Biomedical subjects

Hillel Pratt

Publications and source records attributed to Hillel Pratt.

At least 19 recordsLinked to original sources

PubMed2007

Categorical Perception of Speech (VOT) and Analogous Non-Speech (FOT) signals: Behavioral and electrophysiological correlates.

OBJECTIVE: To determine whether voicing perception is influenced primarily by linguistic experience or if it is due to innate temporal sensitivity to voicing boundaries, by examining behavioral and electrophysiological correlates of speech Voice-Onset-Time (VOT) and nonspeech Formant-Onset-Time (FOT) categorical perception. DESIGN: Behavioral measures and auditory event-related potentials (ERPs) were obtained from 14 normal-hearing Hebrew speakers, whose voicing distinction is different than English, during identification and discrimination of two sets of stimuli: a VOT continuum, created by editing natural productions of /ba/ and /pa/, and an analogous nonspeech continuum, composed of two synthesized formants, varying in their onset time-FOT. RESULTS: VOT and FOT continua yielded similar behavioral identification curves. Differences between the two stimulus types were found in discrimination of within-category differences and in reaction time effects. During identification and discrimination tasks, ERPs were differently affected by the VOT or FOT value of the stimulus: VOT value had a significant effect on N1 latency and on N1 and P2 amplitudes whereas FOT value had a significant effect on P2 amplitude. Additionally, during identification tasks, whereas all speech signals evoked a P3, regardless of overt categorization, only the perceptually "rare" nonspeech stimulus (+15 msec FOT) evoked a P3. CONCLUSIONS: Voicing boundaries corresponded to Hebrew VOT values of production, suggesting that voicing perception in Hebrew is mediated mainly by linguistic experience rather than by innate temporal sensitivity. ERP data differed to VOT versus FOT stimuli as early as N1, indicating that brain processing of the temporal aspects of speech and nonspeech signals differ from their early stages. Further studies to establish the neural response patterns to voicing in speakers of languages that use different voicing categories than English are warranted.

Acoustic Stimulation↗

PubMed2005

The composite N1 component to gaps in noise.

OBJECTIVE: To indicate whether the double peaked N(1) to gaps in continuous white noise is a composite of onset and offset responses to transients or whether it reflects higher processing such as change or mismatch detection and to assess the role of attention in this process. METHODS: Evoked potentials were recorded to two binaural stimulus types: (1) gaps of different durations randomly distributed in continuous white noise; and (2) click pairs at intervals identical to those between gap onsets and offsets in the continuous noise stimulus. Potentials to these stimuli were recorded while subjects read a text and while detecting gaps in noise or click pairs. RESULTS: Potentials were detected to all click pairs and to gaps of 5 ms or longer, corresponding to the subjects' psychoacoustic gap detection threshold. With long gap durations of 200-800 ms, distinct potentials to gap onset and gap offset were observed. The waveforms to all click pairs and to offsets of long gaps were similar and single-peaked, while potentials to gaps of 10 ms and longer, and potentials to onsets of long gaps were double-peaked, consisting of two N(1) negativities, 60 ms apart, irrespective of gap duration. The first (N(1a)), was more frontal in its distribution and similar to that of clicks. The second (N(1b)) peak's distribution was more central/temporal and its source locations and time course of activity were distinct. No effects of attention on any of the varieties and constituents of N(1) were observed. CONCLUSIONS: Comparing potentials to gap onsets, to click pairs and to gap offsets, suggests that potentials to gap onsets involve not only sound onset/offset responses (N(1), N(1a)) but also the subsequent pre-attentive perception of the cessation of an ongoing sound (N(1b)). We propose that N(1b) is distinct from change or mismatch detection and is associated with termination of an ongoing continuous stimulus. We propose to call it the N(egation)-process. SIGNIFICANCE: A constituent of the N(1) complex is shown to be associated with the pre-attentive perception of termination of an ongoing stimulus and to have distinct scalp distribution and intracranial sources.

Acoustic Stimulation↗

PubMed2005

Auditory event related potentials and source current density estimation in phonologic/auditory dyslexics.

