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Purpose: The acoustic source that is attended to by the listener in a mixture can be identified with a certain accuracy on the basis of their neural response recorded during listening, and various phenomena may be used to detect attention. For example, neural tracking (NT) and alpha power lateralization (APL) may be utilized in order to obtain information concerning attention. However, these methods of auditory attention detection (AAD) are typically tested in different experimental setups, which makes it impossible to compare their accuracy. The aim of this study is to compare the accuracy of AAD based on NT, APL, and their combination for a dichotic natural speech listening task. Method: Thirteen adult listeners were presented with dichotic speech stimuli and instructed to attend to one of them. Electroencephalogram of the subjects was continuously recorded during the experiment using a set of 32 active electrodes. The accuracy of AAD was evaluated for trial lengths of 50, 25, and 12.5 s. AAD was tested for various parameters of NT- and APL-based modules. Results: The obtained results suggest that NT of natural running speech provides similar accuracy to APL. The statistically significant improvement of the accuracy of AAD using a combined method has been observed not only for the longest duration of test samples (50 s, p = .005) but also for shorter ones (25 s, p = .011). Conclusions: It seems that the combination of standard NT and APL significantly increases the effectiveness of accurate identification of the traced signal perceived by a listener under dichotic conditions. It has been demonstrated that, under certain conditions, the combination of NT and APL may provide a benefit for AAD in cocktail party scenarios., One of the crucial capabilities of the human auditory system is to consciously focus on meaningful signals and simultaneously ignore the remaining irrelevant or disruptive stimuli. A convincing example is [...]

Auditory sensitivities are common among people with autism spectrum disorder diagnoses (ASD). As underlying factors are unknown, we examined whether ASD adults (N.sub.ASD = 33; N.sub.Typically Developing = 31; 25-45 years; IQ > 70): (1) habituated slower to auditory stimuli; (2) had lower auditory detection thresholds; and (3) whether these mechanisms related to self-reported auditory sensitivities. Two auditory stimuli (tone, siren) were repeated, whilst skin conductance responses were recorded to measure habituation. Detection thresholds were measured by stepwise reductions in tone volume. We found no evidence in favor of our hypotheses, but ASD adults did rate the auditory stimuli as more arousing. Based on explorative analyses, we argue that studying the strength of physiological responses to auditory stimuli is needed to understand auditory sensitivities., Author(s): Marieke W. M. Kuiper [sup.1] [sup.2] , Elisabeth W. M. Verhoeven [sup.1] , Hilde M. Geurts [sup.1] [sup.2] Author Affiliations: (Aff1) Dr. Leo Kannerhuis, Autism Expert Centre, Department of [...]

Background: The amplitude of the auditory evoked N1 component that can be derived from noninvasive electroencephalographic recordings increases as a function of time between subsequent tones. N1 amplitudes in individuals with schizophrenia saturate at a lower asymptote, thus giving rise to a reduced dynamic range. Reduced N1 dynamic range is a putative electrophysiological biomarker of altered sensory memory function in individuals with the disease. To date, it is not clear what determines N1 dynamic range and what causes reduced N1 dynamic range in individuals with schizophrenia. Here we test the hypothesis that reduced N1 dynamic range results from a shift in excitatory/inhibitory (E/I) balance toward an excitation- deficient or inhibition-dominant state. Methods: We recorded auditory-evoked potentials (AEPs) while 4 macaque monkeys passively listened to sequences of sounds of random pitch and stimulusonset asynchrony (SOA). Three independent experiments tested the effect of the W- methyl-D-aspartate receptor channel blockers ketamine and MK-801 as well as the y-aminobutyric acid (GABA) A receptor-positive allosteric modulator midazolam on the dynamic range of a putative monkey N1 homologue and 4 other AEP components. Results: Ketamine, MK-801 and midazolam reduced peak N1 amplitudes for the longest SOAs. Other AEP components were also affected, but revealed distinct patterns of susceptibility for the glutamatergic and GABA-ergic drugs. Different patterns of susceptibility point toward differences in the circuitry maintaining E/I balance of individual components. Limitations: The study used systemic pharmacological interventions that may have acted on targets outside of the auditory cortex. Conclusion: The N1 dynamic range may be a marker of altered E/I balance. Reduced N1 dynamic range in individuals with schizophrenia may indicate that the auditory cortex is in an excitation- deficient or inhibition-dominant state. This may be the result of an incomplete compensation for a primary deficit in excitatory drive., Introduction Individuals with schizophrenia exhibit deficits in simple auditory tasks, such as delayed pitch discrimination. (1-6) These deficits have been linked in part to impaired encoding of information into auditory [...]

