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Nov 1989

Volume 86, Issue S1, pp. S1-S125

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back to top Session MM. Psychological Acoustics VIII and Physiological Acoustics IV: General Physiological and Psychological Acoustics (Poster Session)
Contributed Papers
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Behavioral thresholds for tone pips in 3‐ and 6‐month‐old infants and adults (A)

Lynne Werner Olsho, M. Patrick Feeney, and Richard C. Folsom

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S95-S95 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Infant behavioral thresholds for tone‐pip stimuli at 1, 4, and 8 kHz (3‐cycle rise‐fall and 1‐cycle plateau) were estimated using the observer‐based psychoacoustic procedure (OPP). Behavioral thresholds for these stimuli were also obtained on a group of normal‐hearing adults. Across frequency comparisons revealed that 6‐month‐old infant threshold curves paralleled adult curves, but infant thresholds were elevated 20 to 30 dB. For 3‐month‐old infants, OPP threshold curves were not parallel to adult curves due to relatively poorer infant thresholds at 8 kHz: Furthermore, in comparison with wave V auditory brain‐stem response (ABR) thresholds for the same stimuli, 3‐month‐old infant behavioral thresholds are the same as ABR thresholds at 1 and 4 kHz, whereas behavioral thresholds are poorer at 8 kHz. A similar elevation in threshold at 8 kHz for 3‐month olds has been reported for longer duration stimuli [L. W. Olsho et al., J. Acoust. Soc. Am. 84, 1316–1324 (1988)]. The results suggest a frequency‐dependent maturation of behavioral thresholds between 3 and 6 months for these brief stimuli. [Work supported by NIH.]
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Central processing in patients with cochlear implants (A)

D. M. Daly, F. D. Owens, and P. Stephenson

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S95-S95 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Because of locations and orientations of auditory cortex, studies of central processing in man typically exploit psychophysical phenomena or disease altered structure/functioning. Cochlear implants afford a view of central processing through sparse, specifiable peripheral transfer functions. Six patients were examined who have unilateral implants (cochlear 22 channel; 14–21 active electrodes in BP + 1; 4 AS, 2 AD implants; 2–100 weeks post‐op) using prerecorded sets of BW, GY, BDG, and iɪe delivered directly through the processor [Daly et al., J Neurophysiol. 140 (2), 141‐62 (1980)]. The representation of stimuli was sufficient for three patients to classify stop/glide sets consistently (p<0.001); although in a set which included both BW and GY none distinguished [be] from [gel or [we] from [ye]. Performance reverted to chance when the processor was configured as a single channel device and all stimuli had the same total duration. None distinguished among BDG. One patient classified vowels iɪe consistently; boundaries changed significantly when a central electrode malfunctioned and was inactivated in configuration map. Results suggest, with these stimuli, patients resolved brief temporal changes more accurately than brief frequency changes alone.
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Psychometric functions for level discrimination in simulated and cochlear impairment (A)

Søren Buus, Mary Florentine, and Tilmann Zwicker

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S95-S95 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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To determine whether the form of psychometric functions for 2I, 2AFC level discrimination changes with hearing impairment, measurements were obtained in listeners with cochlear impairments and normal listeners with impairments simulated by masking. Ten increment levels were presented in random order within blocks of 100 trials. Stimuli were tones at 0.25, 1, 8, or 14 kHz or white noises chosen to encompass a wide range of conditions and difference limens. Durations were either 10 or 500 ms and levels ranged from 50 to 90 dB SPL. For each condition, at least 20 blocks were presented in mixed order. Results show that the sensitivity d' is nearly proportional to ΔL( =  20 log [(p + Δp)/p], where p is pressure) over the entire range of difference limens for both simulated and real impairments as well as for normal listeners tested in the quiet. These results indicate that if the transformation from stimulus intensity to decision variable is affected by heating impairment or masking, the change affects both the mean and the standard deviation in the same manner. They also lend support to the notion that ΔL−plotted on a logarithmic scale−is an appropriate representation of level‐discrimination performance. [Work supported by NIH.]
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Electrotactile encoding and recognition of a 16‐obstruent system (A)

