30 research outputs found
Comments on: “what is developmental dyslexia?” brain sci. 2018, 8, 26. the relationship between eye movements and reading difficulties
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. We are writing in response to the review article: Stein. J. (2018). What is Developmental Dyslexia? Brain Sciences, 8, 26, doi:10.3390/brainsci8020026. We consider that the section entitled, “Eye Movement Control”, presents a misleading characterisation of current empirical and theoretical understanding. We outline five specific points relating to Stein’s views on eye movement control and developmental dyslexia with which we disagree and conclude that disruption to oculomotor behaviour occurs as a consequence of processing difficulty that individuals with dyslexia experience as they engage in reading
Vergence responses to vertical binocular disparity during lexical identification
Humans typically make use of both eyes during reading, which necessitates precise binocular coordination in order to achieve a unified perceptual representation of written text. A number of studies have explored the magnitude and effects of naturally occurring and induced horizontal fixation disparity during reading and non-reading tasks. However, the literature concerning the processing of disparities in different dimensions, particularly in the context of reading, is considerably limited. We therefore investigated vertical vergence in response to stereoscopically presented linguistic stimuli with varying levels of vertical offset. A lexical decision task was used to explore the ability of participants to fuse binocular image disparity in the vertical direction during word identification. Additionally, a lexical frequency manipulation explored the potential interplay between visual fusion processes and linguistic processes. Results indicated that no significant motor fusional responses were made in the vertical dimension (all p-values > .11), though that did not hinder successful lexical identification. In contrast, horizontal vergence movements were consistently observed on all fixations in the absence of a horizontal disparity manipulation. These findings add to the growing understanding of binocularity and its role in written language processing, and fit neatly with previous literature regarding binocular coordination in non-reading tasks
Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models
Both community ecology and conservation biology seek further understanding of
factors governing the advance of an invasive species. We model biological
invasion as an individual-based, stochastic process on a two-dimensional
landscape. An ecologically superior invader and a resident species compete for
space preemptively. Our general model includes the basic contact process and a
variant of the Eden model as special cases. We employ the concept of a
"roughened" front to quantify effects of discreteness and stochasticity on
invasion; we emphasize the probability distribution of the front-runner's
relative position. That is, we analyze the location of the most advanced
invader as the extreme deviation about the front's mean position. We find that
a class of models with different assumptions about neighborhood interactions
exhibit universal characteristics. That is, key features of the invasion
dynamics span a class of models, independently of locally detailed demographic
rules. Our results integrate theories of invasive spatial growth and generate
novel hypotheses linking habitat or landscape size (length of the invading
front) to invasion velocity, and to the relative position of the most advanced
invader.Comment: The original publication is available at
www.springerlink.com/content/8528v8563r7u2742
The systematic formulation of population models with distributed maturation period
This chapter looks at the systematic formulation of population models with distributed maturation perio
Delays, demography and cycles: a forensic study
Strict logic implies that a hypothesis can only be proved wrong, but the main motivation of much science is to find out what is true. In this paper, we argue that the process of intuition building works by extending the classical Popperian paradigm of hypothesis and refutation to include a close relative of the legal concept of “reasonable doubt”. We believe that the way in which doubts are eroded involves building up a consistent picture over a wide ranging body of data-a process akin to the forensic investigations common in the legal process. We illustrate our argument by re-analysing A.J. Nicholson's classical data set on the Australian sheep blowfly Lucilia cuprina. We conclude by discussing the implications of the investigative paradigm we describe for the design of experimental and observational programmes
Stability analysis of a continuous age-structured model with specific reference to North Sea cod
We examine the stability of a class of continuous age-structured models. Stability borders are established for the different parameters in the model, including levels required for viability. Two examples are then given, the first is a simple model for which the analysis is straightforward. An example is then shown of the cod population in the North Sea, which involves more complicated life history structures making stability analysis more difficult. The model predicts that the North Sea population will go extinct if fishing levels remain high. We show, however, that if mortality was lowered it would eventually be possible for the population to reach a point where it was stable and within safe biological limits
Formulating population models with differential ageing
This chapter looks at formulating population models with differential agein
The dynamics of population models with distributed maturation periods
An integro-differential equation for the dynamics of a subpopulation of adults in a closed system where only the adults compete and where there is a distribution of maturation periods is described. We show how the careful choice of a general weighting function based on the gamma distribution with a shift in origin enables us to characterize adequately some observed maturation-period distributions, and also makes local stability and numerical analyses straightforward. Using these results we examine the progression in the behavior of the distributed-delay model as the distribution is narrowed toward the limit of a discrete delay. We conclude that while local stability properties approach those of the limiting equation very rapidly, the persistent fluctuation behavior converges more slowly, with the dominant period and maximum amplitude being least affected by the details of the distribution, and the fine structure of solutions being most sensitive. Finally, we examine the consequences for population modeling, and using several examples of insect populations, conclude that although quite often a full maturation-period distribution should be incorporated in a given model, in many cases a discrete-delay approximation will suffice
Instability in mortality estimation schemes related to stage-stuctured models
Current methods of mortality estimation from stage-structured population data fail to extract the detailed mortality information required by field workers. It has been suggested that the formalism of stage-structure population modelling might resolve the problem. Using this approach we derive a per capita death-rate estimator which is robust to sparse and noisy data, but show that there are fundamental instabilities limiting the application of such estimators. We demonstrate that our estimator is useful in prescribed circumstances and discuss the implications of our results for other estimation schemes