1,334 research outputs found
Dynamics of the G-excess illusion
The G-excess illusion is increasingly recognized as a cause of aviation mishaps especially when pilots perform high-speed, steeply banked turns at low altitudes. Centrifuge studies of this illusion have examined the perception of subject orientation and/or target displacement during maintained hypergravity with the subject's head held stationary. The transient illusory perceptions produced by moving the head in hypergravity are difficult to study onboard centrifuges because the high angular velocity ensures the presence of strong Coriolis cross-coupled semicircular canal effects that mask immediate transient otolith-organ effects. The present study reports perceptions following head movements in hypergravity produced by high-speed aircraft maintaining a banked attitude with low angular velocity to minimize cross-coupled effects. Methods: Fourteen subjects flew on the NASA KC-135 and were exposed to resultant gravity forces of 1.3, 1.5, and 1.8 G for 3 minute periods. On command, seated subjects made controlled head movements in roll, pitch, and yaw at 30 second intervals both in the dark and with faint targets at a distance of 5 feet. Results: head movement produced transient perception of target displacement and velocity at levels as low as 1.3 G. Reports of target velocity without appropriate corresponding displacement were common. At 1.8 G when yaw head movements were made from a face down position, 4 subjects reported oscillatory rotational target displacement with fast and slow alternating components suggestive of torsional nystagmus. Head movements evoked symptoms of nausea in most subjects, with 2 subjects and 1 observer vomiting. Conclusions: The transient percepts present conflicting signals, which introduced confusion in target and subject orientation. Repeated head movements in hypergravity generate nausea by mechanisms distinct from cross-coupled Coriolis effects
Human Wavelength Discrimination of Monochromatic Light Explained by Optimal Wavelength Decoding of Light of Unknown Intensity
We show that human ability to discriminate the wavelength of monochromatic light
can be understood as maximum likelihood decoding of the cone absorptions, with a
signal processing efficiency that is independent of the wavelength. This work is
built on the framework of ideal observer analysis of visual discrimination used
in many previous works. A distinctive aspect of our work is that we highlight a
perceptual confound that observers should confuse a change in input light
wavelength with a change in input intensity. Hence a simple ideal observer model
which assumes that an observer has a full knowledge of input intensity should
over-estimate human ability in discriminating wavelengths of two inputs of
unequal intensity. This confound also makes it difficult to consistently measure
human ability in wavelength discrimination by asking observers to distinguish
two input colors while matching their brightness. We argue that the best
experimental method for reliable measurement of discrimination thresholds is the
one of Pokorny and Smith, in which observers only need to distinguish two
inputs, regardless of whether they differ in hue or brightness. We
mathematically formulate wavelength discrimination under this
wavelength-intensity confound and show a good agreement between our theoretical
prediction and the behavioral data. Our analysis explains why the discrimination
threshold varies with the input wavelength, and shows how sensitively the
threshold depends on the relative densities of the three types of cones in the
retina (and in particular predict discriminations in dichromats). Our
mathematical formulation and solution can be applied to general problems of
sensory discrimination when there is a perceptual confound from other sensory
feature dimensions
Low retinal noise in animals with low body temperature allows high visual sensitivity
The weakest pulse of light a human can detect sends about 100 photons through the pupil and produces 10−20 rhodopsin isomerizations in a small retinal area1,2. It has been postulated3 that we cannot see single photons because of a retinal noise arising from randomly occurring thermal isomerizations. Direct recordings have since demonstrated the existence of electrical 'dark' rod events indistinguishable from photoisomerization signals4−6. Their mean rate of occurrence is roughly consistent with the 'dark light' in psychophysical threshold experiments, and their thermal parameters justify an identification with thermal isomerizations5. In the retina of amphibians, a small proportion of sensitive ganglion cells have a performance-limiting noise that is low enough to be well accounted for by these events7−10. Here we study the performance of dark-adapted toads and frogs and show that the performance limit of visually guided behaviour is also set by thermal isomerizations. As visual sensitivity limited by thermal events should rise when the temperature falls, poikilothermous vertebrates living at low temperatures should then reach light sensitivities unattainable by mammals and birds with optical factors equal. Comparison of different species at different temperatures shows a correlation between absolute threshold intensities and estimated thermal isomerization rates in the retina
Improving influenza vaccine virus selectionReport of a WHO informal consultation held at WHO headquarters, Geneva, Switzerland, 14–16 June 2010
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90035/1/j.1750-2659.2011.00277.x.pd
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A high-resolution map of human evolutionary constraint using 29 mammals.