OBJECTIVE: To determine the generality of auditory processing impairment in phonologic dyslexics by studying their auditory Event-Related Potentials (ERPs) and the spatio-temporal distribution of their brain activity to auditory linguistic and non-linguistic stimuli with temporal and spectral discriminating cues. METHODS: Fourteen adult phonologic dyslexics and 14 normal reading students, all with high academic achievements, were compared. ERP waveform analysis and current density source estimation (Low resolution Electromagnetic Tomographic Analysis-LORETA) were conducted on 21-channel records from subjects who passively listened or actively discriminated 4 types of auditory stimuli: linguistic and non-linguistic stimuli that differed in spectral or temporal characteristics. RESULTS: Significant differences were found for all ERP latencies (N1, P2, N2, P3) in response to all stimuli, with dyslexics presenting longer latencies compared to normal readers. Current density distributions and their time courses also differed significantly, regardless of stimulus type or attention allocation. Among normal readers, early activity (around N1) was characterized by a rapid change of maximum activity from right to left temporal lobe. Later activity (around P3) was characterized by a stable temporal activity with bilaterally synchronous peak activity. Among the dyslexics, the early N1 activity was stable with left hemisphere prominence, with no alternation between the hemispheres, while the later P3 activity peaked earlier in the right hemisphere than in the left. CONCLUSIONS: Dyslexics were different from controls in processing all auditory stimuli: verbal and non-verbal stimuli with temporal as well as with spectral discriminating cues. The differences mainly consisted of latency and time courses of current density distributions, beginning as early as N1 and extending to the late P3. SIGNIFICANCE: Differences in processing auditory stimuli by phonologic dyslexics are not restricted to linguistic (phonological) stimuli, supporting a general auditory processing impairment in phonologic dyslexia.

Acoustic Stimulation↗

PubMed2005

The 'F-complex' and MMN tap different aspects of deviance.

OBJECTIVE: To compare the 'F(fusion)-complex' with the Mismatch negativity (MMN), both components associated with automatic detection of changes in the acoustic stimulus flow. METHODS: Ten right-handed adult native Hebrew speakers discriminated vowel-consonant-vowel (V-C-V) sequences /ada/ (deviant) and /aga/ (standard) in an active auditory 'Oddball' task, and the brain potentials associated with performance of the task were recorded from 21 electrodes. Stimuli were generated by fusing the acoustic elements of the V-C-V sequences as follows: base was always presented in front of the subject, and formant transitions were presented to the front, left or right in a virtual reality room. An illusion of a lateralized echo (duplex sensation) accompanied base fusion with the lateralized formant locations. Source current density estimates were derived for the net response to the fusion of the speech elements (F-complex) and for the MMN, using low-resolution electromagnetic tomography (LORETA). Statistical non-parametric mapping was used to estimate the current density differences between the brain sources of the F-complex and the MMN. RESULTS: Occipito-parietal regions and prefrontal regions were associated with the F-complex in all formant locations, whereas the vicinity of the supratemporal plane was bilaterally associated with the MMN, but only in case of front-fusion (no duplex effect). CONCLUSIONS: MMN is sensitive to the novelty of the auditory object in relation to other stimuli in a sequence, whereas the F-complex is sensitive to the acoustic features of the auditory object and reflects a process of matching them with target categories. SIGNIFICANCE: The F-complex and MMN reflect different aspects of auditory processing in a stimulus-rich and changing environment: content analysis of the stimulus and novelty detection, respectively.

Adult↗

PubMed2005

Cortical activity of children with dyslexia during natural speech processing: evidence of auditory processing deficiency.

Children with dyslexia have difficulties with phonological processing. It is assumed that deficits in auditory temporal processing underlie the phonological difficulties of dyslectic subjects (i.e. the processing of rapid acoustic changes that occur in speech). In this study we assessed behavioral and electrophysiological evoked brain responses of dyslectic and skilled reading children while performing a set of hierarchically structured auditory tasks. Stimuli consisted of auditory natural unmodified speech that was controlled for the parameter of changing rate of main acoustic cues: vowels (slowly changing speech cues: /i/ versus /u/) and consonant-vowel (CV) syllables (rapidly changing speech cues: /da/ versus /ga/). Brain auditory processing differed significantly between groups: reaction time of dyslectic readers was prolonged in identifying speech stimuli and increased with increased phonological demand. Latencies of auditory evoked responses (auditory event related potentials [AERPs]) recorded during syllable identification of the dyslectic group were prolonged relative to those of skilled readers. Moreover, N1 amplitudes during vowel processing were larger for the dyslectic children and P3 amplitudes during CV processing were smaller for the dyslectic children. From the results of this study it is evident that the latency and amplitude of AERPs are sensitive measures of the complexity of phonological processing in skilled and dyslectic readers. These results may be signs of deficient auditory processing of natural speech under normal listening conditions as a contributing factor to reading difficulties in dyslexia. Detecting a dysfunction in the central auditory processing pathway might lead to early detection of children who may benefit from phonetic-acoustic training methods.

