. m- ....., -a-..-.._...,---—-M THE EFFECT OF SPEAKER AND PRESSURE‘VARIATION' “ ' 3 on THE VIBROTACTILE‘IRECEPTION 0F SELECTED . SPOKEN ENGLISH PHONEMES. ’ Thesis for the Degree of Ph‘. D. MICHIGAN STATE UNIVERSITY JERRY MITCHELL HIGGINS 1971 |II|IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 3 1293 104311 Y-Hhiul This is to certify that the thesis entitled THE EFFECT OF SPEAKER AND PRESSURE VARIATION ON THE VIBROTACTILE RECEPTION OF SELECTED SPOKEN ENGLTSgby PHONEMES presen Jerry Mitchell Higgins has been accepted towards fulfillment of the requirements for Doctor of Philosophy degreein Audiology and Speech Sciences ‘Qf'flfli’ 7d i/Méor /prof3s?5/1 Date July 111, 1971 0-7639 Q91; ‘2’ 03;} E e4] to. '7, ’33 m 1*:fl‘ 1“: 0‘ ' w T Engn sh 1.9.. a: and a p] were se] Each su Consist finger“; lever m ”Define Vere no tributab tion' Se. all? 01' t; 31ml the 0.05 | the Spea. and ”111: ABSTRACT THE EFFECT OF SPEAKER AND PRESSURE VARIATION ON THE VIBROTACTILE RECEPTION OF SELECTED SPOKEN ENGLISH PHONEMES By Jerry Mitchell Higgins Four subjects responded to tape recordings of five English phonemes spoken by four General American speakers, i.e.. an adult male. an adult female. a pre-adolescent male. and a pre-adolescent female. The experimental phonemes were selected from those used in a 1970 study by Haas. Each subject responded to each speaker under five conditions consisting of different levels of contactor pressure on the fingertip. The transmission system used a single, canti- lever mounted transducer, the Clevite PZT-BB Bimorph. Analysis of variance indicated that for four of the experimental phonemes, i.e., /u/, A\/. A:/. and /n/, there were no significant effects on phoneme threshold levels at- tributable to speaker variation, contactor pressure varia- tion, sex of the receiver (subject). or interactions between any of the preceding factors. For the fifth phoneme, /b/, no significant effects were found for pressure or sex varia- tions or any interactions. but a speaker effect was noted at the 0.05 level of significance. Examination indicated that the speaker effect was a threshold dichotomy between adults and children. The explanation for this dichotomy was not appareI stable female relatit tactile cent fe populat recepti fit as Althoug highly might b lute th; 19‘7813. out as 1 concerne that 15 or Minna the pres BOWEVer, threShol of the p terei to r0110win Jerry M. Higgins apparent; but it was noted that the phoneme /b/ was less stable than the others, particularly for the pre-adolescent female speaker. It was noted that the phoneme /b/ is a relatively weak sound. both in terms of speech power and tactile rank. It was hypothesized that, if the pre-adoles- cent female speaker should prove to be representative of the pOpulation of pre-adolescent female speakers. vibrotactile reception of the phoneme /b/ may not be of significant bene- fit as a supplement to visual reception of that phoneme. Although this would not be of critical importance for the highly visible /b/, it was suggested that the same pattern might be true of other phonemes not tested in this study. Excellent agreement was noted among subjects' abso- lute threshold scores for all speakers at all pressure levels. Although no one pressure or pressure range stood out as being preferable insofar as objective analysis was concerned. subjective evaluations by the subjects indicated that 15 grams of contactor pressure on the fingertip, plus or minus 5 grams. was to be preferred. Comparison of mean thresholds obtained by Haas and the present study showed a significantly high correlation. However, whereas Haas obtained a consistent slope in the thresholds recorded for the experimental phonemes. results of the present study had the three experimental vowels clus- tered together near the same threshold. with the consonants following a lepe similar to that yielded by Haas' subjects. It was noted that means in the present study correlated even more I phone: this I that t the pi except slope Althom son fo: to be 1 morph 1 the 31m study, in the j Jerry M. Higgins more highly with the relative speech power levels of the phonemes than was so in Haas' study, although Haas found this correlation to be significant. Further. it was noted that thresholds for the phonemes were