scholarly journals Constructing Stable Spatial Maps of the Word

Perception ◽  
10.1068/p7392 ◽  
2012 ◽  
Vol 41 (11) ◽  
pp. 1355-1372 ◽  
Author(s):  
David C Burr ◽  
Maria Concetta Morrone
Keyword(s):  
Visual System ◽  
Receptive Fields ◽  
Strong Support ◽  
Neural Representation ◽  
Adaptation Studies ◽  
Visual Stream ◽  
Standard Position ◽  
The World ◽  
Transient System ◽  
The Stability

To interact rapidly and effectively with our environment, our brain needs access to a neural representation—or map—of the spatial layout of the external world. However, the construction of such a map poses major challenges to the visual system, given that the images on our retinae depend on where the eyes are looking, and shift each time we move our eyes, head, and body to explore the world. Much research has been devoted to how the stability is achieved, with the debate often polarized between the utility of spatiotopic maps (that remain solid in external coordinates), as opposed to transiently updated retinotopic maps. Our research suggests that the visual system uses both strategies to maintain stability. f MRI, motion-adaptation, and saccade-adaptation studies demonstrate and characterize spatiotopic neural maps within the dorsal visual stream that remain solid in external rather than retinal coordinates. However, the construction of these maps takes time (up to 500 ms) and attentional resources. To solve the immediate problems created by individual saccades, we postulate the existence of a separate system to bridge each saccade with neural units that are ‘transiently craniotopic’. These units prepare for the effects of saccades with a shift of their receptive fields before the saccade starts, then relaxing back into their standard position during the saccade, compensating for its action. Psychophysical studies investigating localization of stimuli flashed briefly around the time of saccades provide strong support for these neural mechanisms, and show quantitatively how they integrate information across saccades. This transient system cooperates with the spatiotopic mechanism to provide a useful map to guide interactions with our environment: one rapid and transitory, bringing into play the high-resolution visual areas; the other slow, long-lasting, and low-resolution, useful for interacting with the world.

The Detection of Orientation of Small Objects

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 59-59
Author(s):  
J M Zanker ◽  
M P Davey
Keyword(s):  
Visual Field ◽  
Visual System ◽  
Computer Simulations ◽  
Visual Information ◽  
Human Performance ◽  
Receptive Fields ◽  
Experimental Result ◽  
Orientation Tuning ◽  
Basic Question ◽  
Visual Stream

Visual information processing in primate cortex is based on a highly ordered representation of the surrounding world. In addition to the retinotopic mapping of the visual field, systematic variations of the orientation tuning of neurons are described electrophysiologically for the first stages of the visual stream. On the way to understanding the relation of position and orientation representation, in order to give an adequate account of cortical architecture, it will be an essential step to define the minimum spatial requirements for detection of orientation. We addressed the basic question of spatial limits for detecting orientation by comparing computer simulations of simple orientation filters with psychophysical experiments in which the orientation of small lines had to be detected at various positions in the visual field. At sufficiently high contrast levels, the minimum physical length of a line whose orientation can just be resolved is not constant when presented at various eccentricities, but covaries inversely with the cortical magnification factor. A line needs to span less than 0.2 mm on the cortical surface in order to be recognised as oriented, independently of the actual eccentricity at which the stimulus is presented. This seems to indicate that human performance for this task approaches the physical limits, requiring hardly more than approximately three input elements to be activated, in order to detect the orientation of a highly visible line segment. Combined with the estimates for receptive field sizes of orientation-selective filters derived from computer simulations, this experimental result may nourish speculations of how the rather local elementary process underlying orientation detection in the human visual system can be assembled to form much larger receptive fields of the orientation-sensitive neurons known to exist in the primate visual system.

