A feedback model of perceptual learning and categorisation

Top-down, feedback, influences are known to have significant effects on visual information processing. Such influences are also likely to affect perceptual learning. This article employs a computational model of the cortical region interactions underlying visual perception to investigate possible influences of top-down information on learning. The results suggest that feedback could bias the way in which perceptual stimuli are categorised and could also facilitate the learning of sub-ordinate level representations suitable for object identification and perceptual expertise

Top Quark Forward-Backward Asymmetry

The recent forward-backward asymmetry recorded by the CDF Collaboration for the top and anti-top quark pair production indicates more than $2\sigma$ deviation from the Standard Model prediction, while its total production cross section remains consistent. We propose a $W'$ boson that couples to down and top quarks. We identify the parameter space that can give rise a large enough forward-backward asymmetry without producing too many top and anti-top quark pairs. Other models presented erstwhile in the literature that can produce such effects are also discussed.Comment: 11 pages, 3 figures, revtex4, match the published versio

Top-down effects on early visual processing in humans: a predictive coding framework

An increasing number of human electroencephalography (EEG) studies examining the earliest component of the visual evoked potential, the so-called C1, have cast doubts on the previously prevalent notion that this component is impermeable to top-down effects. This article reviews the original studies that (i) described the C1, (ii) linked it to primary visual cortex (V1) activity, and (iii) suggested that its electrophysiological characteristics are exclusively determined by low-level stimulus attributes, particularly the spatial position of the stimulus within the visual field. We then describe conflicting evidence from animal studies and human neuroimaging experiments and provide an overview of recent EEG and magnetoencephalography (MEG) work showing that initial V1 activity in humans may be strongly modulated by higher-level cognitive factors. Finally, we formulate a theoretical framework for understanding top-down effects on early visual processing in terms of predictive coding

Propagation of Cascades in Complex Networks: From Supply Chains to Food Webs

A general theory of top-down cascades in complex networks is described which explains two similar types of perturbation amplifications in the complex networks of business supply chains (the `bullwhip effect') and ecological food webs (trophic cascades). The dependence of the strength of the effects on the interaction strength and covariance in the dynamics as well as the graph structure allows both explanation and prediction of widely recognized effects in each type of system.Comment: 16 pages, 3 figure

The Effects of Alewife on the Zooplankton Community in Townhouse Pond

The purpose of this study was to determine what plankton species was more dominant in Townhouse Pond and what effects predation has on the food web. Plankton size is important when determining pelagic food web structure. Plankton size along with predation determines whether the lake is dominated by top-down or bottom-up control. Plankton size and biomass, grazing rates, light intensity, and chemistry parameters were all determined for Townhouse Pond in October 2008. We concluded that Townhouse Pond is a mesotrophic lake and is mainly dominated by phytoplankton, such as Microystis and Dinobryon. Alewife (Alosa pseudoharengus), planktivorous fish, are dominant in this pond resulting in top-down control. Although various studies were conducted here, further research could determine the abundance of alewife and their prey and specific parameter that effect their predation

Visual search for featural singletons: No top-down modulation, only bottom-up priming.

The present study investigated the effect of top-down knowledge on search for a feature singleton (a "pop-out target"). In a singleton detection task, advance cueing of the dimension of upcoming singleton resulted in cueing costs and benefits (Experiment 1). When the search for the singleton stayed the same but only the response requirements were changed, advance cueing failed to have an effect (Experiments 2 and 3). In singleton search only bottom-up priming plays a role (Experiments 4 and 5). We conclude that expectancy-based, top-down knowledge cannot guide the search for a featural singleton. Bottom-up priming that does facilitate search for a featural singleton cannot be influenced by top-down control. The study demonstrates that effects often attributed to early top-down guidance may represent effects that occur later in processing or represent bottom-up priming effects. © 2006 Psychology Press Ltd

Wikis in elearning and student projects

The paper presents a study which was based on the hypothesis that wikis that are initiated bottom up by students might be used more deliberately than wikis which are introduced top down by teachers. Therefore it examines the specific effects observed in nine different wiki projects at the university of Frankfurt ranging from student wiki projects up to wikis used in seminars and as information tool for institutions