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PubMed1993

The Lombard reflex and its role on human listeners and automatic speech recognizers.

Automatic speech recognition experiments show that, depending on the task performed and how speech variability is modeled, automatic speech recognizers are more or less sensitive to the Lombard reflex. To gain an understanding about the Lombard effect with the prospect of improving performance of automatic speech recognizers, (1) an analysis was made of the acoustic-phonetic changes occurring in Lombard speech, and (2) the influence of the Lombard effect on speech perception was studied. Both acoustic and perceptual analyses suggest that the influence of the Lombard effect on male and female speakers is different. The analyses also bring to light that, even if some tendencies across speakers can be observed consistently, the Lombard reflex is highly variable from speaker to speaker. Based on the results of the acoustic and perceptual studies, some ways of dealing with Lombard speech variability in automatic speech recognition are also discussed.

Acoustic Stimulation↗
PubMed2002

Sound-level-dependent representation of frequency modulations in human auditory cortex: a low-noise fMRI study.

Recognition of sound patterns must be largely independent of level and of masking or jamming background sounds. Auditory patterns of relevance in numerous environmental sounds, species-specific vocalizations and speech are frequency modulations (FM). Level-dependent activation of the human auditory cortex (AC) in response to a large set of upward and downward FM tones was studied with low-noise (48 dB) functional magnetic resonance imaging at 3 Tesla. Separate analysis in four territories of AC was performed in each individual brain using a combination of anatomical landmarks and spatial activation criteria for their distinction. Activation of territory T1b (including primary AC) showed the most robust level dependence over the large range of 48-102 dB in terms of activated volume and blood oxygen level dependent contrast (BOLD) signal intensity. The left nonprimary territory T2 also showed a good correlation of level with activated volume but, in contrast to T1b, not with BOLD signal intensity. These findings are compatible with level coding mechanisms observed in animal AC. A systematic increase of activation with level was not observed for T1a (anterior of Heschl's gyrus) and T3 (on the planum temporale). Thus these areas might not be specifically involved in processing of the overall intensity of FM. The rostral territory T1a of the left hemisphere exhibited highest activation when the FM sound level fell 12 dB below scanner noise. This supports the previously suggested special involvement of this territory in foreground-background decomposition tasks. Overall, AC of the left hemisphere showed a stronger level-dependence of signal intensity and activated volume than the right hemisphere. But any side differences of signal intensity at given levels were lateralized to right AC. This might point to an involvement of the right hemisphere in more specific aspects of FM processing than level coding.

Acoustic Stimulation↗
PubMed1984

Role of cat primary auditory cortex for sound-localization behavior.

Small lesions designed to completely destroy the cortical zone of representation of a restricted band of frequency were introduced within the primary auditory cortex (AI) in adult cats. Physiological mapping was used to guide placement of lesions. Sound-localization performance was evaluated prior to and after induction of these lesions in a seven-choice free-sound-field apparatus. All tested cats had profound contralateral hemifield deficits for the localization of brief tones at frequencies roughly corresponding to those whose representations were destroyed by the lesion. Sound-localization performance was normal at all other test frequencies. In a single adult cat, a massive lesion destroyed nearly all auditory cortex unilaterally, with only the representation of a narrow band of frequency within AI spared by the lesion. This cat had normal abilities for azimuthal sound localization across that frequency band but a profound contralateral deficit for the azimuthal localization of brief sounds at all other frequencies. Recorded sound-localization deficits were permanent. Localization of long-duration tones was not affected by a unilateral AI lesion. These studies indicate that, at least in cats, AI is necessary for normal binaural sound-localization behavior; among auditory cortical fields, AI is sufficient for normal binaural sound-localization behavior; sound-location representation is organized by frequency channel in the auditory forebrain; and AI in each hemisphere contributes to only contralateral free-sound-field location representation.

Animals↗
PubMed1985

Representation of stimulus azimuth by low-frequency neurons in inferior colliculus of the cat.

