ابعاد کنترل روانشناختی والدین: ارتباطات با پرخاشگری فیزیکی و رابطه پیش دبستانی در روسیه

Slowed speed of processing and impaired rapid temporal processing (RTP) have been proposed to underlie specific language impairment (SLI), but it is not clear that these dysfunctions are unique to SLI. We considered the contribution of attention-deficit/hyperactivity disorder (ADHD), which frequently co-occurs with language impairments, to performances on processing tasks. School-aged children who had SLI without concurrent ADHD (n = 14), ADHD without concurrent SLI (n = 14), and typical development (TD, n = 28) performed two nonverbal speeded tasks and one auditory RTP task. RTP impairments were found in many children with SLI and ADHD, and some children with TD. Children with ADHD demonstrated slower processing speed than children with SLI or TD. Overall, findings questioned the uniqueness of these processing dysfunctions to language impairments and the validity of the behavioural paradigms traditionally used to estimate processing dysfunctions. Accounts of SLI should be further scrutinized by considering the influence of other disorders.

Slowed speed of processing and impaired rapid temporal processing have both been proposed to be causally connected to impaired language development and functioning. For example, in the generalized slowing account, children with SLI are thought to have a central dysfunction that involves slowing across all aspects of mental processing (Kail, 1994, Miller et al., 2001 and Windsor and Hwang, 1999). Irrespective of the nature or complexity of the task, children with SLI are proposed to be slower than their peers by a constant factor. The time-dependent nature of speech is thought to make language development especially vulnerable to the effect of slow information processing (Miller et al., 2001). In the rapid temporal processing (RTP) dysfunction account (which some have argued to be subsumed under generalized slowing, see Montgomery & Windsor, 2007), children with SLI are proposed to have a central impairment in processing quick transitions in sensory input (Benasich et al., 2001 and Tallal, 2000). The inability to process rapidly changing elements within the speech signal is viewed as a key contributor to language impairments, because a number of phonemic contrasts are signalled within extremely brief time frames. Thus, an underlying RTP impairment is proposed to interfere with development of the phonological system, and, consequently, spoken and written language (Tallal, 2000). Although empirical evidence exists to support the presence of these processing dysfunctions in children with SLI, the models remain open to debate and controversy. The statistical analysis methods used to support the generalized slowing hypothesis have been challenged, with other analysis methods pointing to process-specific, not generalized, slowing in SLI (Windsor, Milbrath, Carney, & Rakowski, 2001). Although some have concluded that the evidence for a RTP dysfunction in language disorders is compelling (Farmer and Klein, 1995, Habib, 2000 and Leonard, 1998), others have failed to find differences between children with SLI and children with typical language development in RTP (Heltzer et al., 1996, McArthur and Bishop, 2001 and Rosen, 1999). In addition, some authors have argued that this dysfunction is not specific to input that is rapid, but rather may reflect a broader based impairment in auditory processing (Heltzer et al., 1996 and Rosen, 1999). Others have argued that RTP impairments may not be causally linked to language impairments (Bishop, Carlyon, Deeks & Bishop, 1999). Counterarguments to these criticisms have included the fact that RTP dysfunctions do appear in at least a subset of children with language disorders (McArthur & Bishop, 2004) and the fact that failures to identify this dysfunction in some children with language impairment may reflect inadequate measurement sensitivity or maturational changes across different age groups that have been studied (Bishop and McArthur, 2005, Joanisse and Seidenberg, 1998 and McArthur and Bishop, 2005). An additional source of debate arises from the potential confounds introduced by the behavioural paradigms typically used for measuring the processes of interest. Such confounds have been at the forefront of the controversy surrounding the RTP account. Because RTP paradigms place demands on higher level processes (e.g., attention, memory, learning), it is arguably difficult to attribute poor performance directly to impaired RTP. Indeed, Bishop et al. (1999) suggested that poor performances by children with SLI on RTP tasks might reflect attentional problems. Moreover, Ludlow, Cudahy, Bassich, and Brown (1983) found impaired performance on a task measuring RTP in a group of six children with ADHD who did not have concurrent SLI or learning disabilities. Although similar concerns have not been central to the