AUDITORY-VISUAL

PERCEPTION

OF

SPEECH

Norman P. Erber Central Institute for the Deaf, St. Louis, Missouri

Hearing-impaired persons usually perceive speech by watching the face of the talker while listening through a hearing aid. Normal-hearing persons also tend to rely on visual cues, especially when they communicate in noisy or reverberant environments. Numerous clinical and laboratory studies on the auditory-visual performance of normal-hearing and hearing-impaired children and adults demonstrate that combined auditory-visual perception is superior to perception through either audition or vision alone. This paper reviews these studies and provides a rationale for routine evaluation of auditory-visual speech perception in audiology clinics.

Listening is the usual mode of speech perception. Yet, there are certain conditions under which the auditory system is limited in speech-processing ability and another sensory channel, usually vision, is required to provide important speech information. The purpose of this paper is to review what is known about perception of speech through combined auditory and visual modalities. Auditory-visual perception of speech has been studied in both hearing-impaired and normal-hearing persons. The importance of auditory-visual perception to the hearing-impaired is obvious: in order to communicate orally, they usually attend to speech information that is available on the face of the talker. That is, observation of both auditory and visual cues probably is the typical mode of speech perception for most hearing-impaired persons. Normal-hearing persons often need to communicate in noisy or reverberant locations where speech perception through listening alone is difficult or impossible. Under these circumstances, they usually watch the talker's mouth and face for additional speech information. Most studies with normal-hearing observers attempt to duplicate these adverse acoustic conditions. Typically, the acoustic speech signal is degraded with noise or with filters to decrease the observer's auditory speech perception ability, increase his reliance on visual input, and make it possible to examine the interaction between the two modalities. Researchers sometimes have suggested that these special masking or filtering conditions simulate hearing loss and that the results therefore are useful in helping to understand how hearing-impaired persons perceive speech. A U D I T O R Y - V I S U A L SPEECH P E R C E P T I O N

BY N O R M A L - H E A R I N G P E R S O N S When a person with normal hearing attends to a talker in quiet surround481

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482 JOURNALOF SPEECHAND HEARING DISORDERS

ings, he generally receives closely related auditory and visual cues for speech. He may notice that each speech sound tends to be associated with a particular type of oral configuration. But in a quiet environment, vision provides mainly redundant information, and visual speech cues are not necessary for an individual with normal hearing. When the acoustic speech-to-noise (S/N) ratio is less than optimal, however, weaker speech sounds are masked. The more severe the masking situation, the more the normal-hearing observer must rely on lipreading for satisfactory perception of the message intended by the talker. When the observer must decode speech under extremely poor acoustic conditions where no meaningful auditory cues are available, lipreading is the only source of speech information. Reports by O'Neill (1954), Sumby and Pollack (1954), Erber (1969), and Ewertsen and Birk Nielsen (1971) have provided data to support these points. In general, their findings indicate that combined auditory-visual recognition of words is more resistant to noise than is recognition by listening alone. That is, even a normal-hearing listener who has never been trained in lipreading always receives more speech information in noise when he watches the talker's face than when he does not (see Figure 1). In the studies by O'Neill (1954) and Sumby and Pollack (1954), the contribution of visual cues to auditory-visual speech perception was found to increase as the speech-to-noise ratio was decreased. This trend was demonstrated by comparing the subjects' auditory-visual performance with their auditoryonly scores at successively poorer S/N ratios. Erber (1969) has shown that

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SPEECH-TO-NOISE RATIO (DE) Figure I. Auditory and auditory-visua| recogn;tion of 250 spondaic words in broad-band noise by five adults with normal hearing (from Erber, 1969).