H. G. Piroth, S. Gfroerer, and H. G. Tillmann

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S95-S95 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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In continuation of a long‐term training experiment [H. G. Tillmann and H. G. Piroth, J. Acoust. Soc. Am. Suppl. 1 84, S45 (1988)] the recognition of 16 obstruents in Cə syllables was tested using a modified quasiarticulatory coding method. Tactile syllable patterns were delivered by the 16‐channel electrocutaneous system “SEHR‐2” to 16 electrode pairs that were arranged to build four equidistant rings around the left forearm. Consonants were assigned to rings or pairs of rings in order to yield more than four places of articulation. Fricatives were coded as subsequent stimulations of four or eight electrodes (forming one or two rings, respectively) while plosives were represented by oscillating movements between the neighboring electrodes of a ring. The fortis/lenis distinction was coded by different pattern velocities. Since recognition with the initial coding of the two‐ring fricative patterns as parallel and synchronous movements was poor, an alternative coding method was applied with contrarotating movements in order to avoid local masking or inhibition resulting from the stimulation of adjacent electrodes. Using this alternative coding method, one highly trained subject reached 85.6% correct identifications of the 16 obstruents.
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Consonant testing of a tactile hearing aid based on amplitude‐ and time‐quantized speech (A)

Edward M. O'Brien

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S95-S96 (1989); (2 pages)

Online Publication Date: 13 Aug 2005

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Speech was first prefiltered with a second‐order bandpass filter centered at 1.5 kHz. Speech was then amplitude quantized to two levels based on the zero crossings of the waveform. This signal was then time quantized such that it could only change states in association with a clock signal. The intelligibility of the processed speech remains high for clock frequencies above 10 kHz (which was the quantizing rate used for this study). The discrete digital frequencies in the resulting waveform were easily detected with a digital logic circuit. These were then displayed onto the skin of the abdomen with a linear array of concentric ring electrodes. Thirty‐one electrodes (representing frequencies between 151 and 2500 Hz) were used for the array. Biphasic constant current pulses were used as the stimuli. Five normal hearing college age students served as the subjects. Discrimination of consonant pairs was used to test the ability of the tactile aid to transmit speech information to the subjects. The following ranges of accuracy (corrected for guessing) were observed: stops and constituents, 18% to 87%; voiced and unvoiced consonants, 3% to 27%; consonants with different places of articulation, 27% to 90%; nasal, glides, and semivowels, 17% to 49%.
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Noise reduction hearing aids: A tutorial (A)

Ruth A. Bentler and Brenda B. Bergman

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S96-S96 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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In the last few years, there has been a proliferation of (so‐called) noise reduction hearing aids onto the market. While some of these designs are little more than multiband compression circuits, others employ adaptive filtering (dependent upon overall input level), adaptive compression (dependent upon duration of high‐level input signals), and variations thereof. The purpose of this poster session is twofold: (1) using graphics and schematics an explanation of six available “noise reduction” circuits will be provided. This will serve as a tutorial for those audiologists attempting to keep up with design and marketing strategies for noise reduction; (2) preliminary results of a large clinical project begun late in 1988 aimed at determining how effective different circuits are for different configurations and/or degrees of hearing loss in new and experienced users will be presented. Success of effectiveness will eventually be measured over a 12‐month period using (a) speech recognition (in quiet and noise), (b) portions of the Hearing Performance Inventory (Giolas and Owens, 1979), (c) expectations checklist (Seyfried and Anderson, 1989), (d) qualitative measure task (modified from Gabrielson and Lindstrom, 1985), as well as (e) ratings of “satisfaction” taken at 6 months and 12 months post fitting.
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Regression effects in magnitude judgments of line length, and vibrotactile sine and pulse loudness (A)

Amy A. Collins and Roger W. Cholewiak

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S96-S96 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Five observers performed absolute magnitude estimation (AME) and absolute magnitude production (AMP) of line lengths and vibrotactile pulse and sine loudnesses as well as matching of each possible pair. Line lengths, presented visually, could extend over a 7‐ to 950‐mm range. Vibrotactile stimuli were 32‐pps haversine pulses and 250‐Hz sinusoids presented to the palm with 7‐mm diameter contactors and static surrounds. When the AME and AMP data were plotted together, perfect correlation was not seen indicating the influence of regression effects on the data. Regression effects occur when observers making judgments on two perceptual continua (i.e., line magnitude and number magnitude) restrict the range of their responses gravitating toward the mean response. Magnitude balance functions (MB) were calculated from AME and AMP data for the line, sine, and pulse. The cross‐modality matches, made with each stimulus type serving as the standard, showed similar regression effects. These data are discussed with reference to transitivity and the relationships among the data set predicted from the absolute scaling hypothesis. [Work supported by NIH.]
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Evidence for a tight blood‐labyrinth barrier (A)

