bluuebunny/crossref_metadata_2025 huggingface dataset:
Shallow water active sonar issues
Authors: Carey William , Cable Peter G.
Published: October 2005

The central questions in sonar system design concern the limits of coherent processing and are: What is the optimum frequency range and bandwidth?; How large of a receiving aperture is required?; What is the achievable detection range? These questions are determined by the propagation and scattering of sound. In the shallow water channel, under downward refraction, the bottom is the determinant factor. A parametric sonar equation under reverberation limited conditions shows two factors are important, the effective bottom back scatter strength and the coherent signal gain. A parametric analysis is presented that focuses on the frequency-dependent characteristics of the bottom backscattering strength and the effect of coherence on receiving array aperture. Several recent reverberation and signal coherence measurements are presented and the needs for future studies are delineated. The backscattering strength is shown to be strongly frequency dependent and to depend on the depositional sediment layer. The coherence is also found to depend on frequency and range as determined by signal gain measurements.
Autonomous environmental measurement system
Authors: Stevenson J. M. , Olson J. R. , Sotirin B. J.
Published: October 2005

For experiment planning and optimized array deployment, experiment planners and array designers often seek a quick, affordable means to help determine best placement of a underwater acoustic measurement system prior to deployment. Array design geometry relative to ambient noise levels and variability, seafloor morphology, currents, and water column structure (e.g., ducts) is aided by apriori knowledge of the setting. It is desirable to determine some of these unknowns before undertaking the time and effort of a system deployment. Likewise, experiment planners and array designers would like to be able to explore deployment schemes that are locally optimized for the environment in order to reduce sensor sparseness in critical areas. This presentation describes an expendable, inexpensive sensor suite installed approximately one week prior to the deployment of an underwater acoustic measurement system. The instrument collects environmental data and provides advanced information to the experiment planners prior to a final deployment, facilitating optimized placement of the measurement system. Parameters sampled include: Variability and average level of ambient noise, SVPs, seafloor type and sediment thickness, surface wave heights, tidal measurements, and water currents. Characteristics of the system described include its small size, low weight, low power, affordability, and simple, low-bandwidth data collection scheme based on slack line array technology. [Work supported by ONR, Code 321.]
Target range and depth estimation from surface multipath
Authors: Doutt James A. , Hug Edward H.
Published: October 2005

The range and depth of a target are determined and compared with the known depth and the range as derived from differential GPS navigation. The data consists of a single return from a monostatic sonar configuration. The method uses a cost function defined as the sum of the squares of the differences between the arrival times measured from the data and those predicted by ray trace for an assumed target depth and range. The depth and range are then varied so as to minimize the cost function. Only the direct and surface-reflected paths have been used. However, the method is easily generalized to use more arrivals if the bottom depth is known and bottom-interacting arrivals can be identified.
Across-frequency interaural pattern discrimination
Authors: Lentz Jennifer J. , Richards Virginia M.
Published: October 2005

The ability of observers to detect changes in interaural intensity difference across frequencies was tested using multitone complexes. The tonal components ranged in frequency from 200 to 5000 Hz, with amplitudes randomly drawn from a Gaussian distribution having a mean of 60 dB SPL and a given variance. For the standard stimulus, variance was zero, providing equal-amplitude tones. The signal stimulus had a nonzero variance. Because independently drawn signal stimuli were presented to the left and right ears, interaural level differences varied randomly across frequency. Percent correct signal detections were measured as a function of the variance of the signal stimulus. To encourage discrimination based on the pattern of interaural level differences across frequency rather than the change from diotic (standard) to dichotic (standard+signal), the overall levels of the stimuli presented to each ear were independently chosen from a 7-dB range. Because standard and standard+signal power spectra differed, monaural cues to the presence of the signal were available. Thus psychometric functions were separately obtained using the same signal stimulus at both ears. Results indicate that the detectability of changes in interaural level differences across frequency is nearly the same as the detectability of changes in power spectra for diotic presentations. [Work funded by NIH.]
Masking and aging: I. Gerbil auditory brain-stem response thresholds
Authors: Boettcher Flint A. , Mills John H. , Schmiedt Barbara N.
Published: October 2005

Masked thresholds estimated from auditory brain-stem responses (ABR) of aging gerbils are 20–30 dB higher than the masked thresholds of young gerbils when quiet thresholds are equal. In this presentation, we will discuss data on young (6 month) gerbils with normal hearing and aged (36 month) gerbils with a range of hearing levels. ABR thresholds were measured at 1, 2, 4, 8, and 16 kHz in quiet and in the presence of a low-pass filtered noise (1 kHz upper bound) at levels of 50, 60, and 70 dB SPL. Young subjects had linear growth of masking of signals within the passband of the noise. At higher frequencies, only minimal masking was observed. In contrast, aged subjects showed much higher masked thresholds at 2 and 4 kHz compared to young subjects. This occurred for both aged subjects with minimal age-related threshold elevation and those with large hearing losses. In accordance with previous studies, masked ABR thresholds in aging gerbils are much higher than those in young gerbils. This phenomenon is examined in human subjects with behavioral and ABR techniques in the companion presentations. [Work supported by NIDCD.]
Masking and aging: III. Human and gerbil neural input/output functions
Authors: Mills John H. , Matthews Lois J. , Schmiedt Richard A. , Boettcher Flint A. , Dubno Judy R. , Ahlstrom Jayne B.
Published: October 2005