critiques of other processing accounts of SLI, a confounding influence of higher level processes is certainly a plausible issue for studies examining these accounts as well. 2. The role of ADHD Little research has explored whether the aforementioned processing dysfunctions are indeed unique to disorders of language, one of the precursors to proposing causality. Evidence for an impaired aspect of processing in children with SLI relative to children with typical development does not establish whether the process contributes to impaired language development. It is also important to determine that the dysfunctional process is associated with SLI and not another co-occurring disorder in the sample. The high rates with which other developmental and behavioural disorders occur in the SLI population ( Baker & Cantwell, 1991) suggest that this possibility cannot be readily dismissed. It is also important to determine whether children with other disorders besides SLI have dysfunctions in the basic process. If a processing dysfunction is found in children who do not have a core linguistic impairment, it is difficult to argue that the dysfunction is central to impaired language development or is a marker of SLI. ADHD commonly co-occurs with language impairments, thus warranting attention when considering the uniqueness of specific processing dysfunctions to SLI. ADHD is the most common psychiatric/behavioural disorder of childhood, affecting roughly 3–7% of school-aged children (Polanczyk & Jensen, 2008). Children with ADHD present with persistent problems in one or both of two behavioural symptom clusters: inattention and hyperactivity-impulsivity. These symptoms are demonstrated at a frequency and severity that is judged to be inappropriate for the child's level of development and are associated with impairment in daily functioning (American Psychiatric Association, 2000). Of importance here, 20–40% of children with language impairments also have ADHD (Baker and Cantwell, 1991 and Beitchman et al., 1989) and 40–60% of children with ADHD have language impairments (Cohen et al., 1993 and Oram et al., 1999). Few investigators have examined the possible role of other disorders, including ADHD, when examining processing dysfunctions in SLI. Despite prior concerns about the role of attentional problems in RTP task performance, investigators have not been consistent in determining the degree of ADHD co-occurrence in their SLI samples or controlling for its potential influence on their findings. Moreover, examinations of children with ADHD suggest that RTP dysfunctions (Ludlow et al., 1983) and slowed processing speed (e.g., Carte et al., 1996, Kunsti and Stevenson, 2001, Scheres et al., 2001 and Weiler et al., 2000) may also be present in this population. We aimed to contrast the contribution of SLI and ADHD to performances on three measures previously used in the literature to examine processing dysfunctions in children with SLI: two nonverbal speed of processing tasks varying in degree of cognitive load and one auditory rapid temporal processing task. To do so, we tested processing speed and RTP in three groups of children who showed: (1) receptive-expressive SLI without concurrent ADHD, (2) ADHD without concurrent SLI, and (3) typical language and behaviour development. In line with current theories of SLI, we predicted that children with SLI who did not have ADHD, but not children with ADHD who did not have SLI, would show impaired performance on our processing tasks relative to children with typical development.

We have argued that exploring the uniqueness of processing dysfunctions to SLI by examining the influence of other disorders like ADHD is an important precursor to considering causality and viewing a dysfunction as a marker of SLI. The current investigation has demonstrated the value of this approach. Our results strongly supported the need to further scrutinize accounts of SLI through expanded examination of these processes in ADHD as well as other disorders. At a broader scientific level, future investigations into candidate markers of any disorder need to be subjected to similar considerations. For example, interest has increased in the literature in assessing the predictive accuracy of potential markers of disorders using sensitivity and specificity calculations or likelihood ratios (Conti-Ramsden et al., 2001 and Dollaghan and Campbell, 1998). Current findings highlight the need to cast a wider net in making such estimations; specificity analyses (e.g., the probability of children without language impairment being accurately classified as unimpaired) should not be restricted to children who have no developmental or behaviour problems but rather should include all children without language impairment, irrespective of other areas of non-linguistic or behavioural impairment. It is only then that the true promise of proposed phenotypic markers of SLI can be assessed.