The temporal impulse response underlying saccadic decisions

Models of perceptual decision making often assume that sensory evidence is accumulated over time in favor of the various possible decisions, until the evidence in favor of one of them outweighs the evidence for the others. Saccadic eye movements are among the most frequent perceptual decisions that the human brain performs. We used stochastic visual stimuli to identify the temporal impulse response underlying saccadic eye movement decisions. Observers performed a contrast search task, with temporal variability in the visual signals. In experiment 1, we derived the temporal filter observers used to integrate the visual information. The integration window was restricted to the first similar to 100 ms after display onset. In experiment 2, we showed that observers cannot perform the task if there is no useful information to distinguish the target from the distractor within this time epoch. We conclude that (1) observers did not integrate sensory evidence up to a criterion level, (2) observers did not integrate visual information up to the start of the saccadic dead time, and (3) variability in saccade latency does not correspond to variability in the visual integration period. Instead, our results support a temporal filter model of saccadic decision making. The temporal impulse response identified by our methods corresponds well with estimates of integration times of V1 output neurons.

Reaching a verdict

Two experiments, using a mock legal case, confirmed the causal role of arguments in verdict decisions and explored the process involved. Experiment I showed that verdicts varied with the strength of counter-arguments and Experiment 2 showed that the use of background information that undermined such arguments determined the verdict reached. Such results confirm the causal role of arguments but do not speak to the representations constructed. In both experiments we analysed the reasons proposed for verdicts. Participants generally represented the state of affairs, and conjectured state of affairs, to which the arguments referred. Experiment 2 also asked participants about the number of causal possibilities they envisaged. Confidence in the verdict was moderated by the strength of counter-arguments but in different ways for those who envisaged a single causal account as opposed to two causal accounts. In the former case, confidence decreased with the rated strength of counter-arguments. In the latter case, confidence increased. We suggest that verdicts are abductive explanations of the events generated through a process of mental simulation.

Autoregressive conditional kurtosis

This article proposes a new model for autoregressive conditional heteroscedasticity and kurtosis. Via a time-varying degrees of freedom parameter, the conditional variance and conditional kurtosis are permitted to evolve separately. The model uses only the standard Student’s t-density and consequently can be estimated simply using maximum likelihood. The method is applied to a set of four daily financial asset return series comprising U.S. and U.K. stocks and bonds, and significant evidence in favor of the presence of autoregressive conditional kurtosis is observed. Various extensions to the basic model are proposed, and we show that the response of kurtosis to good and bad news is not significantly asymmetric.

Last charge of the knights? Iraq, Afghanistan and the special relationship

At the heart of the ‘special relationship’ ideology, there is supposed to be a grand bargain. In exchange for paying the ‘blood price’ as America's ally, Britain will be rewarded with exceptional influence over American foreign policy and its strategic behaviour. Soldiers and statesman continue to articulate this idea. Since 9/11, the notion of Britain playing ‘Greece’ to America's ‘Rome’ gained new life thanks to Anglophiles on both sides of the Atlantic. One potent version of this ideology was that the more seasoned British would teach Americans how to fight ‘small wars’ in Iraq and Afghanistan, thereby bolstering their role as tutor to the superpower. Britain does derive benefits from the Anglo-American alliance and has made momentous contributions to the wars in Afghanistan and Iraq. Yet British solidarity and sacrifices have not purchased special influence in Washington. This is partly due to Atlanticist ideology, which sets Britain unrealistic standards by which it is judged, and partly because the notion of ‘special influence’ is misleading as it loses sight of the complexities of American policy-making. The overall result of expeditionary wars has been to strain British credibility in American eyes and to display its lack of consistent influence both over high policy and the design and execution of US military campaigns. While there may be good arguments in favour of the UK continuing its efforts in Afghanistan, the notion that the war fortifies Britain's vicarious world status is a dangerous illusion that leads to repeated overstretch and disappointment. Now that Britain is in the foothills of a strategic defence review, it is important that the British abandon this false consciousness.

Deal size, acquisition premia and shareholder gains

This study examines the contradictory predictions regarding the association between the premium paid in acquisitions and deal size. We document a robust negative relation between offer premia and target size, indicating that acquirers tend to pay less for large firms, not more. We also find that the overpayment potential is lower in acquisitions of large targets. Yet, they still destroy more value for acquirers around deal announcements, implying that target size may proxy, among others, for the unobserved complexity inherent in large deals. We provide evidence in favor of this interpretation.

