Relationships between click auditory brainstem response and speech frequency following response with development in infants born preterm

The frequency-following response in late preterm neonates: a pilot study

Introduction

Infants born very early preterm are at high risk of language delays. However, less is known about the consequences of late prematurity. Hence, the aim of the present study is to characterize the neural encoding of speech sounds in late preterm neonates in comparison with those born at term.

Methods

The speech-evoked frequency-following response (FFR) was recorded to a consonant-vowel stimulus /da/ in 36 neonates in three different groups: 12 preterm neonates [mean gestational age (GA) 36.05 weeks], 12 "early term neonates" (mean GA 38.3 weeks), and "late term neonates" (mean GA 41.01 weeks).

Results

From the FFR recordings, a delayed neural response and a weaker stimulus F0 encoding in premature neonates compared to neonates born at term was observed. No differences in the response time onset nor in stimulus F0 encoding were observed between the two groups of neonates born at term. No differences between the three groups were observed in the neural encoding of the stimulus temporal fine structure.

Discussion

These results highlight alterations in the neural encoding of speech sounds related to prematurity, which were present for the stimulus F0 but not for its temporal fine structure.

Developmental Trajectory of the Frequency-Following Response During the First 6 Months of Life

PURPOSE

The aim of the present study is to characterize the maturational changes during the first 6 months of life in the neural encoding of two speech sound features relevant for early language acquisition: the stimulus fundamental frequency (fo), related to stimulus pitch, and the vowel formant composition, particularly F1. The frequency-following response (FFR) was used as a snapshot into the neural encoding of these two stimulus attributes.

METHOD

FFRs to a consonant-vowel stimulus /da/ were retrieved from electroencephalographic recordings in a sample of 80 healthy infants (45 at birth and 35 at the age of 1 month). Thirty-two infants (16 recorded at birth and 16 recorded at 1 month) returned for a second recording at 6 months of age.

RESULTS

Stimulus fo and F1 encoding showed improvements from birth to 6 months of age. Most remarkably, a significant improvement in the F1 neural encoding was observed during the first month of life.

CONCLUSION

Our results highlight the rapid and sustained maturation of the basic neural machinery necessary for the phoneme discrimination ability during the first 6 months of age.

Auditory brainstem response: Key parameters for good-quality recording

Auditory brainstem response (ABR) is widely used in ENT to investigate hearing loss. This test evaluates the response of the ascending auditory pathway, from cochlea to mesencephalon, following auditory stimulation. It provides precise analysis of waves numbered I to V according to location on the auditory pathway, in terms of amplitude, latency and inter-wave interval. Good-quality assessment requires familiarity with the parameters to be used and the factors likely to modify response. We describe the procedure for ABR examination and the recorded responses, with particular attention to factors influencing response to which the examiner must be vigilant. These factors are related to the individual (age, gender, hearing loss, body temperature, drug treatments), transducer (air or bone conduction), stimulation parameters (type, polarity, intensity, calibration, duration, cadence, number of clicks, background noise) and acquisition parameters (analysis window, scale, electrodes). We also briefly describe the clinical applications of this examination.

Neonatal Frequency-Following Responses: A Methodological Framework for Clinical Applications

The frequency-following response (FFR) to periodic complex sounds is a noninvasive scalp-recorded auditory evoked potential that reflects synchronous phase-locked neural activity to the spectrotemporal components of the acoustic signal along the ascending auditory hierarchy. The FFR has gained recent interest in the fields of audiology and auditory cognitive neuroscience, as it has great potential to answer both basic and applied questions about processes involved in sound encoding, language development, and communication. Specifically, it has become a promising tool in neonates, as its study may allow both early identification of future language disorders and the opportunity to leverage brain plasticity during the first 2 years of life, as well as enable early interventions to prevent and/or ameliorate sound and language encoding disorders. Throughout the present review, we summarize the state of the art of the neonatal FFR and, based on our own extensive experience, present methodological approaches to record it in a clinical environment. Overall, the present review is the first one that comprehensively focuses on the neonatal FFRs applications, thus supporting the feasibility to record the FFR during the first days of life and the predictive potential of the neonatal FFR on detecting short- and long-term language abilities and disruptions.

Speech-Evoked Envelope Following Responses in Children and Adults

PURPOSE

Envelope following responses (EFRs) could be useful for objectively evaluating audibility of speech in children who are unable to participate in routine clinical tests. However, relative to adults, the characteristics of EFRs elicited by frequency-specific speech and their utility in predicting audibility in children are unknown.

METHOD

EFRs were elicited by the first (F1) and second and higher formants (F2+) of male-spoken vowels /u/ and /i/ and by fricatives /ʃ/ and /s/ in the token /suʃi/ presented at 15, 35, 55, 65, and 75 dB SPL. The F1, F2+, and fricatives were low-, mid-, and high-frequency dominant, respectively. EFRs were recorded between the vertex and the nape from twenty-three 6- to 17-year-old children and 21 young adults with normal hearing. Sensation levels of stimuli were estimated based on behavioral thresholds.

RESULTS

In children, amplitude decreased with age for /ʃ/-elicited EFRs but remained stable for low- and mid-frequency stimuli. As a group, EFR amplitude and phase coherence did not differ from that of adults. EFR sensitivity (proportion of audible stimuli detected) and specificity (proportion of inaudible stimuli not detected) did not vary between children and adults. Consistent with previous work, EFR sensitivity increased with stimulus frequency and level. The type of statistical indicator used for EFR detection did not influence accuracy in children.

CONCLUSIONS

Adultlike EFRs in 6- to 17-year-old typically developing children suggest mature envelope encoding for low- and mid-frequency stimuli. EFR sensitivity and specificity in children, when considering a wide range of stimulus levels and audibility, are ~77% and ~92%, respectively.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.21136171.

Objective Detection of the Speech Frequency Following Response (sFFR): A Comparison of Two Methods

Speech frequency following responses (sFFRs) are increasingly used in translational auditory research. Statistically-based automated sFFR detection could aid response identification and provide a basis for stopping rules when recording responses in clinical and/or research applications. In this brief report, sFFRs were measured from 18 normal hearing adult listeners in quiet and speech-shaped noise. Two statistically-based automated response detection methods, the F-test and Hotelling’s T² (HT²) test, were compared based on detection accuracy and test time. Similar detection accuracy across statistical tests and conditions was observed, although the HT² test time was less variable. These findings suggest that automated sFFR detection is robust for responses recorded in quiet and speech-shaped noise using either the F-test or HT² test. Future studies evaluating test performance with different stimuli and maskers are warranted to determine if the interchangeability of test performance extends to these conditions.