In the realm of vision science, our ability to perceive optical stimuli is a complex process. It involves the brain efficiently processing millions of visual information bits per second, which are transmitted via thousands of nerve fibres. This intricate process allows us to perceive the world as stable, despite our eyes constantly moving. The mechanism that facilitates this balance is a subject of ongoing research and is yet to be fully comprehended.
A groundbreaking study led by Prof Markus Lappe, a psychologist from the University of Münster, aimed to decipher how this stability of perception is achieved despite the highly dynamic visual input signal on the retina. The team primarily focused on understanding the perception of non-rigid objects, like fire or water, a largely unexplored area.
The research findings, contrary to previous beliefs, suggest that smooth eye movements (smooth pursuit) cannot be performed for all types of visual motion. Furthermore, the researchers established that the compensatory mechanism for rapid eye movements (saccades) fails during certain types of non-rigid movements, resulting in the loss of visual stability. These findings were published in Science Advances journal.
Historically, vision science has postulated that rapid and smooth eye movements respond identically to motion signals. However, as Markus Lappe clarifies, their results reveal a clear distinction between the two. They function differently and are processed through separate neuronal pathways.
During the study, the researchers presented a new visual motion illusion that disrupts spatial perception. To validate the new stimulus concept, fifteen participants were asked to track a simulated rotating vortex moving across a dotted field with their eyes. Typically, the eyes stay fixed on the object, moving at the object’s speed. However, the participants couldn’t track the vortex, causing the eyes to stay static for a while. Rapid eye movement occurred every 400 milliseconds, recentering the vortex on the retina. With each such movement, the vortex seemed to leap forward. This demonstrated an unprecedented combination where the compensatory mechanism for rapid eye movements failed during the vortex’s movement.
To accurately analyze the correlation between the physical stimuli presented and the corresponding perception, the team utilized high-speed infrared cameras, or ‘eye trackers’. These trackers illuminated the eyes with infrared light, capturing and analyzing the reflections on the cornea and pupil, thus determining the exact position and movement of the eyes.
These innovative findings in basic research offer significant benefits for cognitive and brain research. As Markus Lappe points out, the discovery of a movement that disrupts the compensation mechanism permits the testing of old models and development of new ones. The new stimulus concept could also prove valuable in diagnosing and researching neurodegenerative diseases in the future.
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