Purpose: The purpose of this review article is to review evidence from auditory evoked potential studies to describe the contributions of the auditory brainstem and cortex to the generation of the masking level difference (MLD). Method: A literature review was performed, focusing on the auditory brainstem, middle, and late latency responses used in protocols similar to those used to generate the behavioral MLD. Results: Temporal coding of the signals necessary for generating the MLD occurs in the auditory periphery and brainstem. Brainstem disorders up to wave III of the auditory brainstem response (ABR) can disrupt the MLD. The full MLD requires input to the generators of the auditory late latency potentials to produce all characteristics of the MLD; these characteristics include threshold differences for various binaural signal and noise conditions. Studies using central auditory lesions are beginning to identify the cortical effects on the MLD. Conclusions: The MLD requires auditory processing from the periphery to cortical areas. A healthy auditory periphery and brainstem codes temporal synchrony, which is essential for the ABR. Threshold differences require engaging cortical function beyond the primary auditory cortex. More studies using cortical lesions and evoked potentials or imaging should clarify the specific cortical areas involved in the MLD., The abilities of humans to understand speech and localize target signals in noisy backgrounds are attributed to the binaural system. The binaural masking level difference (MLD), so named by Webster [...]

Objective: The purpose of this study was to describe normative aspects of wideband acoustic immittance (WAI) measures obtained from healthy White neonates. Method: In this cross-sectional study, wideband absorbance (WBA), admittance magnitude, and admittance phase were measured under ambient pressure condition in 326 ears from 203 neonates (M age = 45.9 hr) who passed a battery of tests, including automated auditory brainstem response, high-frequency tympanometry, and distortion product otoacoustic emissions. Results: Normative WBA data were in agreement with most previous studies. Normative data for both WBA and admittance magnitude revealed double-peaked patterns with the 1st peak at 1.25-2 kHz and the 2nd peak at 5-8 kHz, while normative admittance phase data showed 2 peaks at 0.8 and 4 kHz. There were no significant differences between ears or gender for the 3 WAI measures. Standard deviations for all 3 measures were highest at frequencies above 4 kHz. Conclusions: The 3 WAI measures between 1 kHz and 4 kHz may provide the most stable response of the outer and middle ear. WAI measures at frequencies above 4 kHz were more variable. The normative data established in the present study may serve as a reference for evaluating outer and middle ear function in neonates., Wideband acoustic immittance (WAI) has emerged as a new clinical tool with greater accuracy than tympanometry in identifying conductive conditions in neonates (S. Aithal, Kei, Driscoll, Khan, & Swanston, 2015; [...]

Purpose: Responses to intensity perturbation during running speech were measured to understand whether prosodic features are controlled in an independent or integrated manner. Method: Nineteen English-speaking healthy adults (age range = 21-41 years) produced 480 sentences in which emphatic stress was placed on either the 1st or 2nd word. One participant group received an upward intensity perturbation during stressed word production, and the other group received a downward intensity perturbation. Compensations for perturbation were evaluated by comparing differences in participants' stressed and unstressed peak fundamental frequency (F0), peak intensity, and word duration during perturbed versus baseline trials. Results: Significant increases in stressed-unstressed peak intensities were observed during the ramp and perturbation phases of the experiment in the downward group only. Compensations for F0 and duration did not reach significance for either group. Conclusions: Consistent with previous work, speakers appear sensitive to auditory perturbations that affect a desired linguistic goal. In contrast to previous work on F0 perturbation that supported an integrated-channel model of prosodic control, the current work only found evidence for intensity-specific compensation. This discrepancy may suggest different F0 and intensity control mechanisms, threshold-dependent prosodic modulation, or a combined control scheme., Communication is dependent as much on what one says (segmental speech) as on how one says it (prosody). It is widely agreed that changes in fundamental frequency (F0), duration, and [...]

