Encoding Of Speech Sounds Research Articles

Exposure to bilingual or monolingual maternal speech during pregnancy affects the neurophysiological encoding of speech sounds in neonates differently.

Exposure to maternal speech during the prenatal period shapes speech perception and linguistic preferences, allowing neonates to recognize stories heard frequently in utero and demonstrating an enhanced preference for their mother's voice and native language. Yet, with a high prevalence of bilingualism worldwide, it remains an open question whether monolingual or bilingual maternal speech during pregnancy influence differently the fetus' neural mechanisms underlying speech sound encoding. In the present study, the frequency-following response (FFR), an auditory evoked potential that reflects the complex spectrotemporal dynamics of speech sounds, was recorded to a two-vowel /oa/ stimulus in a sample of 129 healthy term neonates within 1 to 3 days after birth. Newborns were divided into two groups according to maternal language usage during the last trimester of gestation (monolingual; bilingual). Spectral amplitudes and spectral signal-to-noise ratios (SNR) at the stimulus fundamental (F0) and first formant (F1) frequencies of each vowel were, respectively, taken as measures of pitch and formant structure neural encoding. Our results reveal that while spectral amplitudes at F0 did not differ between groups, neonates from bilingual mothers exhibited a lower spectral SNR. Additionally, monolingually exposed neonates exhibited a higher spectral amplitude and SNR at F1 frequencies. We interpret our results under the consideration that bilingual maternal speech, as compared to monolingual, is characterized by a greater complexity in the speech sound signal, rendering newborns from bilingual mothers more sensitive to a wider range of speech frequencies without generating a particularly strong response at any of them. Our results contribute to an expanding body of research indicating the influence of prenatal experiences on language acquisition and underscore the necessity of including prenatal language exposure in developmental studies on language acquisition, a variable often overlooked yet capable of influencing research outcomes.

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

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. 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). 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. 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.

Assessing the role of auditory access in infancy

Even with the widespread adoption of newborn hearing screening and Early Hearing Detection and Intervention systems, infants who are hard-of-hearing (IHH) remain at increased risk for poor or delayed development of auditory and speech perception skills. Speech perception is positively correlated with better auditory development on functional auditory skills and a variety of language outcomes. However, clinical utilization of speech perception tests has not been broadly accepted. One clinically viable tool to assess speech perception during infancy is our electroencephalography (EEG) procedure, which has been validated as an objective measure of speech discrimination. However, we have not examined the development of infant speech perception among IHH and infants with normal hearing (INH). Perceptual attunement—or “narrowing”—is a model of perceptual learning that posits that perceptual abilities are shaped by environmental experiences over the first year of life. Here, we describe our adapted EEG methods to examine the development of infant speech perception to study periods of perceptual attunement between IHH and INH. Preliminary findings confirm that at 3 months of age, infants demonstrate neural encoding of native and non-native speech sounds, and at 6 months of age results suggest a decrease in non-native speech sound encoding.

Encoding of speech sounds with frequency-following response in infants with Congenital Zika Syndrome: A case-controlled study

Encoding of speech sounds with frequency-following response in infants with Congenital Zika Syndrome: A case-controlled study

Brain encoding of speech sounds in newborns with complex congenital heart disease: Towards the identification of early biomarkers of language delay

Brain encoding of speech sounds in newborns with complex congenital heart disease: Towards the identification of early biomarkers of language delay

Brain encoding of speech sounds in newborns with complex congenital heart disease: Towards the identification of early biomarkers of language delay

Brain encoding of speech sounds in newborns with complex congenital heart disease: Towards the identification of early biomarkers of language delay

Development of speech-sound encoding in bilingual infants and children

Development of speech-sound encoding in bilingual infants and children

N°222 – Analysis of brain encoding of speech sounds in newborns with complex congenital heart disease: Towards the identification of early language delay biomarkers

N°222 – Analysis of brain encoding of speech sounds in newborns with complex congenital heart disease: Towards the identification of early language delay biomarkers

The effect of child development on the components of the Frequency Following Response: Child development and the Frequency Following Response.

