop a paradigm that can efficiently characterize motion percepts in people with low vision and compare their responses with well-known misperceptions made by people with typical vision when targets are hard to see. METHODS: We recruited a small cohort of individuals with reduced acuity and contrast sensitivity (n = 5) as well as a comparison cohort with typical vision (n = 5) to complete a psychophysical study. Study participants were asked to judge the motion direction of a tilted rhombus that was either high or low contrast. In a series of trials, the rhombus oscillated vertically, horizontally, or diagonally. Participants indicated the perceived motion direction using a number wheel with 12 possible directions, and statistical tests were used to examine response biases. RESULTS: All participants with typical vision showed systematic misperceptions well predicted by a Bayesian inference model. Specifically, their perception of vertical or horizontal motion was biased toward directions orthogonal to the long axis of the rhombus. They had larger biases for hard-to-see (low contrast) stimuli. Two participants with low vision had a similar bias, but with no difference between high- and low-contrast stimuli. The other participants with low vision were unbiased in their percepts or biased in the opposite direction. CONCLUSIONS: Our results suggest that some people with low vision may misperceive motion in a systematic way similar to people with typical vision. However, we observed large individual differences. Future work will aim to uncover reasons for such differences and identify aspects of vision that predict susceptibility.

Perceptual consequences of interocular differences in the duration of temporal integration.

Temporal differences in visual information processing between the eyes can cause dramatic misperceptions of motion and depth. Processing delays between the eyes cause the Pulfrich effect: oscillating targets in the frontal plane are misperceived as moving along near-elliptical motion trajectories in depth (Pulfrich, 1922). Here, we explain a previously reported but poorly understood variant: the anomalous Pulfrich effect. When this variant is perceived, the illusory motion trajectory appears oriented left- or right-side back in depth, rather than aligned with the true direction of motion. Our data indicate that this perceived misalignment is due to interocular differences in neural temporal integration periods, as opposed to interocular differences in delay. For oscillating motion, differences in the duration of temporal integration dampen the effective motion amplitude in one eye relative to the other. In a dynamic analog of the Geometric effect in stereo-surface-orientation perception (Ogle, 1950), the different motion amplitudes cause the perceived misorientation of the motion trajectories. Forced-choice psychophysical experiments, conducted with both different spatial frequencies and different onscreen motion damping in the two eyes show that the perceived misorientation in depth is associated with the eye having greater motion damping. A target-tracking experiment provided more direct evidence that the anomalous Pulfrich effect is caused by interocular differences in temporal integration and delay. These findings highlight the computational hurdles posed to the visual system by temporal differences in sensory processing. Future work will explore how the visual system overcomes these challenges to achieve accurate perception.

The hospital difficult airway team: experience and implications for patient care.

The difficult airway involves the complex interaction between patient factors, the clinical setting and the practitioner's skills (Apfelbaum in Anesthesiology 118(2):251-70, 2013 and Mark et al. in Anesth Analg 121(1):127-139, 2015). It can also be a result of preparedness and system failures. Our institution developed a protocol to enhance emergency airway management in settings outside of the operating theatre-the difficult airway (DA) team. The aims of this report are to perform a retrospective review to describe the patient profiles as well as our difficult airway code workflow, and to identify preliminary patterns within DAC activations over an 18-month period (September 2013 to November 2015) in a tertiary university hospital. We believe that these findings may aid institutions in establishing a difficult airway protocol or refining existing airway code workflows. Institutional board approval was granted for medical record review.

Proficiencies of military medical officers in intubating difficult airways.

BACKGROUND: This study sheds light on the proficiency of military medical officers who had received between 2 and 3 years of post-graduate training, in the handling of the difficult airway in a trauma manikin simulator using direct and video laryngoscopes. METHOD: One hundred thirty-three doctors from the Singapore Armed Forces Medical Officer Cadet Course were assessed using high-fidelity simulator models with standardised difficult airways (simulator with tongue-swelling and cervical collar). They used the Macintosh direct laryngoscope (DL), King Vision channelled-blade laryngoscope (KVC), King Vision non-channelled blade laryngoscope (KVNC), and the McGrath (MG) laryngoscope on the same model in a randomised sequence. The intubation success rates and time to intubation were recorded and analysed for the study. RESULTS: The medical officers had a 71.4% intubation success rate with the DL on the difficult airway trauma simulator model and the mean time to intubation of 40.1 s. With the KVC, the success rate is 86.5% with mean intubation time of 40.4 s. The KVNC produced 24.8% success rate, with mean time to intubation of 53.2 s. The MG laryngoscope produced 85.0% success rate, with a mean time of intubation of 37.4 s. CONCLUSION: Military medical officers with 2-3 years of post-graduate training had a success rate of 71.4% success rate intubating a simulated difficult airway in a trauma setting using a DL. Success rates were improved with the use of KVC and the MG laryngoscope, but was worse with the KVNC.