Purpose: This study explored visual speech influence in preschoolers using 3 developmentally appropriate tasks that vary in perceptual difficulty and task demands. They also examined developmental differences in the ability to use visually salient speech cues and visual phonological knowledge. Method: Twelve adults and 27 typically developing 3--and 4-year-old children completed 3 audiovisual (AV) speech integration tasks: matching, discrimination, and recognition. The authors compared AV benefit for visually salient and less visually salient speech discrimination contrasts and assessed the visual saliency of consonant confusions in auditory-only and AV word recognition. Results: Four-year-olds and adults demonstrated visual influence on all measures. Three-year-olds demonstrated visual influence on speech discrimination and recognition measures. All groups demonstrated greater AV benefit for the visually salient discrimination contrasts. AV recognition benefit in 4-year-olds and adults depended on the visual saliency of speech sounds. Conclusions: Preschoolers can demonstrate AV speech integration. Their AV benefit results from efficient use of visually salient speech cues. Four-year-olds, but not 3-year-olds, used visual phonological knowledge to take advantage of visually salient speech cues, suggesting possible developmental differences in the mechanisms of AV benefit., Speech is inherently multimodal (Munhall & Vatikiotis-Bateson, 2004; Yehia, Rubin, & Vatikiotis-Bateson, 1998), and audiovisual (AV) integration is an important part of speech perception (Rosenblum, 2005). In adulthood, visual information [...]

Keywords: dysarthria, ataxic, hypokinetic, differential diagnosis, case study, auditory-perceptual assessment A 53-year-old woman with bilateral striatopallidodentate calcinosis (BSPDC) was referred for motor speech examination, and high-quality acoustic recordings were obtained. [...]

This work tests the hypothesis that the cerebellum is critical to the perception of the timing of sensory events. Auditory tasks were used to assess two types of timing in a group of patients with a stereotyped specific degeneration of the cerebellum: the analysis of single time intervals requiring absolute measurements of time, and the holistic analysis of rhythmic patterns based on relative measures of time using an underlying regular beat. The data support a specific role for the cerebellum only in the absolute timing of single subsecond intervals but not in the relative timing of rhythmic sequences with a regular beat. The findings support the existence of a stopwatch-like cerebellar timing mechanism for absolute intervals that is distinct from mechanisms for entrainment with a regular beat. human | perception | absolute | relative | subsecond doi/ 10.1073/pnas.0910473107

Purpose: Previous research has found that auditory training helps native English speakers to perceive phonemic vowel length contrasts in Japanese, but their performance did not reach native levels after training. Given that multimodal information, such as lip movement and hand gesture, influences many aspects of native language processing, the authors examined whether multimodal input helps to improve native English speakers' ability to perceive Japanese vowel length contrasts. Method: Sixty native English speakers participated in 1 of 4 types of training: (a) audio-only; (b) audio-mouth; (c) audio-hands; and (d) audio-mouth-hands. Before and after training, participants were given phoneme perception tests that measured their ability to identify short and long vowels in Japanese (e.g., /kato/ vs. /kato:/). Results: Although all 4 groups improved from pre- to posttest (replicating previous research), the participants in the audio-mouth condition improved more than those in the audio-only condition, whereas the 2 conditions involving hand gestures did not. Conclusions: Seeing lip movements during training significantly helps learners to perceive difficult second-language phonemic contrasts, but seeing hand gestures does not. The authors discuss possible benefits and limitations of using multimodal information in second-language phoneme learning. KEY WORDS: lips, mouth, hand gesture, auditory learning, phonemic contrasts, second language, Foreign languages pose many challenges for learners. But learning to hear distinctions among novel speech sounds stands out as a particularly difficult obstacle. In the present study, we investigated whether [...]