During childhood, neuronal modifications occur so that typical childhood communicative development occurs. This work aims to contribute to the understanding of differences in the speech encoding of infants and school-age children by assessing the effects of child development, in different phases of early childhood, on the encoding of speech sounds. There were 98 subjects of both sexes, aged from 1 day to 8 years and 9 months who participated in the study. All subjects underwent a Frequency Following Response (FFR) assessment. A regression and linear correlation showed the effects of age in the FFR components, i.e., significant decrease in the latency and increased amplitude of all FFR waves with age. An increase in the slope measure was also observed. Younger infants require more time and show less robust responses when encoding speech than their older counterparts, which were shown to have more stable and well-organized FFR responses.

Neural Processing of Speech Sounds in ASD and First-Degree Relatives

Efficient neural encoding of sound plays a critical role in speech and language, and when impaired, may have reverberating effects on communication skills. This study investigated disruptions to neural processing of temporal and spectral properties of speech in individuals with ASD and their parents and found evidence of inefficient temporal encoding of speech sounds in both groups. The ASD group further demonstrated less robust neural representation of spectral properties of speech sounds. Associations between neural processing of speech sounds and language-related abilities were evident in both groups. Parent–child associations were also detected in neural pitch processing. Together, results suggest that atypical neural processing of speech sounds is a heritable ingredient contributing to the ASD language phenotype.

Deficient neural encoding of speech sounds in term neonates born after fetal growth restriction.

Infants born after fetal growth restriction (FGR)-an obstetric condition defined as the failure to achieve the genetic growth potential-are prone to neurodevelopmental delays, with language being one of the major affected areas. Yet, while verbal comprehension and expressive language impairments have been observed in FGR infants, children and even adults, specific related impairments at birth, such as in the ability to encode the sounds of speech, necessary for language acquisition, remain to be disclosed. Here, we used the frequency-following response (FFR), a brain potential correlate of the neural phase locking to complex auditory stimuli, to explore the encoding of speech sounds in FGR neonates. Fifty-three neonates born with FGR and 48 controls born with weight adequate-for-gestational age (AGA) were recruited. The FFR was recorded to the consonant-vowel stimulus (/da/) during sleep and quantified as the spectral amplitude to the fundamental frequency of the syllable and its signal-to-noise ratio (SNR). The outcome was available in 45 AGA and 51 FGR neonates, yielding no differences for spectral amplitudes. However, SNR was strongly attenuated in the FGR group compared to the AGA group at the vowel region of the stimulus. These findings suggest that FGR population present a deficit in the neural pitch tracking of speech sounds already present at birth. Our results pave the way for future research on the potential clinical use of the FFR in this population, so that if confirmed, a disrupted FFR recorded at birth may help deriving FGR neonates at risk for postnatal follow-ups.

Subcortical measures of individual tolerance to background noise and sensitivity to speech distortions induced by noise-reduction processing

Listeners with sensorineural hearing loss have significant difficulty understanding speech in noisy environments. Thus, current digital hearing aids employ noise-reduction (NR) algorithms to suppress background noise. Unfortunately, the NR algorithms distort some speech cues. Though considerable variability exists in hearing-aid users’ reactions to these conflicting effects, little is known about the neural underpinnings contributing to the variance in perceptual outcomes with the addition of noise and the use of NR processing. Recently, we documented that neuroimaging-based measures of cortical responses can predict individual speech-in-noise perception benefits (or lack thereof) from NR processing. Here, we describe novel objective subcortical measures for quantifying individual noise tolerance and individual sensitivity to speech-cue distortions. Preliminary results show that the effect of adding noise and introducing NR processing on brainstem responses varies considerably across individuals. Because the brainstem responses are relatively unaffected by cognitive processes like selective attention, these preliminary results suggest an independent “bottom-up” contribution to individual variations in NR benefits. We will also discuss how the neurophysiological measures of subcortical encoding of speech sounds relate to individual profiles of peripheral (cochlear) pathophysiology and to individual perceptual outcomes.

