Dept. for Speech, Music and Hearing

Quarterly Progress andStatus Report

Three studies using the KTHspeech tracking procedure

Plant, G. and Gnosspelius, J. and Spens, K-E.

journal: STL-QPSRvolume: 35number: 1year: 1994pages: 103-134

http://www.speech.kth.se/qpsr

STL-QPSR 111 994

Three studies using the KTH speech tracking procedure GeofS Plant, Johan Gnosspelius and Karl-Erik Spens

Abstract This paper describes three studies of speech tracking using the KTH computer-based procedure. The first study investigated whether tracking was a suitable substitute for other forms of training in the use of tactile aids. One subject was trained extensively using speech tracking with five different tactile aids. The results obtained indicated that other forms of training were necessary if optimal use of tactile aids was to be achieved. This appeared to be especially true for the Tactaid VII, a more complex multi-channel vibrotactile aid. This finding was supported by the second study where a training program for the Tactaid VII, combining the use of tracking and analytic training exercises, was provided to one subject. Over the course of the study the subject's performance for lipreading plus the tactile aid was clearly superior to that obtained with lipreading alone. The final study compared two different presentation rates - clear and conversational speech - and examined its efSects on tracking performance. Although the clear speech condition yielded a lower tracking rate overall the number of blockages was greatly reduced. The implications of the studies are discussed and suggestions made for further research.

Introduction Tracking (sometimes called Connected or Continuous Discourse Traclung), "a procedure for training and evaluating the reception of ongoing speech" (De Filippo & Scott, 1978; p. 1186) was first described by De Filippo & Scott in 1978. Since that time the tracking procedure has become a key element in many aural habilitation and rehabilitation programs provided for hearing impaired children and adults.

Although there have been a number of reports on the use of tracking as a training procedure (Danz & Binnie, 1983; Lesner & Kricos, 1987; Osberger et al., 1987; Owens & Raggio, 1987; Owens & Telleen, 1981) its major role, as Tye-Murray & Tyler (1988) have pointed out, has been as an evaluative tool. For example, the tracking procedure has been used in the evaluation of cochlear implants (Dowel1 et al., 1985; Levitt et al., 1986; Martin et al., 1981; Robbins et al., 1985), electronic tactile aids (Brooks et al., 1986; Cholewiak & Sherrick, 1986; Cowan et al., 1991; De Filippo, 1984; Plant, 1988; Weisenberger et al., 1989; ~hngren , 1992) and "natural" tactile approaches such as Tadoma (Reed et al., 1992) and tactiling (Plant & Spens, 1986).

Despite its apparent wide-spread acceptance by research groups there have been criticisms of the use of tracking as a test procedure. The most detailed of these critiques was that of Tye-Murray & Tyler (1988) who argued that "speech traclung is an effective aural rehabilitation strategy but inappropriate as a test procedure" (Tye- Murray & Tyler, 1988; p. 226).

STL-QPSR 1 / 1994

degree of syntactic sophistication of the text. Vocabulary items are of critical importance as even one difficult word which requires extensive use of repair strategies may influence the overall tracking rate in a particular traclung session.

Finally, the degree of text complexity may also have a significant effect on traclung rates. Hochberg et al., (1989) for example, found that traclung rates for texts presented via lipreading alone varied from 62.9 wpm for "easy" materials (controlled vocabulary readers) to 29.5 wpm for "difficult" materials (popular adult detective stories).

Tye-Murray & Tyler (1988) feel that these factors make tracking an unsuitable procedure for across-subject test designs. They do, however, believe that, despite some remaining problems related to sender, receiver and text variables, tracking is suitable for within-subject test designs. They also offer a number of suggestions as to how these problems may be minimised. The suggestions are:

1. The receiver should give a verbatim response. Any other form of response will require a subjective judgement by the sender.

2. Texts used should have simple vocabularies and syntactic structures. 3. A different text should be used from session to session. This will prevent the

receiver from using contextual cues resulting from familiarity with the plot. 4. Both the sender and receiver should have had training in the use of the procedure

prior to any testing being carried out. 5. The same sender should be used for all testing. 6. The sender should use a limited number of repair strategies. Tye-Murray & Tyler

(1988) suggest, for example, that if the receiver is unable to repeat the word after three repeats the sender should either write down or by-pass the word. This will reduce the effects of difficult words on the overall traclung rate.

7. The receiver should always follow a set response pattern such as repeating as many words as s h e has identified. This will provide the sender with feedback which can be used in determining which word(s) are next presented for identification.

There are other ways in which tracking can be more closely controlled for evaluative purposes. The use of recorded materials provides an obvious solution to the problem of speaker variables. Boothroyd's (1987) Computer Assisted Speech Perception Evaluation and Training Program (CASPER), Dempsey's et al., (1992) Computer-Assisted Tracking Stimulation (CATS) and Pichora-Fuller & Cicchelli's (1986) Computer Aided Speechreading Training (CAST) program are all examples of the use of recorded tracking materials. These enable control of speaker variables and allow the use of a strict hierarchy of response and repair strategies. The use of recorded materials may also be beneficial for some hearing-impaired people who find it difficult to relax with a live speaker (Summerfield, 1983). This lack of personal interaction, however, must also be seen as a potential disadvantage of recorded traclung materials. The use of recorded materials also requires relatively expensive equipment such as a video or laser-disc recorder, a monitor and a computer to control presentation and record the subject's responses. Such equipment may not be available to many clinicians who use tracking as an integral part of their rehabilitative approach.

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The KTH computer-based speech tracking procedure The computer-based tracking procedure developed at the Department of Speech Communication and Music Acoustics (Gnosspelius & Spens, 1992; Spens, 1992) represents a compromise between the use of recorded materials and live-voice presentations. The text is presented live voice, but segment length is pre-determined and the use of only one repair strategy is allowed. The text is presented segment-by- segment via the computer screen, and data is stored on the receiver's performance for each traclung session.

Prior to using the KTH speech tracking procedure, the text to be used must be divided into segments for presentation and stored in the computer. In determining the length of the segments a number of factors have to be considered. The most important is to ensure that the segments are both logically and grammatically correct. This will in part determine the length of each segment, but care needs to be taken to ensure that the segments are neither too long nor too short. There are many anecdotal reports and some research evidence (Hnath-Chisolm & Boothroyd, 1992) that longer sentences are more difficult to lipread than short sentences. An obvious problem with excessively long sentences is that receivers will have difficulty recalling them, and this will lead to blockages and a subsequent reduction in tracking rate. Short sentences, on the other hand, may be more easily recalled but the amount of turn taking will have the effect of lowering the tracking rate. The segments are shown on the computer screen, and the sender reads each one completely. This removes any possible influence resulting from variations in the length of presented segments.