Experimenting on contextualism

In this article we refine the design of context shifting experiments, which play a central role in contextualist debates, and we subject a large number of scenarios involving different types of expressions of interest to contextualists, including ‘know’ and color adjectives like ‘green’, to experimental investigation. Our experiment (i) reveals an effect of changing contexts on the evaluation of uses of the sentences that we examine, thereby overturning the absence of results reported in previous experimental studies (so-called null results), (ii) uncovers evidence for a ‘truth bias' in favor of positive over negative sentences, and (iii) reveals previously unnoticed distinctions between the strength of the contextual effects displayed by scenarios involving knowledge ascriptions and scenarios concerning color and other miscellaneous scenarios.

Scattering by infinite one-dimensional rough surfaces

We consider the Dirichlet boundary-value problem for the Helmholtz equation in a non-locally perturbed half-plane. This problem models time-harmonic electromagnetic scattering by a one-dimensional, infinite, rough, perfectly conducting surface; the same problem arises in acoustic scattering by a sound-soft surface. ChandlerWilde & Zhang have suggested a radiation condition for this problem, a generalization of the Rayleigh expansion condition for diffraction gratings, and uniqueness of solution has been established. Recently, an integral equation formulation of the problem has also been proposed and, in the special case when the whole boundary is both Lyapunov and a small perturbation of a flat boundary, the unique solvability of this integral equation has been shown by Chandler-Wilde & Ross by operator perturbation arguments. In this paper we study the general case, with no limit on surface amplitudes or slopes, and show that the same integral equation has exactly one solution in the space of bounded and continuous functions for all wavenumbers. As an important corollary we prove that, for a variety of incident fields including the incident plane wave, the Dirichlet boundary-value problem for the scattered field has a unique solution.

Forecasting economic and financial time series with non-linear models

In this paper we discuss the current state-of-the-art in estimating, evaluating, and selecting among non-linear forecasting models for economic and financial time series. We review theoretical and empirical issues, including predictive density, interval and point evaluation and model selection, loss functions, data-mining, and aggregation. In addition, we argue that although the evidence in favor of constructing forecasts using non-linear models is rather sparse, there is reason to be optimistic. However, much remains to be done. Finally, we outline a variety of topics for future research, and discuss a number of areas which have received considerable attention in the recent literature, but where many questions remain.

Youth unemployment and vocational training

This paper focuses on the determinants of the labor market situation of young people in developed countries and the developing world, with a particular emphasis on the role of vocational training and education policies. We highlight the role of demographic factors, economic growth and labor market institutions in explaining young people's transition into work. Subsequently, we assess differences between the setup and functioning of the vocational education and training policies across major world regions as an important driver of differential labor market situation of youth. Based on our analysis, we argue in favor of vocational education and training systems combining work experience and general education and provide some policy recommendations regarding the implementation of education and training systems adapted to a country's economic and institutional context.

All friends now? Critical conversations, West Indian literature and 'The Quarrel with History'

In this essay Alison Donnell returns to the material object of Edward Baugh's essay, published in the pages of the Trinidadian little magazine Tapia in 1977, in order to re-read the force of its arguments in the context of its own politicocultural history and to assess the significance of its publication venue. Donnell attends to Baugh's own standing in the highly charged field of Caribbean literary criticism as a critic of both Walcott and Naipaul, and acknowledges his creative contribution to this field as a poet. She also considers how, in the years between the original publication of Baugh's article and its republication, the questions of historical invisibility have entered newly disputed territories that demand attention to how gender, indigeneity, spirituality, and sexuality shape ideas of historical and literary legitimacy, in addition to those foundational questions around a politics of race and class.

Rethinking disability theory and practice: challenging essentialism

This edited volume argues that even in recent Critical Disability Studies which have sought to critique essentialist assumptions in relation to Disability, nevertheless essentialisms remain which predetermine and predirect definitions and arguments in the field. This volume analyses such essentialisms in a wide range of areas such as childhood, gender, sexuality, reproduction, ADHD, autism, the animal, d/Deafness, hirsutism, the body, and vision. Particularly issues such as 'agency', 'voice' and 'body' are explored in terms of their political implications.

When innovation becomes inefficient: reexamining Britain's radio industry

I examine the factors underpinning the British radio-equipment sector's particularly poor interwar productivity performance relative to the United States. Differences in socio-legal environments were crucial in allowing key players in the British industry to derive higher monopoly rents than their American counterparts. Higher British rents in turn, had the unintended outcome of stimulating innovation around restrictive patents, initiating a path-dependent process of technical change in favor of expensive multifunctional valves. These valves both raised direct production costs and prevented British firms from following the American path of broadening the radio market beyond the household's prime receiver.