Purpose: Speech shadowing experiments were conducted to test whether alignment (inadvertent imitation) to voice onset time (VOT) can be influenced by visual speech information. Method: Experiment 1 examined whether alignment would occur to auditory /pa/ syllables manipulated to have 3 different VOTs. Nineteen female participants were asked to listen to 180 syllables over headphones and to say each syllable out loud quickly and clearly. In Experiment 2, visual speech tokens composed of a face articulating /pa/ syllables at 2 different rates were dubbed onto the audio /pa/ syllables of Experiment 1. Sixteen new female participants were asked to listen to and watch (over a video monitor) 180 syllables and to say each syllable out loud quickly and clearly. Results: Results of Experiment 1 showed that the 3 VOTs of the audio /pa/ stimuli influenced the VOTs of the participants' produced syllables. Results of Experiment 2 revealed that both the visible syllable rate and audio VOT of the audiovisual /pa/ stimuli influenced the VOTs of the participants' produced syllables. Conclusion: These results show that, like auditory speech, visual speech information can induce speech alignment to a phonetically relevant property of an utterance. KEY WORDS: speech, alignment, audiovisual stimuli, lipreading, Alignment is the unconscious and spontaneous tendency people have to subtly imitate the person with whom they are speaking. Interlocutors tend to align to each other's speaking style (e.g., prosody, [...]

Purpose: Delayed auditory feedback is a technique that can improve fluency in stutterers, while disrupting fluency in many nonstuttering individuals. The aim of this study was to determine the neural basis for the detection of and compensation for such a delay, and the effects of increases in the delay duration. Method: Positron emission tomography was used to image regional cerebral blood flow changes, an index of neural activity, and to assess the influence of increasing amounts of delay. Results: Delayed auditory feedback led to increased activation in the bilateral superior temporal lobes, extending into posterior-medial auditory areas. Similar peaks in the temporal lobe were sensitive to increases in the amount of delay. A single peak in the temporal parietal junction responded to the amount of delay but not to the presence of a delay (relative to no delay). Conclusions: This study permitted distinctions to be made between the neural response to hearing one's voice at a delay and the neural activity that correlates with this delay. Notably, all the peaks showed some influence of the amount of delay. This result confirms a role for the posterior, sensorimotor 'how' system in the production of speech under conditions of delayed auditory feedback. KEY WORDS: delayed auditory information, speech production, positron emission tomography, Speech production is continuously regulated with respect to the current acoustic environment. In noisy situations, talkers unconsciously raise the level of their voices (Lombard, 1911), and if the apparent volume [...]

Male mosquitoes detect flying females using antennal hearing organs sensitive to nanoscale mechanical displacements and that harbor motile mechanosensory neurons. The mechanisms supporting neuronal motility, and their function in peripheral sensory processing, remain, however, puzzling. The mechanical and neural responses reveal a transition that unmasks the onset of synchronization between sensory neurons. This synchronization constitutes an unconventional, mechanically driven, process of communication between sensory neurons. Enhancing auditory sensitivity and selectivity, synchronization between mechanosensors in the mosquito arises from entrainment to twice-frequency forcing and is formally analogous to injection-locking in high-power laser technology. This discovery opens up the enticing possibility that other sensory systems, even nonsensory cell ensembles, coordinate their actions through mechanical signaling. bioacoustics | entrainment | mosquito audition | nonlinear hearing