The only repair strategy used in the KTH speech tracking procedure is to repeat any I

word(s) not correctly identified. The number of repeats can be pre-determined but once that number has been reached the blocked word is displayed using a LED display located just above the sender's head. The letter size is sufficiently large to ensure that the word can be easily read by the receiver. This is especially important if the receiver is using glasses to lipread the sender. The receiver does not have to change glasses in order to read the displayed word. The use of the display also saves time which might otherwise be taken up with the sender writing down the blocked word.

Use of the KTH computer-based speech tracking procedure The first step in the KTH speech traclung procedure is to set a number of parameters for the session. The receiver's name and the testing condition (lipreading alone, lipreading + hearing aids) are entered, along with the number of repeats of a blocked word and the duration (in minutes) of the tracking session. The sender can also set the windows to be shown on the screen during the tracking session. These include an elapsed time window and a record of all words which are presented via the LED display.

Once these parameters have been set, the traclung session can begin. The text is displayed on the computer screen, with the line to be read high-lighted in green. A start button is also displayed, and the tracking session is timed from the moment that this is clicked on, using a mouse. The first line is then presented, and the receiver responds. If the response is completely correct the sender clicks with the right mouse and activates the next text segment. If the receiver is unable to repeat all of the words in the

STL-QPSR 111 994

segment, the sender clicks on the first blocked word with the left mouse button and repeats that word or the blocked word and all subsequent words.

Consider the following example where the number of repeats allowed has been set to two. The presented segment might be: "I was sitting with my friend Sherlock Holmes in our lodgings in Baker Street". The receiver's response is "I was sitting with my friend ....." The sender would then click on the word "Sherlock" with the left mouse button and then either repeat it, or more probably "Sherlock Holmes". If the receiver is still unable to identify the word(s) the sender again clicks on "Sherlock" and repeats the word(s). If the receiver is unable to repeat the word after two repeats the sender again clicks on the left mouse button and the blocked word (Sherlock) is shown on the LED display. The procedure is repeated until the entire segment has been correctly identified. At this point the sender clicks on the right mouse button, and the next segment is highlighted for presentation. This procedure continues for the duration of the session, at which point the test is automatically stopped. The computer stores the last line read so that the text will start at the appropriate place in the next session.

At the end of each test session the following data are stored in a file;

the number of words in each segment presented, the time taken for correct identification of each segment, the number of repetitions of a word or words in the segment, the number and identity of words within an individual segment presented

via the LED display, the total number of words repeated once and then correctly identified, the total number of words presented twice and then correctly identified, the total number of words in the session transmitted via the LED screen, the total number of words presented in the segment, the time elapsed, and the average tracking speed (in wpm) which is the total number of words

divided by the elapsed time.

Using this stored information it is possible to calculate the proportion of blocked words for each traclung session. This is the total number of words clicked on, divided by the total number of words in the session.

Another measure of considerable interest is the receiver's ceiling rate (Spens, 1992). This is the time taken on segments which are correctly identified on the first presentation and represents the maximum tracking speed for a session. This may vary according to the relative ease with which the receiver is able to repeat back the segments. The ceiling rate will probably vary as the sender attempts to accommodate for a receiver's performance in a particular condition, and can perhaps be seen as representing the path of least resistance. If a receiver is able to repeat back all words without error, the sender's speaking rate will probably increase to something approaching normal conversational rate. Picheny et al. (1986) found that this was in the range 160 - 200 wpm. In this case the ceiling rate will be around 80 - 100 wpm, given that the speaker has to present the segment and the receiver repeat it. If the receiver is experiencing difficulty, however, the sender's speaking rate will drop as

STL-QPSR 111 994

slhe attempts to produce clear speech which is maximally intelligible. Pichenyet al. (1986) report speahng rates in the range 90 - 100 wpm for clear speech. This would presumably result in ceiling rates of around 45 - 50 wpm.

Text materials The study by Hochberg et al. (1989) has highlighted the need to use materials of equal difficulty when using tracking as an evaluative tool. In the studies reported in this paper two different materials were used.

! The first was an English translation of Astrid Lindgren's (1973) children's novel I

"The Brothers Lionheart". The choice of text was motivated by a desire to use the comparable tracking materials in both English and Swedish. The Swedish original I ("Broderna Lejonhjiirta") had previously been used in tracking studies conducted at the Department of Speech Communication and Music Acoustics. The full text of this book was segmented and stored in the computer. The text was modified, where necessary, to meet the constraints of the traclung procedure. The aim of the modifications was to attempt to maintain a conversational style throughout the text. An arbitrary maximum

I length of 11 words was set for each segment. A total of 52,001 words are presented in 8,148 segments with an average segment length of 6.4 words. A detailed analysis of segment length is presented in Fig. 1.

The Brothers Lionheart

1 2 3 4 5 6 7 8 9 10 11

Segment length (in words)

Fig. 1. Histogram showing the distribution of segment lengths for the version of "The Brothers Lionheart" used in the studies reported in this paper.

STL-QPSR 1 / 1994

The second text material consisted of four stories ("The Red-Headed League", "A Case of Identity", "The Boscombe Valley Mystery" and, "The Adventure of the Speckled Band") from Sir Arthur Conan Doyle's "The Adventures of Sherlock Holmes". These stories were chosen for use as more difficult tracking materials. Although attempts were made to maintain a conversational flow, the style is more literary than "The Brothers Lionheart". Further, a more extensive vocabulary is used in the Sherlock Holmes stories, and the only constraint on segment length was that a line could not contain more than 73 characters (Gnosspelius & Spens, 1992). Table I presents the total number of words, number of segments and average segment length for the four stories. A detailed analysis of segment length for the four stories is presented in Figure 2.

Table I. Total number of words, total number of segments and average segment length for "The Redheaded League" (REDHEAD), "A Case of Identity" (IDENTITY), "The Adventure of the Speckled Band" (SPECKLED) and "The Boscombe Valley Mystery (BOSCOMBE).

In their recommendations for the use of tracking for within-subject test designs, Tye-Murray & Tyler (1988) suggested that materials used in different traclung sessions should not be taken from the same book. They believe this is necessary "otherwise, the receiver can exploit the story plot for recognising words in later sessions" (Tye-Murray & Tyler, 1988; p. 229). There are, however, difficulties with such an approach. When different stories are used for each session, it is difficult to ensure that they are of equal difficulty. Variations in difficulty may lead to unrealistically large differences in a receiver's performance from session-to-session.

