A Neural Network Model for the Development of Simple and Complex Cell Receptive Fields Within Cortical Maps of Orientation and Ocular Dominance

Prenatal development of the primary visual cortex leads to simple cells with spatially distinct and oriented ON and OFF subregions. These simple cells are organized into spatial maps of orientation and ocular dominance that exhibit singularities, fractures, and linear zones. On a finer spatial scale, simple cells occur that are sensitive to similar orientations but opposite contrast polarities, and exhibit both even-symmetric and odd-symmetric receptive fields. Pooling of outputs from oppositely polarized simple cells leads to complex cells that respond to both contrast polarities. A neural network model is described which simulates how simple and complex cells self-organize starting from unsegregated and unoriented geniculocortical inputs during prenatal development. Neighboring simple cells that are sensitive to opposite contrast polarities develop from a combination of spatially short-range inhibition and high-gain recurrent habituative excitation between cells that obey membrane equations. Habituation, or depression, of synapses controls reset of cell activations both through enhanced ON responses and OFF antagonistic rebounds. Orientation and ocular dominance maps form when high-gain medium-range recurrent excitation and long-range inhibition interact with the short-range mechanisms. The resulting structure clarifies how simple and complex cells contribute to perceptual processes such as texture segregation and perceptual grouping.Air Force Office of Scientific Research (F49620-92-J-0334); British Petroleum (BP 89A-1204); National Science Foundation (IRI-90-24877); Office of Naval Research (N00014-91-J-4100); Defense Advanced Research Projects Agency and the Office of Naval Research (N00014-95-1-0409

Scaling properties of noise-induced switching in a bistable tunnel diode circuit

Noise-induced switching between coexisting metastable states occurs in a wide range of far-from-equilibrium systems including micro-mechanical oscillators, epidemiological and climate change models, and nonlinear electronic transport in tunneling structures such as semiconductor superlattices and tunnel diodes. In the case of tunnel diode circuits, noise-induced switching behavior is associated with negative differential resistance in the static current-voltage characteristics and bistability, i.e., the existence of two macroscopic current states for a given applied voltage. Noise effects are particularly strong near the onset and offset of bistable current behavior, corresponding to bifurcation points in the associated dynamical system. In this paper, we show that the tunnel diode system provides an excellent experimental platform for the precision measurement of scaling properties of mean switching times versus applied voltage near bifurcation points. More specifically, experimental data confirm that the mean switching time scales logarithmically as the 3/2 power of voltage difference over an exceptionally wide range of time scales and noise intensities.Comment: 9 pages, 9 figures, accepted manuscript for publication in the European Physical Journal B, Topical Issue: Non-Linear and Complex Dynamics in Semiconductors and Related Material

Joint Tortfeasors—Validity of Loan Agreements and Use of Pro Tanto Bar—\u3ci\u3eTober v. Hampton\u3c/i\u3e, 178 Neb. 858, 136 N.W.2d 194 (1965)

Loan agreements rely upon the existence of allowable indemnity for their justification and validity in the joint tortfeasor situation. If indemnity is allowed in a given situation, objections to the use of a loan agreement must be rejected. If, however, a suit for indemnity is not allowed between two joint tortfeasors, loan agreements should not allow such a result indirectly. Therefore, it may be concluded that the use of loan agreements in Nebraska in the joint tortfeasor situation will only be upheld when a suit for indemnification would also be upheld. Whether loan agreements are held to be valid or invalid in any given situation should not, however, preclude an injured plaintiff from receiving full compensation for his damages. In applying pro tanto reduction, the court in Tober v. Hampton justifiably held that any amount received under the invalid loan agreement should be deducted from any judgment rendered in a suit against the other joint tortfeasor. The court ruled inconsistently, though, in requiring the plaintiffs to pay back any money received in such a suit to the loaning joint tortfeasor. Since the loan agreement was held invalid, no repayment under it should have been required. As a result of this inconsistent combination of pro tanto reduction and mandatory repayment under an invalid loan agreement, the court\u27s decision that the plaintiffs were not the real parties in interest seems erroneous

Property and Contract Rights in Autocracies and Democracies

We present and test empirically a new theory of property and contract rights. Any incentive an autocrat has to respect such rights comes from his interest in future tax collections and national income and increases with his planning horizon. We find a compelling empirical relationship between property and contract rights and an autocrat's time in power. In lasting -- but not in new -- democracies, the same rule of law and individual rights that ensure continued free elections entail extensive property and contract rights. We show that the age of a democratic system is strongly correlated with property and contract rights.property rights, contract rights, autocracy, democracy

Contract Intensive Money

This paper makes two contributions to the literature. First, it introduces a new, easily accessed and objective measure of the enforceability of contracts and the security of property rights. Second, it uses this measure to provide additional and more direct evidence about the importance of secure property and contract rights for economic growth and investment. In the analysis below, we briefly review the arguments that link the quality of third-party contract enforcement to growth and investment. We then show how the new measure, which we call “contract-intensive money” or CIM, relates to the subjective measures employed in the literature. We test empirically the proposition that this variable, as a measure of the security of contract and property rights, is positively related to income, growth and investment.contract enforcement, property rights, governance, growth

The ethics of interrogation and the American Psychological Association: A critique of policy and process