Neural representations of speech: Decoding bottom-up acoustics and examining top-down effects using electroencephalography

The acoustics of spoken language are highly variable, and yet most listeners easily extract meaningful information from the speech signal. Psycholinguistic work has revealed which acoustic dimensions are relevant when listeners categorize speech sounds, and how listeners use higher-level expectations to shift their categorization responses. However, the real-time neural mechanisms subserving such processes are not well understood. Two questions of interest include which perceptual distinctions are detectable in neural responses and whether higher-level information influences perceptual encoding directly. We present three electroencephalography (EEG) studies that address these issues. First, we examine perceptual encoding of speech sounds using machine learning techniques (N = 27). We contrast two approaches with machine learning and EEG and discuss methodological considerations for researchers using such techniques. We find that this approach can reveal neural sensitivity to phonetic contrasts that are indistinguishable in traditional EEG analyses. Second, we examine how top-down influences, such as sentence context (N = 31) or visual information (N = 33), affect perceptual encoding. We show that neural representations of speech sounds are influenced by listeners’ context-based expectations in limited cases, specifically, when acoustic cues are ambiguous. We compare how task design may impact linguistic processing, and how more naturalistic tasks may lead to richer processing dynamics.

Individuals practicing meditation have enhanced subcortical auditory processing of speech

Background Meditation is a compound mental task that leads to several changes, both physiologically and psychologically. These physiological changes can occur in the auditory system as well, and this can change the way the stimulus gets coded in the auditory system at both the brainstem as well as cortical level. The present study aimed to investigate the encoding of speech at the brainstem in the individuals who practice meditation. Method Two groups of 10 male individuals participated in the study. The first group included ten individuals who practiced meditation for a minimum period of 6 months, and the other group consisted of 10 age-matched individuals who never practiced meditation. Speech evoked ABR was recorded for the right ears for all the individuals. FFT analysis of the waveforms was done, and the latency of wave V and amplitude of F0, F1, and F2 were noted. Results Results of the present study revealed a significantly higher amplitude of F1 and F2 individuals who practiced meditation. However, there was no such significant difference in the latency of wave V and amplitude of F0. Conclusion The present study reveals that meditation can alter the functioning of the encoding of speech sounds in individuals who practice meditation.

The Visual Word Form Area compensates for auditory working memory dysfunction in schizophrenia

Auditory working memory impairments feature prominently in schizophrenia. However, the existence of altered and perhaps compensatory neural dynamics, sub-serving auditory working memory, remains largely unexplored. We compared the dynamics of induced high gamma power (iHGP) across cortex in humans during speech-sound working memory in individuals with schizophrenia (SZ) and healthy comparison subjects (HC) using magnetoencephalography (MEG). SZ showed similar task performance to HC while utilizing different brain regions. During encoding of speech sounds, SZ lacked the correlation of iHGP with task performance in posterior superior temporal gyrus (STGp) that was observed in healthy subjects. Instead, SZ recruited the visual word form area (VWFA) during both stimulus encoding and response preparation. Importantly, VWFA activity during encoding correlated with the magnitude of SZ hallucinations, task performance and an independent measure of verbal working memory. These findings suggest that VWFA plasticity is harnessed to compensate for STGp dysfunction in schizophrenia patients with hallucinations.

The frequency-following response (FFR) to speech stimuli: A normative dataset in healthy newborns

The Frequency-Following Response (FFR) is a neurophonic auditory evoked potential that reflects the efficient encoding of speech sounds and is disrupted in a range of speech and language disorders. This raises the possibility to use it as a potential biomarker for literacy impairment. However, reference values for comparison with the normal population are not yet established. The present study pursues the collection of a normative database depicting the standard variability of the newborn FFR. FFRs were recorded to /da/ and /ga/ syllables in 46 neonates born at term. Seven parameters were retrieved in the time and frequency domains, and analyzed for normality and differences between stimuli. A comprehensive normative database of the newborn FFR is offered, with most parameters showing normal distributions and similar robust responses for /da/ and /ga/ stimuli. This is the first normative database of the FFR to characterize normal speech sound processing during the immediate postnatal days, and corroborates the possibility to record the FFRs in neonates at the maternity hospital room. This normative database constitutes the first step towards the detection of early FFR abnormalities in newborns that would announce later language impairment, allowing early preventive measures from the first days of life.

