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Biomedical subjects

Nina Kraus

Publications and source records attributed to Nina Kraus.

18 recordsLinked to original sources
PubMed2006

Auditory brainstem timing predicts cerebral asymmetry for speech.

The left hemisphere of the human cerebral cortex is dominant for processing rapid acoustic stimuli, including speech, and this specialized activity is preceded by processing in the auditory brainstem. It is not known to what extent the integrity of brainstem encoding of speech impacts patterns of asymmetry at cortex. Here, we demonstrate that the precision of temporal encoding of speech in auditory brainstem predicts cerebral asymmetry for speech sounds measured in a group of children spanning a range of language skills. Results provide strong evidence that timing deficits measured at the auditory brainstem negatively impact rapid acoustic processing by specialized structures of cortex, and demonstrate a delicate relationship between cortical activation patterns and the temporal integrity of cortical input.

Acoustic Stimulation↗
PubMed2005

Brainstem timing: implications for cortical processing and literacy.

The search for a unique biological marker of language-based learning disabilities has so far yielded inconclusive findings. Previous studies have shown a plethora of auditory processing deficits in learning disabilities at both the perceptual and physiological levels. In this study, we investigated the association among brainstem timing, cortical processing of stimulus differences, and literacy skills. To that end, brainstem timing and cortical sensitivity to acoustic change [mismatch negativity (MMN)] were measured in a group of children with learning disabilities and normal-learning children. The learning-disabled (LD) group was further divided into two subgroups with normal and abnormal brainstem timing. MMNs, literacy, and cognitive abilities were compared among the three groups. LD individuals with abnormal brainstem timing were more likely to show reduced processing of acoustic change at the cortical level compared with both normal-learning individuals and LD individuals with normal brainstem timing. This group was also characterized by a more severe form of learning disability manifested by poorer reading, listening comprehension, and general cognitive ability. We conclude that abnormal brainstem timing in learning disabilities is related to higher incidence of reduced cortical sensitivity to acoustic change and to deficient literacy skills. These findings suggest that abnormal brainstem timing may serve as a reliable marker of a subgroup of individuals with learning disabilities. They also suggest that faulty mechanisms of neural timing at the brainstem may be the biological basis of malfunction in this group.

Acoustic Stimulation↗
PubMed2005

Seeing speech affects acoustic information processing in the human brainstem.

Afferent auditory processing in the human brainstem is often assumed to be determined by acoustic stimulus features alone and immune to stimulation by other senses or cognitive factors. In contrast, we show that lipreading during speech perception influences early acoustic processing. Event-related brainstem potentials were recorded from ten healthy adults to concordant (acoustic-visual match), conflicting (acoustic-visual mismatch) and unimodal stimuli. Audiovisual (AV) interactions occurred as early as approximately 11 ms post-acoustic stimulation and persisted for the first 30 ms of the response. Furthermore, the magnitude of interaction depended on AV pairings. These findings indicate considerable plasticity in early auditory processing.

Acoustic Stimulation↗
PubMed2005

Auditory training improves neural timing in the human brainstem.

The auditory brainstem response reflects neural encoding of the acoustic characteristic of a speech syllable with remarkable precision. Some children with learning impairments demonstrate abnormalities in this preconscious measure of neural encoding especially in background noise. This study investigated whether auditory training targeted to remediate perceptually-based learning problems would alter the neural brainstem encoding of the acoustic sound structure of speech in such children. Nine subjects, clinically diagnosed with a language-based learning problem (e.g., dyslexia), worked with auditory perceptual training software. Prior to beginning and within three months after completing the training program, brainstem responses to the syllable /da/ were recorded in quiet and background noise. Subjects underwent additional auditory neurophysiological, perceptual, and cognitive testing. Ten control subjects, who did not participate in any remediation program, underwent the same battery of tests at time intervals equivalent to the trained subjects. Transient and sustained (frequency-following response) components of the brainstem response were evaluated. The primary pathway afferent volley -- neural events occurring earlier than 11 ms after stimulus onset -- did not demonstrate plasticity. However, quiet-to-noise inter-response correlations of the sustained response ( approximately 11-50 ms) increased significantly in the trained children, reflecting improved stimulus encoding precision, whereas control subjects did not exhibit this change. Thus, auditory training can alter the preconscious neural encoding of complex sounds by improving neural synchrony in the auditory brainstem. Additionally, several measures of brainstem response timing were related to changes in cortical physiology, as well as perceptual, academic, and cognitive measures from pre- to post-training.