To account for higher masked ABR thresholds, input–output (I/O) functions of the ABR were examined. For both aging humans and gerbils, amplitudes of the ABR were smaller and slopes of ABR I/O functions were less steep than those of young subjects. Smaller amplitudes could indicate abnormal function of the brainstem or an altered input to the brain stem from the periphery. Analysis of I/O functions of the compound action potential (CAP) of the auditory nerve of aging gerbils also showed a decrease in slope. Decreases in the slope of the CAP can be attributed to a loss of 10%–30% of spiral ganglion cells, to a reduction in synchronous neural activity of the remaining nerve fibers, and to a reduction of the endocochlear potential. Thus, our hypothesis is that the unusual amounts of masking observed in the ABR of both aging humans and gerbils can be accounted for by age-related alterations in the auditory periphery. It is also our hypothesis that behavioral measurements of normal quiet and masked thresholds in aging humans do not necessarily reflect an intact auditory periphery. [Work supported by NIDCD.]
Neural encoding of level in the auditory nerve and anteroventral cochlear nucleus: A study of neural models and physiological responses
Authors: Burock M. A. , Carney L. H.
Published: October 2005

Models for level discrimination based on neural counts require ‘‘pooling’’ of auditory-nerve (AN) fiber responses to explain human performance. Neither the mechanism nor site of this ‘‘pooling’’ is known. This study concerns the transformation of AN responses in the anteroventral cochlear nucleus (AVCN). An AN model with statistics consistent with physiological data [mean-to-variance ratio (α)≊2] provided inputs to coincidence-detecting models for AVCN cells. The α of coincidence-detecting cell models is lower than the α of AN fibers. Responses of most gerbil AVCN neurons to (frozen) wideband noise had α less than 2, consistent with a coincidence-detection mechanism. The lower α implies these cells would not be as effective as AN fibers for encoding level in terms of rate. To optimally ‘‘pool’’ these responses would require either summation of a greater number of elements, or steeper rate-level curves (to compensate for lower α) and thus more elements to span a wide dynamic range. Neural coincidence detection may contribute to processing spectral information (monaurally) and localization information (binaurally). This mechanism does not provide an advantage, and perhaps introduces a disadvantage, for processing intensity information in the form of discharge rate. [Work supported by NIH, Whitaker Foundation.]
Responses of cochlear nucleus units in the chinchilla to best frequency tones amplitude modulated by low-frequency, two-tone complexes
Authors: Shofner W. P. , Sheft S. , Guzman S.
Published: October 2005

A tone that is amplitude modulated by two tones (fmod1 and fmod2) contains no spectral energy at the envelope beat frequency (fmod2−fmod1) for either the stimulus waveform or the half-wave rectified waveform. Preliminary data showed that Fourier analysis of post-stimulus time histograms of chinchilla CN units recorded in response to BF tones that were amplitude modulated by two tones (fmod1, fmod2<64 Hz) yields spectral peaks at fmod2−fmod1 in addition to the peaks at fmod1 and fmod2 [Shofner and Sheft, 2410(A) (1993)]. The magnitudes of these spectral peaks are measures of synchrony at each frequency component. For all units, synchrony at fmod1 and fmod2 is greater than the synchrony at fmod2−fmod1. For a given unit, synchrony at fmod1 and fmod2 remains relatively constant as a function of overall level, whereas synchrony at fmod2−fmod2 decreases as the level increases. Synchrony at fmod1 and fmod2 is largest in chopper units, intermediate in primarylike units, and smallest in onset units. This hierarchy differs from that described in the literature for CN units in response to BF tones modulated at best modulation frequencies. No hierarchy appears to exist for synchrony at fmod2−fmod1. [Work supported by a PPG from NIDCD.]
A comparison of the efficiency and accuracy of medial superior olive cell simulations
Authors: Shackleton Trevor M.
Published: October 2005

Binaural processing of interaural time differences (ITDs) is widely believed to be performed by a cross-correlation mechanism. Cells have been found in the medial-superior olive (MSO) and inferior colliculus which respond most strongly when presented with stimuli with a characteristic ITD (EE cells). These cells are believed to form the basis for such a mechanism. In this study we compare the performance of cells based on simple cross-correlation, coincidence detector cells based on a novel deterministic method, and coincidence detectors based on Monte-Carlo simulation. The deterministic model is based upon the requirement that the probability of a given number of inputs from the auditory nerves of either ear must exceed a threshold amount within a finite time (coincidence window) before the modeled cell can fire. We examine the firing rate and vector strength as a function of ITD, overall level, and interaural level difference (ILD) and compare our results with the data from cells in the MSO. We find that a simple cross-correlation cell is inadequate to describe the data. However, the deterministic cell and Monte-Carlo simulation, both with a coincidence window width of 0.2 ms, describe the data very well. [Work supported by The Wellcome Trust, UK.]
Neural processes of auditory scene analysis observed by magnetencephalography
Authors: Imaizumi S. , Mori K. , Kiritani S. , Yumoto M.
Published: October 2005

