Voice Communication Between Humans and Machines (1994) / Chapter Skim
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Speech Processing for Physical and Sensory Disabilities
Speech Processing for Physical and Sensory Disabilities
Pages 311-344
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From page 311... ...
Speech synthesis is also used in text-to-speech systems for sightless persons. Other applications of assistive technology involving voice communication include voice control of wheelchairs and other devices for people with mobility disabilities.
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Assistive devices for hearing loss are the second most widely used form of assistive technology (4.0 million Americans as compared to the 6.4 million Americans using assistive mobility technology)
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A relatively new form of assistive technology is that of voice control of wheelchairs, hospital beds, home appliances, and other such devices by people with mobility disabilities. This form of assistive technology is not widely used at present, but it is likely to grow rapidly once its advantages are realized.
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From page 314... ...
Not surprisingly, the body of research on assistive hearing technology and on hearing aids, in particular, is large, and much of the present chapter is concerned with this branch of assistive technology. ASSISTIVE HEARING TECHNOLOGY Background Assistive technology for hearing loss includes, in addition to the hearing aid, assistive listening devices (e.g., infrared sound transmission systems for theaters)
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From page 315... ...
The development of assistive technology for people with more than one impairment presents a compelling challenge that is beginning to receive greater attention. Assistive devices for hearing loss have traditionally been categorized by the modality of stimulation-that is, auditory, visual, tactile, or direct electrical stimulation of the auditory nerve (auditory-neural)
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From page 316... ...
Another application of this technology is to allow a hard-ofhearing person to listen to the radio or television at a relatively high level without disturbing others. Most conventional hearing aids and assistive listening devices do not make use of advanced signal-processing technology, and thus a detailed discussion of such devices is beyond the scope of this chapter.
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The potential for incorporating advanced speech-processing techniques into the coming generation of hearing instruments (digital hearing aids, new types of assistive listening devices) opens up new possibilities for the application of technologies developed for human-machine communication.
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are still highly experimental. In one such application of speech recognition technology, the output of a speech recognizes was used to drive a special-purpose speech synthesizer in which important phonetic cues in the speech signal are exaggerated (Levitt et al., 1993~.
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The visible speech translator (VST) , which, in essence, is a realtime-version sound spectrograph, belongs in the category of sensory aids that take the average characteristics of the speech signal into account (Table 2, row 2~.
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These studies showed that the device was of limited value as an aid to speech recognition (House et al., 1968) , although several subsequent studies have shown that speech spectrum displays can be of value in speech training (Stark, 1972~.
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Experimental evaluations of visual supplements to speechreading have shown significant improvements in speech recognition provided the supplemental cues are extracted from the speech signal without error (Goldberg, 1972~. In practice, the supplemental cues need to be extracted automatically from the speech signal, usually in real time and often in the presence of background noise and reverberation.
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From page 322... ...
Displays of this type, as categorized by row 4 of Table 2, depend on the use of speech recognition, either by machine or other human beings. In the case of a telephone relay service, the speech produced by the hearing party in a telephone conversation is recognized by a typist at a central location who types out the message, which is then transmitted to the deaf party by means of a text telephone (or TTY/TDD)
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From page 323... ...
A second limitation is that both parties in a telephone conversation need to have text telephones. The recently introduced telephone relay service eliminates the need for a text telephone by the hearing party, but the rate of communication is slow and there is a loss of privacy when using this service.
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Issues that need to be considered in converting the output of a text telephone to speech in real time include: · whether synthesis should proceed as typed, on a word-byword basis, or whether to introduce a delay and synthesize on a phrase or sentence basis, so as to control intonation appropriately and reduce pronunciation errors due to incorrect parsing resulting from incomplete information; . rules for preprocessing that take into account the abbreviations, nonstandard syntactic forms, and sparse punctuation typically used with text telephones; and · methods for handling typing errors or ambiguous outputs.
