Treatment of early and late reflections in a hybrid computer model for room acoustics

Graham Naylor
1992 Journal of the Acoustical Society of America  
IaEAI. The sinale European market •nd its influence on measurement and specification standards for ultrasonie•. Roy C. Preston (Div. of Radiation Sc_.i. and Acoust., Natl. Phys. Lab., Teddington, Middlesex TW11 0LW, UK) The Single European Market and European Directives will have an enormous impact on all aspects of commercial activities worldwide. In acoustics, Directives dealing with noise at work, machinery noise, and medical devices will have greatest impact. In ultrasonics, the General
more » ... cal Device Directlye will deal with medical ultrasonic equipment and will lay down comprehensive essential safety requirements that will require manufacturers to comply with standards published by the Comit6 Europ6an de Normalisation Electrotechnique (CENELEC), in most cases based on International Electrotechnical Commission (IEC) standards. The initial thrust is to establish "horizontal" standards or "generic" standards that will apply to a wide range of equipment. At the specific product level, "vertical" standards will be required dealing with specific aspects of safety for a product type. For instance, standards will be prepared for diagnostic ultrasonic equipment, therapeutic ultrasonic equipment, and extracorporeal !ithotriptera. IEC Technical Committee 62: Electrical Equipment in Medical Practice is responsible for the preparation of these standards. These standards will themselves make reference to technical standards dealing with methods of measurement and characterization of ultrasonic fields prepared by Technical Committee 87: Ultrasorties. The current status of standards, either already published or being developed by Technical Committee 87, will be reviewed with particular emphasis on their applicability to the EC Medical Device Directire. INSERM unit6 281, 151 Cours Albert Thomas, 69424 Lyon Cedex 03, France), Dominique Cathignol, and Aiain Biter (INSERM unit6 281, Lyon, France) Recently, shock wave generators (electrohydraulic, electromagnetic, or piezoelectric) have become of common use for the treatment of renal calculi and gallstones. In all these generators, the focal zone is fixed. This is a major drawback since it is well known that the stones move according to the respiratory cycle. Consequently, the shock waves are not always well focused on the stone, which results in an increase of the duration of the treatment and the development of lesions in the neighboring tissues. To resolve this problem, a piezoelectric electronically focused shock wave generator has been designed. Measurements of the sound field produced in water by the first prototype of this novel generation of extracorporal lithotripters are presented, which clearly demonstrate the advantages of this type of focusing. laEA3. Abstract withdrawn. 9:35 have been made in our lab. The frequency-transducer size relation has been set by a 30-dB sidelobe suppression criterion. Theoretical design and experimental verification are presented. A 6-in.-diam Gaussian transducer that works at even lower frequency is in progress. [Work supported by ONT.] 10:05 IaEAS. A systematic experimental investigation of a highly intense pressure field generated by a plane circular transducer. Sylvain Nachef (Technomed International S. A., Bron, France and INSERM unit6 281, Lyon, France), Dominique Cathignol (INSERM unit6 281, Lyon, France), and Jacqueline Naze Tj•tta ( This work is part of a study of highly intense sound beams with application to medical therapy in mind. A systematic experimental investigation of a sound beam propagated into water from a plane circular transducer was for the first time, it is believed, performed for a large range of cw excitation levels. The fundamental frequency was I MHz and the on-source pressure ranged from 0.8 to 24 bar (shock formation distance to Rayleigh distance ratio ranging from !.8 to 0.06). The pressure amplitude distributions of the five first harmonic components, along and across the acoustic axis, are presented and discussed. New nonlinear effects are uncovered: a nonlinear self-defocusing of the beam and an alteration of the near-field structure of the harmonic components. 