Presenting different stories for each session may also serve to reduce the enjoyment many hearing-impaired people derive from tracking a complete novel. Aural rehabilitation sessions necessarily include a number of components which are repetitive and relatively boring for many hearing-impaired people. The use of a continuous story for tracking can help alleviate this problem by providing a high interest component in every rehabilitative session.

REDHEAD

IDENTITY

SPECKLED

BOSCOMBE

Total No. of Words

9,554

7,384

10,834

13,012

Total No. of Segments

1,154

853

1,222

1,264

Average Segment Length

8.2 words

8.7 words

8.9 words

10.3 words

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Redhead

v, 250 8 g 200 L

$ 150

100 * 0

0 50 z 0

m m P - Q ) 7 m 7 7

Segment length (in words)

Speckled

m 250

200 2 5 150 0 0 0 100 * 0

0 50 Z

0 r n L n Q ) ? r n

v 7

Segment length (in words)

Identity

v, 150 a, 0 c E loo 3 0 0 0

50 0 Z

0 I - O W P - Q ) - M L ~

7 7 7

Segment length (in words)

Boscom be

v, 350 Q, o, 300 92 L 250 2 200 "o50 'co 100

50 Z 0

- m L n b Q ) r O L n b Y - 7 7

Segment length (in words) 1

Fig. 2. Histograms showing the distribution of segment lengths for the four Sherlock Holme's stories used in Study 1. The stories were; "The Red Headed League" (Redhead), "A Case of Identity" (Identity), "The Adventure of the Speckled Band" (Speckled), and "The Boscombe Valley Mystery" (Boscombe).

The use of different stories may also frustrate receivers with poor receptive communication s l l l s . The first author's experience with tracking in clinical situations has shown that many hearing-impaired people have severe difficulties at the start of a new traclung text. After a number of sessions, however, as they become more familiar with the story, their performance improves and their degree of frustration is

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consequently reduced. The very problem cited by Tye-Murray & Tyler (1988), that of exploiting the story plot, may also help receivers learn to use contextual information in everyday communication. It also should be pointed out that within any traclung text there are usually several major topic changes, as well as more subtle shifts in topic. For these reasons it was decided to use a limited number of tracking texts but to continue testing across a relatively long period of time. It was hoped that in this way interest in the text could be maintained and any frustration minimised.

The sender De Filippo (1988) and Tye-Murray & Tyler (1988) suggest that the talker used in tracking sessions should have received training in the procedure. The talker in the studies reported in this paper was the first author, a male native speaker of General Australian English who had been using conventional speech tracking as a routine clinical training and evaluative tool since 1979. Prior to undertaking studies using the KTH speech traclung procedure, the author had a number of practice sessions to become familiar with the procedure. This was necessary, as the procedure requires some practice to become proficient in the use of the mouse to mark blockages and to move from segment-to-segment. It was also necessary to learn to use no repair strategy other than repeats of the blocked word(s).

Study 1 - Introduction The first study used the KTH speech tracking procedure to evaluate whether tracking could serve as a stand-alone training method for tactile aid usage. Danz & Binnie (1983) investigated the use of tracking for training auditory-visual speech reception. They reported a number of significant improvements in performance post-training and suggested that traclung may be a suitable alternative to more traditional training approaches. A number of tactile researchers (Alcantara et al., 1990; Saunders et al., 1976; Sparks et al., 1979; Weissenberger & Miller, 1987), however, have suggested that tactile training should include an analytic component. Alcantara et al. (1990) suggest that analytic training orients the user to the tactile aid's display at a relatively simple level and provides himher with the confidence needed to use this information in more complex communication situations.

Subject The subject was an adult female native speaker of General Australian English. The subject was normally-hearing and had had no previous experience in lipreading experiments or in the use of tactile aids.

Tactile aids The tactile aids evaluated over the course of the study were the Minivib 4, the Tactaid 11, the Tactaid II+, the Tactaid VII, and an experimental aid presenting information from a throat microphone worn by the speaker.

STL-QPSR 111 994

The Minivib 4 is a single-channel vibrotactile aid which encodes time and intensity variations in the frequency range 500 - 2,300 Hz at 220 Hz.

The Tactaid II is a two-channel vibrotactile aid which presents temporal patterns from two band-pass filters (100 - 1,500 Hz, 1,500 - 6,000 Hz) as a fixed frequency of 375 Hz. Spatial separation of the output transducers enables discrimination of the "high" and "low" bands. The Tactile 11+ uses a similar processing scheme but the output frequency is 250 Hz.

The Tactaid V I I is a seven-channel vibrotactile aid which divides the incoming speech signal into the following channel frequencies: Channel 1 - 200 - 400 Hz, Channel 2 - 400 - 600 Hz, Channel 3 - 600 - 800 Hz, Channel 4 - 800 - 1,200 Hz, Channel 5 - 1,200 - 1,600 Hz, Channel 6 - 1,600 - 3,000 Hz, and Channel 7 - 3,000 - 7,000 Hz.

In the experimental aid, the output from a throat microphone (AB Transistor Tc 26216) worn by the sender was amplified by the Siemens Monophonator and presented via the hand-held vibrator from Traunmuller's (1980) Sentiphone. This device was designed to be similar to Ohngrents (1992) Tactilator. There were, however, some differences between the two devices. The Tactilator consisted of a contact microphone placed on the speaker's throat, a wireless transmitter and receiver, and a hand-held bone conductor. Ohngren (1992) used the Tactilator with 16 deafened adults, and compared their performance for conventional tracking for unaided and aided 1 lipreading. She found that all the subjects immediately obtained higher tracking rates in the aided lipreading condition.

The Minivib 4, Tactaid I1 and 11+ and the Tactaid VII are all provided with vibrators I

designed to be worn on the wrist (Minivib 4, Tactaid I1 and II+), chest (Tactaid 11, 11+ and VII) or the back of the neck (Tactaid VII). Although these stimulation sites make the aids suitable for everyday use, they do not provide the user with optimal tactual information. Studies of vibrotactile receptor systems (see Verrillo and Gescheider, 1992 for a review) and tactile aids (Spens, 1980) have shown that the best results are obtained when the hands, and especially the fingertips, are stimulated.

For this reason it was decided that, where necessary, the aids would be modified so that their output transducers could be comfortably hand-held. The Minivib 4 transducer could be hand-held without modification but the vibrators from the Tactaid 11, 11+ and VII required mounting in a handpiece. The handpieces for these aids were moulded to the shape of the subject's hands using Cernit modelling material. The vibrators were then set into the handpieces. The handpiece for the Tactaid VII was arranged so that Channel 1 was transmitted to the thumb, Channels 2 to the fore-finger, Channel 3 to the middle finger, Channel 4 to the ring finger and Channel 5 to the little finger. Channels 6 and 7 stimulated the palm of the hand.