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As transducer technology has improved, coupled with improved signal-processing capabilities, corresponding improvements in speech recognition using tactile aids have been obtained. In a recent study by Brooks et al.
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for both speech production and speech reception. These devices, however, are not as widely used as spectrum-based tactile aids, possibly because they are not yet ready for commercialization.
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This problem is particularly difficult for wearable sensory aids because the signal picked up by the microphone on the wearable aid is contaminated by environmental noise and reverberation. Tactile sensory aids involving speech recognition processing (row 4, column 3 of Table 2)
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From page 328... ...
One possible explanation for this is that the deafness may be due to damage to the hair cells in the cochlea which convert mechanical vibration to neural firings, but that the neurons connected to these hair cells may still be functional and can be triggered by the electromagnetic field generated by a cochlear implant. Most of the early cochlear implants consisted of a single wire electrode inserted in the cochlea (House and Urban, 1973~.
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An advantage of this type of prosthesis, known as an extracochlear implant, is that electrodes are not inserted into the cochlea with the attendant danger of
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Significant improvements in speechreading ability were obtained using this technique. Much controversy exists regarding the relative efficacy of the various cochlear implants that have been developed.
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Noise Reduction A common problem with all sensory aids is the damaging effects of background noise and reverberation on speech understanding. These distortions also reduce overall sound quality for hearing aids and cochlear implants.
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High-pass filters are typically used to reduce this type of environmental noise, but these filters also eliminate the speech signal in those frequency bands, thereby reducing intelligibility when only speech is present. To address this problem, adaptive filtering is used in which the cutoff frequency of the filter is adjusted automatically depending on the level of the signals to be amplified.
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From page 333... ...
An important practical limitation of these techniques, however, is that they will not provide any benefit in a highly reverberant acoustic environment or if both speech and noise come from the same direction. OTHER FORMS OF ASSISTIVE TECHNOLOGY INVOLVING VOICE COMMUNICATION Speech Processing for Sightless People People with severe visual impairments are heavily dependent on the spoken word in communicating with others and in acquiring information.
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From page 334... ...
For the special case of a sightless person with hearing loss, a possible approach for improving intelligibility is to enhance the acoustic characteristics of those information-bearing components of speech that are not easily perceived as a result of the hearing loss. The thrust of this research is similar to that underlying the development of the speech recognition/speech synthesis hearing aid (Levitt et al., 1993~.
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From page 335... ...
Techniques of this type have also been used with a Touchstones keypad so that a hearing person using a Touch-Tone telephone can communicate with a deaf person using a text telephone (Harking et al., 1992~. Even with these innovations, this technique has not met with much success among people who are not obliged to use a reduced set keyboard.
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From page 336... ...
Recent advances in speech technology coupled with an increased understanding of the nature of speech production have resulted in significant improvements in the development of artificial larynxes (Barney et al., 1959; Sekey, 1982~. Recent advances include improved control of speech prosody and the use of microprocessorgenerated glottal waveforms based on recent theories of vocal cord vibration in order to produce more natural-sounding speech (Alzamora et al., 1993~.
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From page 337... ...
Examples of this new technology include voice control of telephones, home appliances, powered hospital beds, motorized wheelchairs, and other such devices (Amori, 1992; Miller, 1992~. In each case the set of commands to control the device is small, and reliable control using a standardized set of voice commands can be achieved using existing speech recognition technology.
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. Hearing Aids-A Review of Past Research of Linear Amplification, Amplitude Compression and Frequency Lowering.
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. Assessment of dysarthric speech for computer control using speech recognition: Preliminary results.
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. Speaker-dependent speech recognition as the basis for a speech training aid.
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In Proceedings of the Second International Conference on Tactile Aids, Hearing Aids, and Cochlear Implants, A Risberg, S
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. Effects of an adaptive filter hearing aid on speech recognition in noise by hearing-impaired subjects.
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processing strategy for multichannel cochlear implants.
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