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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 8  |  Issue : 2  |  Page : 114-118

An in-depth examination of visuospatial functions in a group of Turkish children with dyslexia


1 Uskudar University, Health Sciences Institute, Neuroscience Department, Istanbul, Turkey
2 Uskudar University, Faculty of Humanities and Social Sciences, Psychology Department, Istanbul, Turkey

Date of Submission13-Apr-2021
Date of Decision01-Jul-2021
Date of Acceptance07-Jul-2021
Date of Web Publication13-Aug-2021

Correspondence Address:
Merve Çebi
Altunizade Mh., Haluk Turksoy Sk. 14, 34662 Uskudar, Istanbul
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jnbs.jnbs_16_21

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  Abstract 


Aim: Developmental dyslexia is basically defined as a learning disorder characterized by reading, writing, spelling, and word comprehension difficulties. Phonological deficits in dyslexia are well established in literature, yet, research also indicates some visuospatial difficulties. The aim of this study was to examine the visuospatial functions in Turkish children with dyslexia and to show the interrelationship of visuospatial perception, visual memory, and executive functions. Methods: The sample of this study was composed of 20 children (9 female and 11 male) with developmental dyslexia and 20 age-matched controls (11 female and 9 male). The children in dyslexia group were previously diagnosed as dyslexic according to Diagnostic and Statistical Manual of Mental Disorder-IV criteria in a private rehabilitation center. Rey-Osterreich complex figure test (ROCF), Clock Drawing Test (CDT), and Judgment of Line Orientation test (JLOT) were used to evaluate visuospatial functions of the children. Results: Comparison analyses showed that dyslexia group significantly differed from the control group in all visuospatial test scores (P < 0.05 for all). In addition, a positive correlation was present between JLOT score and ROCF direct copying score, ROCF immediate memory score, ROCF delayed memory score, and CDT score for the dyslexic group (P < 0.05 for all). Conclusion: Our findings confirm the presence of visuospatial problems in dyslexia and highlight the importance of interaction between perceptual and executive processes indicating a more fundamental cognitive deficit.

Keywords: Developmental dyslexia, executive functions, Turkish population, visuospatial functions


How to cite this article:
Mersin Y, Çebi M. An in-depth examination of visuospatial functions in a group of Turkish children with dyslexia. J Neurobehav Sci 2021;8:114-8

How to cite this URL:
Mersin Y, Çebi M. An in-depth examination of visuospatial functions in a group of Turkish children with dyslexia. J Neurobehav Sci [serial online] 2021 [cited 2021 Sep 20];8:114-8. Available from: http://www.jnbsjournal.com/text.asp?2021/8/2/114/323801




  Introduction Top


As being one of the most common neurodevelopmental disorders, developmental dyslexia is defined as a specific learning disability showing itself with difficulty in fluent and accurate reading, writing, spelling, and word comprehension abilities.[1] In addition to language-related deficits, children with dyslexia have problems in a wide range of cognitive domains, such as perception, attention, memory, right-left discrimination, orientation, and motor coordination.[2]

Although developmental dyslexia is primarily characterized by phonological difficulties, research suggests that dyslexic children also suffer from visuospatial deficits.[3] For example, Lipowska et al.[4] reported that dyslexic children had significantly decreased performance on visuospatial functions. Studies investigating attentional processes in dyslexia further revealed the limited sustained attention capacity and difficulties in orienting selective attention.[5] Plenty of studies also demonstrated decreased performance on executive functions in dyslexic children as compared to their age-matched controls.[6] Owing to the fact that executive functions comprise various high-level cognitive abilities as working memory, planning, and reasoning all of which have both verbal and nonverbal components; it would not be surprising to see that a wide range of cognitive domains can be impaired in dyslexia. In fact, many cognitive models have been developed aiming to explain the inseparable pattern of those domains.[7]

Contrary to the good evidence for the impaired visual functions, as mentioned above, it has been also reported that dyslexia may be accompanied by superior visuospatial skills.[8],[9] According to a neurological model, it is hypothesized that dyslexic people have an exceptional brain with a greater symmetry between two hemispheres. Namely, Geschwind-Galaburda hypothesis suggests that dyslexic people tend to overuse their right hemisphere which is thought to be associated with enhanced visuospatial skills.[10] Consistent with this argument, supporting evidence was provided by several studies. According to the general pattern of these findings, individuals with dyslexia perform better in activities that require nonverbal reasoning skills and visuospatial thinking strategies.[11],[12],[13] As a different approach, a recent meta-analysis revealed lower mean scores but greater variability in visuospatial functions in dyslexia.

Given that reading and writing involve a range of visuoperceptual skills such as eye movement control, focusing, and orienting visual attention, it is reasonable to see visual dysfunctions in children with dyslexia. In this study, the primary aim was to make an in-depth investigation for visuospatial functions of children with dyslexia in Turkish population and to shed more light into the conflicting literature.


  Methods Top


The ethics committee approval has been obtained from the Uskudar University non-interventional research ethics committee (2019-400).

