A Common Left Occipito-Temporal Dysfunction in Developmental Dyslexia and Acquired Letter-By-Letter Reading?

We used fMRI to examine functional brain abnormalities of German-speaking dyslexics who suffer from slow effortful reading but not from a reading accuracy problem. Similar to acquired cases of letter-by-letter reading, the developmental cases exhibited an abnormal strong effect of length (i.e., number of letters) on response time for words and pseudowords.Corresponding to lesions of left occipito-temporal (OT) regions in acquired cases, we found a dysfunction of this region in our developmental cases who failed to exhibit responsiveness of left OT regions to the length of words and pseudowords. This abnormality in the left OT cortex was accompanied by absent responsiveness to increased sublexical reading demands in phonological inferior frontal gyrus (IFG) regions. Interestingly, there was no abnormality in the left superior temporal cortex which--corresponding to the onological deficit explanation--is considered to be the prime locus of the reading difficulties of developmental dyslexia cases.The present functional imaging results suggest that developmental dyslexia similar to acquired letter-by-letter reading is due to a primary dysfunction of left OT regions

Modeling working memory: An interference model of complex span

This article introduces a new computational model for the complex-span task, the most popular task for studying working memory. SOB-CS is a two-layer neural network that associates distributed item representations with distributed, overlapping position markers. Memory capacity limits are explained by interference from a superposition of associations. Concurrent processing interferes with memory through involuntary encoding of distractors. Free time in-between distractors is used to remove irrelevant representations, thereby reducing interference. The model accounts for benchmark findings in four areas: (1) effects of processing pace, processing difficulty, and number of processing steps; (2) effects of serial position and error patterns; (3) effects of different kinds of item-distractor similarity; and (4) correlations between span tasks. The model makes several new predictions in these areas, which were confirmed experimentally

Kinetic Modeling and Simulation of In Vitro Transcription by Phage T7

Abstract: This study provides a mathematical model of T7 RNA polymerase (T7 RNAP) kinetics under in vitro conditions targeted at application of this model to simulation of dynamic transcription performance. A functional dependence of transcript synthesis rate is derived based on: (a) essential reactant concentrations, including T7 RNAP and its promoter, substrate nucleotides, and the inhibitory byproduct inorganic pyrophosphate; (b) a distinction among vector characteristics such as recognition sequences regulating transcription initiation and termination, respectively; and (c) specific properties of the nucleotide sequence including both transcript length and nucleotide composition. Inactivation kinetics showed a half-life of T7 RNAP activity of 50 min under the conditions applied in vitro using the isolated enzyme. Model parameters and their precision are estimated using dynamic simulation and nonlinear regression analysis. The particular novelty of this model is its capability to incorporate linear genomic sequence information for simulation of nonlinear in vitro transcription kinetics.