Acoustic Stimulation↗

PubMed2004

Time course and nature of stimulus evaluation in category induction as revealed by visual event-related potentials.

Category induction involves abstraction of features common to two or more stimuli. We predicted that category induction affects processing of each stimulus, before completion of perceptual analysis. Event-related potentials (ERPs) were recorded from ten 11-13-year olds while they were performing visual category-induction tasks. Subjects viewed a series of two geometric shapes belonging to the same perceptual category (size, color, or shape), defined by one or two shared features, and decided if a probe stimulus shared membership in that category. Large frontal N120, frontal-central N300 and smallest P450 were elicited by the first stimulus; number of shared features affected P150, N170, and P450 amplitudes to the second stimulus. Principal Component Analysis (PCA) indicated networks of frontal, parietal and occipital activity, different to each stimulus. Results suggest that in young adolescents category induction affects early stages of stimulus processing. Processing is based on selective analysis of stimuli for shared features, not exhaustive examination of all features of all stimuli.

Adolescent↗

PubMed2004

Auditory middle-latency components to fusion of speech elements forming an auditory object.

OBJECTIVE: The purpose of this study was to define early brain activity associated with fusion of speech elements to form an auditory object in the middle-latency range preceding the F-Complex. METHODS: Stimuli were binaural formant transition and base, that were presented separately or fused to form the vowel-consonant-vowel sequence /ada/. Eleven right-handed, adult, native Hebrew speakers listened to 2/s presentations, and the brain potentials from C(z) during the 250 msec following transition onset (in the responses to transition and to the fused word) or following the time it would have been presented (in the response to base alone) were recorded. The net-fusion response was extracted by subtracting the sum of potentials to the base and the formant transition from the potentials to the fused sound. RESULTS: Auditory middle-latency components, comprising of 9 peaks and troughs were recorded in response to the base, to the formant transition and to the fused /ada/. In general, the responses to the fused object were significantly smaller in peak amplitude and in total activity (area under the curve) resulting in the difference waveform of the net-fusion response that also included 9 peaks, but with opposite polarities. CONCLUSIONS: The early middle-latency components to fusion indicate that the fusion of speech elements to a word involves inhibition, occlusion or both. The results are in line with the uniqueness of speech perception and the early role of the auditory cortex in speech analysis.

Acoustic Stimulation↗

PubMed2004

The combined effects of forward masking by noise and high click rate on monaural and binaural human auditory nerve and brainstem potentials.

OBJECTIVE: To study effects of forward masking and rapid stimulation on human monaurally- and binaurally-evoked brainstem potentials and suggest their relation to synaptic fatigue and recovery and to neuronal action potential refractoriness. METHODS: Auditory brainstem evoked potentials (ABEPs) were recorded from 12 normally- and symmetrically hearing adults, in response to each click (50 dB nHL, condensation and rarefaction) in a train of nine, with an inter-click interval of 11 ms, that followed a white noise burst of 100 ms duration (50 dB nHL). Sequences of white noise and click train were repeated at a rate of 2.89 s(-1). The interval between noise and first click in the train was 2, 11, 22, 44, 66 or 88 ms in different runs. ABEPs were averaged (8000 repetitions) using a dwell time of 25 micros/address/channel. The binaural interaction components (BICs) of ABEPs were derived and the single, centrally located equivalent dipoles of ABEP waves I and V and of the BIC major wave were estimated. RESULTS: The latencies of dipoles I and V of ABEP, their inter-dipole interval and the dipole magnitude of component V were significantly affected by the interval between noise and clicks and by the serial position of the click in the train. The latency and dipole magnitude of the major BIC component were significantly affected by the interval between noise and clicks. Interval from noise and the click's serial position in the train interacted to affect dipole V latency, dipole V magnitude, BIC latencies and the V-I inter-dipole latency difference. Most of the effects were fully apparent by the first few clicks in the train, and the trend (increase or decrease) was affected by the interval between noise and clicks. CONCLUSIONS: The changes in latency and magnitude of ABEP and BIC components with advancing position in the click train and the interactions of click position in the train with the intervals from noise indicate an interaction of fatigue and recovery, compatible with synaptic depletion and replenishing, respectively. With the 2 ms interval between noise and the first click in the train, neuronal action potential refractoriness may also be involved.

