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.

How do we ignore stimuli that are salient but irrelevant when our task is to select a lower salient stimulus? Since bottom-up processes favor high saliency, detection of a low-salient target in the presence of highly salient distractors requires top-down attentional guidance. Previous studies have demonstrated that top-down attention can modulate perceptual processing and also that the control of attention is driven by frontoparietal regions. However, to date, there is no direct evidence on the cause and effect relationship between control regions and perceptual processing. Here, we report the first evidence demonstrating a neural circuit for the downregulation of salient distractors when a low-salient target is selected, combining brain imaging using functional magnetic resonance imaging with brain stimulation by transcranial magnetic stimulation. Using these combined techniques, we were able to identify a cause and effect relationship in the suppression of saliency, based on an interaction between the left intraparietal sulcus (IPS) and a region implicated in visual processing in our task (the left occipital pole). In particular, low-salient stimuli were selected by the left IPS suppressing early visual areas that would otherwise respond to a high-saliency distractor in the task. Apart from providing a first documentation of the neural circuit supporting selection by saliency, these data can be critical for understanding the underlying causes of problems in ignoring irrelevant salience that are found in both acquired and neurodevelopmental disorders (e.g., attention deficit/hyperactivity disorder or autism).

Aims/hypothesesIn adults, type 2 diabetes and obesity have been associated with structural brain changes, even in the absence of dementia. Some evidence suggested similar changes in adolescents with type 2 diabetes but comparisons with a non-obese control group have been lacking. The aim of the current study was to examine differences in microstructure of gray and white matter between adolescents with type 2 diabetes, obese adolescents and healthy weight adolescents.MethodsMagnetic resonance imaging data were collected from 15 adolescents with type 2 diabetes, 21 obese adolescents and 22 healthy weight controls. Volumetric differences in the gray matter between the three groups were examined using voxel based morphology, while tract based spatial statistics was used to examine differences in the microstructure of the white matter.ResultsAdolescents with type 2 diabetes and obese adolescents had reduced gray matter volume in the right hippocampus, left putamen and caudate, bilateral amygdala and left thalamus compared to healthy weight controls. Type 2 diabetes was also associated with significant regional changes in fractional anisotropy within the corpus callosum, fornix, left inferior fronto-occipital fasciculus, left uncinate, left internal and external capsule. Fractional anisotropy reductions within these tracts were explained by increased radial diffusivity, which may suggest demyelination of white matter tracts. Mean diffusivity and axial diffusivity did not differ between the groups.Conclusion/interpretationOur data shows that adolescent obesity alone results in reduced gray matter volume and that adolescent type 2 diabetes is associated with both white and gray matter abnormalities.

This study compared the effects of age on the perception of translational, radial, and rotational global motion patterns. Motion coherence thresholds were measured for judging the direction of each motion type as a function of contrast (visibility) and temporal sampling rate in young and elderly participants. Coherence thresholds decreased as dot contrast increased asymptoting at high dot contrasts but were higher in elderly compared to young participants. This equated to global motion impairment in the elderly of a factor of around 2, characterized by a shift of the threshold vs. contrast function along the horizontal axes (dot contrast). The effect of contrast interacted with the temporal sampling rate. Old participants were deleteriously affected by reduced temporal sampling particularly at low contrasts. The findings suggest that age-related changes in global motion perception may be driven principally by deficits in contrast encoding, rather than by deficits in motion integration and suggest a role for increased internal noise in the older visual system.