Genes, Not Culture, Predispose Speed of Eye Movements

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When considering the speed at which a person’s eyes move, research indicates that genes – not culture – are the more important factor. Researchers from the University of Liverpool examined people of Asian and Caucasian descent to determine if differences in saccades, which are the jumping movements of the eye, could be better explained by one’s genetic “nature” over their “nurtured” cultural upbringing. The evidence indicates that perhaps genetic variants more commonly found in people of Chinese descent predispose individuals to eye movements that are faster than those of their Caucasian counterparts.

A person reading the text written here will do so by executing a series of specific eye movements called “saccades.” Saccades are rapid, ballistic eye movements in which the eye jumps its focus abruptly from point to point. These points of focus can be close together (such as on a smartphone screen) or far apart (such as different points on the horizon). Though many might describe the experience of reading as smoothly sweeping the eyes from left to right, the eyes are in fact jumping from one position on a page to the next.

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The human brain is quite adept at interpreting this jerky, jumping saccade movement into a smooth transition of focus. While most people are capable of reading words on a page, errors in this visual tactic become evident when people are asked to focus on moving objects. When asked to visually follow an object that starts to move, a person’s brain must calculate where the next point of focus will be. The time it takes for the brain to calculate where to focus on next is called a “latency” period. After this estimation is made, the eye must then move to refocus on the targeted point. If an object changes its direction or moves quickly away from that original point of focus during the time it takes for the brain to calculate and the eyes to move, the eye does not focus on the correct spot and a “motor error” occurs. This is why it can be difficult to follow fast-moving objects such as a ball in a pinball machine.

In previous studies, researchers have shown that different populations of humans show differences in the lengths of saccade latency periods. In particular, Chinese subjects were demonstrated to have slower latency “reaction times.” In most humans, a typical latency period lasts 200 ms. However ,about a third of Chinese subjects demonstrated “express” saccades—saccades with latency periods of only 80 to 130 ms. Conversely, only three percent of Caucasian subjects demonstrated such rapid brain calculations.

On average, the human brain has a 200 millisecond latency period between eye movements in which it must calculate where to next focus. Errors in such calculations can occur when a person is attempting to focus on an object that is moving very quickly or erratically, as seen in many video games. Such mistakes lead the eyes to “miss” their target.

Researchers were curious to know if these rapid eye movements are the product of genetic influences or cultural upbringing. To answer this question, they examined the eye movements of subjects from three groups: people born from Chinese parents who were raised in China, people of Chinese parents who were brought up in the United Kingdom, and a group of Caucasian students raised in the UK.

The results of the study indicated that the ethnically Chinese but culturally English subjects are, like their Chinese-born-and-raised counterparts, ten times more likely to have the superfast express saccades.

While this study examines a fascinating variation in human traits, it is important to note that the relationship between ethnic heritage and saccade latency periods is only a correlation—not a demonstrated causational relationship. Other research has shown that inherited genes  influence the eye movements of zebrafish, but the study discussed here did not conduct any further genetic investigations to identify potentially influential genes. Therefore, while current interpretation of the research results suggests genes are more important than cultural upbringing in determining the speed at which a person’s eyes move, the question is far from definitively resolved.

By Sarah Takushi

Sources:
AsianScientist .com
Experimental Brain Research
Journal of Neuroscience
Neuroscience, 2nd Edition
PLOS ONE

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