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ERBER. Perception of Speech 483

greater between-subject variability also is associated with auditory-visual scores at poorer S/N ratios. He suggested that this is the result of differences in lipreading skill among untrained normal-hearing observers and therefore reflects their greater reliance on vision as the acoustic speech signal is degraded. It is not clear whether observers continue to process the visual signal in the same way as the S/N ratio is decreased throughout a wide range. In moderate S/N environments, they seem to use lipreading primarily as a compliment to reduced auditory input, in which case vision provides articulatory cues that are not available through hearing. In very noisy surroundings where no acoustic cues for speech are available, it is necessary for the observer to process the visual cues alone, perhaps as a special form of language that is encoded through oral shapes and movements. It has been shown that for a given S/N ratio, combined auditory-visual performance typically is better than is recognition through listening alone (Neely, 1956). The findings of O'Neill (1954), Sumby and Pollack (1954), Erber (1969), and Ewertsen and Birk Nielsen (1971) also indicate that normal-hearing subjects can achieve high speech-perception scores at a lower S/N ratio through auditory-visual perception than they can obtain through auditory perception alone. To illustrate this point, in broad-band noise, normal-hearing adults typically can tolerate about a 5-10 dB poorer S/N ratio for 80% auditory-visual word recognition than they require for 80% recognition through auditory perception alone. This sort of information can be used to establish S/N criteria for auditory or auditory-visual perception of speech in noisy areas where communication must occur, as in industrial, military, or educational environments. Sumby and Pollack (1954) demonstrated that an observer's ability to recognize words in a noisy background could be improved by reducing the number of alternatives in the response set. They found that word-recognition scores were highest for both auditory and auditory-visual observation tasks involving a small number of alternatives. These results support earlier findings of Miller, Heise, and Lichten (1951) who examined the effects of context (including number of alternatives) on auditory word recognition in noise. Miller and Nicely (1955) hypothesized that an observer might be able to tolerate a considerable loss of high-frequency acoustic speech energy without a great decrease in intelligibility on an auditory-visual speech-perception task. This result would be anticipated because place-of-articulation cues that are available to the observer through lipreading complement the manner-of-articulation information that remains in the low-frequency acoustic speech signal (Erber, 1974b). Sanders and Goodrich (1971) have provided data from normalhearing adults to support this hypothesis. Their subjects scored only 24% correct on an auditory word-recognition test while listening through a 400-Hz low-pass filter, but when they were allowed to lip-read also, their scores increased dramatically to 78% correct. Binnie, Montgomery, and Jackson (1974) showed that even when broad-band masking (--12 dB S/N) eliminated all but voicing and nasality features in the acoustic speech signal, normal-hearing

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adults recognized consonants through combined auditory-visual perception considerably better (83%) than when they merely listened alone (34%). They attributed this increase in consonant recognition to replacement by lipreading of the place-of-articulation information that was masked by the noise. Costello and Purcell (1968) described a study in which normal-hearing adults learned to associate word-letter pairs presented orally by a talker. The subjects' performance was much better when they lip-read while listening through a 1140Hz low-pass filter ( m e a n - 42.6/60 correct) than when they either lip-read alone (17.0]60) or listened to low-frequency cues alone (28.4/60). The age of the subject also seems to be an important variable in auditoryvisual studies. Ewertsen and Birk Nielsen (1971) compared perception of words in noise by normal-hearing adults 20, 50, and 70 years of age. They found that auditory, visual, and auditory-visual scores all diminished progressively as a function of the age of the subjects. Similar age-dependent performance has been reported by Farrimond (1959) for a lipreading task. AUDITORY-VISUAL

