Search

Resistive switching in photocross-linkable polymer memory devices was found to occur in localized areas of the device. In order to elucidate the reason behind the switching, we used focused ion-beam to prepare a cross-section of the device. It was found that after the device was switched to the high conductive state, in certain parts of the device, the electrodes were only about 5 nm apart. This was probably caused by a combination of high electric field and metal injection into the polymer film. Gold injection into the polymer film by locally enhanced electric field was confirmed by transmission electron microscope-energy dispersive x-ray analysis. This model was in agreement with both the temperature dependent and transient behavior of our device. We conclude that the non-uniformities at the nanoscale interface of the electrode dominated the device characteristics while the polymer played only a secondary role. [ABSTRACT FROM AUTHOR]

The kinetics of the photoreduction of acridine guest molecules in fluorene single crystals has been investigated theoretically. The abstraction has been modeled using the golden-rule approach and proceeds by vibrationally assisted tunneling. Parameter values have been taken from experimental data and from semiempirical force-field calculations. The calculated temperature and isotope effects are in good agreement with the experimental data for acridine and phenazine guests [B. Prass, J. P. Colpa, and D. Stehlik, J. Chem. Phys. 88, 191 (1988)]. While a fluorene lattice vibration is the likely promoting mode, NH wagging in the radical-pair product plays an essential role. [ABSTRACT FROM AUTHOR]

Intensity distributions of electronic transitions in O2 and CO within a vibrational progression resulting from electron impact excitation are studied theoretically and experimentally. The multireference single- and double-excitation configuration interaction (MRD-CI) method is used to elucidate details of selected electronic transitions. In particular, the adiabatic MRD-CI approach can account for the variation of the Franck–Condon envelope with scattering angle that has been reported for the B 1Σ+←X 1Σ+ transition in CO and also was recently observed in the B’ 3Σ-u←X 3Σ-g transition of O2. This behavior contrasts with the relative stability of the intensity distribution observed within the CO A 1Π←X 1Σ+ vibrational progression. In the former cases the excited state undergoes changes with internuclear separation because of the presence of an avoided crossing. Since a transition from the zeroth vibrational level in the ground electronic state to an individual vibrational level in the excited electronic state tends to select a particular internuclear distance (R centroid), each vibrational band may behave as a transition to a separate electronic level. This happens because the excited-state wave function undergoes a compositional change with internuclear separation between the adiabatic partners of the avoided crossing. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In an earlier study [I. V. Nábeˇlek, A. K. Nábeˇlek, and I. J. Hirsh, J. Acoust. Soc. Am. 48, 536-553 (1970)] of the pitch of a sound burst with two frequencies connected by a linear frequency change (a glide), it was found that the pair of frequencies, initial and final, are sometimes perceptually fused and sometimes perceptually separated. In the present study, the pitch of the same kind of bursts is compared with the pitch bursts in which the glide is supplanted by a pause. The method of adjustment was used. Some differences in the pitch perception of bursts with glides and those with pauses were found. Prolongation of the glide made separation more difficult and fusion easier, while prolongation of the pause made separation easier and fusion more difficult. Prolongation of either the glide or the final frequency of the burst casued the pitch to be shifted toward the final frequency, while the prolongation of the pause (0-40 msec) did not change the pitch. For an explanation of this discrepancy it seems to be necessary to take central processing into consideration. [ABSTRACT FROM AUTHOR]

The pitch of tone bursts containing a linear change of frequency, either throughout 100% or for only a portion (5% and 25%) of the total burst duration, was studied. Pitch judgments for the tone bursts with the frequency change throughout the burst duration show that a single pitch can be assigned to the burst as long as the frequency change and duration are not too large. The single-pitch character of such a glide deteriorates as the product of the burst duration and frequency change increases and seems to follow the change of spectra. For the bursts with short transitions, when the frequency change is not too large, the pitch assigned to the burst changes smoothly from the final to the initial frequency according to the delay of the transition onset. For larger frequency changes, bursts can be matched by either initial or final frequency, a case called separation, as distinguished from the more singular fusion. The change from fusion to separation corresponds to the change from spectra with one maximum to those with two maxima, as long as the frequency selectivity of the auditory system permits the formation of corresponding excitation patterns. Results obtained from measurements are compared with those calculated from a model. [ABSTRACT FROM AUTHOR]

Time-dependent dielectric breakdown (TDDB) is one of themost important reliability issues in Cu/low-k technology development. With continuous technology scalings to nanometer scales, TDDB issue is further exacerbated. In this paper, two failure mechanisms were investigated: the Ta ions migration model and the line-edge-roughness (LER) model, which is rendering the observed TDDB failure. Complimentary Raman and FTIR spectroscopy was applied to investigate the dielectric bonding characteristics. Our experimental results revealed the TDDB degradation behavior of Cu/ultralow- k interconnects, suggesting the intrinsic degradation of the ultra-low-k dielectric. No out-diffusion of Cu ions was observed in Cu/Ta/TaN/SiCOH structures. Extensive TEM analysis further verified the migration of Ta ions from the Ta/TaN barrier bi-layer into the ultra-low-k dielectrics. Based on the LER model analysis, a comparative study in both passing and failing die elaborates that the sloped trench/via profile affected the TDDB performance. [ABSTRACT FROM AUTHOR]

