The Mystery of Saccadic Suppression

 The Mystery of Saccadic Suppression 

The process of moving our eyes several times per second is characterized by saccadic movements, which are vast images shifting on the retina. Visual stability across saccades tends to vary throughout the visual system, and has different effects on prioritization as opposed to fixation. The process of fixation seems to be more feasible and time efficient when looking at prioritization effects, due to saccadic suppression occurring. Studies have shown evidence for saccadic suppression by comparing fixation points and saccadic eye movements when viewing real-world objects.

In the study “Overt Attentional Prioritization of New Objects and Feature Changes During Real-world Scene Viewing,” Michi Matsukura and colleagues observed the extent to which a color change or appearance of a new object would have a greater effect on subjects during real-world scene viewing. Matsukura et al. (2009) found that both types of these scene changes produced effects in capturing gaze, but the appearance of new objects caught more attention than a color change during fixation. During saccadic eye movements, however, none of these scene changes captured attention due to saccadic suppression. Despite this suppression, memory-based mechanisms still have the ability to prioritize these scene changes compared to other stagnant objects in the picture. Matsukura and colleagues concluded that online memory for object identity and some object features work in detecting changes to live scenes. Fixations were accompanied by transient motion signals, which was why attention was captured more quickly than during saccades, which eliminated these transient signals. 

An article published on ScienceDaily called, “The Mystery of Visual Stability” from Tohoku University explains the mechanisms underlying saccadic eye movements. These fast movements of the eye force the visual system to work hard to uphold a stable perceptual world. This is compensated for by remapping the retinal image; however, even with remapping, errors in actual eye movements cause image shifts. Research led by Professor Satoshi Shiorir investigated the processes underlying Saccadic Suppression of Displacement (SSD). Similar to the study with Matsukura et al. (2009), this psychological experiment included subjects staring at a fixation point, and after this point disappeared, the subjects shifted their eyes to a target on the opposite side. Researchers observed the targets before and after saccades occurred in order to control the retinal input power. The article discusses the results from this experiment, explaining that there are two visual pathways responsible for two different effects. These two major pathways are the parvo-pathway and magno-pathway, which are involved in suppressing inaccurate motion information through saccades, and detecting displacements, respectively. The bridge between this news article and the research conducted by Matsukura et al. (2009) is the suppression of saccadic eye movements, resulting in quicker prioritization during fixation. 

While much more work needs to be done to fully grasp the understanding of visual stability across saccades, the work of Matsukura et al. (2009) and Professor Satoshi Shiorir of Tohoku University provides a strong foundation for how these processes occur. Even though SSD stays a mystery to neuroscientists, improvements in technology and methods can help them further understand the processes associated with saccadic eye movements, particularly saccadic suppression. 

Sources: 

Brockmole, J.R., Henderson, J.M., Matsukura, M. (2009). Overt attentional prioritization of new objects and features changes during real-world scene viewing. Visual Cognition, 17 (6/7), 835-855. https://doi.org/10.1080/13506280902868660

Tohoku University (2020). The mystery of visual stability. ScienceDaily. https://www.sciencedaily.com/releases/2020/06/200611094213.htm