SPEECH PERCEPTION

BY HEARING-IMPAIRED

PERSONS

Testing normal-hearing subjects under poor acoustic conditions in order to simulate deafness is of questionable value, because it is not known how to simulate the perceptual effects of hearing loss. The use of masking noise, filters, or vibratory input probably only approximates the distortion produced by the ears of hearing-impaired people. The way in which hearing-impaired people perceive speech through lipreading also is not completely understood. Although they may visually identify syllables in a similar way, there is little reason to believe that congenitally deaf persons visually recognize connected speech material in the same manner as do normal-hearing people. Many congenitally deaf individuals, or those impaired early in their lives, acquire language in an abnormal way-mainly through the visual sense. Thus, they probably do not perceive, process, or comprehend language stimuli, through listening or lipreading, in the same way as do normal-hearing persons. For all of these reasons, if one's goal is to investigate auditory-visual speech perception by the hearing impaired, it is preferable for hearing-impaired rather than normal-hearing persons to serve as subjects. A patient's hearing loss, his educational experience, and the sensory modes through which he learned language all probably influence the way in which he processes auditory and visual speech stimuli. Therefore, whenever a hearingimpaired subject participates in a speech-perception study, it is important to specify these personal characteristics. Whereas the auditory-visual perception of normal-hearing subjects has been studied mainly under laboratory conditions, the auditory-visual communication abilities of hearing-impaired persons have been evaluated both in the laboratory and in the clinic. Researchers test normal and hearing-impaired observers in a laboratory setting to determine which cues they can perceive

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ERBER:Perceptionof Speech 485 under controlled auditory, visual, or combined auditory-visual stimulation. Audiologists usually evaluate hearing-impaired persons in the clinic to diagnose their communication problems and devise ways to overcome them. Unfortunately, most clinical evaluations have been dominated by auditory measures, often to the exclusion of examining visual and auditory-visual speech perception ability.

Laboratory Studies of Auditory-Visual Perception Erber (1972b) reported the results of a laboratory study in which normalhearing, severely hearing-impaired, and profoundly deaf children 1 were required to perceive the distinction between eight common consonants ]p, b, m, t, d, n, k, g/ in the bisyllabic context /a/-C-/a/. T h r o u g h lipreading alone, all three groups were able to distinguish between the places of articulation (bilabial, alveolar, velar) but not within each place category. W h e n normal-hearing children received acoustic information only, they recognized the consonants nearly perfectly. Severely hearing-impaired children distinguished accurately between voiceless and voiced stops and nasal consonants through listening alone. However, the listening scores of the profoundly deaf group were very low, and they perceived even voicing and nasality cues unreliably. Although both the normal-hearing and the severely hearing-impaired groups achieved nearly perfect consonant-recognition scores through simultaneous auditoryvisual reception, the auditory-visual performance of the profoundly deaf group was very similar to that which they demonstrated through lipreading alone. Walden, Prosek, and Worthington (1975) have evaluated military personnel whose hearing losses result primarily from noise exposure, and their studies have concentrated on perception of consonants within CV syllables. Visual cues were found to enhance transmission of place-of-articulation, frication, and duration features on an auditory-visual task. Lipreading had much less effect on the transmission of sonorant and voicing information. T h e improvement in transmission resulting from visual input was relatively constant across patients who demonstrated a wide range of auditory word-recognition scores. Walden, Prosek, and Worthington (1974) reported that most hearingimpaired adults with normal language are very similar in their ability to distinguish visually between the "homophenous" consonant categories of Woodward and Barber (1960). Yet in a later study, Walden, Prosek, and Sherr (1974) trained hearing-impaired adults to distinguish visually within the Woodward and Barber (1960) consonant categories. A filmed pretest indicated that numerous patients categorized the postdental consonants ]t, d, n, 1, r, s, z, j', 5[ together. A two-week training program consisted of distinguishing between XThese groups usually are distinguished on the basis of the average pure-tone threshold for 500-1000-2000 Hz. Averages between 70 and 95 dB (ANSI, 1969) have been used to describe severe hearing impairment, while averages ~ 95 dB indicate profound deafness. Erber (1974b, c) recently has described an auditory spondee-identification test to further differentiate the two groups.

