Psychology. Specific Language Impairment and Dyslexia


The International Dyslexia Association (IDA) gives specific definition to dyslexia admitting its neurobiological origin “characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and encoding abilities” (Snowling and Hayiou-Thomas, 2006, p. 110). In this respect specific language impairment (SLI) is a disorder affecting expressive and receptive language at once (Campbell, 2009). In terms of the severity hypothesis some scholars tend to recognize SLI as a “more severe form of dyslexia” (Snowling and Hayiou-Thomas, 2006, p. 111). One of the definitions in Campbell’s Psychiatric Dictionary reads that dyslexia is “a form of language disorder, with a history of delayed receptive and expressive oral language acquisition” (Campbell, 2009, p. 311).

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Psychologists, neurologists, and linguists combined their forces to maintain and better learn the extent of overlap between SLI and dyslexia in the phonological processing. In this respect contemporary and previous studies provide a huge range of methods and principles to state several hypotheses on this issue. Hence, the role of phonology is of high significance for this study in order to make out its use for decreasing levels of language disorders. Phonology is also an applicable means to set points on understanding between a practicing counselor or teacher and a child with SLI or dyslexia. This process is too hard to resolve it. A dyslexic brain needs “specific” and rationally mature means, as a treatment for phonological processing.

Literature Review

Farrell (2005) makes up a deep analysis of dyslexia as such in terms of all its manifestations and prerequisites that condition the disease. In this respect the researcher lays special attention on the phenomenon of cognitive delay in children. It is the main reason to provoke impairments in different aspects of language performance. Thus, it is considerable to think over the main conditions for dyslexia to progress in a child, despite some physical drawbacks as of mental activity. These conditions can be examined in the following way:

  • Asperger’s syndrome;
  • Attention deficit hyperactivity disorder;
  • Specific language impairment;
  • Dysgraphia;
  • Deficit of attention and motor perception (Farel, 2005).

Thereupon, verbal and non-verbal skills are contradicted in a person of a child. The thing is that one with SLI is not particularly affected in terms of non-verbal skills. This point stimulates researchers in designating whether phonological reality at earlier stage of children’s development is a dimension to think of dyslexia and SLI as one.

Discussing genetic grounds for reasoning dyslexia and SLI, Bishop (2008) provides a set of explanations as for the diseases and factors to provoke them. First of all, it is a problem caused initially in the left cerebral hemisphere of brains. This area is responsible for language formation, adaptation, and provision. Even a tiny physical or physiological damage can result in problems with language skills and their acquisition. Furthermore, a congenital affection can be deepened in a child due to quantitative and qualitative inputs of language (Bishop, 2008). Impairments on one of the language dimension can cause problems in phonology processing in a child. Thus, data gathered in this study provide a statement that SLI and dyslexia can be supposed as two manifestations of one disorder, namely phonological impairment.

Messaoud-Galusi and Marshall (2010) admit that the cases with dyslexia in children occur rather frequently that can be predicted at the time. The observation touches upon the significance of implementing qualitative rather than quantitative differences between dyslexia and SLI in the phonological aspect (Messaoud-Galusi & Marshall, 2010). In this respect the overlap between dyslexia and SLI is presupposed due to co-morbidity in terms of clinical and theoretical domains. Rating 5% to 10% people affected such disease within the population; there is a danger for people with dyslexia to faced SLI (Messaoud-Galusi & Marshall, 2010). Such statement of the researchers is terrific and needs more attention on the cure for children with dyslexia. Thereupon the researchers pay more attention to the classification of phonological aspects, as follows:

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  • “Classic” meta-linguistic tasks alongside paradigms involving implicit phonological processing (lexical gating and forced-choice identification tasks);
  • Levels of processing range from the early auditory processing involved in speech perception, through to language specific rules (morpho-phonological alternations) (Messaoud-Galusi & Marshall, 2010, p. 3).