Sample

Twenty dyslexic (9 female and 11 male) and 20 age-matched control children (11 female and 9 male) were included in the study. The dyslexic children were recruited from a special education and rehabilitation center who were previously diagnosed as having Specific Learning Disability according to Diagnostic and Statistical Manual of Mental Disorder-IV criteria. All children were native Turkish speakers. To validate the presence/absence of dyslexia, all children's reading and writing skills were assessed by the researcher through a validated learning test included reading, comprehension, writing, copying basic figures, and right-left distinction tasks (2 points for each part, a total of 10 points). Exclusion criteria were determined as any history of a neuropsychiatric disease other than specific learning disability, head trauma, and any sensory deficit. An informed consent was taken from all parents of the participants. The study was approved by the Local Ethical Committee of Uskudar University.

Measurement instruments

Rey–Osterrieth complex figure test

The Rey–Osterrieth complex figure test (ROCF) is a well-known neuropsychological test to measure visuospatial construction and visual memory processes. However, since it requires intact organization, planning, and problem-solving abilities, it has been also regarded as one of most useful methods to evaluate executive functions. ROCF is firstly developed by Rey in 1941 and scoring is standardized by Osterrieth in 1944. The administration of the test basically includes a complex figure to be copied by the participants and followed by an immediate recall, delayed recall, and delayed recognition parts. The original Meyers and Meyers scoring system was used.[14]

Clock drawing test

Clock Drawing Test (CDT) is a widely used cognitive screening test firstly developed for measuring constructional apraxia.[15] In today's clinical settings, however, it is a reliable measure to evaluate visuospatial and executive functions. Although multiple versions and scoring systems of CDT are present in literature, the general application is followed as instructing participants to draw a cycle to be a clock, then to add the numbers in and then set the time to 11.10. In this study, clocks were scored using the Shulman method as being one of the most commonly used scoring systems of CDT. In this method, the score ranges between 0 and 5 where the highest score is 5. Zero point is given if there is no representation of a clock, 1 point is given for a severe disorganization of numbers, 2 point is given for moderate disorganization, 3 point is given for acceptable organization with inaccurate hands, 4 point is given for minor organizational errors, and 5 point is given for well-organized numbers with accurate hands.

Judgment of line orientation test

Judgment of Line Orientation test (JLOT) was developed by Benton et al.[16] to measure the visuospatial abilities. The test includes a spiral booklet consisting of 35 pages with an array of 11 lines, each drawn by 18° of angles. The participants are instructed to match the pair of lines on each page with those 11 lines, by visually estimating their angles. Following the first 5 practice trials, the test consists of 30 trials and the maximum score can be taken from the test is 30.

Data analysis

All statistical analyses were performed using IBM SPSS Statistics (21). Normality of data was assessed using skewness and kurtosis of the distribution. Since all test scores fall within the normal range of distribution (−1.5–+1.5), parametric analyses were selected. Group differences were examined using independent sample t-tests. A Pearson correlation analysis was performed to assess the relationship between ROCF, CDT, and JLOT scores. Effect sizes (Cohen's d or Cramer's V) were reported as appropriate.


  Results Top


Descriptive statistics and group differences for demographic variables are presented in [Table 1].
Table 1: Demographics of the sample

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Accordingly, no significant difference was present between the groups in terms of age, education, and gender (P > 0.05 for all). As expected, the dyslexic group (male: 6.40 ± 1.87) scored significantly lower than the control group (male: 9.65±0.67) on the learning test (t{38}: −7.29, P < 0.001).

When the visuospatial test scores of the groups were compared, the following results were found:

First of all, an independent samples t-test showed that ROCF direct copying score was significantly different between the groups (t{38}: −3.52, P < 0.01). Accordingly, the mean ROCF direct copying score of the dyslexia group (male: 30.42 ± 6.59) was significantly lower than the control group (male: 35.65 ± 0.69). Similarly, ROCF immediate memory score and the ROCF delayed recall score of the dyslexia group were significantly lower than the control group (t{38}: −3.26, P < 0.01; t{38}: −2.85, P < 0.01, respectively). Finally, the true recognition score was significantly higher for the control group as compared to dyslexia (t{38}: −3,671, P < 0.001); and false recognition group was significantly lower (t{38}: 2.087, P < 0.05). CDT performance of the children was compared by an independent t-test and it was found that dyslexic group had significantly lower score on CDT as compared to the control group (t{38}: −5.17, P < 0.01). Finally, JLOT score of the groups was compared. An independent samples t-test showed that dyslexic group had significantly lower performance on JLOT as compared to the control participants (t{38}: −3.51, P < 0.01).

The visuospatial test scores of the groups are presented in [Table 2].
Table 2: Visuospatial test scores for groups

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Pearson correlation analyses showed a positive correlation between JLOT score and ROCF direct copying, ROCF immediate memory, ROCF delayed memory, and CDT score for the dyslexic group (r = 0.58, P < 0.05; r = 0.46, P < 0.05; r = 0.48, P < 0.05; r = 0.61, P < 0.05, respectively). CDT score was not found to be significantly correlated with ROCF scores (P > 0.05 for all). For the control group, however, JLOT score was not found to be significantly correlated with ROCF and CDT scores (P > 0.05 for all). A positive correlation was present between CDT score and ROCF direct copying (r = 0.46, P < 0.05).