Two effects of reverberation on the identification of consonants were evaluated for ten normal-hearing subjects: (1) the overlap of energy of a preceding consonant on the following consonant, called ''overlap-masking''; and (2) the internal temporal smearing of energy within each consonant, called ''self-masking.'' The stimuli were eight consonants /p,t,k,f,m,n,l,w/. The consonants were spoken in /s-at/ context (experiment 1) and generated by a speech synthesizer in /s-at/ and /-at/ contexts (experiment 2). In both experiments, identification of consonants was tested in four conditions: (1) quiet, without degradations; (2) with a babble of voices; (3) with noise that was shaped like either natural or synthetic /s/ for the two experiments, respectively; and (4) with room reverberation. The results for the natural and synthetic syllables indicated that the effect of reverberation on identification of consonants following /s/ was not comparable to masking by either the /s/-spectrum-shaped noise or the babble. In addition, the results for the synthetic syllables indicated that most of the errors in reverberation for the /s-at/ context were similar to a sum of errors in two conditions: (1) with /s/-shaped noise causing overlap masking; and (2) with reverberation causing self-masking within each consonant. [ABSTRACT FROM AUTHOR]

Vowel identification in quiet, noise, and reverberation was tested with 40 subjects who varied in age and hearing level. Stimuli were 15 English vowels spoken in a /b-t/ context in a carrier sentence, which were degraded by reverberation or noise (a babble of 12 voices). Vowel identification scores were correlated with various measures of hearing loss and with age. The mean of four hearing levels at 0.5, 1, 2, and 4 kHz, termed HTL4, produced the highest correlation coefficients in all three listening conditions. The correlation with age was smaller than with HTL4 and significant only for the degraded vowels. Further analyses were performed for subjects assigned to four groups on the basis of the amount of hearing loss. In noise, performance of all four groups was significantly different, whereas, in both quiet and reverberation, only the group with the greatest hearing loss performed differently from the other groups. The relationship among hearing loss, age, and number and type of errors is discussed in light of acoustic cues available for vowel identification. [ABSTRACT FROM AUTHOR]

Perceptual distances among single tokens of American English vowels were established for nonreverberant and reverberant conditions. Fifteen vowels in the phonetic context /b-t/, embedded in the sentence ''Mark the /b-t/again'' were recorded by a male talker. For the reverberant condition, the sentences were played through a room with a reverberation time of 1.2 s. The CVC syllables were removed from the sentences and presented in pairs to ten subjects with audiometrically normal hearing, who judged the similarity of the syllable pairs separately for the nonreverberant and reverberant conditions. The results were analyzed by multidimensional scaling procedures, which showed that the perceptual data were accounted for by a three-dimensional vowel space. Correlations were obtained between the coordinates of the vowels along each dimension and selected acoustic parameters. For both conditions, dimensions 1 and 2 were highly correlated with formant frequencies F2 and F1, respectively, and dimension 3 was correlated with the product of the duration of the vowels and the difference between F3 and F1 expressed on the Bark scale. These observations are discussed in terms of the influence of reverberation on speech perception. [ABSTRACT FROM AUTHOR]

The effects of noise and reverberation on the identification of monophthongs and diphthongs were evaluated for ten subjects with moderate sensorineural hearing losses. Stimuli were 15 English vowels spoken in a /b-t/ context, in a carrier sentence. The original tape was recorded without reverberation, in a quiet condition. This test tape was degraded either by recording in a room with reverberation time of 1.2 s, or by adding a babble of 12 voices at a speech-to-noise ratio of 0 dB. Both types of degradation caused statistically significant reductions of mean identification scores as compared to the quiet condition. Although the mean identification scores for the noise and reverberant conditions were not significantly different, the patterns of errors for these two conditions were different. Errors for monophthongs in reverberation but not in noise seemed to be related to an overestimation of vowel duration, and there was a tendency to weight the formant frequencies differently in the reverberation and quiet conditions. Errors for monophthongs in noise seemed to be related to spectral proximity of formant frequencies for confused pairs. For the diphthongs in both noise and reverberation, there was a tendency to judge a diphthong as the beginning monophthong. This may have been due to temporal smearing in the reverberation condition, and to a higher masked threshold for changing compared to stationary formant frequencies in the noise condition. [ABSTRACT FROM AUTHOR]

Intelligibility of speech at two positions in a large auditorium was compared for the public address system (PA) and two assistive listening systems: Frequency modulation of radio frequencies (FM) and modulation of infrared light waves (IR). Listening groups were: (1) normal-hearing adults, (2) hearing-impaired, (3) hearing aid users, (4) elderly, and (5) non-native. Word-identification scores were obtained with the Modified Rhyme Tests. Analysis of variance indicated that the main effects of systems, groups, and listening position were significant. Also significant were the two-way interactions. For all groups, the assistive listening systems provided better scores than the PA system. The difference between the two systems was statistically significant, but very small. It can be concluded that both listening systems provide improved speech intelligibility for various types of listeners. [ABSTRACT FROM AUTHOR]