Naoki Inamura, Alec N. Salt, and Ruediger Thalmann

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S96-S96 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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The entry of a small tracer ion (FW 135.6) from blood into perilymph and cerebrospinal fluid (CSF) has been monitored using ion‐selective electrodes. The tracer, trimethylphenylammonium (TMPA) can be detected in extremely low concentrations (< 1 μm) by electrodes, allowing entry to be accurately quantified. Electrodes were sealed into the cochlea to ensure that artifactual fluid leakages did not distort the results. A constant level of TMPA in plasma (approximately 0.5 mM) was maintained by continuous venous infusion of tracer. TMPA entry into CSF was extremely slow, reaching only 13% of the plasma level within 90 min (n = 3). Tracer entered perilymph even more slowly, reaching 6.5% (n = 5) and 3.7% (n = 5) of the plasma level in 90 min for ST and SV, respectively. The slow entry of such a small ion into perilymph demonstrates the existence of a tight barrier between blood and perilymph, and eliminates the possibility that perilymph is generated by mechanisms such as ultrafiltration. In two animals where bleeding was noted at the electrode insertion site, a much more rapid rate of tracer entry was recorded, probably as a result of plasma leakage into perilymph. Treatment with epinephrine (giving a brief blood pressure increase) also opens the barrier, allowing rapid tracer entry.
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Action potential tuning curves recorded with a derived response technique (A)

Philip Garcia and Alec N. Salt

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S96-S96 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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A number of laboratories use tonal masking methods in conjunction with the cochlear action potential (AP) to generate AP tuning curves. In these studies, the amplitude of AP elicited by a probe stimulus is monitored as the level of masker is varied. An amplitude reduction (AR) by a specified amount (25%–100%) is used to indicate masking of the response. An alternative method was investigated in which interaction of the probe and masker is monitored by digital subtraction of the unmasked and masked responses, generating a tone‐derived (TD) response. An amplitude criterion of 10‐μV TD response is used to indicate masker/probe interaction. Tuning curves were recorded from the round window of anesthetized guinea pigs using AR and TD methods. With near threshold probe stimuli, similar tuning curves were obtained. With higher levels however, markedly different results were observed. AR tuning curves became elevated and sharper while TD curves became lower and broader. The TD method appears to better represent the frequency spread of responses with increasing stimulus level as demonstrated at the single unit level. In addition, TD tuning curves were able to detect second harmonic distortions of the probe stimulus, while AR tuning curves did not. [Work supported by Program project grant P01 NS24372 and Training Grant NS 07278.]
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Coding of phase structure in complex sounds by bullfrog auditory‐nerve fibers (A)

Andrea Megela Simmons and Michael Ferragamo

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S96-S96 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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This experiment explored how the peripheral coding of the spectral and temporal structure of a complex communication signal is affected by the phase relations between individual frequency components in the sound. Complex sounds with 21 components, all of which were harmonics of a common, low‐frequency fundamental (100 Hz), were digitally synthesized. The frequencies and amplitudes of the individual components matched those of the bullfrog's species‐specific advertisement call. For one stimulus, the 21 components were generated in cosine phase, and for the other stimulus, the 21 components were in random phase. Most amphibian papilla (AP) and basilar papilla (BP) fibers synchronized to the envelope only of the phase‐coherent stimulus, and the complex spectral structure of the stimulus was not accurately encoded by population firing patterns. Envelope synchronization to the random‐phase stimulus was not seen in the responses of some mid‐frequency‐sensitive AP and BP fibers, although low‐frequency‐sensitive AP fibers responded similarly to both stimuli. Behavioral experiments suggest that bullfrogs can discriminate between in‐phase and random‐phase versions of their advertisement calls.
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Post‐discharge recovery effects in gerbil auditory‐nerve period and PST histograms (A)