Attention↗
PubMed2005

Correlation between brainstem and cortical auditory processes in normal and language-impaired children.

A functional relationship between brainstem and cortical auditory processing was shown to be abnormal in children with language-based learning problems (LP). Auditory evoked potentials were used to investigate brainstem and cortical responses to the speech sound /da/. The duration of the wave V-V(n) complex of the auditory brainstem response was studied, as was the effect of noise on correlations between cortical responses to repeated stimuli. The group of LP children (n = 11) demonstrated abnormal encoding of speech sounds on both individual measures of brainstem and cortical processing; prolonged wave V-V(n) duration and pronounced susceptibility of cortical correlations to degradation by noise were both interpreted as reflecting diminished synchrony of response generator mechanisms. Furthermore, the LP group as a whole failed to demonstrate a relationship between brainstem and cortical measures that was demonstrated to be quite strong across all normal children (NL, n = 9). However, a subset of roughly three-quarters of the LP children appeared to demonstrate the normal relationship between brainstem and cortical processing, suggesting that they share a common functional connection with NL children. This relatively normal relationship between brainstem and cortical auditory processing in most LP children, as well as the exceptions to this relationship reflected by a smaller portion of LP children, may delineate different subclasses of auditory-language-based learning problems. This suggests the potential for use of these measures as diagnostic tools.

Acoustic Stimulation↗
PubMed2005

Brainstem origins for cortical 'what' and 'where' pathways in the auditory system.

We have developed a data-driven conceptual framework that links two areas of science: the source-filter model of acoustics and cortical sensory processing streams. The source-filter model describes the mechanics behind speech production: the identity of the speaker is carried largely in the vocal cord source and the message is shaped by the ever-changing filters of the vocal tract. Sensory processing streams, popularly called 'what' and 'where' pathways, are well established in the visual system as a neural scheme for separately carrying different facets of visual objects, namely their identity and their position/motion, to the cortex. A similar functional organization has been postulated in the auditory system. Both speaker identity and the spoken message, which are simultaneously conveyed in the acoustic structure of speech, can be disentangled into discrete brainstem response components. We argue that these two response classes are early manifestations of auditory 'what' and 'where' streams in the cortex. This brainstem link forges a new understanding of the relationship between the acoustics of speech and cortical processing streams, unites two hitherto separate areas in science, and provides a model for future investigations of auditory function.

Animals↗
PubMed2005

Brain stem response to speech: a biological marker of auditory processing.

The auditory brain stem response to speech mimics the acoustic characteristics of the speech signal with remarkable fidelity. This makes it possible to derive from it considerable theoretical and clinically applicable information relevant to auditory processing of complex stimuli. Years of research have led to the current characterization of these neural events with respect to the underlying acoustic information they reflect. The majority of data reviewed here originates from studies using a /da/ syllable to elicit the brain stem response, which consists of transient and periodic (frequency following) neural activity. We describe how the human auditory brain stem response separately encodes source and filter characteristics of the acoustic signal, which reflects paralinguistic and linguistic information simultaneously conveyed in speech. In normal-hearing individuals, these two classes of response components (source and filter) are highly correlated within a class but not between classes. This response dissociation becomes pronounced when stimuli are presented in background noise or with faster stimulus rates. In addition, some learning-impaired children show a selective deficiency in the neural encoding of acoustic features associated with the filter characteristics of speech. These children show no deficits in the encoding of source components, further supporting the notion of separate neural mechanisms. Overall, the auditory brain stem response to speech provides a way to access subcortical auditory processing mechanisms and may be used as a biological marker of deficient sound encoding associated with learning and auditory processing disorders.

Acoustic Stimulation↗
PubMed2004

Learning impaired children exhibit timing deficits and training-related improvements in auditory cortical responses to speech in noise.

