Attentional modulation of firing rate and synchrony in a model cortical network

When attention is directed into the receptive field of a V4 neuron, its contrast response curve is shifted to lower contrast values (Reynolds et al, 2000, Neuron 26:703). Attention also increases the coherence between neurons responding to the same stimulus (Fries et al, 2001, Science 291:1560). We studied how the firing rate and synchrony of a densely interconnected cortical network varied with contrast and how they were modulated by attention. We found that an increased driving current to the excitatory neurons increased the overall firing rate of the network, whereas variation of the driving current to inhibitory neurons modulated the synchrony of the network. We explain the synchrony modulation in terms of a locking phenomenon during which the ratio of excitatory to inhibitory firing rates is approximately constant for a range of driving current values. We explored the hypothesis that contrast is represented primarily as a drive to the excitatory neurons, whereas attention corresponds to a reduction in driving current to the inhibitory neurons. Using this hypothesis, the model reproduces the following experimental observations: (1) the firing rate of the excitatory neurons increases with contrast; (2) for high contrast stimuli, the firing rate saturates and the network synchronizes; (3) attention shifts the contrast response curve to lower contrast values; (4) attention leads to stronger synchronization that starts at a lower value of the contrast compared with the attend-away condition. In addition, it predicts that attention increases the delay between the inhibitory and excitatory synchronous volleys produced by the network, allowing the stimulus to recruit more downstream neurons.Comment: 36 pages, submitted to Journal of Computational Neuroscienc

Corruption and Positive Selection in Privatization

We consider the supply of a public good based on a publicly-owned facility. The Government has a choice between provision in-house and privatizing the facility and then outsourcing the production. In particular, we focus on corruption in the decision to privatize and on its effect on social welfare when there is asymmetric information on the public and private manager's efficiency. Our analysis shows that a corrupt Government, that chooses to privatize only in exchange for a bribe, makes a positive selection on the private firm's efficiency and, thus, may raise expected social welfare above what an honest Government could get.Corruption, Privatization, Private vs. public provision.

Quantum transport properties of ultrathin silver nanowires

The quantum transport properties of the ultrathin silver nanowires are investigated. For a perfect crystalline nanowire with four atoms per unit cell, three conduction channels are found, corresponding to three $s$ bands crossing the Fermi level. One conductance channel is disrupted by a single-atom defect, either adding or removing one atom. Quantum interference effect leads to oscillation of conductance versus the inter-defect distance. In the presence of multiple-atom defect, one conduction channel remains robust at Fermi level regardless the details of defect configuration. The histogram of conductance calculated for a finite nanowire (seven atoms per cross section) with a large number of random defect configurations agrees well with recent experiment.Comment: 4 pages, 6 figure

REVOLUTIONS FROM NORTHERN AFRICA: A GRAND QUESTION FOR MANKIND?

The spring of the indignations against the presidents of the North African states and in the Middle East has aroused worldwide interest, not only in terms of their political effects in those states, but rather in terms of how these events have been suppressed by authoritarian regimes and the effects on the global economy and geopolitics

Corruption as an Alternative to Limit Pricing

We explore to what extent bribery can be an alternative way of fighting rivals’ entry on the market when there is uncertainty about the degree of corruption in the public sector. For high levels of corruption, “covert” fight through bribery is the optimal choice of an incumbent. For low degree of corruption, instead, the incumbent prefers to act strategically but overtly by playing a limit pricing game.Corruption, Bribery, Production licence, Moral cost, Covert/overt fight

A role for recurrent processing in object completion: neurophysiological, psychophysical and computational"evidence

Recognition of objects from partial information presents a significant challenge for theories of vision because it requires spatial integration and extrapolation from prior knowledge. We combined neurophysiological recordings in human cortex with psychophysical measurements and computational modeling to investigate the mechanisms involved in object completion. We recorded intracranial field potentials from 1,699 electrodes in 18 epilepsy patients to measure the timing and selectivity of responses along human visual cortex to whole and partial objects. Responses along the ventral visual stream remained selective despite showing only 9-25% of the object. However, these visually selective signals emerged ~100 ms later for partial versus whole objects. The processing delays were particularly pronounced in higher visual areas within the ventral stream, suggesting the involvement of additional recurrent processing. In separate psychophysics experiments, disrupting this recurrent computation with a backward mask at ~75ms significantly impaired recognition of partial, but not whole, objects. Additionally, computational modeling shows that the performance of a purely bottom-up architecture is impaired by heavy occlusion and that this effect can be partially rescued via the incorporation of top-down connections. These results provide spatiotemporal constraints on theories of object recognition that involve recurrent processing to recognize objects from partial information

Occupation and working outcomes during the Coronavirus Pandemic

Using data from the recent SHARE COVID-19 survey and additional information collected in the previous waves of SHARE, we explore the effects of occupation’s characteristics on two outcomes: (i) the probability of work interruptions during the pandemic, coupled with the length of such interruptions and (ii) the probability of switching to homeworking during the lockdown. In order to assess how job features affected the likelihood of having experienced work interruptions or shifted to teleworking, we define six occupation categories by classifying the ISCO job titles according to two criteria: the safety level of the occupation and the essential (unessential) nature of the good or service provided. We find that characteristics of the occupation are major determinants of the probability of experiencing work interruptions and determine the length of such interruptions. Working from home also largely depends on the features of the job, even controlling for many other covariates at the individual level. In addition, we show that labour market outcomes of women, self-employed and less educated workers are negatively affected by the pandemic to a much larger extent than men

Occupation and working outcomes during the Coronavirus Pandemic

Using data from the first wave of the SHARE COVID-19 Survey and additional information collected from the previous waves of SHARE (Survey of Health Ageing and Retirement in Europe), we explore the effects of job characteristics on two outcomes: (i) the probability of work interruptions and (ii) the length of such interruptions during the first phase of the Coronavirus Pandemic. In order to assess the relationship between job features and labour market outcomes, we define two indexes proxying the pre-COVID-19 technical remote work feasibility as well as the level of social interaction with other people while working. Moreover, we use an indicator that classifies ISCO-08 3-digit job titles based on the essential nature of the good or service provided. We find that job characteristics have been major determinants of the probability of undergoing work interruptions and their duration. In addition, we show that women have been negatively affected by the Pandemic to a much larger extent than men, suggesting the relevance of the intrinsic characteristics of jobs they are mainly involved in, and the role of gender selection into specific activities. Not only females were more likely to have undergone work interruptions but they also exhibited larger probabilities of longer work breaks. A similar impact is seen for self-employed and less-educated workers