Speech perception by subjects with sensorineural hearing impairment was studied using various types of short-term (syllabic) amplitude compression. Average speech level was approximately constant. In quiet, a single-channel wideband compression (WBC) with compression ratio equal to 10, attack time 10 ms and release time 90 ms produced significantly higher scores than a three-channel multiband compression (MBC) or no compression when a nonsense syllable test (City University of New York) was used. The scores under MBC, WBC, or no compression were not significantly different when the modified rhyme test (MRT) was used. But when overshoots caused by compression were clipped, the MRT scores improved significantly. The influence of MBC on reverberant speech and of WBC on noisy speech were tested with the MRT. Reverberation reduced the scores, and this reduction was the same with compression as without. Noise added to speech before compression also reduced the scores, but the reduction was larger with compression than without. When noise was added after compression, an improvement was observed when WBC had a compression ratio of about 5, attack time 1 ms, and release time 30 ms. Other compression modes (e.g., with high-frequency pre-emphasis) did not show an improvement. The results indicate that WBC with a compression ratio around 5, attack time shorter than 3 ms, and release time between 30 and 90 ms can be beneficial if signal-to-noise ratio is large, or, if in a noisy or reverberant environment, the effects of noise or reverberation are eliminated by using listening systems. [ABSTRACT FROM AUTHOR]

The Modified Rhyme Test (MRT) was processed through a room (volume 165 m3, reverberation time T = 0.4, 0.8, and 1.2 s). For both binaural and monaural earphone listening the tests were recorded with a manikin (Kemar) and equalization filters to compensate for the ear canal effect. Six groups of subjects, ten subjects each, had mean ages of 10, 27, 42, 54, 64, and 72 years and average hearing threshold levels, HTLs (for 0.5, 1, and 2 kHz) of 2.7, 5.6, 6.0, 10.9, 14.4, 17.5 dB, respectively. The individual scores for the MRT without reverberation were between 90% and 100% at 70 dB SPL. Children and the elderly required from 10 to 20 dB higher SPLs than young adults to obtain maximum scores. An analysis of variance showed that all the main effects: T, age, and monaural versus binaural listening were significant. The scores declined with T for all ages. The best scores were obtained by the young adults (27 year olds). The binaural scores were about 5% better than monaural scores. Factors contributing to the results and practical implications for amplification are discussed. [ABSTRACT FROM AUTHOR]

Masked thresholds for constant and gliding tones were determined by the method of adjustment for durations between 0.5 and 5000 ms in three overlapping frequency regions between 0.25 and 3.3 kHz. The masker was a continuous white noise at 70-dB SPL. Listening was monaural; subjects had normal hearing. Below 10 ms the thresholds for upward glides were lower and those for downward glides higher than the thresholds for constant tones. In the 10-300-ms duration range, which encompasses formant transitions of speech, the highest thresholds are for downward glides and the lowest ones for constant tones. These differences could result from different time courses of neural decay and inhibition for constant tones, upward and downward glides. The differences between upward and downward glides indicate that the phase spectra influence sound detectability. The thresholds for constant tones reach minimum around 1 s. The thresholds for glides continue to decrease at least up to 5 s. The ''critical'' duration for constant tone integration can result from the overriding of integration effects by adaptation effects, the latter ones being eliminated by changing frequency. The curves for constant-tone threshold between 10- and 1000-ms duration were fitted by a product of exponential and hyperbolic functions. [ABSTRACT FROM AUTHOR]

The influence of the precedence effect on word identification was investigated binaurally and monaurally with normally hearing and hearing-impaired subjects. The Modified Rhyme Test was processed through a PDP-12 computer to produce delay times of 0, 5, 10, 20, 40, 80, or 160 ms. The sounds were reproduced in a room by two loudspeakers positioned at ±30° azimuths in front of a subject at 50 dB SPL for normals and at the most comfortable level for impaireds. A babble of eight voices was added to reduce scores about 15% from the best values measured in quiet. Binaural and monaural word identification remained constant over a range of delays from 0 to 20 ms and declined for longer delays for both groups of subjects. The shapes of the word-identification curves were explained by self-masking (an overlap of consonants with their own repetitions) and masking (an overlap of consonants with preceding vowels or preceding and following words in sentence). Binaural responses for ten selected initial and final consonants showed various patterns of perception with delay. Some hearing impaireds showed more deterioration in word identification than others which might indicate that they experience more perceptual difficulties than normal listeners in places with reverberation or sound amplification. [ABSTRACT FROM AUTHOR]

Perception of F2 trajectories in synthetic vowels was investigated. Perceptual boundaries (50% response points of identification functions) of 20-step /[inverted_cap_omega]-[small_capital_eye]/ continua with various shapes of F2 trajectories were determined and compared with the boundary for vowels with steady-state F2. In experiment 1, the vowels were synthesized in either /j-j/ or /w-w/ context resulting in parabolic trajectories, then the stimuli were split into halves resulting in quadratic F2 trajectories. All stimuli were 200 ms long. For the /wVw/, and /wV/ stimuli, the boundaries were at lower stimulus numbers than for the stimuli with steady-state F2, indicating that the nonlinear F2 trajectories were perceived as having frequencies beyond the extreme values actually synthesized in the stimuli. This type of signal processing has been termed 'perceptual compensation.' For the /jVj/ stimuli, there was only a trend for perceptual compensation of F2 trajectories. For the /Vw/, /Vj/, and /jV/ stimuli, the boundaries were at stimulus numbers corresponding to frequencies of the relatively steady-state vowel-like segments. In experiment 2, the quadratic F2 trajectories of the /wV/ stimuli were changed to linear trajectories and F1 and F3 trajectories were either quadratic, linear, or steady state. The results indicated that the shape of F1 and F3 trajectories had no effect on the boundaries. For the linear F2 trajectories, as for the quadratic F2 trajectories in the /wV/ stimuli, the boundaries were at lower stimulus numbers than for the stimulus with steady-state F2, indicating presence of perceptual compensation. In the experiment 3, the F1 and F3 were steady state and the linear F2 trajectories had three different values of frequency difference, ΔF, between the initial and final frequencies. The perceptual compensation was found for the 200-ms stimuli with large ΔF up to 500 Hz over 200-ms stimulus duration, and perceptual enhancement of final frequencies was found for the stimuli with ΔF=280 Hz. © 1997 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

