Figure 2.

Trial types and predictions. (A) Arrangement of fixation point (FP) and targets (A–D) in our experimental paradigm. (B) Before saccade adaptation is induced, single saccades are aimed at targets A, B, and D and are generally quite accurate. (C) Two sequences of double saccades (note double arrowheads) are tested: FP–A–B and FP–C–D. The location of the targets for the second saccade in each sequence is actually jittered horizontally around targets B and D. Targets are arranged so that, on average, the vector for second saccade in the FP–A–B sequence is equal to the vector of saccades aimed directly at target D. Similarly, the vector of the second saccade in the FP–C–D sequence is equal to the vector of saccades aimed directly at target B. (D) After adaptation is induced, vectors $\overrightarrow{GB}$ and $\overrightarrow{MB}$ are dissociated. (E) If saccades involving target C are excluded, the paradigm reduces to the Final Target Dissociation paradigm (Figure 1C). (F) If saccades involving target A are excluded, the paradigm reduces to the Parallel Target Dissociation paradigm (Figure 1D). (G) According to the goal updating hypothesis, the second saccade end points for FP–A–B sequence will not change after adaptation; in contrast, the end points for the FP–C–D sequence will change (red arrow), approximately in the same way as the end points of saccades aimed directly at target B. (H) According to the motor updating hypothesis, the second saccade end points for FP–C–D sequence will not change after adaptation; in contrast, the end points for the FP–A–B sequence will change (blue arrow), following the changes in the end points of saccades aimed directly at target B.