Beverly A. Wright b-wright@northwestern.edu
Department of Communication Sciences and Disorders
Knowles Hearing Center
Northwestern University
2240 Campus Drive
Evanston IL 60208-3550
Julia Jones Huyck julia.huyck@queensu.ca
Department of Psychology and Centre for Neuroscience Studies
Queens University
62 Arch Street
Kingston Ontario K7L 3N6
Carmen Aliyeva carmen_aliyeva@yahoo.com
Department of Communication Sciences and Disorders
Northwestern University
2240 Campus Drive
Evanston IL 60208-3550
Popular version of paper 1pPP6
Presented Monday afternoon (3:20 PM), May 23, 2011
161st ASA Meeting, Seattle, Wash.
LAY LANGUAGE VERSION
Approximately 8 percent of the population has some form of reading disorder (dyslexia)characterized by a marked difficulty reading despite having normal intelligence. The effects of these disorders are far-reaching. Affected individuals often experience considerable personal stress in their school, work, and social lives. The cost to society in terms of special education services, lost productivity, and un- and underemployment amounts to billions of dollars annually.
We, along with many others, are trying to determine what causes reading disorders so that they can be treated more effectively. From this collective effort, we know that individuals with these disorders can show impairments on a wide range of abilities other than reading, including perceptual, language, and thinking skills. A complete explanation of reading disorders therefore must be able to account for this array of abnormalities.
One proposal is that, in individuals with a reading disorder, some aspects of brain development occur later than normal and then are halted in early adolescence (Wright and Zecker, 2004; see Figure 1). A clear prediction of this idea is that skills that take the most time to develop are the most likely to be deficient in adults. We tested that idea here by examining the response to perceptual training in adults with a reading disorder.
Figure 1: Schematic illustration of the idea that some aspects of brain development in individuals with a reading disorder (red line) may be delayed relative to normal (blue line) and then halted during adolescence. A clear prediction of this idea is that skills that take the most time to develop are the most likely to be deficient in adults with a reading disorder.
We chose to examine the response to perceptual training for two reasons. First, as described below, the response takes a long time to fully mature (to become the same as in adults). We therefore could use it to test the prediction that long-developing skills are most likely to be impaired in adults with a reading disorder. Second, the response is a measure of a particular type of learningperceptual-skill learningso we could actually examine learning in a population characterized as having a learning problem.
Though most people dont think about their sensory perceptionsuch as their hearing or visionas being changeable, many perceptual skills can be improved with practice. This type of skill learning appears to depend on different brain functions than does the learning of facts. In a recent investigation, we asked at what age the response to perceptual training on a simple auditory skill becomes adult-like (Huyck and Wright, 2011). The skill we examined was the ability to distinguish as small a difference as possible in the duration of a silent interval between two short tones (see Figure 2 and Sound Example 1). Similar abilities are involved when we distinguish between different particular speech sounds, like ba and pa, and between different musical rhythms. We measured listeners performance of this skill before, during, and after they practiced it for ~1 hour per day for 10 days. Among the normally developing listeners we tested, this amount of practice yielded learning in all adults, but in no 11-year-olds and in only half of 14-year-olds. Thus, the response to this training experience is not adult-like until late in adolescence. This outcome suggests that it takes a long time for the brain processes that enable this learning to fully mature.
Figure 2: Schematic illustration of the skill we examined: the ability to distinguish as small a difference as possible in the duration of a silent interval between two short tones (Sound Example: On each trial, we asked the listener to indicate whether the longer interval came first or second. In this example, the first interval between the two tones is 100 milliseconds (one tenth of a second) and the second interval is 122 milliseconds. This difference in interval duration reflects the discrimination threshold of a typical adult prior to training.
So if these aspects of brain development are delayed and then prematurely halted in individuals with a reading disorder then, with the same amount of training, fewer adults with a reading disorder should improve on this skill than adults with normal reading skills. To test this idea, we examined how 6 (rather than 10) days of this perceptual training scheme affected the performance of ten adults who had previously been diagnosed with a learning problem and who, at the time we tested them, performed more poorly on reading tests than would be expected based on their IQ scores.
The group of adults with a reading disorder responded to the training more like adolescents than like adults with normal reading skills. Of the ten adults with a reading disorder, four improved over the 6 days of training, but the remaining six did not. This distribution is reminiscent of what we had previously observed in 14-year-olds with normal reading skills who were trained for 10 days (four improved and four did not). However, it more accurately reflects group performance that is between normally functioning 14-year-olds and adults, because none of the 14-year-olds but all of the adults with normal reading improved significantly over the first 6 of their 10 days of training (see Figure 3).
Figure 3: Percentage of total listeners in each group who learned over 6 days of training. Over this time frame, 0% of the normally developing 14-year-olds, 40% of the adults with a reading disorder (red bar), and 100% of the adults with normal reading skills (blue bar) improved on the trained auditory skill. Thus, as a group, the adults with a reading disorder showed immature learning.
These results are consistent with the idea that a number of the abnormalities observed in individuals with a reading disorder may reflect delayed and then prematurely halted brain development. They also add to the growing evidence of deficient skill learning in individuals classified as having a learning problem. Finally, they illustrate that viewing differences between impaired and normal populations in a developmental context can provide valuable insights into what underlies reading disorders.
REFERENCES
Huyck, J.J., and Wright, B.A. (2011) Late maturation of auditory perceptual learning, Developmental Science, 14, 614-621.
Wright, B.A., and Zecker, S.G. (2004) Learning problems, delayed development, and puberty, Proceedings of the National Academy of Sciences, 101, 9942-9946.