UCSF Team Reveals How the Brain Recognizes Speech Sounds

UC San Francisco researchers are reporting a detailed account of how speech sounds are identified by the human brain, offering an unprecedented insight into the basis of human language.

The finding, they said, may add to our understanding of language disorders, including dyslexia.

Scientists have known for some time the location in the brain where speech sounds are interpreted, but little has been discovered about how this process works.

Now, in the Jan. 30 edition of Science Express, the fast-tracked online version of the journal Science, the UCSF team reports that the brain does not respond to the individual sound segments known as phonemes – such as the b sound in “boy” – but is instead exquisitely tuned to detect simpler elements, which are known to linguists as “features.”

This organization may give listeners an important advantage in interpreting speech, the researchers said, since the articulation of phonemes varies considerably across speakers, and even in individual speakers over time.

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In Dyslexia, Less Brain Tissue Not to Blame for Reading Difficulties

In people with dyslexia, less gray matter in the brain has been linked to reading disabilities, but now new evidence suggests this is a consequence of poorer reading experiences and not the root cause of the disorder.

It has been assumed that the difference in the amount of gray matter might, in part, explain why dyslexic children have difficulties correctly and fluently mapping the sounds in words to their written counterparts during reading. But this assumption of causality has now been turned on its head.

The findings from anatomical brain studies conducted at Georgetown University Medical Center (GUMC) in the Center for the Study of Learning led by neuroscientist Guinevere Eden, DPhil, were published online today in The Journal of Neuroscience.

The study compared a group of dyslexic children with two different control groups: an age-matched group included in most previous studies, and a group of younger children who were matched at the same reading level as the children with dyslexia.

“This kind of approach allows us to control for both age as well as reading experience,” explains Eden, a professor of pediatrics at GUMC. “If the differences in brain anatomy in dyslexia were seen in comparison with both control groups, it would have suggested that reduced gray matter reflects an underlying cause of the reading deficit. But that’s not what we observed.”

The dyslexic groups showed less gray matter compared with a control group matched by age, consistent with previous findings. However, the result was not replicated when a control group matched by reading level was used as the comparison group with the dyslexics.

“This suggests that the anatomical differences reported in left hemisphere language processing regions appear to be a consequence of reading experience as opposed to a cause of dyslexia,” says Anthony Krafnick, PhD, lead author of the publication. “These results have an impact on how we interpret the previous anatomical literature on dyslexia and it suggests the use of anatomical MRI would not be a suitable way to identify children with dyslexia,” he says.

The work also helps to determine the fine line between experience-induced changes in the brain and differences that are the cause of cognitive impairment. For example, it is known from studies in illiterate people who attain reading skills as adults that this type of learning induces growth of brain matter. Similar learning-induced changes in typical readers may result in discrepancies between them and their dyslexic peers, who have not enjoyed the same reading experiences and thus have not undergone similar changes in brain structure.

Smithsonian experts find e-readers can make reading easier for those with dyslexia

As e-readers grow in popularity as convenient alternatives to traditional books, researchers at the Smithsonian have found that convenience may not be their only benefit. The team discovered that when e-readers are set up to display only a few words per line, some people with dyslexia can read more easily, quickly and with greater comprehension. Their findings are published in the Sept. 18 issue of the journal PLOS ONE.

An element in many cases of dyslexia is called a visual attention deficit. It is marked by an inability to concentrate on letters within words or words within lines of text. Another element is known as visual crowding—the failure to recognize letters when they are cluttered within the word. Using short lines on an e-reader can alieviate these issues and promote reading by reducing visual distractions within the text.

"At least a third of those with dyslexia we tested have these issues with visual attention and are helped by reading on the e-reader," said Matthew H. Schneps, director of the Laboratory for Visual Learning at the Smithsonian Astrophysical Observatory and lead author of the research. "For those who don’t have these issues, the study showed that the traditional ways of displaying text are better."

An earlier study by Schneps tracked eye movements of dyslexic students while they read, and it showed the use of short lines facilitated reading by improving the efficiency of the eye movements. This second study examined the role the small hand-held reader had on comprehension, and found that in many cases the device not only improved speed and efficiency, but improved abilities for the dyslexic reader to grasp the meaning of the text.

The team tested the reading comprehension and speed of 103 students with dyslexia who attend Landmark High School in Boston. Reading on paper was compared with reading on small hand-held e-reader devices, configured to lines of text that were two-to-three words long. The use of an e-reader significantly improved speed and comprehension in many of the students. Those students with a pronounced visual attention deficit benefited most from reading text on a handheld device versus on paper, while the reverse was true for those who did not exhibit these issues. The small screen on a handheld device displaying few words (versus a full sheet of paper) is believed to narrow and concentrate the reader’s focus, which controls visual distraction.

"The high school students we tested at Landmark had the benefit of many years of exceptional remediation, but even so, if they have visual attention deficits they will eventually hit a plateau, and traditional approaches can no longer help," said Schneps. "Our research showed that the e-readers help these students reach beyond those limits."