The responses to changes in stimulus azimuth of 204 neurons in the inferior colliculus of the cat with best frequencies of less than 3 kHz were studied. Three main unit classes were identified: omnidirectional units uninfluenced by speaker azimuth (39%); multipeaked units with several azimuthal regions at which peak firing occurred (9%); and azimuth-selective units that showed clear preferences for a discrete range of sound-source azimuths (52%). Alterations in stimulus intensity produced little change in the shapes of profiles relating firing rate to stimulus azimuth (azimuth functions), but the peaks of these functions could shift by up to 20 degrees. Similar observations were made for a small sample of units, each of which was examined with a variety of stimulus frequencies. The pinnae were removed bilaterally in 11 cats, and azimuth functions for 35 units were measured both binaurally and with the ipsilateral or contralateral ear occluded. Evidence was found for facilitative or suppressive interactions, as a function of stimulus azimuth, between monaural inputs. The sharpness of an azimuth function was expressed by the half-width of the function, i.e., the number of degrees of azimuth between the peak of the function and the point at which 50% of maximum firing occurred on the medial side of the peak. When half-widths were plotted as a function of best frequency, it was found that the sharpest azimuth functions occurred for units with best frequencies between 1.1 and 1.5 kHz. Most units in the lowest two octaves (0.1-0.4 kHz) or having best frequencies between 2 and 3 kHz were omnidirectional. The relationship between half-width and the azimuth at which peak firing occurred (best azimuth) revealed that a range of best azimuths between 10 and 40 degrees contralateral contained the sharpest azimuth functions. When best frequency was plotted against best azimuth, it was observed that the majority of units (93%) had best azimuths in the contralateral hemifield. For frequencies between 0.7 and 1.7 kHz, best azimuths occurred relatively evenly between 10 and 60 degrees contralateral. These data suggested that for frequencies between 1.2 and 1.4 kHz, at least, the best azimuths of different units with the same best frequency collectively provide information about stimulus location across much of the contralateral hemifield.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1997

Two-tone distortion on the basilar membrane of the chinchilla cochlea.

Basilar membrane responses to pairs of tones were measured, with the use of a laser velocimeter, in the basal turn of the cochlea in anesthetized chinchillas. Frequency spectra of basilar membrane responses to primary tones with frequencies (f1, f2) close to the characteristic frequency (CF) contain prominent odd-order two-tone distortion products (DPs) at frequencies both higher and lower than CF (such as 2f1-f2, 3f1-2f3, 2f2-f1 and 3f2-2f1). For equal-level primaries with frequencies such that 2f1-f2 equals CF, the magnitude of the 2f1-f2 DP grows with primary level at linear or faster rates at low stimulus levels, but it saturates or decreases slightly at higher levels. For a fixed level of one of the primary tones, the magnitude of the 2f1-f2 DP is a nonmonotonic function of the level of the other primary tone. For low intensities of the variable tone, the 2f1-f2 DP grows at a rate of approximately 2 dB/dB with f1 level and 1 dB/dB with f2 level. DP magnitudes decrease rapidly with increasing primary frequency ratio (f2/f1) at low stimulus levels. For more intense stimuli, DP magnitudes remain constant or decrease slowly over a wide range of frequency ratios until a critical value is reached, at which DP magnitudes fall with slopes as steep as -300 dB/octave. As stimulus level grows, DP phases increasingly lag for large f2/f1 ratios, but exhibit leads for small f2/f1 ratios. Cochlear exposure to an intense tone that produces large sensitivity losses for the primary frequencies (but only small losses for tones with frequency equal to 2f1-f2) causes a substantial decrease in magnitude of the 2f1-f2 DP. This result demonstrates that the 2f1-f2 DP originates at the basilar membrane region with CFs corresponding to the primary frequencies and propagates to the location with CF equal to the DP frequency. 2f1-f2 DPs on the basilar membrane resemble those measured in human psychophysics in most respects. However, the magnitude of basilar membrane DPs does not show the nonmonotonic dependence on f2/f1 ratio evident in DP otoacoustic emissions.

Animals↗
PubMedDate not supplied

2f1-f2 distortion product otoacoustic emissions in White Leghorn chickens (Gallus domesticus): effects of frequency ratio and relative level.

