Brainstem auditory evoked potentials: a comparison of two high-frequency filter settings.

Filter bandpass characteristics are important elements in all modalities of evoked potential recordings. We studied the brainstem auditory evoked potentials by changing the bandpass of the recording system between 150 to 1500 Hz and 150 to 3000 Hz. The 150- to 1500-Hz bandpass prolonged the absolute latencies of the various waves, whereas the interpeak latencies (I to III, IIII to V, III to IV/V, I to V, or I to IV/V) were not significantly altered. The 150- to 1500-Hz filter reduced notched or multipeaked wave forms by decreasing the raw high-frequency input activity.

Assessing short-term recognition memory with forced-choice psychophysical methods.

The rationale and methodology for using computer-controlled forced-choice psychophysical methods to assess short-term recognition memory in human subjects are presented. Here, we use non-verbal computer-synthesized auditory and visual stimuli with an adaptive psychophysical procedure. Sequence-length thresholds (SLTs, span lengths) for randomly generated binary auditory and visual-sequential patterns and simultaneous visual-spatial patterns are determined to assess short-term memory capacity. The SLTs can also be used to equate for initial retention level for delayed matching-to-sample (DMS) or delayed matching-to-non-sample (DMNS) tasks which assess memory decay. The DMS/DMNS tasks have also been modified for use with the forced-choice paradigm. In contrast to many verbal paradigms requiring immediate ordered recall, non-verbal stimuli in a forced-choice paradigm provide a more direct measure of sensory memory because long-term memory, complex encoding/decoding processes, and motor-sequencing factors are minimized or avoided. Furthermore, the forced-choice recognition memory tasks are applicable over a broad age range, are less sensitive to socio-economic factors and educational level, and avoid complex instructions. Taken together, these factors enhance the applicability of these tasks in children and adults with CNS lesions, particularly where cognitive status may be compromised.

Some poststimulatory effects on the whole nerve action potential.

Short-term poststimulatory effects on the N1 component of the auditory-nerve compound action potential (CAP) were investigated in Mongolian gerbils. Some effects of conditioner level, conditioner frequency and probe level were assessed. In most cases, poststimulatory decrements occurred. The decrements were independent of probe intensity when the conditioner was close in frequency and of equal or less intensity than the probe. At some other conditioner frequencies, decrements decreased as probe intensity increased. Departures from these relationships occurred when a more intense conditioner was applied. In some instances, increases in CAP amplitude were also observed. The roles of single unit responses including spread of cochlear excitation, and possible mechanisms for poststimulatory facilitation are discussed.

T complex hemispheric asymmetries: effects of stimulus intensity.

The T complex component of the human auditory evoked potential (AEP) is thought to be produced in auditory cortex, on the posterior lateral surface of the temporal lobe. Recorded over temporal scalp, it consists of an 80-90 ms positive peak, Ta, and a 120-140 negative peak, Tb. As part of an effort to develop the clinical usefulness of the T complex in assessing auditory cortical function, we studied the effects of change in monaural stimulus intensity (20-80 dB SL) on T complex latency, amplitude, and hemispheric differences in normal adults. Ta and Tb peak latencies decreased as stimulus intensity increased. These latency changes were not dependent on ear or hemisphere. Right hemisphere Ta latency was shorter with contralateral than with ipsilateral stimulation; while left hemisphere Ta latency was not dependent on the ear stimulated. Tb latency was shorter over the left hemisphere, and over the contralateral hemisphere. Ta-b amplitude increased as stimulus intensity increased. This amplitude change was not dependent on ear or hemisphere. Ta-b amplitudes were larger over the right hemisphere and over the contralateral hemisphere. Hemispheric asymmetries were not significantly affected by stimulus intensity.

Anomalous cross-modal plasticity following posterior fossa surgery: some speculations on gaze-evoked tinnitus.

A unique and intriguing form of subjective tinnitus evoked by eye gaze is reviewed. A new perspective is presented because this condition is sufficiently different from other forms of subjective tinnitus and its manifestation cannot be adequately explained by existing models or conceptual frameworks. Our examination of this topic considers pathophysiologic changes in the central nervous system in the context of deafferentation-induced plasticity. Potential neuroanatomical areas contributing to this effect include a number of distributed and functionally diverse areas in the brainstem and neocortex involved in the auditory control of eye movements. We also consider contemporary psychophysical methods to evaluate the perceptual correlates of this phenomenon and tools for the development of objective tinnitus measurements. Although theoretical and speculative in nature, this article is intended to stimulate interest in, advance knowledge of, and provide a better understanding about this condition.

