Perception of transient nonspeech stimuli is normal in specific language impairment: Evidence from glide discrimination

Twenty 9to 12-year-olds with specific language impairment (SLI) were compared with 18 agematched controls on auditory discrimination tasks, using a three-interval, two-alternative forced-choice format. The first task used minimal word pairs in silence and in noise. Nonspeech tasks involved discriminating direction of frequency glides and had two versions: (a) the glide moved from 500 to 1500 Hz, and duration was adaptively decreased; (b) all glides lasted 250 ms, and the frequency range was adaptively modified until a threshold was reached. Control and SLI groups did not differ on the glide tasks. Around half the children in both groups accurately discriminated 20 ms glides. There was a small but significant group difference on the speech-in-noise task, and scores were weakly related to literacy level. Perception of brief, transient, nonspeech stimuli is not abnormal in the majority of school-aged children with SLI. When a child has difficulty understanding spoken language, an obvious question is whether the problem is related to poor auditory perception. Many children with comprehension problems do not have any peripheral hearing loss, and can pass a hearing test that involves detecting sounds at low intensity. Nevertheless, this does not necessarily mean that auditory function is normal; the possibility remains that there is a problem in distinguishing salient properties of sounds. Tallal and Piercy (1973a) proposed that low-level auditory perceptual problems are implicated in causing specific language impairment (SLI), that is, developmental language difficulties that cannot be accounted for in terms of general developmental delay, peripheral hearing loss, autistic disorder, or physical handicap. Tallal and Piercy (1973a) used a task known as the Auditory Repetition Test (ART), in which they presented children with two-tone sequences separated by variable interstimulus intervals (ISIs). Children were first trained to associate a © 2005 Cambridge University Press 0142-7164/05 $12.00 Applied Psycholinguistics 26:2 176 Bishop et al.: Auditory discrimination and language impairment complex tone with a high fundamental frequency (305 Hz) with one button press and a complex tone with a low fundamental frequency (100 Hz) with another button press. For the two-tone sequences, the task was to press the buttons corresponding to the sequence of tones that was presented (high–high, high–low, low–high, or low–low). Children with SLI performed close to ceiling levels when tones were separated by 305 ms or more, but their performance deteriorated at shorter ISIs. In contrast, control children maintained good levels of performance down to ISIs of 8 ms. Tallal and Piercy (1973b) went on to show that performance on this task by children with SLI was much worse with brief tones (75 ms) than with longer tones (125–250 ms). Such results led to development of the auditory temporal processing theory, which attributes SLI to a problem in discriminating auditory signals that are brief or rapid. Brevity of stimuli alone is not sufficient to create problems: Tallal and Stark (1981) showed that children with SLI had no difficulties in discriminating between two steady-state 40-ms vowels with different formant structures. However, if the same stimuli were followed immediately by another vowel, creating a diphthong, then these children did much worse. This led Tallal and Stark to suggest that brief stimuli lead to problems if they are followed in rapid succession by other acoustic cues. Tallal (2000) argued that poor auditory temporal resolution made it difficult to form fine-grained phonological representations, so children rely instead on coarse, syllable-based representations. This would lead to difficulties in language comprehension and problems in developing a phonic reading strategy. Tallal’s auditory temporal processing theory has been influential: at the time of this writing, the original 1973 Tallal and Piercy paper in Nature had over 200 citations in the Science Citation Index over the past 20 years. Clark, Rosen, Tallal, and Fitch (2000) argued that the accumulated research findings “overwhelmingly support the view that individuals with developmental language disabilities have a fundamental dysfunction in the ability to process brief auditory stimuli followed in rapid succession by other acoustic information (i.e. rapid auditory processing)” p. 829. Troia and Whitney (2003) noted that a computerized intervention package based on the theory, FastForWord R ©, has been administered to over 65,000 children in the United States. Nevertheless, recent years have seen a number of challenges to the auditory temporal resolution theory. WHAT DOES THE ART MEASURE? A number of researchers have questioned whether the results obtained with the ART are indicative of poor auditory temporal processing. In the ART, the child must learn to associate each of two frequencies with a specific keypress and remember this association over