9:50 IAEA4. Kilohertz Gaussian transducer design and fabrication. M.A. Breazeale and Dehua Huang (Natl. Ctr. for Phys. Aeonst., Univ. of Mississippi, University, MS 38677) The Gaussian distribution of an ultrasonic field has attracted attention and interest because of its unique features: analytic mathematical solution for a sound field in a homogeneous medium; no maxima or minima in Fresnel zone; a single beam free of sidelobes in the Fraunhofer region. Heretofore the mathematical attractiveness of the Gaussian function has been used in many physical theories. It has been used in connection with underwater acoustics, interface problems, medical ultrasonics, nondestructive evaluation, acoustical microscopy, nonlinear acoustics, etc. The Gaussian beam not only is an ideal mathematical model, but it is beginning to be physically realizable. Several methods reported to be successful in the megahertz frequency range have failed to produce a Gaussian distribution in the kilohertz range. This paper presents an improved design that is successful for a kilohertz Gaussian transducer. It has worked in the megahertz frequency range also. Gaussian transducers at 375 kHz (4 in. diana) and at 332 kHz (5 in. diam) 10:20 IAEA6. Theoretical model for the unimorph flexural disk transducer. Daniel M. Warren, L. Dwynn Lafleur, and F. Douglas Shields (Natl. Ctr. for Phys. Acoust., Coliseum Rd., University, MS 38677) The unimorph is a very popular piezoelectric transducer used in consumer products ranging from musical greeting cards to smoke alarms. Recently unimorphs have been used to construct low-frequency hydrophone projectors [D. M. Warren et aL, J. Acoust. Soc. Am. 91, 2325 (A) (1992)]. Despite their popularity, no mathematical analysis adequately addresses this unique transducer. The unimorph is a bilaminate disk---one layer piezoelectric, the other metal. The metal layer has a larger radius than the piezoelectric and the thicknesses of the layers are not necessarily equal. Theoretical treatments of other flexural disk transducers, like the bimorph disk, assume layers of the same material [E.G. Thurston, J. Acoust. Soc. Am. 24, 656 (1952)], elasticity controlled by a single layer [T. D. Sullivan and J. M. Powers, J. Acoust. Sac. Am. 63, 1396 ( 1978)], or effective elastic constants to be measured experimentally [S. Hanish, NRL Rep. 5259 (1959)]. Furthermore, all assume equal radii. The current theory offers a more suitable treatment of a simply supported unimorph operating against a vacuum. Calculations of the surface velocity profile are compared to laser Doppler measurements. [Work supported by ONR.] 10:35 IAEA7. A low-frequency one-sided flextensional transducer. Didier Boucher (DGA-DCN-DCN Toulon CERDSM, Le Brusc, 83140 Six-Fours-Les-Plages, France) In this paper, a one-sided flextensional projector, which has been designed and constructed, is presented. Roughly, it looks like a class IV flextensional transducer but with only a partial aluminum shell defining the radiating part. Inside the shell, longitudinal piezoelectric stacks are tightly inserted, with regular spacing, parallel to the shell pseudo-major axis. Steel inserts are fixed at both ends of these stacks and conventional 2292 tie rods are used for prestressing. A steel housing situated behind the shell as well as top and bottom caps ensure watertightness. Under an electrical drive, the stacks undergo a longitudinal vibration that is transmitted to the shell and converted into flexural motion with a larger mechanical displacement. Nevertheless, despite the similarities, the operating mode of this projector is very different from the conventional flextensional operating principle. Such an original behavior has been obtained by a careful design of the transducer. A trial-and-error procedure has been carried out with a numerical analysis tool to optimize the main electromechanical parts. Fairly accurate comparisons with experimental results have been obtained for the transmitting voltage response as well as for directivity patterns. It is confirmed that this one-sided flextensional transducer is directire, leading to a front-to-hack ratio equal to about 10 dB in the frequency range of interest. Close-packed arrays can be easily realized with the one-sided flextensional transducer type. Some new array designs are discussed and illustrated with theoretical results. The variational principle is an approximation method that allows one to obtain accurate estimates of a quantity using relatively crude trial functions for the physical behavior. This principle is applied to transdacer analysis by coupling a variational principle developed for the driving element (including piezoelectric effects) to one for the shell. The motion of the transducer is, in turn, coupled to a variational principle for the pressure in a fluid medium. The modeling of a class V flextensional ring-shell projector will be presented in detail. The in-•acuo resonance frequencies for the piezoelectric ring and spherical shell, as well as the in-•acuo mode shapes for the driver-shell combination will be compared with existing theory and finite element analyses. Results for a free-flooded piezoelectric ring and immersed spherical shell will be presented as tests of the variational fluid loading formulation. Admittance calculations and beam patterns for a single element will be compared with experimental data, equivalent circuit, and finite element analyses. The extension of the variational method to array interaction modeling will also be discussed. 