generally poorer in the present study than those obtained by Haas, with the exception of the threshold for'flo/. Various possible explanations for the differences in 810pe and threshold shown by the two studies were discussed. Although it was not possible to state specifically the rea- son for the discrepancies, the most obvious potential cause to be investigated seemed to be possible differences in Bi- morph responses to speech signals. It was pointed out that the Bimorph used by Haas was damaged subsequent to his study. and a different Bimorph of the same type was utilized in the present study. THE EFFECT OF SPEAKER AND PRESSURE VARIATION ON THE VIBROTACTILE RECEPTION OF SELECTED SPOKEN ENGLISH PHONEMES BY Jerry Mitchell Higgins A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Audiology and Speech Sciences 1971 ‘—__ — _ __ .— 4- . c —§ .—.. _. ..—___ ~—. '__. A .— .— __ ._—.._ _ .— page a had a j to do ‘ is due invest: Judith 1Ytica: "1th el senemt Patrici and Er. ACKNOWLEDGMENTS New ways of expressing appreciation on the printed page are hard to come by. Nevertheless. many people have had a part. either directly or indirectly. in enabling me to do this study. To all of them, a special note of thanks is due. With regard to those directly involved in this investigation, I was most fortunate to be able to tap Dr. Judith Frankmann's knowledge of statistical design and ana- lytical techniques, as well as Mr. Donald Riggs' expertise with electronic equipment. Both were very helpful and generous with their time. Equally cooperative were Mrs. Patricia Bainbridge. Miss Ellen Smitley, Mr. Robert Lindberg. and Mr. Jerod Goldstein, who served as my subjects. I am particularly grateful to Dr. Herbert J. Oyer, who served as chairman of my committee. From the day of our first interview. when I came to explore the possibility of embarking on a new career, I have found Dr. Oyer easy to approach, liberal with his time. and sincerely interested in helping me develop professionally. The same should be said of Dr. Leo V. Deal. Finally, I want to thank my wife. Janet, and my children, Jeff and Jill. Not only has Janet provided a 11 _m—_—_____———_.__~M~__AA_—_— pleas: with 1 and t1 Jill's tience physic attent pleasant home environment and constant moral support. but, with regard to this specific study, her editorial assistance and typing skills have been a great help as well. Jeff and Jill's contribution has been primarily in the form of pa- tience with parents who were too busy, during the actual physical preparation of this manuscript. to give them the attention they warranted. iii l lull.‘ l [| l l 1[I'I|1 [ Ill {II I [e [‘l I‘ ll .III‘ Ill IV, TABLE OF CONTENTS LIST OF TABLES O O O O O O O O O 0 O O O O O O O O O 0 LIST OF FIGURES O O 0 O O O O O O O O O O O O O 0 O 0 LIST OF APPENDICES O O O O O O O O O O O O O O O O O 0 Chapter I. II. III. IV. INTRODUCTION 0 O O I O O O O O O O O O O O O 0 Statement of Problem and Purpose of Study. Importance Of the StUdy e e e o e e e e e DefinitionSoe one. access. Organization of the Research Project . . . REVIEW OF THE LITERATURE . . . . . . . . . . . IntrOdUCtion e e e e e e e e e e o e e e e 0 History of Investigations into Cutaneous Speech Reception . . . . . . Research Specifically Pertinent to this St'lldyeeeeeeoeeeeeeeeeeeo SUBJECTS, MATERIALS, EQUIPMENT, AND PROCEDURES. SUbJGCtB e e e o o e e e e e o e e e e e e 0 Materials 0 e e e e e e e e o e e o e e e 0 Equipment 0 e e e e o e e e e e e e e e e 0 Procedures 0 e o e o e e e e e e e e e e e 0 Experiment I e e e e e e e e e e e e e 0 Experiment II o e e e e e e e e e e e e e hperiment III e e e e e e e e e e e e 0 Experiment IV 0 e e o e e e e e e e e e 0 Experiment V . . . . . . . . . . . . . . RESULTS AND DISCUSSION 0 e o e e e e e e e o 0 Effects of Speaker, Contactor Pressure, and Sex of Receiver . Phoneme /U./ o e e e e e e e e e e e e e e Phoneme //\/ e e e e e e e e e e e e e e e Phoneme /O./ o o e e e e e e e e e e o e e Phoneme /n/ e e e o o e e e o e o e e e o Phoneme /b/ iv V111 [lllll‘tlll’ll.[[’lllllllllilllll[ l, 14 Agreement Among Subjects' Absolute Threshold Scores . Agreement Between Mean Thresholds: Haas and Present Study . Discussion . V. Summary Conclusions Recommendations for Further Research BIBLIOGRAPHY APPENDICES 0 SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS 56 62 72 72 76 78 82 Ill l I [I III‘ III I [[I'l‘ l [’l'llll‘ .