Rapid Auditory Processing Research Articles

The neurochemical basis of human cortical auditory processing: combining proton magnetic resonance spectroscopy and magnetoencephalography

BackgroundA combination of magnetoencephalography and proton magnetic resonance spectroscopy was used to correlate the electrophysiology of rapid auditory processing and the neurochemistry of the auditory cortex in 15 healthy adults. To assess rapid auditory processing in the left auditory cortex, the amplitude and decrement of the N1m peak, the major component of the late auditory evoked response, were measured during rapidly successive presentation of acoustic stimuli. We tested the hypothesis that: (i) the amplitude of the N1m response and (ii) its decrement during rapid stimulation are associated with the cortical neurochemistry as determined by proton magnetic resonance spectroscopy.ResultsOur results demonstrated a significant association between the concentrations of N-acetylaspartate, a marker of neuronal integrity, and the amplitudes of individual N1m responses. In addition, the concentrations of choline-containing compounds, representing the functional integrity of membranes, were significantly associated with N1m amplitudes. No significant association was found between the concentrations of the glutamate/glutamine pool and the amplitudes of the first N1m. No significant associations were seen between the decrement of the N1m (the relative amplitude of the second N1m peak) and the concentrations of N-acetylaspartate, choline-containing compounds, or the glutamate/glutamine pool. However, there was a trend for higher glutamate/glutamine concentrations in individuals with higher relative N1m amplitude.ConclusionThese results suggest that neuronal and membrane functions are important for rapid auditory processing. This investigation provides a first link between the electrophysiology, as recorded by magnetoencephalography, and the neurochemistry, as assessed by proton magnetic resonance spectroscopy, of the auditory cortex.

Cracking the Language Code: Neural Mechanisms Underlying Speech Parsing

Word segmentation, detecting word boundaries in continuous speech, is a critical aspect of language learning. Previous research in infants and adults demonstrated that a stream of speech can be readily segmented based solely on the statistical and speech cues afforded by the input. Using functional magnetic resonance imaging (fMRI), the neural substrate of word segmentation was examined on-line as participants listened to three streams of concatenated syllables, containing either statistical regularities alone, statistical regularities and speech cues, or no cues. Despite the participants' inability to explicitly detect differences between the speech streams, neural activity differed significantly across conditions, with left-lateralized signal increases in temporal cortices observed only when participants listened to streams containing statistical regularities, particularly the stream containing speech cues. In a second fMRI study, designed to verify that word segmentation had implicitly taken place, participants listened to trisyllabic combinations that occurred with different frequencies in the streams of speech they just heard ("words," 45 times; "partwords," 15 times; "nonwords," once). Reliably greater activity in left inferior and middle frontal gyri was observed when comparing words with partwords and, to a lesser extent, when comparing partwords with nonwords. Activity in these regions, taken to index the implicit detection of word boundaries, was positively correlated with participants' rapid auditory processing skills. These findings provide a neural signature of on-line word segmentation in the mature brain and an initial model with which to study developmental changes in the neural architecture involved in processing speech cues during language learning.

Impaired duration mismatch negativity in developmental dyslexia

A mismatch negativity event-related potential protocol was administered to dyslexic children and their respective controls to test whether a specific auditory deficit concerning phonetic processing or a lower level auditory processing deficit was present in developmental dyslexia. Three different contrast conditions were explored, including nonphonological sounds, contrasted in pitch and duration, and phonemes. Mismatch negativity amplitudes differed significantly between groups in the duration condition, whereas no differences were found in the frequency and phoneme conditions. Moreover, the dyslexic children had delayed mismatch negativity latencies in the three contrast conditions. Our results suggest a deficit in low-level auditory discrimination in dyslexic children, in particular when detecting stimulus duration, and support the rapid auditory processing theory of dyslexia.