Auditory-evoked magnetic field elicited by three sound stimuli consisting of a spoken word, a click, and their overlapping version, was measured using BTi 37ch SQUID MEG system from the contra lateral hemisphere of the stimulated ears of seven normal hearing subjects. Three stimuli were presented in a random order with a random interstimulus interval between 1 and 2 s at the most comfortable hearing level. Two tasks were imposed: One is to count the click, and the other is to count the spoken word. Significant differences in the response were observed between the tasks. For both the tasks, a neural activity in the left and right temporal auditory cortices was observed for all the stimuli. When counting the click, a wide spread activity was elicited by the overlapping click suggesting possible contribution of a frontal neural activity in the right hemisphere. The results suggest that plural neural mechanisms may concern the auditory scene analysis by which the overlapping sound objects are distinctively perceived. The temporal-lobe activity may reflect automatic memory trace construction, and the frontal-lobe activity may concern attentional selection of a memory trace.
Elastic scattering of a spherical acoustic wave by an infinite fluid-filled cylindrical shell
Authors: Dodd Stirling S. , Loeffler Charles M.
Published: October 2005

A method of describing spherical acoustic waves in cylindrical coordinates is applied to the problem of point source scattering by an elastic infinite fluid-filled cylindrical shell. Léon etal. developed the scattering matrix for plane-wave scattering by an infinite hollow cylindrical shell [Léon etal., 1388–1397 (1992)]. By using a method of expressing a spherical wave in cylindrical coordinates in a form similar to that of a plane wave in cylindrical coordinates [Li and M. Ueda, 1871–1879 (1990)], the result of Leon etal. is manipulated into an exact solution for the spherical wave, fluid-filled scattering problem. The exact solution is in an integral form that is treated numerically. It is applied to distributed source and receiver arrays by treating them as sets of point sources and point receivers and then integrating over their spatial extent.
Effects of modality on subjective estimates of frequency and recency of spoken and printed words
Authors: Gaygen Daniel E. , Luce Paul A.
Published: October 2005

Previous research (Pisoni and Garber, 1990; Garber and Pisoni, 1991) has demonstrated that subjective familiarity judgments for words are not differentially affected by the modality (visual or auditory) in which the words are presented, suggesting that subjects base their judgments on fairly abstract, modality-independent representations in memory. However, in a recent large scale study in Japanese (Amano etal., in press), markedly modality effects on familiarity ratings were observed. The current research further examines possible modality differences in subjective ratings and their implications for word recognition. Specially selected words were presented to subjects for frequency and recency judgments. In particular, subjects were asked how frequently (or recently) they READ, WROTE, HEARD, or SAID a given spoken or printed word. These ratings were then used to predict accuracy and processing times in auditory and visual lexical decision and naming tasks. Our results suggest modality dependence for some lexical representations, primarily for words that occur fairly rarely in the language. [Work supported by NIDCD.]
Speechreading with and without auditory F0 supplementation: Effects of lexical and sentential context
Authors: Waldstein Robin S. , Boothroyd Arthur
Published: October 2005

This study examined the effects of lexical and sentential context on speechreading with and without supplementation by an auditory indicator of voice fundamental frequency (F0) in 12 adults with normal hearing. Lexical context effects were assessed by measuring phonetic segment and syllable recognition in CVC words and nonwords. Sentential context effects were assessed by measuring word recognition in normal sentences, in syntactically correct but semantically anomalous sentences, and in isolation (i.e., no context). For the lexical contexts, improved performance was seen by both speechreading plus F0 and speechreading alone in CVC words relative to CVC nonwords. F0 supplementation contributed to improved consonant recognition, presumably due to the provision of cues to voicing presence or absence. For the sentence contexts, F0 supplementation resulted in best recognition of words in normal sentences, while recognition of words in anomalous sentences was comparable to that for words in isolation. By contrast, results by speechreading alone revealed similar recognition of words in normal sentences and words in isolation, and poorer recognition of words in anomalous sentences. The study showed that F0 supplementation significantly enhanced the visual perception of both segments and word and phrase boundaries, and interacted with context. [Work supported by NIH Program Project Grant ♯5PO5DC00178.]
Age-related differences in performance measures for a cross-modal auditory Stroop task
Authors: Hawks John W. , Caruso Anthony J. , Chodzko-Zajko Wojtek W.
Published: October 2005