Trainingltesting procedure The subject was seated in an audiometric test booth and observed the speaker through a glass window. Frontal illumination of the speaker's face was provided to maximise visual cues. The distance from speaker to receiver was approximately 1.5 - 2 metres. The subject wore headphones which provided sufficient masking noise to ensure that she could hear neither the sender's voice nor any acoustic output from the tactile

STL-QPSR 1 / 1994

transducers. The receiver's spoken responses were picked up by a microphone in the test booth and presented to the sender via a loudspeaker.

The materials used over the course of the testing were in turn "The Brothers Lionheart" and three of the Sherlock Holmes stories - "The Red-Headed League", "The Adventure of the Speckled Band" and "A Case of Identity".

Prior to undertaking the study with the tactile aids, the subject was provided with practice using the KTH speech traclung procedure. This was done lipreading alone, lipreading supplemented by speech low-pass-filtered (LPF) at 1,000 Hz and 250 Hz and lipreading supplemented by the hand held Minivib 4. Four 5-minute tracking sessions were conducted for each of the conditions. The practice was carried out over two testing sessions (2 x 5-minute tracking sessions in each condition in each test session). In each session the order of presentation was randomly varied to minimise any possible learning or fatigue effects.

Once the subject was familiar with the procedure the trainingltesting sessions commenced. A trainingltesting session consisted of 2 x 5 minute tracking sessions for each of the conditions being tested. No other testing or training was carried out via lipreading alone or in any of the aided lipreading conditions.

The details of the trainingltesting program are presented in Table 11. This shows the point in the program at which a particular aid was introduced. It can be seen that traclung via lipreading alone and lipreading plus the Minivib 4 was carried out in all sessions. The Tactaid I1 was introduced in Session 6 and was used for the following eleven sessions. At this point, unfortunately, it developed a fault and testing was discontued with this aid. The Tactaid VII was introduced in Session 12 and the Tactaid 11+ in Session 24. The experimental aid was added to the program in Session 28.

Table II. Summary of the testing/training program undertaken with the subject. The crosses indicate the conditions contrasted in the session block. The conditions shown are lipreading alone (LR), lipreading plus speech low-pass-filtered at 250 Hz (LR+250), lipreading plus the Minivib 4 (LR+MV), lipreading plus the Tuctaid II (LR+TII), lipreading plus the Tactaid 11+ (LR+TII+), lipreading plus the Tactaid VII (LR+TVII) and lipreading plus the experimental aid (LR+ Ex).

It should be noted that a total of four sessions were presented with lipreading supplemented by speech LPF at 1,000 Hz. These were conducted during the practice period and in the first two testingltraining sessions.

Session No.

1 - 5 6 - 11 1 2 - 1 6 17 - 23 24 - 27 28 - 33

LR + 250

X

LR

X X X X X X

LR + MV

X X X X X X

LR + TI1

X X

LR + TII+

X X

LR + TVII

X X X X

LR + Ex

X

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There were a total of 33 sessions presented via lipreading alone and lipreading plus the Minivib 4. In each session there were 2 x 5 minute traclung sessions for each condition. This gives a total of 330 minutes (5.5 hours) for each of the testing conditions. The total number of sessions for the remaining aids, with the number of hours experience shown in parenthesis, were: Tactaid I1 - 11 sessions (1.8 hours), Tactaid 11+ - 10 sessions (1.7 hours), Tactaid VII - 22 sessions (3.7 hours) and the experimental aid - 6 sessions (1 hour).

Data analysis I The subject's tracking rates, ceiling rates and other performance measures were stored on the computer after each tracking session. When the practice sessions are included, a total of 278 individual traclung sessions were administered over the course of the study. To reduce the data and to minimise effects of subject fatigue and text segments which were either unusually difficult or unusually simple, it was decided to calculate the mean scores obtained in each condition across blocks of five testingltraining sessions. Each data point obtained, therefore, represents the results for 10 five-minute tracking sessions.

The aim of the study was to compare performance for lipreading alone and lipreading supplemented by each of the tactile aids. This was achieved by linlung the lipreading alone score in each session with the score obtained for each of the aided conditions. In this way a set of data points was obtained which compared each lipreading alone and aided lipreading condition across the period of the study.

In order to obtain some comparative data, however, it was decided to include the data for the last five testingltraining sessions (Sessions 29 - 33). In these sessions the following conditions were tested - lipreading alone, and lipreading plus the Minivib 4, Tactaid II+, Tactaid VII, and the experimental tactile aid. These sessions were also those in which the more difficult Sherlock Holmes stories were used.

I

Results I

The mean tracking rates and ceiling rates for the four sessions where lipreading was supplemented by speech LPF at 1,000 Hz condition were 108 wpm and 11 1 wpm,

I respectively. The mean proportion of blocked words was .006 reflecting very few blockages in any of the tracking sessions.

A total of seven practice or testingltraining sessions were administered for the lipreading supplemented by speech LPF at 250 Hz condition. The subject's mean scores for the first five practice or testingltraining sessions were calculated. This

I showed a mean tracking rate of 75.6 wpm and a mean ceiling rate of 98.6 wpm. The proportion of blocked words for this condition was .04.

The mean results obtained for 30 testltraining sessions (Sessions 1 - 25 and 27 - 31) for lipreading alone and lipreading plus the Minivib 4 are summarised in Figure 3. The mean tracking rate for lipreading alone across the 30 sessions was 48.0 wpm, compared to 48.6 wpm obtained when the Minivib 4 supplemented lipreading. An examination of the ceiling rates, proportion of blocked words and the number of words repeated once, twice and three times reveals strikingly similar results for the two

STL-QPSR 111 994

Figure 4 presents the comparative results for lipreading alone and lipreading plus the Tactaid VII. Again, there appear to be few, if any differences between the two conditions. The mean tracking rates across the 20 sessions for lipreading alone and lipreading plus the Tactaid VII were 5 1.0 wpm and 5 1.9 wpm, respectively.

Fig. 4. The tracking results for the subject in Study 1 for materials presented via lipreading alone (filled bars)and lipreading plus the Tactaid VII (unfilled bars). For a detailed explanation of this figure see the legend for Figure 3.

im

QO

&I

70

m

50

PO

30

20

10

0

1-5 610 11-15 1 620

k . u o n no

Propoltion d Mocked words

025

0 2

015

- --

--

W r d m g + ~octard VII

I

1-5 610 1 1 15 14-20

Sorvon no

3 repeals 1 repeal

10 + Toclad

* 0 " VII Y P " VII 10 15 P A $

Seubn no Session no Seubn no L

2 repeats

Figure 5 shows the scores obtained for lipreading alone compared with lipreading plus the Tactaid 11.

