SIGNAL-PROCESSING DURING AND ACROSS SACCADES

Visual perceptual processing has been found to occur exclusively durin g fixations of the eye (Sanders and Houtmans, 1985; Sanders and Rath, 1991). Does fixation time also reflect postperceptual processes such a s target classification and response selection as well, or can these p rocesses continue during a saccade? In a series of experiments on this question two signals were presented at an angular distance of 100-deg rees. At the start of a trial subjects fixated the left signal (S1), w hich was always a letter that did or did not belong to a predefined ta rget set of variable size. Then they moved to the right signal (S2) wh ich indicated the mapping of target and no target responses onto the r esponse keys. Subjects were capable of starting the saccade upon ident ification of S1, so that target classification of S1 might occur eithe r during the saccade or while fixating S2. Although the duration of th e saccade was long enough to complete target classification, the effec t of set size was still partially reflected in the fixation duration o f S2. This could either be due to incomplete processing during the sac cade or to interference while integrating S1 and S2. The results of tw o additional conditions were in support of the latter hypothesis, sinc e they showed similar effects while no saccade was involved. Subsequen t experiments confirmed the conclusion that target classification can continue during a saccade. The final experiment showed that response s election can continue during a saccade as well: The effect of S-R comp atibility was reduced in case of a small saccade (8-degrees) and disap peared altogether when a large saccade was carried out (100-degrees).