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Biomedical subjects

A K Nábĕlek

Publications and source records attributed to A K Nábĕlek.

At least 19 recordsLinked to original sources
PubMed1997

Perception of nonlinear and linear formant trajectories.

Perception of F2 trajectories in synthetic vowels was investigated. Perceptual boundaries (50% response points of identification functions) of 20-step/U-I/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, delta F, between the initial and final frequencies. The perceptual compensation was found for the 200-ms stimuli with large delta F up to 500 Hz over 200-ms stimulus duration, and perceptual enhancement of final frequencies was found for the stimuli with delta F = 280 Hz.

Humans↗
PubMed1996

Cues for perception of synthetic and natural diphthongs in either noise or reverberation.

The relationship between relative intensity of transition segments and identification of diphthongs has been investigated. In the first experiment, synthesized 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 [diphthong in text] 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 [diphthong in text] responses and the hearing-impaired subjects gave only 20% [diphthong in text] responses in quiet. However, in noise, both groups of subjects gave 70% [diphthong in text] responses and in reverberation, the normal-hearing subjects gave 95% and the hearing-impaired subjects gave 90% [diphthong in text] responses. Generally, less transition attenuation was needed for the hearing-impaired than for the normal-hearing subjects to give [diphthong in text] 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 [diphthongs in text] from the Nábĕlek 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.

Adult↗
PubMed1994

Cues for perception of the diphthong /aI/ in either noise or reverberation. Part I. Duration of the transition.

Location of boundaries (the 50% response point) and slopes of identification functions were determined for synthesized /a-aI/ 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 /aI/ are discussed.

Acoustic Stimulation↗
PubMed1993

Vowel boundaries for steady-state and linear formant trajectories.

Locations of boundaries and slopes of identification functions were tested for /I-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/ and /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 /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.

Acoustic Stimulation↗
PubMed1992

The influence of talker differences on vowel identification by normal-hearing and hearing-impaired listeners.

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.

Adult↗
PubMed1990

English consonant recognition in noise and in reverberation by Japanese and American listeners.

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.

Adult↗
PubMed1989

Reverberant overlap- and self-masking in consonant identification.

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.

Adult↗
PubMed1988

Similarities of vowels in nonreverberant and reverberant fields.

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.

Adolescent↗
PubMed1988

Identification of vowels in quiet, noise, and reverberation: relationships with age and hearing loss.

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.

Adult↗
PubMed1986

Comparison of amplification systems in an auditorium.

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: normal-hearing adults, hearing-impaired, hearing aid users, elderly, and 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.

Acoustic Stimulation↗
PubMed1986

Vowel errors in noise and in reverberation by hearing-impaired listeners.

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.

Adult↗
PubMed1986

Comparison of amplification systems in a classroom.

"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 individual control of sound pressure level and minimize the effects of background noise and room reverberation. Three listening systems, based on 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 a 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 room 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 of the tested listening systems are suitable for listeners with various degrees of hearing losses.

Acoustic Stimulation↗
PubMed1986

Induction loop listening system designed for a classroom.

The principles of designing an induction loop listening system are discussed. Step-by-step procedures for building an induction loop are presented. The loop described was installed in a medium-size classroom and listening tests were performed comparing the loop and loudspeakers. Two groups of hearing impaired listeners were used. One group of listeners wore hearing aids while the other group did not. Result indicated that for both groups, speech perception was enhanced with the loop system.

Correction of Hearing Impairment↗
PubMed1982

Monaural and binaural speech perception in reverberation for listeners of various ages.

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.

Adult↗
PubMed1980

An influence of binaural hearing aids on positioning of sound images.

An influence of binaural hearing aids on positioning of sound images produced by signals from two loudspeakers was investigated with normally hearing and hearing-impaired subjects. The image can be positioned along a horizontal line connecting the centers of the sources by adjusting the relative sound pressure levels of signals. When the listener is a symmetrical receiver, the image appears on the midline (0 degrees azimuth) for equal levels or away from the midline for unequal levels. Any asymmetry of the receiver causes a shift of the image away from the midline. In the study, the level differences, delta Ls, necessary to position sound images at 0 and +/- 12 degrees azimuths were measured. The baseline data were collected for 10 normally hearing subjects in unaided and aided conditions. In the aided conditions binaural aids were balanced (equal gains) or unbalanced (10 dB disparity in gains). The normally hearing subjects positioned the image on the midline with a group mean delta L of 0 dB in both unaided and balanced aided conditions. To position the image at +12 or -12 degrees azimuth they needed mean delta Ls that could be predicted from a theoretical equation. With unbalanced aids, a group mean delta L of +3 or -3 dB was needed for the midline image. The delta Ls for the side images also were shifted. For 12 hearing-impaired subjects with bilateral lossses, the midline delta Ls in unaided condition were within the normal range (+/- 2 dB). For two monaural hearing aid users with long experience, the midline delta Ls were greater than normal. The delta Ls for the side images were equal to or greatr than delta Ls for normally hearing subjects. In aided balanced and/or unbalanced conditions, some hearing-impaired subjects needed delta Ls for the midline image outside the normal range, and some could not position the image at the side azimuths. It was concluded that the binaural hearing aids can be a source of receiver asymmetry.

Adult↗
PubMed1978

Influence of the precedence effect on word identification by normally hearing and hearing-impaired subjects.

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 degrees 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.

Adult↗