1-5 610

S . w n no.

Propoltion of blocked words

1 -5 610

Souion no.

I 1 repeat 1) 2 n p b 11 3 repoats I

I -

1-5 610 1-5 610

Session no.

Fig. 5. The tracking results for the subject in Study I for materials presented via lipreading alone (filled bars)and lipreading plus the Tactaid II (unfilled bars). For a detailed explanation of this figure see the legend for Figure 3.

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The final aid tested was the experimental device. Results were only obtained for five sessions with this aid. The traclung rates for unaided and aided lipreading with this device were 41.4 wpm and 44.2 wpm, respectively. The ceiling rates were almost identical (unaided = 78.2 wpm, aided = 78.9 wpm). There was only a slight difference in the proportions of blocked words for the two conditions (unaided = 0.23, aided = 0.20).

Discussion The results of this study show few instances where aided performance exceeds that obtained in the unaided condition. There are, however, some exceptions to this trend.

In the second block of sessions undertaken with the Minivib 4 the aided tracking rate is 7.2 wpm greater than the unaided. The ceiling rates for these two conditions are almost identical but the proportions of blocked words do differ (lipreading alone = 0.16, aided lipreading = 0.12). This block of sessions was when the Tactaid I1 was introduced, and it is interesting to compare the subject's performance with this device. The traclung rate, ceiling rate and proportion of blocked words for lipreading plus the Tactaid I1 during these sessions were 54.7 wpm, 88.3 wpm and 0.12, respectively. That is, it was almost exactly the same advantage over lipreading alone as that found for the Minivib 4. In seelung to explain the advantage for the two aided conditions, it should be recognised that the subject's previous experience with the Minivib 4 may have also assisted her in rapidly assimilating the information provided by the Tactaid 11. It is possible that the information available via the low frequency channel of the Tactaid I1 is very similar to that provided by the Minivib 4. What the aids may have been providing at this point were cues which enabled segmentation of the lipread signal into meaningful syllables and words.

In the following block of five testingltraining sessions the tracking rates for lipreading alone, lipreading plus the Minivib 4 and lipreading plus the Tactaid I1 were 48.5 wpm, 50.4 wpm and 56.4 wpm, respectively. The ceiling rates for the three conditions remain very similar (84.8 wpm, 83.9 wpm and 84.1 wpm, respectively) as do the proportions of blocked words for lipreading alone and lipreading plus the Minivib (0.13 for both). The proportion of blocked words for the lipreading plus the Tactaid I1 condition, however, was 0.10. It would appear, therefore, that at this point the Minivib offers little assistance to lipreading and this continued for the duration of the study. It is possible that by Sessions 11 - 15 the subject was able to perform the segmentation task equally well lipreading alone and lipreading plus the Minivib. Thus, any advantage previously offered by the Minivib 4 was now negated although it might have been invaluable in enabling the subject to learn how to segment the lipreading alone signal.

The additional information provided by the Tactaid 11's dual channels might now be responsible for the continuing advantage it appears to offer over lipreading alone. Testing of the Tactaid 11 at the syllabic level (Plant, 1988) has revealed that it can provide useful segmental information. Plant (1988) in a study of one subject found that use of the Tactaid I1 in conjunction with lipreading led to enhanced perception of consonant voicing, sibilance and nasality. This subject's performance over twenty

STL-QPSR 1 / 1994

sessions using conventional traclung found an advantage of around 10 wpm when the Tactaid I1 supplemented lipreading.

It is unfortunate that the testing with the Tactaid I1 was unable to continue to see if this advantage was maintained over time. When the Tactaid 11+ was introduced into the study there were no differences in performance between unaided and aided performance over the first block of five testingltraining sessions. The unaided and aided tracking rates for this block were 54.7 wpm and 54.4 wpm, respectively. In the second block of five sessions with the more difficult text materials there was an advantage of around 8.5 wpm for the aided condition. Despite an increased ceiling rate in the aided condition (84.7 wpm compared to 78.2 wpm) the proportion of blocked words in the aided condition (0.17) was considerably less than that found in the unaided condition (0.23).

The results for the Tactaid VII over the duration of the study show very similar scores for the aided and unaided conditions. There are at least two possible explanations for this. The first is that the Tactaid VII is not an effective aid to lipreading. The second is that the aid's seven channel display is so complex that, unlike the dual channel Tactaid I1 or II+, subjects need to have special training before they can use this information to supplement lipreading. This latter view is supported by the results of Study 2 reported in this paper.

Finally, the results for the experimental aid indicate little, if any, advantage for the aided over the unaided lipreading condition. It should be remembered, however, that the subject had very little experience with this aid. This result, however, is at variance with that reported by Ohngren (1992) for the Tactilator, where every one of her 16 subjects immediately improved in the aided traclung condition. There are a number of possible explanations for the differences in the findings of this study and those of 0hngren (1992). The equipment used in the two studies was not the same, and this may have resulted in the different performance. Another possible explanation is related to the argument presented above, relating to the performance differences between the Minivib 4 and the Tactaid 11. The signal from the Tactilator may have enabled the subjects in Ohngrenls (1992) study to segment the speech signal more efficiently and this then led to their improved performance in the aided condition. By the time the subject in the present study was exposed to the experimental aid, however, she had quite possibly become very proficient at speech segmentation via lipreading alone, and as a result she derived no immediate benefit from the aid. With extended, appropriate training, however, such an aid might provide the subject with access to segmental cues such as consonant voicing and nasality and thus lead to enhanced tracking performance. Ohngren et al. (1992) have reported the results obtained in testing a subject with long-term experience in the use of the sensory information provided by the Tactilator. These show enhanced perception of stop, nasal and fricative consonants, and of consonant voicing when lipreading is supported by the Tactilator.

Despite her previous lack of experience in lipreading studies or the use of tactile aids, the subject's lipreading ability proved to be very high. In some of the last lipreading alone sessions using "The Brothers Lionheart" as the text, the subject's tracking rate approached 80 wpm. This compares quite well with the tracking rate of 108 wpm obtained when lipreading was supplemented by speech LPF at 1,000 Hz.

STL-QPSR 1 / 1 994

There was a steady improvement in lipreading performance over the course of the program. The subject's mean tracking rate lipreading alone for the first block of five testingltraining sessions was 43 wpm with a ceiling rate of 87.2 wpm and a proportion of blocked words of 0.17. Her mean performance for the same measures in Sessions 21 - 25 were 56.4 wpm, 88.9 wpm and 0.14, respectively. The tracking rate has increased by 13.4 wpm while the ceiling rate has remained relatively stable and the proportion of blocked words has decreased by 0.03.