11:05 IAEA9. Fabrication of a high-frequency polymer projector. A high-frequency projector was fabricated using solvent-east piezoelectric polyvinylidene trifluorocthylenc P (VF2/EF•) copolymer film. It has a higher electromechanical coupling factor, (kr•0.3) [Ohigashi and Koga, Jpn. $. Appl. Phys. 21 (8), [.455-457 ( 1982)], than P homopolymer and it does not require stretching to align the polymer chains. 75% P(VF2/EF3) copolymer dissolved in methyl ethyl ketone was cast into a 200-to 300-/•m sheet, annealed at 130øC, and slow cooled. A thin layer of conductive metal was sputtered onto either side of the copolymer. The metalized film was subsequently poled in a heated oil bath in the thickness direction. The samples (6.5 cm 2) were tested with and without brass electrodes. The brass brought the resonance frequency down to the 700-kHz range. Measured parameters included coupling, quality factor, piezoelectric constant, and transmit voltage response. The transducer was modeled using a modified Mason equivalent circuit, which is similar to that demonstrated by Brown and Carlson [IEEE Trans. Ultrason. Ferroelec. Freq. Control UFFC-36, 313-318 (1989)]. Measured and calculated parameters are compared with values obtained for representative P(VF2) homopolymer. 11:20 IaEAI0. Image derived second-order differential microphones. J.E. Second-order differential (SOD) toroidal and uniaxial microphones derived using a first-order differential (FOD) sensor and a reflecting plane are described. For a uniaxial implementation a dipole FOD sensor is positioned with its axis perpendicular to and suspended a few centimeters from a large acoustically reflecting surface. The resulting sensor image is phase reversed resulting in a transducer that is a linear quadrupole. The linear quadrupole can be described by two dimensions, the distance corresponding to the FOD sensor dipole distance and the distance from the reflecting plane. If the reflecting surface is large enough, or if the wall of an enclosure is used, the resulting microphone becomes a SOD axial microphone. The cl øse match between the sensor and its image from a good acoustic reflector results in a uniaxial SOD microphone with a 3-rib beamwidth of 66'. The sensor will operate as a differential microphone at frequencies below 3 kHz for a 2.5-cm spacing between the sensor and reflecting surface. A wall-mounted toroid can be formed by using two FOD sensors at right angles to each other and with the axis of each sensor at 45' to the reflecting surface. Also, the spacing between sensors is twice the height of the sensors from the reflecting plane. Measurements show that these transducers can be realized with existing commercially available eleetret condenser dipole sensors. 11-35 laEAII. Inteusity-modulated fiber-optic microphone. A fiber-optic microphone has been developed that can detect low acoustic sound pressure levels. The microphone is an extrinsic intensitymodulated fiber-optic level sensor. The optical mechanisms involved and the effect on performance of fiber placement with respect to the optical element will be discussed. Plots of frequency response, sensitivity, and a tape recording made using the microphone will be presented. A fiber-optic lever microphone has been developed for hightemperature applications. The sensitivity of the microphone is determined from a pistonphone calibration at room temperatug. The electrostatic actuator method is used for the frequency response calibration of the microphone at room temperature and 1000 'F. The microphone is placed inside an oven, and is excited by the electrostatic force between the actuator electrode and the microphone membrane. The frequency response of the microphone, along with the background noise, is analyzed on an leFT analyzer. For a 0.072 in. diameter of the membrane, the typical sensitivity of the microphone is 1.3/zV/Pa, and the typical bandwidth is 47 kHz. The background noise includes contributions from the microphone and the phatodeteetor, in which the shot nole• is the dominant source of noise. 2293 A simple model has been developed that accounts for the excitation signal to the transducer, the transducer characteristics, and the diffraction of the sound for the purpose of flaw sizing. The goal has been to seck the ramp response that is the second integral of the impulse response. The ramp response yields volume and cross-sectional area information about the flaw. This research has demonstrated that all of the above mechanisms are high-pass frequency filters whereas the frequency content needed for the ramp response is low, namely ka < 2. Unfortunately the physical mechanisms reduce the low-frequency content well below the noise levels and it is impossible to extract the information required even though the transducer is driven with a signal that contains a large amount of low-frequency content. 