Signal processing during and across saccades

Visual perceptual processing has been found to occur exclusively during fixations of the eye (Sanders and Houtmans, 1985; Sanders and Rath, 1991). Does fixation time also reflect postperceptual processes such as target classification and response selection as well, or can these processes continue during a saccade? In a series of experiments on this question two signals were presented at an angular distance of 100 degrees. At the start of a trial subjects fixated the left signal (S1), which was always a letter that did or did not belong to a predefined target set of variable size. Then they moved to the right signal (S2) which indicated the mapping of target and no target responses onto the response keys. Subjects were capable of starting the saccade upon identification of S1, so that target classification of S1 might occur either during the saccade or while fixating S2. Although the duration of the saccade was long enough to complete target classification, the effect of set size was still partially reflected in the fixation duration of S2. This could either be due to incomplete processing during the saccade or to interference while integrating S1 and S2. The results of two additional conditions were in support of the latter hypothesis, since they showed similar effects while no saccade was involved. Subsequent experiments confirmed the conclusion that target classification can continue during a saccade. The final experiment showed that response selection can continue during a saccade as well: The effect of S-R compatibility was reduced in case of a small saccade (8 degrees) and disappeared altogether when a large saccade was carried out (100 degrees).