First,
change detection tasks require the subject to detect a discrepancy between a presaccadic and a postsaccadic stimulus. Inferences about the contents of transsaccadic memory then rely on the assumption that discrimination performance reflects the amount of task-relevant presaccadic information that is retained until after the saccade. The classical finding in this line of research is that intrasaccadic displacements of stimuli are significantly more difficult to detect than displacements occurring during a fixation (Bridgeman, Hendry, & Stark,
1975), leading to the speculation that little or no visual information is retained across saccades, and perception starts from scratch following each saccade (Bridgeman, Van Der Heijden, & Velichkovsky,
1994). However, Verfaillie, De Troy, and Van Rensbergen (
1994) noted in their study on transsaccadic perception of biological motion that while position information was poorly retained, detection of changes in orientation was only slightly affected by the presence of a saccade. Moreover, Verfaillie (
1997) showed that detection of intrasaccadic position changes could be moderately improved by providing more biological motion walkers as reference objects (also see Deubel,
2004). Measuring change detection during visual scene exploration, Hollingworth and Henderson (
2002; Henderson & Hollingworth,
2003) found that even within-category object changes could be detected rather well, though global changes in scene luminance or contrast were still almost imperceptible (Henderson, Brockmole, & Gajewski,
2008). But perhaps the most striking finding was reported by Deubel, Schneider, and Bridgeman (
1996), who showed that briefly blanking the display immediately after saccade landing could improve intrasaccadic change detection performance of stimulus location significantly (also see Gysen, Verfaillie, & De Graef,
2002). In another study (Deubel, Schneider, & Bridgeman,
2002), it was shown that this blanking effect could be generalized to change detection of stimulus identity. This suggests that the results of change detection tasks are not so much a function of whether information was retained in transsaccadic memory, but rather whether it was retained
and subsequently available for comparison to the postsaccadic stimulus. De Graef and Verfaillie (
2002) proposed that a detailed visual store exists that could support transsaccadic integration, the so-called visual analog. Also described as “informational persistence”, this memory store is precategorical, short-lived (up to a few hundred milliseconds), and maskable (Irwin & Yeomans,
1986). In further experiments, Germeys, De Graef, Van Eccelpoel, and Verfaillie (
submitted for publication) presented subjects with circular arrays of letters and observed that presenting a short location cue during a blank interval immediately following the saccade could drastically improve detection performance of changes to individual items within such an array. They propose that this cue and blank interval are needed to quickly read out detailed information from the visual analog to a more durable store, before its contents are masked away by the postsaccadic stimulus. In general, this line of research can be summarized as showing that the inability to detect small intrasaccadic changes does not necessarily indicate the absence of the task-relevant visual information in transsaccadic memory.