A second interpretation of our results is that saccadic adaptation modifies the perceived location of the pre-saccadic target (as suggested by Awater et al.,
2005; Bruno & Morrone,
2007; Collins, Doré-Mazars, & Lappe,
2007). If such perceptual mislocalizations occurred, pre-saccadic targets at 10° would be perceived at, say, 8.5° and a saccade of this amplitude prepared. Supposing the efference copy matches the saccade, this would lead to stationary reports for backward-stepped targets, and forward reports for stationary targets, i.e., the pattern of results observed. According to this hypothesis, efference copy would carry correct metric information about adapted saccades, based on a modified perceived target location. This interpretation has the merit of also explaining some other mislocalization data (Awater et al.,
2005; Bruno & Morrone,
2007; Collins et al.,
2007), which the previous interpretation cannot do. Awater et al. (
2005) tested probe localization in the vicinity of the saccade target and observed local perceptual mislocalizations many hundreds of milliseconds before a saccade, suggesting that saccadic adaptation induced a remapping of visual space. Furthermore, Collins et al. (
2007) showed—as in the present study—that these mislocalizations were not proportional to the amplitude of the performed saccade. Instead, they were proportional to the adaptation of the saccade to the probe, suggesting that adaptation induced a common modification of perception and action in a particular region of space. Finally, Bruno and Morrone (
2007) found that both verbal and pointing reports of perceived location shifted with adaptation, suggesting again a similar recalibration of action and perceptual maps. These studies suggest that saccadic adaptation is accompanied by a local modification of perceived location of visual objects. Our results are compatible with this hypothesis. Furthermore, other studies have shown that adaptation is taken into account in motor tasks requiring efference copy. In particular, correctly programming a sequence of memory-guided saccades requires combining visual information about the second saccade target, encoded before sequence onset, with an efference copy of the intervening first saccade (Sommer & Wurtz,
2004). When the first saccade was adapted, second saccades remained accurate and compensated for the adaptation, showing that the efference copy provided correct information about the adapted metrics of the first saccade (Doré-Mazars, Vergilino-Perez, Collins, Bohacova, & Beauvillain,
2006).