Walter R. Bosch

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S97-S97 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Excitation‐function (EF) and recovery‐function (RF) parameters of a self‐exciting point process (SEPP) model for auditory nerve discharges were estimated [M. I. Miller, J. Acoust. Soc. Am. 77, 1452–1464 (1985)] for neural discharges recorded in gerbil in response to continuous‐tone and tone‐burst stimuli. The mean discharge intensity (MDI) of the SEPP model (expected value of the PST or period histogram) was computed from the EF and RF estimates by solving an integral equation [K. Jones et al., J. Acoust. Soc. Am. 78, 90–94 (1985)]. Period histograms computed from neural discharges in response to continuous‐tone stimuli were found to agree almost exactly with the corresponding MDI over a range of stimulus sound‐presSUre levels from 0 to 50 dB above threshold, indicating that the SEPP model accounts well for post‐discharge recovery effects in period histograms under these stimulus conditions. PST histograms computed from the neural response to tone‐burst stimulation also agreed quite well with the computed MDI for the conditions tested. [Work supported by NIH grants NS21592 and RR01379.]
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Neurophysiological observations on the auditory cortex in the FM bat, Eptesicus fuscus (A)

Cynthia F. Moss, Jonathan Fritz, Michael Ferragamo, and James A. Simmons

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S97-S97 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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The echolocating FM bat, Eptesicus fuscus, integrates target range and shape (range profile) into unified images along a synthetic target‐range axis. The response properties contained in single‐ and multi‐unit recordings from the auditory cortex of Eptesicus in relation to the process of image formation revealed in psychophysical data were examined. A tonotopic map was found in primary auditory cortex similar to what has been described previously, but also a much larger auditory cortical representation than hitherto reported. Echo delay‐tuned neurons are interspersed with frequency‐tuned neurons, showing no apparent topographic organization. The response profiles of some echo‐delay‐tuned and delay‐tracking neurons are dependent on the harmonic structure of the FM stimuli, as required for representing the unusual dual time‐ and frequency‐domain images that the bat perceives. Strong suppression effects may sharpen perceived target range and be the basis for encoding the depth structure of sonar targets in Eptesicus.
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ABER latencies are prolonged in rat pups fed a biotin deficient diet (A)

L. P. Rybak, C. Whitworth, V. Scott, and B. Bhardwaj

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S97-S97 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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The effects of biotin deprivation on ABER were studied in rat pups fed a diet that lacked this compound. Pregnant rats were either fed a normal rat diet (controls) or a special diet without biotin (Teklad, Harlan Sprague Dawley, Madison, WI). After weaning, the respective diets were continued in pups from each group. ABER was tested under chloral hydrate anesthesia (380 mg/kg) using clicks (100 μs, 5/s) and tone bursts (3‐ms duration, 1.5‐ms rise‐fall time at 2, 8, 16, and 32 kHz) presented free field with a driver suspended 8 cm above the vertex in the median plane. Responses were obtained using an active lead from the vertex with a reference electrode in the nose. Blood levels of biotin were measured using a microbiological assay. Animals on the biotin‐free diet showed alopecia and dry, scaly skin. There was no significant difference in ABER threshold in control versus experimental animals. However, there was a significantly longer brain‐stem transmission time (interpeak latencies from waves I to IV) in biotin‐deficient animals. The lowering of serum biotin in experimentals was confirmed by microbiologic assay. These findings suggest that biotin deficiency in the developing rat adversely affects auditory‐nerve and/or brain‐stem development. These effects could be mediated by a delayed myelination of these structures. [Work supported by Deafness Research Foundation.]
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Auditory‐nerve discharge characteristics that distinguish between basilar papilla neurons and amphibian papilla neurons in the leopard frog, Rana pipiens (A)