Powered Air Purifying Respirator (PAPR) restores the N95 face mask induced cerebral hemodynamic alterations among Healthcare Workers during COVID-19 Outbreak.

BACKGROUND AND AIM: COVID-19 pandemic has resulted in an unprecedented increased usage of Personal protective equipment (PPE) by healthcare-workers. PPE usage causes headache in majority of users. We evaluated changes in cerebral hemodynamics among healthcare-workers using PPE. METHODS: Frontline healthcare-workers donning PPE at our tertiary center were included. Demographics, co-morbidities and blood-pressure were recorded. Transcranial Doppler (TCD) monitoring of middle cerebral artery was performed with 2-MHz probe. Mean flow velocity (MFV) and pulsatility index (PI) were recorded at baseline, after donning N95 respirator-mask, and after donning powered air-purifying respirator (PAPR), when indicated. End-tidal carbon-dioxide (ET-CO2) pressure was recorded for participants donning PAPR in addition to the N95 respirator-mask. RESULTS: A total of 154 healthcare-workers (mean age 29 ± 12 years, 67% women) were included. Migraine was the commonest co-morbidity in 38 (25%) individuals while 123 (80%) developed de-novo headache due to N95 mask. Donning of N95 respirator-mask resulted in significant increase in MFV (4.4 ± 10.4 cm/s, p < 0.001) and decrease in PI (0.13 ± 0.12; p < 0.001) while ET-CO2 increased by 3.1 ± 1.2 mmHg (p < 0.001). TCD monitoring in 24 (16%) participants donning PAPR and N95 respirator mask together showed normalization of PI, accompanied by normalization of ET-CO2 values within 5-min. Combined use of N95 respirator-mask and PAPR was more comfortable as compared to N95 respirator-mask alone. CONCLUSION: Use of N95 respirator-mask results in significant alterations in cerebral hemodynamics. However, these effects are mitigated by the use of additional PAPR. We recommend the use of PAPR together with the N95 mask for healthcare-workers doing longer duties in the hospital wards.

Predicting the Partition of Behavioral Variability in Speed Perception with Naturalistic Stimuli.

A core goal of visual neuroscience is to predict human perceptual performance from natural signals. Performance in any natural task can be limited by at least three sources of uncertainty: stimulus variability, internal noise, and suboptimal computations. Determining the relative importance of these factors has been a focus of interest for decades but requires methods for predicting the fundamental limits imposed by stimulus variability on sensory-perceptual precision. Most successes have been limited to simple stimuli and simple tasks. But perception science ultimately aims to understand how vision works with natural stimuli. Successes in this domain have proven elusive. Here, we develop a model of humans based on an image-computable (images in, estimates out) Bayesian ideal observer. Given biological constraints, the ideal optimally uses the statistics relating local intensity patterns in moving images to speed, specifying the fundamental limits imposed by natural stimuli. Next, we propose a theoretical link between two key decision-theoretic quantities that suggests how to experimentally disentangle the impacts of internal noise and deterministic suboptimal computations. In several interlocking discrimination experiments with three male observers, we confirm this link and determine the quantitative impact of each candidate performance-limiting factor. Human performance is near-exclusively limited by natural stimulus variability and internal noise, and humans use near-optimal computations to estimate speed from naturalistic image movies. The findings indicate that the partition of behavioral variability can be predicted from a principled analysis of natural images and scenes. The approach should be extendable to studies of neural variability with natural signals.SIGNIFICANCE STATEMENT Accurate estimation of speed is critical for determining motion in the environment, but humans cannot perform this task without error. Different objects moving at the same speed cast different images on the eyes. This stimulus variability imposes fundamental external limits on the human ability to estimate speed. Predicting these limits has proven difficult. Here, by analyzing natural signals, we predict the quantitative impact of natural stimulus variability on human performance given biological constraints. With integrated experiments, we compare its impact to well-studied performance-limiting factors internal to the visual system. The results suggest that the deterministic computations humans perform are near optimal, and that behavioral responses to natural stimuli can be studied with the rigor and interpretability defining work with simpler stimuli.

Intubation with channeled versus non-channeled video laryngoscopes in simulated difficult airway by junior doctors in an out-of-hospital setting: A crossover manikin study.

