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The effects of crowding on eye movement patterns in reading
Crowding is a phenomenon that characterizes normal periphery limiting letter identification when other letters
surround the signal. We investigated the nature of the reading limitation of crowding by analyzing eyemovement
patterns. The stimuli consisted of two items varying across trials for letter spacing (spaced, unspaced
and increased size), lexicality (words or pseudowords), number of letters (4, 6, 8), and reading modality (oral
and silent). In Experiments 1 and 2 (oral and silent reading, respectively) the results show that an increase in
letter spacing induced an increase in the number of fixations and in gaze duration, but a reduction in the first
fixation duration. More importantly, increasing letter size (Experiment 3) produced the same first fixation
duration advantage as empty spacing, indicating that, as predicted by crowding, only center-to-center letter
distance, and not spacing per se, matters. Moreover, when the letter size was enlarged the number of fixations
did not increase as much as in the previous experiments, suggesting that this measure depends on visual acuity
rather than on crowding. Finally, gaze duration, ameasure ofword recognition, did not changewith the letter size
enlargement. No qualitative differences were found between oral and silent reading experiments (1 and 2),
indicating that the articulatory process did not influence the outcome. Finally, a facilitatory effect of lexicality
was found in all conditions, indicating an interaction between perceptual and lexical processing. Overall, our
results indicate that crowding influences normal word reading bymeans of an increase in first fixation duration,
a measure of word encoding, which we interpret as a modulatory effect of attention on critical spacing