Effect of intensive training on auditory processing and reading skills

Abstract

This study assessed the ability of seven children to accurately judge relative durations of auditory and visual stimuli before and after participation in a language remediation program. The goal of the intervention program is to improve the children’s ability to detect and identify rapidly changing auditory stimuli, and thereby improve their language-related skills. Children showed improved accuracy on a test of auditory duration judgement following the intervention without analogous improvements in the visual domain, supporting the assertion that intensive training with modified speech improves auditory temporal discrimination. However, these improvements did not generalize to reading skills, as assessed by standard measures of phonological awareness and non-word reading.

Introduction

It has been proposed that training with acoustically modified speech can improve the auditory language skills of individuals with specific language impairment (SLI) and dyslexia (Habib et al., 1999; Tallal, Merzenich, Miller, & Jenkins, 1998; Tallal et al., 1996). SLI is generally characterized as a difficulty with age-appropriate use of expressive and receptive language without other cognitive impairments and is thought to affect 3–10% of children (Bishop, 1994). In addition to their linguistic difficulties, individuals with SLI are often found to also have deficits in non-linguistic domains such as planning complex oral-motor patterns, working memory, sound perception, and visual imagery (Joanisse & Seidenberg, 1998).

According to some research, approximately 50% of children with specific language impairment have reading problems when tested in second and fourth grades (Catts, Fey, Tomblin, & Zhang, 2002). Although the cause of SLI remains controversial, some suggest that it is due to a deficit processing input in the auditory domain (Skipp, Windfuhr, & Conti-Ramsden, 2002; van der Lely & Christian, 2000) and others that the deficit is specific to grammar (Bishop, 2000; Sahlen, Reuterskiold-Wagner, Nettelbladt, & Radeborg, 1999). The role of audition has also been examined in developmental dyslexia, a reading disorder that affects 5–10% of the population. Individuals with dyslexia fail to achieve normal reading skills despite adequate intelligence, educational opportunities, and socioeconomic status (Shaywitz, Shaywitz, Fletcher, & Escobar, 1990). Several studies have reported that children with SLI and dyslexia cannot differentiate between rapidly changing consonant–vowel (CV) syllables when presented at normal speed (Tallal, Miller, & Fitch, 1993; Tallal et al., 1996). It has been suggested that this ability is important for language acquisition and the development of phonological awareness and reading skills (Talcott et al., 2000; Tallal et al., 1993) and that deficits in this domain may result in impaired language facility including reading.

The intervention program studied here attempts to address such deficits by modifying normal speech in such a way that the most rapidly changing components are extended in time by 50% and amplified by up to 20 dB (Nagarajan et al., 1998; Tallal et al., 1996). These increases in duration and volume are designed to enhance the salience of the fastest-changing components of speech, facilitating their perception by the listener. This modified speech is embedded in computer games that are presented to children over the course of the training, which usually lasts about 6 weeks. During training, the speed and volume of the CV syllables are gradually returned to the levels found in normal speech. Hence, at the end of training, the speech presented by the program is almost the same as normal speech in terms of volume and rate of presentation (Tallal et al., 1996).

This program has been studied in a laboratory setting, exposing children with SLI to the acoustically modified speech for three hours a day, five days a week for four weeks (Merzenich et al., 1996; Tallal et al., 1996). Following training, the children improved by approximately 2 years on standardized measures of speech discrimination and language processing, improvements that endured at least 6 weeks after training (Tallal et al., 1996). In a second experiment, conducted by the same investigators, children with SLI were recruited and divided into two groups. One group received training with the modified speech while the other received equal training using unmodified speech. After 4 weeks of training, both groups showed improvements on measures of receptive language skills, but the group that received training with the modified speech showed significantly greater improvements (Merzenich et al., 1996; Tallal et al., 1996).

Reading skills, including non-word decoding, and phonological awareness were not assessed by these studies (Merzenich et al., 1996; Tallal et al., 1996). Although additional investigations have been performed outside the laboratory in clinics and classrooms, enrolling individuals diagnosed with SLI, attention deficit disorder, autism, and dyslexia (Tallal, 2000; Tallal et al., 1998), reading gains have not been reported to date. Language skills, however, were assessed by professionals in the clinics and the authors reported that significant improvements were observed on standardized measures of speech and language, regardless of which measures were used by the various clinics. Results from these studies have led the authors to conclude that the Fast For Word program is effective for individuals with a range of language and communication disorders (Tallal et al., 1998; Tallal, 2000).

Further support for acoustically modified speech as an effective intervention comes from an investigation in 12 children diagnosed with pure phonological dyslexia (Habib et al., 1999). Experimenters subdivided their population into an experimental group that received intervention using the modified speech and a control population that received training using normal speech. Their results indicated that after 5 weeks of training, the experimental group showed significantly greater improvements on a phonological task in which they had to identify the non-rhyming word in a set of four words than did the control group (Habib et al., 1999).

These results suggest that training with modified speech improves receptive language and phonological skills in children. However, it has not yet been determined whether these improvements in oral language are due to an increased ability to accurately perceive and process auditory stimuli or if they might be better explained by other mechanisms. For example, the intense monitoring of stimuli on the computer screen might lead children to attend more effectively. A related question, which pertains to all intervention programs, is whether the improvements are specific to the particular tasks that comprise the program or if the observed gains generalize to other skills, such as reading.

This study addressed two questions: first, can the original findings from a laboratory setting reported by Tallal et al. (1996) be reproduced in a clinical setting? Specifically, are there measurable gains in auditory processing that are not directly trained by the intervention program? Second, does training with acoustically modified speech result in reading gains? To address the first question, subjects were recruited from and tested at a local clinic. Although this allowed for less stringent inclusion/exclusion criteria for the subject population and administration of the intervention program, it more accurately represented the environment in which the intervention program was delivered to these children. To address the question of the specificity of training, a task measuring the ability of participants to accurately judge relative duration in both the auditory and the visual domain was administered to children participating in the program. Previous studies have used measures of oral language skill, but not reading achievement, as outcome measures (Tallal et al., 1996). Further, these language outcome measures and the actual intervention program share many common features, so that improvement in these tasks is not unexpected. In the present study, the tasks were designed to be an independent measure of auditory duration judgement not specifically trained. The visual modality was chosen as a control condition in which improved performance is expected if the intervention induces general changes in attention (or other) processes and not in auditory processes per se. It was hypothesized that subjects would improve on the auditory duration judgment task but not on the visual task. It was further hypothesized that intervention would improve skills associated with non-word decoding and phonemic awareness, skills related to reading acquisition.