The effects of primary tone frequency ratio (f2/f1 ratio) and relative level (L2/L1) on the amplitude of the cubic difference tone (CDT: 2f1-f2) distortion product otoacoustic emissions (DPOAEs) were investigated in adult White Leghorn chickens (Gallus domesticus). In experiment 1, 9 f2/f1 ratios ranging from 1.05 to 1.8 were investigated. Measurements were obtained from both ears of 4 chickens at 7 f1 frequencies ranging from 0.8 to 4.0 kHz. The primary tones were equal in level, and varied from 20 to 80 dB SPL. The mean CDT amplitude increased with increasing primary tone level once the measurement noise floor was exceeded. The input/ output functions assumed one of two shapes: one in which there was a systematic increase in DPOAE amplitude with increasing primary tone level, and the other in which there was a plateau in the input/output function near 65-70 dB SPL. At the highest primary tone level (80 dB SPL), there was a decrease in the CDT amplitude with increasing f2/f1 ratio. At high primary tone levels, the f2/f1 ratio which produced the largest CDT was 1.05 or 1.1, while at lower primary tone levels the largest CDT occurred at f2/f1 ratios of 1.2-1.3. In experiment 2, L2 was held constant at 70 dB SPL, and L1 varied from 50 to 80 dB SPL. For f1 frequencies of 0.8 and 3.2 kHz, there was an increase in the CDT amplitude with increasing L1, followed by an asymptote at higher levels. In contrast, for 1.6 and 2.0 kHz f1 frequencies, the amplitude increased, plateaued and then increased again at higher levels. Informal measurements suggest that spontaneous otoacoustic emissions (SOAEs) are rarely seen in chickens. However, a reliable SOAE was observed in 1 chicken, which could be suppressed by external sounds and anoxia.

Acoustic Stimulation↗
PubMed2005

Left auditory cortex specialization for vertical harmonic structure of chords.

The representation of consonant and dissonant chords in the auditory cortex was investigated using low-noise functional magnetic resonance imaging and different experimental paradigms to separate the effects of vertical harmony from those of other musical features. The results revealed higher activation by consonant compared with dissonant chords in the left posterior auditory cortex, suggesting contributions of mechanisms of encoding the acoustical chord structure rather than mechanisms based on sequential integration of chords.

Acoustic Stimulation↗
PubMed1994

Harmonic and rhythmic influences on musical expectancy.

The effects of harmony and rhythm on expectancy formation were studied in two experiments. In both studies, we generated musical passages consisting of a melodic line accompanied by four harmonic (chord) events. These sequences varied in their harmonic content, the rhythmic periodicity of the three context chords prior to the final chord, and the ending time of the final chord itself. In Experiment 1, listeners provided ratings for how well the final chord in a chord sequence fit their expectations for what was to come next; analyses revealed subtle changes in ratings as a function of both harmonic and rhythmic variation. Experiment 2 extended these results; listeners made a speeded reaction time judgment on whether the final chord of a sequence belonged with its set of context chords. Analysis of the reaction time data suggested that harmonic and rhythmic variation also influenced the speed of musical processing. These results are interpreted with reference to current models of music cognition, and they highlight the need for rhythmical weighting factors within the psychological representation of tonal/pitch information.

Acoustic Stimulation↗
PubMed1991

[Clinical study of speech understanding in noise].