[ .E I ll [Ill [ l l l 10, 11. 12. 13. 14. 15. Table l. 2. 3. 7. 8. 9. 10. 11. 12. 13. 1b. 15. LIST OF TABLES Page Phoneme /u/. Analysis of Variance: ThreShOld Data 0 o o c o o o o o o o c o o o o o “1 Phoneme /A/. Analysis of Variance: ThreSh°1d Data 0 c o o o o o o o o o o o o o o o 4“ Phoneme fi1/. Analysis of Variance: ThreShOId Data 0 o o o o o o o o c o o o o o o o a? Phoneme /n/. Analysis of variance: ThreShOId Data 0 o o o o o c o o o o o o o o o . 50 Phoneme /b/. Analysis of variance: Thr68h01d Data 0 o o o o c o c o o o o o o o o o 53 Agreement Among Subjects' Absolute Thresholds: 5 Grams . . . . . . . . . . . . . . 57 Agreement Among Subjects' Absolute Thr38h01d8‘ 10 Grams o c o o o c o o o o o o o o 58 Agreement Among Subjects' Absolute ThreShOIdSI 15 Grams c c c o o o c o o o o o o o 59 Agreement Among Subjects' Absolute Thresholds: 20 Grams c o o o o e c o o o o o o o 60 Agreement Among Subjects' Absolute ThreShOIdSI 25 Grams c o o o o o o o o o c o o o 61 Mean Threshold Agreement: H333 and Present StUdy o o o o c o o o o o o o o 62 Absolute Thresholds for Emperimental Phonemes: Haas and Present Study . . . . . . . . 69 Haas' Thresholds for English Phonemes . . . . . 82 A Comparison of Means for Four Versus Eight Thresholds O O O O I I O O O O O O O O I O O O O 8 9 Relative Intensities (Speech Powers) of Phonames o o o c o c o o o o o o o o o o o e o o 90 V1 j[{l[[([({((l[i[[[[l[{1 Ill. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 3o. 31. 32. 33. 34. 35. 36. 37. Five Speaker Orders 0 o o o o 0 Speaker Order Assignments to Subjects Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject One Raw Data: 5 Grams . One Raw Data: 10 Grams One Raw Data: 15 Grams One Raw Data: 20 Grams One Raw Data: 25 Grams Two Raw Data: 5 Grams . Two Raw Data: 10 Grams Two Raw Data: 15 Grams Two Raw Data: 20 Grams Two Raw Data: 25 Grams Three Raw Data: 5 Grams Three Raw Data: 10 Grams Three Raw Data: 15 Grams Three Raw Data: 20 Grams Three Raw Data: 25 Grams Four Raw Data: 5 Grams Four Raw Data: 10 Grams Four Raw Data: 15 Grams Four Raw Data: 20 Grams Four Raw Data: 25 Grams 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 LIST OF FIGURES Figure 7. 8. 9. 10. 11. 12. 13. 11+. 15. Photograph of Hand Properly Positioned in Bimorph Housing . . . . . . . . . Phoneme /u/. Each Speaker Versus Subjects at All Pressures . . . . Phoneme /u/. Each Speaker Versus Sexes at All Pressures . . . . . Phoneme [k/Q Each Speaker Versus Subjects at All Pressures . . . . Phoneme AA/. Each Speaker Versus Sexes at All Pressures . . . . . Phoneme fla/. Each Speaker Versus Subjects at All Pressures . . . . Phoneme [a/. Each Speaker Versus Sexes at All Pressures . . . . . Phoneme /n/. Each Speaker Versus Subjects at All Pressures . . . . Phoneme /n/. Each Speaker Versus Sexes at All Pressures . . . . . Phoneme /b/. Each Speaker Versus Subjects at All Pressures . . . . Phoneme /b/. Each Speaker Versus Sexes at A11 Pressures . . . . . All Both All Both All Both All Both All Both Overall 3: Speaker Versus Phoneme . . . Absolute Thresholds for Experimental Phonemes: Haas and Present Study Cantilever Mounted Bimorph (PZT-SB) . . Apparatus for Housing Bimorph (PZT -5B) V111 Page 32 #2 “3 45 #6 #8 49 51 52 54 55 65 69 8h 85 16 17. . I V I [if [tI‘l‘ti‘iIl‘tt-ll [ll 16. Schematic Diagram of Stimulus Transmission System, Test Room and Adjoining Control Room . . 86 17c SUbJeCt ThreShOId Data Form 0 o o o o o o o o c 95 ix 1{|[|l\[.{ [.l [‘ll‘l-‘l V LIST OF APPENDICES Appendix Page 1. Haas' Mean Vibrotactile Thresholds for Spoken English Phonemes . . . . . . . . . . . . 82 2. Characteristics of the Bimorph . . . . . . . . 83 3. A Comparison of Methods for Determining Absolute Vibrotactile Thresholds . . . . . . . 88 4. Relative Intensities (Speech Powers) of Phonemescoo-00000000000000. 90 5. Response Characteristics of Recording Equipment . . . . . . . . . . . . . . . . . . . 91 6. Frequency Response Characteristics of the Tactile Stimulus Transmission System . . . . . 93 7. Subject Threshold Data Form . . . . . . . . . . 95 8. Equipment Calibration . . . . . . . . . . . . . 96 9. Order of Speaker Presentation . . . . . . . . . 