The Experts below are selected from a list of 96924 Experts worldwide ranked by ideXlab platform
René Marois - One of the best experts on this subject based on the ideXlab platform.
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distinct Capacity Limits for attention and working memory evidence from attentive tracking and visual working memory paradigms
Psychological Science, 2006Co-Authors: Daryl Fougnie, René MaroisAbstract:A hallmark of both visual attention and working memory is their severe Capacity Limit: People can attentively track only about four objects in a multiple object tracking (MOT) task and can hold only up to four objects in visual working memory (VWM). It has been proposed that attention underlies the Capacity Limit of VWM. We tested this hypothesis by determining the effect of varying the load of a MOT task performed during the retention interval of a VWM task and comparing the resulting dual-task costs with those observed when a VWM task was performed concurrently with another VWM task or with a verbal working memory task. Instead of supporting the view that the Capacity Limit of VWM is solely attention based, the results indicate that VWM Capacity is set by the interaction of visuospatial attentional, central amodal, and local task-specific sources of processing.
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posterior parietal cortex activity predicts individual differences in visual short term memory Capacity
Cognitive Affective & Behavioral Neuroscience, 2005Co-Authors: J. Jay Todd, René MaroisAbstract:Humans show a severe Capacity Limit in the number of objects they can store in visual short-term memory (VSTM). We recently demonstrated with functional magnetic resonance imaging that VSTM storage Capacity estimated in averaged group data correlated strongly with posterior parietal/superior occipital cortex activity (Todd & Marois, 2004). However, individuals varied widely in their VSTM Capacity. Here, we examined the neural basis of these individual differences. A voxelwise, individualdifferences analysis revealed a significant correlation between posterior parietal cortex (PPC) activity and individuals’ VSTM storage Capacity. In addition, a region-of-interest analysis indicated that other brain regions, particularly visual occipital cortex, may contribute to individual differences in VSTM Capacity. Thus, although not ruling out contributions from other brain regions, the individual-differences approach supports a key role for the PPC in VSTM by demonstrating that its activity level predicts individual differences in VSTM storage Capacity.
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Capacity Limit of visual short-term memory in human posterior parietal cortex
Nature, 2004Co-Authors: J. Jay Todd, René MaroisAbstract:At any instant, our visual system allows us to perceive a rich and detailed visual world. Yet our internal, explicit representation of this visual world is extremely sparse: we can only hold in mind a minute fraction of the visual scene. These mental representations are stored in visual short-term memory (VSTM). Even though VSTM is essential for the execution of a wide array of perceptual and cognitive functions, and is supported by an extensive network of brain regions, its storage Capacity is severely Limited. With the use of functional magnetic resonance imaging, we show here that this Capacity Limit is neurally reflected in one node of this network: activity in the posterior parietal cortex is tightly correlated with the Limited amount of scene information that can be stored in VSTM. These results suggest that the posterior parietal cortex is a key neural locus of our impoverished mental representation of the visual world.
Pawel Koteja - One of the best experts on this subject based on the ideXlab platform.
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Limits to sustained energy intake xxiii does heat dissipation Capacity Limit the energy budget of lactating bank voles
The Journal of Experimental Biology, 2016Co-Authors: Edyta T Sadowska, Elzbieta Krol, Katarzyna M Chrzascik, Agata M Rudolf, John R Speakman, Pawel KotejaAbstract:Understanding factors Limiting sustained metabolic rate (SusMR) is a central issue in ecological physiology. According to the heat dissipation Limit (HDL) theory, the SusMR at peak lactation is constrained by the maternal Capacity to dissipate body heat. To test that theory, we shaved lactating bank voles (Myodes glareolus) to experimentally elevate their Capacity for heat dissipation. The voles were sampled from lines selected for high aerobic exercise metabolism (A; characterized also by increased basal metabolic rate) and unselected control lines (C). Fur removal significantly increased the peak-lactation food intake (mass-adjusted least square means ± s.e.; shaved: 16.3 ± 0.3 g day(-1), unshaved: 14.4 ± 0.2 g day(-1); P<0.0001), average daily metabolic rate (shaved: 109 ± 2 kJ day(-1), unshaved: 97 ± 2 kJ day(-1); P<0.0001) and metabolisable energy intake (shaved: 215 ± 4 kJ day(-1), unshaved: 185 ± 4 kJ day(-1); P<0.0001), as well as the milk energy output (shaved: 104 ± 4 kJ day(-1); unshaved: 93 ± 4 kJ day(-1); P=0.021) and litter growth rate (shaved: 9.4 ± 0.7 g 4 days(-1), unshaved: 7.7 ± 0.7 g 4 days(-1); P=0.028). Thus, fur removal increased both the total energy budget and reproductive output at the most demanding period of lactation, which supports the HDL theory. However, digestive efficiency was lower in shaved voles (76.0 ± 0.3%) than in unshaved ones (78.5 ± 0.2%; P<0.0001), which may indicate that a Limit imposed by the Capacity of the alimentary system was also approached. Shaving similarly affected the metabolic and reproductive traits in voles from the A and C lines. Thus, the experimental evolution model did not reveal a difference in the Limiting mechanism between animals with inherently different metabolic rates.
John R Speakman - One of the best experts on this subject based on the ideXlab platform.