These findings suggest that this reading method can be an effective intervention for struggling readers and that e-readers may be more than new technological gadgets: They also may be educational resources and solutions for those with dyslexia.

Brain scans may help diagnose dyslexia

Differences in a key language structure can be seen even before children start learning to read.

About 10 percent of the U.S. population suffers from dyslexia, a condition that makes learning to read difficult. Dyslexia is usually diagnosed around second grade, but the results of a new study from MIT could help identify those children before they even begin reading, so they can be given extra help earlier.

The study, done with researchers at Boston Children’s Hospital, found a correlation between poor pre-reading skills in kindergartners and the size of a brain structure that connects two language-processing areas.

Previous studies have shown that in adults with poor reading skills, this structure, known as the arcuate fasciculus, is smaller and less organized than in adults who read normally. However, it was unknown if these differences cause reading difficulties or result from lack of reading experience.

“We were very interested in looking at children prior to reading instruction and whether you would see these kinds of differences,” says John Gabrieli, the Grover M. Hermann Professor of Health Sciences and Technology, professor of brain and cognitive sciences and a member of MIT’s McGovern Institute for Brain Research.

Gabrieli and Nadine Gaab, an assistant professor of pediatrics at Boston Children’s Hospital, are the senior authors of a paper describing the results in the Aug. 14 issue of the Journal of Neuroscience. Lead authors of the paper are MIT postdocs Zeynep Saygin and Elizabeth Norton.

The path to reading

The new study is part of a larger effort involving approximately 1,000 children at schools throughout Massachusetts and Rhode Island. At the beginning of kindergarten, children whose parents give permission to participate are assessed for pre-reading skills, such as being able to put words together from sounds.

“From that, we’re able to provide — at the beginning of kindergarten — a snapshot of how that child’s pre-reading abilities look relative to others in their classroom or other peers, which is a real benefit to the child’s parents and teachers,” Norton says.

The researchers then invite a subset of the children to come to MIT for brain imaging. The Journal of Neuroscience study included 40 children who had their brains scanned using a technique known as diffusion-weighted imaging, which is based on magnetic resonance imaging (MRI).

This type of imaging reveals the size and organization of the brain’s white matter — bundles of nerves that carry information between brain regions. The researchers focused on three white-matter tracts associated with reading skill, all located on the left side of the brain: the arcuate fasciculus, the inferior longitudinal fasciculus (ILF) and the superior longitudinal fasciculus (SLF).

When comparing the brain scans and the results of several different types of pre-reading tests, the researchers found a correlation between the size and organization of the arcuate fasciculus and performance on tests of phonological awareness — the ability to identify and manipulate the sounds of language.

Phonological awareness can be measured by testing how well children can segment sounds, identify them in isolation, and rearrange them to make new words. Strong phonological skills have previously been linked with ease of learning to read. “The first step in reading is to match the printed letters with the sounds of letters that you know exist in the world,” Norton says.

The researchers also tested the children on two other skills that have been shown to predict reading ability — rapid naming, which is the ability to name a series of familiar objects as quickly as you can, and the ability to name letters. They did not find any correlation between these skills and the size or organization of the white-matter structures scanned in this study.

Brian Wandell, director of Stanford University’s Center for Cognitive and Neurobiological Imaging, says the study is a valuable contribution to efforts to find biological markers that a child is likely to need extra help to learn to read.

“The work identifies a clear marker that predicts reading, and the marker is present at a very young age. Their results raise questions about the biological basis of the marker and provides scientists with excellent new targets for study,” says Wandell, who was not part of the research team.

Early intervention

The left arcuate fasciculus connects Broca’s area, which is involved in speech production, and Wernicke’s area, which is involved in understanding written and spoken language. A larger and more organized arcuate fasciculus could aid in communication between those two regions, the researchers say.

Gabrieli points out that the structural differences found in the study don’t necessarily reflect genetic differences; environmental influences could also be involved. “At the moment when the children arrive at kindergarten, which is approximately when we scan them, we don’t know what factors lead to these brain differences,” he says.

The researchers plan to follow three waves of children as they progress to second grade and evaluate whether the brain measures they have identified predict poor reading skills.

“We don’t know yet how it plays out over time, and that’s the big question: Can we, through a combination of behavioral and brain measures, get a lot more accurate at seeing who will become a dyslexic child, with the hope that that would motivate aggressive interventions that would help these children right from the start, instead of waiting for them to fail?” Gabrieli says.

For at least some dyslexic children, offering extra training in phonological skills can help them improve their reading skills later on, studies have shown.

Fiber-optic pen helps see inside brains of children with learning disabilities

For less than $100, University of Washington researchers have designed a computer-interfaced drawing pad that helps scientists see inside the brains of children with learning disabilities while they read and write.