Clinical applications of otoacoustic emissions in sudden hearing loss.

Sudden hearing loss (SHL) is a controversial topic for which no definitive practical guidelines exist. Studies employing vasodilators, plasma expanders, anticoagulants, and carbogen inhalations have shown no improvement over the rate of spontaneous recovery. At present, there is insufficient evidence to support medical treatment for SHL, except steroid therapy in selected patients. Distortion product otoacoustic emissions (DPOAEs) are sensitive to cochlear disorders and are absent in ischemic injury to the cochlea, but can persist in cochlear neuritis. In a prospective study of 10 patients who presented to Albany Medical Center from 1995 to 1996, three patients with intact DPOAEs at presentation had an average improvement of 33 dB in the pure-tone average (PTA) of 0.5, 1.0, and 2.0 kHz with steroid therapy, whereas five of seven patients with absent DPOAEs had no improvement in hearing despite steroid therapy in six patients. The presence of DPOAEs may be a useful prognostic factor that positively correlates with recovery from SHL.

Advances in the development of the interferometric otoscope.

Present measurement techniques for middle ear function have inherent limitations because they are either spatially insensitive (acoustic immittance) or descriptive and qualitative in nature (otoscopy). By integrating advances in electrooptic technology (fiber optics, miniature diode lasers, solid-state detector arrays) and digital processing, further advances are possible. On the basis of measurements taken with electronic speckle-pattern interferometry on human temporal bones and models, we demonstrate quantitative static and dynamic vibration/displacement characteristics of the tympanic membrane with high spatial resolution. Our presentation emphasizes advantages of optically based methods and demonstrates computerized signal processing capable of fringe localization, enhancement, and counting. Miniaturization and real-time digital image processing in the clinical setting is the goal of this research.

Estimation of formant frequencies in infant cry.

The formant frequencies (F1, F2, F3) of normal infant crying were measured using three different estimation techniques: sound spectrography, linear predictive coding (LPC), and power spectrum analysis. Results found all three techniques to be highly similar for estimation of F1. However, the techniques differed significantly in the estimation of F2 and F3. Power spectrum analysis tended to yield the highest F2 and F3 values, while LPC consistently provided the lowest F2 and F3 values. Based on the results of the study, serious questions arise whether formant estimates of cry are accurate or appropriate for use as a metric of infant vocal tract resonance.

Acoustic features of normal-hearing pre-term infant cry.

Acoustic features of expiratory cry vocalizations were studied in 125 pre-term infants prior to being discharged from a level-3 neonatal intensive care unit. The purpose was to describe various phonatory behaviors in infants in whom significant hearing loss could be ruled out. We also compared these results with normal-hearing full-term infants, and evaluated whether linkage exists among acoustic cry features and various anthropometric, diagnostic and treatment variables obtained throughout the peri- and neonatal periods. Our analysis revealed that cry duration was significantly related to total days receiving respiratory assistance. The occurrence of other complex spectral and temporal aspects of acoustic cry vocalizations including harmonic doubling and vibrato also increased in infants receiving some form of respiratory assistance. The presence of harmonic doubling also depended on weight and conceptional age at test. The discussion focuses on the implication of these relationships and directions for future research.

Swallowing disorders in a population of children with cerebral palsy.

One of the disabilities in patients with cerebral palsy (CP) is dysphagia. To establish the prevalence of dysphagia in a population of children with CP, and to determine if any factors are related to dysphagia, we studied 56 CP patients, 5-21 years, enrolled in a primary school for the disabled. Fifteen patients (27%) had either radiographic or clinical evidence of dysphagia. These 15 patients were compared to the remaining 41 patients without dysphagia. Using data obtained from chart review and interviews with speech pathologists, several factors that contributed to dysphagia were found. These included: bite reflexes, slowness of oral intake, poor trunk control, inability to feed independently, anticonvulsant medication, coughing with meals, choking, and pneumonia. We also noted trends in the following factors: presence of tongue thrusting, presence of drooling, severity of CP, poor head control, severity of mental retardation, seizures, and speech disorders. Factors not related to the presence of dysphagia include: subject age, cause of CP, and type of CP. Early, aggressive work-up and identification in CP patients with the risk factors outlined above can reduce the associated pulmonary complications.

Effects of tonsillectomy and/or adenoidectomy on vocal function: laryngeal, supralaryngeal and perceptual characteristics.