Don A. Ronken

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S97-S97 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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The frog's inner ear has two sensory organs for auditory reception. One organ, the amphibian papilla (ap), has many of the complexities of mammalian ears. The other organ, the basilar papilla (bp), is much simpler and offers special opportunities for comparison to the mammalian inner hair cell configuration. These anatomical differences make it important to identify the site of the receptor cell when recording from individual afferent neurons in the main trunk of the auditory nerve. In routine experiments, this can be a difficult problem, since the characteristic frequency (cf) of the highest‐frequency (ap) neurons overlaps the cf of bp neurons in many species. To approach this problem, a statistical data base was created using responses to tone bursts and clicks, tuning curve characteristics, and spontaneous rates. A standard statistical method, discriminant analysis, produced reliable classification of neurons without using cf estimates and offers the possibility of a fully automated decision procedure. [Work supported by NIH grants NS21592 and RR01379.]
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Cochlear mechanical model stability (A)

John W. Matthews and Charles E. Molnar

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S97-S97 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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The introduction of nonlinear damping into computational simulations of stable active cochlear mechanical models has introduced instability in computational simulations of models used here. Nonlinear dynamical systems theory provides tools that give insight into the possible sources of such instability. Analysis of differential equations for a simplified cochlear mechanical model with a computer program (“AUTO” by Eusebius Doedel) suggests that the unstable behavior of earlier simulations is an artifact of the computations rather than an inherent feature of the differential equation model. [Work supported by NIH grants NS21592 and RR01379.]
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Perceptual fusion of tonal and noisy sounds (A)

Dik J. Hermes

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S97-S97 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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If stationary noise is added to a tonal, periodic sound, the noise is, to a large extent, perceived as a separate sound coming from a source other than the periodic sound. Perceptual fusion of noise with a periodic sound requires specific conditions. Results will be presented that indicate that the temporal envelope of the noise plays an important role in this matter. In experiments in which this envelope had the same peridocity as the tonal stimulus, perceptual fusion did occur. Furthermore, the energy content of the noise within successive periods of the envelope was made more or less constant. These results were obtained in an experimental setup in which a quantitative measure was obtained for the extent to which the noise integrated with the periodic sound. It will be argued that perceptual fusion as reported here cannot be explained by a peripheral mechanism such as adaptation, but must be the result of a central process which groups components from a wide range of frequency bands into one or more sound images.
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Vowel formant frequencies produced with and without auditory feedback (A)

Emily A. Tobey and Christy Murchison

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S97-S98 (1989); (2 pages)

Online Publication Date: 13 Aug 2005

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Several authors have hypothesized that auditory feedback is used to refine articulatory gestures in children developing speech. In order to examine the role of auditory feedback in children, vowel production was examined in 12 children ranging in age from 3–13 years who received a multichannel cochlear implant. Data were collected 1 year after using the implant. Speech samples consisted of ten repetitions of the word, “head,” spoken under four conditions: implant on, immediately after the implant was turned off, 20 min after nonuse, and immediately after the implant was turned on. Formant frequencies, fundamental frequencies, and duration were measured. Significant shifts in vowel formant frequencies were found when the implant was turned off (p < 0.0001) and returned to more nearly normal values when the implant was turned on. Two of the youngest subjects were unable to produce stimuli after 20 min of nonuse with the implant. Data support the hypothesis that auditory feedback may assist in refining the articulatory gestures of some speech sounds.
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Extracting stable measures from unstable psychometric performance (A)

Marjorie R. Leek, Thomas R. Hanna, and Lynne Marshall

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S98-S98 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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At the last meeting of the Acoustical Society of America, a new method of estimating slopes of psychometric functions when thresholds were varying over the course of an experiment was reported. Computer simulations were used to calculate the relationship between the true slope of the function and the variability across pairs of trials in two interleaved adaptive tracks. Further, the variability across all trials in the two tracks was shown to indicate the stability of the function over time. Here, the validation of that procedure in the measurement of human performance is reported. Listeners were asked to detect a 1000‐Hz tone in a narrow band of noise, the level of which was either fixed or varied sinusoidally from trial to trial. This masker variation imposed systematic threshold shifts analogous to those in the simulations. The period of sinusoidal shift ranged from 16–128 trials per cycle, and the amplitude of shift was either 4 or 8 dB. Psychometric functions for individual listeners were constructed both by traditional methods of fitting the trial‐by‐trial data, and by using the functional relationship between slope and variability determined from the computer simulations. When the imposed threshold shift did not occur too rapidly, the newer method provided more stable slope estimates than did the traditional fitting methods. Under certain conditions the procedure was able to identify the unstable performance. These results show that this interleaved tracking technique can produce more stable slope estimates, and can alert experimenters to drifting in subject performance.
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Prior auditory stimulation influences the precedence effect (A)