Rapid auditory processing and learning deficits in rats with P1 versus P7 neonatal hypoxic-ischemic injury

Hypoxia-ischemia (HI) is associated with premature birth, and injury during term birth. Many infants experiencing HI later show disruptions of language, with research suggesting that rapid auditory processing (RAP) deficits (i.e., impairment in the ability to discriminate rapidly changing acoustic signals), play a causal role in language problems. We recently bridged these lines of research by showing RAP deficits in rats with unilateral-HI injury induced on postnatal days 1, 7, or 10 (P1, P7, or P10 [McClure MM, Peiffer AM, Rosen GD, Fitch RH. Auditory processing deficits in rats with neonatal hypoxic-ischemic injury. Int J Dev Neurosci, 2005;23:351–362]). While robust RAP deficits were found in HI animals, it was suggested that our within-age sample size did not provide sufficient power to detect age-at-injury differences within the pooled HI group. The current study sought to examine differences in neuropathology and behavior following unilateral-HI injury on P1 versus P7 in rats. Ages chosen for HI induction reflect differential stages of neurodevelopmental maturity, and subsequent regional differences in vulnerability to reduced blood flow/oxygen (modeling age-related differences in premature/term HI injury). Results showed that during the juvenile period, both P1 and P7 HI groups exhibited significant RAP deficits, but deficits in the P1 HI group resolved with repeated testing (compared to shams), while P7 HI animals showed lasting deficits in RAP and spatial learning/memory through adulthood. The current findings are in accord with evidence that HI injury during different stages of developmental maturity (age-at-injury) leads to differential neuropathologies, and provide the novel observation that in rats, P1 versus P7 induced pathologies are associated with different patterns of auditory processing and learning/memory deficits across the lifespan.

Auditory temporal processing deficits in children with reading disabilities

The role of central auditory processing in reading skill development and reading disorders is unclear. The purpose of this study was to examine whether individuals with specific reading disabilities (SRD) have deficits in processing rapidly presented, serially ordered non-speech auditory signals. To this end, we compared 12 children with SRD and 12 children without SRD on their ability to detect differences and similarities in pure tones of 1000 and 2000 Hz when these signals were presented in pairs (same or different tones, randomly ordered) with short (50 ms) versus long (500 ms) inter-stimulus intervals (ISI). Results showed that the children with SRD had significant difficulty in discriminating between pure tones with short, but not long ISI, whereas the controls performed well with both short and long ISI. The two groups did not differ significantly on measures of attention (d2) and performance IQ, and there were no significant correlations between these measures and ISI performance. There were significant correlations between the short ISI performance and phonologic awareness test results when the two groups were combined. These findings support the specific rapid auditory processing deficit hypothesis of SRD. Examination of intra-subject variability in performance indicated that children from the SRD group showed both decrement in performance with time on task and high overall variability in performance as compared to the controls. These findings underpin the importance of using time-series analyses of performance.

The effects of erythropoietin on auditory processing following neonatal hypoxic–ischemic injury

Neonatal hypoxia–ischemia (HI) is a common cause of brain damage and subsequent behavioral deficits in premature/term infants. Rapid auditory processing deficits have been suggested to play a role in later language impairments in this population. We have previously shown auditory deficits in rats with neonatal HI injury and now report novel effects of behavioral sparing and neuroprotection following treatment with a low dose of Erythropoietin using this HI injury model.

What is the Role of Audition in Literacy?

What is the Role of Audition in Literacy?

Auditory processing deficits in unilaterally and bilaterally injured hypoxic–ischemic rats

Hypoxic-ischemic represents a common cause of damage to the prenatal brain and can co-occur with prematurity. Prematurity is associated with emergent language impairments, and it has been suggested that rapid auditory processing deficits play a causal role in language difficulties. We previously demonstrated rapid auditory processing deficits in juvenile rats receiving neonatal unilateral hypoxic-ischemic injury, but these deficits appeared to resolve by adulthood. The current study compared unilaterally and bilaterally injured hypoxic-ischemic rats on auditory tasks, to assess whether rapid auditory processing recovery in adulthood is related to this aspect of injury. Current results indicate that while neonatal unilateral and bilateral hypoxic-ischemic injury both lead to rapid auditory processing deficits in the juvenile period, only rats with bilateral hypoxic-ischemic injury exhibit deficits that persist into adulthood.

The infant as a prelinguistic model for language learning impairments: Predicting from event-related potentials to behavior

Associations between efficient processing of brief, rapidly presented, successive stimuli and language learning impairments (LLI) in older children and adults have been well documented. In this paper we examine the role that impaired rapid auditory processing (RAP) might play during early language acquisition. Using behavioral measures we have demonstrated that RAP abilities in infancy are critically linked to later language abilities for both non-speech and speech stimuli. Variance in infant RAP thresholds reliably predict language outcome at 3 years-of-age for infants at risk for LLI and control infants. We present data here describing patterns of electrocortical (EEG/ERP) activation at 6 month-of-age to the same non-verbal stimuli used in our behavioral studies. Well-defined differences were seen between infants from families with a history of LLI (FH+) and FH− controls in the amplitude of the mismatch response (MMR) as well as the latency of the N 250 component in the 70 ms ISI condition only. Smaller mismatch responses and delayed onsets of the N 250 component were seen in the FH+ group. The latency differences in the N 250 component, but not the MMR amplitude variation, were significantly related to 24-month language outcome. Such converging tasks provide the opportunity to examine early precursors of LLI and allow the opportunity for earlier identification and intervention.