Acoustic Stimulation↗

PubMed2004

Attenuation of cerebral oxygen toxicity by sound conditioning.

HYPOTHESIS: Sound conditioning might reduce cerebral oxygen toxicity. BACKGROUND: Cerebral oxygen toxicity is related to high levels of reactive oxygen species. Noise-induced hearing loss has been shown to result from ischemia-reperfusion, in which reactive oxygen species play a major role. Repeated exposure to loud noise at levels below that which produces permanent threshold shift prevented noise-induced hearing loss and was associated with significant elevation of the antioxidant enzymes measured in the inner ear. We tested the hypothesis that sound conditioning might reduce cerebral oxygen toxicity. METHODS: Forty-five guinea pigs were prepared for electroencephalography and auditory brainstem recording. The auditory brainstem recording detection threshold was determined to confirm baseline normal hearing. The animals were divided into three equal groups and subjected to the following procedures: Group 1, electroencephalography electrode implantation and auditory brainstem recording only; Group 2, exposure to oxygen at 608 kPa (the latency to the first electrical discharge in the electroencephalogram preceding the appearance of seizures was measured); and Group 3, sound conditioning followed by oxygen exposure. The animals were killed, and the brains were excised and homogenized. Brain levels of superoxide dismutase, catalase, glutathione peroxidase, glutathione transferase, glutathione reductase, glucose-6-phosphate dehydrogenase, and thiobarbituric acid reactive substances were compared among the groups. RESULTS: Latency to the first electrical discharge was compared between Groups 2 and 3, and was found to be significantly longer in Group 3 (27.9 +/- 11 versus 20.4 +/- 7.6 min, p < 0.03). No significant changes were found in brain levels of superoxide dismutase, catalase, glutathione peroxidase, glutathione transferase, glutathione reductase, glucose-6-phosphate dehydrogenase, or thiobarbituric acid reactive substances. CONCLUSION: Our data show that sound conditioning prolongs the latency to oxygen-induced convulsions. This effect was not accompanied by significant changes in whole-brain antioxidant enzyme activity or the magnitude of lipid peroxidation.

Animals↗

PubMed2003

High-frequency sound transmissions under water and risk of decompression sickness.

We tested the possible occurrence of a neurological insult secondary to high-frequency sound exposure. Immersed, anesthetized rats were subjected to a simulated diving profile designed to induce decompression sickness, while exposed to the transmission of an acoustic beacon. Intermittent sound at a pressure level of 184.5 dB re 1 microPa at 1 m (1.7 kPa), a frequency of 37 kHz, and with a duration of 4 ms, was transmitted in a duty cycle of 0.26%. Four groups, each containing nine animals, were included in the study as follows: group 1, immersion only, no sound exposure; group 2, immersion with sound exposure; group 3, diving simulation when immersed, no sound exposure; group 4, diving simulation when immersed, with sound exposure. Somatosensory evoked potentials (SSEPs) were recorded the day before the study, and a second recording was made 30 min after immersion. Some of the SSEP components disappeared after the dive in 3 rats from group 3 and 2 rats from group 4. SSEP components could not be identified in a significantly larger number of animals from groups 3 and 4, compared with groups 1 and 2. No differences were found in wave latency, amplitude or conduction time. Our data show that the high-frequency sound exposure employed did not contribute to the development of the neurological insult.

Animals↗

PubMed2003

The cumulative effect of high click rate on monaural and binaural processing in the human auditory brainstem.