9:15 IaPA2. Laser generation of Rayleigh and Lamb waves for ultrasonic testing. R. The thermoelastic generation of surface waves by a Q-switched ruby laser is investigated both experimentally and analytically. The motivation is to improve the amplitude and to control the frequency content of the ultrasonic signal by taking advantage of the tremendous flexibility that one has in controlling the size and the shape of the thermoelastic source. Waveforms have been recorded for several source geometries at the surface of an aluminum block: spot source, line source, periodic array of spot sources, and periodic array of line sources. Also, focusing effects have been measured with a periodic array of curved line sources obtained with a Fresnel lens. In all cases, the waveforms are reasonably well predicted by a simple and efficient convolution technique. Waveforms have also been generated in a l-ram-thick aluminum plate and recorded over a distance of 50 mm at increments of 0.5 ram. Processing of these waveforms in the frequency-wave-number domain allows for the extraction of the dispersion curve and the various modes propagating in the plate. [Work supported by NSF.] 9',30 IaPA3. An 'investigation using an optical probe to study ultrasonic pulses. Io Hays-Stang and Bill D. Cook (With care and working within well-defined constraints, it has been previously demonstrated that a laser beam and a fast responding light detector could be made to behave as a linear line receiver of low megahertz sinusoidal ultrasonic waves. It is a sufficiently good line receiver so that the principles of tomography can be used to unfold the sound field. Many of the constraints are frequency dependent and the question arises as to whether a laser beam could be used to investigate a pulse of moderate bandwidth. The studies show that major features of the signal from the line detector can be accounted for when the sound field is produced by a commercial NDE transducer driven with a known Gaussian time pulse. 9:45 IaPA4. Acoustic wave propagation in multilayer systems. Ra61 Theoretical studies are performed on the propagation of •'•coustic waves in multilayer systems using a transfer matrix approach similar to that developed for the studies of optical filters [L. I. Epstein, J. Opt. Soc. Am. 42, 806-810 (1952)] and metallic superlattices [E. L. Olazagasti el a/. , Solid State Commun. 78, 9-12 (1991)]. The formalism presented here is used to calculate the reflectivity R of sound waves on multilayer structures. Comparisons are made with experimental results lB. G. Martin, L Acoust. SOc. Am. 91, 1469-1473 (1992)] for a three-layer structure, in the normal incidence case. The calculated resonances are in good agreement with the experimental ones. For the same system, in the non-normal incidence of sound waves, the spectra of R suggests surface waves coupling. Finally, to show the usefulness of the theory, a Kronig-Penney type structure is studied, calculating the dispersion relation of the normal modes of an infinite system and the reflectivity for the semiinfinite case. laPAS. Ultrasonic flux imaging in anisotropic solids. Richard L. A new method is discussed for characterizing acoustic flux propagation in anisotropic media. The technique utilizca a pair of waterimmersion focused acoustic transducers as a point source and point detector. Raster scanning of either the source or detector over a slab-like specimen of an anisotropic solid produces a transmission pattern that exhibits the anisotropies in acoustic flux previously known as "phonon focusing." Unlike phonon focusing images, however, the pattern is modulated by "internal diffraction" fringes arising from interference between sheets on the acoustic wave surface. In addition to the diffraction effects, the images reveal interesting critical-cone structures associated with the water/solid interface. These images may be understood theoretically by taking into account the full anisotropy of the medium, the boundary conditions between the solid and the water, and the pressure fields produced by the immersion transducers. The theoretical predic-2294 An acoustical reflection experiment is intuitively based on (i) downward wave propagation from the acquisition surface into the medium, (ii) reflection by inhomogeneities inside the medium, and {iii) upward propagation of the reflected waves to the acquisition surface. The acoustic and elastodynamic wave equations do not explicitly account for this intuitive distinction between downward and upward propagation. These wave equations govern the total wave field, which may be seen as a superposition of downward propagating and upward propagating wave fields. For this reason these equations are referred to as the two-wa3, wave equations and their solutions are called two-way wavefielda Analogously, the equations that explicitly govern downward and upward propagation are referred to as the one-way wave equations and their solutions are called one-way wa• fields. In this paper reciprocity and representation theorems are developed for one-way wave fields. These theorems are the basis for a systematic discussion of acoustic reflection imaging in inhomogeneous fluids and in inhomogeneous anisotropic solids. 