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CV-syllable pairs as well as identifying spoken syllables containing the key consonants. After training, the patients demonstrated considerable improvement in recognizing items within this confusable set of postdental consonants. Many laboratory studies have used common words as stimuli. Numbers and Hudgins (1948), Murray (1951), Hopkins (1953), Hudgins (1954), Prall (1957), Clarke (1957), Van Uden (1960, 1970), Evans (1960), Sanders (1968), and Ross et al. (1972) all have examined the auditory, visual, and auditoryvisual word-recognition abilities of hearing-impaired children. Each of these investigations showed that when young subjects both look and listen, their mean word-recognition scores are better than when they either look alone or listen alone (Figure 2a, b). The mean advantage of auditory-visual perception over lipreading alone usually is greater for severely (19-28% gain) than for profoundly deaf children (1-15% gain), presumably because of the greater contribution of audition to auditory-visual perception in the severe group. In fact, the word-recognition scores of severely hearing-impaired children often approach 100% under combined auditory-visual conditions. Only a few investigators have used sentences as stimuli in auditory-visual research, probably because it is very difficult to construct diagnostically useful sentences and to score them reliably. Craig (1964) compared severely/profoundly deaf children's auditory-visual perception of sentences with their perception of the same sentences through vision alone. Mean auditory-visual performance was 5.0-8.5% better than that obtained through lipreading. Gammel ~ tested profoundly deaf children on a videotaped paragraph comprehension test which was presented for visual and auditory-visual perception. He found a relatively small mean increment (3.3%) for auditory-visual perception relative to visual alone. Several researchers have investigated auditory-visual word recognition in low-frequency noise to determine how typical noise environments affect speech perception in the hearing impaired. Erber (1971) reported that hearing-impaired children require quieter environments (0 to + 5 dB S/N) than do normalhearing children (--10 dB S/N) to achieve maximum auditory-visual identification of words. Profoundly deaf children require a higher signal-to-noise ratio ( + 5 dB S/N) than do severely hearing-impaired children (0 dB S/N). Miller and Niemoeller (1967) have demonstrated that auditory-visual perception can be improved in noise if the hearing aid microphone is held close to the talker's mouth. Erber (1972a, 1974b, c) has suggested that the speech information received through the ears of profoundly deaf children is similar to that perceived vibrotactually: that is, these children perceive the time-intensity patterns of speech and very little spectral information. Many years ago, Gault (1926, 1927, 1928) recommended the use of vibratory cues for speech as an alternative to acoustic input for deaf children and adults. In numerous laboratory studies, 2C. Gammel, Preliminary development and investigation of a connected-discourse speechreading test. Unpublished study, Central Institute for the Deaf, St. Louis (1974).

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ERBER: Perception of Speech

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SENSE Figure 2b. Mean recognition of spoken wards by profoundly deaf children through vision cdone and through vision plus another sensory system (from Erber, 1972a).

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he found that providing vibrotactile stimulation improved visual identification of words and sentences, and combined visual-vibrotactile perception typically was 10-15% better than was visual perception alone. T h a t amount of gain is very comparable to the amount observed for auditory-visual perception of speech by profoundly deaf children relative to their lipreading performance alone (Figure 2b). Recently, researchers at several laboratories have begun to develop special vibratory devices as aids to lipreading for profoundly deaf persons (Pickett, 1963; Kringlebotn, 1968; Martony, et al., 1974; Miller, Engebretson, and De Filippo, 1974). It is not yet clear whether these special instruments will be more valuable to the profoundly deaf than are conventional hearing aids. Clinical Evaluation of Auditory-Visual Perception

