**Participants.** 10 participants will be recruited through word of mouth and campus mailing lists. Each participant will complete three sessions of approximately 1 hour. Participants will receive 8 Euros per session and 2 Euros as a bonus for the completion of all four sessions (altogether 26 Euros). We will obtain written informed consent from all subjects prior to inclusion in the study. **Apparatus.** Stimuli will be projected onto a 16:9 (250.2 x 141.0 cm) video-projection screen (Stewart Silver 5D Deluxe, Stewart Filmscreen, Torrance, CA), mounted on a wall, 340 cm in front of the participant. The projector is a PROPixx (Vpixx Technologies, Saint-Bruno, QC, Canada) running at 1440 Hz vertical refresh rate and a resolution of 960 x 540 pixels. The experimental code is implemented in MATLAB (Mathworks, Natick, MA, USA), using the Psychophysics and Eyelink toolboxes (Kleiner et al., 2007; Cornelissen et al., 2002) and runs on a Dell Precision T7810 Workstation with a Ubuntu 18.04 operating system. Eye movements of both eyes are recorded via a TRACKPixx3 tabletop system (Vpixx Technologies, Saint-Bruno, QC, Canada) running firmware version 11 at a sampling rate of 2000 Hz, while participants rest their head on a chin rest. Responses are collected with a standard US-english keyboard. **Procedure.** Each trial starts with the display of a six-stimulus circular array (10 dva eccentricity), while the participant is fixating the area of 1.5 dva radius around a central fixation dot for 400 ms. The stimulus array will contain two types of dissimilar noise patches, in alternating order. After successful fixation, an exogenous cue will be presented, i.e., the target noise patch (one of the two types) increasing and decreasing its size for 50 ms (see Stimuli), signaling the saccade target. As soon as the saccade is detected (see Online saccade detection), the cued stimulus will move 30 deg in a clockwise or counterclockwise direction for 14.6 ms, while in static conditions they will remain in their locations. All other noise patches will be removed for the time of target movement and displayed at their post-movement locations as soon as moving stimulus reaches its final position. Importantly, in apparent motion / no-streak conditions, no continuous path of the stimulus will be shown for 14.6 ms. After the stimulus movement is concluded, participants' saccades will land between two noise patches (each of one type and of which one is the one initially cued), so that a secondary saccade is made to either of them in order to correct for the displacement. If their gaze position will not fall within a circular region with a radius of 2 dva around the initial target location, they will receive feedback about not having reached the target area and the trial will be repeated. Crucially, with varying onset asynchrony (0, 25, 50, 100, 200, 600 ms) a pixel noise mask will occlude the identity of the stimuli, limiting participants' time to use stimulus surface features to guide the secondary saccade. After a total time of 650 ms after stimulus movement offset, the trial is concluded. Video of a few trials (60 fps instead of 1440 fps, mouse cursor represents gaze position): https://osf.io/f48rm/ ![Figure 1][1] **Figure 1.** Plot of stimulus movement in respective experimental conditions. Six stimuli are organized in an array around the central fixation point, if which one is cued exogenously (empty circles). After online saccade detection, the cued stimulus moves (continuously vs apparently) clockwise or counterclockwise for 30 degrees until its final position is reached (empty triangles). In static conditions, no movement takes place. **Stimuli.