Apparently distinct profiles of dyslexia and SLI can be outlined through several models. The researchers tend to highlight the “severity” of the disease and tend to think that along with phonological should be used non-phonological (encapsulating semantic, syntactic) language (Messaoud-Galusi & Marshall, 2010). Another suggestion requires basing models of overlap between two diseases on the drawbacks with reading more than with language impairments. It is sparingly vital to make emphasis on the Plaut et al (1996) Triangle model to explain the relationships between oral and written speech. In this respect one should presume such particular language units as semes and phonemes. Snowling and Hayiou-Thomas (2006) ruminate over this model stating: “…reading is conceptualized as the interaction of a phonological pathway mapping between orthographic and phonological units and a semantic pathway mapping between orthography and phonology via meaning” (112). Hence, the aspect of semantics stays in the center of discourse-grammatical and orthographic-phonological conceptual unities.

Christo et al. (2009) state merely the same assumptions on the phonological processing among children with dyslexia and SLI as it is shown in Messaoud-Galusi & Marshall 2010). Thereupon, it is vital to admit that phonological deficits are more apparent among children having problems in reading. Strong skills in using and developing language can compensate poor phonology. It concerns the model presupposing that only dyslexic affection impacts phonology and only SLI affection reflects on problems with reading. This position is debatable due to statements of various researchers. In this case Christo et al. (2009) outline the statement that a separate nature of both diseases reaches common point at their comorbidity.

Weerdenburg et al. (2010) are about to determine and reduce language impairments on linguistic and cognitive levels in children. In this respect the scholars tried to scope out the most appropriate factors that reason dyslexia and SLI in children. Neurological approach was taken into consideration to make up a picture of related processes of phonological illiteracy that can turn out to be a great obstacle resulted in SLI for children with dyslexia and in dyslexia for those with SLI initially. Catts et al. (2005) have reported on their peer-reviewed experiment to define the extent of phonological overlap between children solely with dyslexia and solely with SLI and those with both typical diseases. Dyslexia and SLI can simply lead to more aggravated consequence like dysphasia.

Tallal (2006) in The Dyslexic Brain provides a receipt for making progress in understanding phonological overlap in dyslexia as started with SLI. It sounds likewise the title reads: “Process faster, talk earlier, read better” (Tallal, 2006, p. 49). However, to respond to the issue of SLI/dyslexia close relation, the author uses a broader term, i.e. language learning impairments (LLI). The research outlines that oral and written language is centered on the specific too difficult mechanisms in brain. That makes possible to state that speech-centered character of phonological processing can be presupposed by the author through several models. These are the rate-processing constraint hypothesis, the double-deficit hypothesis, the attentional dwell time hypothesis, and maturational lag hypothesis (Tallal, 2006).

However applicable these models, the research showed that due to critical moments experienced in different areas of brain its structure can alter. Such alteration, from the viewpoint of neuroplasticity, can be prevented by means of neuroplasticity-based interventions (Tallal, 2006). However, even in a sign language the severity of impairments is stated as such (Mason et al., 2010). In this respect the question of effective impacts to learn phonological overlap of dyslexia and SLI leaves a space for more detailed analysis. Thereupon, there are enough grounds to infer the following: “While considerable attention has been placed on metacognitive aspects of phonological awareness deficits in dyslexics, it is important to emphasize that lower speech perception has also been shown to play a substantial role” (Cited in Tallal, 2006, p. 52).

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Thus, the methodology in aforementioned Weerdenburg et al. (2010) presupposed a sample of 527 participants: children from kindergarten, and 2nd, 4th and 8th grades of school. Children were divided into two groups identifying their commonplace characteristics. The first study provided results stating limited but noteworthy overlap between two diseases. The second study showed that participants with dyslexia or its combination with SLI promoted barely well performance in phonological processing than those with SLI only (Catts et al., 2005). This fact complements a point of view that phonological less performance is a direct result of dyslexia impacts than of SLI only. These findings were taken into consideration by Messaoud-Galusi & Marshall (2010). A common conclusion on the overlap between two diseases was fixed in this study claiming that “nonphonological language deficit underlies SLI” (3). Hence, one might take two diseases as for their separate nature as a given. Snowling and Hayiou-Thomas (2006) previously had strong persuasion stating the following idea: “The clearest evidence for the association between phonological deficits and decoding difficulties comes from children with “discrepancy-defined” dyslexia” (113).