Unveiling the Theoretical Mistakes in the World Bank Formation and its Implication on Survival of Africa Monetary Union

2019 ◽  
Vol 10 (1) ◽  
pp. 119-124
Author(s):  
Olatunji Abdul Shobande ◽  
Kingsley Chinonso Mark
Keyword(s):  
World Bank ◽  
Monetary Union ◽  
Political Interest ◽  
World Bank Group ◽  
Policy Makers ◽  
The World Bank ◽  
The World ◽  
Bank Group ◽  
The Stability ◽  
Developed Nations

Abstract The quest for urgent solution to resolve the world liquidity problem has continued to generate enthusiastic debates among political economists, policy makers and the academia. The argument has focused on whether the World Bank Group was established to enhance the stability of international financial system or meant to enrich the developed nations. This study argues that the existing political interest of the World Bank Group in Africa may serve as lesson learned to other ambitious African Monetary Union.

Four Conceptions of Authority in International Relations

2021 ◽  
pp. 1-25
Author(s):  
Jorg Kustermans ◽  
Rikkert Horemans
Keyword(s):  
International Relations ◽  
Emotional Experience ◽  
Political Actors ◽  
International Authority ◽  
The World ◽  
Authority Relations ◽  
The Stability

Abstract There is increasing agreement that states and other political actors on the world stage sometimes achieve international authority. However, there is less agreement about the nature and functioning of international authority relations. What determines whether an actor will be recognized as an authoritative actor? And what are the effects thereof? In this essay, we identify four distinct conceptions of authority in the study of international relations: authority as contract, authority as domination, authority as impression, and authority as consecration. Consideration of the typology leads to two important insights. First, the phenomenon of authority has an essentially experiential dimension. Subordinate actors’ emotional experience of authority determines their response to authority and thus also has a fundamental impact on the stability of authority. Second, the emergence of forms of international authority does not entail, at least not necessarily, the weakening of the sovereignty of states, but can equally be argued to strengthen it.

Application of ABAQUS in Surrounding Rock Stability Analysis of Shallow Large Cross-Section Tunnel

2015 ◽  
Vol 777 ◽  
pp. 8-12 ◽  
Author(s):  
Lin Zhen Cai ◽  
Cheng Liang Zhang
Keyword(s):  
Numerical Simulation ◽  
Rock Mass ◽  
Strong Support ◽  
Surrounding Rock ◽  
Tunnel Engineering ◽  
Tunnel Excavation ◽  
Rock Stability ◽  
Rock Bolting ◽  
Excavation Support ◽  
The Stability

HuJiaDi tunnel construction of Dai Gong highway is troublesome, the surrounding-rock mass give priority to full to strong weathering basalt, surrounding rock integrity is poor, weak self-stability of surrounding rock, and tunnel is prone to collapse. In order to reduce disturbance, taking advantage of the ability of rock mass, excavation adopt the method of "more steps, short footage and strong support". The excavation method using three steps excavation, The excavation footage is about 1.2 ~ 1.5 m; The surrounding rock bolting system still produce a large deformation after completion of the first support construction, it shows that the adopted support intensity cannot guarantee the stability of the tunnel engineering. Using ABAQUS to simulate tunnel excavation support, optimizing the support parameters of the tunnel, conducting comparative analysis with Monitoring and Measuring and numerical simulation results, it shows that the displacement - time curves have a certain consistency in numerical simulation of ABAQUS and Monitoring and Measuring.

scholarly journals Effects of Maximal Sodium and Potassium Conductance on the Stability of Hodgkin-Huxley Model

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Yue Zhang ◽  
Kuanquan Wang ◽  
Yongfeng Yuan ◽  
Dong Sui ◽  
Henggui Zhang
Keyword(s):  
Experimental Data ◽  
Mathematical Method ◽  
Bifurcation Point ◽  
Potassium Conductance ◽  
Maximal Conductance ◽  
Computing Model ◽  
The World ◽  
Stability And Bifurcations ◽  
The Stability ◽  
Sodium And Potassium