With respect to enormous inter-individual differences in sound perception, this article aims to review the research background of the neural basis of individual sound perception. Principally, two basic listening types can be distinguished: 'holistic' or 'synthetic' listeners recognize the sound as a whole, and appreciate its pitch and timbre as characteristic qualities of the entire sound; and 'spectral' or 'analytical' listeners break up the sound into its harmonic constituents, at the expense of timbral qualities of the sound as a whole. In-between these two extreme listening modes, intermediate listeners perceive holistic and spectral cues simultaneously to varying degrees (auditory ambiguity). Several recent neurological investigations have pinpointed these perceptual differences to neuroanatomical and neurophysiological measures of the auditory cortex. Furthermore, it has been shown that individual auditory perception bias corresponds to musical instrument preference and musical performance style. Multimodal research findings point towards an individual 'fingerprint' of auditory cortex and perception profiles; however, whether these properties are shaped by intense training or rather reflect innate, genetically determined predisposition remains a matter of unresolved debate. Keywords: Interindividual Variability; Sound Perception; Pitch; Timbre; Heschl's Gyrus DOI: 10.1080/07494460903404402

Three auditory identification experiments were designed to specify the prime-response retrieval model of negative priming (S. Mayr & A. Buchner, 2006), which assumes that the prime response is retrieved in ignored repetition trials and interferes with probe responding. In Experiment 1, shortly before (in Experiment 1A) or after (in Experiment 1B) the prime, a cue signaled whether participants were to respond (go trials) or not (no-go trials) to the prime. Negative priming was found in either case. A prime-response retrieval effect--an increase in prime response errors to the probe targets of ignored repetition trials--was found for go trials only. In Experiment 2, prime trials with go cues always demanded a response, whereas the response to no-go trials depended on motor discrimination: For left-(right-) hand responses, the response had to be withheld (valid no-go); for right- (left-) hand responses, the response had to be executed (invalid no-go). The prime-response retrieval effect was present only for go and invalid no-go trials. This implies that execution of the prime response is a precondition for prime-response retrieval, whereas a response preparation plan and a response description in task-specific terms are not sufficient. Keywords: negative priming, prime-response retrieval, motor responses, go/no-go task

Purpose: Recovery of skilled upper limb movement remains a critical focus of rehabilitation in individuals post stroke. Conventional treatments, however, have demonstrated limited capability to produce substantial improvements in poststroke [...]

Hemispheric asymmetries of speech and music processing might arise from more basic specializations of left and right auditory cortex (AC). It is not clear, however, whether such asymmetries are unique to humans, i.e., consequences of speech and music, or whether comparable lateralized AC functions exist in nonhuman animals, as evolutionary precursors. Here, we investigated the cortical lateralization of perception of linearly frequency-modulated (FM) tones in gerbils, a rodent species with human-like low-frequency hearing. Using a footshock-reinforced shuttle-box avoidance go/no-go procedure in a total of 178 gerbils, we found that (i) the discrimination of direction of continuous FM (rising versus falling sweeps, 250-ms duration) was impaired by right but not left AC lesions; (ill the discrimination of direction of segmented FM (50-ms segments, 50-ms silent gaps, total duration 250 ms) was impaired by bilateral but not unilateral AC lesions; (iii) the discrimination of gap durations (10-30 ms) in segmented FM was impaired by left but not right AC lesions. AC lesions before and after training resulted in similar effects. Together, these experiments suggest that right and left AC, even in rodents, use different strategies in analyzing FM stimuli. Thus, the right AC, by using global cues, determines the direction of continuous and segmented FM but cannot discriminate gap durations. The left AC, by using local cues, discriminates gap durations and determines FM direction only when additional segmental information is available. asymmetry | lateralization | rodents

Introduction: Auditory sensory processing dysfunction is a core component of schizophrenia, with deficits occurring at 50 ms post-stimulus firmly established in the literature. Given that the initial afference of primary [...]

