Figure 1 illustrates the experimental procedure. On each trial, participants had to initially fixate within a 2.0 degree radius around a central fixation target (FT) – a black (approximately 0 cd/m
2) and white (approximately 44 cd/m
2) bull's eye (radius: 0.4 degrees) – presented on a gray background (approximately 22 cd/m
2). Upon correct fixation for 200 ms, 13 equidistant flickering stimulus streams were presented along an imaginary semicircle (radius: 10°) to the right side of the FT. Stimulus streams alternated every 25 ms (40 Hz) between a vertical Gabor patch (spatial frequency: 2.5 cpd; 100% contrast; random phase selected at each stream refresh; SD of the Gaussian window: 1.1 degrees; mean luminance: approximately 22 cd/m
2) and a Gaussian pixel noise mask (consisting of 0.23 degree width pixels with the same Gaussian envelope as the Gabors; see
Wollenberg et al., 2019 for a video demonstration, and
Hanning, Deubel, & Szinte, 2019 for a sample code). Between 300 and 600 ms after the onset of the stimulus streams, we presented a saccade target (ST) to which participants had to move their eyes, together with a nearby distractor (DIST), which participants should ignore. ST and DIST were equiluminant relative to the background and appeared in the form of black (approximately 0 cd/m
2) and white (approximately 44 cd/m
2) circles (radius: 1.1 degrees; width: 0.2 degrees) surrounding 2 stimulus streams separated by an angular distance of 30 degrees until trial end. The color configuration of ST and DIST was counterbalanced across participants but constant for each participant across the experiment (5 participants: white ST/black DIST; 4 participants: black ST/white DIST). Importantly, we systematically varied the spatial predictability of the ST and DIST locations via pre-block instructions (8 blocks of each type played in random order). Depending on the block type, participants were either unaware of the ST and DIST locations (ST/DIST
variable), informed about the fixed location of ST (ST
fixed), or informed about the fixed location of DIST (DIST
fixed). Note that, as ST and DIST always appeared at an angular distance of 30 degrees, participants could also predict the DIST location in the ST
fixed condition and the ST location in the DIST
fixed condition with a probability of 50% (i.e. either two stimulus streams clockwise or counterclockwise to the fixed location). Moreover, to investigate the dynamics of attentional and oculomotor selection as a function of visual processing time prior to saccade onset, we systematically delayed saccades. Participants were instructed to move their eyes as fast and accurately as possible upon the offset of FT (rather than the onset of ST and DIST), which was randomly delayed by 0, 100, 200, or 300 ms (delay
0, delay
100, delay
200, and delay
300) relative to ST and DIST onset. In order to assess the deployment of visual attention during saccade preparation, a discrimination target (DT) was presented shortly before saccade onset. The DT consisted of a slightly tilted Gabor (either clockwise or counterclockwise at a rotation angle of 12 degrees relative to the vertical), which was presented for a duration of 25 ms and disappeared at either −100, +50, or +100 ms relative to the FT offset (saccadic go-signal). Note that, whereas the positive discrimination target offset asynchronies (DTOAs, defined as the duration between FT offset and DT offset) of +50 and +100 ms were used across all saccadic go-signal delays (delay
0, delay
100, delay
200, and delay
300), the negative DTOA of −100 ms was only introduced in half of the trials without a saccadic go-signal delay (i.e. delay
0). These trials were used to evaluate potential effects of spatial predictability on the endogenous deployment of visual attention prior to the actual presentation of ST and DIST. The DT location was randomly selected among five possible stimulus streams at: the saccade target (ST), the distractor (DIST), in between the saccade target and the distractor (BTW), adjacent to the saccade target (ST
adjacent), or adjacent to the distractor (DIST
adjacent). Discrimination performance was averaged across the latter two locations to derive a robust baseline measure (CTRL) of visual orientation sensitivity. On approximately 2% of trials, no DT was presented in order to evaluate potential influences of the DT appearance on saccade latencies. Eight hundred ms after the onset of ST and DIST, all stimuli were erased from the screen. At the end of each trial, participants reported the DT orientation (two alternative forced choice: clockwise versus counterclockwise) via button press on the keyboard (right versus left arrow). A feedback sound was played upon incorrect manual responses and the next trial was launched once the manual discrimination response was registered.