Hodgkin-Huxley (HH) equation is the first cell computing model in the world and pioneered the use of model to study electrophysiological problems. The model consists of four differential equations which are based on the experimental data of ion channels. Maximal conductance is an important characteristic of different channels. In this study, mathematical method is used to investigate the importance of maximal sodium conductanceg-Naand maximal potassium conductanceg-K. Applying stability theory, and takingg-Naandg-Kas variables, we analyze the stability and bifurcations of the model. Bifurcations are found when the variables change, and bifurcation points and boundary are also calculated. There is only one bifurcation point wheng-Nais the variable, while there are two points wheng-Kis variable. The (g-Na,  g-K) plane is partitioned into two regions and the upper bifurcation boundary is similar to a line when bothg-Naandg-Kare variables. Numerical simulations illustrate the validity of the analysis. The results obtained could be helpful in studying relevant diseases caused by maximal conductance anomaly.

Foreign exchange earnings of the countries of the world from international trade in fruit and berry products

2021 ◽  
pp. 45-56
Author(s):  
Rafail R. Mukhametzyanov ◽  
◽  
Nikolay G. Platonovskiy ◽  
Akhmed M. Khezhev ◽  
Tatiyana V. Ostapchuk ◽  
...  
Keyword(s):  
International Trade ◽  
Foreign Exchange ◽  
Import Substitution ◽  
World Order ◽  
Climatic Conditions ◽  
The European Union ◽  
The World ◽  
Increasing Demand ◽  
Processed Products ◽  
The Stability

In the context of the modern global financial world order, an important element of the stability of the national monetary unit of the overwhelming majority of countries in the world, especially developing countries, is foreign exchange earnings. For some countries with favorable natural and climatic conditions, the production, processing and export of agricultural products plays a significant role in the overall structure of foreign exchange earnings in the country. The constantly increasing demand from consumers for fruits, berries, nuts and their processed products allows economic entities of national fruit and berry subcomplexes to increase the volume of growing and exporting these types of products. This study analyzes the change in the volume of exports and imports of fruit and berry products in value terms for the period 2010-2019. It is revealed that some states, being the largest exporters of fruits, berries, nuts and products of their processing, occupy significant positions in the import of these types of products from abroad. Based on the author’s calculations, the top 30 countries of the world have been compiled in terms of net foreign exchange earnings from international trade in this type of product. According to this indicator, the first line with a level of $ 7.506 billion was occupied by Spain, while it increased it by $ 1.675 billion over 10 years. As for Russia, despite the counter-sanctions against the countries of the European Union and some other countries of the world, as well as the ongoing policy of import substitution, including in domestic gardening, it continues to be one of the main importers of fruits, berries, nuts and their processing products in the world. Thus, our country supports both foreign producers and other commercial structures that carry out the processes of commodity circulation of fruit and berry products, and the receipt of foreign exchange earnings in these powers.

Consumer Behavior Changes Post Pandemic Covid-19

2020 ◽  
Vol 2 (2) ◽  
pp. 84-89
Author(s):  
Tati Maryati
Keyword(s):  
Consumer Behavior ◽  
Eating Habits ◽  
Supply And Demand ◽  
Health Economy ◽  
Behavior Changes ◽  
The World ◽  
The Stability ◽  
The Many ◽  
New Consumer ◽  
At Home

The Corona virus or Covid-19 which is unexpected will come to us, has an impact on health, economy and also humanity throughout the world and is able to fundamentally change the world. Supplements are disrupted because production is stopped, retail stores close, causing consumers to change their behavior, which had previously gone offline shopping. Not just shopping, when a pandemic, the way of thinking becomes different. Consumers around the world are looking for products and brands through new ways and new habits are formed. Online transactions focus more on basic products to make ends meet. The fact that Covid-19's anti-virus has not been found raises concerns about disrupted health and the Government's regulation to work and stay at home also raises concerns about disrupted businesses. Differences from habits and interests or preferences that are different for each person, provide different responses to the problems faced and solutions for the future. The habit of shopping offline has a tendency to continue for complementary products while food products are more directed towards offline. The rest eating habits at home can be continued because it provides more hygiene guarantees. The new habit of holding online meetings with distant relatives or colleagues will be increasingly considered given the many more positive things that can be obtained. Likewise with work problems, working from home is more interesting to consider because it is more efficient and effective and the results can be more productive. This new consumer behavior is adjusted to provide satisfaction for many parties, with the assistance of institutions or governments that oversee the security of supply and demand and maintain the stability of both. 

