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Peripheral Vision & Crowds

Posted by Ilena Di Toro | Posted on February 7, 2023

Peripheral vision and navigating through crowds, what do they have in common? For the most part nothing. Yet they are two examples of how information from the eye is coming into the brain and is being processed so that we can act accordingly. Two studies, one at the National Eye Institute (NEI) and the other at Brown University looked into these two things and here is what they found.

Something off to the side
Peripheral vision is something we are all familiar with, since we do it all the time. Small involuntary eye movements, known as microsaccades, can occur while a person is staring at a fixed point in space. The microsaccades can align towards an object of interest, even when a person is paying attention to something in the peripheral vision. Research by NEI investigators showed that while the microsaccades seem to boost or diminish the strength of the brain signals underlying attention, the eye movements are not leading to these brain signals.

Richard Krauzlis, Ph.D., chief of the NEI Section on Eye Movements and Visual Selection, and senior author of this study, found in his earlier research that peripheral vision causes a change in certain signals in a part of the brain known as the superior colliculus, which is involved in the detection of events. When attention is paid to a particular area, such as peripheral vision on the right side, signals in the superior colliculus related to that area receive an extra boost. Signals related to events occurring elsewhere, like the left side, are depressed.

Researchers wanted to see if attention-based signals changes in the superior colliculus are driven by microsaccades or if the two processes can be separated. So, they trained monkeys to hold their eyes straight ahead, while attending to their peripheral vision. The researchers would prompt either the left or right side by flashing a ring on the prompt side. After the prompt, the monkeys would release the joystick if they noticed a color change on the cued side, while ignoring the color changes on the uncued side.

Researchers measured the changes in the neuronal activity on both sides of the superior colliculus and found a boost to the cued side and lower signals on the uncued side. They also used high-resolution eye tracking cameras to measure the microsaccades. Sometimes there would be no microsaccades, other times the monkeys would make a microsaccades toward the cued side or away from the cued side. The researchers found that the signals for attention in the superior colliculus were present before the microsaccade and would be re-established after the microsaccade. That means the signals for attention occurred independent of eye movement signals and the microsaccades aren’t the driver of changes in the brains neurons when it comes to visual attention.

Not just a face in the crowd
Before lockdown, have you ever looked out a window of an office building in a downtown area during the morning or afternoon rush and noticed how people were walking en masse to their destination. Yet, they are different people of different ages and different walking speeds. Once they are all together, they walk at the same pace. Why is that?

Scientists at Brown University wanted to learn more about this type of behavior, so they used virtual reality headsets and their findings were very accurate at predicting crowd flow. The headsets allowed for the participant’s viewpoint. Previous models were based on physics, such as the forces of attraction and repulsion, but they didn’t explain why humans in a group interacted the way that they do.

Participants wearing the virtual reality headsets were placed in a large room. The headsets showed animated 3D humans who moved in different way, such as turning left or right. The participants were instructed to walk with the crowd and the researchers tracked their movements. By using virtual reality headsets, researchers found that a pedestrian controls his or her walking direction and speed by using two visual motions.

First, the participants walk in a way that reduces the sideways motion of others in the field of view and they also walk to reduce both the expansion and contraction in the field of view when a fellow pedestrian gets closer or further way. Using these two variables to control walking, the participant matches the average speed and direction of the crowd.

While, as expected, the participants responded less to those who were farther away, there were two reasons for that and they are: The law of optics that states things that are farther away in space have smaller visual motions and the principle of occlusion, which states that those who are farther away are likely to be partially blocked by others, making them harder to see and follow.

This study demonstrated that people in a group use visual information to guide their walking. This is known as visual coupling and others in the group are acting according to the same principle.

Both studies show that the eyes and brain are taking in a great deal of information. In turn, that information is being utilized to either focus on an object or not bump into other people while walking on a crowded street.


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