A Nier-type mass spectrometer and its associated electronic units have been constructed for the purpose of measuring small variations in the abundances of oxygen of mass 18 and of carbon of mass 13 in carbon dioxide, and of oxygen of mass 18 in oxygen gas, to an accuracy of ±0.01 percent of the abundance of these isotopes. The electronic units of the necessary stability for this degree of accuracy are described. A gas feed system is described which permits fast alternate introduction of the sample of gas to be analyzed and a standard gas into the mass spectrometer. All measurements of the variation in the abundance of the oxygen and carbon isotopes are made with reference to a standard.
Published studies assessing the association between cognitive performance and speech-in-noise (SiN) perception examine different aspects of each, test different listeners, and often report quite variable associations. By examining the published evidence base using a systematic approach, we aim to identify robust patterns across studies and highlight any remaining gaps in knowledge. We limit our assessment to adult unaided listeners with audiometric profiles ranging from normal hearing to moderate hearing loss. A total of 253 articles were independently assessed by two researchers, with 25 meeting the criteria for inclusion. Included articles assessed cognitive measures of attention, memory, executive function, IQ, and processing speed. SiN measures varied by target (phonemes or syllables, words, and sentences) and masker type (unmodulated noise, modulated noise, >2-talker babble, and ≤2-talker babble. The overall association between cognitive performance and SiN perception was r = .31. For component cognitive domains, the association with (pooled) SiN perception was as follows: processing speed (r = .39), inhibitory control (r = .34), working memory (r = .28), episodic memory (r = .26), and crystallized IQ (r = .18). Similar associations were shown for the different speech target and masker types. This review suggests a general association of r≈.3 between cognitive performance and speech perception, although some variability in association appeared to exist depending on cognitive domain and SiN target or masker assessed. Where assessed, degree of unaided hearing loss did not play a major moderating role. We identify a number of cognitive performance and SiN perception combinations that have not been tested and whose future investigation would enable further fine-grained analyses of these relationships.
Ageing is associated with declines in both perception and cognition. We review evidence for an interaction between perceptual and cognitive decline in old age. Impoverished perceptual input can increase the cognitive difficulty of tasks, while changes to cognitive strategies can compensate, to some extent, for impaired perception. While there is strong evidence from cross-sectional studies for a link between sensory acuity and cognitive performance in old age, there is not yet compelling evidence from longitudinal studies to suggest that poor perception causes cognitive decline, nor to demonstrate that correcting sensory impairment can improve cognition in the longer term. Most studies have focused on relatively simple measures of sensory (visual and auditory) acuity, but more complex measures of suprathreshold perceptual processes, such as temporal processing, can show a stronger link with cognition. The reviewed evidence underlines the importance of fully accounting for perceptual deficits when investigating cognitive decline in old age.
We examined the contributions of the human pulvinar to goal directed selection of visual targets in 3 patients with chronic, unilateral lesions involving topographic maps in the ventral pulvinar. Observers completed 2 psychophysical tasks in which they discriminated the orientation of a lateralized target grating in the presence of vertically-aligned distracters. In experiment 1, where distracter contrast was varied while target contrast remained constant, the patients' contralesional contrast thresholds for discriminating the orientation of grating stimuli were elevated only when the task required selection of a visual target in the face of competition from a salient distracter. Attentional selectivity was restored in the patients in experiment 2 where target contrast was varied while distracter contrast remained constant. These observations provide the first evidence that the human pulvinar plays a necessary role in modulating physical saliency in attentional selection, and supports a homology in global pulvinar structure between humans and monkey.salience ͉ visual attention M ultiple items within a visual scene compete for our focal attention. This competition is resolved on the basis of both the perceptual salience of the stimulus and its behavioral salience in relation to the goals of ongoing behavior (1). Visual items can compete for representation in ventral occipito-temporal brain areas, with this competition varying according to the physical distinctiveness of the items and according to whether they demand processing through the same receptive fields (2, 3). The competition can also be biased in favor of less conspicuous objects if they are nonetheless more relevant for behavior (2,4,5). These ''goaldriven'' attentional control signals arise within dorsal frontoparietal networks (6-8) and they lead to behavioral improvements in discriminating the features of the attended object (9, 10). What remains unclear is how such ''dorsal'' attentional signals are communicated to ventral occipital and temporal areas to bias visual analysis. Here, we report the first direct behavioral evidence in humans for the role of the pulvinar in coordinating these goaldriven and stimulus-driven interactions. We used a sensitive psychophysical task to examine target selection in a special group of patients with well documented chronic, unilateral lesions involving topographic maps in the ventral pulvinar. Our findings demonstrate that the pulvinar plays an important role in filtering irrelevant but salient visual distracters.The pulvinar nucleus of the thalamus has been hypothesized to play a central role in coordinating attentional effects on visual processing (11,12). Most of our current knowledge on patterns of connectivity of the pulvinar stems from anatomical studies in non-human primates. The primate pulvinar has extensive connectivity with the cortex. Based on this connectivity, several general organising principles within the pulvinar have been suggested: a global dorsal/ventral division, and an anterior/ posterior org...
The ability to attend to relevant events and to ignore irrelevant stimuli is crucial to survival. Theories disagree on whether this ability is dependent solely on increased neural activation for relevant items or whether active ignoring can also play a role. The authors examined the active ignoring of stimuli using a preview search procedure, where irrelevant faces appeared prior to relevant house stimuli. They found increased activation in brain regions associated with spatial memory and in content-specific faceprocessing areas when participants ignored the irrelevant faces. Differences arose even on trials when only previewed faces appeared, and the magnitude of these differences predicted how well faces were ignored in search. Activation associated with active ignoring decreased when a secondary task was imposed during the preview. The data reveal a neural marker for the process of actively ignoring the content and locations of irrelevant stimuli.
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