Auditory inhibitory gating in the amygdala: Single-unit analysis in the behaving rat

Inhibitory sensory gating has been proposed to be a fundamental physiological process that filters neural input. Its temporal properties could allow for a rapid influence on vigilance and attention processes. Inhibitory mechanisms are reflected by reductions in neural responsiveness to repeated and well-predicted stimuli; for auditory gating, this translates into an inhibition of the neural activation to subsequent tone stimuli embedded within sequential and identical tone presentations. Here we expand previous neurophysiological data on inhibitory gating by examining gating in the amygdala using single-unit recording in freely moving animals. Previous data have shown the amygdala to be important in mediating rapid auditory sensory processing involved in emotional conditioning. We measured inhibitory gating with two matching auditory tones presented in a repetitive fashion (10 ms tones, ISI = 500 ms and 10 s between pairs) for 1 h (360 pairs). The majority of the tone responsive units showed inhibitory gating (78/95 units) located in both the medial and lateral subnuclei of the amygdala. Different types of tone responses were gated, including both shorter- and longer-duration excitatory tone responses as well as inhibitory tone responses. Different degrees of gating were found ranging from 100% inhibition (complete gating category) to 25% inhibition (graded gating category). The degree of gating varied over short-term and long-term time intervals. These findings demonstrate the existence of inhibitory gating in the amygdala and provide a detailed description of the basic properties of this rapid neural inhibition that could play an important role in filtering stimulus input.

Auditory processing deficits in rats with neonatal hypoxic-ischemic injury

Hypoxia-ischemia (HI) refers to reduced blood oxygenation and/or a diminished amount of blood perfusing the brain, and is associated with premature birth/very low birth weight (VLBW). HI represents a common cause of injury to the perinatal brain. Indeed, a significant number of premature/VLBW infants go on to demonstrate cognitive/behavioral deficits, with particularly high incidence of disruptions in language development. Auditory processing deficits, in turn, have been suggested to play a causal role in the development of language impairments. Specifically, the inability to identify fast elements in speech is purported to exert cascading detrimental effects on phonological discrimination, processing, and identification. Based on this convergent evidence, the current studies address auditory processing evaluation in a rodent model of HI injury induced on postnatal days 1, 7, or 10 (which in turn is well accepted as modeling HI-related injury to the perinatal human). Induced injuries were followed by a battery of auditory testing, and a spatial maze assessment, performed both during juvenile and adult periods. Results indicate that rats suffering from these early HI insults performed significantly worse than shams on tasks requiring rapid auditory processing, and on a test of spatial learning (Morris water maze (MWM)), although these effects were not seen on simpler versions of auditory tasks or on a water escape assessment (thus ruling out hearing/motor impairments). Correlations were found between performance on rapid auditory and spatial behavioral tasks and neuroanatomical measures for HI animals such as: the volume of the hippocampus, cerebral cortex, ventricles, and/or the area of the corpus callosum. Cumulative findings suggest that perinatal HI injury in the rat may lead to neurodevelopmental damage associated, in turn, with auditory processing and/or learning and memory impairments. As such, the current model may have critical implications for the study of neurophysiological underpinnings of cognitive deficits in premature/VLBW infants.

Impaired gap detection in juvenile microgyric rats

Previous research with adult animal models links the presence of cortical neuromigrational anomalies (i.e., microgyria similar to that found in brains of dyslexics) with rapid auditory processing (RAP) impairments. RAP impairments are in turn found in children with specific language impairment (SLI) and also in individuals with dyslexia. Gap detection, a simple measure of auditory temporal acuity, appears to be impaired in children with SLI but not in dyslexic adults, even though both groups exhibit impaired processing on more complex, rapid auditory tasks. In the current study, juvenile rats with bilateral microgyria, but not their adult counterparts, exhibited impaired detection of short duration silent gaps in white noise when compared to age-matched sham littermates. Results lend further support to: (1) an association between neuromigrational anomalies and RAP impairments; and (2) the validity of an animal model of RAP impairments associated with language disturbances in humans. Current results also support the view that auditory processing disturbances associated with cortical malformations may be evident early in development at a relatively “low” level (e.g., simple gap detection), but may require “higher-order” auditory discrimination tasks (e.g., tone sequences, phonemic discriminations) to be elicited later in life.

