Scientists Discover Why Dyslexic People Struggle With Natural Speech

People who have dyslexia struggle with reading and identifying speech sounds, hindering their ability to learn and process language. In a new study, scientists experimented with acoustic variation, or how different pitches of speech affect dyslexic patients.

Children with dyslexia typically fall behind in learning words and speech as they tend to reverse letters or sounds due to confusion and how they see letters, numbers, and colors. As it develops into adulthood, reading and writing become slow and labor-intensive.

Some complications the disability may cause include social problems when it is left untreated. Without proper emotional and learning support, anxiety, aggression, low self-esteem, and other behavioral problems are possible outcomes.

The new study focuses on neurological evidence that dyslexic patients struggle with hearing variations in natural speech, particularly different pitch sounds. Even if the sounds are in their native language, and in this case Finnish, the continuous acoustic variation of the sounds /æ/ and /i/ allowed the team to see how dyslexic patients performed compared to adults without the disorder.

Responding to Phonemes

Dr. Paula Virtala from the University of Helsinki, said, 'In our study, dyslexic participants had difficulties, particularly when [the] acoustic variation was added to the speech sound stream. In the absence of this variation, neural speech sound processing did not differ between dyslexic and typical readers. This seems to reflect a difficulty in categorizing speech sounds in the native language phoneme classes.' In other words, monotonous speech would have been more comfortable for participants with dyslexia.

Unfortunately, natural speech involves acoustic variation sounds, usually with vowels, hindering individuals with dyslexia from auditory learning. A new study brings neural-level evidence that the continuous variation in natural speech makes the discrimination of phonemes challenging for adults suffering from developmental reading-deficit dyslexia.

The brain understands speech effortlessly when phonemes, or distinct sounds in a particular language, are detected accurately. For example in English, those with dyslexia may have trouble differentiating the words 'sin' and 'sing.'

By understanding dyslexia on the neurological level, medical experts can design specific rehabilitation methods for learning, especially for younger children. Those with dyslexia have a different level of metabolic activation within the brain than people without the disorder. As a result, the left hemisphere of the brain fails to function well when the individual reads.

The team compared the electroencephalography (EEG) brain scans of 18 dyslexic individuals and 20 typically reading adults. They listened to Finnish variations of /æ/ and /i/ at different pitches passively. In the second part of the experiment, they listened actively by pressing a response button when a change in the speech was detected. Those with dyslexia didn't score as accurately as those without.

Dyslexia Baby

'These kinds of studies conducted in adults allow for longer recording sessions and a broader range of methods compared to studies in children. We can utilize these findings in our longitudinal DyslexiaBaby study,' neurologist Paula Virtala explains.

DyslexiaBaby is an ongoing study at the Cognitive Brain Research Unit at the University of Helsinki and the University of Jyväskyl. The project studies early language developments and investigates how early the disorder can be detected in infants and to discover how to effectively alleviate and prevent dyslexia.