T h e traditional role of an audiologist has included the measurement of hearing and the remediation of the effects of hearing loss. In general, his test materials, his equipment, and to an extent his rehabilitation procedures and devices (for example, hearing aids) all have emphasized acoustic stimuli and hearing. More recently, audiologists have begun to recognize the importance of evaluating a patient's combined auditory-visual perception of speech as well as his auditory abilities. Hutton, Curry, and Armstrong (1959), Hutton (1959, 1960), Duffy (1967), and Siegenthaler and Gruber (1969) all have demonstrated that when patients both listen through a hearing aid and observe the talker through lipreading, their word-identification scores generally are much higher than they can obtain by merely listening alone. Dodds and Harford (1968) and Ewertsen, Birk Nielsen, and Scott Nielsen (1970) have reported similar results for sentence material. These data indicate that audiologists should consider amplification devices not only as hearing aids but also as aids to lipreading and should make recommendations with both functions in mind. Auditory-visual evaluation of patients, however, still is not a routine procedure in many audiologic centers. There are several reasons that audiologists should consider evaluating each patient's auditory visual perception of speech as part of the audiologic test battery. Clinical experience has suggested the following: 1. Most hearing-impaired patients typically receive speech through both auditory and visual modalities during everyday communication. This means that they usually watch the mouth and face of the talker to maximize perception of speech information. Auditory-visual evaluation in the clinic can give the audiologist a valid estimate of the patient's ability to communicate socially in his usual manner. 2. Auditory-visual testing may provide a more realistic indicator of how much a hearing aid helps a patient than would auditory testing alone, especially for profoundly deaf persons, who typically score low on auditory word-identification tests. Research is required to determine whether it is possible to select hearing aids for profoundly deaf individuals by comparing their aided auditory-visual results with their lipreading scores for the same speech material.

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ERBER. Perception of Speech 489

3. If single speech elements are used as test stimuli, an analytical evaluation of the auditory and visual errors in recognition can help the audiologist determine how well the patient uses the two types of sensory information to complement one another. The test results may suggest to the clinician whether the patient should receive rehabilitative emphasis in the auditory or visual modality. In this regard, a method for quantifying the redundancy between the auditory and visual elements in auditory-visual speech recognition recently has been reported (Walden et al. 1974). 4. Often, a moderately hearing-impaired patient needs to be convinced of the value of using lipreading in combination with listening through his hearing aid. A comparison of his auditory-visual score with his auditory-only performance usually will demonstrate to him that he has some lipreading ability and can benefit from its use. 5. Conversely, a profoundly deaf person may reject the use of a hearing aid because of his inability to understand speech through it alone. The patient may be motivated to attend to acoustic cues, if it can be demonstrated that his speech comprehension improves when he uses the aid in combination with lipreading. 6. Occasionally, the auditory-visual score of a profoundly deaf child is poorer than is his lipreading performance alone. The audiologist can attempt to determine why acoustic cues decrease lipreading scores in such cases and whether special training can improve auditory-visual perception for these children. It may be that the hearing aid simply is not adjusted correctly and that a small change in the gain setting will improve auditory-visual performance (Numbers and Hudgins, 1948). T h e r e is a need to develop a variety of clinical tests to evaluate hearing-impaired persons through audition alone, vision alone, and combined auditoryvisual modalities. Such descriptive tests could evaluate performance at the level of syllables, words, sentences, or paragraphs. Each type of test material on this c o n t i n u u m has its own diagnostic value as well as its own shortcomings. Whereas syllables and words allow precision in measurement, sentences and brief stories are more like the stimuli of daily conversation. Studies by H u t t o n et al. (1959), Ewertsen, Birk Nielsen, and Scott Nielsen (1970), Ewertsen and Birk Nielsen (1971), Danielson (1973), Ludvigsen (1973), Binnie et al. (1974), and Walden et al. (1974) have suggested directions for development of test materials. T h e r e clearly is a need for standardization and validation of auditory-visual stimulus items. Although it is more valid for a live talker to present test material, filmed or videotaped materials generally are preferred because they can be presented in a standard, repeatable way, and results from several laboratories or clinics can be compared. Initial attempts to construct a standardized auditory-visual test probably should be directed to the development of videotaped lists of common sentences to be presented to patients for evaluation of their everyday perceptual skills. A test of this sort could be used for diagnostic as well as evaluative purposes if sentences varying in length, internal redundancy, or syntactic complexity were employed, and separate scores were given for each sentence type. Audiologists also require specialized tests which can quantify the effect of certain environmental variables on auditory, visual, and combined auditoryvisual perception of speech. For example, it is i m p o r t a n t to specify how a