The Psychological Ethics and National Security (PENS) task force was assembled by the American Psychological Association (APA) to guide policy on the role of psychologists in interrogations at foreign detention centers for the purpose of U.S. national security. The task force met briefly in 2005, and its report was quickly accepted by the APA Board of Directors and deemed consistent with the APA Ethics Code by the APA Ethics Committee. This rapid acceptance was unusual for a number of reasons but primarily because of the APA's long-standing tradition of taking great care in developing ethical policies that protected anyone who might be impacted by the work of psychologists. Many psychological and non-governmental organizations (NGOs), as well as reputable journalists, believed the risk of harm associated with psychologist participation in interrogations at these detention centers was not adequately addressed by the report. The present critique analyzes the assumptions of the PENS report and its interpretations of the APA Ethics Code. We demonstrate that it presents only one (and not particularly representative) side of a complex set of ethical issues. We conclude with a discussion of more appropriate psychological contributions to national security and world peace that better respect and preserve human rights

The Ethics of Interrogation and the American Psychological Association: A Critique of Policy and Process

The Psychological Ethics and National Security (PENS) task force was assembled by the American Psychological Association (APA) to guide policy on the role of psychologists in interrogations at foreign detention centers for the purpose of U.S. national security. The task force met briefly in 2005, and its report was quickly accepted by the APA Board of Directors and deemed consistent with the APA Ethics Code by the APA Ethics Committee. This rapid acceptance was unusual for a number of reasons but primarily because of the APA\u27s long-standing tradition of taking great care in developing ethical policies that protected anyone who might be impacted by the work of psychologists. Many psychological and non-governmental organizations (NGOs), as well as reputable journalists, believed the risk of harm associated with psychologist participation in interrogations at these detention centers was not adequately addressed by the report. The present critique analyzes the assumptions of the PENS report and its interpretations of the APA Ethics Code. We demonstrate that it presents only one (and not particularly representative) side of a complex set of ethical issues. We conclude with a discussion of more appropriate psychological contributions to national security and world peace that better respect and preserve human rights

The Ethics of Interrogation and the American Psychological Association: A Critique of Policy and Process

The Psychological Ethics and National Security (PENS) task force was assembled by the American Psychological Association (APA) to guide policy on the role of psychologists in interrogations at foreign detention centers for the purpose of U.S. national security. The task force met briefly in 2005, and its report was quickly accepted by the APA Board of Directors and deemed consistent with the APA Ethics Code by the APA Ethics Committee. This rapid acceptance was unusual for a number of reasons but primarily because of the APA\u27s long-standing tradition of taking great care in developing ethical policies that protected anyone who might be impacted by the work of psychologists. Many psychological and non-governmental organizations (NGOs), as well as reputable journalists, believed the risk of harm associated with psychologist participation in interrogations at these detention centers was not adequately addressed by the report. The present critique analyzes the assumptions of the PENS report and its interpretations of the APA Ethics Code. We demonstrate that it presents only one (and not particularly representative) side of a complex set of ethical issues. We conclude with a discussion of more appropriate psychological contributions to national security and world peace that better respect and preserve human rights

Seascape Genetics: A Coupled Oceanographic-Genetic Model Predicts Population Structure of Caribbean Corals

SummaryPopulation genetics is a powerful tool for measuring important larval connections between marine populations [1–4]. Similarly, oceanographic models based on environmental data can simulate particle movements in ocean currents and make quantitative estimates of larval connections between populations possible [5–9]. However, these two powerful approaches have remained disconnected because no general models currently provide a means of directly comparing dispersal predictions with empirical genetic data (except, see [10]). In addition, previous genetic models have considered relatively simple dispersal scenarios that are often unrealistic for marine larvae [11–15], and recent landscape genetic models have yet to be applied in a marine context [16–20]. We have developed a genetic model that uses connectivity estimates from oceanographic models to predict genetic patterns resulting from larval dispersal in a Caribbean coral. We then compare the predictions to empirical data for threatened staghorn corals. Our coupled oceanographic-genetic model predicts many of the patterns observed in this and other empirical datasets; such patterns include the isolation of the Bahamas and an east-west divergence near Puerto Rico [3, 21–23]. This new approach provides both a valuable tool for predicting genetic structure in marine populations and a means of explicitly testing these predictions with empirical data (Figure 1)

Propagule Pressure and Stream Characteristics Influence Introgression: Cutthroat and Rainbow Trout in British Columbia

Hybridization and introgression between introduced and native salmonids threaten the continued persistence of many inland cutthroat trout species. Environmental models have been developed to predict the spread of introgression, but few studies have assessed the role of propagule pressure. We used an extensive set of fish stocking records and geographic information system (GIS) data to produce a spatially explicit index of potential propagule pressure exerted by introduced rainbow trout in the Upper Kootenay River, British Columbia, Canada. We then used logistic regression and the information-theoretic approach to test the ability of a set of environmental and spatial variables to predict the level of introgression between native westslope cutthroat trout and introduced rainbow trout. Introgression was assessed using between four and seven co-dominant, diagnostic nuclear markers at 45 sites in 31 different streams. The best model for predicting introgression included our GIS propagule pressure index and an environmental variable that accounted for the biogeoclimatic zone of the site (r2¼0.62). This model was 1.4 times more likely to explain introgression than the next-best model, which consisted of only the propagule pressure index variable. We created a composite model based on the model-averaged results of the seven top models that included environmental, spatial, and propagule pressure variables. The propagule pressure index had the highest importance weight (0.995) of all variables tested and was negatively related to sites with no introgression. This study used an index of propagule pressure and demonstrated that propagule pressure had the greatest influence on the level of introgression between a native and introduced trout in a human-induced hybrid zone