Physiologic and task performance measures are compared for young and elderly subjects on a simple speeded task, an auditory Stroop task and a cross-modal auditoryvisual Stroop task using verbal responses. The results suggested that all three tasks are perceived as physiologically stressful by both subject groups and that older subjects were more physiologically reactive to visual stimuli than younger subjects. Differences in reaction times suggested a longer overall processing time for older subjects, as well as greater interference in processing incongruent stimuli. However, analysis of response errors indicated significantly better accuracy on difficult tasks for the older subjects. The implications of these findings will be discussed in terms of task strategic differences and resource conservation.
The role of visual information in speaker normalization of fricatives
Authors: Strand Elizabeth A.
Published: October 2005

This study examines the role of visual information in speaker normalization of fricatives by comparing listeners’ responses to auditory stimuli only with responses to audiovisual (McGurk-type) stimuli to determine the effect that visual cues have in speaker normalization. Voices judged by listeners as auditorily ambiguous and unambiguous with respect to gender were used to construct four continua of tokens from /sad/ ‘‘sod’’ to /shad/ ‘‘shod’’; the continua were synchronized with videos of visually unambiguous male and female faces saying the same words. The audiovisual stimuli, as well as the auditory signals only, were then presented to listeners for identification as either ‘‘sod’’ or ‘‘shod.’’ Preliminary results suggest that visually disambiguating information affects the perception of auditorily ambiguous voices. This paper will present the results of additional tests on a larger pool of listeners. [Work supported by NIH.]
The effect of face and lip inversion on audiovisual speech integration
Authors: Yakel Deborah A. , Rosenblum Lawrence D. , Green Kerry P. , Bosley Chantel L. , Vasquez Rebecca A.
Published: October 2005

Seeing a speaking face can influence observers’ auditory perception of syllables [McGurk and McDonald, Nature 264, 746–748 (1976)]. This effect decreases when the speaker’s face is inverted [e.g., Green, 3014 (1994)]. Face recognition is also inhibited with inverted faces [e.g., Rock, Sci. Am. 230, 78–85 (1974)] suggesting a similar underlying process. To further explore the link between face and audiovisual speech perception, a speech experiment was designed to replicate another face perception effect. In this effect, an inverted face and an inverted face containing upright lips are perceived as looking normal, but an upright face with inverted lips looks grotesque [Thompson, Perception 9, 438–484 (1980)]. An audiovisual speech experiment tested four presentation conditions: Upright face-upright mouth, upright face-inverted mouth, inverted face-inverted mouth, inverted face-upright mouth. Various discrepant audiovisual syllables were tested in each condition. Visual influences occurred in all but the upright face-inverted mouth condition for some of the syllable combinations thereby mimicking the face perception effect. However, other syllable combinations revealed visual influences in all four conditions. Results are interpreted in terms of articulatory dynamics and the vertical symmetry of the visual stimuli.
Auditory localization and audiovisual speech perception
Authors: Jones J. A. , Munhall K. G.
Published: October 2005

The influence of the spatial position of the acoustic signal in audiovisual speech perception was investigated in a series of experiments using the McGurk effect. Subjects viewed video disk recordings of faces producing visual VCV nonsense syllables while simultaneous acoustic VCV stimuli were presented from one of 7 different speakers locations. The speakers were positioned in a semicircular array in front of the subject. In separate studies subjects were required to name the intervocalic consonant, indicate the location of the sound source using a computerized pentiometer system, or perform both tasks. Preliminary results suggest that the subjects’ ability to localize the position of the auditory stimulus was influenced by the presence of a visual stimulus. Specifically, subjects tended to localize the sound closer to the position of the monitor showing the visual stimulus. However the strength of the McGurk effect was not influenced by the spatial position of the sound source. Subjects perceived the visual /g/ and the auditory /b/ combination as /d/ equally often at all sound locations. The independence of the ventriloquist effect and audiovisual integration in the perception of the McGurk effect will be discussed in terms of spatial constraints on the cross-modal perception of speech.
Wavelet packets as a tool for sound processing
Authors: Coifman Ronald
Published: October 2005

Wavelet packet analysis of sound corresponds to an optimized musical transcription in which the sound is organized in different structures (orchestration), each of which is described by a ‘‘musical score.’’ This representation is a superposition of wavelet packets (notes) of different duration, pitch, location in time, and amplitude. Fast algorithms permit real-time transcriptions with a minimal number of notes. In this talk we will give a precise definition of these statements as well as applications to audio compression, denoising, recognition, and modeling.
One-dimensional blood flow measurement methods: Narrow-band versus wideband/wavelet transform techniques
Authors: Weiss Lora G.
Published: October 2005

The goal of blood flow velocimetry is to obtain an accurate measurement of the velocity of the blood as it flows through a blood vessel. If the measurement technique underestimates the blood flow velocity, then the measurement may appear normal and an occlusion may go undetected. To prevent an incorrect diagnosis, new methods for blood flow velocimetry are needed. This paper presents a technique for blood flow velocimetry using wavelet transforms, and it compares this technique to the conventional narrow-band Doppler methods often applied. Ultrasonic signals with high fractional bandwidths and/or large time-bandwidth products are processed with wavelet transforms. By applying wavelet transforms, many narrow-band assumptions typically invoked when measuring blood flow may be removed. With the wavelet method presented, instead of measuring the Doppler shift associated with the reflection of a signal, the time-scaling of the signal is obtained along with the round trip travel time. This time scaling more accurately reflects the effects of motion on the signals than does a Doppler shift since a Doppler shift is an approximation to time scaling. The continuous wavelet transform is then used to obtain the axial velocity of scatterers.
Signal and echo arrival-time estimation using wavelets
Authors: Ainsleigh Phillip L.
Published: October 2005