The relationship between relative intensity of transition segments and identification of diphthongs has been investigated. In the first experiment, synthesized /@sa i/ stimuli were used. The stimuli differed in the amount of attenuation of the transition segment which ranged from 0 to 15 dB. It was expected that /@sa/ responses would be obtained for stimuli with attenuated transitions. The stimuli were tested in quiet, noise, and reverberation with ten normal-hearing and seven hearing-impaired subjects. For the stimulus with the most attenuated transition, the normal-hearing subjects gave no /@sa/ responses and the hearing-impaired subjects gave only 20% /@sa/ responses in quiet. However, in noise, both groups of subjects gave 70% /@sa/ responses and in reverberation, the normal-hearing subjects gave 95% and the hearing-impaired subjects gave 90% /@sa/ responses. Generally, less transition attenuation was needed for the hearing-impaired than for the normal-hearing subjects to give /@sa/ responses. These findings indicated that identification errors in noise and reverberation for naturally produced diphthongs might be related to the intensity of their transition segments. In the second experiment, naturally produced diphthongs /@sa i, @sau, @soi/ from the Nábeˇlek et al. [J. Acoust. Soc. Am. 92, 1228-1246 (1992)] study were spectrally analyzed. There were 30 different tokens for each diphthong. The results of the analyses indicated significant correlations between the number of identification errors for these diphthongs made by either normal-hearing or hearing-impaired subjects and the relative intensities of the F2 transition segment. In both noise and reverberation there were fewer errors for the diphthong tokens characterized by high intensity F2 transitions. © 1996 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Location of boundaries (the 50% response point) and slopes of identification functions were determined for synthesized /@sa i/ vowel continua. Within each continuum, the stimuli contained a steady-state segment followed by a transition in which the frequencies of formants changed in time. Here, F1 changed in a downward direction and F2 changed in an upward direction. Total duration of each stimulus was 200 ms. The duration of the transition was increased in steps from 0 to 140 ms. Two patterns of formant transition were used: (1) formants changing in the direction of, but not reaching, target frequencies (except in the end-point stimulus), and (2) formants reaching F1 and F2 targets. The data were collected with ten normal-hearing and ten hearing-impaired subjects. The boundaries and slopes were determined for four listening conditions: quiet, noise, short reverberation (0.8 s), and long reverberation (1.1 s). The location of boundaries depended upon: (1) pattern of formant transitions, (2) listening condition, and (3) status of subjects' hearing. Generally, longer transitions were needed for formants changing in the direction of, but not reaching, target frequencies, than for those reaching F1 and F2 targets. The required transition durations were similar in quiet and noise, but were longer in reverberation. The hearing-impaired subjects generally required longer transitions to reach the boundaries than normal-hearing subjects. The slopes of the identification functions were shallower in either noise or reverberation than in quiet and were shallower for hearing-impaired than for normal-hearing subjects. In reverberation, the slopes for formants reaching targets were shallower than the slopes for stimuli with formants changing in the direction of target frequencies. The relationships between these findings and identification errors for naturally produced tokens of the diphthong /@sa i/ are discussed. [ABSTRACT FROM AUTHOR]

Locations of boundaries and slopes of identification functions were tested for i[variant_greek_epsilon] vowel continua with steady-state and linearly changing formant trajectories. In experiment 1, the boundaries and slopes for arbitrarily selected trajectory directions were determined for ten normal-hearing and ten hearing-impaired subjects in three listening conditions: Quiet, noise, and reverberation. The boundaries did not depend upon the group of subjects or the listening condition. A boundary shift was found for stimuli with F1 changing in a downward direction relative to boundaries for stimuli with either only F1 or with both F1 and F2 changing in an upward direction. The slope of the identification function for stimuli with F1 changing in a downward direction was shallower than the slopes for stimuli with steady-state formants or stimuli with F1 changing in an upward direction. The slopes obtained from the hearing-impaired subjects were shallower than those of the normal-hearing subjects and were shallower in noise than in either quiet or reverberation. In experiment 2, boundaries and slopes for the trajectory directions found in the natural vowels i[variant_greek_epsilon] and i[variant_greek_epsilon], F1 changing in an upward direction and F2 in a downward direction, were determined for nine normal-hearing subjects in two listening conditions, quiet and reverberation. The boundary for stimuli with both F1 and F2 changing in directions characteristic for natural vowels was shifted relative to the boundary for stimuli with steady-state formants. The directions of the boundary shifts in experiments 1 and 2 indicated a perceptual emphasis on the initial sections of changing F1 and F2. Sound quality of the end-point /i/ and /[variant_greek_epsilon]/ stimuli depended upon F1 and F2 trajectories. For both vowels, the best quality judgments were found for the stimuli with natural F1 and F2 trajectory directions. The quality judgments were weakly correlated with the slopes of identification functions, with better quality judgments being associated with steeper slopes. [ABSTRACT FROM AUTHOR]

