Coleman, Michael; (2000) Primary and secondary processes in normal and dyslexic word identification. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Skilled visual word identification is an effortless component of fluent reading, subserved by a relatively fast, automatic, primary lexical access process. Experimental tasks and neuropsychological conditions that restrict information flow to primary process invoke task specific or secondary process mediated identification. These secondary processes may be alternative routes to identification, used infrequently by skilled readers, but more frequently while acquiring literacy, or when primary process fails. They are sometimes referred to as guessing and meta-linguistic functions. The focus of mainstream research on primary lexical access has meant that they remain relatively unexplored components of normal word recognition. The thesis proposes a limited set of secondary 'completion' processes, to avoid using the term 'guess'. Completion processes 'complete' degraded input to deliver candidate identifications. Lexical completions are mediated by the orthographic input lexicon, and involve the amplification of sub-threshold representations, either by serial deployment of attention to enhance letter level representations, or by parallel attentional modulation of word level activation. Sublexical completion processes explicitly identify letters, and 'retrieve' or 'assemble' words from letter identities or names. These completions are under constant 'revision' in the normal, motivated, system. In conjunction with primary process, these secondary processes form a broader view of normal word recognition formalised in a flow model call the primary secondary process model Experimental results indicate that lexical completion is associated with inhibitory effects of neighbourhood size, and that sublexical completion may result in inhibitory or facilitatory effects of neighbourhood size depending on the nature of fragments and procedures used. Neuropsychological results indicate that secondary process deficits may restrict the compensatory strategies open to peripheral dyslexics, and hence, that their performance is best described in terms of both residual primary and residual secondary processes. The explanatory role of secondary processing may extend beyond peripheral dyslexia and fragment completion, to encompass strategic and individual differences in adult performance, and developmental differences in the acquisition of literacy.

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