2295 d. 163 Music and Dramatic Arts Contributed Papers 8:30 IaPPI. Precedence effect with and without interaural differeaces•Sound localization in three planes. Brad Rakerd (Dept. of Audio and Speech Sci., Michigan State Univ., East Lansing, MI 48824) and William Morris Hartmann (Michigan State Univ., East Lansing, MI 48824) Separate experiments measured the precedence effect for sound localization in the horizontal, frontal, and sagittal planes. The first two planes involve interaural differences, the third does not. Listeners (N = 8) were required to localize trains of clicks, presented by loudspeakers in an artechole room. A target click originating in a particular plane was followed by a simulated reflection of equal level from a different location within that plane. The delay between target and reflection was the principal independent variable; it varied from 0 to 10 ms. The results of the experiments showed that the precedence effect is more effective in eliminating localization confusion due to reflections when interaural differences are present. However, the functional dependence of target identification upon delay was similar whether interaural differences were present or not. For all three planes there were identical regions of summing localization, of increasing precedence effect, and of confusion caused by echoes. These results show that there is a sagittal plane precedence effect, and, therefore, that the precedence effect does not require interaural differences for its operation. [Work supported by the NIDCD, DC00181.] 9:00 laPP3. Experiments involving auditory localization over headphones using synthesized cues. Mark A. Ericson and Richard L. McKinley (AL/CFBA, Wright-Patterson AFB, OH 45433-6573) An auditory localization cue synthesizer has been developed that can electronically encode directional information on various auditory signals and present the sounds over headphones. Performance of the synthesizer has been evaluated in several laboratory studies to validate its reproduction of free-field cues and its potential for various applications. Data were collected for localization in noise, binaural intelligibility level difference, and target acquisition experiments. Subjects were able to localize sounds in spectrally similar noise at low ( -10 to -20 dB) signal-to-noise ratios. A 3-to 6-dB release from masking was observed in various single talker and competing message experiments. Directional audio information facilitated visual target acquisition under high visual workload conditions. A comparison between these data and free-field localization data indicates that the synthesizer is capable of reproducing the free-field cues necessary to localize sounds over headphones. The technology for generating localization cues over headphones has shown beneficial effects in these applications without additional training by the listeners. 8:45 laPP2. Auditory spectral resolution and the Ioealination of clicks in the sagittal plane. William Morris Hartmann (Dept. of Phys., Michigan State Univ., East Lansing, MI 48824) and Brad Rakerd (Michigan State Univ., East Lansing, MI 48824) In a sagittal plane localization experiment, listeners (N=8) were required to localize a train of eight clicks that originated from a source that was either directly in front, overhead, or behind. Click trains were made from 25-/.ts pulses, separated by 110 ms, and were presented in an artechole room. The principal experimental parameter was the peak level of the clicks: 68, 74, 80, 86, 92, or 98 dB SPL. All listeners except one showed a level disadvantage: The localization error rate increased with increasing level, on the average by a factor of 10 over the range of levels. It was conjectured that the level disadvantage arises from a failure of the auditory system to resolve details of the spectral shaping caused by pinna, head, and upper torso in the case of a high-level pulse. Resolving these details is necessary for localization in the sagittal plane. This conjecture was tested in headphone experiments on filtered click discrimination. Many instances of level disadvantage were found, but none so strong or consistent as the original localization effect. [Work supported by the NIDCD, DC00181.] 