At the present time, most investigators believe that severe speech disorders in children are the result of some causes during the development of the fetus or at birth (Davies, 2014). The fetus developing in the mother’s womb is exposed to various impacts determined primarily by the influence of external conditions upon the mother. Such effects are described by the model of the instability of development. According to that, it is almost impossible for an external observer to trace little external influences which lead to various inconsistencies of the organs of the left and right sides of the body (one ear can be slightly longer, shorter or longer fingers, etc. (Yeo, Gangestad, & Thoma, 2007).
Such features may be more common in those who have a changed language lateralization (Sandmann et al., 2007). It is supposed that the lateralization of speech is based on deeper mechanisms than those directly associated with speech (Fitch, Miller, & Tallal, 1997). It is reckoned that the left hemisphere is responsible for the fast temporal processing (that is why the centre of speech is located in it), while the right hemisphere is responsible not for temporal but for the spectral constituents of information processing (Shtyrov, 2000; Poeppel, 2003).
The formation of speech zones in a child occurs long before he or she begins to learn to speak (Werker & Tees, 1984). The EEG studies find that the both hemispheres are involved in the speech processing in children, although their role in this process is different (Segalowitz & Cohen, 1989).
Functional neuroimaging studies indicate that the right and left upper temporal gyrases participate in the fundamental analysis of the spectral-temporal modulation regardless of the linguistic content of sounds (Meyer et al., 2005b; Specht et al., 2005). However, the hemispheres are involved in processing to a different extent (Meyer et al., 2005a; Rimol et al., 2005; Scott & Wise, 2004).
Changes in the brain activation during the speech production are detected in children with language learning impairment (Tallal, 2004). The deficit is associated with the speed of the change of acoustic parameters (keys) in the speech signal that makes it difficult to identify the speech production (Tallal & Gaab, 2006; Gordon-Salant et al., 2006). Difficulties associated with the temporal processing of speech information are connected with the asymmetry of the neuronal representations of speech (Bellis, Nicol, & Kraus, 2000). The transcranial magnetic stimulation leads to the improvement of the state of children with linguistic impairments (Pinchuk et al., 2015) and changes in the lateralization of the brain structures: a greater activation of the left hemisphere during the processing of the speech signal. Diffusive tensor imaging tractography is used to describe the asymmetry of an arcuate fasciculus, a pathway that connects the temporal and inferior frontal language cortices (Glasser & Rilling, 1991). It is supposed that the arcuate fasciculus consists of two segments with different functions: one terminates in the posterior superior temporal gyrus (STG), and another terminates in the middle temporal gyrus (MTG). It has turned out that the STG terminations are strongly left-lateralized and overlapped with phonological activations in the left but not the right hemisphere. One may suppose that only the left-hemisphere phonological cortex is directly connected with the frontal lobe via the arcuate fasciculus. The MTG terminations are also strongly left-lateralized overlapping with left-lateralized lexical-semantic activations. Smaller right-hemisphere MTG terminations overlap with right-lateralized prosodic activations.
At the same time, the variety of authors note reduction in the severity of the left-sided asymmetry for one reason or another during the certain speech disorders (Key et al., 2007; Kurth et al., 2018; Naoufal et al., 2016; Wilson & Bishop, 2018). One of the most common causes associated with the growth of speech problems is called left-handedness (Nikolaeva et al., 1995).
Then, there is an evidence that the speech development is influenced by many parameters in the family, for example, the age of parents at birth, the number of children in the family and the order of a child birth. These factors are related to the fact that the older the parents, the more likely it is that the mother carries the child in a more comfortable environment, and immediately after birth, the child receives more support compared to the situation of a child birth in family with very young parents. The more children in the family, the fewer time parents spend communicating with each child. And the first child is more likely to receive maximum attention from adult family members (Nikolaeva, 1998; Nikolaeva, Goncharov, & Borisenkova, 2017). That is why the purpose of this work was to identify the features of lateral preferences and efficiency of the simple sensorimotor response (the go/go paradigm) in children with speech disorders of different severity, taking into account the characteristics of the families in which they were raised.
2. Materials and Methods
The study involved 90 children without any speech disturbances (45 boys and 45 girls, the mean age 5.6 ± 0.8) and 52 children with speech disturbances (28 boys and 24 girls, the mean age 5.8 ± 0.7 years). The children with speech problems were divided into two groups: 26 individuals (13 girls and 13 boys) had only complex speech disturbances (CSD), 26 children had speech disturbances combined with intellectual disturbances (CSD + ID) (13 boys and 13 girls).
The parents of all participants gave informed consent, and child participants provided informed assent.
1) The leading hand identification. To identify the handedness, the child was offered with the most common tests presented in the literature (Vergunov et al., 2018). Each test was performed three times. These included the following tests: the grip of the fingers, the pose of Napoleon and the shoulder test. The choice of the tests was stipulated by their efficiency: it was proved that their results correlate significantly with the results of dichotic testing (Nikolaeva & Brisberg, 2018; Vergunov et al., 2018).
Each result had a numerical value: if the test was performed in the left way—1, right—3, the child changed the method of execution from time to time—2.
2) The evaluation of the efficiency of the simple sensorimotor response (the go/go paradigm) by means of a computer version of the Biofeedback response (Nikolaeva & Borisenkova, 2009).
Circles of different colours were presented to the children on the computer at the same interval. According to the instruction, one should have pressed the enter key as quickly as possible when the circle appeared.
3) The parents of the children filled in the questionnaire in which they reported their age at birth, the level of education and the number of children in the family.