OBJECTIVE: The objective of the present study was to compare the effects of high stimulus rate and click position in the train on monaurally and binaurally evoked activities in the human auditory brainstem and suggest their possible physiological mechanism. METHODS: Auditory brainstem evoked potentials (ABEPs) were recorded from 15 normally and symmetrically hearing adults from 3 channels, in response to 50dB nHL, alternating polarity clicks, presented at a rate of 21/s as well as separately to each click in a train of 10 with an interstimulus interval of 11ms. Click trains were presented at a rate of 5.13/s. The binaural interaction components (BICs) of ABEPs were derived by subtracting the response to binaural clicks from the algebraic sum of monaural responses. Single, centrally located equivalent dipoles were estimated as concise measures of the surface-summated activity of ABEPs and BICs generators. RESULTS: A significant effect of click position in the train on equivalent dipole latency of ABEP component V and on equivalent dipole magnitude of III were found. Latency was prolonged and amplitude was increased the later the click's position in the train. A significant effect of click position in the train on equivalent dipole latencies of all components of BICs was found. Latencies were prolonged if the click's position occurred later in the train, with most of the latency shift achieved by the third click in the train for the first major BIC and by the seventh click for other BIC components. No significant effects on equivalent dipole magnitudes of BICs were found. No significant effect of click position in the train on orientation of any of the equivalent dipoles of ABEP or BIC was found. CONCLUSIONS: The progressive prolongation of latency of ABEP and BIC components with advancing position in the train may be attributed to cumulatively decreased synaptic efficacy at high stimulus rates, resulting in prolonged synaptic delays along the auditory pathway. The paradoxic enhancement of ABEP dipole III magnitude with advancing click position in the train may reflect higher sensitivity of inhibitory brainstem neurons to increased stimulus rate, resulting in disinhibition. The absence of significant effects on BIC dipole magnitudes may reflect the amplifying effect of divergence in the ascending auditory pathway, as has been observed for the monaurally evoked ABEP components from the upper pons.

Acoustic Stimulation↗

PubMed2003

The electrophysiological net response ('F-complex') to spatial fusion of speech elements forming an auditory object.

OBJECTIVE: The purpose of this study was to define and analyze the brain activity associated with fusion of speech elements to form an auditory object and to study the effects of presenting the elements at different spatial locations (duplex stimulus). METHODS: Stimuli were formant transitions (presented to the front, left or right of the subject) and base (presented to the front), that fused to result in V-C-V sequences /aga/ and /ada/. Ten right-handed, adult, native Hebrew speakers discriminated each fused stimulus, and the brain potentials associated with performance of the task were recorded from 21 electrodes. The net-fusion response, the 'F(fusion)-complex', was extracted by subtracting the sum of potentials to the base and formant transitions from the potentials to the fused sound. Low resolution electromagnetic tomography analysis (LORETA) was performed to assess the timing and brain location of the fusion process. RESULTS: The 'F-complex', comprising of the difference N(1), P(2), N(2b) (FN(1), FP(2), FN(2b)) components could be identified for each of the stimuli and reflected a process indicating inhibition, occlusion or both, with right ear advantage in fusion. LORETA analyses indicate sequential processing of speech fusion in the temporal lobes, beginning with right prominence in FN(1) and FP(2) shifting to a more symmetrical pattern in FN(2). CONCLUSIONS: The electrophysiological correlates of speech fusion highlight the uniqueness of speech perception and the brain areas involved in its analysis.

Acoustic Stimulation↗

PubMed2003

Evoked potentials to auditory movement sensation in duplex perception.

