Effects of a developmental dyslexia remediation protocol based on the training of audio-phonological cognitive processes in dyslexic children with high intellectual potential: study protocol for a multiple-baseline single-case experimental design

Studies on learning disabilities in children with high intellectual potential (HIP) are underrepresented in the scientific literature, although their number has been increasing gradually over the years. However, the high prevalence of HIP children in the school-age population, approximately 2.3% of French school children [1], and the high rate of comorbidity with learning disabilities has increased the demand for speech and language therapy care. Some studies claim that the prevalence of HIP among dyslexic readers is higher than the prevalence of HIP among normal readers. For instance, Toffalini [2] and al. reported a proportion of 5.06% HIP children among dyslexic readers compared to 1.82% HIP children among normal readers. Pradeille [3] indicates a proportion of 10% HIP children within a sample of 209 dyslexic readers. According to Winner [4], dyslexia is the most frequent developmental disorder associated with HIP. However, the diagnosis and rehabilitation of children with a high intellectual potential and developmental dyslexia (HIP-DD) remains difficult due to the co-existence of both cognitive features.

Individuals with high intellectual potential represent a small percentage of the population whose intelligence quotient (IQ) is higher than 130 on the Weschler intelligence scale, Wisc IV [5]. However, some authors question the total IQ measure as the only diagnostic tool for these individuals [5‐10]. Indeed, the diagnosis of high intellectual potential cannot be limited to the measurement of their IQ, but must also consider the specific characteristics of their brain’s operation. Besides the high IQ score, an HIP child has specific intellectual characteristics, as well as a different cognitive organization [11, 12]. Some authors discuss the presence of specific psycho-affective characteristics in HIP individuals, but there is no consensus on this topic in the literature. Despite this, there are objectively detectable differences on a purely cerebral level. The cerebral particularities of HIP children have been identified in many neuroimaging studies. An increased transmission of information between the left temporal and left central regions, between the left temporal and left parietal regions, and between the left central and left parietal regions has been demonstrated in individuals with HIP compared to neurotypical individuals during a scientific hypothesis generation task [13]. Thus, there appears to be a different distribution of brain activity in HIP individuals, who seem to more efficiently distribute the cognitive resources needed for hypothesis generation [13]. The brains of HIP individuals also differ from neurotypical ones in their strength; there is greater activation of certain brain areas in HIP children during certain cognitive tasks, especially in the prefrontal cortex, the anterior cingulate cortex, and the posterior parietal cortex [14]. In 2021, Christoph Fraenz demonstrated that the strength of neuronal connections at rest between frontal and parietal regions correlates with performance in reasoning tests such as those used in IQ tests [15]. Thus, a higher IQ may mean better quality connections between frontal and parietal regions. Differences in connection between the two hemispheres of the brain were also found in the 2007 study by Luders et al. who found a link between corpus callosum thickness and intelligence scores in adulthood [16]. In addition, numerous studies demonstrate a brain volume proportional to IQ, with a consistent increase in volume as IQ increases [17]. Regarding possible emotional and psycho-affective particularities, there is no consensus in the scientific literature.

Concerning developmental dyslexia (DD), the DSM-V defines it as a severe and persistent disorder that affects reading acquisition, despite a normal intelligence and the absence of neurological or psychiatric pathology, visual and auditory sensory deficits, or socio-educational deficiencies [18]. Developmental dyslexia is a neurodevelopmental disorder that disturbs the automatization of associations between written linguistic units (graphemes) and oral linguistic units (phonemes) [19]. This alphabetic decoding disorder leads to an identification disorder of written words, which can have severe consequences on school learning, on daily and professional life, and on the self-esteem of the patients. The phonological causal hypothesis is currently the most widespread [20]. However, over the last few years, the single cause theory has been criticized in favor of a multi-factorial causal theory [21‐23] involving multiple underlying cognitive deficits (UCD) [24, 25]. The two types of UCD most described in the literature are audio-phonological deficits and visuo-attentional deficits. In 2019, Ziegler et al. [26] acknowledged the multifactorial nature of dyslexia but concluded that phonological deficits tended to prevail over the other types of UCD. According to Saksida's study [20], in the non-HIP dyslexic population, the most frequent UCD concerns phonological awareness (PA) and rapid automatized naming (RAN). PA is a cognitive process that allows individuals to manipulate language syllables, rhymes, or phonemes [27]. In the dyslexic population, it is mainly the manipulation of phonemes that is affected [28] and is thus referred to as phonemic awareness. RAN refers to the rapid retrieval of phonological information from a word presented as a picture, followed by its immediate oral production. RAN and phonological awareness are two distinct phonological processes directly involved in dyslexia [29]. In a more recent study [30], phonological awareness was identified as a predictor of word decoding skills and RAN as a predictor of word recognition and reading comprehension. Other researchers agree that the phonological processing deficit in dyslexia is the result of a more fundamental deficit in the perceptual processing of auditory information. Indeed, some dyslexic readers have an allophonic perception of speech sounds which leads to a poor discrimination of acoustic differences, a perceptual deficit in phoneme categorization and consequently a phonological processing deficit. Increased sensitivity to phonemic contrasts between variants of the same phoneme seems to lead to disorders in phoneme categorical perception (CP) [31]. Thus, instead of perceiving sounds in phonemic units, dyslexic readers could perceive them in allophonic units [32].

