Reading in Autism Spectrum Disorders: A Literature Review

The increasing number of children with a diagnosis of autism spectrum disorders (ASD) in the school system demands consistent information about the characterization of their reading abilities and the results of different intervention alternatives.

ASD have been the focus of many studies based on several different perspectives. These may vary from genetic and neurologic correlates [1,2,3,4] to social and emotional impact [5,6,7], or educational issues [8,9], family perspectives [10,11] and different intervention proposals [12,13].

The definitions and diagnostic criteria for ASD vary significantly in different studies [14,15], and therefore the conclusions can hardly be compared or accumulated, providing consistent data. The changes in the definition of what should be included within the autism spectrum are just one of the many variations that must be considered [16,17].

The changes implemented in the DSM-5 classification criteria will probably lead to different groups of individuals receiving the diagnosis of ASD [18,19]. Therefore, comparing the results of studies conducted before and after these changes may become even more complicated. It can be assumed that the vast majority of the subjects in studies published until 2015 were diagnosed according to the DSM-IV criteria. However, it is virtually impossible to determine a time frame from which all papers refer to subjects diagnosed according to the DSM-5 criteria.

On the other hand, the broad ASD diagnosis used in the last three decades and the resulting changes in the prevalence of these disorders [20,21] have led to a relevant increase in the number of children diagnosed with ASD in the school system [22].

Regarding reading abilities, studies should describe whether they refer to decoding, such as performance in tasks of word recognition performance, or in a broader sense to word reading comprehension [23]. Children with ASD are often characterized as showing precocious word reading abilities [24], but even though these children may have good decoding skills, comprehension is impaired in most cases.

Considering these aspects, it is relevant to know, at this point, what the recent literature describes about reading abilities in children with ASD and the intervention approaches proposed to improve such skills. Therefore, a literature review was performed with the purpose to address the questions: ‘do children with autism have specific reading impairments?' and ‘do interventions with focus on reading abilities of children with autism have positive results?'.

The purpose of this review was to identify the different profiles of reading abilities of children with ASD and the results of different intervention methods reported in the literature.

A review of the literature was conducted to answer the questions stated above. The Web of Sciences (WoS) and PubMed (PM) databases were searched with the keywords ‘autism' AND ‘read*' with the filter 2010-2015.

Inclusion criteria were: articles published in the last 5 years in peer-reviewed journals indexed in WoS and PM databases with the focus on a description of reading abilities and intervention with individuals with ASD. Review articles were excluded.

In order to obtain an overview of the available information about the characterization of reading abilities and intervention proposals no further criteria were applied in the selection of the reviewed papers.

The first search resulted in 782 articles; 604 in WoS and 178 in PM. The initial analysis aimed to determine which of them focused specifically on both autism and reading. This process resulted in 58 papers in WoS and 32 in PM, a total of 90 articles. They were further analyzed to eliminate duplicates (i.e. articles that were included both in WoS and PM) and publications that did not have enough data; this search resulted in 72 articles that were analyzed according to their content. Among these, 14 articles were reports on literature reviews and were, therefore, excluded. The remaining 58 were divided into two categories: (a) those that described the reading abilities of individuals with ASD (n = 27) and (b) those that reported intervention procedures towards reading development (n = 31) (fig. 1). Further inspection of the articles helped specifying the details of each study, number of participants, measures of literacy skills used, and main conclusions. The results are presented in tables 1 and 2.

It can be observed that the number of participants in each study varied significantly. There are several papers describing studies with a relatively large numbers (59% of them report studies with more than 20 participants), some single-case studies (7%), and 4 studies that did not report the number of subjects (14%). Only 11% of 27 articles described studies with adults.

Regarding the type of measures used to evaluate literacy skills, most studies (44%) focused on single-word reading and text comprehension measures, some (29%) assessed cognitive abilities that are related to reading such as memory and oral language skills, whereas only 2 studies investigated spelling skills in this specific population.

Although the inclusion criteria for the participants in each study are not equivalent across the different papers, thus preventing a true meta-analysis, some tentative conclusions can be drawn.

- Performance in single-word reading tasks is better than reading comprehension.

- The oral language level is associated with reading comprehension.

- Persons with ASD have difficulties with reading comprehension despite eventually good or intact decoding skills.

- There is no confirmation of the weak central coherence hypothesis; it seems that the lack of association between meaning and word recognition is based on other factors.

- Nonverbal social and cognitive abilities are associated with reading comprehension and reading performance.

- Phonological processing seems to be less associated with reading comprehension performance than semantics and syntactic knowledge.

Contrary to what could be observed in articles describing reading abilities of persons with ASD, most of the papers describing intervention procedures had a small number of subjects [22 papers (70%) had 6 participants or less]. In total, these papers reported on 62 children and 5 adults. Six articles reported interventions with more than 18 participants, leading to a total of 143 children in these larger-number studies.

The intervention procedures described can be divided in two groups: those aiming to improve single-word reading and those directed to reading comprehension. Behavioral techniques are the basis for the strategies used in studies that focused on improving single-word reading. The conclusions of these articles imply that not all progress was generalized or maintained after the end of the training programs. The papers reporting programs for enhancing reading comprehension describe different approaches such as computer-assisted instruction, direct instruction, talking about a book, graphic organizers, story maps and prompting. Generalization to other abilities and stability of improvement were reported by these studies.

Three other articles refer to suggestions of intervention strategies such as scaffolding and the use of software designed to improve reading comprehension. These approaches are described as flexible, allowing one-to-one adaptations.

Characteristics of the reading process of persons with ASD were described in 27 articles that included 1,490 individuals. Direct comparisons and associations are prevented by the different inclusion criteria used in the different studies. However, it is possible to propose some preliminary conclusions that should be confirmed by further studies. Reading comprehension seems to be more associated with semantic and syntactic abilities in oral language than with phonological development. Decoding skills, apparently, are not directly associated with reading comprehension, thus leading to better performance in single-word reading tests than in reading comprehension. Nonverbal social and cognitive abilities seem to be associated with reading comprehension and reading performance, especially in what refers to the association of meaning to a word.

Intervention proposals regarding reading abilities of persons with ASD are reported in 31 articles that refer to a total of 210 subjects, including just 5 adults. Not all studies provide the detailed descriptions of the intervention procedures that would be necessary to make comparisons and associations between them. Very few studies include information about the duration of the intervention and the prior training of the therapists. Therefore, any conclusion about the reasons for the reported results would be premature. Better and more stable results are described by the articles that report interventions focused towards the improvement of reading comprehension, as opposed to the studies regarding the use of behavioral techniques to increase single-word reading abilities. However, there is not enough data about the duration of the intervention processes, specific characteristics of the participants before the intervention, training of the therapists in the area, specific material or resources used to allow hypotheses about better or more successful intervention methods.

Literacy acquisition in children and adults with ASD demand further assessment. The large individual variations of the autism spectrum may be reflected in the reading performance of persons with ASD, therefore resulting either in hyperlexia or in different forms of reading deficits. The identification of different reading strategies and specific profiles of abilities and impairments depends on efficient assessment tools that are essential to the design of more efficient intervention procedures.