The device and research using it to study the brain patterns of children will be presented June 18 at the Organization for Human Brain Mapping meeting in Seattle. A paper describing the tool, developed by the UW’s Center on Human Development and Disability, was published this spring in Sensors, an online open-access journal. “Scientists needed a tool that allows them to see in real time what a person is writing while the scanning is going on in the brain,” said Thomas Lewis, director of the center’s Instrument Development Laboratory. “We knew that fiber optics were an appropriate tool. The question was, how can you use a fiber-optic device to track handwriting?”

To create the system, Lewis and fellow engineers Frederick Reitz and Kelvin Wu hollowed out a ballpoint pen and inserted two optical fibers that connect to a light-tight box in an adjacent control room where the pen’s movement is recorded. They also created a simple wooden square pad to hold a piece of paper printed with continuously varying color gradients. The custom pen and pad allow researchers to record handwriting during functional magnetic resonance imaging, or fMRI, to assess behavior and brain function at the same time.Other researchers have developed fMRI-compatible writing devices, but “I think it does something similar for a tenth of the cost,” Reitz said of the UW system. By using supplies already found in most labs (such as a computer), the rest of the supplies – pen, fiber optics, wooden pad and printed paper – cost less than $100.The device connects to a computer with software that records every aspect of the handwriting, from stroke order to speed, hesitations and liftoffs. Understanding how these physical patterns correlate with a child’s brain patterns can help scientists understand the neural connections involved.

Researchers studied 11- and 14-year-olds with either dyslexia or dysgraphia, a handwriting and letter-processing disorder, as well as children without learning disabilities. Subjects looked at printed directions on a screen while their heads were inside the fMRI scanner. The pen and pad were on a foam pad on their laps.

Subjects were given four-minute blocks of reading and writing tasks. Then they were asked to simply think about writing an essay (they later wrote the essay when not using the fMRI). Just thinking about writing caused many of the same brain responses as actual writing would.

“If you picture yourself writing a letter, there’s a part of the brain that lights up as if you’re writing the letter,” said Todd Richards, professor of radiology and principal investigator of the UW Integrated Brain Imaging Center. “When you imagine yourself writing, it’s almost as if you’re actually writing, minus the motion problems.”

Richards and his staff are just starting to analyze the data they’ve collected from about three dozen subjects, but they have already found some surprising results.

“There are certain centers and neural pathways that we didn’t necessarily expect” to be activated, Richards said. “There are language pathways that are very well known. Then there are other motor pathways that allow you to move your hands. But how it all connects to the hand and motion is still being understood.”

Besides learning disorders, the inexpensive pen and pad also could help researchers study diseases in adults, especially conditions that cause motor control problems, such as stroke, multiple sclerosis and Parkinson’s disease.

“There are several diseases where you cannot move your hand in a smooth way or you’re completely paralyzed,” Richards said. “The beauty is it’s all getting recorded with every stroke, and this device would help us to study these neurological diseases.”

Not all reading disabilities are dyslexia

A common reading disorder goes undiagnosed until it becomes problematic, according to the results of five years of study by researchers at Vanderbilt’s Peabody College of education and human development in collaboration with the Kennedy Krieger Institute/Johns Hopkins School of Medicine. Results of the study were recently published online by the National Institutes of Health.

Dyslexia, a reading disorder in which a child confuses letters and struggles with sounding out words, has been the focus of much reading research.

But that’s not the case with the lesser known disorder Specific Reading Comprehension Deficits or S-RCD, in which a child reads successfully but does not sufficiently comprehend the meaning of the words, according to lead investigator Laurie Cutting, Patricia and Rodes Hart Chair at Peabody.

“S-RCD is like this: I can read Spanish, because I know what sounds the letters make and how the words are pronounced, but I couldn’t tell you what the words actually mean,” Cutting said. “When a child is a good reader, it’s assumed their comprehension is on track. But 3 to 10 percent of those children don’t understand most of what they’re reading. By the time the problem is recognized, often closer to third or fourth grade, the disorder is disrupting their learning process.”

Researchers have been able to pinpoint brain activity and understand its role in dyslexia, but no functional magnetic resonance imaging or fMRI studies, until now, have examined the neurobiological profile of those who exhibit poor reading comprehension despite intact word-level abilities.

Neuroimaging of children showed that the brain function of those with S-RCD while reading is quite different and distinct from those with dyslexia. Those with dyslexia exhibited abnormalities in a specific region in the occipital-temporal cortex, a part of the brain that is associated with successfully recognizing words on a page.

But those with S-RCD did not show abnormalities in this region, instead showing specific abnormalities in regions typically associated with memory.

“It may be that these individuals have a whole different neurobiological signature associated with how they read that is not efficient for supporting comprehension,” Cutting said. “We want to understand the different systems that support reading and see which ones help different types of difficulties, and how we can target the cognitive systems that support those skills.”

The study, an ongoing 10-year effort supported by National Institutes of Health grant No. M01-RR000052, has enrolled more than 300 children to date.