Beaton (2004) grounds his statement about influence of dyslexia on phonology as a result of poor reading activity. In turn the question of any treatment grounded on phonology arises. The researcher singles out that with more points on reading a child becomes capable of recognizing phonetic, morphologic, and syntactic units. However, the author points that the problem of dyslexia and SLI should be treated on the early stage of its emergence in children. It is accordant to what the statement defines as “poor phonology is more closely associated with reading than with language impairments” (Messaoud-Galusi & Marshall, 2010, p. 4). Otherwise, such developmental delay in language capabilities may successively turn into a developmental dysphasia (Beaton, 2004). This statement is emphasized by the fact that genetically there is no set of functions or features that could contradict emergence of SLI or dyslexia.

However, the study provided by Bree and Kerkhoff (2010) identified differences between children with dyslexia and those with SLI on morpho-phonological level. The study investigated particular differences in the way Dutch children at risk of dyslexia and those with SLI form singular-plural pairs of various nouns. The methodology touched upon defining the extent between alternating and nonalternating words among three groups of children with appropriate diseases. The findings highlighted that at-risk group was more capable to produce plurals correctly than the SLI group. Moreover, SLI group was less sensitive to lexical frequencies and to distributing different morphemes in the way they should apply. In accordance with the rhyme realization of the singular, researchers tend to strictly note:

For all three groups, words led to higher correct scores than nonwords, indicating that novel phonological representations are less specified than those of words. This difference was more pronounced for the at-risk and SLI group than for the control group, rendering the interaction between group and stimulus type (Bree & Kerkhoff, 2010, p. 101).

The study concludes that dyslexia is more relevant to phonological deficits than SLI. Hence these two forms of allegedly typical diseases should be recognized separately. The main ground for such statement is that the overall experiment proved the hypothesis on phonological deficit as pursuant to dyslexia.

Vandewalle et al. (2010) researched precursors for appearance of dyslexia among children in kindergarten. Thus, the methodology was constructed as per the long run (2 years) of experimenting. The researchers identified three direct predictors of different rank of developing grounds for dyslexia. In this respect phonological awareness (PA), verbal short-term memory (vSTM) and random automatized naming (RAM) (Vandewalle et al., 2010). The latter is inferred to be a strong predictor for having dyslexia in case if SLI children failed on it since the start of the research. However, the researchers noticed a peculiarity (or non-completed nature of the findings) implied in the main focus on Dutch. They comment on such aspect in the following way:

Because the empirical data are limited to the Dutch language, one may think that the conclusions about the small role of PA and the important role of RAN in the development of reading in children with SLI may be restricted to transparent languages (Vandewalle et al., 2010, p. 79).

Thus, direct RAM interventions provided within the preschool period of development might diminish the negative influence of inability to recognize words correctly. Such idea continues on the fact that stimulation of non-verbal reality by means of concrete and distinct oral cues can in turn improve PA and vSTM.

Martin et al. (2007) gives concrete examples that not always dyslexia and SLI appears among physiologically and neurologically damaged children. The thing is that children at early stage of their language proficiency may have problems with reproducing sounds and words in balance with grammar. The phonological implication states that children have capacity to recognize long vowels more than short or reduced ones (Martin et al., 2007). The researchers conclude that it is supposed to take place in the analytical languages (English, French, etc.).

The specificity of dyslexia runs the gamut in the reality of Chinese children. Wong et al. (2010) rely in their research on the investigation of the phonological overlap between dyslexia and ISL. Thus, the research was performed particularly in the same was as illustrated in Catts et al. (2005). Cantonese-Chinese-speaking children aged 6-11 were divided in accordance with their diagnosed diseases into two groups: SLI-only and SLI-D (combined with dyslexia). Textual understanding and recognition was poor in SLI-only group in comparison to SLI-D group. However, the sensational outcome of the research is supposed with the fact that both SLI-only and SLI-D groups showed no difference in phonological abilities and in morphological awareness (Wong et al., 2010). This constitutes that the overlap between dyslexia and SLI is apparent regarding phonological processing.

