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LEWISBURG, Pa. - Two sets of lines - one straight, the other crooked - flash on a computer screen.
The lines appear alternately for just a fraction of a second, but that's enough for the brain to register a reaction. Some notice just a slight difference between the parallel and non-parallel lines. Others note a great distinction.
It has been long known that humans - even in their infancy - have a natural preference for symmetry. But to what degree we react to those preferences could hold the key to better understanding a range of disorders including autism, obsessive-compulsive disorder and other spectrum conditions, researchers at Bucknell University and Geisinger Health System have discovered.
"Everyone has a preference for symmetry, but in some disorders this preference turns into a preoccupation," said David Evans, a professor of psychology and director of the neuroscience program at Bucknell University. "Someone with OCD can't function if objects around them are not arranged just so. They can't go to work because the pictures on the wall are not just right,
"They start ordering and arranging, and checking and re-ordering and re-arranging. If they walk by a piece of furniture and accidentally brush it with their right hand, they may feel an irresistible urge to go back and brush the furniture with the left hand to achieve a sense of evenness, balance and symmetry"
In a paper published in the online journal PLoS ONE on June 13, Evans, student researchers and collaborators at Geisinger explain how perceptions of parallel and asymmetric images coincide with even subtle symptoms of OCD and autism. "Human Preferences for Symmetry: Subjective Experience, Cognitive Conflict and Cortical Brain Activity," describes a study at Bucknell in which human subjects who have not been diagnosed with OCD or autism showed varying degrees of sensitivity to symmetry when presented with a series of parallel and asymmetrical images. || See full text in PLoS ONE. || See Ask the Experts: David Evans
The Bucknell-Geisinger study could offer insight into the varying degrees - or spectrum - of neurodevelopmental and neuropsychiatric disorders, thus aiding in early intervention and treatment, said Evans, whose research focuses on the assumption that more is learned through the study of what is "normal" rather than determining what is abnormal.
"When we capture the very subtle differences that exist between people in terms of their preferences for symmetry, their need for order, etc., we are finding that we also see subtle differences in brain function," Evans said. "There is evidence that the brains of people with OCD and ASD may work differently than the brains of other people. But what we are finding is that when you use measures that are sensitive to the more subtle manifestations of OC or ASD-like behaviors, you see similar patterns of brain activity under certain circumstances. There is a sense in which we are all 'on the spectrum,' and to some degree our brains reflect this."
Preferences for symmetry are common in humans and nonhumans alike. Honeybees, for example, show preference for flowers with radial symmetry. Symmetry also has been shown to play a role in attraction, Evans noted. Infants begin to show an appreciation for symmetry in their first few months.
Based on the assumption that we all carry traits common to OCD and autism, the Bucknell-Geisinger experiment involved young adults who have not been diagnosed with any neurodevelopmental or neuropsychiatric disorders. The subjects, all introductory psychology students at Bucknell, first were asked to sort images and words with symmetrical and asymmetrical meanings. Next, they paired symmetrical words with a photo of a smiling woman and asymmetrical words with a photo of the same woman showing disgust. Then, they completed the tasks in reverse order so symmetrical images were paired with the disgusted face.
The participants consistently showed more cognitive conflict when asked to pair asymmetrical words with happy faces, making errors and taking significantly longer to respond, Evans said. Those who reported having some obsessive-compulsive behavior such as "checking" or arranging had the slowest reaction times when asked to associated asymmetrical words with happiness.
In the next part of the study, subjects were asked to look at a series of parallel and crooked lines while an EEG monitored their brain activity. The subjects who had the most difficulty in pairing asymmetry with happiness and symmetry with disgust also demonstrated greater sensitivity when presented with unparallel lines.
"We would expect that most people would notice the difference between parallel and unparallel lines, but what we found was that people who had a demonstrated strong bias for linking disgust and happiness with uneven and even lines, respectively, their brains registered greater and faster responses to symmetry," Evans said.
The Bucknell-Geisinger study challenges the current standards for diagnosing and understanding disorders like autism, according to Evans.
"The current standards tend to focus on whether a child is or is not autistic, and this approach fails to recognize that behaviors associated with disorders like ASD present on a spectrum," Evans said. "In fact, we are finding that when a family has a child who reaches the traditional criteria for an autism diagnosis, even if their sibling or parent does not meet these strict criteria, they may still show some subtle signs of autistic-like behaviors. That means we can do early screening and identify subtle signs of disorders in children who do not meet the threshold for autism or OCD."
Early intervention with autism and related disorders is essential because children's brains are more changeable and flexible, and tend to respond better to treatment.
"It is almost effortless for a child to learn language in the first few years of life," Evans said. "It is much harder for an adult. With brain maturation, the pathways are more honed, established and consolidated. In a child, interventions hold the promise of essentially rewiring brain-behavior links, making connections between neurons that aren't connected but generally should be, as well as undoing connections that have been established, but under typical circumstances should not be connected."
Evans' collaborators were researchers Patrick Orr, a post-doctoral fellow at Geisinger, and David Ledbetter, CEO of research at Geisinger Health System as well as Steven Lazar, Class of '13; Daniel Breton, Class of '11; Jennifer Gerard, Class of '14; Kathleen Janosco, Class of '11; Jessica Dotts, Class of '10; and Holly Batchelder, Class of '10.
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