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Limits to sustained energy intake xxiii does heat dissipation Capacity Limit the energy budget of lactating bank voles
The Journal of Experimental Biology, 2016Co-Authors: Edyta T Sadowska, Elzbieta Krol, Katarzyna M Chrzascik, Agata M Rudolf, John R Speakman, Pawel KotejaAbstract:Understanding factors Limiting sustained metabolic rate (SusMR) is a central issue in ecological physiology. According to the heat dissipation Limit (HDL) theory, the SusMR at peak lactation is constrained by the maternal Capacity to dissipate body heat. To test that theory, we shaved lactating bank voles (Myodes glareolus) to experimentally elevate their Capacity for heat dissipation. The voles were sampled from lines selected for high aerobic exercise metabolism (A; characterized also by increased basal metabolic rate) and unselected control lines (C). Fur removal significantly increased the peak-lactation food intake (mass-adjusted least square means ± s.e.; shaved: 16.3 ± 0.3 g day(-1), unshaved: 14.4 ± 0.2 g day(-1); P<0.0001), average daily metabolic rate (shaved: 109 ± 2 kJ day(-1), unshaved: 97 ± 2 kJ day(-1); P<0.0001) and metabolisable energy intake (shaved: 215 ± 4 kJ day(-1), unshaved: 185 ± 4 kJ day(-1); P<0.0001), as well as the milk energy output (shaved: 104 ± 4 kJ day(-1); unshaved: 93 ± 4 kJ day(-1); P=0.021) and litter growth rate (shaved: 9.4 ± 0.7 g 4 days(-1), unshaved: 7.7 ± 0.7 g 4 days(-1); P=0.028). Thus, fur removal increased both the total energy budget and reproductive output at the most demanding period of lactation, which supports the HDL theory. However, digestive efficiency was lower in shaved voles (76.0 ± 0.3%) than in unshaved ones (78.5 ± 0.2%; P<0.0001), which may indicate that a Limit imposed by the Capacity of the alimentary system was also approached. Shaving similarly affected the metabolic and reproductive traits in voles from the A and C lines. Thus, the experimental evolution model did not reveal a difference in the Limiting mechanism between animals with inherently different metabolic rates.
Rene-jean Essiambre - One of the best experts on this subject based on the ideXlab platform.
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Capacity Limits of Optical Fiber Networks
Journal of Lightwave Technology, 2010Co-Authors: Rene-jean Essiambre, G.j. Gerard J Foschini, Peter J P.j. Winzer, Gerhard Kramer, Bernhard GoebelAbstract:We describe a method to estimate the Capacity Limit of fiber-optic communication systems (or ¿fiber channels¿) based on information theory. This paper is divided into two parts. Part 1 reviews fundamental concepts of digital communications and information theory. We treat digitization and modulation followed by information theory for channels both without and with memory. We provide explicit relationships between the commonly used signal-to-noise ratio and the optical signal-to-noise ratio. We further evaluate the performance of modulation constellations such as quadrature-amplitude modulation, combinations of amplitude-shift keying and phase-shift keying, exotic constellations, and concentric rings for an additive white Gaussian noise channel using coherent detection. Part 2 is devoted specifically to the "fiber channel.'' We review the physical phenomena present in transmission over optical fiber networks, including sources of noise, the need for optical filtering in optically-routed networks, and, most critically, the presence of fiber Kerr nonlinearity. We describe various transmission scenarios and impairment mitigation techniques, and define a fiber channel deemed to be the most relevant for communication over optically-routed networks. We proceed to evaluate a Capacity Limit estimate for this fiber channel using ring constellations. Several scenarios are considered, including uniform and optimized ring constellations, different fiber dispersion maps, and varying transmission distances. We further present evidences that point to the physical origin of the fiber Capacity Limitations and provide a comparison of recent record experiments with our Capacity Limit estimation.
J. Jay Todd - One of the best experts on this subject based on the ideXlab platform.
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posterior parietal cortex activity predicts individual differences in visual short term memory Capacity
Cognitive Affective & Behavioral Neuroscience, 2005Co-Authors: J. Jay Todd, René MaroisAbstract:Humans show a severe Capacity Limit in the number of objects they can store in visual short-term memory (VSTM). We recently demonstrated with functional magnetic resonance imaging that VSTM storage Capacity estimated in averaged group data correlated strongly with posterior parietal/superior occipital cortex activity (Todd & Marois, 2004). However, individuals varied widely in their VSTM Capacity. Here, we examined the neural basis of these individual differences. A voxelwise, individualdifferences analysis revealed a significant correlation between posterior parietal cortex (PPC) activity and individuals’ VSTM storage Capacity. In addition, a region-of-interest analysis indicated that other brain regions, particularly visual occipital cortex, may contribute to individual differences in VSTM Capacity. Thus, although not ruling out contributions from other brain regions, the individual-differences approach supports a key role for the PPC in VSTM by demonstrating that its activity level predicts individual differences in VSTM storage Capacity.
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Capacity Limit of visual short-term memory in human posterior parietal cortex
Nature, 2004Co-Authors: J. Jay Todd, René MaroisAbstract:At any instant, our visual system allows us to perceive a rich and detailed visual world. Yet our internal, explicit representation of this visual world is extremely sparse: we can only hold in mind a minute fraction of the visual scene. These mental representations are stored in visual short-term memory (VSTM). Even though VSTM is essential for the execution of a wide array of perceptual and cognitive functions, and is supported by an extensive network of brain regions, its storage Capacity is severely Limited. With the use of functional magnetic resonance imaging, we show here that this Capacity Limit is neurally reflected in one node of this network: activity in the posterior parietal cortex is tightly correlated with the Limited amount of scene information that can be stored in VSTM. These results suggest that the posterior parietal cortex is a key neural locus of our impoverished mental representation of the visual world.
