Visual word recognition insights from MEG and implications for developmental dyslexia

The ability to fluently and, seemingly effortlessly, read words is one of few uniquely special human attributes, but one which has assumed inordinate significance because of the role that this activity has come to have in modern society. A disadvantage in reading ability not only has profound personal impact for the individuals concerned, but in terms of economic and social problems also has a wider negative influence on society at large. According to current government figures in the UK, some 22% of 11 year olds do not reach the minimum standard required in English national curriculum tests. Despite its importance, however, the scientific understanding of the neural basis of reading, and more particularly the visual aspect of visual word recognition, is relatively poorly understood. Thus far, a coherent overarching model, that spans the various conceptual levels, from behaviour through functional description to neuroanatomy, has proven extraordinarily challenging to elucidate. A fuller understanding of the computational processing and neurophysiological basis of how the reading system functions would therefore represent significant progress. As with most complex behaviours, visual word recognition is thought to result from the dynamic interplay between the elements of a distributed cortical and sub-cortical network. To fully understand how visual word recognition is achieved therefore, and how it may fail in developmental dyslexia, we need to identify not only the necessary and sufficient complement of nodes that comprise this network – its functional anatomy - but we also need to understand how information flows through this network with time and indeed how the structure of the network itself may adapt in both the short and long term. In this chapter we take a historical approach to reviewing recent MEG (magnetoencephalography) research which elucidates these temporal dynamics, focusing particularly on events with the first 300ms of a visually presented word, and which we believe should set crucial constraints on models of visual word recognition and reading