The goal of this study was to determine the extent to which the difficulty frequently experienced by hearing-impaired listeners in understanding noisy speech can be clinically described in terms of the auditory site of lesion. To this end, shifts of speech reception threshold in noise, using standardized franco-québécois bisyllabic word lists, were obtained from noise-exposed workers and compared to Plomp's model to ascertain content validity. Shifts resulted from monaural listening to a broad-band speech spectrum noise held constant at 0 dB signal-to-noise ratio. In this manner, increasing the presentation levels of both speech and noise was expected to progressively minimize the contribution of Plomp's class A attenuation component to speech hearing loss and eventually show an unequivocal manifestation of its distortion component (class D speech hearing loss). Listeners were 457 noise-exposed workers giving a total of 914 observations. Rejection of those ears with suspected middle-ear pathology led to a reduction to a total of 709 observations representing various degrees of permanent hearing impairment. An additional 98 observations showed normal hearing sensitivity in spite of noise exposure averaging 9.6 years. Results indicated the presence of five categories of speech threshold shifts varying independently of hearing sensitivity. 59.8% of those observations with permanent hearing impairment (424/709) simultaneously showed a problem understanding speech in noise. On 78 occasions, listening in noise was so disturbed that the 50% performance level corresponding to the speech threshold could no longer be established within reasonable limits, that is up to 65 dB above the speech threshold in a quiet environment. Conversely, 26.5% of the observations with essentially normal hearing sensitivity (26/98) showed reduced speech reception in noise. Fitting Plomp's model confirmed our expectations for two of the five categories of scores. A principal component analysis identified similar behaviour of speech threshold shifts in noise compared with Plomp's class D speech hearing loss. Hence, these speech threshold shifts in noise were interpreted as predominantly reflecting peripheral auditory disorders, that is defective frequency selectivity and temporal resolution. The remaining categories were found to be under the predominant influence of two other mechanisms: (1) band width reduction resulting from impaired hearing; (2) disorders associated with certain non-auditory cognitive factors, namely selective attention and the ability to make use of the redundancy of the message.

Adult↗
PubMed1986

[The promontory test and electrocochleography with reference to indications for cochlear implant].

A successful cochlear implant demands a functioning auditory nerve. A subjective and qualitative recording can be obtained by promontory testing (PT) whereas cochlear microphonics (CM) give information about the status of the hair-cells in the inner ear. The results of both tests together show different patterns: in sensory deafness in which a cochlear implant is indicated, no CM and no compound action potentials (CAP) can be obtained, whereas the patient reports hearing sensations (PT positive) in response to promontory testing. Deafness caused by lesions close to the second neurone of the auditory pathways can be localized by preserved CM and CAP, but there is no response to promontory testing. A ganglionic deafness ie. of the first neurone can be distinguished by preserved CM, absent CAP and a negative PT. The combined results of electrocochleography and promontory testing help in deciding whether a cochlear implant is indicated, and in localising the origin of the deafness, eg. neural or sensorineural. The possible results are illustrated by examples.

Adult↗
PubMed1985

[Bilateral caloric long-term irrigation as a method for the differentiation of tonal tinnitus].

In 307 subjects with tinnitus aurium, the parameters frequency, loudness, and masking levels did not correlate significantly with the basic diseases. As a new possibility in differentiation between tinnitus of central or peripheral origin, bilateral caloric long-term irrigation of the ear canal is presented. Using warm water leads to an increase, cold water to a decrease in the loudness of tinnitus. Such results were found in cases of Menière's disease and noise-induced hearing loss. An explanation of this phenomenon lies in the hypothesis of tinnitus genesis established by Tonndorf.

Adult↗
PubMed1984

Hearing and vestibular abnormalities in primary fibrositis syndrome.

A prospective neurootological study of 30 cases of primary fibrositis syndrome (PFS) and 30 sex and age matched healthy volunteers was performed. Results showed that 70% of the PFS patients had decreased painful sound threshold, 40% hyperreactivity of perrotatory nystagmus without neurological or peripheral vestibular lesions, and 27% asymptomatic sensorineural hearing loss at low frequencies. Such abnormal data were not found in the matched controls. These findings suggest that otological problems may be part of the nonrheumatic features encountered in PFS.

Adult↗
PubMed1982

Auditory brainstem responses and masking level differences from persons with brainstem lesion.

Twenty subjects with abnormal auditory brainstem responses (ABR) and diagnosed brainstem lesion or disease were studied. Normal listeners were used as controls. The objective of the project was to examine the relationship of the particular ABR patterns exhibited by these subjects to the binaural masking level differences (MLD) and transbrainstem acoustic reflex (AR) patterns yielded by the same subjects. Patients whose ABR abnormalities commenced with brainstem potentials I, II, or III had small or no MLD and absent or abnormal AR. Patients whose ABR abnormalities commenced with brainstem potentials IV or V yielded normal MLD and AR behavior. Most important, these findings suggest that MLD size is influenced by activity which also contributes importantly to the development of the early auditory brainstem potentials.