Taking Attention Away from the Auditory Modality: Context-dependent Effects on Early Sensory Encoding of Speech

Increasing visual perceptual load can reduce pre-attentive auditory cortical activity to sounds, a reflection of the limited and shared attentional resources for sensory processing across modalities. Here, we demonstrate that modulating visual perceptual load can impact the early sensory encoding of speech sounds, and that the impact of visual load is highly dependent on the predictability of the incoming speech stream. Participants (n = 20, 9 females) performed a visual search task of high (target similar to distractors) and low (target dissimilar to distractors) perceptual load, while early auditory electrophysiological responses were recorded to native speech sounds. Speech sounds were presented either in a ‘repetitive context’, or a less predictable ‘variable context’. Independent of auditory stimulus context, pre-attentive auditory cortical activity was reduced during high visual load, relative to low visual load. We applied a data-driven machine learning approach to decode speech sounds from the early auditory electrophysiological responses. Decoding performance was found to be poorer under conditions of high (relative to low) visual load, when the incoming acoustic stream was predictable. When the auditory stimulus context was less predictable, decoding performance was substantially greater for the high (relative to low) visual load conditions. Our results provide support for shared attentional resources between visual and auditory modalities that substantially influence the early sensory encoding of speech signals in a context-dependent manner.

Effects of linguistic experience on brainstem encoding of speech sounds

Linguistic experience has been demonstrated repeatedly over the past decades as an important factor influencing the perception of speech sounds. At the behavioral level, speakers of different languages identify and discriminate speech sounds differentially (e.g., categorical perception). This has been observed at the cortical level as a reduced Mismatch Response, a measure that can reflect the sensitivity of the cortex to the differences between sounds. Yet, the effect of linguistic experience at an earlier stage of speech processing, namely, the brainstem, is scarcely studied. In the current study, we therefore aimed to examine specifically whether linguistic experience affects speech sound processing at the brainstem level. Twenty native Spanish speakers and twenty monolingual English speakers are recruited and their brainstem response to speech sounds will be measured with EEG. Specifically, we will use synthesized speech sounds: /ba/ with a + 10 ms and a -40 ms voice-onset-time (VOT). We hypothesize that while the encoding by the two groups will be similar for the + 10 ms /ba/ (common to English and Spanish), English speakers’ encoding of -40 ms prevoiced /ba/s (Spanish only) will be reduced relative to Spanish speakers. Data will be analyzed and interpreted with regards to these hypotheses.

Involvement of the Serotonin Transporter Gene in Accurate Subcortical Speech Encoding.

The accurate encoding of speech sounds in the subcortical auditory nervous system is of paramount relevance for human communication, and it has been shown to be altered in different disorders of speech and auditory processing. Importantly, this encoding is plastic and can therefore be enhanced by language and music experience. Whether genetic factors play a role in speech encoding at the subcortical level remains unresolved. Here we show that a common polymorphism in the serotonin transporter gene relates to an accurate and robust neural tracking of speech stimuli in the subcortical auditory pathway. This indicates that serotonin transporter expression, eventually in combination with other polymorphisms, delimits the extent to which lifetime experience shapes the subcortical encoding of speech.

Encoding of speech sounds at auditory brainstem level in good and poor hearing aid performers

IntroductionHearing aids are prescribed to alleviate loss of audibility. It has been reported that about 31% of hearing aid users reject their own hearing aid because of annoyance towards background noise. The reason for dissatisfaction can be located anywhere from the hearing aid microphone till the integrity of neurons along the auditory pathway. ObjectivesTo measure spectra from the output of hearing aid at the ear canal level and frequency following response recorded at the auditory brainstem from individuals with hearing impairment. MethodsA total of sixty participants having moderate sensorineural hearing impairment with age range from 15 to 65 years were involved. Each participant was classified as either Good or Poor Hearing aid Performers based on acceptable noise level measure. Stimuli /da/ and /si/ were presented through loudspeaker at 65dB SPL. At the ear canal, the spectra were measured in the unaided and aided conditions. At auditory brainstem, frequency following response were recorded to the same stimuli from the participants. ResultsSpectrum measured in each condition at ear canal was same in good hearing aid performers and poor hearing aid performers. At brainstem level, better F0 encoding; F0 and F1 energies were significantly higher in good hearing aid performers than in poor hearing aid performers. Though the hearing aid spectra were almost same between good hearing aid performers and poor hearing aid performers, subtle physiological variations exist at the auditory brainstem. ConclusionThe result of the present study suggests that neural encoding of speech sound at the brainstem level might be mediated distinctly in good hearing aid performers from that of poor hearing aid performers. Thus, it can be inferred that subtle physiological changes are evident at the auditory brainstem in a person who is willing to accept noise from those who are not willing to accept noise.