The physiological mechanisms that contribute to abnormal encoding of speech in children with learning problems are yet to be well understood. Furthermore, speech perception problems appear to be particularly exacerbated by background noise in this population. This study compared speech-evoked cortical responses recorded in a noisy background to those recorded in quiet in normal children (NL) and children with learning problems (LP). Timing differences between responses recorded in quiet and in background noise were assessed by cross-correlating the responses with each other. Overall response magnitude was measured with root-mean-square (RMS) amplitude. Cross-correlation scores indicated that 23% of LP children exhibited cortical neural timing abnormalities such that their neurophysiological representation of speech sounds became distorted in the presence of background noise. The latency of the N2 response in noise was isolated as being the root of this distortion. RMS amplitudes in these children did not differ from NL children, indicating that this result was not due to a difference in response magnitude. LP children who participated in a commercial auditory training program and exhibited improved cortical timing also showed improvements in phonological perception. Consequently, auditory pathway timing deficits can be objectively observed in LP children, and auditory training can diminish these deficits.

Acoustic Stimulation↗
PubMed2004

Atypical brainstem representation of onset and formant structure of speech sounds in children with language-based learning problems.

This study investigated how the human auditory brainstem represents constituent elements of speech sounds differently in children with language-based learning problems (LP, n = 9) compared to normal children (NL, n = 11), especially under stress of rapid stimulation. Children were chosen for this study based on performance on measures of reading and spelling and measures of syllable discrimination. In response to the onset of the speech sound /da/, wave V-V(n) of the auditory brainstem response (ABR) had a significantly shallower slope in LP children, suggesting longer duration and/or smaller amplitude. The amplitude of the frequency following response (FFR) was diminished in LP subjects over the 229-686 Hz range, which corresponds to the first formant of the/da/ stimulus, while activity at 114 Hz, representing the fundamental frequency of /da/, was no different between groups. Normal indicators of auditory peripheral integrity suggest a central, neural origin of these differences. These data suggest that poor representation of crucial components of speech sounds could contribute to difficulties with higher-level language processes.

Child↗
PubMed2004

Brainstem responses to speech syllables.

OBJECTIVE: To establish reliable procedures and normative values to quantify brainstem encoding of speech sounds. METHODS: Auditory brainstem responses to speech syllables presented in quiet and in background noise were obtained from 38 normal children. Brainstem responses consist of transient and sustained, periodic components-much like the speech signal itself. Transient peak responses were analyzed with measures of latency, amplitude, area, and slope. Magnitude of sustained, periodic frequency-following responses was assessed with root mean square, fundamental frequency, and first formant amplitudes; timing was assessed by stimulus-to-response and quiet-to-noise inter-response correlations. RESULTS: Measures of transient and sustained components of the brainstem response to speech syllables were reliably obtained with high test-retest stability and low variability across subjects. All components of the brainstem response were robust in quiet. Background noise disrupted the transient responses whereas the sustained response was more resistant to the deleterious effects of noise. CONCLUSIONS: The speech-evoked brainstem response faithfully reflects many acoustic properties of the speech signal. Procedures to quantitatively describe it have been developed. SIGNIFICANCE: Accurate and precise manifestation of stimulus timing at the auditory brainstem is a hallmark of the normal perceptual system. The brainstem response to speech sounds provides a mechanism for understanding the neural bases of normal and deficient attention-independent auditory function.

Acoustic Stimulation↗
PubMed2003

Integration of heard and seen speech: a factor in learning disabilities in children.

Normal-learning children (NL) and children with learning disabilities (LD) reported their perceptions of unisensory (auditory or visual), concordant audiovisual (e.g. visual /apa/ and auditory /apa/) and conflicting (e.g. visual /aka/ and auditory /apa/) speech stimuli in quiet and noise (0 dB and -12 dB signal-to-noise ratio, SNR). In normal populations, watching such conflicting combinations typically changes auditory percepts ('McGurk effect'). NL and LD children identified unisensory auditory and congruent audiovisual stimuli similarly in all conditions. Despite being less accurate identifying unisensory visual stimuli, LD children were more likely than NL children to report hearing only the visual component of incongruent audiovisual stimuli at -12 dB SNR. Furthermore, LD children with brainstem timing deficits demonstrated a distinctive pattern of audiovisual perception. The results suggest that the perception of simultaneous auditory and visual speech differs between NL and LD children, perhaps reflecting variations in neural processing underlying multisensory integration.

