**5. Time duration analysis**

**Figure 6.** Evaluation of the feature analysis for cases. The correct classification is shown in blue (or at a higher position), and incorrect classification is shown in red (or at a lower position) or in grayscale. Samples with a more successful classification are at a higher position in the upper graph. The histogram represents the distributions of the correct classifications of controls and incorrect classifications of cases (more classifications in the right) in the middle graph. The boxplots show significant differences between the correct (the left boxplot) and incorrect classifications (the right

boxplot) in the bottom chart.

**Feature analysis: evaluation of percent success rate**

14 Learning Disabilities - An International Perspective

**Age category Classification of participants Success rate [%]**

H-CH (1) 44 41 93.18 **∑(1 + 2) 98 95 96.94**

**Table 4.** Evaluation of percent success rate of method based on the acoustic features. The final success rate is in bold.

**Group Correct Wrong** All P\_SLI (2) 54 0 100.00

> The children with language impairment, regardless of the severity, had reduced processing and response speeds on a range of tasks. Generally, it can be assumed that analogies to this issue will be related to questions about the average duration of spoken utterances.

> The procedure of the experiment was as follows. The average duration was calculated for all words and all participants. Obtained values were divided into two groups. The first group contained the values from controls, and the second group contained the values from cases. Both groups were compared with an average duration of each word.

> The evaluation of the time duration is displayed in **Figure 7**. The *x*-axis represents all words, and the *y*-axis represents time (s). The time values for cases are displayed in blue (the lower curve), and the time values for controls are displayed in red (the upper curve) or grayscale. **Table 5** illustrates the average duration of all words for both groups. The result is an average duration for cases that is approximately 27.56% higher than that of controls.

> The table and figure show that the children with SLI had a longer duration of words than the typical children. This experiment verified the hypotheses about the speed of processing and response for a range of tasks.

**Figure 7.** Average duration of words at controls and cases. The time values for cases are displayed in blue (the lower curve), and the time values for controls are displayed in red (the upper curve) or grayscale.


**Table 5.** The success of classification. The final percent rate of difference of the time duration between controls and cases in bold.

### **6. Formant analysis**

The ability to produce and perceive speech originates in certain parts of the human brain. SLI is described as a neurological disorder of the brain [20–22]. Formants are normally defined as the spectral peaks of the sound spectrum of the voice (or the concentration of acoustic energy in the vicinity of a specific frequency). In speech frequency, there are multiple instances of such peaks (or formants) and each of them is found at a different frequency. A physical dimension of the formants as a classification parameter is based on the presence of an acoustic energy across the speech spectrum, that is, the formants are affected by the movement of the articulatory system based on the human brain activity. This hidden relationship of formants can be used for classifying children with SLI. One of the conditions for using formants as classification parameters is the ability to calculate formants with a minimal error rate. Originally, the extraction of formant frequencies from speech signals was done by using PRAAT [33] acoustic analysis software. However, since the use of the PRAAT software produced formant classification errors in the course of the analysis, the results obtained using this approach could not be treated as relevant (specifically the use of Burg's algorithm to compute formants with method: *"To Formants (burg)…"*). To acquire suitable formants (formants with a minimal error rate), FORANA, a software tool, was developed [34].

Formants provide information about the vowels in the frequency spectrum when the two conditions are fulfilled, that is, the formants must be correctly classified and the utterance must be properly spoken. Especially if we put the first two formants (F1 and F2) into context with each other, we get what we refer to as vocalic triangle. The triangle divides individual vowels into three different categories, depending on the position of the given formant. The first category is represented by the vowel *"a"*, the second category is represented by *"e"* and *"i"* and the third category is represented by *"o"* and *"u"* for the Czech speech. The main idea of using formants and vocalic triangle is to verify the correctness of the spoken utterances by using precisely defined vowel locations in the vocalic triangle. Participants from cases (children with SLI) have problems with correctly speaking difficult utterances or words compared with participants from controls (typically children). Formant analysis clearly verifies whether the vowels are correctly pronounced. Otherwise, if there are any errors in the analyzed vowel, there is a shift in the frequency spectrum. This observation means that the speakers have articulatory organs in a bad position and the distribution of articulatory cavities is the wrong shape for forming vowels. This positioning leads to the malfunction of speech control in the brain, which can be used to classify and identify children with SLI. More about this issue can be found in prior studies [35–38].

**6. Formant analysis**

in bold.

