An investigation of attention allocation during sequential eye movement tasks.

Allocation of visuo-spatial attention during dynamic viewing was investigated with a dual task. Primary tasks (reading, scanning, searching) all required sequential left-to-right eye movements. An additional speeded manual response was made to a visual probe that appeared early or late after the onset of a randomly determined fixation (25 or 170 msec probe delay). The probe appeared to the left, directly above, or to the right of the currently fixated character (-10, -5, 0, +5, or +10 characters probe eccentricity). Faster probe detection near the location of the forthcoming eye fixation was found in the search task, but not during reading or scanning. Fixation times increased and saccade lengths decreased as a consequence of probing in all three tasks. Fixations were, however, less prolonged when the probe appeared in the right than when it appeared in the left hemifield, and saccades were greatest when the probe appeared at +10 characters. The results extend the notion of goal-directed attention shifts to free viewing and highlight the impact of task-specific processing requirements.