OBJECTIVE: The purpose of this study was to examine the processing of auditory movement sensation accompanying duplex perception in binaural hearing. METHODS: Stimuli were formant transitions (presented to the front, left or right of the subject) and base (presented to the front), that fused to result in vowel-consonant-vowel (V-C-V) sequences /aga/ and /ada/. An illusion of auditory movement (duplex sensation) accompanied the fusion of these V-C-V sequences when the spatial locations of the formant transitions and base were different. Ten right-handed, adult, native Hebrew speakers discriminated each fused stimulus, and the brain potentials associated with performance of the task were recorded from 21 electrodes. The processing of auditory movement was studied by a factorial design (ANOVA) and statistical non-parametric mapping (SnPM) of low resolution electromagnetic tomography (LORETA) images of the net-fusion response. Brain regions implicated in auditory movement processing were expected to be associated with the lateralized formant location, which gave rise to duplex perception. In addition, the time-course of significant activation in brain areas that differentiated between fusion conditions was determined. RESULTS: The posterior parietal, anterior cingulate and premotor cortices were found to be implicated in duplex processing. Auditory cortex involvement was also evident, and together with the latter two brain regions was affected by right-ear advantage. CONCLUSIONS: Duplex perception resulting from fusion of spatially separate sounds forming an auditory object results in activation of a network of brain regions reflecting enhanced allocation of attention and the effect of language processing.

Acoustic Stimulation↗

PubMed2003

High-resolution time course of hemispheric dominance revealed by low-resolution electromagnetic tomography.

OBJECTIVE: Auditory event-related brain potentials (ERPs) were recorded during a lexical decision task in response to linguistic and non-linguistic stimuli, to assess the detailed time course of language processing in general, and hemispheric dominance in particular. METHODS: Young adults (n=17) were presented with pairs of auditory stimuli consisting of words, pseudowords and words played backwards in a lexical decision task. ERPs were recorded from 21 scalp electrodes. Current densities were calculated using low-resolution electromagnetic tomography (LORETA). Statistic non-parametric maps of activity were derived from the calculated current densities and the number of active brain voxels in the left and right hemispheres was compared throughout the processing of each stimulus. RESULTS: Our results show that hemispheric dominance is highly time dependent, alternating between the right and left hemispheres at different times, and that the right hemisphere's role in language processing follows a different time course for first and second language. The time course of hemispheric dominance for non-linguistic stimuli was highly variable. CONCLUSIONS: The time course of hemispheric dominance is dynamic, alternating between left and right homologous regions, with different time courses for different stimulus classes.

Acoustic Stimulation↗

PubMed2003

Linguistic processing in idiopathic generalized epilepsy: an auditory event-related potential study.

PURPOSE: Auditory processing of increasing acoustic and linguistic complexity was assessed in children with idiopathic generalized epilepsy (IGE) by using auditory event-related potentials (AERPs) as well as reaction time and performance accuracy. METHODS: Twenty-four children with IGE [12 with generalized tonic-clonic seizures (GTCSs), and 12 with absence seizures (ASs)] with average intelligence and age-appropriate scholastic skills, uniformly medicated with valproic acid (VPA), and 20 healthy controls, performed oddball discrimination tasks that consisted of the following stimuli: (a) pure tones; (b) nonmeaningful monosyllables that differed by their phonetic features (i.e., phonetic stimuli); and (c) meaningful monosyllabic words from two semantic categories (i.e., semantic stimuli). RESULTS: AERPs elicited by nonlinguistic stimuli were similar in healthy and epilepsy children, whereas those elicited by linguistic stimuli (i.e., phonetic and semantic) differed significantly in latency, amplitude, and scalp distribution. In children with GTCSs, phonetic and semantic processing were characterized by slower processing time, manifested by prolonged N2 and P3 latencies during phonetic processing, and prolongation of all AERPs latencies during semantic processing. In children with ASs, phonetic and semantic processing were characterized by increased allocation of attentional resources, manifested by enhanced N2 amplitudes. Semantic processing also was characterized by prolonged P3 latency. In both patient groups, processing of linguistic stimuli resulted in different patterns of brain-activity lateralization compared with that in healthy controls. Reaction time and performance accuracy did not differ among the study groups. CONCLUSIONS: AERPs exposed linguistic-processing deficits related to seizure type in children with IGE. Neurologic follow-up should therefore include evaluation of linguistic functions, and remedial intervention should be provided, accordingly.

Acoustic Stimulation↗

PubMed2003

Electrophysiological correlates of azimuth and elevation cues for sound localization in human middle latency auditory evoked potentials.