a lengthy set of trials that are typically given without feedback. Furthermore, the order of a sequence of tones must be reproduced. It has been argued that performance on this task may be affected by multiple factors other than auditory temporal resolution, including frequency discrimination, associative memory for tone–button pairings, short-term memory for tone sequences, perceptual learning, skill in classifying perceptually similar stimuli, and ability to make strategic use of verbal labels for the stimuli (Heath, Hogben, & Clark, 1999; Marshall, Snowling, & Bailey, 2001; McArthur & Bishop, 2001, 2004b; Applied Psycholinguistics 26:2 177 Bishop et al.: Auditory discrimination and language impairment McArthur & Hogben, 2001; Nittrouer, 1999; Tomblin & Quinn, 1983). One might argue that the influence of such factors would predict deficits at long as well as short ISIs, but the original task used by Tallal and Piercy (1973a) gave ceiling effects at long ISIs. Indeed, a number of recent studies found no evidence of a selective deficit at short ISIs in children with SLI or reading deficits, provided ceiling effects were avoided (Bishop et al., 1999; Breier, Gray, Fletcher, Foorman, & Klaas, 2002; Bretherton & Holmes, 2003; Lincoln, Dickstein, Courchesne, Elmasian, & Tallal, 1992; Nittrouer, 1999; Norrelgen, Lacerda, & Forssberg, 2002; Share, Jorm, Maclean, & Matthews, 2002; Van der Lely, Rosen, & Adlard, 2004; Waber et al., 2001). One way of reducing the labeling and sequencing demands inherent in the ART is by asking children to judge whether two tones are the same or different, rather than reproduce the sequence. Tallal and Piercy (1973a) found that deficits were still apparent in children with SLI when this method was used, and some other studies also found deficits on the ART (although with long as well as short ISIs) using a same–different format in children with reading disability (Goswami et al., 2002) or SLI (Van der Lely et al., 2004). However, other studies of readingdisabled children found deficits only when the original “repetition” version of the test was used (Farmer & Klein, 1993; Heiervang, Stevenson, & Hugdahl, 2002). THE RELATIONSHIP BETWEEN ART PERFORMANCE AND PHONOLOGICAL PROCESSING In a review of the area, Rosen (2003) noted that evidence was particularly weak for a causal link between low-level auditory perceptual problems on the one hand, and impairments of speech perception and phonological processing of written language on the other. Tallal (1980) reported a very high correlation between errors in a nonword reading test and ART performance, but this has not been replicated (Breier et al., 2002; Bretherton & Holmes, 2003; Heath et al., 1999; Nittrouer, 1999; Norrelgen et al., 2002; Share et al., 2002; Van der Lely et al., 2004). Witton and colleagues (Talcott et al., 1999, 2000; Witton et al., 1998) found positive associations between children’s ability to detect slow (2 Hz) frequency modulation and their phonological reading skills, and this has been interpreted as supportive of Tallal’s theoretical position. However, the rates of modulation used in this task are far slower than occur within consonants, and the task could be failed because of poor frequency resolution rather than poor temporal processing. Furthermore, Bishop, Carlyon, Deeks, and Bishop (1999) failed to replicate this association in children with SLI. Hulslander et al. (2004) did find positive associations between tests of frequency modulation detection and literacy skills but showed that these could be accounted for in terms of effects of IQ or attention. One possible reason for variable findings in previous studies is that the participants have ranged from children with SLI (Bishop, Bishop et al., 1999; Bishop, Carlyon et al., 1999; Norrelgen et al., 2002; Van der Lely et al., 2004), those with clinically diagnosed reading disability (Goswami et al., 2002), poor readers without SLI (Breier et al., 2002; Stark & Tallal, 1988), children referred for evaluation of learning disabilities (Waber et al., 2001), children with reading impairments identified from mainstream classrooms (Heiervang et al., 2002), to unselected samples (Nittrouer, 1999; Share et al., 2002). Tallal (1980) argued that Applied Psycholinguistics 26:2 178 Bishop et al.: Auditory discrimination and language impairment the auditory temporal processing theory could account for phonological deficits in children with reading disability, but in her own work (Stark & Tallal, 1988) and that of Heath et al. (1999), auditory temporal deficits were not seen in children with reading disability if oral language was unimpaired. Even among those with SLI, it is clear that the auditory temporal deficits are found only in a subset of cases (Neville, Coffey, Holcomb, & Tallal, 1993; Tallal, Townsend, Curtiss, & Wulfeck, 1991). In the current study, we focused on the core group of children for whom the auditory temporal processing hypothesis was first postulated: those with severe and unexplained receptive language impairments. A DIFFERENT APPROACH TO THE ASSESSMENT OF AUDITORY