Vowel identification was tested in quiet, noise, and reverberation with 20 normal-hearing subjects and 20 hearing-impaired subjects. Stimuli were 15 English vowels spoken in a /b-t/ context by six male talkers. Each talker produced five tokens of each vowel. In quiet, all stimuli were identified by two judges as the intended targets. The stimuli were degraded by reverberation or speech-spectrum noise. Vowel identification scores depended upon talker, listening condition, and subject type. The relationship between identification errors and spectral details of the vowels is discussed. [ABSTRACT FROM AUTHOR]

English consonant recognition in undegraded and degraded listening conditions was compared for listeners whose primary language was either Japanese or American English. There were ten subjects in each of the two groups, termed the non-native (Japanese) and the native (American) subjects, respectively. The Modified Rhyme Test was degraded either by a babble of voices (S/N=-3 dB) or by a room reverberation (reverberation time, T=1.2 s). The Japanese subjects performed at a lower level than the American subjects in both noise and reverberation, although the performance difference in the undegraded, quiet condition was relatively small. There was no difference between the scores obtained in noise and in reverberation for either group. A limited-error analysis revealed some differences in type of errors for the groups of listeners. Implications of the results are discussed in terms of the effects of degraded listening conditions on non-native listeners' speech perception. [ABSTRACT FROM AUTHOR]

Reception of consonants was studied with normal-hearing subjects in a sound-treated classroom, at reverberation times T ≃0.3 and 0.6 sec, to compare binaural and monaural reception, with and without hearing aids, in the presence of an impulsive noise (16 imp/sec) and a quasisteady noise (a babble of eight voices). The consonants were spoken in words inbedded in a rapidly spoken carrier phrase. The speech and noise sources subtended an angle of 60° on a circle 11 ft in radius centered on the listener, to give a large advantage for binaural reception. Binaural gain was taken as the difference in speech-to-noise ratios for 60% correct reception comparing binaural and monaural results. The binaural gain at short reverberation, with unaided listening, was 5 dB in the presence of the babble and 4 dB in the presence of the impulsive noise. The introduction of hearing aids and the increase in reverberation each caused the binaural gain to decrease to 3 dB. The small increase in reverberation caused a substantial decrease in reception under the noise conditions tested. Analysis of the consonant responses to reflect reception of the phonetic features of voicing, manner, and place, for both initial and final consonants, indicated that the acoustic conditions of reverberation and binaural listening affected feature reception in predictable ways. [ABSTRACT FROM AUTHOR]

Nanotwinned copper has been shown to greatly improve the yield strength while maintaining good electrical conductivity. It has great potential to be incorporated in the very-large-scale integration of Cu interconnect technology. The influence of stress/strain on nanotwin formation is studied using first principles calculations of the total crystal binding energy. Under biaxial stress, the total energy of strained Cu can be larger than that of strain-relaxed periodic nanotwinned Cu. We propose that, during pulse electrodeposition of Cu films, highly strained Cu can undergo recrystallization and grain growth to relax stress and form strain-relaxed nanotwins. [ABSTRACT FROM AUTHOR]

Reports that a deep level with a continuously varying activation energy and capture cross section has been observed in CdS/CdTe thin film solar cells. Results of deep-level transient spectroscopy experiments.

Obtains strong room-temperature photoluminescence peaks from erbium (Er)-doped thin-film silicon (Si) layers prepared by laser ablation. Optimum photoluminescence peaks produced by the Si sample at an annealing temperature; Thermal quenching of the luminescence intensity; Photoluminescence excitation measurements.

Speech perception in reverberation was compared for native English speaking and non-native listeners. The Modified Rhyme Test was recorded with reverberation times (T) of 0.4, 0.8, and1.2 s. Testing was monaural. The mean word identification scores without reverberation were similar for both groups. With T=0.8 and 1.2 s, non-native listeners scored 10% lower than the native listeners. These results indicate that non-native listeners who understand English very well in the absence of reverberation might have difficulty understanding speech in the presence of even moderate reverberation. [ABSTRACT FROM AUTHOR]

Nonsense syllables /s/C/at/, where C was /p,t,k,f,m,n,l,w/, were recorded then degraded either by noise or by reverberation. The goal was to compare the effects of reverberant overlap of high-frequency energy of /s/ with masking by speech spectrum noise on the identification of the consonants. The results for 10 normal-hearing subjects indicated that the identification of consonants could be degraded by both noise and reverberation. In noise there was a predominance of manner errors whereas in reverberation there was a predominance of place errors. It is possible that the place errors in reverberation were not related to masking by overlapping energy from /s/ but to temporal smearing within the consonants, which obscured the offset of the consonants. To assess if any masking by energy from /s/ could degrade identification of following consonants, the same syllables were tested with a white noise shaped with spectrum of /s/. In this condition, the consonants were highly identifiable. While energy in the consonant /s/ was relatively high, there was little overlapping of the high-frequency spectrum of /s/ with the low-frequency spectra of tested consonants. It is speculated that degrading effects of reverberation were related to the internal smearing within the consonants. [Work supported by NIH.] [ABSTRACT FROM AUTHOR]

