Fig. 1.

Timeline of events. (A) To make a response, participants used the mouse to rotate a bar to match the perceived orientation of the discrimination stimulus. (B) Events in each trial. Participants fixated in the centre of the screen, and pressed a key to begin the trial. After a random delay, the saccade target appeared at 15 degrees to the left or right of fixation and stayed there for the remainder of the trial. The fixation cross disappeared 200 ms after the onset of the saccade target. Depending on the type of trial, the pre-saccadic discrimination stimulus was shown at the same location as the saccade target. When a saccade was detected (when the eye moved more than 2 degrees horizontally from the fixation cross), the pre-saccadic stimulus switched to the post-saccadic stimulus. At a variable SOA after key press, a distractor appeared between fixation and target for 100 ms. The post-saccadic stimulus was displayed for the same duration as the pre-saccadic stimulus (both pre- and post- saccadic stimuli were presented for the saccade latency of that trial), after which time the participants made their response using the mouse. (C) Potential discrimination stimulus and distractor locations. On each trial the discrimination stimulus appeared on either the left or right of the screen, and the distractor appeared either 4 degrees above or below the horizontal centre of the screen, halfway between the fixation cross and the discrimination stimulus. (D) Example cumulative density function (red) fitted to the perceptual error judgements from one observer (blue). JNDs were measured as the standard deviation of this curve. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)