Further investigations need to be undertaken to determine whether training lipreading with tactile aids leads to improvements in lipreading alone performance. This has been a comment made to the first author by a number of profoundly deafened adults he has worked with over the past ten years. They believed that tactile aids not only provided direct benefit when used in conjunction with lipreading but that they had also assisted in the development of better lipreading alone skills.

This study has an obvious flaw in that it used only one subject, but the results do indicate that tracking alone may not provide sufficient training for effective use of tactile aids. This view is supported by the results of the next study, where a training program was provided which presented both analytic materials and trachng exercises.

Study 2 The aim of this study was to investigate the provision of a training program which incorporated analytic training exercises, as well as synthetic exercises including tracking, using the KTH speech tracking procedure.

Method Subject The subject of this study was one of the authors (JG) of this paper. He is an adult normally-hearing male native speaker of Swedish who spoke English as a second language. Although the subject had been responsible for writing the computer software program for the KTH speech tracking procedure, he had very limited experience as a subject in lipreading experiments. He had no previous experience in lipreading English, nor in using tactile aids as lipreading supplements.

Aid The aid chosen for this study was the Tactaid VII. The subject used the same handpiece as the subject in Study 1. He reported that this was comfortable and he was able to feel tactile pattern differences with it.

Materials A variety of training materials was prepared for the training period. These included analytic exercises which introduced and contrasted [a], [i] and [3], the "point" vowels of Australian English, in isolation, in words and syllables and in connected discourse. Other exercises introduced and contrasted the alveolar consonants [t], [dl, [n] , and [s] and the post-alveolar [J]. A series of tactile word learning exercises were also used to

STL-QPSR 1 / 1 994

highlight the spectral information provided by the aid. The text material used for the tracking sessions in this study was the English translation of "The Brothers Lionheart". This was felt to be of an appropriate level of difficulty.

Training and testing procedure The test conditions for this study were the same as those outlined for Study 1. The subject was seated in the audiometric test booth and wore headphones with noise

I masking at a level sufficient to ensure that he could hear neither the speaker's voice nor 1 any acoustic output from the vibrators.

All the training and testing in this study was carried out by the first author. Prior to 1 the start of the training and testing period, the subject took part in a study which used the KTH speech tracking procedure to compare lipreading of conversational speech and clear speech (see Study 3). A total of ten 5-minute traclung sessions were provided 1 by the author in each condition. These sessions were conducted with lipreading supplemented by speech LPF at 250 Hz.

The subject received a total of 21 testing and training sessions over a period of approximately one and a half months. Each of these sessions lasted around one hour, and consisted of approximately equal periods of analytic training exercises and speech traclung. In each session at least 2 x 5-minute tracking sessions were administered in both the lipreading alone and the lipreading plus the Tactaid VII conditions. Because it was initially felt that the tracking materials might prove overly difficult, it was decided to supplement the visual signal with auditorily presented speech LPF at 250 Hz. This was discontinued after the fifth session, and the remaining tracking sessions were presented via lipreading alone or lipreading plus the Tactaid VII.

Results There were, in all, 25 (2 x 5-minutes) tracking sessions presented in each of the two sensory conditions over the course of the study. This represents a total of 250 minutes in each condition. As in Study 1 the data were analysed in blocks of ten 5-minute tracking sessions for each condition. The results of this analysis are shown in Figure 7.

The subject's mean unaided and aided traclung rates for the entire study were 33.5 wpm and 39.5 wpm, respectively. The mean unaided and aided ceiling rates were very similar overall at 72.4 wpm and 73.8 wpm, respectively. It should be noted, however, that the ceiling rate for lipreading alone is slightly lower in Sessions 16 - 20 and 21 - 25. The mean proportions of blocked words for the aided and unaided lipreading conditions over the course of the study were 0.30 and 0.23.

There is a clear superiority for the aided condition for the tracking rates obtained in the last 20 testingltraining sessions - that is, those sessions where the subject was forced to rely on lipreading alone or lipreading supplemented by the Tactaid VII. In the sessions where auditorily presented speech LPF at 250 Hz was provided to the subject, his tracking scores were about the same in both test conditions. In Sessions 6 - 10 the advantage in the aided condition was 6.5 wpm. A similar advantage (5.9 wpm) was found in Sessions 11 - 15. The differences between aided and unaided lipreading in Sessions 16 - 20 and 21 - 25 were 6.6 wpm and 9.5 wpm, respectively.

STL-QPSR 111 994

1-5 6-10 11-15 16-20 2 1-25

Souion no.

Propodion d Mocked words

1-5 6-10 11-15 1620 21-25

S e a n no.

30

23

10 bpreadlng

n + Tactaid

1 repeat

I Seuion no. I( k v ~ n no. II Souion no.

Fig. 7. The tracking results for the subject in Study 2 for materials presented via lipreading alone (filled bars)and lipreading plus the Tactaid VII (unfilled bars). Note that in Sessions 1 - 5 the subject was also receiving speech low-pass-filtered at 250 Hz via audition. For a detailed explanation of this figure see the legend for Figure 3.

2 repods 3 repeats

STL-QPSR 1 / 1994

The proportion of blocked words for the unaided and aided conditions, respectively, over the last twenty sessions were: Sessions 6 - 10: 0.37, 0.27; session 11 - 15: 0.36, 0.28; session 16 - 20: 0.32, 0.25; session 21 - 25: 0.32, 0.21. The most strilung difference between the two presentation conditions was the number of words which were repeated twice and then shown on the LED display. The mean number of words displayed in a tracking session in the unaided and aided conditions, respectively, were: sessions 6 - 10: 10.4, 8.0; sessions 11 - 15: 10.8, 8.9; sessions 16 - 20: 8.7, 5.9; sessions 21 - 25: 9.0, 5.3.

Discussion The results of this study show that the subject had learned to effectively use the Tactaid VII as an aid to lipreading. The mean advantage in traclung rate of 6.0 wpm for aided lipreading over the course of the study represents an improvement of 17.9% over lipreading alone. The largest improvement was in the last block of testingltraining sessions, where the aided traclung rate of 41.0 wpm represented an improvement of 30.1 % over that obtained in the unaided condition (3 1.5 wpm).

