Twins don’t just look alike; they also look alike . . .


A recent study co-led by PBS professors Daniel Kennedy and Brian D’Onofrio, which tracked the eye movement of twins, found that genetics plays a strong role in how people attend to their environment.

Conducted in collaboration with researchers from the Karolinska Institute in Sweden, the study offers a new angle on the emergence of differences between individuals and the integration of genetic and environmental factors in social, emotional and cognitive development. The implications of the findings are great insofar as visual exploration is also one of the first ways infants interact with the environment, before they can reach or crawl.

“The majority of work on eye movement has asked, ‘What are the common features that drive our attention?’” said Kennedy. “This study is different. We wanted to understand differences among individuals and whether they are influenced by genetics.”

Kennedy and D’Onofrio study neurodevelopmental problems from different perspectives: Kennedy uses eye tracking methods to study individuals, while D’Onofrio traces the genetic and environmental contributions to various traits, using data from large populations. This work brought together their contrasting methods in one of the largest-ever eye tracking studies.

In the experiment, 233 pairs of twins (466 children in total) looked at 80 snapshots of scenes they might encounter in daily life, half of which included people. Using an eye tracker, researchers measured the children’s eye movements as each child looked at the scene. They also examined general “tendencies of exploration”; for example, if a child looked at only one or two features of a scene or at many different ones.

Published in the journal Current Biology, the study found a strong similarity in gaze patterns within sets of identical twins, who tended to look at the same features of a scene in the same order. It found a weaker, but still pronounced similarity between fraternal twins.

This suggests that genetics strongly influence the way individuals visually explore their environments: Given that both identical and fraternal twins each share a common environment with their twin, the researchers can infer that the more robust similarities among identical twins are due to their shared genetic makeup. The researchers also found that they could reliably identify a twin with their sibling from among a pool of unrelated individuals based on their shared gaze patterns -- a novel method they termed “gaze fingerprinting.”

“This is not a subtle statistical finding,” Kennedy said. “How people look at images is diagnostic of their genetics. Eye movements allow individuals to obtain specific information from a space that is vast and largely unconstrained. It’s through this selection process that we end up shaping our visual experiences.

The findings may broaden our understanding of cognitive development. After early childhood, the study suggests, genes influence at the micro-level -- through the immediate, moment-to-moment selection of visual information -- the environments individuals create for themselves.

“Our eyes are moving constantly, roughly three times per second,” Kennedy said. “We are always seeking out information and actively engaged with our environment, and ultimately where you look affects your development.”

“Less known are the biological underpinnings of the process,” he added. “From this work, we now know that our biology affects how we seek out visual information from complex scenes. It gives us a new instance of how biology and environment are integrated in our development.”

“This finding is quite novel in the field,” explained D’Onofrio. “It is going to surprise people in a number of fields, who do not typically think about the role of genetic factors in regulating such processes as where people look.”

Additional researchers on the paper are Patrick D. Quinn, a postdoctoral student in PBS, and Sven Bölte, Paul Lichtenstein and Terje Falck-Ytter of the Karolinska Institute.

“We now know that our biology affects how we seek out visual information from complex scenes. It gives us a new instance of how biology and environment are integrated in our development.” -DANIEL KENNEDY