Dynamic allocation of visual attention during the execution of sequences of saccades

Most laboratory tasks used to study vision and attention require steady fixation. By contrast, natural visual processing occurs during the pauses between successive saccades. We assessed vision during intersaccadic pauses as subjects made repetitive sequences of saccades. Displays contained 6 outline squares located along the perimeter of an imaginary circle (diam 4 deg). Saccades were made to every other square. The visual task was to identify the orientation (2AFC) of a Gabor test stimulus that appeared briefly (90 ms) along with superimposed noise in one of the squares during a randomly selected intersaccadic pause. Gabor location was cued before each trial and noise frames were presented in all squares to avoid drawing attention to the location of the visual test. Contrast thresholds during intersaccadic pauses were as much as two times higher than in control trials with steady fixation. Surprisingly, slowing down scanning rate in an effort to pay more attention to the cued location did not help. Thresholds improved over time during the intersaccadic pause. Lowest thresholds relative to steady fixation were found for the pair of locations that were the targets of the next 2 saccades in the sequence. Highest thresholds relative to steady fixation were found for the location intermediate between the current fixation position and the target of the next saccade. These results show that vision during intersaccadic pauses is modulated by the distribution of attention, as well as by visual suppression that may be related to the execution of saccades. Attention is allocated to targets for the entire saccadic sequence, not exclusively to the target of the next saccade. Changes in visual thresholds accompanying sequences of saccades are larger than those reported prior to the execution of single saccades, and larger than those induced by attentional cuing during steady fixation.