The comparison of related genomes has emerged as a powerful lens for genome interpretation. Here we report the sequencing and comparative analysis of 29 eutherian genomes. We confirm that at least 5.5% of the human genome has undergone purifying selection, and locate constrained elements covering ∼4.2% of the genome. We use evolutionary signatures and comparisons with experimental data sets to suggest candidate functions for ∼60% of constrained bases. These elements reveal a small number of new coding exons, candidate stop codon readthrough events and over 10,000 regions of overlapping synonymous constraint within protein-coding exons. We find 220 candidate RNA structural families, and nearly a million elements overlapping potential promoter, enhancer and insulator regions. We report specific amino acid residues that have undergone positive selection, 280,000 non-coding elements exapted from mobile elements and more than 1,000 primate- and human-accelerated elements. Overlap with disease-associated variants indicates that our findings will be relevant for studies of human biology, health and disease
A Positive Feedback Synapse from Retinal Horizontal Cells to Cone Photoreceptors
Cone photoreceptors and horizontal cells (HCs) have a reciprocal synapse that
underlies lateral inhibition and establishes the antagonistic center-surround
organization of the visual system. Cones transmit to HCs through an excitatory
synapse and HCs feed back to cones through an inhibitory synapse. Here we report
that HCs also transmit to cone terminals a positive feedback signal that
elevates intracellular Ca2+ and accelerates neurotransmitter
release. Positive and negative feedback are both initiated by AMPA receptors on
HCs, but positive feedback appears to be mediated by a change in HC
Ca2+, whereas negative feedback is mediated by a change in
HC membrane potential. Local uncaging of AMPA receptor agonists suggests that
positive feedback is spatially constrained to active HC-cone synapses, whereas
the negative feedback signal spreads through HCs to affect release from
surrounding cones. By locally offsetting the effects of negative feedback,
positive feedback may amplify photoreceptor synaptic release without sacrificing
HC-mediated contrast enhancement
Queer In AI: A Case Study in Community-Led Participatory AI
Queerness and queer people face an uncertain future in the face of ever more widely deployed and invasive artificial intelligence (AI). These technologies have caused numerous harms to queer people, including privacy violations, censoring and downranking queer content, exposing queer people and spaces to harassment by making them hypervisible, deadnaming and outing queer people. More broadly, they have violated core tenets of queerness by classifying and controlling queer identities. In response to this, the queer community in AI has organized Queer in AI, a global, decentralized, volunteer-run grassroots organization that employs intersectional and community-led participatory design to build an inclusive and equitable AI future. In this paper, we present Queer in AI as a case study for community-led participatory design in AI. We examine how participatory design and intersectional tenets started and shaped this community’s programs over the years. We discuss different challenges that emerged in the process, look at ways this organization has fallen short of operationalizing participatory and intersectional principles, and then assess the organization’s impact. Queer in AI provides important lessons and insights for practitioners and theorists of participatory methods broadly through its rejection of hierarchy in favor of decentralization, success at building aid and programs by and for the queer community, and effort to change actors and institutions outside of the queer community. Finally, we theorize how communities like Queer in AI contribute to the participatory design in AI more broadly by fostering cultures of participation in AI, welcoming and empowering marginalized participants, critiquing poor or exploitative participatory practices, and bringing participation to institutions outside of individual research projects. Queer in AI’s work serves as a case study of grassroots activism and participatory methods within AI, demonstrating the potential of community-led participatory methods and intersectional praxis, while also providing challenges, case studies, and nuanced insights to researchers developing and using participatory methods
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