First, regression analysis is carried out to determine which parameters of the parent questionnaire are in favour of the probability of the speech diagnosis in the child. Linear regression analysis was used in this work, which means that a negative beta value indicates an inverse correlation between variables. In this case, R square tells us how much variance in the dependent variable is explained by the independent variable.
Table 1 and Table 2 show that the probability of speech disturbances in the children depends upon the age of the mother at birth and the level of the mother’s education. The younger she is, the more likely speech disorders are; and the higher education, the less likely speech disorders in the child are.
The distribution of the children according to the types of handedness is in Table 3.
Table 1. The influence of the independent variable “the mother’s age” on dependent variables.
Table 2. The influence of the independent variable “the mother’s education” on dependent variables.
Table 3. The distribution of the children according to the types of handedness (%).
Note: *= differences between the groups for p ≤ 0.05 (Student’s criterion).
It shows that the group with speech disturbances and intellectual disability differs from the others in the number of the mixed-handed children and decrease in the number of the left-handed children. The children without any speech disturbances are right- and left-handed at the different probability, while the children with CSD and ID are likely to have mixed-handedness. Our data do not correspond to the idea that speech problems are typical of left-handed children.
Table 4 shows the result of the regression analysis which assesses the influence of independent variable of handedness. It has turned out that that parameter affects the speed of the response in this sample: the more right-handed the child is, the faster he responses in the simple sensorimotor reaction.
Table 5 shows the response speed and the number of omissions during the first and second series of the simple sensorimotor response. The first and second parts are identical. The healthy children perform the first part rather slowly making a small number of mistakes. Having understood the essence of the task, they perform it significantly faster and with a better quality. At the beginning, the children with CSD perform the task faster but with a large number of mistakes, and the quality of the execution has not changed over time. The children with the dual diagnosis are evidently tired by the end, and some have missed almost all the stimuli.
Table 6 and Table 7 show the results of regression analysis in the group of the children without any speech disorders. The influence of the age of the mother and father on the response speed of the child during the second part of the simple sensorimotor reaction has been identified.
In the both cases, the older the parent’s age is, the more (as to the faster execution by the children of the whole group) the response time during the second part is. No similar results have been obtained for the children of the other two groups.
Table 4. The influence of the independent variable “handedness” on dependent variables in the children.
Table 5. Parameters of the simple sensorimotor reaction in the children.
Note: *—(see Table 3) the difference in the task performance by the children of the same group, p ≤ 0.05.
Table 6. The influence of the independent variable “mother’s age” on dependent variables in norm.
Table 7. The influence on the independent variable “father’s age” on dependent variables in norm.
The study tested the hypothesis of the relationship of the speech problems of children with left-handedness and the performance of some high-speed reactions, in particular, the simple sensorimotor response in the paradigm of go/go.
When identifying the preferred hand, we used the tests that correlated with dichotic testing. Each test was repeated (not in a row but with a certain time interval) three times to avoid any incidental execution. Our data indicated that among the children with speech problems, the number of the left-handers was even less than in the group without any speech problems. At the same time, in that group, the number of children with the mixed handedness increases, that is, they perform different tests by different hands. Our data confirm the idea of that central asymmetry (hemispheric asymmetry) is not directly connected to lateral preferences, i.e. peripheral asymmetry.
The obtained data indicate that the likelihood of the diagnosis depends on the mother’s age at birth and her level of education. We may assume that this is due to the following. During the first year of life, the child’s brain is extremely flexible, and therefore, the activity and adequate actions of the mother can lead to the rehabilitation of the processes disturbed during the pregnancy or childbirth. The older the mother, the more carefully she prepares for pregnancy, the more adequately during the pregnancy toward the needs of the child she behaves and prepares for childbirth, and the more attentive she is to the problems of the child immediately after birth. The higher the mother’s education, the more she reads the necessary literature, the oftener in case of some problems in the child she consults specialists and carefully follows the instructions. All this leads to a quality care of the child and decrease the likelihood of speech problems.
In the norm group, we have also found associations between the parents’ age and the response speed of the child’s during the second part of the task. One may suppose that the older the parents, the more attention they pay to the discipline of the child and the arrangement of his/her activity. Therefore, the child is more effective in the second part of the task and more attentive when children from the other two groups are tired.
Children with speech problems are often not left-handed but mixed-handed in comparison with children without any speech disturbances. The probability of a speech diagnosis is connected with the mother’s age at birth and her level of education. The older the mother is at birth, and the higher the level of her education is, the less likelihood of a speech diagnosis. Children without any speech diagnosis are more steady and better at the task performance in the go/go paradigm in comparison with children with the speech diagnosis. The stability of the work during the second part of the task is associated with the age of the parents. The older the father and mother, the more efficient the child works during the second part of the work (when most other children are tired).
All procedures performed in studies involving human participants were in accordance with the ethical standards of the Institutional and/or National Research Committee and with the1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Limitations and Future Directions
One primary limitation of the current investigation was a size of groups of children with speech problems. Perhaps increasing the sample would lead to differences in lateral preferences between children with speech disorders of varying severity. We think that children with more pronounced speech disorders will have more left-sided preferences than children with less pronounced speech disorders.
The second limitation is the used method. We have used go/go paradigm, but we sure that more interesting results could be in go/no-go paradigm since children with more pronounced speech disorders may have unformed inhibitory сontrol. Now we are beginning this type of research.
The present work is supported by the Russian Fundamental Research Fund, project #18-013-00323 А.
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