Fig. 1.

A: stimulus configuration and basis of perceptual judgment. Upon presaccadic target presentation (top), the corollary discharge (CD) vector can be used to predict the saccadic landing site (gray cross). In this example, the planned saccade will fall short of the presaccadic target. After saccade initiation (bottom), the presaccadic target is extinguished and reappears displaced to the left or right. If the presaccadic target has been appropriately remapped, then the vector a between this remapped location and the postsaccadic target should roughly match the actual target displacement. Because, in this example, the postsaccadic target appears to the left of the presaccadic target, proper remapping would predict that participants will judge the displacement as backward. Alternatively, saccade landing site could serve as a proxy of the presaccadic target location, predicting that the location of the postsaccadic target relative to the saccadic landing site (vector b) drives the judgment (forward in this example). B: predictions in schizophrenia patients (SZP) and healthy controls (HC). If CD is disturbed in schizophrenia, we expect SZP to use the actual landing site as a proxy for the presaccadic target, rather than its remapped location. Consequently, we expect that SZP rely less on the target displacement predicted from remapping (vector a in A) and thus make more perceptual judgment errors. As a result of impaired remapping in SZP, we expect that they will show an increased relationship between the percentage of forward responses and the saccadic landing site error (top): the more hypometric a saccade, the more likely SZP should be to report “forward.” In the relationship between the percentage of forward responses and target displacement (bottom), less reliance on the actual target displacement in SZP should manifest in a larger just noticeable difference (JND). The perceptual null location (PNL) denotes the postsaccadic target location at which participants report an equal proportion of forward and backward jumps. Because we expect patients to rely more on saccade landing site when making a judgment, we expect that SZP with shorter average saccade amplitudes should perceive the postsaccadic target as jumping forward more frequently (as it will more often fall forward of saccade landing site). This increase in forward judgments will result in a smaller PNL. Thus we expect a positive relationship between mean saccade amplitude and PNL in SZP but not in HC (see inset). C: trial procedure. Dotted circles denote eye position. See methods for details.