9:15 laPP4. Masking level differences for tones and speech in elderly listeners with relatively normal audiograms. E. A. Poth and J. H. (}rose (Div. ofOtolaryngnlogy/Head & Neck Surgery, Univ. of North Carolina, Chapel Hill, NC 27599) Masking level differences (MLDs) were measured for both tones and speech in a group of elderly listeners with normal, or near-normal, audiometric sensitivity. The tonal MLD was obtained for the detection of a •OO-Hz tone masked by a 100-Hz wide band of noise centered at 500 Hz. The speech MLD was obtained for the recognition of spondaic words masked by speech-shaped noise. For both types of stimuli, the MLDs measured in the elderly listeners were significantly smaller than those measured in a control group of normal-hearing young listeners. This reduction was primarily due to an elevation of the NoS•r thresholds in the elderly group. The results support the hypothesis that a reduced binaural advantage may contribute to the difficulty of understanding speech in noise reported by the elderly listeners. Furthermore, the use of listeners with normal, or near-normal, audiometric sensitivity suggests that factors other than peripheral sensitivity loss may play a role in speech understanding in noisy listening conditions. Binaural performance was measured for children ages 7 to 12 with and without a history of otitis media on three tests: binaural detection, localization, and speech'intelligibility. NoSo and NoS•r thresholds were measured for pure-tone and l/3-octave noise targets in narrow and wideband noise maskera as a function of frequency. Localization in the horizontal plane (nine locations from -90 ø to +90 ø) was measured using short phrases. lntelligibility of monosyllabic words was assessed with the speech at 0' in quiet and in noise. Localization and speech intelligibility were measured in anechoic and reverberant environments. Results of the detection tests show smaller masking-level differences (MLDs) for children with a history of otitis media than children with no history. Localization and speech intelligibility are also generally poorer for the children with a history ofofitis media. Localization for all children is independent of environment, but speech inte!ligibility is better in the anechoic environment. Performance for all three tests also appears to improve as a function of age. Overall, good binaural detection tends to be associated with good localization and speech intelligibility, and children with a history of otitis media have more difficulty with tasks requiting binaural interaction. [Work supported by UCRF and Sertoma Club of Baton Rouge.] 9:45 laPP6. Investigation of phase distortion in the synthesis of head-related transfer functions. Synthesizing over headphones the free-field to ear-canal transfer functions, or head-related transfer functions (HRTFs), of the human auditory system poses several difficulties from the standpoint of digital signal processing. Since the order of the HRTF is unknown, it is necessary to assume a particular value when estimating the HRTF from responses obtained in an anechoic chamber. Additionally, while standard filter designs minimize the squared error between the desired and designed response, applications soeh as HRTF synthesis are likely to require error metrics that are sensitive to disparities between the log magnitude response of each system. A new design algorithm is proposed that is based on a logarithmic distortion metric and it is shown how this algorithm can be used to obtain minimum phase, low-order pole-zero approximations to HRTFs. Psyehophysical results characterizing audibility sensitivity to such HRTF approximation errors are presented in order to establish an audible limit for the distortion in such designs. These results are compared with similar experimental results for the widely used least-squares metric. [Research supported by a grant from the NIDCD of the National Institute of Health.] 10.'00-10:IS Break 10:.15 laPP7. Auditory spectral cues for the resolution of front-back confusion in humans. Simon Carlilt and Daniele Pralong (Univ. Lab. of Physiology, Oxford OXI 3PT, UK) The interaural level and timing difference cues are ambiguous for sound location and give rise to the so-called cones of confusion. Paychophysieal work has demonstrated that spectral cues furnished by the auditory periphery are critical for resolving these front-back ambiguities. The transfer functions were recorded from each auditory canal in human subjects for 365 locations in artechole space. For anterior locations there are substantial gains around 34 kHz and above 13 kHz and a notch in the transfer function that moves up in frequency (8 to 12 kHz) for locations away from the midline. These features remain reasonably consistent over a 60' change in elevation about the interaural horizontal plane (IAP). For posterior sound locations, transmission is relatively fiat for locations below the IAP but a sharp notch centered on 9 kHz is evident for locations above the IAP. The changes in the interaural spectral differences are relatively symmetrical for horizontal locations about the interaural axis, although at high frequencies ( > 12 kHz) there are some features that might provide front-back information for locations cla•e to the interaural axis. These acoustical data identify several spectral features in the human mortaural transfer functions that may provide potent, unambiguous cues to a sounds location. [Work supported by the Belt Foundation, MeDonnel Pew Centre for Cognitive Neurosciences, Swiss National Science Foundation, and Foundation for the 450th Birthday of the University of Lausanne.] 