Eye-Tracking Study Reveals Retinal Mechanisms Behind Visual Stability

A recent eye-tracking study led by Prof. Markus Lappe from the University of Münster has uncovered new insights into how the brain maintains a stable perception of the world, despite constant eye movements. Published in Science Advances, the study sheds light on the retinal mechanisms and neural pathways involved in processing dynamic visual stimuli, particularly those with non-rigid motion, like fire or water.

Visual Perception and Stability: The Challenge for the Brain

The brain must process over 10 million visual inputs every second, transmitted from the eyes through thousands of nerve fibers. This immense data stream allows us to perceive our surroundings as stable, even though our eyes are continuously moving. Experts suggest that this stability is due to a complex compensatory mechanism within the visual system, though its specifics have remained unclear.

The Study’s Focus: Eye Movements and Non-Rigid Motion Perception

Lappe’s research team investigated how our visual system maintains stability when processing non-rigid motion, a type of movement that’s rarely studied in vision science. They found that traditional smooth eye movements, or "smooth pursuit," are not possible for all visual motions. Specifically, rapid eye movements (saccades) fail to compensate for certain non-rigid motions, leading to a loss of visual stability.

“Our results show a clear separation of the two systems,” explains Prof. Lappe. “They are functionally distinct and run along different neuronal pathways.”

Experiment Design: Tracking Visual Disruptions in Motion Perception

The study introduced a novel visual illusion that disrupts spatial perception, designed to test how the brain responds to complex motion stimuli. Fifteen participants were asked to follow a simulated rotating vortex moving across a field of dots. Although typically the eyes would follow the object’s path continuously, the vortex’s unique motion caused the eyes to remain momentarily static.

       • Key Observation: A phase of rapid eye movement occurred approximately every 400 milliseconds, bringing the vortex back to the center of the retina. However, each time this adjustment occurred, the vortex appeared to “jump” forward, disrupting the brain’s typical compensatory mechanism.

“The usual compensatory mechanism for rapid eye movements failed when the vortex moved,” notes Ph.D. student Krischan Alexander Koerfer. “This is a previously unknown combination of visual perception and eye movement response.”

Methodology: Advanced Eye-Tracking with Infrared Cameras

The research team used high-speed infrared eye trackers to capture precise eye positions and movements in real time. Infrared light illuminated the eyes, and reflections on the cornea and pupil were recorded and analyzed, allowing the researchers to measure the exact eye positions and movements during the visual illusion.

Implications for Cognitive and Brain Research

The study’s findings have significant implications for cognitive and brain research. By presenting a type of motion where the compensatory mechanism fails, traditional visual models can now be tested and refined.

“The fact that, for the first time, a movement is presented in which the compensation mechanism fails means that old models can be tested and new ones developed,” says Lappe.

In the long term, this new stimulus concept may offer applications in diagnosing and studying neurodegenerative diseases, potentially advancing understanding of the visual system’s role in various brain functions.

Resource:

Krischan Koerfer et al, Inability to pursue nonrigid motion produces instability of spatial perception, Science Advances (2024). DOI: 10.1126/sciadv.adp6204