** Stimuli will be achromatic, random noise (Gaussian noise with SD=1) patches bandpass-filtered from 0.25 to 1 cycles/dva, displayed on a grey background. To maximize the dissimilarity between the two types of noise patches (without just creating black and white surfaces), 75% of a noise SD will be added or substracted from the initial noise patch, thus increasing or decreasing its luminance (Figure 2). Differences in spatial frequency and orientation content in the pairs of noise patches that might be caused by this procedure will be investigated in later stages of the project using a Gabor filter approach (as in Li et al., 2016). All noise patches are at full contrast to maximize their intra-saccadic visibility. Bandpass-filtered noise patches, initially of 3 dva diameter, are enveloped in a Gaussian aperture with a standard deviation of 0.5 dva. Masks displayed at post-movement locations have the same dimension, but will consist of random black-white pixel noise. For each trial, six similar noise masks are generated. The fixation dot used is a white circle of 0.3 dva radius. When fixated, the area within the circle will be filled by another white circle of 0.1 dva radius. The exogenous saccade cue will be a the a short looming of the cued stimulus, displayed for 50 milliseconds: During the first 25 ms, the noise patch will linearly increase its size to twice its initial size and then shrink back to its initial size (see trial video). Stimulus movement - clockwise or counterclockwise - will cover 30 degrees, thus approximately 5.2 dva given the stimulus eccentricity relative to the screen center of 10 dva. Movement duration will be 14.6 milliseconds (21 frames at 1440 fps), leading to a stimulus velocity of approximately 360 dva/s. ![Figure 2][2] Figure 2. Examples of pairs of noise patches created individually in each trial. **Design.** Each of the three sessions will consist of 1152 trials. Altogether there will be 3456 Trials. They are determined by the following factors: - Stimulus cued (6 levels). Participants will make 10 dva saccades to one of six stimulus locations. - Initial position of the stimulus array (2 levels). Initial positions of stimuli 1-6 in angle relative to screen center can be either {0, 60, 120, 180, 240, 300} degrees (Figure 1, bottom row) or {30, 90, 150, 210, 270, 330} degrees (Figure 1, top row). - Global movement direction (3 levels). Stimulus arrays will rotate for 30 degrees in a clockwise direction (Figure 1, middle column), counter-clockwise direction (Figure 1, left column), or remain static altogether (Figure 1, right column). - Type of stimulus movement (2 levels). Movement of the cued stimulus will either occur in a continuous or step-wise fashion, thus inducing an intra-saccadic motion streak or not, respectively. - Post-movement mask SOA (6 levels). To limit the time that stimulus surface features are available after their movement offset, they are occluded by a black-white pixel noise patch after either 0, 25, 50, 100, 200, or 600 milliseconds. **Online saccade detection.** Saccades will be detected online using a custom-made velocity-based detection algorithm, inspired by Engbert & Mergenthaler (2006), which was used already in previous preregistered experiments, e.g., osf.io/r5gst. The saccade detection algorithm will be run on data from both eyes, detecting a saccade only if detection was successful in both cases. Two samples are needed to detect a saccade, with a lambda of 10 and a direction restriction of +/- 40 degrees of the cued saccade direction. **References** Cornelissen, F. W., Peters, E. M., & Palmer, J. (2002). The Eyelink Toolbox: eye tracking with MATLAB and the Psychophysics Toolbox. Behavior Research Methods, 34(4), 613-617. Engbert, R., & Mergenthaler, K. (2006). Microsaccades are triggered by low retinal image slip. Proceedings of the National Academy of Sciences, 103(18), 7192-7197. Kleiner, M., Brainard, D., Pelli, D., Ingling, A., Murray, R., & Broussard, C. (2007). What’s new in Psychtoolbox-3. Perception, 36(14) Li, H.-H., Barbot, A., & Carrasco, M. (2016). Saccade preparation reshapes sensory tuning. Current Biology, 26(12), 1564-1570. [1]: https://mfr.de-1.osf.io/export?url=https://osf.io/9pb2g/?action=download&mode=render&direct&public_file=False&initialWidth=848&childId=mfrIframe&parentTitle=OSF%20%7C%20position_plot.svg.png&parentUrl=https://osf.io/9pb2g/&format=2400x2400.jpeg [2]: https://mfr.de-1.osf.io/export?url=https://osf.io/j5yce/?action=download&mode=render&direct&public_file=False&initialWidth=848&childId=mfrIframe&parentTitle=OSF%20%7C%20stimulus_pairs.png&parentUrl=https://osf.io/j5yce/&format=2400x2400.jpeg