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patient performs in the presence of acoustic or optical distractions such as noise, reverberation, shadow, or glare (Erber, 1971, 1974a; Berger, Martin, and Sakoff, 1970), how he perceives talkers with different degrees of optical and acoustic clarity in their speech (Berg and Fletcher, 1970, p. 301), and how effectively the patient takes advantage of contextual and situational cues while communicating (Pelson and Prather, 1974). These effects should be quantified to enable the audiologist to specify the circumstances which create communication difficulties for the patient. If the clinician can define the patient's problem, he can recommend special practice under conditions which cause the patient difficulty-with the hope of minimizing his problem. For example, if he finds that a given patient has difficulty in auditory-visual perception in a noisy environment, he might train the patient to listen in noise. Tobias (1972) has demonstrated the value of listening practice under conditions of noise or distortion. The practical value of combining auditory and visual cues in communication has been recognized for a long time. Investigators have begun to examine the complicated interaction of audition and vision in speech perception only recently. In order to make use of both kinds of knowledge, more work will be needed in several areas: (1) basic studies of auditory-visual perception of speech, (2) the creation of clinical test materials to evaluate these abilities, and (3) the development of methods to improve the auditory-visual skills of patients who request our help. ACKNOWLEDGMENT Preparation of this manuscript was supported by Program Project Grant NS 03856 from the National Institute of Neurological Diseases and Stroke to the Central Institute for the Deaf. Another version of the paper was presented at the VI Danavox Symposium (Copenhagen, September 1974). Requests for reprints should be sent to Norman P. Erber, Central Institute for the Deaf, 818 South Euclid Avenue, St. Louis, Missouri 63110.

REFERENCES BERg, F. S., and FLETCHER,S. G., The Hard o] Hearing Child. New York: Grune and Stratton, 301 (1970). BERGER,K. W., MAR'rXN,J., and SAKOFF, R., The effect of visual distractions on speechreading performance. Teach. Deal, 68, 384-387 (1970). Btr~Nm, C. A., MorcrGOMERY, A. A., and JACKSOr~, P. L., Auditory and visual contributions to the perception of selected English consonants. J. Speech Hearing Res., 17, 619-630 (1974). Ct.ARKE, B. R., Use of a group hearing aid by profoundly deaf children. In A. W. G. Ewing (Ed.), Educational Guidance and the Deal Child. Washington, D.C.: Volta Bureau, 128-159 (1957). COSa~LLO, M. R., and PURCELL,G., Perception of defective visual and acoustic verbal patterns. Int. Audiol., 7, 5-8 (1968). CRMG, W. H., Effects of preschool training on the development of reading and lipreading skills of deaf children. Am. Ann. Deal, 109, 280-296 (1964). DM~mLSEN, K., Audio-visual discrimination test for children. Scand. Audiol., 2, 177-183 (1973). DOl~DS, E., and HA~Om), E., Application of a lipreading test in a hearing aid evaluation. J. Speech Hearing Dis., 33, 167-173 (1968). DurrY, J. K., Audio-visual speech audiometry and a new audio and audio-visual speech perception index. Maico Audiol. Lib. Series, 5:9 (1967).