98 10. Raw Data: Subject Threshold Responses 100 “AM F- m V“ PF ”W- —A__ A m into cept. appa: Of-he affli handi their CHAPTER I INTRODUCTION Various investigators through the years have looked into the possibility of utilizing the cutaneous sensory re- ceptors as an avenue of communication. An immediately apparent objective is to aid the deaf and profoundly hard- of-hearing in the understanding of speech, since those afflicted with the loss of a sensory modality are obviously handicapped and will benefit from more efficient use of their intact senses. Aside from the physically handicapped. Bliss (1963) suggests that others would also benefit if it should somehow prove possible to use the cutaneous channel for efficient communication. For example, with some of today's complex equipment the visual and auditory channels of the operator may easily become overloaded: it would be advantageous to have other avenues of communication available. Today's air- craft are a case in point. Pilots must be visually alert to a myriad of dials and gauges and auditorily receptive to various radio transmissions. Additional visual or auditory input might be impractical. whereas tactile stimulation might still prove useful. Further, for military and other purposes, it is sometimes necessary for communications to be re sy. pu] lim apps not the c 2 surreptitious: it would be most helpful if a small tactile communication system could be concealed on the body and any transmitted messages could be felt rather than seen or heard. In the 1920's it was thought that cutaneous speech reception could be used to circumvent totally the auditory system, and both mechanical vibrations and electrical 1m- pulses were used in experimental situations. Although limited success was achieved, investigators became increas- ingly more aware of difficulties to be overcome and the apparently inherent limitations of the cutaneous system. not the least of which is the skin's limited response within the critical speech range. Research continues and basic data are being accumu- lated. Still, little is known. As Geldard (1969) says: We are . . . dealing with a tissue that is equipped with overlapping neural networks that must be relatively unlimited in their information- processing potentialities. And what do we . . . know about these possibilities? Precious little. For one and a third centuries . . . we have period- ically tabulated and graphed two functions. the two-point limen and single-point localization. This. together with a modicum of very crude information concerning perception by graphesthesia and the re- curring discovery that appreciation of form tactu- ally is a practical impossibility in the absence of exploratory manipulations . . . constitute pretty much the full catalogue. Gibson (1968) underscores the need for more informa- tion when he states: Major progress in cutaneous communication re- quires knowledge of perceptual properties of touch. The presently limited nature of cutaneous communica- tion reflects the failure to make effective use of these properties. rather than reflecting any inherent SY’ be. de: thi has tile Was cutaJ bliss Which mecrja“ tion, 3 limitations of the touch sense. To find whether the cutaneous channels are effective for receiving more than simple, unidimensional warning informa- tion, or slow speech transliteration, it is essen- tial to determine the perceptual properties of stimuli varied systematically along temporal and spatial dimensions. Part of the difficulty in determining the cutaneous system's capability for the transmission of information has been due to the lack of adequately sophisticated vibratory devices. Continuing strides are being made in resolving this problem: but as Bliss (1963) states, ”no device as yet has fully utilized all the informational capacity of the tac- tile and kinesthetic senses.” This is as true today as it was when Bliss made the comment. Attempts to transmit specific information.by means of cutaneous stimulation have taken a number of different forms. Bliss (1963) suggests that they can be subdivided into those which depend on simple contact or pressure. those which use mechanical vibration, those which use electrical stimula- tion. and those which stimulate by use of an air jet. Braille is