Ruth Y. Litovsky, Richard L. Freyman, Uma Balakrishnan, and Rachel K. Clifton

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S98-S98 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Previous studies have demonstrated that echo threshold for clicks is elevated by a preceding click train. The present study examined the influence of a preceding click train for three variables presented in 16 combinations: click rate (1–16/s), number of clicks in the train (3–17), and duration of train (0.5–8.0 s). Subjects were tested in an anechoic chamber, with two speakers positioned at 45 deg left and right of midline. Leading clicks were always presented from the left speaker, while lagging clicks were presented from the right speaker with delays ranging between 2–14 ms. Each trial consisted of a click train followed by the test click. Subjects pressed a button when they heard the lagging test click on the right. Subjects' echo threshold was defined as the click delay at which the echo was reported on 50% of trials. Relative to an isolated test click, thresholds were elevated approximately 3 to 6 ms when preceded by a click train. The most critical variable influencing magnitude of shift in echo threshold was the number of clicks in the preceding train. For a constant number of clicks, duration of the train had little effect, whereas rate sometimes interacted with number. [Work supported by NSF.]
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Is a power function description of intensity‐jnd data compatible with the loudness function? (A)

William S. Hellman and Rhona P. Hellman

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S98-S98 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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A sequence of approximation for calculating loudness functions from the intensity‐jnd function for a 1‐kHz tone is performed. It is shown that a single power function representation of pure tone intensity‐jnd data can generate a loudness function from a McGill‐Goldberg type model in better agreement with loudness measurements than has heretofore been demonstrated. This improvement arises from the presence of an integration constant that had been previously ignored. The inclusion of the integration constant markedly improves the overall shape of the derived loudness function, somewhat more at low then at high intensity levels. Using the same near miss power function, the consequences of setting the integration constant equal to zero are indicated. These effects are compared to those obtained from the unaltered intensity‐jnd data [W. S. Hellman and R. P. Hellman, J. Acoust. Soc. Am. Suppl. 1 82, S25 (1987)]. Corrections resulting from going beyond first order in the calculational procedure are discussed. [Partially supported by the Rehabilitation R&D Service of the VA.]
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Increased CMR resulting from lowered levels of masker band (A)

Marion F. Cohen

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S98-S98 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Comodulation masking release (CMR) for a 1000‐Hz, 50‐ms sinusoidal signal was measured in the usual manner, except that the overall level of the 100‐Hz‐wide masking noise band was varied from 18 to 78 dB SPL in 20‐dB steps. The cue band was always 78 dB SPL. Presentation was either monotic or dichotic, with the cue band presented to the nonsignal ear only. Results show CMR values averaging as high as 7 dB when the cue band was centered at 8000 Hz, three octaves away from the signal, and 12 dB when it was two octaves away. CMR was greatly reduced when the two noise bands were at equal levels. These results were essentially replicated dichotically, except that CMR was somewhat smaller. These data relate to previous results showing poorer detectability of a noise‐band signal when a synchronous noise band is introduced at a distant frequency [M. F. Cohen and E. D. Schubert, J. Acoust. Soc. Am. 81, 721–723 (1987); D. McFadden, J. Acoust. Soc. Am. 81, 1519–1527 (1987)]. [Work supported by AFOSR.]
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Homophasic and antiphasic masking as a function of signal bandwidth and frequency region (A)