10:30 laPPS. Minimum audible angles for synthesized localization cues presented over headphones. Richard L. McKinley, Mark Ericson (AL/CFBA, Wright-Patterson AFB, OH 45433-6573), David Perrot (Cal. State Univ., Several methods can be used to synthetically generate auditory localization cues over headphones. Very little traditional auditory performance data have been presented for these types of synthesizers. The data were collected using stimuli similar to those used by Mills [J. Acoust. Soc. Am. •0, 237-246 ( 1958)]: 500-Hz tone, I s on, I s off, 1 s on, 70-ms ramps for on period, and 500 ms off after response before the next stimulus was presented. The paradigm used was the two-source two-interval experiment described by Hartmann and Rakerd [J. Acoust. Soc. Am. aS, 2031-2041 ( 1985)]. The minimum audible angle (MAA) was measured at seven locations in the horizontal plane for synthetic stimuli presented over headphones. MAA data will be presented for 10 normal hearing subjects for each of the seven locations. The MAA data using headphones will be compared with free-field MAA data from the literature and with mean localization error data using headphones. 10:4S laPP9. On the measurement of source separation. It has been conjectured that certain acoustic cues present in a complex waveform are used by the auditory system to decompose that waveform into a set of auditory sources. The disparity between the perceived source(s) and the physical sources in such phenomena as stereophony suggests that there is not necessarily a one-to-one correspondence between the acoustic composition of signals and the perceptual decomposition of the combined signal into auditory sources. In an earlier paper [Wakefield and Runkle, Issues in Advanced Hearing Aid Research Conference (May 1992)], a method was proposed for measuring the strength of such cues adaptively, however, the hypothesis that the measuring technique itself was responsible for the results could not be rejeered. In the present paper, an alternative measuring tool is introduced that is capable of independently suppressing and enhancing different spectral regions, unlike the original tool. Results are presented concerning the salience of co-modulation, harmonicity, onset and offset cues, and amplitude spectrum with respect to auditory sources using the new tool. A recognition paradigm is integrated into the proposed method to help validate the results. [Work supported by grants from the NIH NIDCD and from Ford Motor Company.] 11:00 laPP10. The correlation between responses under monaural and binaural conditions. R. H. Gilkey (Dept. of Psychol., Wright State Univ., Dayton, OH 45435 and Armstrong Lab., AL/CFBA, Wright-Patterson AFB, Dayton, OH 45433-6573) Giikey et al. [J. Acoust. Soc. Am. 78, 1207-1219 (1985)] compared "monaural" (NoSo) and "binaural" (NoS•r) performance in a reproducible noise masking task. Despite a large masking level difference, the responses to individual noise samples under the NoSo and NoS•r conditions were highly correlated (p,•0.001). Isabelle and Colburn [J. Acoust. Soc. Am. 89, 352-359 (1991)], on the other hand, found correlations that were weak, and sometimes negative. Gilkey et al. used wideband masking noise, whereas Isabelle and Colburn used narrowband maskers. On that basis, Isabelle and Colburn argued that the correlation observed by Gilkey et al. might be more appropriately attributed to similarities in across-critical-band processing, rather than to similarities in within-critical-band processing. The present study examined both wideband and narrow-band maskers and found highly significant correlations between monaural and binaural performance for both maskers (p,•O.005). [Work supported by NIH-DC-000786 and AFOSR-91-0289.] 11:15 IaPPII. An artificial neural network model of human sound localization. T. R. Anderson (Armstrong Lab., AL/CFBA, Wright-Patterson AFB, Dayton, OH 45433-6573), J. A. Janko (Wright State Univ., Dayton, OH 45435), and R. H. Gilkey (AL/CFBA, Wright-Patterson AFB, Dayton, OH 45433-6573 and Wright State Univ., Dayton, OH 45435) An artificial neural network was trained to identify the location of sound sources using the head-related transfer functions (HRTFs) of Wightman and Kistler [J. Acoust. Soc. Am. g5, 858-867 (1989)].