A wavelet-based method is introduced for estimating the arrival times of signals and echoes observed in noisy multipath environments. This problem arises when trying to model any signal containing overlapping segments of direct and reflected components. The method presented is more general than cepstrum-based techniques since it is not limited to echoes that are scaled replicas of the direct signal. The statistics of the wavelet coefficients are derived for pyramid-algorithm wavelet decompositions, and these are employed in a statistical detection algorithm for obtaining the arrival-time estimates. The method will be used to estimate signal and echo arrival times in data observed during underwater transducer calibration experiments conducted in small pressurized tanks.
Effects of amplitude envelope expansion and compression on nonsense sentence recognition
Authors: Freyman Richard L. , Speicher Debra , Nerbonne G. Patrick
Published: October 2005

When spectral information in speech is obscured, listeners presumably fall back on secondary cues such as those contained within the gross waveform envelope. This study examined the extent to which listeners’ ability to use such cues is resistant to distortions of the envelope. Signal correlated noise samples, created individually to follow the amplitude envelopes of 200 nonsense sentences, were used as maskers of those sentences, with signal-to-noise ratios of −4, −2, 0, and +2 dB. The resulting waveforms preserved the original wideband envelopes, but spectral information was degraded to a degree determined by the S-N ratio. The sentences were presented monaurally to normal hearing subjects at 70 dB SPL. Recognition of key words in these sentences was compared to that obtained for waveforms that had been processed with two different levels of amplitude expansion and two levels of compression. The results indicated that amplitude expansion severely reduced recognition scores, while compression had little effect. [Work supported by NIH ♯DC01533.]
Defining features of steady-state timbres
Authors: Hall Michael D. , Pastore Richard E.
Published: October 2005

While several dimensions contribute to voice and instrument timbre, perceptual interactions between dimensions have not been adequately assessed. As a result, the information used in timbre identification is unclear. Three experiments sought to define steady-state timbral features. First, Garner classification reflected the perceptual integrality of spectral slope and formant structure (a source and filter property, respectively); classification speed along either dimension depended upon variability along the other dimension. Feature detection then was evaluated within arrays of distractor pitches with homogeneous timbre. When targets had /á/ vowel formants with shallow spectral slopes, search time increased as a log function of array size consistent with parallel processing. Parallel search was not obtained for targets with /i/ formants and steep slopes, suggesting a feature coded as the presence or absence of /a/ formants with shallow slopes. A final search experiment using heterogeneous distractor timbres showed that this feature was separable from pitch. Search times for conjunctions of pitch and timbre linearly increased with array size, implying serial processing. Thus attention was needed to conjoin attributes to perceive tonal objects. Implications are discussed for the nature of attention and the perception of properties relevant to communication. [Work supported by AFOSR.]
Attention and grouping in vowel perception
Authors: Hukin R. W. , Darwin C. J.
Published: October 2005

The effective contribution of a 500-Hz component of a steady-state vowel was measured by the position of the vowel boundary on a /I/–/e/ continuum varying only in first formant (F1) frequency. Shifts in the vowel boundary were calibrated against those produced by level changes in the 500-Hz component. When the 500-Hz component was given an ITD of 666 μs and the remaining components an ITD of −666 μs, there was a small but significant reduction in the 500-Hz component’s contribution to phonetic quality. When the vowel was embedded in a sequence of six 500-Hz tones, each having the same ITD as the 500-Hz component of the vowel, there was a significant reduction its contribution compared to when all components had the same ITD. When the sequence conditions were presented in the same experimental block as the previous ITD conditions, then the latter conditions did show an effect of grouping by common ITD. These results show that listeners can group sounds on the basis of ITD information, but their ability to do so is greatly enhanced if the position and frequency have been previously cued. [Work supported by UK MRC.]
A comparison of two procedures for studying auditory image formation
Authors: Roberts Richard A. , Rappold Patrick W. , Cannito Michael P. , Muelkar Madhuri S.
Published: October 2005

