Cascaded and thresholded processing in visual word recognition: does the Dual Route Cascaded model require a threshold?

The current thesis aims to investigate cascaded processing in visual word recognition by testing the predictions of the Dual Route Cascaded (DRC) model of reading. Despite widespread acceptance of the idea that visual language processing is cascaded, there are circumstances in which such an account is not easily reconciled with the data produced by skilled readers. Recent experiments involving factorial manipulations in reading showed, in particular, additive effects of stimulus quality (i.e., clear vs. degraded stimuli) with letter string length and orthographic neighbourhood size in nonword reading and with word frequency and lexicality when words and nonwords were mixed in the task, thus suggesting that information processing implicated in visual word recognition must be at least partially thresholded. Six experiments have been presented in this thesis: on one hand, a new variable that has a role when the stimuli are degraded – the Total Letter Confusability – has been introduced; on the other hand, the effects due to list composition have been analyzed when the stimuli were degraded in the task. In general, the results obtained suggest a novel interpretation of the additivities previously observed; these findings have been explained within the DRC model which also correctly simulates a significant amount of the data. The empirical evidence collected so far clearly indicates that there is currently no need to assume thresholded processing in the reading system.