The remarkable sensitivity and frequency selectivity of the mammalian cochlea is attributed to a unique amplification process that resides in outer hair cells (OHCs). Although the mammalian-specific somatic motility is considered a substrate of cochlear amplification, it has also been proposed that somatic motility in mammals simply acts as an operating-point adjustment for the ubiquitous stereocilia-based amplifier. To address this issue, we created a mouse model in which a mutation (C1) was introduced into the OHC motor protein prestin, based on previous results in transfected cells. In C1/C1 knockin mice, localization of C1-prestin, as well as the length and number of OHCs, were all normal. In OHCs isolated from C1/C1 mice, nonlinear capacitance and somatic motility were both shifted toward hyperpolarization, so that, compared with WT controls, the amplitude of cycle-by-cycle (alternating, or AC) somatic motility remained the same, but the unidirectional (DC) component reversed polarity near the OHC's presumed in vivo resting membrane potential. No physiological defects in cochlear sensitivity or frequency selectivity were detected in C1/C1 or C1/+ mice. Hence, our results do not support the idea that OHC somatic motility adjusts the operating point of a stereocilia-based amplifier. However, they are consistent with the notion that the AC component of OHC somatic motility plays a dominant role in mammalian cochlear amplification. cochlear amplification | mechanosensory | prestin

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jvoice.2004.12.002 Byline: Dianna T. Kenny, Helen F. Mitchell Abstract: Long-term average spectra (LTAS) have identified features in the sounds of singers and have compared different vocal qualities based on energy changes that occur during different vocal tasks. In this study, we compared the perceptual ratings of vocal quality of expert pedagogues with acoustic measures performed on LTAS. Fifteen expert judges rated 24 samples with six repeats of six advanced singing students under two conditions: 'optimal' (O), which represented the application of the maximal open throat technique; and 'suboptimal' (SO), which represented the application of the reduced open throat technique. LTAS were performed on each singing sample, and two conventional assessments of peak energy height [singing power ratio (SPR)] and peak area [energy ratio (ER)] were calculated on each LTAS. Perceptual scores, SPR, and ER were rank ordered. We then compared perceptual rankings with rankings of acoustic measures (SPR and ER) to assess whether these acoustic measurements matched the perceptual judgments of vocal quality. Although we found the expected significant relationship between SPR and ER, there was no relationship between perceptual ratings of vocal samples or singers based on SPR or ER. These findings suggest that because LTAS measures are not consistent with perceptual ratings of vocal quality, such measurements cannot define a voice of quality. Future research with LTAS to assess vocal quality should consider alternative measures that are more sensitive to subtle differences in vocal parameters. Author Affiliation: From the Australian Centre for Applied Research in Music Performance (ACARMP), Sydney Conservatorium of Music, The University of Sydney, New South Wales, Australia Article History: Accepted 9 December 2004 Article Note: (miscellaneous) New South Wales, Australia

The phenomenon commonly known as subjective accenting refers to the fact that identical sound events within purely isochronous sequences are perceived as unequal. Although subjective accenting has been extensively explored using behavioral methods, no physiological evidence has ever been provided for it. In the present study, we tested the notion that these perceived irregularities are related to the dynamic deployment of attention. We disrupted listeners' expectancies in different positions of auditory equitone sequences and measured their responses through brain event-related potentials (ERPs). Significant differences in a late parietal (P3-like) ERP component were found between the responses elicited on odd-numbered versus even-numbered positions, suggesting that a default binary metric structure was perceived. Our findings indicate that this phenomenon has a rather cognitive, attention-dependent origin, partly affected by musical expertise.

A number of trait measures, possibly reflective of prenatal hormonal effects, were obtained in studies of otoacoustic emissions (OAEs) and auditory evoked potentials (AEPs) carried out with male and female heterosexual and homosexual/bisexual college students. Most of the measures were from a self-report questionnaire; others were from experimenters' ratings or cognitive tests (Mental Rotation Test and Water Level Test). The questionnaire, test, and rating measures included physical characteristics (e.g., height, body type, eye color); spatial abilities; sex roles and sexual orientation; childhood gender nonconformity; and, in the OAE study, presence of homosexuality or bisexuality among relatives. Correlations with sexual orientation were most often consistent with the hypothesis that male homosexuals were undermasculinized and female homosexuals overmasculinized. Some correlations of the questionnaire, test, and rating measures with auditory measures were observed, but most of these were reduced or eliminat ed by statistically controlling for sex. In supplementary analyses, pigmentation measures appeared to be unrelated to OAEs, and data relevant to several hypotheses in the sexual orientation literature were briefly examined, including childhood gender nonconformity, X-linkage, handedness, and the tendency of homosexuality to run in families. KEY WORDS: homosexuality; auditory evoked potentials; otoacoustic emissions; prenatal androgens.