an example of a communication medium which utilizes simple contact or pressure. Several machines have been developed which automatically transmit braille to the fingertip. There have been various methods devised which utilize mechanical vibration. Gault, in the 1920's, attempted to apply speech energy directly to the skin. As was previously mentioned, whereas some limited success was achieved with versions of Gauit's Teletactor, no practical communication 3373 cut and: pos: to v defi spec supp. rehal to a forms that ‘ Quenci tionec What t neous L: system has as yet evolved. and it is now generally held that cutaneous receptivity cannot be used as a substitute for auditory receptivity. However, this does not rule out the possibility that it might serve as an effective supplement to whatever limited information might be received through a deficient auditory system. Although he has made very little specific information available, Guberina (1965) utilizes supplementary tactile information in his approach to aural rehabilitation. having his students grasp a device similar to a bone conduction receiver. Part of the problem in attempting to interpret in- formation transmitted by means of mechanical vibration is that the cutaneous system responds efficiently only to fre- quencies within a limited range, as has already been men- tioned. Contemporary authorities disagree as to precisely what this range is. although many agree that efficient cuta- neous response is limited to those frequencies at or below the lower end of the critical speech range. For example, Von Bekesy (1967) states that the range spans 50 to 500 Hz, whereas Kringlebotn (1968) would locate the upper limit at about 800 Hz. However, some research contradicts this. Russian studies have shown responses up to 2.000 Hz which have potential practical usefulness, according to Sokol- yanskiy (1968). In addition. it is difficult to distinguish between a change in intensity and a change in frequency. Some have sought to circumvent these problems by transposing the th tex is son bee I l‘ l I l ‘ II I | EU“ ~ det be : and it i orge stil 5 speech frequencies to a lower range more compatible with cutaneous sensitivity. Others have used many small vibra- tors in such a way that the filtered but otherwise unal- tered speech frequencies were mapped into spatial locations. Many variations on these types of themes have been developed and investigated, with varying degrees of success. Other approaches have utilized other types of stim- uli. including air jets and electricity. Researchers at the Massachussetts Institute of Technology have experimented with small air jets, as in handwriting on the skin. Cuta- neous stimulation with electricity has been hampered by the small dynamic range between the threshold of feeling and the threshold of pain, with the consequent need to avoid pain presenting definite problems. The preceding overview serves to underscore the fact that many means of utilizing the cutaneous channel as a sys- tem of information transmission are being investigated. As is apparent, even the optimum method of stimulating the somesthetic senses for information transmission has not yet been agreed upon. Once that has been discovered, the opti- mum procedure for coding the desired message remains to be determined. Bliss (1963) contends that "it will probably be necessary to develop more complex information-processing and coding methods in order to transform the message so that it is better matched to the channel and the human perceptual organization abilities.” To this end. basic research is still essential. Therefore, investigators continue to tioz more dete be 1. 