We investigated the dynamics of spatial attention in an active viewing task, namely reading, and the effects of the load of target words on these dynamics. We showed that, over the course of a fixation, attention was modulated by the load of the fixated word and the upcoming word.
The load of words was manipulated by varying word frequency and the orthographic familiarity of the first trigram in words. In a variation of the dynamic-orienting paradigm (Fischer, 1999), participants read sentences or strings of words for the primary task and discriminated gaze-contingent probes - occurring with variable spatial and temporal offsets from the first fixations on words - for the secondary task. Reading was evidenced by longer fixation durations on words with lower frequencies. The accuracy of probe discrimination was used to index attention.
Early in a fixation, attention was focused on the gaze more when the fixated word was lower in frequency. This early effect of frequency was revealed for reading sentences and strings of words provided words were previewed before being fixated. Attention defocused over time and, by halfway through a fixation, orienting towards the to-be-fixated location (i.e., towards the right) began. Late in a fixation, attention had oriented more to the right of the gaze for high- than low-frequency words. Shortly before the saccade to the upcoming word, and during preview of this word, its processing was sufficiently advanced to affect attention: specifically, less attention remained at the gaze location when the first trigram of the upcoming word was orthographically less familiar.
In sum, we showed that the moment-to-moment processing load of words affects the dynamics of spatial attention.