I Although there are small differences in the ceiling rates for the two conditions over

tracking sessions 16 - 25 this does not seem to have been an important factor in the subject's overall better performance in the aided condition. The reduction in blockages I in the aided condition seems to have been of far greater significance. This is most apparent in the number of words which had to be presented via the LED display. Across the study, the mean number of words per session which had to be shown on the LED display in the unaided condition was 8.7. The mean number of words per session for the aided condition was 6.5. This represents a reduction in the number of words which had to be shown in their written form of around 25%.

Although this study also suffers from the obvious deficiency of having only one subject, his performance supports the contention that specialised training is required to take advantage of the Tactaid VII's complex display. The analytic training exercises provided were specifically designed to introduce the subject to the general characteristics of the tactile patterns presented by the aid. As a result, the subject became aware of the tactile patterns for the extreme vowel positions, nasality, stops and sibilants. Testing of the subject's abilities throughout the training program indicated that he was able to reliably identify these general features via the tactile aid alone (Plant, 1994).

The use of LPF speech in the first five testingltraining sessions might also have provided the subject with the opportunity to more easily assimilate the information provided by the aid. The subject was able to compare the visuallauditory signal with the visualltactual signal, and this may have been a critical factor influencing his later performance. Such a technique might also prove to be useful in introducing this and other complex tactile aids to deaf people. Potential users of tactile aids will probably not be able to benefit from LPF speech, but the use of highly redundant or very familiar materials might have the same effect. The aim in the introductory phase should be to provide the new aid user with experiences which are sufficiently easy that they allow herlhim to attend closely on the aid's display. The use of complex materials

STL-QPSR 111 994

at this point may serve to distract the user's attention from the aid's display, and lead to its eventual rejection.

Finally, the study supports the contention that, although tracking is a very important part of a training program for tactile aids, other forms of training, especially analytic exercises, also need to be provided. This is probably especially true for relatively complex tactile displays such as the Tactaid VII and the Tickle-Talker (Alcantara et al., 1990). It should be pointed out, however, that the analytic training program provided for one aid may differ significantly from that provided for another. The specific contrasts presented will obviously depend on the information provided by the individual aid. This implies that people developing training programs for a specific tactile aid should have a detailed knowledge of its performance characteristics.

Study 3 - Introduction A study by Picheny et al. (1985) showed the importance of clear speech for auditory speech reception by hearing-impaired people. Three male talkers were recorded producing sentences conversationally and clearly. In the clear speech condition the talkers were instructed to "enunciate consonants more carefully and with greater effort ....., and to avoid slurring words together" (Picheny et al., 1985; p. 97). The recorded conversational and clear sentences were then presented to a group of five hearing- impaired listeners in a variety of listening conditions. The results obtained showed an average increase in intelligibility resulting from clear speech of 17 percentage points. Subsequent acoustic analyses of the clear and conversational speech (Picheny et al., 1986) revealed a number of differences between the two speaking styles. When the talkers were attempting to speak clearly their average spealung rate was around half that found for conversational speech. Clear speech was characterised by more and longer pauses, and increased syllable and segment durations. Other changes in clear speech included a decrease in vowel modification and the release of stop consonant bursts.

The benefits of clear speech for lipreading reception have also been demonstrated. In a summary of published research, Lesner (1988) reported that characteristics which enhanced a talker's lipreadability included "a slightly slower-than-normal spealung rate, precise articulation ....... and inclusion of appropriate pauses" (Lesner, 1988; p. 96).

Lesner (1988) also cites a study by Witter-Merithew & Siple (1985) which found that talkers who were difficult to lipread could be improved with training. They reported improvements in lipreading intelligibility as great as 22% after training.

These studies indicate that changes in speaking style can lead to changes in a hearing-impaired person's auditory and visual speech perception performance. The current study investigated the effects of speaking style changes on speech traclung performance. The KTH speech tracking procedure offered the opportunity to examine not only changes in tracking rate resulting from changes in speaking style but also the effects on such related parameters as ceiling rate and the proportion of blocked words.

STL-QPSR 111 994

Method Subjects The subjects were those used in Studies 1 and 2 of this report. In summary, both subjects were normally hearing, Subject one was a female native speaker of General Australian English. Subject two was a male native speaker of Swedish who spoke English as a second language.

Text material The text used in this study was the English translation of Astrid Lindgren's "The Brothers Lionheart". I

Procedure The testing conditions were the same as those used in Studies 1 and 2. The subject was seated in an audiometric test booth and observed the speaker through a glass window. The subject wore headphones which provided sufficient noise maslung to ensure that slhe was unable to hear the speaker's voice or, where appropriate, the acoustic output of the Tactaid VII's vibrators.

The talker in this study was again the first author. Tracking sessions were presented using two different speaking styles - clear and conversational. In the clear speech condition the talker attempted to carefully articulate each word in the segment presented for identification. If a blockage occurred, the speaker would repeat the word(s) using the same spealung rate and style. In the conversational condition the speaker attempted to produce speech using normal articulatory patterns. If a blockage occurred, the speaker attempted to repeat the word(s) at the conversational speaking rate. The speaker was able to monitor his speaking style by observing his reflection in the glass window of the audiometric test booth. This was especially useful in ensuring that clear speech was produced with appropriate articulatory patterns.

Subject 1 was presented with clear and conversational speech in two sensory conditions. Ten test sessions were conducted using lipreading plus the Tactaid VII. A total of 20 x 5-minute traclung sessions was presented for both clear speech and conversational speech.

The second sensory condition used with Subject 1 was lipreading alone. Again, a total of 20 x 5-minute tracking sessions were administered using both clear speech and conversational speech.

In each testing session the subject was administered 2 x 5 minute tracking sessions

I with clear speech, and 2 x 5 minute tracking sessions with conversational speech. The order of presentation of the two speaking styles was changed from test session to test session to minimise any possible order andlor fatigue effects.

The sensory condition used with Subject 2 was lipreading plus auditorily presented speech LPF at 250 Hz. This condition was chosen as it was felt that this subject, as an English as a second language speaker, would experience excessive difficulty with conversational speech presented via lipreading alone. This subject received a total of 10 x 5-minute tracking sessions for each of the two spealung styles.

STL-QPSR 11 1 994

1-5

Session no.

I - LC (Clear) I I + LC (Conv.) -1

Proportion of blocked words

1-5

Session no.

1 repeat

Session no.

2 repeats

1-5

Session no.

3 repeats

Session no.

Fig. 9. The tracking rates for Subject 2 in Study 3. The conditions tested were clear speech (filled bars) and conversational speech (unfilled bars). All sessions were presented via lipreading supplemented by speech low-pass-filtered at 250 Hz via audition. For a detailed explanation of this figure see the legend for Figure 3.