A prospective, non-randomized study evaluated the effects of tonsillectomy and/or adenoidectomy (T +/- A) on acoustic and perceptual aspects of vocal function. Thirty-one children, ranging in age from 4 to 15 years participated and measurements were made prior to and 3 months following surgery. Twenty-three children had T +/- A and eight had adenoidectomy alone. Quantitative acoustic measures included: laryngeal (vocal fundamental frequency, FO) and supralaryngeal characteristics of sustained vowels (F1 and F2 formants, formant bandwidths, two-dimensional measures of vowel space) and temporal properties of consonant-vowel productions (diadochokinetic syllable rates). Perceptual measures were based on samples of continuous speech, using the Buffalo voice profile (BVP) and parental interviews/questionnaires were used to evaluate other aspects of surgery (i.e. subjective speech changes, protracted pain, difficulty swallowing, bleeding, etc.). Based on ANOVA, no significant post-surgical changes were detected for the majority of acoustic speech measures studied (vocal F0, formant bandwidths, measures of vowel space or diadochokinetic rates). However, the F2 formant frequency for vowels /i/ and /a/ increased and F1 decreased for /o/ following surgery. These changes had the largest effect on the structure of vowel /i/, which became more acute and diffuse following surgery. Furthermore, of the majority of perceptual measured studied with the BVP, 92% showed no change postoperatively. However, in the category of resonance, a significant decrease in hyponasality was detected. These results demonstrate that removing soft tissue from the oropharynx has only minimal impact on quantitative or qualitative (perceptual) aspects of vocal function, when measurements are made approximately 15 weeks post surgery.

Central deafness in a young child with Moyamoya disease: paternal linkage in a Caucasian family: two case reports and a review of the literature.

A case of 'central deafness' is presented in a 3-year-old male Caucasian child with Moyamoya disease (MMD); a rare, progressive and occlusive cerebrovascular disorder predominantly affecting the carotid artery system. Documentation of normal peripheral auditory function and brainstem pathway integrity is provided by acoustic admittance, otoacoustic emission and brainstem auditory evoked potential measurements. The lack of behavioral response to sound, and absent middle and long latency auditory evoked potentials suggest thalamo-cortical dysfunction. Magnetic resonance imaging showed diffuse ischemic damage in subcortical white matter including areas of the temporal lobes. In addition, there were multiple and focal cortical infarctions in both cerebral hemispheres, focused primarily in the frontal, parietal and temporal areas. Taken together, these structural and functional abnormalities in addition to severely delayed speech and language development are consistent with the diagnosis of central deafness and suggest a disconnection between higher brainstem and cortical auditory areas. The child's father also has MMD, but was diagnosed only recently. The presence of paternal linkage is informative since it rules out x-linked recessive and maternal inheritance. To our knowledge, this represents the first documented case of paternal linkage in MMD with central deafness in a Caucasian child with no apparent Japanese ancestry. Herein, we focus on central auditory dysfunction and consider how lesion-induced changes have contributed to a deficit in basic auditory responsiveness, including a severe disturbance in receptive and expressive auditory-based speech and language skills.

Central auditory processing disorder in school-aged children: a critical review.

The rationale to evaluate for central auditory processing disorder (CAPD) in school-aged children is based on the assumption that an auditory-specific perceptual deficit underlies many learning problems including specific reading and language disabilities. A fundamental issue in this area is whether convincing empirical evidence exists to validate this proposition. Herein, we consider the issue of modality specificity by examining the extent to which reading, language, and attention disorders in school-aged children involve perceptual dysfunctions limited to a single sensory modality. Difficulty in validating CAPD as a diagnostic label is due in large part to use of the unimodal inclusive framework, which has biased the diagnosis to favor sensitivity of test results over documenting the specificity of the deficit. Indeed, empirical research documenting modality-specific auditory-perceptual dysfunction in this population is scarce. Therefore, the existing literature on this topic has not clarified the "true" nature of the problem, and has left many questions about this disorder unanswered. It is argued that demonstrating modality specificity is one way to rule out supramodal disorders as explanations for observed dysfunction. Multimodal perceptual testing is one logical approach to help clarify this area of investigation.

Temporal-order discrimination for selected auditory and visual stimulus dimensions.