Failure to secure the airway is an important cause of morbidity and mortality during resuscitations. We compared the rate of successful intubation of the King Vision™ aBlade™ channeled and non-channeled video laryngoscopes, and McGRATH™ MAC video laryngoscope when used by junior doctors to intubate a simulated difficult airway in an out-of-hospital setting. 105 junior doctors were recruited in a crossover study to perform tracheal intubation with the three video laryngoscopes on a simulated difficult airway using the SimMan® 3G manikin. Primary outcome was the rate of successful intubations. Secondary outcomes were time-to-visualization, time-to-intubation and ease of use. Rates of successful intubations were higher for King Vision channeled and McGrath compared to the King Vision non-channeled (85.7% and 82.9% respectively versus 24.8%; p<0.001). Amongst the participants who had successful intubations, King Vision channeled and McGrath had shorter mean time-to-intubation compared to the King Vision non-channeled (41.3±20.3s and 38.5±18.7s respectively versus 53.8±23.8s, p<0.004;). There was no significant difference in the rate of successful intubation and mean time-to-intubation between King Vision channeled and McGrath. The King Vision channeled and McGrath video laryngoscopes demonstrated superior intubation success rates compared to King Vision non-channeled laryngoscope when used by junior doctors for intubating simulated difficult airway in an out-of-hospital setting. We postulated that the presence of a guidance channel in the King Vision channeled laryngoscope and the familiarity of the blade curvature and handling of the McGrath could have accounted for their improved intubation success rates.

A New Strategy for Intestinal Drug Delivery via pH-Responsive and Membrane-Active Nanogels.

Oral administration of hydrophobic and poorly intestinal epithelium-permeable drugs is a significant challenge. Herein, we report a new strategy to overcome this problem by using novel, pH-responsive, and membrane-active nanogels as drug carriers. Prepared by simple physical cross-linking of amphiphilic pseudopeptidic polymers with pH-controlled membrane-activity, the size and hydrophobicity-hydrophilicity balance of the nanogels could be well-tuned. Furthermore, the amphiphilic nanogels could release hydrophobic payloads and destabilize cell membranes at duodenum and jejunum pH 5.0-6.0, which suggests their great potential for intestinal drug delivery.

Inferior vena cava displacement during respirophasic ultrasound imaging.

BACKGROUND: Ultrasound measurement of dynamic changes in inferior vena cava (IVC) diameter can be used to assess intravascular volume status in critically ill patients, but published studies vary in accuracy as well as recommended diagnostic cutoffs. Part of this variability may be related to movements of the vessel relative to the transducer during the respiratory cycle which results in unintended comparison of different points of the IVC at end expiration and inspiration, possibly introducing error related to variations in normal anatomy. The objective of this study was to quantify both craniocaudal and mediolateral movements of the IVC as well as the vessel's axis of collapse during respirophasic ultrasound imaging. METHODS: Patients were enrolled from a single urban academic emergency department with ultrasound examinations performed by sonographers experienced in IVC ultrasound. The IVC was imaged from the level of the diaphragm along its entire course to its bifurcation with diameter measurements and respiratory collapse measured at a single point inferior to the confluence of the hepatic veins. While imaging the vessel in its long axis, movement in a craniocaudal direction during respiration was measured by tracking the movement of a fixed point across the field of view. Likewise, imaging the short axis of the IVC allowed for measurement of mediolateral displacement as well as the vessel's angle of collapse relative to vertical. RESULTS: Seventy patients were enrolled over a 6-month period. The average diameter of the IVC was 13.8 mm (95% CI 8.41 to 19.2 mm), with a mean respiratory collapse of 34.8% (95% CI 19.5% to 50.2%). Movement of the vessel relative to the transducer occurred in both mediolateral and craniocaudal directions. Movement was greater in the craniocaudal direction at 21.7 mm compared to the mediolateral movement at 3.9 mm (p < 0.001). Angle of collapse assessed in the transverse plane averaged 115° (95% CI 112° to 118°). CONCLUSIONS: Movement of the IVC occurs in both mediolateral and craniocaudal directions during respirophasic ultrasound imaging. Further, collapse of the vessel occurs not at true vertical (90°) but 25° off this axis. Technical approach to IVC assessment needs to be tailored to account for these factors.

Ionotropic glutamate receptor mRNA expression in the human thalamus: absence of change in schizophrenia.