Concerning HIP-DD diagnosis, the DSM-V reports that compensatory strategies implemented by HIP-DD children may delay the onset of reading disorders and therefore prevent early diagnosis. Indeed, the cognitive profile of HIP-DD children seems to differ from that of HIP-normal readers, but also from that of dyslexic children without HIP [33, 34]. Their double cognitive particularity, HIP and dyslexia, often complicates the interpretation of scores obtained on IQ subtests, but also the interpretation of scores obtained on diagnostic tasks for DD. HIP-DD children, because of their reading difficulties, rarely reach the cut-off score of 130 IQ points determined as an indicator of high intellectual potential. For some authors, it is even meaningless to calculate an IQ when the patient has dyslexia [33]. Similarly, because of their HIP, dyslexic readers sometimes obtain non-pathological scores on the reading and writing tasks used to diagnose dyslexia [35, 36]. The diagnosis of HIP DD children is made difficult by reading and spelling performances that fall between the performances of non-HIP normo-readers and the performances of non-dyslexic HIP [35]. The diagnosis of dyslexia in an HIP child is therefore delayed because of performances that are considered normal by some tests that were not standardized on an HIP population. With their protective factors, HIP children should score above average on some subtests. Thus, when their scores are only average, it often means that their results are actually below what should be expected of them. Several authors describe a phenomenon of "discrepancy" [37, 38], in which dyslexia overshadows HIP and HIP masks dyslexia [33]. So, the cognitive profile of HIP DD is characterized both by phonological deficits related to dyslexia and by often higher verbal and visual-spatial working memory skills, as well as richer vocabulary and grammar than non-HIP readers [34]. Moreover, the study conducted by Van Viersen [35] asserts that the HIP-DD children's UCD primarily concern RAN and phonological awareness. Targeted interventions on RAN or phonological awareness significantly improve reading skills in dyslexic populations [39]. We also know that phonological awareness training combined with print knowledge is more effective than phonological awareness training alone [40, 41]. The effects of RAN training on reading performances have also been proven in a study published in 2019 [42]. Also, an intervention on categorical perception of French phonemes has shown effects on phonemic awareness and reading skills in dyslexic readers [43]. However, remediation methods focused on PA, RAN and CP have not been tested on the specific population of HIP-DD children. Given the large number of differences in brain function between HIP and non-HIP, it would therefore seem appropriate to conduct more studies to improve the therapy of these "twice-exceptional" children. This term refers to individuals with a double particularity; on the one hand, a high intellectual potential, and on the other hand, a comorbid learning disability [44]. Thus, the purpose of this study is to present a single-case experimental protocol proposing an intervention on phonological processes in dyslexic children with high intellectual potential. The detailed methods of this intervention are derived from an ongoing group study evaluating the effectiveness of a UCD intervention on dyslexic children aged 8 to 13 years [45]. The training programs described in this protocol are tailored to the cognitive profile of each participant and can therefore be applied to HIP-DD children.

This paper presents an experimental protocol for a single-case multiple-baseline design across 4 participants to observe the effects of an intensive audio-phonological training program on the phonological and reading skills of four children with developmental dyslexia and HIP (HIP-DD). The lack of data regarding the remediation of HIP-DD children forces clinicians to use non-specific remediation methods for twice-exceptional children, which are often not very effective.

The results of this study, if successful, will provide a partial answer to this problem. Furthermore, the link between the single-case design and Evidence Based Practice (EBP) [72], which is widely used by clinicians in their daily practice, opens a real gateway between the research and clinical worlds. The American Speech-Language-Hearing Association has also recommended the use of EBP in interventions for communication disorders since 2005 [73]. Most speech and language therapists are therefore familiar with the use of baselines and with the within-subject control approach. Thus, if the results are consistent, they can be directly interpreted by clinicians, and the data regarding remediation can be easily adapted and quickly applied in their practice.

Furthermore, small sample studies allow for a detailed qualitative analysis and are a good alternative to group studies when the target population is rare. The single-case design allows a more exhaustive qualitative analysis of the anamnesis and screening data in order to better understand the cognitive language profile of each participant. The staggered configuration of the participants' timeline allows a control of temporal and session number variables. Despite the thorough attention paid to respecting scientific criteria that ensure the highest reliability of the outcomes, some limitations were found when preparing this protocol. To avoid cognitive overload and participant dropout, an intervention targeting all underlying cognitive deficits was excluded. First, the time required for a measurement session would be excessive, as would the total duration of the protocol. Also, since phonological theory is still the most widely believed causal hypothesis of developmental dyslexia [66], an intervention that only targets the audio-phonological processes involved in dyslexia was selected. Thus, only RAN and CP were measured and offered as training in this study. A similar protocol focusing on visual-attentional aspects could be considered at a later stage. If the results are conclusive, a remediation protocol focusing on all underlying cognitive deficits should be tested in a larger sample study without the constraints of repeated measurements induced by the SCED.

In conclusion, the population of HIP-DD patients represents a significant part of speech and language therapists' patient base but remains underrepresented in the scientific literature. Consequently, the therapeutic approaches for these patients are still not sufficiently structured and validated. The results of this study should constitute a starting point for further progress in the remediation of written language disorders in children with HIP, both in the clinical and the research fields.