Adolescent↗
PubMed2003

Neural plasticity following auditory training in children with learning problems.

OBJECTIVE: This study examined the plasticity of the central auditory pathway and accompanying cognitive changes in children with learning problems. METHODS: Children diagnosed with a learning disability and/or attention deficit disorder worked with commercial auditory processing training software for 8 weeks; control groups consisted of normal-learning and learning-impaired children who did not participate in any remedial programs. Auditory brainstem function was evaluated in response to click and speech stimuli in quiet; cortical responses to speech stimuli were obtained in quiet and noise. Academic achievement and cognitive abilities were assessed with standardized measures. RESULTS: Compared to controls, the trained group improved on measures of auditory processing and exhibited changes in cortical responses in quiet and in noise. In quiet, cortical responses reflected an accelerated maturational pattern; in background noise, cortical responses became more resistant to degradation. Brainstem responses did not change with training. CONCLUSIONS: Children with learning problems who practiced with auditory training software exhibited plasticity of neural encoding of speech sounds at the cortical, but not subcortical, level of the auditory pathway. This plasticity was accompanied by improvement in behavioral performance. SIGNIFICANCE: This study demonstrates that in learning-impaired children working with commercial auditory processing training programs affects both the perception and the cortical representation of sound.

Achievement↗
PubMed2003

Speaking clearly for children with learning disabilities: sentence perception in noise.

This study compared the speech-in-noise perception abilities of children with and without diagnosed learning disabilities (LDs) and investigated whether naturally produced clear speech yields perception benefits for these children. A group of children with LDs (n = 63) and a control group of children without LDs (n = 36) were presented with simple English sentences embedded in noise. Factors that varied within participants were speaking style (conversational vs. clear) and signal-to-noise ratio (-4 dB vs. -8 dB); talker (male vs. female) varied between participants. Results indicated that the group of children with LDs had poorer overall sentence-in-noise perception than the control group. Furthermore, both groups had poorer speech perception with decreasing signal-to-noise ratio; however the children with LDs were more adversely affected by a decreasing signal-to-noise ratio than the control group. Both groups benefited substantially from naturally produced clear speech, and for both groups, the female talker evoked a larger clear speech benefit than the male talker. The clear speech benefit was consistent across groups; required no listener training; and, for a large proportion of the children with LDs, was sufficient to bring their performance within the range of the control group with conversational speech. Moreover, an acoustic comparison of conversational-to-clear speech modifications across the two talkers provided insight into the acoustic-phonetic features of naturally produced clear speech that are most important for promoting intelligibility for this population.

Child↗
PubMed2002

Deficits in auditory brainstem pathway encoding of speech sounds in children with learning problems.

Auditory brainstem responses were recorded in normal children (NL) and children clinically diagnosed with a learning problem (LP). These responses were recorded to both a click stimulus and the formant transition portion of a speech syllable /da/. While no latency differences between the NL and LP populations were seen in responses to the click stimuli, the syllable /da/ did elicit latency differences between these two groups. Deficits in cortical processing of signals in noise were seen for those LP subjects with delayed brainstem responses to the /da/, but not for LPs with normal brainstem measures. Preliminary findings indicate that training may be beneficial to LP subjects with brainstem processing delays.

Acoustic Stimulation↗
PubMed2002

Effects of noise and cue enhancement on neural responses to speech in auditory midbrain, thalamus and cortex.