Classical temporal integration (TI) is often viewed as a frequency-dependent, energy-based detection process. Detection thresholds for brief sinusoidal increments in either a fixed-level or a random-level broadband pedestal are reported that refute this traditional perspective of TI. Instead, evidence is presented that indicates (a) detection of absolute energy is not necessary for the TI effect and (b) the frequency dependence of TI is consistent with variations across frequency in peripheral auditory tuning, rather than the integration process per se. When peripheral frequency selectivity is controlled, TI can be explained by a frequency-invariant integration process over at least the frequency range from 500 to 4000 Hz. This process is characterized by threshold improvements of 8-9 dB per decade increase in duration for increment durations between 10 and 300 ms. KEY WORDS: temporal integration, energy detection, increment detection, raving-level paradigm, masked detection, Investigators have known for at least 125 years that auditory detection for brief signals improves as signal duration is increased (Exner, 1876). A number of different theories have been proposed [...]

Mechanisms of hair cell tuning are discussed with focus on features intrinsic to the hair cells that are active in tuning and mechanosensitivity. Special emphasis is placed on mechanical tuning the the transduction apparatus. Evidence that mammals employ electrical tuning over any frequency range has not been found. The active electromechanical output of the hair bundle may have intrinsic frequency limitations.

Timing in the vertebrate brain stem auditory nuclei is discussed. In all higher vertebrates the timing of electrical signaling carries acoustic information. Precision is in tens of microseconds in pathways from cochlea to midbrain, and different facets of timing information are used and pulled out along parallel pathways. Strong evidence that mammals and birds detect interaural phase differences for localization of low-frequency sound in the medial superior olive (MSO) and in the horizontal plane in the nucleus laminaris, respectively.

Hemispheric bias underlies the acoustic perception of adult rhesus monkeys Macaca mulatta. This was concluded in a study of whether asymmetries in perception are sensitive to changes in the temporal characteristics of the monkeys' calls. Results reveal that for some call types within the rhesus repertoire, temporal properties provide crucial information about whether the signal is conspecific or not. The left hemisphere of the brain is found to play a dominant role in this processing task.

We used both structural and functional brain imaging techniques to investigate the neural basis of absolute pitch (AP), a specialized skill present in some musicians. By using positron emission tomography, we measured cerebral blood flow during the presentation of musical tones to AP possessors and to control musicians without AP. Listening to musical tones resulted in similar patterns of increased cerebral blood flow in auditory cortical areas in both groups, as expected. The AP group also demonstrated activation of the left posterior dorsolateral frontal cortex, an area thought to be related to learning conditional associations. However, a similar pattern of left dorsolateral frontal activity was also observed in non-AP subjects when they made relative pitch judgments of intervals, such as minor or major. Conversely, activity within the right inferior frontal cortex was observed in control but not in AP subjects during the interval-judgment task, suggesting that AP possessors need not access working memory mechanisms in this task. MRI measures of cortical volume indicated a larger left planum temporale in the AP group, which correlated with performance on an pitch-naming task. Our findings suggest that AP may not be associated with a unique pattern of cerebral activity but rather may depend on the recruitment of a specialized network involved in the retrieval and manipulation of verbal-tonal associations.

