Posterior parietal cortex damage causes endpoint biases relative to the visual target during anti-saccades

Anti-saccades are eye movements in which the saccade is executed in the opposite direction of a visual target. Because the visual target and saccade goal are decoupled, it has been suggested that competition between the two locations occurs and needs to be resolved. The posterior parietal cortex (PPC) has been implicated in anti-saccade production. To gain insight into the processes of competition and saccade planning within the PPC, we investigated anti-saccade performance in three patients with PPC lesions and 21 age-matched controls on three different anti-saccades paradigms: 90° away across hemifields, 90° away within the same hemifield and 180° away (diagonally opposite). Specifically, we examined how saccade endpoints demonstrated the extent of competition, i.e., the visual target’s interference with anti-saccade programming and execution processes. We observed that anti-saccade endpoints showed bias toward the visual target in all of control participants, and this appeared exacerbated in two of our patients. Our third patient showed, instead, a strong bias away from the visual target. Modified t-tests revealed a significant difference between two of patients and their controls in terms of amplitude relative to the visual target for the across and classic conditions, and no significant difference for the within condition. However, one patient showed no significant difference compared to controls across all conditions. Overall, we showed some evidence of a stronger bias relative to the visual target in our patients. This suggests that the PPC may contribute to competition resolution between visual target and saccade goal during anti-saccades.