Sex differences in rapid auditory processing deficits in microgyric rats

Early neocortical injury has been associated with rate-specific auditory processing deficits using rodent models. In the few cases where females were studied, they appeared less vulnerable than males to the behavioral consequences of early neocortical injury. In the current study, male rats with neocortical microgyria were found to exhibit significant impairments in detecting tone sequences at short but not long inter-stimulus intervals (ISI) as compared to sham-operated male littermates. Microgyric females, however, performed similarly to sham-operated female littermates on this task at all durations. Current findings support an association between focal cortical malformations and impaired rapid auditory processing in males, and less vulnerability in females to the behavioral consequences of these malformations on a task eliminating confounds of motivation, experience, and estrus.

Rapid auditory processing deficits in dyslexia: a commentary on two differing views

Rapid auditory processing deficits in dyslexia: a commentary on two differing views

Theories of developmental dyslexia: insights from a multiple case study of dyslexic adults.

A multiple case study was conducted in order to assess three leading theories of developmental dyslexia: (i) the phonological theory, (ii) the magnocellular (auditory and visual) theory and (iii) the cerebellar theory. Sixteen dyslexic and 16 control university students were administered a full battery of psychometric, phonological, auditory, visual and cerebellar tests. Individual data reveal that all 16 dyslexics suffer from a phonological deficit, 10 from an auditory deficit, four from a motor deficit and two from a visual magnocellular deficit. Results suggest that a phonological deficit can appear in the absence of any other sensory or motor disorder, and is sufficient to cause a literacy impairment, as demonstrated by five of the dyslexics. Auditory disorders, when present, aggravate the phonological deficit, hence the literacy impairment. However, auditory deficits cannot be characterized simply as rapid auditory processing problems, as would be predicted by the magnocellular theory. Nor are they restricted to speech. Contrary to the cerebellar theory, we find little support for the notion that motor impairments, when found, have a cerebellar origin or reflect an automaticity deficit. Overall, the present data support the phonological theory of dyslexia, while acknowledging the presence of additional sensory and motor disorders in certain individuals.

Sex differences in rapid auditory processing deficits in ectopic BXSB/MpJ mice.

Prior research with rodent models, performed predominantly in males, has demonstrated a significant association between focal neocortical malformations (e.g. ectopias and microgyria) and rate-specific auditory processing deficits. In the current study and consistent with prior findings, we report that ectopic male BXSB/MpJ mice exhibit impairments in detecting a two-tone oddball stimulus at short but not long inter-stimulus interval durations when compared to non-ectopic male littermates. However, ectopic female littermates showed no rapid auditory processing deficit when compared to non-ectopic females on this same task. Current results add growing support to: (1) an association between focal cortical malformations and impaired auditory processing in males; and (2) the existence of sex differences in the behavioral consequences of focal cortical malformations.

Rapid auditory processing and MGN morphology in microgyric rats reared in varied acoustic environments

Adult male rats with induced microgyric lesions exhibit significant deficits in rapid auditory processing, as well as morphological alterations in the medial geniculate nucleus (MGN) of the thalamus. These findings are considered striking in light of similar anatomical and auditory processing anomalies in language disabled humans. Given evidence from clinical and animal studies that acoustic experience may alter sensory processing at behavioral and neurophysiological levels, the current study examined effects of developmental exposure to auditory stimulation on behavioral and anatomical indices in microgyric and sham rats. Stimulation (E7–P70) included: (1) chronic white noise (80 dB) with standard housing; (2) 3 h/day of 78 dB filtered light classical music with social housing; or (3) standard acoustic environment (control) with standard housing. Microgyric effects on auditory processing and thalamic morphology were evident regardless of environmental condition. In sum, the effects of microgyria on brain and behavior appear to be robust, and largely orthogonal to any main effect of acoustic stimulation on auditory processing. These findings suggest that a more active form of acoustic stimulation (e.g., training) may be required to ameliorate the deleterious behavioral and anatomical consequences of focal microgyric lesions.

