JCPSLP Vol 23 Issue 2 2021

Materials and procedure Participants completed a 14-item questionnaire developed by Highman et al. (2008) regarding the presence and age of emergence of vocalisations, language and developmental milestones, and feeding and dribbling. Parents were encouraged to use any methods they could to support completion of the questionnaire such as talking to relatives or using their child’s infant health record book. Ethics approval was obtained from the Curtin University Human Research Ethics Committee (HREC2019-0396). Participants provided written consent. Due to cohort age differences, internal validity was threatened by selection bias, specifically initial non-group equivalence (Pring, 2005). The period of time that parents were required to recall information from was dependent on their child’s age. Despite significant age differences, there were no significant differences in parental rating of recall ability, as indicated by the number of unsure responses, Kruskal-Wallis H (d.f. = 3) = 3.24, p = .35. Data analysis Statistical analyses were conducted through the IBM Statistical Package for the Social Sciences software package (Version 25; IBM Corp, 2017). Group differences were analysed using pair-wise comparisons as reported in Highman et al. (2008), with an alpha level of .05. Tukey’s least significance difference contrasts were used when data were continuous after confirming significance for the group effect in the omnibus analysis of variance. Categorical outcomes (frequency data) were compared between groups using either chi square analysis or the Fisher’s exact test (FET). Only statistical contrasts between the PD and comparison groups are reported below (see Highman et al., 2008, for details of contrasts between sCAS, DLD and TD groups). Results Frequency and age of emergence results are presented together (see Tables 1 and 2, respectively, for descriptive summaries). Vocalisations and babbling Makes many sounds As shown in Table 1, all children in the PD group were reported by their parents to make many sounds as an infant. This percentage was significantly higher than the sCAS group, FET p < .001, and the DLD group, FET p = .024, but equivalent to the TD group. Planned comparisons showed the mean rating of recalled volubility for the PD group (M = 4.35, SD = .76), where 1 is vocalised rarely and 5 is vocalised often , did not differ significantly from the TD group, p = .72, but was significantly higher than the sCAS and DLD groups, p < .001 for both comparisons (M = 4.25, 2.34, 2.58, for TD, sCAS & DLD, respectively). Vowel sounds A higher percentage of children in the PD group were reported as producing vowel sounds compared to sCAS and DLD, although this difference was not statistically significant, FET p = .118, FET p = .5, respectively (Table 1). The PD group also did not differ from TD, FET p = .244. The groups differed significantly in the age of emergence of vowel sounds, F (3, 60) = 5.424, p = .002, N 2 = .213. Similar to what was observed for the TD group (see Table 2), the age of emergence of vowel sounds for the PD group was reported by parents to be significantly earlier than the sCAS group, p = .015, and DLD group, p = .013.

Consistent with previous reports and theoretical predictions in the literature, the children with sCAS were reported to be significantly less vocal, less likely to babble, later in the emergence of first words, and later in the emergence of two-word combinations than the typically developing children. However, the children with DLD were reported similarly to the sCAS group (Highman et al., 2008), except children with sCAS were less likely to have babbled and the age of emergence of two-word combinations was later when also compared to children with DLD (Highman et al., 2008). These findings were limited by the lack of a group of children with phonological impairment, who are often reported to share many of the characteristics observed in CAS (Iuzzini-Seigel et al., 2017). Therefore, it was not clear to what extent the differences we observed between the sCAS and DLD groups reflected something specific to sCAS, or to speech disordered children in general. The present paper extends our work by replicating the methodology of Highman et al. (2008) to obtain parental report of early vocalisations in children with phonological delay (PD), and to compare the children with PD with the typically developing, sCAS and DLD children from the 2008 paper. Delayed phonological development was chosen (rather than inconsistent speech disorder, for example), as this is the most common phonological disorder type in young children. The questionnaire also included items relating to motor milestones and other features often reported to co-occur with CAS, such as feeding and dribbling (Davis & Velleman, 2000; Highman et al., 2008). Our research questions for this study were: 1. Do parents of children with PD report differences in vocalisations compared to parents of TD children, and those with sCAS or DLD? 2. Do parents of children with PD report differences in language and developmental milestones compared to parents of TD children, and those with sCAS or DLD? 3. Do parents of children with PD report differences in feeding and dribbling compared to parents of TD children, and those with sCAS or DLD? Method Participants Participants were parents of children ( n = 20) with PD. PD was accepted as the presence of phonological processes beyond age-expected norms in absence of non- developmental processes (e.g., backing) (McLeod & Baker, 2017). A sample of 20 was required to match that reported in Highman et al. (2008). Inclusionary criteria included: PD, normal hearing, and monolingual English-speakers. Exclusionary criteria included: presence of motoric involvement and diagnosed or suspected neurological disorders. Convenience sampling was employed with participants recruited via managing SLPs within the Perth metropolitan area. Data in the present study were compared to that of parents of children with sCAS ( n = 20), DLD ( n = 20), and TD speech and language ( n = 20), detailed in Highman et al. (2008). A significant difference in mean age was identified, F(3, 76) = 14.813, p < .001, N 2 = .369. The sCAS group (M = 48 months, SD = 7.6) was significantly younger than the PD (M = 54 months, SD = 8.6), DLD (M = 60 months, SD = 6.9), and TD (M = 61 months, SD = 11.3) groups. There were no significant differences in gender ratios, p > .05.

Neville Hennessey (top) and Suze Leitão

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JCPSLP Volume 23, Number 2 2021

Journal of Clinical Practice in Speech-Language Pathology