Bishop and Leonard (2001) correlate the problem of dyslexia in terms of several determinants among which determinant of outside-in/inside-out skills and of reading outcomes are noteworthy. The scholars admit that dyslexic children are lack of having enough possibilities to read. Thus, in the early age they are imparted from the natural process of age development trapped in the decline of acquiring outside-in and inside-out language skills. It is seen in preschool age and during elementary school. In this respect Fraser et al. (2010) attempt observing the alleged overlap between SLI and dyslexia in phonological aspect experimentally as well. The experiment provided particular set of procedures as for children aged 9-11 and with developmental dyslexia and SLI. The controls were separated into ones with specific reading disability (SRD) and those with SLI. The results showed that impairments among SRD and SLI groups considered pervasive difficulties of phonological and auditory processing (Fraser et al., 2010).

Snowling (2000) gives a reason of why the researchers should first take a glance at word recognition supposed to have place in accordance with reading competencies of a child. SLI is stated in the study to be analyzed in a “broader language deficits” (Snowling, 2000). This hallmark correlates the discussion toward finding out the ways that are helpful to realize the problem on the whole. The researchers should not mix dyslexic symptoms with just poor comprehension of words and their sounding. Scholars remark: “In contrast to dyslexia, poor comprehenders have language-processing deficits beyond the phonological module” (Snowling & Hayiou-Thomas, 2006, p. 113). On the experimental basis it is seen that children with normal IQ rates made mistakes in recognizing words. In particular, it was closer to grammatical and semantic domains of language. The main difficulties touched upon “semantic judgment tasks, poor semantic fluency, and reduced semantic priming of categorically associated items” (Snowling & Hayiou-Thomas, 2006, p. 113).

On the other hand, Bedi (2001) hypothesizes on the fact that rapid acoustic cues (RAC) should be taken by therapist and educators into account, as the extremely necessary way to improve speech comprehension. This point is developed throughout the research to make up a complex of training programs to invoke mental mechanisms of speech perception in dyslexic children. The research presupposes looking at the practical side of the methods through the principles of Temporal processing theory of speech (Bedi, 2001). Cognitive remediation in terms of language comprehension can be developed and improved owing to neural plasticity which grounds merely on appropriate experience-based skills of a child. In fact, RAC is a procedure a bit similar to aforementioned RAM in the study by Vandewalle et al. (2010). At this point the cognitive reaction of mind can be increased critically. In turn, it might serve as one of the main treatments for reducing overlap between dyslexia and SLI, first of all. Later on, such approach is applicable in diminishing the severity of dyslexic symptoms.

Heim and Benasich (2006) provide complex assumptions on SLI and dyslexia through the viewpoints developmental psychopathology. In fact, they ground their research on the controversy between normal and pathological reality concerning health. The problem of development language disorders is seen in the research to be too difficult. Thus, the authors recommend working it out by means of typical and atypical trajectories using the variables of SLI and dyslexia. The main problem stated in the observation is that 50% of children experiencing SLI are at direct risk to develop dyslexia (Heim and Benasich, 2006). This is why there should be an efficient cure that is based on the reasons and prophylactics of SLI and/or dyslexia. The study by Miles and Miles (2004) who state on phonological aspect of dyslexia in terms of recollecting speech sounds and putting them in right order.


To conclude, the observation of different researches in the paper showed pervasive truth of that there are points to suppose on the overlap between dyslexia and SLI in terms of phonological aspect of language. Different researches that came out to be in different places of the world and on the base of different languages (English, French, Chinese, Dutch, etc.) showed several noteworthy points. First of all, dyslexia and SLI should not be mixed up as they are characterized by different symptoms and extent of affection on recognizing and producing sounds and word forms. Second, SLI may continue on to develop dyslexia in half cases (Heim & Benasich, 2006). Third and the principal, theoretically and practically the emergence of overlapping dyslexia and SLI is apparent due to several studies based on direct experiments among children.

All these points should serve as evidence to state for overlap between two language-based disorders in further studies. Provided study is also a credible ground for setting up additional arguments on the topic. In this respect a researcher should take a look at what has been achieved currently and then provide supporting research. All in all, the whole observation puts one into the picture of current attainments in the juncture of linguistics, neurology, psychology and education. The hypothesis stated as well as results acquired do contradict one another in terms of scientific sharpness.


Beaton, A. (2004). Dyslexia, reading, and the brain: a sourcebook of psychological and biological research. Los Angeles, CA: Psychology Press.

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