scholarly journals Role of the Zebra Finch Auditory Thalamus in Generating Complex Representations for Natural Sounds

2010 ◽  
Vol 104 (2) ◽  
pp. 784-798 ◽  
Author(s):  
Noopur Amin ◽  
Patrick Gill ◽  
Frédéric E. Theunissen
Keyword(s):  
Receptive Fields ◽  
Neural Representation ◽  
Natural Sounds ◽  
Auditory Midbrain ◽  
Complex Sounds ◽  
Auditory Thalamus ◽  
Spectrotemporal Receptive Fields ◽  
Primary Sensory Cortex ◽  
Relay Nucleus ◽  
Field L

We estimated the spectrotemporal receptive fields of neurons in the songbird auditory thalamus, nucleus ovoidalis, and compared the neural representation of complex sounds in the auditory thalamus to those found in the upstream auditory midbrain nucleus, mesencephalicus lateralis dorsalis (MLd), and the downstream auditory pallial region, field L. Our data refute the idea that the primary sensory thalamus acts as a simple, relay nucleus: we find that the auditory thalamic receptive fields obtained in response to song are more complex than the ones found in the midbrain. Moreover, we find that linear tuning diversity and complexity in ovoidalis (Ov) are closer to those found in field L than in MLd. We also find prevalent tuning to intermediate spectral and temporal modulations, a feature that is unique to Ov. Thus even a feed-forward model of the sensory processing chain, where neural responses in the sensory thalamus reveals intermediate response properties between those in the sensory periphery and those in the primary sensory cortex, is inadequate in describing the tuning found in Ov. Based on these results, we believe that the auditory thalamic circuitry plays an important role in generating novel complex representations for specific features found in natural sounds.

scholarly journals Development of population receptive fields in the lateral visual stream improves spatial coding amid stable structural-functional coupling

NeuroImage ◽  
2019 ◽  
Vol 188 ◽  
pp. 59-69 ◽  
Author(s):  
Jesse Gomez ◽  
Alexis Drain ◽  
Brianna Jeska ◽  
Vaidehi S. Natu ◽  
Michael Barnett ◽  
...  
Keyword(s):  
Receptive Fields ◽  
Functional Coupling ◽  
Spatial Coding ◽  
Visual Stream

scholarly journals Dynamical Latent State Computation in the Posterior Parietal Cortex

2022 ◽  
Author(s):  
Kaushik J Lakshminarasimhan ◽  
Eric Avila ◽  
Xaq Pitkow ◽  
Dora E Angelaki
Keyword(s):  
Parietal Cortex ◽  
Posterior Parietal Cortex ◽  
Target Location ◽  
Neural Representation ◽  
World Model ◽  
Population Activity ◽  
The World ◽  
Neural Interactions ◽  
Posterior Parietal ◽  
Hidden States

Success in many real-world tasks depends on our ability to dynamically track hidden states of the world. To understand the underlying neural computations, we recorded brain activity in posterior parietal cortex (PPC) of monkeys navigating by optic flow to a hidden target location within a virtual environment, without explicit position cues. In addition to sequential neural dynamics and strong interneuronal interactions, we found that the hidden state -- monkey's displacement from the goal -- was encoded in single neurons, and could be dynamically decoded from population activity. The decoded estimates predicted navigation performance on individual trials. Task manipulations that perturbed the world model induced substantial changes in neural interactions, and modified the neural representation of the hidden state, while representations of sensory and motor variables remained stable. The findings were recapitulated by a task-optimized recurrent neural network model, suggesting that neural interactions in PPC embody the world model to consolidate information and track task-relevant hidden states.

Sign in / Sign up

Export Citation Format

Share Document