Thresholds for the discrimination of temporal order were determined for selected auditory and visual stimulus dimensions in 10 normal-adult volunteers. Auditory stimuli consisted of binary pure tones varying in frequency or sound pressure level, and visual stimuli consisted of binary geometric forms varying in size, orientation, or color. We determined the effect of psychophysical method and the reliability of performance across stimulus dimensions. Using a single-track adaptive procedure, Experiment 1 showed that temporal-order thresholds (TOTs) varied with stimulus dimension, being lowest for auditory frequency, intermediate for size, orientation, and auditory level, and longest for color. Test performance improved over sessions and the profile of thresholds across stimulus dimensions had a modest reliability. Experiment 2 used a double-interleaved adaptive procedure and TOTs were similarly ordered as in Experiment 1. However, TOTs were significantly lower for initially ascending versus descending tracks. With this method, the reliability of the profile across stimulus dimensions and tracks was relatively low. In Experiment 3, psychometric functions were obtained for each of the stimulus dimensions and thresholds were defined as the interpolated 70.7% correct point. The relative ordering of TOTs was similar to those obtained in the first two experiments. Non-monotonicities were found in some of the psychometric functions, with the most prominent being for the color dimension. A cross-experiment comparison of results demonstrates that TOTs and their reliability are significantly influenced by the psychophysical method. Taken together, these results support the notion that the temporal resolution of ordered stimuli involves perceptual mechanisms specific to a given sensory modality or submodality.

Principles of functional magnetic resonance imaging: application to auditory neuroscience.

Functional imaging based on magnetic resonance methods is a new research frontier for exploring a wide range of central nervous system (CNS) functions, including information processing in sensory, motor, cognitive, and linguistic systems. Being able to localize and study human brain function in vivo, in relatively high resolution and in a noninvasive manner, makes this a technique of unparalleled importance. In order to appreciate and fully understand this area of investigation, a tutorial covering basic aspects of this methodology is presented. We introduce functional magnetic resonance imaging (fMRI) by providing an overview of the studies of different sensory systems in response to modality-specific stimuli, followed by an outline of other areas that have potential clinical relevance to the medical, cognitive, and communicative sciences. The discussion then focuses on the basic principles of magnetic resonance methods including magnetic resonance imaging, MR spectroscopy, fMRI, and the potential role that MR technology may play in understanding a wide range of auditory functions within the CNS, including tinnitus-related activity. Because the content of the material found herein might be unfamiliar to some, we provide a broad range of background and review articles to serve as a technical resource.

Comparisons of memory for nonverbal auditory and visual sequential stimuli.

Properties of auditory and visual sensory memory were compared by examining subjects' recognition performance of randomly generated binary auditory sequential frequency patterns and binary visual sequential color patterns within a forced-choice paradigm. Experiment 1 demonstrated serial-position effects in auditory and visual modalities consisting of both primacy and recency effects. Experiment 2 found that retention of auditory and visual information was remarkably similar when assessed across a 10s interval. Experiments 3 and 4, taken together, showed that the recency effect in sensory memory is affected more by the type of response required (recognition vs. reproduction) than by the sensory modality employed. These studies suggest that auditory and visual sensory memory stores for nonverbal stimuli share similar properties with respect to serial-position effects and persistence over time.

On the loudness of complex stimuli and its relationship to cochlear excitation.

Two experiments were conducted to reexamine the relation between loudness and the bandwidth of complex stimuli. In experiment 1, experimental stimuli consisting of a 2000-Hz pure tone and ten computer-generated multitonal complexes ranging in bandwidth from 0.26-3.16 oct, logarithmically centered at 2000 Hz, were matched in loudness to a 2000-Hz comparison pure tone presented at 90, 70, and 30 dB SPL. The SPL of the experimental stimuli required for equal loudness was linearly related to bandwidth (in octaves) for each of the three comparison stimulus levels. In experiment 2, the loudness behavior of narrow-bandwidth stimuli within the previously reported critical band region was examined. The results indicated a linear relation similar to that obtained in experiment 1. These results are consistent with an auditory filter concept in which frequency is continuously encoded along the basilar membrane and in which loudness of complex stimuli is linearly related to area of excitation.

Level effects in complex stimulus discrimination.

The dependence of spectral-shape discriminations upon presentation level was studied using stimuli consisting of a bandpass noise and a less intense pure tone. The level of the noise band was held constant (+10 dB) relative to the level of the tone, and the minimum change in the intensity of the tone was measured across a range of presentation levels. The results demonstrated that, for tonal frequencies located near the upper edge of the noise band, subject's optimal performance occurred at intermediate presentation levels and became considerably poorer at high levels. This result is in accordance with upward spread of masking and emphasizes that presentation level is an important parameter to consider when measuring discriminations of complex spectral shapes.