Speech perception depends on the auditory system's ability to extract relevant acoustic features from competing background noise. Despite widespread acknowledgement that noise exacerbates this process, little is known about the neurophysiologic mechanisms underlying the encoding of speech in noise. Moreover, the relative contribution of different brain nuclei to these processes has not been fully established. To address these issues, aggregate neural responses were recorded from within the inferior colliculus, medial geniculate body and over primary auditory cortex of anesthetized guinea pigs to a synthetic vowel-consonant-vowel syllable /ada/ in quiet and in noise. In noise the onset response to the stop consonant /d/ was reduced or eliminated at each level, to the greatest degree in primary auditory cortex. Acoustic cue enhancements characteristic of 'clear' speech (lengthening the stop gap duration and increasing the intensity of the release burst) improved the neurophysiologic representation of the consonant at each level, especially at the cortex. Finally, the neural encoding of the vowel segment was evident at subcortical levels only, and was more resistant to noise than encoding of the dynamic portion of the consonant (release burst and formant transition). This experiment sheds light on which speech-sound elements are poorly represented in noise and demonstrates how acoustic modifications to the speech signal can improve neural responses in a normal auditory system. Implications for understanding neurophysiologic auditory signal processing in children with perceptual impairments and the design of efficient perceptual training strategies are also discussed.

Acoustic Stimulation↗
PubMed2002

Auditory training induces asymmetrical changes in cortical neural activity.

Pre-attentive cortical evoked potentials reflect training-induced changes in neural activity associated with speech-sound training. Seven normal-hearing young adults were trained to identify two synthetic speech variants of the syllable /ba/. As subjects learned to correctly identify the two stimuli, changes in P1, N1, and P2 amplitudes were observed. Of particular interest is that P1, N1, and P2 components of the N1-P2 complex responded differently to listening training. That is, significant changes in P1 and N1 amplitude were recorded over the right but not the left hemisphere. In contrast, increases in P2 were observed bilaterally. These results indicate that training-related changes in neural activity are reflected in far-field aggregate neural responses and that distinct patterns of neural change, perhaps reflecting hemispheric specialization, likely represent different aspects of auditory function.

Acoustic Stimulation↗
PubMed2002

Neurophysiology of cochlear implant users II: comparison among speech perception, dynamic range, and physiological measures.

OBJECTIVE: The overall objective of this study was to relate electrically evoked potentials recorded from different levels of the auditory pathway with behavioral measures obtained from adult cochlear implant subjects. The hypothesis was that adult recipients of cochlear implants who have open-set speech perception and those recipients with no open-set speech perception would differ in their neurophysiologic responses recorded at one or more levels of the auditory pathway. DESIGN: The subjects were 11 adults implanted with the Clarion cochlear implant. The electrical auditory brainstem response (EABR, Wave V), electrical auditory middle latency response (EAMLR, Na-Pa complex), and the electrical late auditory response (ELAR, N1-P2 complex), were recorded from three intra-cochlear electrodes. The stimuli used to record the evoked potentials varied in rate and amplitude. Behavioral measures (between threshold and upper limit of comfortable loudness) were used to define the subject's dynamic range at the different stimulus rates. Word and sentence recognition tests evaluated subjects' speech perception in quiet and noise. Evoked potential and behavioral measures were examined for statistical significance using analysis of variance for repeated measures and correlational analyses. RESULTS: Subjects without open-set speech recognition demonstrated 1) poorly formed or absent evoked potential responses, 2) reduced behavioral dynamic ranges, 3) lack of change in the size of the dynamic range with a change in stimulus rate, and 4) longer periods of auditory deprivation. The variables that differentiated the best performers included 1) presence of responses at all three levels of the auditory pathway, with large normalized amplitudes for the EAMLR, 2) lower evoked potential thresholds for the Na-Pa complex, 3) relatively large dynamic ranges, and 4) changes in the size of the dynamic range with changes in stimulus rate. CONCLUSIONS: In this study, the inability to follow changes in the temporal characteristics of the stimulus was associated with poor speech perception performance. Results also illustrate that variability in speech perception scores of cochlear implant recipients relates to neurophysiologic responses at higher cortical levels of the auditory pathway. Presumably, limited neural synchrony for elicitation of electrophysiologic responses underlies limited speech perception. Results confirm that neural encoding with electrical stimulation must provide sufficient physiologic responses of the central nervous system to perceive speech through a cochlear implant.

Adult↗