Abnormalities in glutamate neurotransmission are thought to be among the major contributing factors to the pathophysiology of schizophrenia. Although schizophrenia has been regarded mostly as a disorder of higher cortical function, the cortex and thalamus work as a functional unit. Existing data regarding alterations of glutamate receptor subunit expression in the thalamus in schizophrenia remain equivocal. This postmortem study examined mRNA expression of ionotropic glutamate receptor (iGluR) subunits and PSD95 in 5 precisely defined and dissected thalamic subdivisions (medial and lateral sectors of the mediodorsal nucleus; and the ventral lateral posterior, ventral posterior, and centromedian nuclei) of persons with schizophrenia and matched controls using quantitative PCR with normalization to multiple endogenous controls. Among 15 genes examined (NR1 and NR2A-D subunits of the NMDA receptor; GluR1-4 subunits of the AMPA receptor; GluR5-7 and KA1-2 subunits of the kainate receptor; PSD95), all but two (GluR4 and KA1) were expressed at quantifiable levels. Differences in iGluR gene expression were seen between different thalamic nuclei but not between diagnostic groups. The relative abundance of transcripts was: NR1>>NR2A>NR2B>NR2D>NR2C for NMDA, GluR2>GluR1>GluR3 for AMPA, and KA2>GluR5>GluR7>GluR6 for kainate receptors. The expression of PSD95 correlated with the expression of NR1, NR2A, NR2B, NR2D and GluR6 in all nuclei. These results provide detailed and quantitative information on iGluR subunit expression in multiple nuclei of the human thalamus but suggest that alterations in their expression are not a prominent feature of schizophrenia.

Altered serotonin 2C receptor RNA splicing in suicide: association with editing.

In an earlier study, we showed increases in serotonin 2C receptor (5-HT2CR) pre-mRNA editing in prefrontal cortex that were specific to suicide victims irrespective of associated psychiatric diagnoses. Here we demonstrate that the ratio between the two 5-HT2CR splice variants is increased in people who committed suicide, but does not vary among the diagnostic groups. This provides further evidence for suicide-specific neurobiology and suggests that, as it was previously shown in vitro, 5-HT2CR editing modulates its splicing in human brain. The association analysis indicates, however, that the efficiency of 5-HT2CR editing is an imperfect predictor of the splicing outcome, and that splice site selection is only partially controlled by the level of editing in vivo.

Schizophrenia and sex associated differences in the expression of neuronal and oligodendrocyte-specific genes in individual thalamic nuclei.

Considerable evidence based on the study of postmortem brain tissue suggests deficits in both neuronal and myelin systems in schizophrenia (SZ). To date, the majority of the biochemical and molecular biological studies have focused on the cerebral cortex. Most information traveling to or from the cortex is relayed or synaptically gated through the thalamus, and numerous studies suggest structural and functional abnormalities in interconnected regions of the thalamus and cortex in SZ. The present study extends our gene expression studies of neuronal and myelin systems to the thalamus. Quantitative PCR was employed to assess the expression of 10 genes in 5 divisions of the thalamus which were precisely harvested using Laser Capture Microdissection. The divisions studied were present on coronal sections at the level of the centromedian nucleus (CMN) taken from 14 schizophrenic and 16 normal control postmortem brains. The genes examined were specific for oligodendrocytes (MAG, CNP, MBP), neurons (ENO2), glutamatergic neurons (VGlut1, VGlut2, PV, CB) or GABAergic neurons (GAD65, GAD67). Expression levels for each of these markers were quantitated and compared between diagnoses, between sexes, and across nuclei. CB was much more highly expressed in the CMN in SZs compared to NCs. No other diagnosis related differences in gene expression were observed. The expression levels of CNP and MAG, but not MBP, were highly correlated with one another and both, but not MBP, were much more highly expressed in females than in males in all thalamic divisions examined. All markers were differentially expressed across nuclei.

Myelin-associated mRNA and protein expression deficits in the anterior cingulate cortex and hippocampus in elderly schizophrenia patients.

Microarray and other studies have reported oligodendrocyte and myelin-related (OMR) deficits in schizophrenia. Here, we employed a quantitative approach to determine the magnitude of OMR gene expression deficits and their brain-region specificity. In addition, we examined how expression levels among the studied OMR genes are interrelated. mRNA of MAG, CNP, SOX10, CLDN11, and PMP22, but not MBP and MOBP, was reduced in the hippocampus and anterior cingulate cortex but not in the putamen of patients with schizophrenia. Expression of the only protein examined (CNP) was decreased in the hippocampus but not in the putamen. Correlation and factor analyses revealed that mRNA levels for genes that did exhibit differential expression in schizophrenia (MAG, CNP, SOX10, CLDN11, and PMP2), as opposed to those that did not (MOBP and MBP), loaded on separate factors. Thus, OMR gene and protein expression deficits in schizophrenia are brain-region specific, and the affected components may share regulatory elements.