摘要:

The growth of intelligibility of speech stimuli as a function of level above hearing threshold can be computed from the “circuit parameters” of the hearing mechanism by applying Shannon's concepts of channel capacity, equivocation, and “bits.” In the ear, the unit of response is an effective “least count,” derived from experimental data on hearing by means of the equations for a model resembling a frequency‐selective circuit [E. Corliss, J. Acoust. Soc. Amer.41, 1500–1516 (1967)]. The model predicts that the number of least counts available rises as the one‐fourth power of the signal intensity above threshold. Experimentally, this growth rate is observed for the intensity‐resolving power of the ear. Approximately the same power law is observed for the sensation of loudness. The model ascribes both effects to the same mechanism. From the observed integration time of the ear, the model predicts the rate at which transitions of single counts can be detected. From the counting rate and the integration time, the channel capacity available at the ear and its increase with level above threshold can be computed. The information content of speech as a source function is evaluated from the rate at which single “distinctive features” of speech phonemes are produced. Intelligibility scores can be predicted from the ratio between the rate at which information is being produced by the source and the rate at which the receptor can accept the source material. The scores predicted agree fairly closely with experimental data on random‐word and random‐syllable intelligibilities. This agreement shows that the listener need recognize no more than a single distinctive feature of each phoneme to display the recognition functions that have been observed. From a theorem of C. Shannon [Inform. and Control1, 6–25 (1957)] relating code length and error probability, one can show that the channel capacity required for polysyllabic words is lower than the channel capacity required for monosyllabic words because the duration of correlated utterance may be taken as a code length. Evidently, contextual effects are not prominent in the intelligibility of random‐word lists; the hearing process involved is primarily recognition of groups of sounds; meaning is secondary. The results also lead to the inference that a direct relation may exist between channel capacity and perceived loudness when speech is transmitted over a broad‐band system, and suggest that loudness functions for impaired ears might prove to be correlated with intelligibility functions.

ISSN:0001-4966    

DOI:10.1121/1.1912682

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

High‐speed cinefluorographic films were taken of four normal subjects speaking English sentences containing various combinations of nasal consonants (N), consonants (C), and vowels (V) at normal speaking levels and rates of production. Word and syllable boundaries were designed to fall across the sequences in various ways. From frame‐by‐frame tracings, measures of velar movement and velopharyngeal opening were made. Results indicate extensive anticipatory coarticulation of velar movement toward velopharyngeal opening in CVN and CVVN sequences such that velar movement toward opening began during the approach to the initial vowel in all cases and some velopharyngeal opening was observed on all vowels. For NC and NCN sequences, velar movement toward closure for the consonant usually began during the preceding nasal such that some velar closure was observed during all plosive and fricative consonants used. These results directly contradict the hypothesis that a CV‐type syllable is the minimal unit of coarticulation and production. The data are consistent with the predictions of a model which assumes phone‐sized input unit and which incorporates a “look ahead” mechanism whereby an articulatory feature can be systematically anticipated prior to the occurrence of the phone with which that feature is associated.

ISSN:0001-4966    

DOI:10.1121/1.1912683

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The spatial and temporal movement characteristics of the jaw while subjects spoke under delayed auditory feedback was investigated. An analog‐digital‐analog computer system was used to instrument the delayed speech signal and a strain‐gauge transducer was used to monitor the movements of the jaw. The speech sample consisted of the high, middle, and low front vowels /i/, /ɛ/, and /æ/ embedded in the carrier phrase: “That's a CVC a month.” Measurements were made of maximal jaw opening distances during the vowel segment, jaw activity duration throughout the utterance, and jaw velocity during the opening and closing phases of the vowel gesture. The disruptive effects caused by the temporally delayed speech signal were found to be specific to the: (1) magnitude of the delay interval; (2) vowel context; and (3) space‐time dependent variable being measured. Increased jaw‐opening excursions were found, depending upon the vowel context, and a positional target overshoot was noted at the 0.3‐sec delay interval, especially for the midvowel /ɛ/. The time period of active jaw articulation was considerably lengthened at the 0.1‐sec delay interval, especially for the high vowel /i/. The jaw velocity measures showed increased movement rates for both opening and closing vowel gestures as a function of vowel openness.

ISSN:0001-4966    

DOI:10.1121/1.1912684

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The dominant part of the acoustic absorption of liver tissue and its components results from macromolecular relaxation processes. The absorption has been investigated over the frequency range 1–10 MHz and the following results have been obtained: (1) About two‐thirds of the total absorption arises at the macromolecular level, with the remainder caused by macroscopic structure. (2) The specific absorption of tissue macromolecules, as expressed in absorption per weight percent, varies considerably from one biopolymer to another. (3) The absorption is related to the structure of the biological macromolecule or its hydration and changes with heat denaturation andpH. (4) A similar frequency dependence results for all materials investigated. This dependence is to be expected if one assumes that the molecular processes of absorption are characterized by a broad spectrum of relaxational time constants and activation energies extending over a range of at least 1:7.

ISSN:0001-4966    

DOI:10.1121/1.1912685

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The auditory sensitivity of one strain (Belgian Waterschlager) of common canary (Serinus canarius) was measured by behavioral audiometry. Four birds were trained by instrumental avoidance conditioning in a double‐grille cage, and their thresholds for pure tones (0.25–9.0 kHz) were measured. Auditory sensitivity is greatest between 2.0 and 4.0 kHz with a possible maximum at 2.8 kHz, declines about 15 dB/oct for frequencies below 2.0 kHz, declines about 25 dB between 4.0 and 8.0 kHz, and 13 dB between 8.0 and 9.0 kHz. The acoustic power in the songs and calls of the Belgian Waterschlager falls primarily in the range 1.8–4.5 kHz as do the critical frequencies of a substantial proportion of the neural units in the cochlear nucleus of the canary. Thus, the auditory sensitivity and the neural machinery of the peripheral auditory system appear to be matched to the long‐term‐average power spectrum of the songs. In addition, these facts are compared to those for other birds and mammals, and speculations as to some of the selective pressures that influenced the evolution of hearing are presented. Certain relevant problems of the biophysics of hearing are also discussed.

ISSN:0001-4966    

DOI:10.1121/1.1912686

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Behavioral audiograms of five ringtail lemurs, determined by a single‐lever shock avoidance method, are reported. The frequency range, 0.1–40 kHz, is compared with data from a previous study. Increased sensitivity in the middle frequencies are reported by this method.

ISSN:0001-4966    

DOI:10.1121/1.1912687

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A literature survey indicates lack of standardization of a speech‐level measure among published experiments. In addition, experiments reported here show that the measure most commonly used, the VU (volume unit), exhibits high variability, especially among nonexpert observers. The possibility of better measures of speech level is demonstrated by a completely objective measure based on an assumed log uniform distribution of instantaneous voltage levels. It is concluded that there is a need to reassess the general problem of speech‐level measurement and to propose new approaches.

ISSN:0001-4966    

DOI:10.1121/1.1912689

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP