Read My Lips: speech processing differences in children with developmental language disorder

Katie Reeder | December 04, 2012 2:53 pm

Image from Ranmore Consulting Group http://www.ranmore.co.uk/ranmore.aspx?page=26

Meet Landon. He’s in the third grade, loves to build things, and is both learning disabled and ADD. He has reading difficulties, which doctors have attributed to an auditory processing disorder. Children with auditory processing disorders have normal hearing abilities but struggle with interpreting changes in tone. However, Landon also struggles in math, but interestingly enough, he finds it much easier to solve the problems when working them out vertically as opposed to horizontally. He is not lacking in intelligence; like other children with learning disabilities, he just learns differently than “normal” children. In order to create more suitable learning environments for learning disabled children, researchers are working on understanding and identifying the key characteristics that set these children apart.

Previous research on child language learning impairments has focused primarily on the auditory component (the part of speech that is heard) of speech processing (how speech is interpreted). However, in their recent study Auli, Kalsa, Jari, and Timo remedied this one-sided analysis by studying both the auditory and the visual components of speech processing in children with and without developmental language disorder (DLD). In order to qualify for a diagnosis of DLD, children must develop their language skills at a much slower rate than children with normal language development, and there must be no apparent causal factor, such as hearing loss or mental retardation, behind this slowed rate.

Researchers wanted to see how the manipulation of the signal-to-noise ratio (SNR) affected whether the children relied more on visual stimuli or auditory stimuli in order to interpret speech. The SNR is defined as the level of a target sound someone is listening for as compared to the level of background noise. The higher the SNR, the more reliable the incoming auditory information is. When there is a lower SNR, people tend to rely more on visual cues to interpret the information. This tendency is called the McGurk effect: that is, the influence lip reading has on hearing when visual cues and auditory cues do not match. For example, a person experiencing the McGurk effect sees the “g” sound being mouthed while listening to the “b” sound but interprets the stimulus as the “d” sound.

In the first trial, researchers tested the strength of the McGurk effect by showing a video that incorporated both audio and visual stimuli. The video was of a woman mouthing the “t” sound but emitting the “p” sound. As the SNR decreased, normal children exhibited a significant decrease in the number of auditory-based responses and a significant increase in visually based responses. In other words, normal children relied less on what they were hearing and more on what they were seeing as sound quality decreased. However, the fluctuations in responses among children with DLD were insignificant, meaning that these fluctuations were random and had little to do with changes in sound quality. The difference in responses between the two groups was found to be significant with lower SNRs. This suggests that children with DLD are less susceptible to the McGurk effect and that there are fundamental differences in how these two groups process speech, which could mean that traditional teaching methods may not be the best way for children with DLD to learn.

To better understand the individual components of speech processing, researchers also measured the independent effects of auditory and visual stimuli. To test the effects of auditory stimuli, the visual component of the video was removed. There was no significant difference in the performance levels of the two groups in distinguishing strictly auditory stimuli. However, normal children performed significantly better when it came to distinguishing strictly visual stimuli. In this task, children had to read the woman’s lips in order to draw meaning from the stimulus. This poorer lip-reading ability in children with DLD explains why they experienced a weaker McGurk effect. Since they could not efficiently interpret the visual component of speech, they relied more on the auditory component. This is further evidence to suggest that there are fundamental differences in how children with DLD and normal children process speech, once again indicating that different teaching methods may be needed to help children with DLD.

Image from Auli article: Comparison of performance of normal children and children with DLD in recognizing strictly auditory and strictly visual stimuli

These results support earlier findings that children with DLD experience difficulty in identifying the basic sounds that serve as the building blocks of speech and that they have below average phonological processing capabilities. This means that they struggle to efficiently distinguish and interpret differences in speech sounds. These difficulties also impair their ability to interpret visual speech stimuli and explain why the children with DLD had trouble reading lips. A great deal of attention has been given to the auditory processing disorders in children with DLD. However, this study clearly demonstrates that multiple modalities (referring to the five senses: sight, touch, hearing, etc.) of perception are impaired in children with DLD.

Doctors have not determined whether Landon’s struggles in math and reading are two separate disorders or if they are different results of the same factors. This study suggests that his true problem may be more complex than just an auditory processing disorder. However, as can be seen when he solves math problems, he is still very capable of learning. This is true for most children with learning disabilities. If educators just take the time to see how they learn best, great progress can be made.

Not Exactly Rocket Science

Read My Lips: speech processing differences in children with developmental language disorder