Deaf studies scholar Naomi Caselli and a team of researchers found that American Sign Language (ASL) signs that are challenging to perceive — those that are rare or have uncommon handshapes — are made closer to the signer’s face, where people often look during sign perception. By contrast, common ones, and those with more routine handshapes, are made further away from the face, in the perceiver’s peripheral vision. Caselli, a Boston University Wheelock College of Education & Human Development assistant professor, says the findings suggest that ASL has evolved to be easier for people to recognize signs. The results were published in Cognition.

“Every time we use a word, it changes just a little bit,” says Caselli, who’s also codirector of the BU Rafik B. Hariri Institute for Computing and Computational Science & Engineering’s AI and Education Initiative. “Over long periods of time, words with uncommon handshapes have evolved to be produced closer to the face and, therefore, are easier for the perceiver to see and recognize.”

Although studying the evolution of language is complex, says Caselli, “you can make predictions about how languages might change over time, and test those predictions with a current snapshot of the language.”

With researchers from Syracuse University and Rochester Institute of Technology, she looked at the evolution of ASL with help from an artificial intelligence (AI) tool that analyzed videos of more than 2,500 signs from ASL-LEX, the world’s largest interactive ASL database. Caselli says they began by using the AI algorithm to estimate the position of the signer’s body and limbs.

“We feed the video into a machine learning algorithm that uses computer vision to figure out where key points on the body are,” says Caselli. “We can then figure out where the hands are relative to the face in each sign.” The researchers then match that with data from ASL-LEX — which was created with help from the Hariri Institute’s Software & Application Innovation Lab — about how often the signs and handshapes are used. They found, for example, that many signs that use common handshapes, such as the sign for children — which uses a flat, open hand — are produced further from the face than signs that use rare handshapes, like the one for light (see videos).

This project is part of a new and growing body of work connecting computing and sign language at BU.

“The team behind these projects is dynamic, with signing researchers working in collaboration with computer vision scientists,” says Lauren Berger, a Deaf scientist and postdoctoral fellow at BU who works on computational approaches to sign language research. “Our varying perspectives, anchored by the oversight of researchers who are sensitive to Deaf culture, helps prevent cultural and language exploitation just for the sake of pushing forward the cutting edge of technology and science.”

Understanding how sign languages work can help improve Deaf education, says Caselli, who hopes the latest findings also bring attention to the diversity in human languages and the extraordinary capabilities of the human mind.

“If all we study is spoken languages, it is hard to tease apart the things that are about language in general from the things that are particular to the auditory-oral modality. Sign languages offer a neat opportunity to learn about how all languages work,” she says. “Now with AI, we can manipulate large quantities of sign language videos and actually test these questions empirically.”

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Materials provided by Boston University. Original written by Gina Mantica. Note: Content may be edited for style and length.

The study, led by researchers from the University of Michigan in collaboration with Florida Atlantic University, Temple University, and the National Institute on Deafness and Other Communication Disorders, National Institutes of Health, used genetically engineered mice to examine the neural and behavioral effects of a choline transporter (CHT) variant. Prior work by the team has shown that the variant associated with heightened distractibility in humans, though whether the variant was itself causal for inattention was unclear.

In the new study, researchers made a single change in the gene encoding the neuronal CHT and then searched for physiological changes in the brain, focusing on their ability to sustain production and release of the powerful brain chemical acetylcholine, which is synthetized from choline.

In humans, disruption of acetylcholine signaling impairs one’s capacity to filter distractors and to perform focus-demanding tasks. A total loss of CHT function in mice and people leads to early death due to the role played by acetylcholine in muscle contraction, particularly the muscles that control breathing. Lesser reductions in CHT activity allow for normal growth and movement, but mice with these changes exhibit premature fatigue when made to run on a treadmill. Work from the new study reveals that the mice show signs of mental fatigue as well.

Results of the study, published in The Journal of Neuroscience, indicate that the CHT gene variant known as Val89, reduces the rate of choline uptake and the capacity to sustain acetylcholine production during attention-demanding conditions, effects that lead to diminished cognitive performance when the mice are faced with attentional challenges. Evidence from the mouse studies provides direct evidence that Val89 drives increased vulnerability to distraction and provides a mechanistic basis for the diminished frontal cortex activation observed in Val89-expressing humans.

“Our mouse studies, along with prior behavioral and brain imaging studies, indicate that a single copy of the variant is sufficient to change acetylcholine availability and its resulting cognitive effects,” said Randy D. Blakely, Ph.D., co-author, executive director of the FAU Stiles-Nicholson Brain Institute and professor, FAU Schmidt College of Medicine. “Seeing effects from a single copy of Val89 suggests that choline transport may be mediated by a pair of CHT proteins such that one poorly functioning copy can impact the normal function of the other, leading to stronger effects than expected from simply having one copy compromised.”

This finding has been reported before in people with neuromuscular disorder causing CHT mutations, but this also appears to be the case for brain function.

“Val89 mice lack cognitive flexibility in response to an attentional challenge,” said Eryn Donovan, lead author and a graduate student in the Department of Psychology, University of Michigan. “Our findings from this mouse model suggest the potential for a more complete investigation of the effects of the CHT Val89 mutation in the brain as well as the development of therapeutic strategies for those with disrupted acetylcholine signaling.”

According to the United States Centers for Disease Control and Prevention, the estimated number of children ever diagnosed with ADHD, according to a 2016 parent survey, is 6.1 million. This same survey shows that 6 in 10 children with ADHD had at least one other mental, emotional or behavioral disorder and 62 percent were taking ADHD medication. Although ADHD most often occurs in children, it also can be diagnosed in adulthood.

“We think that the CHT Val89 mouse can be a valuable model to study heritable risk for cognitive disorders that arise from cholinergic dysfunction,” said Blakely. “We now can gain much more insight into the brain effects of the Val89 variant in ways that cannot be done in humans and possibly lead to new ways to treat disorders associated with brain acetylcholine signaling that appear in childhood, such as ADHD, or during aging, as with Parkinson’s disease and Alzheimer’s disease.”

In addition to new insights into a potential risk factor for psychiatric and neurological disorders, Martin Sarter, Ph.D., a professor of psychology and neuroscience at the University of Michigan and the communicating author of the study says that their findings explain why healthy humans expressing this genetic variant exhibit robust attentional vulnerabilities.

“As this genetic variant is quite common, occurring in about 9 to 10 percent of humans, we now understand exactly how this variant influences the brain mechanisms that are essential for paying attention,” said Sarter.

Other study co-authors are Cassandra Avila, a graduate student and Sarah Klausner, an undergraduate student, Department of Psychology, University of Michigan; Vinay Parikh, Ph.D., an associate professor of psychology and neuroscience, Temple University; Maria Cristina Fenollar Ferrer, Ph.D., Laboratory of Molecular Genetics, Section of Human Genetics, National Institute on Deafness and Other Communication Disorders.