  Discussion Top


To our knowledge, this was the first study to examine all aspects of visuospatial functions of children with dyslexia in a Turkish sample. The main findings of the present study revealed that children with dyslexia suffered from an overall visuospatial difficulty as compared to healthy children. These findings are consistent with the existing literature, despite the presence of some parsimonious evidence suggesting the opposite. Indeed, numerous studies have discussed the origins of visual deficits in dyslexia. While it is possible to account the deficit for a problem in visual neural networks, strong evidence suggests that central executive domain might be the real responsible. Many studies already reported the altered executive functioning in dyslexia.[17],[18]

First of all, the ROCF is one of the most classical and widely accepted visual tasks measuring visuospatial organization as well as visual memory in healthy and clinical populations. As expected, dyslexic children in this study were significantly more impaired than healthy controls on copying, immediate recall, and delayed recall. Their recognition was also worse. The ROCF findings are in keeping with most of the other studies, while source of the poorer performance is still under discussion. Similar to our study, Lipowska et al.[4] used ROCF to assess visual deficits in 129 dyslexic children and reported that they display difficulty in visuospatial processes, tend to miss the details, and either forget or misplace the elements.

Considering the visuospatial skills, the JLOT appears to be one of the most sensitive measurement tools. Indeed, in many studies, a strong association has been shown between right posterior parietal lesions and impaired performance on JLOT.[19] Therefore, our findings support the notion that dyslexia might not be a core phonological deficit. Particularly, considering the working memory as a part of executive functions, missing the details on ROCF, and more failing in the difficult items on JLOT provide evidence for impaired visual attention in dyslexia. A recent fMRI study reported the activation of dorsolateral prefrontal areas in addition to visuospatial areas, especially during performing difficult JLOT items.[20] This finding suggests the involvement of an executive control as visual tasks get complicated. Bacon et al.[21] also suggested a central executive deficit by using the Corsi block task. They showed that dyslexic group had difficulty in adapting visual strategies for the reverse order, which points out an executive dysfunction.

Finally, CDT is considered to be one of the most reliable measures for executive control, despite a wide range of cognitive skills is required to perform the task. In our study, the lower performance on CDT in dyslexic children implies for a difficulty in orienting visual attention. Notably, it was observed that the dyslexic group tended to use one side of the circle (right or left) and neglected the other side in drawing the clock. This indicates that children with dyslexia have deficits in their right hemispheres, which play a role in directing attention to space. Similar to our finding, Eden et al.[22] reported that children with dyslexia tended to put the numbers toward the right face of the clock.

Our findings are in line with the well-documented relationship between visuospatial perception, visual memory, and executive functions. Given its broad definition, executive functions already include visual attention and constructional processes and in turn have an interrelationship with visual memory. In the previously mentioned study, Lipowska et al. reported a strong correlation between CDT and ROCF scores.[4] In this study, we showed a strong correlation between JLOT, ROCF recall, and CDT scores for the dyslexic group indicating a parallel reduction in all visual test performances. Therefore, this finding suggests a more distributed cognitive weakness in dyslexia.

Regarding this discussion, it is worth to underline a recent theory suggesting impaired function of magnocellular visual pathway in dyslexia. As magnocellular pathway is more specialized for directing visual attention, researchers relate the poor reading ability of dyslexic people with the slower information processing of magnocellular cortical pathways leading to reduced visuospatial perceptual speed.[23] Although a wealth of controversies about the magnocellular deficit theory still remains, it is quite reasonable to assume that phonological problems are derived from a fundamental visual perceptual deficit in dyslexia rather than to think the vice versa.

This study had some limitations to be addressed. The first limitation is the relatively small sample size, since it was difficult to recruit children with developmental dyslexia without any other comorbidity. Second, verbal and performance intelligence quotients of the children were not measured.

Therefore, if intellectual abilities could be controlled as a confounding variable, the group effect would be better clarified. Last but not the least, the present study solely provides behavioral evidence. Future research combining neuropsychological tests with functional neuroimaging data as well as the usage of machine learning methods for group classifications would be valuable so as to investigate the activity of related neural networks as well as their interactions.


  Conclusion Top


The findings of this study suggest that in addition to phonological deficits of dyslexia, there is a multifactorial cognitive impairment including visuospatial perception, executive functions, and visual memory. Therefore, cognitive rehabilitation programs for early childhood dyslexia can be planned to enhance their visual functions. Further studies exploring neural networks are also required to shed more light into the emergence of cognitive deficits in dyslexia.

Patient informed consent

Patient informed consent was obtained.

Ethics committee approval

The ethics committee approval has been obtained from the Uskudar University non-interventional research ethics committee (2019-400).

Financial support and sponsorship

No funding was received.

Conflicts of interest

There are no conflict of interest to declare.

Author contribution subject and rate

  • Yeşim Mersin (50%): collected and analyzed the data
  • Merve Çebi (50%): designed the research and wrote the whole manuscript.


Acknowledgments

The authors thank all participating children and their families



 
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