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ERBER. Perception of Speech 491 ERBER, N. P., Interaction of audition and vision in the recognition of oral speech stimuli. J. Speech Hearing Res., 12, 423-425 (1969). E~ER, N. P., Auditory and audiovisual reception of words in low-frequency noise by children with normal hearing and by children with impaired hearing. ]. Speech Hearing Res., 14, 496-512 (1971). ElU;ER, N. P., Speech-envelope cues as an acoustic aid to lipreading for profoundly deaf children. ]. acoust. 8oc. Am., 51, 1224-1227 (1972a). E~ER, N. P., Auditory, visual, and auditory-visual recognition of consonants by children with normal and impaired hearing. ]. Speech Hearing Res., 15, 413-422 (1972b). E~ER, N. P., Effects of angle, distance, and illumination on visual reception of speech by profoundly deaf children. 1. Speech Hearing Res., 17, 99-112 (1974a). ERBER, N. P., Visual perception of speech by deaf children: Recent developments and continuing needs. J. Speech Hearing Dis., 39, 178-185 (1974b). ERBER, N. P., Pure-tone thresholds and word-recognition abilities of hearing-impaired children. J. speech Hearing Res., 17, 194-202 (1974c). EVANS, L., Factors related to listening and lipreading. Teach. Deaf, 58, 417-423 (1960). EWERTSEN, H. W., and BmK NIELSEN, H., A comparative analysis of the audiovisual, auditive, and visual perception of speech. Acta oto-lar., 72, 201-205 (1971). EWERTSEN, H. W., BIRK NIELSEN, H., and SCOTT NIELSEN, S., Audiovisual speech perception. Acta oto-lar. Suppl. 263, 229-230 (1970). FARRIMOND, T., Age differences in the ability to use visual cues in auditory communication. Lang. Speech, 2, 179-192 (1959). GAULT, R. H., The interpretation of speech by tactual and visual impression. Archs. Otolar., 3, 228-239 (1926). GAULT, R. H., On the identification of certain vowel and consonantal elements in words by their tactual qualities and by their visual qualities as seen by the lip-reader. ]. abnorm. Psychol., 22, 33-39 (1927). GAULT, R. H., Interpretation of spoken language when the feel of speech supplements vision of the speaking face. Volta Rev., 30, 379-386 (1928). HOPKINS, L. A., The relationship between degree of deafness and response to acoustic training. Volta Rev., 55, 32-85 (1953). HUVGINS, C. V., Auditory training: Its possibilities and limitations. Volta Rev., 56, 339-349 (1954). HuvroN, C., Combining auditory and visual stimuli in aural rehabilitation. Volta Rev., 61, 316-319 (1959). HuTroN, C., A diagnostic approach to combined techniques in aural rehabilitation. ]. Speech Hearing Dis., 25, 267-272 (1960). HUTTON, C., CURRY, E. T., and ARMSTRONG, M. B., Semidiagnostic test materials for aural rehabilitation. J. Speech Hearing Dis., 24, 318-329 (1959). KRINGLEBOTN,M., Experiments with some visual and vibrotactile aids for the deaf. Am. Ann. DeaL 113, 311-317 (1968). LUDVlGSEN, C., Auditive and audio-visual perception of PB-words masked with white noise. Scand. Audiol., 2, 107-111 (1973). MARTONY, J., A6ELFOm, E., BLOMeERG, M., BOBERG,G., ELrNIUS, K., P-dSB~G, A., SPENS, K-E., and OSTER, A-M., Experiments with electronic lipreading aids. Speech Commun. Seminar, Vol. 4, 93-96, Stockholm (1974). MILLER, G. A., HEISE, G. A., and LICHTEN,W., The intelligibility of speech as a function of the context of the test materials. 1. exp. Psychol., 41, 329-335 (1951). MILLFR, G. A., and NICELY, P. E., An analysis of Perceptual confusions among some English consonants. ]. acoust. Soc. Am., 27, 338-352 (1955). MILLER, J. D., ENGEBRETSON,A. M., and DE FILIPPO, C. L., Preliminary research with a threechannel vibrotactile speech-reception aid for the deaf. Speech Commun. Seminar, Vol. 4, 97-103, Stockholm (1974). MILLER, J. D., and NIZMOrLLER,A. F', Hearing aid design and evaluation for a patient with a severe discrimination loss for speech. ]. Speech Hearing Res., 10, 367-372 (1967). MURBAY, N. E., Interim report on hearing aids and classification of deaf children. Commonwealth Acoustic Laboratories, Informal Report 1R-2, Sydney, Australia (1951). NEELY, K. K., Effect of visual factors on the intelligibility of speech. 1. acoust. Soc. Am., 28, 1275-1277 (1956).

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481-492

1975

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Auditory-visual perception of speech.

Hearing-impaired persons usually perceive speech by watching the face of the talker while listening through a hearing aid. Normal-hearing persons also...
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