-The simulated signals were either filtered clicks or pure tones, with speaker placements separated in steps of 15 deg in azimuth of 18 deg in elevation. After the signals were passed through the HRTFs, the inputs to the nets were computed as the difference of left ear and right ear phase spectra or the difference of the power at the output of left and right ear third-octave or twelfth-octave filter banks. Back propagation was used to train the nets. Separate nets were trained for each signal type and for each type of input data. Better than 90% correct identification of the source speakers location can be achieved in either the horizontal or median planes. The results for the horizontal plane are compared to the predictions of the duplex theory of sound localization. In a series of experiments frequency and duration discrimination thresholds of short, linear rising or falling, speech-like transitions were determined by means of same/different paired comparison tasks. Difference limens of single formant transitions varying in frequency extent at a constant duration (experiment 1 ), decreased with increase of transition duration. They were, on average, 70, 63, and 57 Hz for 20, 30, and 50 ms, respectively. However, when transition duration varied at a constant frequency extent (experiment 2), difference limens were, on average, 2.7, 4.5, and 4.9 ms for standard transitions of 20, 30, and 50 ms, respectively. In both experiments, thresholds between rising and falling transitions, determined in two frequency regions, and between transitions with either higher or lower rates of frequency change than the standard transition, were comparable. The extent to which the first formant transition and the steady-state interfere with discrimination of the second formant transition is studied further with single and combined formants, bounded by plateaus (experiment 3). The data suggest that, although transition rate is varied, different psychoacoustical cues are extracted by the auditory mechanism. 2298 IaSP2. Human newborns show a "perceptual maguet effect" for nst/re /angunge and non-naffve language prototypes. Gall Walton and Tina Socotch (Univ. of Texas at Dallas, Box 830688 GR 4.1, Richardson, TX 75083-0688) Kuhl demonstrated that adults and 6-month-old human infants showed a "perceptual magnet effect" for vowel prototypes. Kuhl et al. also showed that Swedish infants do not show a magnet effect for phoneme categories that are not present in their native language. This study demonstrated that the "perceptual magnet effect" was also present in human newborns. Newborns of English-and Spanish-speaking mothers were presented phoneme exemplars around the prototypes/i/and/•/, and also around non-prototypical /i/ and /•/. Neonares of Spanishspeaking mothers demonstrated the magnet effect for the prototype/i/, a speech sound present in their native language, and also for the prototype /•/, a sound not present in their native language. The results suggest that newborns enter the world with "platonic forms" for phoneme categories that are influenced by subsequent linguistic experience. 8:30 laSP3. Phoneroes and syllables as units of speech perception in newborns. Kelley L. Kaye (Univ. of Texas at Dallas, Box 830688 GR 4.1, Richardson, TX 75083-0688) There is some controversy concerning what constitutes the perceptual unit of speech. Bertoncini and Mehler [Infant Behav. Der. 4, 247-260 (1981)] have presented evidence from infants supporting the syllable over the phoneme. The present study investigated this issue with newborns. Twenty-four subjects were presented with lists of nonsense syllables (CVC's) over carphones, using an operant choice preference sucking procedure. The lists varied in number of syllables (length) and also in number of phonemes (complexity). Two contradictory effects occurred: the number of sucks produced decreased as syllables were added, and the number of sucks increased as prohemes were added. Speech perception in newborns thus requires two processes: the multidimensional space of the utterances is defined in terms of distinctive features, requiring a large number of presentations. Subsequently, the infant operates on the units defined in that space, with processing largely occurring in memory whereby the increased memory load suppresses sucking. An experiment to test this interpretation has been carried out, and will also be discussed. 8:45 1aSP4. Evidence for activation of sublexical units in auditory lexical decision. Emily A. Lyons and Paul A. Luce (Language Perception Many words in English (e.g., HEMLOCK) contain component syllables that are themselves words (HEM and LOCK). Some research on spoken word recognition has attempted to determine if these component words are activated when the longer word is heard. If so, what effect does activation of the component words have on the recognition of the longer word? A lexical decision experiment was performed that examined reaction times to bisyllabic spoken words that contained syllables that were themselves either words or nonwords. The results demonstrated that subjects were faster to respond to bisyllabic words in which the first syllable was a word (e.g., KIDNEY) than to bisyllabic words in which the first syllable was a nonword (e.g., CHIMNEY). These findings are consistent with earlier research using cross modal priming techniques that has demonstrated that embedded words can speed responding to a visually presented related word. Additionally, these findings suggest that the activation of component words has a demonstrable effect on recognition time.
doi:10.1121/1.404930 fatcat:xeehcxepjvhuzmnaeudpqxtnvu