Cortical representational plasticity has been well documented after peripheral and central injuries or improvements in perceptual and motor abilities. This has led to inferences that the changes in cortical representations parallel and account for the improvement in performance during the period of skill acquisition. There have also been several examples of rapidly induced changes in cortical neuronal response properties, for example, by intracortical microstimulation or by classical conditioning paradigms. This report describes similar rapidly induced changes in a cortically mediated perception in human subjects, the ventriloquism aftereffect, which presumably reflects a corresponding change in the cortical representation of acoustic space. The ventriloquism aftereffect describes an enduring shift in the perception of the spatial location of acoustic stimuli after a period of exposure of spatially disparate and simultaneously presented acoustic and visual stimuli. Exposure of a mismatch of 8 [degrees] for 20-30 min is sufficient to shift the perception of acoustic space by approximately the same amount across subjects and acoustic frequencies. Given that the cerebral cortex is necessary for the perception of acoustic space, it is likely that the ventriloquism aftereffect reflects a change in the cortical representation of acoustic space. Comparisons between the responses of single cortical neurons in the behaving macaque monkey and the stimulus parameters that give rise to the ventriloquism aftereffect suggest that the changes in the cortical representation of acoustic space may begin as early as the primary auditory cortex.

Maturation of peripheral hearing and auditory brainstem following perinatal asphyxia was investigated by longitudinal recording of brainstem auditory evoked potentials (BAEP) during the first year of life in affected infants. The general maturational course of the BAEP following asphyxia was similar to that in a control group of infants with normal births, although there were some abnormalities in the BAER Response threshold elevation seen in a few asphyxiated infants improved significantly during the first 3 months. The interpeak intervals in the asphyxiated infants did not differ significantly from that of the control-group infants except in the first month, when the I-V and III-V intervals were significantly prolonged in the severe asphyxia group. In contrast, wave V amplitude and V/I ratio were always smaller when compared to that of the control-group infants. Amplitude reduction of wave V was more sustained than the prolonged I-V interval. Persistent hearing loss and brainstem auditory impairment were seen in 6.8% and 14.6% of the asphyxiated infants, respectively. These findings suggest that asphyxia does not interfere significantly with the maturation of the auditory system in most asphyxiated infants and that sustained peripheral hearing loss and brainstem impairment occur only in a small proportion of affected infants. KEY WORDS: neural development, auditory maturation, hearing, auditory evoked potential, asphyxia

Phonotaxis by female crickets to the calling song of males, is an important model for investigating the neural basis of auditory behavior. Recent advances make it possible to explain some components of this behavior and its hormonal control, at the level of identified neurons and molecular expression within those neurons. Tonotopically arranged afferents from the cricket's ear, project to local and intersegmental prothoracic interneurons. Bilateral processing of signals and some temporal-pattern specific processing occurs in the prothoracic ganglion and influences acoustic information that is sent to the brain via ascending interneurons that are demonstrably involved in phonotaxis. High, low and band- pass interneurons in the brain continue temporal pattern processing which matches the selectivity of phonotaxis and may be filters for recognition of the calling song. Neurons descending from the brain and prothoracic ganglion, direct multimodal signals (including auditory) to more posterior regions, possibly the leg motor neurons that are responsible for phonotaxis. Age-related changes or artificially induced changes in Juvenile Hormone III levels regulate the threshold for phonotaxis in Acheta domesticus, by varying the threshold of L1, a prothoracic ascending interneuron that is necessary for phonotaxis to low intensity calling songs. Results from in situ hybridization suggest that this might be accomplished, in part, by controlling the levels of nicotinic acetylcholine receptor-like mRNA expressed in L1, presumably by increasing its neurotransmitter receptor density. L3 is a prothoracic ascending interneuron that exhibits band-selective response properties to the syllable period of the calling song. L3's response is age and JHIII related, and is correlated to phonotactic selectivity. These changes in L3 might be accomplished, at least in part by JHIII regulating the expression of nicotinic acetylcholine receptor-like mRNA in L3.

One approach to the problem of specifying the contribution of the primary auditory cortex to auditory perception has been based on single-neuron recording techniques in animals. These experiments measure the response rates of individual neural elements to parametric variations in 1 or more stimulus dimensions. The patterns of response rates and response failures revealed by these manipulations are quantitative descriptions of the form and fidelity of the cortex's representation of those stimulus dimensions. This strategy has been used to advantage in studies of the cortical representation of the spectral content of auditory events, the spatial location of a sound, and the time structure of sounds. The data constitute new links between neural coding and behavioral performance in normal and impaired listeners.