**Word duration: controls vs. cases**

1 Controls 0.54

16 Learning Disabilities - An International Perspective

The ability to produce and perceive speech originates in certain parts of the human brain. SLI is described as a neurological disorder of the brain [20–22]. Formants are normally defined as the spectral peaks of the sound spectrum of the voice (or the concentration of acoustic energy in the vicinity of a specific frequency). In speech frequency, there are multiple instances of such peaks (or formants) and each of them is found at a different frequency. A physical dimension of the formants as a classification parameter is based on the presence of an acoustic energy across the speech spectrum, that is, the formants are affected by the movement of the articulatory system based on the human brain activity. This hidden relationship of formants can be used for classifying children with SLI. One of the conditions for using formants as classification parameters is the ability to calculate formants with a minimal error rate. Originally, the extraction of formant frequencies from speech signals was done by using PRAAT [33] acoustic analysis software. However, since the use of the PRAAT software produced formant classification errors in the course of the analysis, the results obtained using this approach could not be treated as relevant (specifically the use of Burg's algorithm to compute formants with method: *"To Formants (burg)…"*). To acquire suitable formants (formants with a minimal

**Table 5.** The success of classification. The final percent rate of difference of the time duration between controls and cases

**ID Group Average duration [s] Comparison Difference [%]**

2 Cases 0.69 2 vs. 1 **27.51**

The percentage rates of correct classification of the method used to distinguish the two groups.

Formants provide information about the vowels in the frequency spectrum when the two conditions are fulfilled, that is, the formants must be correctly classified and the utterance must be properly spoken. Especially if we put the first two formants (F1 and F2) into context with each other, we get what we refer to as vocalic triangle. The triangle divides individual vowels into three different categories, depending on the position of the given formant. The first category is represented by the vowel *"a"*, the second category is represented by *"e"* and *"i"* and the third category is represented by *"o"* and *"u"* for the Czech speech. The main idea of using formants and vocalic triangle is to verify the correctness of the spoken utterances by using precisely defined vowel locations in the vocalic triangle. Participants from cases (children with SLI) have problems with correctly speaking difficult utterances or words compared with participants from controls (typically children). Formant analysis clearly verifies whether the vowels are correctly pronounced. Otherwise, if there are any errors in the analyzed vowel, there is a shift in the frequency spectrum. This observation means that the speakers have articulatory organs in a bad position and the distribution of articulatory cavities is the wrong shape for forming vowels. This positioning leads to the malfunction of speech control in the brain, which can be used to classify and identify children with SLI. More about this issue can be found in prior studies [35–38].

error rate), FORANA, a software tool, was developed [34].

**Figure 8.** Vocalic triangles, upper chart, obtained from child with SLI and vocalic triangles, lower chart, obtained from typically child. Both children were at age 10 years.

This experiment is based on the comparison of two different vocalic triangles for all tested individuals. Speech signal analysis was performed for the following two types of participants. Participants were chosen randomly, and both were at the same age. One was from cases (from the SLI-CH II group), and the other was from controls (from group H-CH). Both participants were analyzed by using the same utterances, namely isolated vowels and word "*různobarevný*" (in en: "*varicoloured*"). This particular word contains all vowels, and it therefore makes it possible for us to make a comparison between the different vowels. The upper chart (part A in **Figure 8**) represents participant from cases, and the bottom chart (part B in **Figure 8**) represents participant from controls. Both charts show two vocalic triangles, a blue (or the one on the left) one for the isolated vowels and a red (or the one on the right) one for the vowels in *"různobarevný"* (in en: *"varicoloured"*). The vocalic triangle is presented for simple speech, that is, for isolated vowels; on the other side, the vocalic triangle is absent for more complex speech, that is, for word "různobarevný" (in en: "varicoloured"). The arrows point to the positions where the vowels should be located under ideal circumstances. This corresponds to the situation in the upper chart (part A in **Figure 8**). This particular example can be used to demonstrate a relationship between the complexity of the words being spoken and the shift in the speech sound frequency spectrum in children with specific language impairments. Bottom chart (part B in **Figure 8**) shows the vocalic triangles obtained from participant from controls; the triangle is present for both situations (simple speech and speech that is more complex).


Twenty-one participants were classified into the correct class, controls vs. cases, one participant was classified into the wrong class and two participants were not classified (based on real example, two recordings were analyzed for one participant; the result obtained from the first recording was determined as controls, and the result obtained from the second recording was determined as controls).

**Table 6.** Success rate of method is based on the vocalic triangle classification.

The experiment only involved participants from cases. A total of 24 participants were randomly selected with 54 recordings. Some participants had one speech recording on record, and some had several. The whole experiment was based on the comparison of the two different vocalic triangles, namely isolated vowels (*"a", "e", "i", "o", "u"*) and multisyllabic word *"různobarevný"* (in en: *"varicoloured"*). A prerequisite of this method is the difference in the shape of the vocalic triangles, that is, for isolated vowels, it has the correct shape, while the shape for multisyllabic word is misshapen. The three possible classifications were obtained, that is, correct, wrong and not classified. The results obtained from the vocalic triangle classification method are shown in **Table 6**.