Sensori-neural hearing-impaired individuals often exhibit a loudness function with a steeper slope at low levels than normally hearing people. At progressively higher levels the slope of the loudness function for the hearing-impaired approaches that of the normally hearing. Reducing the signal level differences at high levels (high-level compression, HLC) makes an abnormal loudness function, more so, while, reducing level differences at low levels (low-level compression, LLC) should result in a more normally appearing loudness function. CVC words (MRT) were processed under three conditions: (a) only levels between Lr -25 dB and Lr - 13 dB (Lr is the average maximal rms levels of the test words' vowels) were compressed (LLC) with a compression ratio CR = 4:1: (b) only levels above Lr -13 dB were compressed (HLC) with CR = 4:1: and (c) only levels above Lr -25 dB were compressed with the average compression ratio between Lr and Lr -25 dB in conditions 'a' and 'b' equal to 1.7. All three conditions had attack and release times of 1.5 and 30 ms. respectively. The performance of nine sensori-neural hearing-impaired subjects did not significantly differ among the three conditions investigated; this confirms Lippmann's (1978) findings with the compression system restoring normal equal loudness contours. [Work supported by NIH NS 12946.] [ABSTRACT FROM AUTHOR]

Introduction of compression into hearing aids increases the number of variable electroacoustic parameters of hearing aids. The evaluation of the influence of each individual parameter on hearing aid performance is difficult even with ordinary hearing aids. In addition to the variability in the frequency range, regularity of frequency response, harmonic distortion, etc., hearing aids with compression differ in the range of compression, degree of compression, threshold of compression, etc. One of the significant characteristics is the time constant of compression. Its importance in hearing aids performance is still to be clarified. In the paper the necessity of good description and specification of this parameter for comparability of measurements in different laboratories will be discussed. The values of the release and attack durations, and of overshoots, as determined by measurement, are dependent on the choice of several parameters. The influence of the hearing aid volume control setting, of the operating point on the input-output curve, of the range of the input SPLs, and of frequency will be discussed and shown in several examples. [ABSTRACT FROM AUTHOR]

A previous presentation reported on spectra of whispered and phonated speech and on comparison of identification of whispered voiced and voiceless consonants when those consonants were presented in C/a/ syllables. The cues for voicing in whispered plosives were studied using spectrograms. In a follow-up study, spectrographic analysis of whispered monosyllables with plosives in various vowel environments was performed. The results of the analysis-with respect to the voicing differences-will be presented and discussed. [ABSTRACT FROM AUTHOR]

Ten normal-hearing subjects listened to a recorded list of 120 whispered consonant-vowel syllables spoken by a male talker. The consonants were six plosives /b,p,d,t,g,k/, the vowel was /a/. Each syllable was repeated 20 times in random order. The overall consonant identification score was 85.2%. The scores for the voiced consonants were lower than for the voiceless ones, but they were still rather high. The highest average identification score of 96% was obtained for /k/. The average scores were 91%, 88.5%, 83%, 81%, and 71.5% for /t/, /d/, /p/, /b/, and /g/, respectively. A pairwise comparison showed that the difference between /k/ and /g/ scores was significant. With respect to place, alveolars and bilabials had the highest and the lowest scores, respectively. Whispered /b,d,g/ were more often confused with their cognates than vice versa; cognate errors were more numerous than place errors. These results indicate that the voicing contrast is indeed useful for distinguishing voiced and voiceless plosives, however that there are other cues which allow the discrimination between voiced and voiceless consonants if the voicing contrast is absent. [ABSTRACT FROM AUTHOR]

Vowels produced by a female talker were less identifiable than previously investigated vowels produced by a male talker [A. K. Nábeˇlek and P. A. Dagenais, J. Acoust. Soc. Am. 80, 741-748 (1986)]. Matrices of responses were obtained for normal-hearing and hearing-impaired subjects for three conditions: quiet, noise (S/N = 0 dB), and reverberation (T = 1.2 s). The vowels which were confused by normal-hearing subjects were also confused by hearing-impaired subjects. However, there were some pairs of vowels which were confused only by hearing-impaired subjects. There were also some differences between errors for the female voice and errors collected previously for the male voice. Differences in errors for the two talkers and two groups of subjects will be discussed. [Work supported by NIH.] [ABSTRACT FROM AUTHOR]

Listeners with either hearing loss or perceptual problems require a good speech-to-noise ratio and short reverberation for their best speech discrimination. These conditions are sometimes difficult to achieve. Assistive listening systems, in which signal is transmitted by infrared light (IR) or modulated ratio waves (FM) are promoted for the special listeners. We compared the effectiveness of assistive systems in a classroom and in a large auditorium with several groups of listeners: normal hearing, hearing impaired, hearing aid users, elderly, and nonnative. In both rooms, the IR and FM systems allowed for better speech perception scores than through loudspeakers. The difference between the two assistive systems was very small. While all groups performed better through the assistive listening systems, the groups who achieved the greatest advantage had the poorest performance in the sound field. Since both systems were equally effective in improving speech intelligibility in less than optimal listening conditions, selection of a system should be based on such factors as cost, maintenance, and expected interferences. [Work supported by NIH.] [ABSTRACT FROM AUTHOR]