Impaired Processing of Brief, Rapidly Presented Auditory Cues in Infants With a Family History of Autoimmune Disorder

Studies have shown that individuals with language disorders, such as developmental dyslexia and specific language impairment, exhibit impairments in the processing of brief, successive, or rapidly changing auditory information. It is also the case that a higher rate of autoimmune disorders have been identified in those with language-based learning disorders and, conversely, that individuals with autoimmune disorders show a higher incidence of language-related disorders. The rapid auditory processing (RAP) deficits described for older individuals with language impairments may also be used as a behavioral marker to identify infants at higher risk for language delays. Thus, we were interested in examining RAP abilities in a subset of infants with a positive family history of autoimmune disorders. Eleven infants from our ongoing prospective longitudinal studies were identified based on parental response to a question about the presence of a family history of autoimmune disease and compared to 11 matched controls. The RAP threshold of each infant was assessed at 6 and 9 months of age using a conditioned head-turn procedure (using tone pairs with brief interstimulus intervals) and an auditory-visual habituation-recognition memory task using computer-generated consonant-vowel syllables (/ba/ vs. /da/). A visual habituation-recognition memory task that did not require processing of brief temporal cues was also administered. Group differences emerged on the infant RAP tasks, and on language outcome measures at 12 and 16 months of age. Infants from families with a history of autoimmune disorder had significantly higher (i.e., poorer) RAP thresholds and lower language scores than did control infants, whereas visual discrimination scores did not differ between family history infants and controls. Moreover, when brief auditory cues were necessary for the discrimination of /ba/ vs. /da/, infants with a family history of autoimmune disorder performed significantly more poorly than did controls. These findings lend support to the hypothesis that a similar mechanism, perhaps a neural-immune interaction, may underlie the observed co-occurrence of autoimmune disorders and learning impairments.

Infant discrimination of rapid auditory cues predicts later language impairment

The etiology and mechanisms of specific language impairment (SLI) in children are unknown. Differences in basic auditory processing abilities have been suggested to underlie their language deficits. Studies suggest that the neuropathology, such as atypical patterns of cerebral lateralization and cortical cellular anomalies, implicated in such impairments likely occur early in life. Such anomalies may play a part in the rapid processing deficits seen in this disorder. However, prospective, longitudinal studies in infant populations that are critical to examining these hypotheses have not been done. In the study described, performance on brief, rapidly-presented, successive auditory processing and perceptual-cognitive tasks were assessed in two groups of infants: normal control infants with no family history of language disorders and infants from families with a positive family history for language impairment. Initial assessments were obtained when infants were 6–9 months of age ( M=7.5 months) and the sample was then followed through age 36 months. At the first visit, infants’ processing of rapid auditory cues as well as global processing speed and memory were assessed. Significant differences in mean thresholds were seen in infants born into families with a history of SLI as compared with controls. Examination of relations between infant processing abilities and emerging language through 24 months-of-age revealed that threshold for rapid auditory processing at 7.5 months was the single best predictor of language outcome. At age 3, rapid auditory processing threshold and being male, together predicted 39–41% of the variance in language outcome. Thus, early deficits in rapid auditory processing abilities both precede and predict subsequent language delays. These findings support an essential role for basic nonlinguistic, central auditory processes, particularly rapid spectrotemporal processing, in early language development. Further, these findings provide a temporal diagnostic window during which future language impairments may be addressed.

The importance of rapid auditory processing abilities to early language development: evidence from converging methodologies.

The ability to process two or more rapidly presented, successive, auditory stimuli is believed to underlie successful language acquisition. Likewise, deficits in rapid auditory processing of both verbal and nonverbal stimuli are characteristic of individuals with developmental language disorders such as Specific Language Impairment. Auditory processing abilities are well developed in infancy, and thus such deficits should be detectable in infants. In the studies presented here, converging methodologies are used to examine such abilities in infants with and without a family history of language disorder. Behavioral measures, including assessments of infant information processing, and an EEG/event-related potential (ERP) paradigm are used concurrently. Results suggest that rapid auditory processing skills differ as a function of family history and are predictive of later language outcome. Further, these paradigms may prove to be sensitive tools for identifying children with poor processing skills in infancy and thus at a higher risk for developing a language disorder.