The results from an off-line procedure (scaling) were compared to those from an on-line procedure (‘‘rate adjustment’’) for effectiveness in examining the fusion strength of partials within two, three-tone complexes. In both procedures fusion strength was inferred by the ease in which a tone presented in isolation (captor tone), and alternately with a complex, was able to capture a member (target tone) of the complex into a sequential stream. In the rate adjustment procedure the interstimulus-interval (ISI) between captor and target was decreased until the listener judged the prominence of streaming to be greater than that of fusion. In the scaling procedure the ISI was held constant. On a visual analog scale, having its end points labeled ‘‘fast’’ and ‘‘slow,’’ subjects judged the prominence of the rate at which they heard the pitch of the captor tone. Stimulus factors were tone relationship (octave/inoctave) and tone position (low, middle, high). More of the total variation was explained by the rate adjustment procedure, but the coefficients of variation for each tone position were smaller for the scaling procedure. Neither procedure showed an effect of tone relationship (octave/inoctave), and both procedures showed the same effect of tone position.
The effects of narrow-band noise maskers on overshoot
Authors: Marvit Peter , Richards Virginia M.
Published: October 2005

The elevation of detection thresholds for a short signal added just after the onset of a masker versus when it is added later during the masker has been called ‘‘overshoot.’’ Previous work with broadband maskers suggests masker frequency component near, but not at, the signal frequency produce overshoot. The relative contribution of different frequency regions to the overshoot effect was investigated here with narrow-band noise maskers of different center frequencies. The 350-ms maskers were 1/2 octave wide with center frequencies ranging from 1400 to 8500 Hz. The 10-ms signal was 2500-Hz tone added 4 or 325 ms after the onset of the masker. Masker spectrum levels were 35 dB SPL. The three subjects generally showed little or no overshoot when the masker spectrally overlapped the signal, but showed a maximum overshoot of 8–12 dB for masker bands centered 1/2 to 1 octave above and below the signal frequency; increased signal-masker frequency difference diminished but did not abolish the overshoot effect. Detection thresholds were maximal when the masker band spectrally overlapped the signal and fell as signal-masker frequency separation grew. A similar pattern of results was obtained using low-pass, high-pass, band-pass, and notched noise maskers bounding on a 750-Hz-wide region around the 2500-Hz signal frequency. [Work supported by NIH.]
Forward-masked intensity discrimination: Duration effects
Authors: Schlauch Robert S. , Lanthier Nicole
Published: October 2005

Forward-masked intensity discrimination shows elevated just-noticeable differences (jnd’s), for mid-level standards, a finding argued to be consistent with sensory adaptation [F. Zeng and C. W. Turner, 782–787 (1992)]. Accordingly, the size of jnd’s should increase with increases in masker duration. We tested this notion by measuring forward-masked jnd’s as a function of level for 1000-Hz tones in four listeners with normal hearing. Jnd’s were measured for 10-ms standards in quiet and in the presence of a 1000-Hz masker with either a 10-ms or a 250-ms duration. The masker level was fixed at 90 dB SPL and the interval between masker offset and standard onset was 100 ms. Forced-choice procedures were employed. The results show significantly less masking for the longer duration masker (250 ms) than for the short one (10 ms). These results are contrary to the results reported for forward-masked detection. Listening bands revealed by measuring jnd’s as a function of masker frequency suggest that off-frequency listening may be responsible for this finding [Work supported by the Bryng Bryngelson Fund.]
Modeling loudness growth and loudness summation in hearing-impaired listeners
Authors: Launer S. , Hohmann V. , Kollmeier B.
Published: October 2005

The goal of this study is to model the effect of sensorineural hearing impairment on loudness perception for stationary stimuli of variable bandwidth. Loudness growth functions were obtained employing a categorical scaling technique with 10 categories. Loudness scaling was performed with 9 normal-hearing and 14 sensorineural hearing-impaired subjects employing bandfiltered noises with bandwidths between 1–6 critical bands. For normal-hearing listeners, categorical scaling revealed similar differences across stimulus conditions as with loudness balancing. The loudness functions of the hearing-impaired listeners show both, a steeper increase (recruitment) and reduced loudness summation. Both aspects were successfully modeled by Zwicker’s loudness model with three extensions to take account of hearing impairment. Raised audiometric threshold is modeled by a frequency-dependent attenuation after calculation of excitation patterns. Increasing the exponent in calculating the specific loudness yields recruitment. Reduced frequency selectivity is accounted for by the normal dependence of filter bandwidth on level in the excitation patterns. The extended model describes well the measured individual loudness growth functions of hearing-impaired subjects for stimuli of differing bandwidth.
Efficiency of selective listening by normal-hearing and hearing-impaired listeners
Authors: Doherty Karen A. , Lutfi Robert A.
Published: October 2005

A COSS analysis procedure [B. G. J. Berg, J. Acoust. Soc. Am. 88, 149–158 (1990)] was used to estimate the efficiency with which 15 normal-hearing and 15 hearing-impaired listeners detected a level increment in a target tone embedded in a multitone complex. The complex was comprised of 6 oct frequencies from 250–8000 Hz and the target tone was selected as either the 250-, 1000-, or 4000-Hz tone. The hearing-impaired listeners had moderate, sloping, high-frequency sensorineural hearing impairments. Two efficiency measures were used to account for the listeners’ less than ideal performance on the task; weighting efficiency (ηwgt), which measures how well the listener attends to or weighs the target, and noise efficiency (ηnoise), which accounts for all other factors unrelated to weights. Weighting efficiencies were significantly higher for hearing-impaired listeners than normal-hearing listeners for the 4000-Hz target, which was in the region of hearing loss. No significant ηwgt differences between normal-hearing and hearing-impaired listeners were observed for the other two target tones. Even though hearing-impaired listeners sometimes weighted information more efficiently than normal-hearing listeners their overall performance on the task was significantly poorer as was reflected by smaller values of ηnoise.
On measuring psychometric functions
Authors: Dai Huanping
Published: October 2005