The effects of noise and reverberation on identification of monothongs and diphthongs were evaluated using ten subjects with moderate sensorineural hearing losses. Stimuli were 15 English vowels, spoken between /b/ and /t/ and recorded in a carrier sentence. The test was recorded without reverberation under quiet conditions then degraded either by recording in a room with reverberation time 1.2 s or by adding babble of 12 voices at speech-to-noise ratio of 0 dB. Both degradations caused statistically significant reductions of mean identification scores, but the difference between degraded means was not significant. The pattern of errors was different in noise and reverberation. Errors for monothongs in reverberation seemed to be related to an overestimation of vowel duration and to a tendency to perceive the pitch of the formant frequencies as being higher than without reverberation. Errors for monothongs in noise were not related to duration or pitch overestimation. Errors involving diphthongs were more frequent in reverberation than in noise. In reverberation, there was a tendency to judge a diphthong as the beginning monothong. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effect of individual formant elimination on the identification scores of natural voiceless consonants in noise. The consonants were tested with the vowels /i/, /[open_aye]/, or /u/ in both initial and final positions. Each syllable had the energy eliminated at the frequencies of the first, second, or third formant of the vowels. The syllables were mixed with cafeteria noise and presented to young and elderly normally hearing listeners and to noise-induced hearing loss listeners. The difference between the speech and noise levels was 15 dB. In general, the effects of formant elimination were dependent on individual sounds and groups of listeners. When the first formant was eliminated, the identification scores were similar to those obtained under the wideband setting. The identification of /h/, /[barred_oh]/, /p/, /t/, and /k/ was affected most by the elimination of the second formant for all groups of listeners. The maximal reduction of identification scores of /t[sh]/ and /[sh]/ occurred when the third formant was absent. [ABSTRACT FROM AUTHOR]

Listening systems are used for hearing-impaired listeners as an alternative to public address systems (PA) used for the general public. These listening systems allow for individual control of sound pressure level and minimize the effects of background noise and room reverberation. Three listening systems: an audio induction loop (AL), frequency modulation of radio frequencies (FM), and modulation of infrared light (IR) were compared among themselves and with a PA system in a medium-size classroom. Listening groups were normal hearing, hearing impaired, hearing aid users, and elderly. Word-identification scores were obtained with the Modified Rhyme Test at two conditions: with a babble of 12 voices at speech-to-noise ratio (S/N) of + 8 dB and without the babble at S/N of + 20 dB. Analysis of variance indicated that the main effects of systems, groups, and S/N were significant. Also significant were interactions of systems by groups and systems by S/N. For all groups, the three listening systems provided better scores than the PA system. It can be concluded that all three tested listening systems are suitable for listeners with various degrees of hearing losses. [Work supported by NIH.] [ABSTRACT FROM AUTHOR]

Durations and formant frequencies of /i/ and /I/ as produced by native and non-native American speakers were compared. The non-native speakers included one Thai female and one Slovak male. Their languages have only one vowel in place of the /i/ and /I/ and both speakers speak English with an accent. We wanted to determine which parameters of /i/ and /I/ are responsible for their incorrect pronunciation. The test words in which /i/ or /I/ were imbedded in /p-p/, /t-t/, or /k-k/ were uttered in the sentence 'Say.../test word/...yet.' The preliminary data indicate that the durations of /i/ and /I/ were generally in the range of native American speakers, but that the Thai speaker overemphasized the difference in durations of /I/ and /i/. She also had the formant frequency ratios F2/F1 and F3/F1 for both /i/ and /I/ in the /p-p/ condition in the same range as the natives; her F2/F1 and F3/F1 for both /i/ and /I/ in the /t-t/ condition were too large. The Slovak had F2/F1 and F3/F1 smaller for /i/ and larger for /I/ than the native Americans in the /p-p/ condition; in the /t-t/ condition his F3/F1 was appropriate for /i/ but larger for /I/ than of the native Americans. Both Thai and Slovak speakers had all the formant frequency ratios in the correct ranges in /k-k/ conditions for which the native Americans showed the smallest differences between /i/ and /I/. These data indicate that the foreign accent of /i/ and /I/ of these two speakers is caused by spectral deviations from the American English, and not by durations. [ABSTRACT FROM AUTHOR]

For many years, listening systems have been used for the hearing-impaireds in schools for the deaf and the general public for simultaneous transmission in several languages. Recently, listening systems started to be installed for pleasure listening in theaters, churches and concert halls. For multi-lingual conferences, the main emphasis was on separation of the channels. This is usually achieved by hard-wired connections with limited frequency response to the range most important for speech intelligibility. The systems for the hard-of-hearing have also limited frequency response, a philosophy inherited from hearing aids. The priority here was adequate gain allowed by the system, provision to couple with personal hearing aids, and sometimes flexibility in seat selection. The modern listening systems installed in public places should serve both the general public and hard-of-hearing listeners. They are designed for both speech and music transmission and quality of sound becomes the primary objective. The authors have examined several listening systems installed in the New York City and Washington, D. C. areas and will share some observations which can be helpful for the designers of the systems. [Work supported by NIH.] [ABSTRACT FROM AUTHOR]