John P. Preece, David A. Eddins, and Richard H. Wilson

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S98-S98 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Thresholds for homophasic and antiphasic multicomponent tonal complexes were measured as a function of bandwidth in broadband noise to replicate and to extend the classic masking experiment [G. Gässler, Acoustica 4, 408–414 (1954)]. Gässler reported that masked thresholds for tonal complexes were nearly constant for bandwidths less than a nominal “critical bandwidth,” beyond which thresholds increased 3 dB/oct. Three experiments were conducted in broadband noise employing (a) homophasic signals similar to Gässler's (1 to 20 sinusoids spaced 20 Hz apart extending downward from 1100 Hz); (b) homophasic and antiphasic signals composed of 1 to 23 sinusoids centered at 500, 1000, and 2000 Hz; and (c) homophasic and antiphasic signals centered at 500 Hz with bandwidths to 800 Hz (71 sinusoids). The slope of the threshold/signal bandwidth function beyond 100 Hz was < dB/oct at each center frequency, ranging from 0.3 dB/oct (2000 Hz) to 1.9 dB/oct (1000 Hz). The data indicate that the integration of signal energy continued beyond the so‐called “critical band” estimates reported by Gässler. There were no substantial differences between the slopes of the homophasic and antiphasic conditions at 500, 1000, and 2000 Hz. [Work supported by VA Medical Research Service.]
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Psychometric functions for unattended tones (A)

Huanping Dai, Soren Buus, and Bertram Scharf

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S98-S99 (1989); (2 pages)

Online Publication Date: 13 Aug 2005

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Listeners detect attended tones better than unattended tones. To determine how much better, percentage correct detection was measured as a function of signal level for tones at 24 unattended frequencies, all more than a critical band from the attended or primary frequency of 1000 Hz. The primary was presented as a cue at the beginning of every trial (2I, 2AFC) and also as the signal on 67% of the trials. On the rest of the trials, the signal could be any one of 24 different probe frequencies. All signals were presented against a wide‐band noise at 62 dB. Nearly 6000 trials by three experienced subjects yielded a mean psychometric function for the probes that was parallel to that for the primary, but shifted to the right, showing poorer detection of the probes. Closer analysis revealed that the 14 probes at frequencies above 1000 Hz were “attenuated” 2 to 3 dB, and the 10 probes below were attenuated 4 to 6 dB. These and earlier results suggest that probe frequencies may be effectively attenuated 6 dB or more. [Work supported by NIH.]
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Functional involvement of auditory cortex in fine frequency discrimination of biosonar signals in the bat (A)

H. Riquimaroux, S. J. Gaioni, and N. Suga

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S99-S99 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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The auditory cortex of the mustached bat, Pteronotus parnellii, has a highly specialized region, the DSCF (Doppler‐shift constant frequency) area, which overrepresents the frequencies of Doppler‐shifted echoes (about 61 kHz), and, hence, may play a role in the fine frequency discrimination necessary for detailed velocity measurements (Suga, 1984). This function of the DSCF area was behaviorally tested using reversible ablation with muscimol, a potent GABA agonist (Hilosaka et al., 1985). Bats were trained on a discriminated shock avoidance task requiring a leg flexion response. The stimuli were trains of artificial pulse‐echo pairs (tone bursts). For S +, the pulse and echo were the same frequency (e.g., 61.0 kHz), while, for S −, they were different frequencies (e.g., 61.0 and 61.1 kHz). Following baseline testing, 0.1–0.2 μl of muscimol (1 μg/μl saline) was bilaterally applied to the DSCF area. The bats failed on previously successful discriminations of small frequency differences (e.g., 50 Hz), but succeeded on discriminations of large frequency differences (e.g., 2 kHz). Discrimination performance returned to baseline levels within 24 h. These data indicate that the DSCF area is necessary for fine frequency discriminations involving biosonar signals. [Work supported by AFOSR Grant No. 8743250.]
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Evaluation of a physiologically based auditory model using psychophysical data (A)

Patricia S. Jeng and Joseph L. Hall

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S99-S99 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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A physiologically based auditory model [O. Ghitza, J. Phon. 16(1), 109–123 (1988)] was tested against human psychophysical data. The model consists of a set of cochlear filters inferred from frequency selectivity of primary auditory fibers in cat, rate‐level processing, and synchrony extraction. Isoloudness contours for pure tones are calculated from the model and are compared to those measured in human by Fletcher and Munson (1933) and by Robinson and Dadson (1956). The model is also used to simulate Scharf's [J. Acoust. Am. 31, 365–370 (1959)] critical‐band measurements using complex sounds of four components. In addition, both calculated and measured critical‐band results are plotted as a function of cochlear place using formulas for human and cat cochlear maps in Greenwood's recent paper (submitted to J. Acoust. Soc. Am.). The comparison of calculated and measured data suggests possible improvements of the model. Laboratories, Acoustics Research Department.
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