6 investigate the frequency and intensity ranges to which the skin will best respond. Further, contemporary researchers are seeking to determine the most sensitive physiological locus for the stimulator. the response of cutaneous recep- tors to multiple versus individual stimuli, the optimum size of the contactor, and other related areas. The investiga- tions have encompassed both pure tones and speech. With more carefully controlled investigations. much more has been determined about tactile reception. Still, much remains to be learned. Statement of Problem and Purpose of Study, In 1970, at Michigan State University, Haas sought "basic information relative to the functional utility of cutaneous reception of the speech code." Part of the basic information he obtained was the intensity level needed to reach vibrotactile absolute thresholds for each of the English phonemes. His results are contained in Appendix 1 of this study. In establishing these thresholds. Haas used one adult male General American speaker to provide the stim- ulus materials. As he pointed out in his final chapter, "it is clear that the future success of tactile reception of oral speech is contingent upon knowledge of the variability due to speaker effects.” Therefore. the first goal of the present study will be to duplicate Haas' experimental situa- tion and determine whether or not speaker variation affects the threshold level for phonemes. 7 Following the advice of Dr. Frank A. Geldard at the Princeton University Cutaneous Research Laboratory, Haas chose to utilize the piezoelectric ceramic Bimorph developed and made commercially available at the Clevite Corporation of Bedford, Ohio. as his tactile stimulus transmission sys- tem. The reasons he cited included the Bimorph's ”simplic- ity of design, broad frequency response characteristics, almost instantaneous 'on-time' of transmitted signals, and excellent manageability for coupling with the skin.” (See Appendix 2 for further information about the Bimorph.) At the advice of Dr. C. E. Sherrick, an associate of Geldard's, Haas elected to use a mechanical contactor pressure of 15 grams (1 5 grams) beyond that point where the subject first indicated he could feel the tip of the contactor. However, as Haas pointed out, no literature speaks to "the effects of varying amounts of applied pressure when employing canti- lever mounted vibrators.” On the other hand, using other types of vibrators, Verillo (1966) has established the fact that increased contactor pressure results in decreased thresholds for pure tones. It is likely that this is true for speech stimuli also. Obviously, if vibrotactile stimu- lation is ever to be used for the transmission of oral speech, it is essential that information be available with regard to how the cutaneous threshold is affected by varia- tions in contactor pressure. Further, a determination of the optimal range of pressure should be made. Therefore, the second goal of the present study will be to determine 8 whether or not variation in contactor pressure influences the threshold level for phonemes, and which pressure or range of pressures is optimal. Weinstein (1968) has established that, for pure tones, women demonstrated greater sensitivity to pressure than men. The third goal of the present study will be to determine whether or not the sex of the receiver (subject) affects the threshold level for phonemes. Finally, it will be of interest to note whether or not there are any interactions resulting from the manipula- tion of the speaker-pressure, speaker-sex of subject, or pressure-sex of subject variables. This will be the fourth question in the present study. To recapitulate, this study will seek to duplicate the basic experimental conditions of the Haas study. The exceptions will be the number of speakers and the number of contactor pressures used. Given the restrictions of the Haas experimental conditions, the purposes of the study will be to answer the following questions: 1. Does varying the speaker affect the threshold level for phonemes? 2. Does variation in contactor pressure influence the threshold level for phonemes? 3. Does the sex of the receiver (subject) affect the threshold level for phonemes? 9. Are there interactions attributable to manipu- lation of the speaker-pressure, speaker-sex of subject, or pressure-sex of subject vari- ables? III-{[[llAll‘l {l1 ' 111' 9 As implied previously, in seeking answers to the above questions, it was decided to reproduce the conditions of that portion of the Haas study which related to the deter- mination of vibrotactile thresholds. This decision specifi- cally influenced the method of preparation of stimulus mate- rials, the tactile stimulus transmission system used, and the methods employed in obtaining subject responses. Importance of the Study As has been pointed out, it is generally agreed that cutaneous stimulation