Psychometric functions of simulated observers were obtained using the conventional constant-stimulus method and an adaptive up–down method through a post-hoc analysis of the track. The form of the psychometric functions was assumed to be Pc=Ψ(d’/21/2), where Ψ is the cumulative Gaussian probability function. The detectability d’, is related to the signal level x by d’=axk, where a and k are the two parameters to be estimated. Among the factors considered in the simulation were step size and number of trials. For small number of trials (n≤120), and particularly when the step size was also small, the slope values (k) estimated using the adaptive method were systematically greater than the true slopes. Such biases were smaller with the constant-stimulus method. When the number of trials was reasonably large (n≥300), the constant-stimulus method showed no clear advantage over the adaptive method. The only apriori information required in the adaptive method is the starting stimulus level, whereas the constant-stimulus method requires pilot measurements in order to set all the stimulus levels properly. Thus the adaptive method is reasonably efficient for measuring psychometric functions. [Work supported by NIH.]
The effects of criterion variability on relative operating characteristics
Authors: Brown William S. , Emmerich David S.
Published: October 2005

The form of the relative operating characteristic (ROC) describing auditory detection typically differs from that expected based on the assumption that the observer’s responses reflect underlying distributions that are normal and of equal variance [e.g., Green and Swets, SignalDetectionTheoryandPsychophysics]. Specifically, it is found that binormal ROCs often have slopes less than one, and are not strictly linear [Watson etal., 283–288 (1964)]. It has been suggested that nonlinear binormal ROCs may be the result of extreme criteria being more variable than those more centrally positioned [Emmerich and Binder, J. Acoust. Soc. Am. Suppl. 1 65, S59 (1979)]. The forms of rating ROCs obtained in an experiment designed to reveal the effects of such variability were consistent with the proposition that criteria associated with ‘‘no’’ responses are more variable than those associated with ‘‘yes’’ responses. Criterion operating characteristics [Wickelgren, J. Math. Psychol. 5, 102–122], which reflect the relative locations and variances of the boundaries of confidence categories, favored the same interpretation. It is concluded that the variability of criteria defining categories of rated confidence is sizable and not necessarily constant across criteria, and that such variability significantly influences the forms of empirical ROCs determined using confidence ratings in auditory signal detection.
Temporally directed attending in the discrimination of tempo: Further support for an entrainment model
Authors: McAuley J. Devin , Kidd Gary R.
Published: October 2005

The effect of deviations from temporal expectations on tempo discrimination was investigated using four-tone isochronous sequences. On each trial, a standard sequence was followed by a comparison sequence that was slightly faster or slower than the standard. Listeners judged which sequence was faster. Temporal deviations consisted of advancing or delaying the onset of the comparison pattern in relation to an onset predicted by an extension of the periodicity of the standard (i.e., an ‘‘expected’’ onset, based on an entrainment model’s predictions). The interonset-interval in the standard sequence was always 400 ms, and the onset of the comparison sequence was manipulated in relation to an ‘‘expected’’ interval of 800 ms between the onset of the last tone of the standard sequence and the onset of the comparison sequence. Discrimination thresholds were determined for conditions in which the comparison pattern onset was early, late, or at the expected temporal location. Thresholds for ‘‘early’’ conditions were found to be significantly higher than for the ‘‘expected’’ condition, but this was not the case for ‘‘late’’ conditions. These data will be compared with the quantitative predictions of an entrainment model [McAuley and Kidd, 3257 (1994)]. [Work supported by NIMH and NIDCD.]
The effect of different component means and variances on the discrimination of temporal patterns
Authors: Sadralodabai Toktam , Sorkin Robert D.
Published: October 2005

Listeners were presented with two successive 9-tone sequences. The task was to discriminate between the temporal patterns defined by the intertone times in each sequence (tone duration=25 ms, tone frequency=1000 Hz). The listener had to indicate whether the two patterns had the same or different (partially correlated) temporal envelopes. A technique suggested by Lutfi [R. Lutfi, 1339 (1995)], was used to determine the importance of each temporal position on the listener’s decision. In the first experiment, one of the intertone times was assigned a different (either higher or lower) mean duration than the others. This intertone time occurred either at an early temporal position (2nd) or at a late position (6th). Results indicated that two positions, the first temporal position and the position with the different mean, had more influence on the listener’s decision than other positions. In the second experiment, the first 4 intertone times were assigned a different variance than the last occurring 4 intertone times. Initial results suggest that listeners give higher weights to the temporal positions with the lower variance. [Work supported by AFSOR.]
Detection and recognition of familiar sounds in noise
Authors: Stellmack Mark A. , Lutfi Robert A.
Published: October 2005

