Reducing saccadic artifacts and confounds in brain imaging studies through experimental design

Abstract

Saccades constitute a major source of artifacts and confounds in brain imaging studies. Whereas some artifacts can be removed by omitting segments of data, saccadic artifacts cannot be typically eliminated by this method because of their high occurrence rate even during fixation (1-3 per second). Some saccadic artifacts can be alleviated by offline-correction algorithms, but these methods leave nonnegligible residuals and cannot mitigate the saccade-related visual activity. Here, we propose a novel yet simple approach for diminishing saccadic artifacts and confounds through experimental design. We suggest that specific tasks can lead to substantially less saccade occurrences around the time of stimulus presentation, starting from slightly before its onset and lasting for a few hundred milliseconds. In three experiments, we compared the frequency and size of saccades in a variety of tasks. Results of Experiment 1 showed that a foveal change-detection task reduced the number and sizes of saccades, relative to a parafoveal orientation-discrimination task. Experiment 2 replicated this finding with a parafoveal object recognition task. Experiment 3 showed that both foveal and parafoveal continuous change detection tasks induced fewer and smaller saccades than a discrete orientation-discrimination task. We conclude that adding a foveal or a parafoveal continuous task reduces saccades' number and size. This would lead to better artifact correction and enable the omission of contaminated data segments. This study may be the first step toward developing saccade-free experimental designs.

Gaze-based and attention-based rehearsal in spatial working memory.

“…The first one is that Experiment 3 did not include eye-tracking, and hence we could not assert that the visuospatial distraction task indeed inhibited shifts of gaze back to the locations of the memoranda. We reasoned that this was very likely because: (a) results of Experiment 3 were similar to the ones obtained for the central-fixation condition of Experiment 2 in which eye-tracking was conducted, and (b) Tal and Yuval-Greenberg (2018) demonstrated that a similar task inhibited saccades to a sudden onset target and also reduced the accuracy of reporting the target’s feature. The second caveat is that our implementation of the visuospatial distractor task was low demanding: changes in brightness occurred relatively infrequently and only once during the retention interval.…”

“…This task binds visuospatial attention to the fixation cross, leading to a lower processing rate of other visual objects (Poth, Petersen, Bundesen, & Schneider, 2014). This task has also been found to inhibit the occurrence of saccades towards the sudden-onset of a parafoveal stimulus, leading to costs to its processing (Tal & Yuval-Greenberg, 2018). Furthermore, combining this task with a multiple-object tracking task which requires rapid shifts of visuospatial attention across different locations on the screen to track the whereabouts of moving targets leads to costs for the processing of both tasks (Souza & Oberauer, 2017).…”

“…To do so, we applied a dual-task condition, requiring participants to keep their visuospatial attention on the screen center. In the dual-task conditions of Experiment 3, participants had to monitor the fixation cross for a low-salient change in brightness occurring during the retention interval (Souza & Oberauer, 2017; Tal & Yuval-Greenberg, 2018; Williams, Pouget, Boucher, & Woodman, 2013). This task binds visuospatial attention to the fixation cross, leading to a lower processing rate of other visual objects (Poth, Petersen, Bundesen, & Schneider, 2014).…”

In sync with your child: The potential of parent–child electroencephalography in developmental research

“…For example, the presence of another person in the experimental room, even without an explicit task, diminishes oscillatory behavior (Rolison et al., 2020). Additionally, the effect of movements—which is especially a problem in research with infants—may introduce artifacts in the EEG data (e.g., see Georgieva et al., 2020; Köster, 2016; Tal & Yuval‐Greenberg, 2018), and may thereby influence power, phase estimations, and intra‐ and interpersonal correlations. Especially in the naturalistic settings of hyperscanning experiments, movement artifacts such as saccades (eye movements) and micro‐interactions are closely linked to social interaction and thus neural epochs of interest.…”