Acoustic criteria for auditoriums have been developed for listeners with normal perceptual skills. In consequence, these criteria applied to room acoustics may not be good enough for listeners with perceptual deficiencies. Perceptual problems are usually associated with congenital or acquired hearing losses, but also, elderly listeners who might have only slightly less acute hearing then their younger counterparts find listening in some auditoriums very difficult. Three parameters contribute to such problems: sound pressure level too low, speech-to-noise ratio too low, and reverberation too long. When acoustic conditions become unsatisfactory, many listeners cease attending lectures, art performances, etc. In some communities loss of elderly listeners might consist of a significant reduction in public support of drama theaters or concerts. The so-called 'group amplification systems' or 'listening devices' can provide help for listeners with perceptual problems. The main principle of such devices is to pick up the signal close to the source and deliver it directly to the listener's ears. In such a way the signal can be individually amplified and delivered without background noise and reverberation. The following systems which are presently in use will be discussed: (1) hard wired, (2) induction loop, (3) amplitude modulation, (4) frequency modulation, and (5) infrared. All these systems will be discussed for the use of listeners with and without hearing aids. [Work supported by NIH.] [ABSTRACT FROM AUTHOR]

The Modified Rhyme Test (MRT) was processed through a room (volume 165 m3, reverberation time T= 0.4, 0.8, and 1.2 s). The tests were recorded for binaural and monaural earphone listening with a manekin Kemar and equalization amplifiers to compensate for the ear canal effect. Six groups of normally hearing subjects, 10 subjects each, had mean ages of 10, 27, 42, 54, 64, and 72 years and average Hearing Threshold Levels (HTLs) (for 0.5, 1, and 2 kHz) of 4, 6, 10, 14, 18, and 18 dB, respectively. The individual scores for MRT without reverberation were between 90% and 100%. The mean group scores for the 27-year-old group were the same for unreverberated speech and 0.4-s condition but declined for 0.8- and 1.2-s conditions. All other groups performed poorer than the young adults, e.g., the scores of the 72 year olds and the children were 16% and 8% lower, respectively. In all comparisons, the binaural scores were better than monaural ones by an average of 5%. There was a tendency for greater binaural advantages for older subjects. [Work supported by NIH.] [ABSTRACT FROM AUTHOR]

It is postulated that the amount of information carried by speech can be altered by speech modifications which can be perceived aurally. Therefore, amplitude compression might increase intelligibility if a reduction of level differences between strong and weak speech sound is perceivable. Difference limen for attack (TA) and release (TR) times of compression for various compression ratios (CR's) based on a quality change was determined by the adjustment or ABX methods. A 1.7-s-long utterance with approximately constant maximal rms levels of words was submitted to wide-band compression. Masking noise added after compression at -10 dB (re speech) equalized the noise background for various conditions. The smaller the CR or the TA, the shorter the TR had to be to provide a perceptible change in quality; e.g., experienced normally hearing subjects needed TR equal to or smaller than 420 and 250 ms to discriminate a quality change when CR = 5 and TA equal to 10 and 3 ms, respectively, from linear amplification. Naive normally hearing listeners needed a much shorter TR (between 30 and 40 ms for the same conditions). Testing of hearing impaired listeners is presently in progress. [Work supported by NIH NS 12946.] [ABSTRACT FROM AUTHOR]

Modified rhyme test words and CVC nonsense syllables were processed without or with background pink noise through a wideband amplitude compressor set for a 2.5:1 compression ratio and various attack (TA = 1 through 42 ms) and release (TR = 10 through 370 ms) times. These stimuli were presented to nine subjects with sensori-neural hearing impairment. The compression threshold was set 25 dB below the average maximal rms level of the vowels in the test words or CVC syllables. The compressed signal was amplified with individually adjusted frequency responses and delivered to the listeners via a circumaural earphone. The presentation of speech was always at the same, comfortable level for each individual listener. The signal compressed without noise was sometimes mixed with a masking pink noise at - 10, - 5, and 0 dB re speech. There were no significant differences in mean performances for different time constants, or between compressed and noncompressed stimuli. Performance slightly increased with compression, only when masking noise was added to the signal after processing (Ls - Ls <= 5 dB) and the attack and release times were shorter than 3 and 90 ms, respectively. [Work supported by NIH NS 12946.] [ABSTRACT FROM AUTHOR]

Ear dominance for nine subjects was determined for dichotically presented amplitude modulated (AM) sinusoids as a function of modulated and modulation frequencies. Ear dominance for five of these subjects was also determined for pure tone pairs centered around one of the modulated frequencies and around one of the modulation frequencies, so that ear dominance for pure tone pairs could be compared to that for AM signals in the frequency region of AM signal energy and in the frequency region of periodicity pitch of the AM signals. All signals were presented in a 2AFC paradigm such that competing tonal sequences were heard at each ear. Subjects reported the pitch sequence heard for each trial, and estimates of ear dominance were then inferred from the data. Ear dominance was observed for one-third of the subjects tested with AM signals, and it decreased as the center frequency of the test signals was increased. No definite effect of modulation frequency (component frequency spacing) was observed. All subjects tested with pure tone signals exhibited ear dominance to some degree. In general, ear dominance for AM signals was more closely related to the one pure tones centered around the modulation frequency than to that for pure tones centered around the modulated frequency. [ABSTRACT FROM AUTHOR]