Adult↗
PubMed1994

[Studies of sound condition in the reconstructed middle ear with a hydrophone. Initial results].

The acoustic result following reconstruction of the middle ear is often disappointing and unpredictable. Apart from biologic factors, this is due to insufficient knowledge of the mechanism of sound transmission through the operated middle ear. Therefore, temporal bone experiments with simulated middle ear operations were set up to investigate the sound transmission following different prosthesis' designs, materials, etc. We developed a tiny hydrophone which has a frequency range from 100 Hz to 10 kHz in order to measure the sound pressure in the cochlear fluid. By comparing the sound pressure in the inner ear with the sound pressure at the drum membrane, we were able to analyze the transfer function of the manipulated middle ear. First results with different reconstruction techniques, prosthesis' designs and attachments demonstrated the usefulness of this measuring technique for the development of acoustically better middle ear reconstructions.

Bone Conduction↗
PubMed1996

Perception of musical tension in short chord sequences: the influence of harmonic function, sensory dissonance, horizontal motion, and musical training.

This study investigates the effect of four variables (tonal hierarchies, sensory chordal consonance, horizontal motion, and musical training) on perceived musical tension. Participants were asked to evaluate the tension created by a chord X in sequences of three chords [C major-->X-->C major] in a C major context key. The X chords could be major or minor triads major-minor seventh, or minor seventh chords built on the 12 notes of the chromatic scale. The data were compared with Krumhansl's (1990) harmonic hierarchy and with predictions of Lerdahl's (1988) cognitive theory, Hutchinson and Knopoff's (1978) and Parncutt's (1989) sensory-psychoacoustical theories, and the model of horizontal motion defined in the paper. As a main outcome, it appears that judgments of tension arose from a convergence of several cognitive and psychoacoustics influences, whose relative importance varies, depending on musical training.

Auditory Perception↗
PubMed1999

Neural coding of sound frequency by cricket auditory receptors.

Crickets provide a useful model to study neural processing of sound frequency. Sound frequency is one parameter that crickets use to discriminate between conspecific signals and sounds made by predators, yet little is known about how frequency is represented at the level of auditory receptors. In this paper, we study the physiological properties of auditory receptor fibers (ARFs) by making single-unit recordings in the cricket Teleogryllus oceanicus. Characteristic frequencies (CFs) of ARFs are distributed discontinuously throughout the range of frequencies that we investigated (2-40 kHz) and appear to be clustered around three frequency ranges (</=5.5, 10-12, and >/=18 kHz). A striking characteristic of cricket ARFs is the occurrence of additional sensitivity peaks at frequencies other than CFs. These additional sensitivity peaks allow crickets to detect sound over a wide frequency range, although the CFs of ARFs cover only the frequency bands mentioned above. To the best of our knowledge, this is the first example of the extension of an animal's hearing range through multiple sensitivity peaks of auditory receptors.

Animals↗
PubMed2000

Pitch estimation by early-deafened subjects using a multiple-electrode cochlear implant.

Numerical estimates of pitch for stimulation of electrodes along the 22-electrode array of the Cochlear Limited cochlear implant were obtained from 18 subjects who became deaf very early in life. Examined were the relationships between subject differences in pitch estimation, subject variables related to auditory deprivation and experience, and speech-perception scores for closed-set monosyllabic words and open-set Bamford-Kowal-Bench (BKB) sentences. Reliability in the estimation procedure was examined by comparing subject performance in pitch estimation with that for loudness estimation for current levels between hearing threshold and comfortable listening level. For 56% of subjects, a tonotopic order of pitch percepts for electrodes on the array was found. A deviant but reliable order of pitch percepts was found for 22% of subjects, and essentially no pitch order was found for the remaining 22% of subjects. Subject differences in pitch estimation were significantly related to the duration of auditory deprivation prior to implantation, with the poorest performance for subjects who had a longer duration of deafness and a later age at implantation. Subjects with no tonotopic order of pitch percepts had the lowest scores for the BKB sentence test, but there were no differences across subjects for monosyllabic words. Performance in pitch estimation for electrodes did not appear to be related to performance in the estimation procedure, as all subjects were successful in loudness estimation for current level.

Adolescent↗