The role of word knowledge in error detection: a challenge to the broken error monitor account of dyslexia.

Dyslexic children often fail to correct errors while reading aloud, and dyslexic adolescents and adults exhibit lower amplitudes of the error-related negativity (ERN)-the neural response to errors-than typical readers during silent reading. Past researchers therefore suggested that dyslexia may arise from a faulty error detection mechanism that interferes with orthographic learning and text comprehension. An alternative possibility is that comprehension difficulty in dyslexics is primarily a downstream effect of low-quality lexical representations-that is, poor word knowledge. On this view, the attenuated ERN in dyslexics is a byproduct, rather than a source, of underdeveloped orthographic knowledge. Because the second view implies a direct association of the error response with comprehension skill in populations of all ability levels, the present study evaluates these alternatives through a reanalysis of behavioral and neural data from 31 typical adult readers. If it is true that faulty error processing can manifest as dyslexia, a model in which error monitoring contributes directly to comprehension should outperform a model in which it does not. ERNs recorded during spelling judgments were used as a measure of error detection aptitude in path analyses of reading comprehension. The data were better fit by a model in which error detection aptitude was a consequence of word knowledge than a model in which it contributed directly to comprehension. The findings challenge the notion that comprehension difficulty in dyslexics is attributable to error processing deficits and are consistent with the hypothesis that comprehension difficulty in dyslexics is partially attributable to low-quality word knowledge.

ERP evidence for memory and predictive mechanisms in word-to-text integration.

During reading, word-to-text integration processes proceed quickly and incrementally through both prospective (predictive) and retrospective (memory) processes. Across a sentence boundary, where prediction may be less functional, memorial processes may be especially important. We tested predictive and memory mechanisms with event-related potentials (ERPs) recorded on the first content word across a sentence boundary by manipulating the direction of association between this word and one from the preceding sentence. For comparison with this text comprehension (TC) task, we tested these same word pairs in a word meaning judgment (MJ) task. In both tasks we found reduced N400 amplitudes over central scalp electrodes when the two words were either forward-associated (FA) or backward-associated (BA), relative to task-specific baseline conditions. In the MJ task, FA pairs produced a greater reduction in the N400 reduction than BA pairs over right parietal areas. However, in the TC task, BA pairs produced a greater N400 reduction than FA pairs over left parietal electrodes. A temporal principal component analysis of TC and MJ data showed a component reflecting the central N400. Additional components from TC data reflected FA-BA differences during early (N200) and late (parietal N400 and LPC) phases of processing. Comprehension skill predicted association effects in the MJ task, especially FA, and the BA central N400 effects in the TC task. The results demonstrate that, beyond N400 indicators of prediction effects, ERPs reflect the role of memory processes in word-to-text integration across sentences, part of a dynamic interplay between anticipatory and memorial processes that support comprehension.

Error-related negativities during spelling judgments expose orthographic knowledge.

In two experiments, we demonstrate that error-related negativities (ERNs) recorded during spelling decisions can expose individual differences in lexical knowledge. The first experiment found that the ERN was elicited during spelling decisions and that its magnitude was correlated with independent measures of subjects' spelling knowledge. In the second experiment, we manipulated the phonology of misspelled stimuli and observed that ERN magnitudes were larger when misspelled words altered the phonology of their correctly spelled counterparts than when they preserved it. Thus, when an error is made in a decision about spelling, the brain processes indexed by the ERN reflect both phonological and orthographic input to the decision process. In both experiments, ERN effect sizes were correlated with assessments of lexical knowledge and reading, including offline spelling ability and spelling-mediated vocabulary knowledge. These results affirm the interdependent nature of orthographic, semantic, and phonological knowledge components while showing that spelling knowledge uniquely influences the ERN during spelling decisions. Finally, the study demonstrates the value of ERNs in exposing individual differences in lexical knowledge.