STL-QPSR 1 / 1994

in speaking rate by the receiver. It is interesting to note that Picheny et al. (1986) found speaking rates in the range 160 - 200 wpm for conversational speech and 90 - 100 wpm for clear speech. When the time for the receiver to repeat the segment is included Picheny et al.'s (1986) results appear to be very similar to the ceiling rates found in the present study.

Speaking clearly also serves to greatly reduce the number of blockages that occur in the traclung session. For the lipreading alone and lipreading plus the Tactaid VII conditions, Subject 1's proportions of blocked words for clear speech were 66.6% and 56.8% less than those found for conversational speech. The difference was even more ! strihng for Subject 2, whose proportion of blocked words in the clear speech condition was 77.3% less than that found for conversational speech.

The decline in traclung rate which accompanies clear speech would seem to be off- set, to a large extent, by the reduction in the number of blockages which occur in the tracking session. The true extent of this reduction in blockages can be seen in the results for Subject 2. The average number of words repeated once, twice and three times in clear speech were 6.8, 1.4 and 2.1, respectively. This represents an average of 15.9 repeats per session. The average results for conversational speech show 32.8 words repeated once, 7.18 repeated twice and 7.6 words repeated three times. This gives a total number of repeats per tracking session of almost 70 repeats per 5-minute session which is around 14 repeats per minute. The reduction in tracking rate was only 7 wpm but the number of repeats was reduced from around 14 per minute to approximately 3 per minute.

Both subjects, when asked for their opinions of the two speaking rates, gave a similar response. Not unexpectedly they reported that they found it much easier to lipread clear speech, but they did have some reservations about speech presented in this way. Both said that it was extremely difficult to remember long segments, and commented that by the time a segment had come to an end they had forgotten its beginning. It should be remembered, at this point, that a maximum segment length of 11 words had been set for the text used in this study. The subjects felt that there must be some compromise rate between these two extremes which would give optimal performance. This is an area which warrants further study.

It is quite possible, however, that over a number of traclung sessions a particular senderlreceiver pair will arrive at a good approximation of the ideal transmission rate. Speakers tend to modify their productions to meet the specific needs of a receiver. Thus, if the receiver is experiencing difficulty the speaker will slow down and articulate more clearly. If the receiver is then able to identify most of what is said then the speaker will gradually increase herlhis speaking rate to the maximum rate at which low-error transmission is possible. Over time the sender will become aware of the optimal speaking rate and the optimal repairlrepeat rate for the individual receiver. The speaking rate used for repeats will probably be considerably slower than the overall speaking rate as senders try to provide maximum information to overcome a blockage.

Both receivers also commented that one of the most difficult aspects of the conversational speech was that the repeats were given at the same rate as the initial presentation. In most normal communication situations the speaker will repeat words creating problems more slowly. As the sender in this study, the author found it

I

STL-QPSR 1 / 1 994

extremely difficult and unnatural to maintain conversational speed for repeats. Finally, the subjects both reported that it was often difficult to pick up word boundaries in conversational speech. A slightly slower than normal speaking rate (a lower ceiling rate) may allow effective segmentation without adversely affecting the overall traclung rate.

The results of this study indicate that care needs to be taken to ensure that similar ceiling rates are used in tracking sessions comparing different conditions such as aided and unaided lipreading. For example, a rise in tracking rate could be related to a change in presentation rate rather than improved performance. The use of a system such as the KTH tracking procedure, providing measures of ceiling rate and blockages as well as tracking rate, can help ensure that observed changes in traclung rate are related to the receiver's performance, not that of the sender.

The results of the study may also be useful for clinicians who wish to provide advice on how the family members and friends of deaf people can best speak to them. Encouraging a slightly less than normal speaking rate, and experimentation with other speaking rates and styles when blockages occur may assist in the development of optimal speech patterns for a particular speakerlreceiver pair. Guided practice using tracking might also assist in the development of improved communication between the deaf person and hislher significant other(s).

Conclusion Live voice presentation of speech tracking will always involve some compromises compared to recorded materials. The KTH speech traclung procedure, however, does allow a high degree of control of a number of potential variables. The use of only one repair strategy, although unnatural, does eliminate to a large extent the problem of the "gifted" sender; that is the sender who is able to develop a wide repertoire of effective repair strategies. The results provided by the procedure provide valuable insights into factors underlying a subject's performance. Ceiling rate changes over time, for example, may reflect changes in performance which are not shown in the traclung rate. This information may be useful in developing more appropriate communication strategies for individual hearing-impaired people.

The KTH speech traclung procedure should also prove to be a very useful technique for clinical training. Modifications may be needed to suit the individual approach of therapists, but it does provide a basic framework for training sessions using speech tracking. Case studies represent a valuable source of information on aids and training approaches. The use of a standard procedure should allow better comparisons between such studies. The KTH speech tracking procedure is an important step towards better control of training and experimental studies, and warrants continued use and study.

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Boothroyd, A. (1987). "CASPER. Computer assisted speech perception evaluation and training". In: Proceedings of the 10th Annual Conference of the Rehabilitation Society of North America. Association for the Advancement of Rehabiltation Technology, Washington, D.C., pp. 734-736

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Cholewiak, R.W. & Sherrick, C.E. (1986). "Tracking skill of a person with long-term tactile experience. A case study", J. Rehab. Res. & Dev. 23, pp. 20-26.

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Osberger, M.J., Johnson, D.L. & Miller, J.D. (1987). "Use of connected discourse tracking to train functional speech skills", Ear & Hear. 8, pp. 3 1-36.

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Picheny, M.A., Durlach, N.I. & Braida, L.D. (1985). "Speaking clearly for the hard of hearing. I. Intelligibility differences between clear and conversational speech", J. Speech & Hear. Res. 28, pp. 96-103. ! Picheny, M.A., Durlach, N.I. & Braida, L.D. (1986). "Speaking clearly for the hard of hearing. 11. Acoustic characteristics of clear and conversational speech", J. Speech & Hear. Res. 29, pp. 434-446.

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Pichora-Fuller, M.K. & Cicchelli, M. (1986). "Computer-aided speechreading training - CAST". Owners Manual. University of Toronto Department of Otolaryngology, Mount Sinai Hospital.

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Verrillo, R.T. & Gescheider, G.A. (1992). "Perception via the sense of touch". In: I. Summers, ed., Tactile Aids for the Hearing Impaired. London: Whurr, pp. 1-36.

Weisenberger, J.M., Broadstone, S.M. & Saunders, F.A. (1989). "Evalaution of two multi- channel tactile aids for the hearing impaired". J. Acoust. Soc. Am. 86, pp. 1764-1775.

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