Analysis of the components of Frequency-Following Response in phonological disorders

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Abstract

Introduction

When identifying the auditory performance of children with phonological disorders, researchers assume that this population has normal peripheral hearing. However, responses at more central levels might be atypical.

Objective

To investigate the effect of phonological disorders on Frequency-Following Responses (FFRs) in the time domain. Methods: Participants were 60 subjects, aged 5 to 8:11 years, divided into two groups: a control group, composed of 30 subjects with normal language skills; and a study group composed of 30 subjects diagnosed with Phonological Disorder (PD). All subjects were tested for Frequency-Following Responses.

Results

In the group of children with PD there was an increase in the latency of all FFR components, with a significant statistical difference for components V (p = 0.015); A (<0.001); C (0.022); F (<0.001); and O (0.001). There was also a reduction in the Slope measure in the group with PD (p = 0.004).

Conclusion

The FFR responses are altered in children with PD. This suggests that children with PD present a disorganization in the neural coding of complex sounds. This could compromise specially the development of linguistic/phonological abilities, which can reflect in daily communication.

Introduction

Speech Sound Disorders (SSDs) are a common pathology in children of preschool and school age; they have various etiologies and can impair speech production at different levels. SSD refers to any combination of difficulties of perception, phonological representation, planning, or motor programming of speech sounds that directly affects their intelligibility [1,2]. Difficulties in speech production affect not only the academic performance of children, but also their communication with their peers and adults [3].

There are different proposals to classify the SSDs [[4], [5], [6], [7]]. The differential diagnosis of these disorders are classified in terms of qualitative analyses of speech errors and underlying cognitive linguistic abilities [4,5]. This classification differentiates the disorder related mainly with the motor aspect of the speech, of the disorder related with the phonological aspect.

Articulation disorder or phonetic disorder is diagnosticated when children present substitutions or distortions of the sound in isolation and in all phonetic contexts. Lateral lisp is an example of the sound's distortion. Phonological disorder (PD) includes children aged 3–8 years 11 months with disorder related to the linguistic organization of speech sounds, i.e. phonemic disorder, which present mainly omissions and substitutions of sounds in isolation and in all phonological contexts [1,2,8].

Measuring the hearing of children with PD is an important aspect of research into the central auditory processing of this population [9]. In this field, auditory evoked potentials help in evaluating the underlying neurophysiology. Studies support the hypothesis that children with PD have normal peripheral hearing, but it is the responses at the central level which are dysfunctional [9,10].

Perception of sound, and especially speech, directly affects a child's developing representation of language and their phonological abilities. Indeed, the perception and proper processing of the acoustic characteristics of dynamic speech – that is, fast temporal changes of this complex signal – are the immediate cues for language development [11].

From this perspective, one test capable of probing this particular aspect of speech processing is the Frequency-Following Response (FFR). The FFR is an auditory evoked potential that provides information on the integrity of the process by which speech sounds are encoded [12,13]. This signal makes it possible to evaluate the auditory processing behind everyday communication skills, and can be applied clinically to understand the fidelity of the input in cases where there is a disorder of language and gauge the associated risks of communication breakdown [12,13]– as in children with hearing loss [14], autism [15], learning disability [16], and phonological disorder [14], among others.

Research to date on this subject has shown that children with PD are less skillful in perceiving speech sounds [17,18]. Further research, analyzing the processing of complex sounds in terms of their neural conduction speed and synchrony may help understand what is going wrong at a behavioral level.

This study aims to investigate how PD affects the major features responses of the Frequency-Following Response in the time domain.

Section snippets

Ethical aspects

This work is an observational, analytical, descriptive, and quantitative cross-sectional study approved by the Research Ethics Committee of the institution of origin (number CAAE 81,117,517.0.0000.5346 and opinion 2,538,043). Those responsible for the subjects were informed about the purpose of the research and signed an informed consent form; participants signed a term of assent. The norms and regulatory guidelines for research with human beings of Resolution 466/12 of the Brazilian National

Results

Statistical analysis produced mean values for the latencies of FFR components for both groups. The latencies of five components (V, A, C, F, and O) in children with PD were significantly different to those in the control group (Fig. 1).

As shown in Fig. 2, the analysis of the slope measurement (ms/μV) indicated a significant difference between the groups (p = 0.004). The mean slope in the group of children with typical phonological acquisition was 0.55, and in the PD group it was 0.38. Mean

Discussion

Together, the findings of this research reveal that children with PD have impaired neural coding of complex sounds. They demonstrated higher temporal values in the FFR evaluation, with greater loss in the transient portion. This suggests that the physiological basis of PD relates to the processing of speech sounds. The findings are consistent with the literature and identify FFR as a reliable and useful tool in evaluating speech disorders [14].

PD is one of the most frequent speech disorders in

Conclusion

The FFR responses are altered in children with Phonological Disorders. This suggests that children with Phonological Disorders present a disorganization in the neural coding of complex sounds. This could compromise specially the development of linguistic/phonological abilities, which can reflect in daily communication.

Competing interests

The authors have declared that no competing interests exist.

Funding

This work was supported by Capes and by the Project “Record of analysis of the auditory evoked potentials of the neonatal period to adolescence”. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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