Three experiments compared listeners’ detection and recognition in broadband noise of five familiar and five unfamiliar sounds with identical long-term spectra. The familiar sounds were ice in a glass, zipper, crashing wood blocks, creaking door, and gas station bell. The unfamiliar sounds were these same five sounds played backwards. Thresholds were obtained using a single-interval, yes–no procedure. In the first two experiments, detection thresholds were measured for each sound by playing the same sound within each block of trials (fixed signal), and by playing one of the ten sounds with equal probability on each signal trial (random signal). In the third experiment, both detection and recognition thresholds were obtained for three of the familiar sounds played forward and backward. On each trial, listeners were asked first to make a yes/no detection judgment and then to identify which signal was played regardless of their first judgment. In all three experiments, there were no significant differences between thresholds obtained for the sounds played forward and thresholds for corresponding sounds played backwards. There was a small (1 dB) but statistically significant difference between thresholds for fixed and random signals. These results suggest that naturally occurring, familiar sounds have no special status among auditory stimuli in simple detection and recognition tasks [Research supported by NIDCD.]
Binaural detection with reproducible narrow-band maskers
Authors: Isabelle Scott K. , Colburn H. Steven
Published: October 2005

Responses of five subjects for the binaural detection of a 500-Hz, 300-ms, interaurally out-of-phase tone masked by statistically independent samples of narrow-band, interaurally identical noise are reported. A set of 30 noise samples were taken from a noise process with a power spectrum that is 115 Hz wide, centered at 500 Hz. The rms noise pressure was 75 dB SPL. For each subject, the responses show good self-consistency and a strong dependence on individual noise samples. (For example intrasubject correlation coefficients for subsets of the results were typically 0.85 and always higher than 0.72). However, there are significant differences between subjects in the pattern of responses across the set of masker samples. (Intersubject correlation coefficients were lower than 0.7). Subjects’ performance values for individual noise samples are compared to the predictions of psychophysical models for binaural detection. Sample-level predictions of models for which the decision variable is dominated by the energy in the particular noise sample have no significant correlation with the patterns of responses across noise samples for any subject. In contrast, models that are based on variability of the interaural differences have predictions that are statistically significantly correlated with most subjects’ responses (although no correlation coefficients were larger than 0.7). [Work supported by NIDCD (Grant DC00100).]
Efficient finite-impulse-response filter models of the head-related transfer function
Authors: Kulkarni Abhijit , Colburn H. Steven
Published: October 2005

The head-related transfer function (HRTF) is empirically measured as a finite-impulse-response (FIR) filter e.g., Wightman and Kistler, 1989. In this study we explore reduced-order approximations of measured HRTFs for use in virtual acoustical displays. The HRTFs tested were measured from human subjects and provided by Dr. Fred Wightman. In all model reconstructions it is assumed that HRTFs can be approximated as minimum-phase functions. Theoretical results are derived which allow for two model-order reduction strategies with optimal criteria. First, we demonstrate that the partial energy contained in the first n taps of a minimum-phase FIR filter is optimal in the Parseval sense. Secondly, we demonstrate that the HRTF expressed by its cepstral coefficients (Oppenheim and Schafer, 1979) constitutes a Fourier series. A partial sum from this Fourier series then provides the best mean-square approximation to the log-magnitude function of the HRTF. The validity of the reconstructed HRTFs was assessed psychophysically using a 4I-2AFC procedure. Using a 80-ms white noise stimulus and testing a new position on each trial, for a 64-tap HRTF reconstruction by both methods, subjects performed close to chance for most of the 13 representative positions tested. [Work supported by NIDCD (Grant DC00100).]
Evaluation of three-dimensional (3D) auditory beacons for navigation of remote-controlled vehicles
Authors: Tran Tuyen V. , Letowski Tomasz R. , Abouchacra Kim S.
Published: October 2005

A series of experiments was conducted to evaluate 3D auditory beacons to be used by drivers of remote-controlled vehicles. The auditory beacons were generated from an external sound source, conditioned using the ConvolvotronTM and then presented through Sennheiser HD-580 earphones. In addition, a pink noise masker was presented through an overhead loudspeaker at a level of 80 dBA measured under the earphones. Ten listeners with normal hearing were asked to (1) judge sound quality of nine auditory beacons, and (2) move a beacon from a predetermined starting location to a position directly in front of the listener in the 3D display. The beacons differed regarding type of sound as well as rate and mode (continuous versus noncontinuous and single versus oscillating sound source) presentation. Results of the experiments indicate that listeners preferred (1) continuous versus interrupted presentation of the beacons, (2) nonspeech versus speech beacons, and (3) a rate of 1.1 repetitions per second over 0.7 or 2.5 repetitions per second. Mode of presentation did not affect the overall localization accuracy or the number of front versus back confusions made by the listeners. Results of the experiments will assist in the selection of beacons for auditory displays used for operation of remote-controlled vehicles.