578 Dorothy V.M. Bishop et al. latency and only one had abnormal P2. However, in a similar active paradigm, Ors, Lindgren, Blennow, Nettel- bladt, Sahlén and Rosén (2002) failed to ﬁnd any group differences in N1-P2 in a comparison of 10 children with SLI and 10 control children aged from 10 to 14 years. Neville, Coffey, Holcomb and Tallal (1993) suggested that inconsistent ﬁndings might reﬂect heterogeneity in the SLI population, with only a subset of children having auditory processing problems. In a complex experiment where tones were presented at different SOAs, they found no overall difference between 22 children with SLI and 12 control children for amplitude or latency of N1 and P2. However, when children were subdivided according to their performance on an auditory temporal processing task, those with low scores showed a trend for delayed N1, especially over the parietal and temporal regions of the left hemisphere. This supports the idea that we need to move away from group analyses and develop methods for iden- tifying abnormality of ERPs in individual children. The goal of analysing auditory ERPs in individual children is complicated by the fact that at fast presenta- tion rates, N1 and P2 peaks are often not seen in ERPs of children under 12 years of age (Albrecht, von Suchodoletz & Uwer, 2000; Ponton, Eggermont, Kwong & Don, 2000). Thus if we want to study early cortical responses to sounds in children we need a method that does not depend on identifying speciﬁc peaks. McArthur and Bishop’s (2004) solution to the latter problem was to use a method for analysing auditory ERPs that enabled one to establish how far a child’s waveform was age-appropriate, without requiring that speciﬁc peaks be identiﬁed. They used the intraclass correlation (ICC) statistic to quantify the extent of similarity between an individual’s auditory ERP and a normative grand average. The ICC gives a global index of similarity between two waveforms and is sensitive to both amplitude and latency differences in peaks and troughs. In an initial study using this method, McArthur and Bishop (2004) showed that young people with SLI had lower ICCs than a group of matched controls. In a follow-up study using many of the same participants, Bishop and McArthur (2005) replicated this ﬁnding. Overall, these studies suggested that the ICC measure might be more sensitive than conventional measures of peak latency and amplitude in identifying cases where the auditory ERP was not age-appropriate. However, the study by McArthur and Bishop (2004) included only 16 participants with SLI aged from 10 to 19 years and 16 controls matched for age and IQ. The authors noted that the generalizability of their ﬁndings needed to be tested against a much more substantial normative background. A sample of children with SLI (Uwer et al., 2002) pro- vided an opportunity to do this. We focused on the time © 2007 The Authors. Journal compilation © 2007 Blackwell Publishing Ltd. 5 to 6 years 7 to 8 years 9 to 10 years Total Methods Participants Table 1 Numbers of females and males in typically develop- ing (TD) and SLI groups, by age Female 3 8 9 20 TD Male 8 12 7 27 Total Female 11 20 16 47 3 3 3 9 SLI Male 5 20 8 33 Total 8 23 11 42 period 100–228 ms post stimulus onset, as this was the interval over which McArthur and Bishop (2004) had found atypical ERPs in their SLI group. The data came from Uwer et al. (2002) and Albrecht et al. (2000). The characteristics of typically developing and SLI samples is described in detail by Uwer et al. (2002) and summarized in Table 1. In brief, children with SLI were aged from 5 to 10 years and either attended special schools for children with language impairments, or had been referred to a clinic for developmental problems. All had nonverbal IQs of 85 or above (receptive SLI mean = 98, SD = 10.1; expressive SLI mean = 103, SD = 11.2). Children with receptive SLI scored 2 SD or more below the normative mean on a test of grammatical comprehen- sion, and those with expressive SLI scored this poorly on a test of imitating grammatical structures. The typically developing sample consisted of 5- to 10-year-old children matched in age to the SLI sample and with nonverbal IQ in the normal range (mean 108, SD = 11.2). Individuals with psychiatric disorders, peripheral hearing loss or neurological impairment were excluded from the sample. All the control children in this sample were included in the larger sample of typically developing children analysed by Bishop et al. (see Bishop, Hardiman, Uwer & von Suchodoletz, 2007). Behavioural test of auditory discrimination As described more fully by Uwer et al. (2002), all chil- dren with SLI and 16 of their matched controls were tested for their ability to discriminate the standard and deviant stimuli used in the ERP session. They were played pairs of stimuli and asked to judge if they were the ‘same’ or ‘different’. For each of four contrasts (tones contrasting in frequency or duration, and /da/ vs. /ba/ or /ga/ ) 15 same and 15 different pairs were pre- sented. The total number of errors was recorded.