OBJECTIVE: To study, in humans, the effects of sound source azimuth and elevation on primary auditory cortex binaural activity associated with sound localization. DESIGN: Middle Latency Auditory Evoked Potentials (MLAEPs) were recorded from three channels, in response to alternating polarity clicks, presented at a rate of 5/sec, at nine virtual spatial locations with different azimuths and elevations. Equivalent dipoles of Binaural Interaction Components (BICs) of MLAEPs were derived from 15 normally and symmetrically hearing adults by subtracting the response to binaural clicks at each spatial location from the algebraic sum of responses to stimulation of each ear alone. The amplified potentials were averaged over 4000 repetitions using a dwell time of 78 micro sec/address/channel. Variations in magnitudes, latencies and orientations of the dipole equivalents of cortical activity were noted in response to the nine spatial locations. RESULTS: Middle-latency BICs included six major components corresponding in latency to the vertex-neck recorded components of MLAEP. A significant decrease of equivalent dipole magnitude was observed for two of the components: Pa2 in response to clicks in the backward positions (medium and no elevation); and Nb in response to clicks in the back and front positions (medium and no elevation) in the midsagittal plane. In the coronal plane, Pa2 equivalent dipole magnitude significantly decreased in response to right-horizontal (no elevation) clicks. Significant effects on equivalent dipole latencies of Pa2 were found for backward positions (no elevation) in the midsagittal plane. No significant effects on Pa2 and Nb equivalent dipole orientations were found across stimulus conditions. CONCLUSIONS: The changes in equivalent dipole magnitudes and latencies of MLAEP BICs across stimulus conditions may reflect spectral tuning in binaural primary auditory cortex neurons processing the frequency cues for sound localization.

Adult↗

PubMed2003

Equivalent dipoles of the binaural interaction components and their comparison with binaurally evoked human auditory 40 Hz steady-state evoked potentials.

OBJECTIVE: The purpose of this study was to acquire the Binaural Interaction (BI) components of the auditory middle-latency steady-state 40 Hz potentials, compare them with those of the binaurally evoked 40 Hz response and with transient-evoked Auditory Middle Latency Evoked Potentials (AMEP) and suggest possible contributors and generators of the composite 40 Hz BI. METHODS: Potentials were recorded from 15 normal-hearing adults in response to 40/sec clicks. BI was derived by subtracting the binaurally evoked potentials from the algebraic sum of the evoked potentials to left and to right ear stimulation. Latencies, magnitudes and orientations of the dipole equivalents of 40 Hz components were compared with their BI counterparts, as estimated by three-channel Lissajous' trajectories. Comparison of the transient AMEP to binaural stimulation with the BI of the steady-state 40 Hz response was also conducted to elucidate the contributions of different levels along the auditory pathway to the 40 Hz BI responses. RESULTS: Each cycle of the BI of the steady-state 40 Hz AMEP included four components that corresponded in latency, amplitude, and dipole orientation to their counterparts in the binaurally evoked waveform. Amplitudes of BI components were 50 to 60% of the respective values in the binaurally evoked potentials. Orientations of BI components matched those of the cortical components in the transient-evoked AMEP. CONCLUSIONS: The results suggest that the main contribution to the 40 Hz BI is from rate resistant thalamo-cortical neurons. The results also suggest that the binaural cortical neurons contributing to the 40 Hz BI are less affected by increased rate than monaural neurons.

Acoustic Stimulation↗

PubMed2003

Semantic processing of unattended words and pseudowords in first and second language: an ERP study.

We recorded event related brain potentials to assess stages of linguistic processing of first (L1) and second (L2) language and of pseudowords when subjects were engaged in a different task and did not attend to the words. Young adults (n = 15) were presented with pairs of auditory stimuli consisting of words and pseudowords in L1 and L2 with different voice onset times (VOT), which served as distracters in a short-term memory task. ERPs were recorded from 11 scalp electrodes. The ERP peak amplitudes and latencies were subjected to analysis of variance for the effects of language, meaning and scalp location as well as priming of the second word in the pair by the preceding word. Behavioral results showed that attention was drawn to the primary task and away from the words; yet significant, including semantic, processing was evident in the ERPs to the words, with significant effects of language, meaning and priming. Even with barely any awareness of the stimuli, the brain processes words including distinguishing between L1 and L2 and relating to the stimuli's context.

Acoustic Stimulation↗