cannot be expected to substitute for the auditory reception of ongoing speech. On the other hand, various sources do claim that the cutaneous channel can con- tribute significantly as a supplement to defective auditory reception. Assuming that this is true, it behooves one to discover those parameters of the cutaneous system which are of importance in the reception of speech signals. It seems apparent that the thresholds of phoneme reception would be among these important parameters. Likewise, it is clear that we need to know whether or not different speakers yield essentially the same results. It is to be expected that in- dividual subjects would vary somewhat, for purely physio- logical reasons, but it would be of interest to discover whether or not one sex is more sensitive to vibrotactile stimulation with speech sounds than is the other. It is recognized that different equipment and dif- ferent techniques might yield different results. It is 10 further recognized that the individual, isolated phoneme is an artificial entity insofar as ongoing speech is concerned. However, it is obvious that a beginning has to be made some- where. Geldard (1969) quotes Helmholtz as stating that ” . . . there is little hope that he who does not begin at the beginning of knowledge will ever arrive at its end.” The present investigator feels that Haas' study began at the beginning and was a step in the right direction, and that building on it is a logical next step. Definitions In that this study is an outgrowth and replication of the basic conditions of the Haas study, the same defini- tions have been adopted, wherein they apply, and a defini- tion for relative intensity levels has been added. The definitions are as follows: Vibrotactile stimulation: Vibrotactile stimulation refers to the specific treatment to which the skin receptors are exposed when acoustic energy is transduced by electro- mechanical means. Electromechanical transducer: The transducer of choice for this research was a piezoelectric ceramic mate- rial called a Bimorph. Geldard (Haas, 1970) stated that the Bimorph is the latest and most efficient transducer deve- loped for purposes such as Haas' and this study. It has virtually no “on-time" lag and responds to frequencies above 20,000 Hz. Its basic construction is a two ceramic plate sandwich-type structure. 11 Absolute threshold of detectability: The threshold of detectability for a specified signal is the minimum effective stimulus level of the signal that is capable of evoking a tactual sensation 50 percent of the time. In this case, the signals are selected English phonemes presented by the psychophysical method of limits. Psychophzsical method of limits: Underwood (1966) has described the psychophysical method of choice for the determination of absolute thresholds. For half the trials the stimulus is initially clearly present and then is de- creased gradually until the subjeet reports ”not present.” For the other trials the intensity is not of the magnitude to be perceived as present initially, and is increased grad- ually until the subject reports ”present." For each trial a threshold measurement is ob- tained, momentary as it may be. But an average of a series of trials would give a fair estimate of the value which is detected 50 percent of the time. For the purposes of Haas' research, each subject was given eight trials. Four of these trials were of the ascending order, and four of the descending order. His raw data for those phonemes selected to be used in the present study will by found in Appendix 3. For the purposes of the present research, each subject was given four trials, two each of the ascending and descending order. Phonemes: Phonemes are the basic linguistic units which, when combined, comprise words and sentences. Taken individually, they do not symbolize any object or concept. However, in relation to other phonemes they distinguish one 12 word from another (Denes and Pinson, 1969). Phonemes may be considered as speech sound families, with specific sym- bols (phonetic symbols) used to identify these families, with each symbol representing a group of 'slightly varying sounds that includes all of the variations which are per- ceived acoustically as the sound under consideration" (Judson and Weaver, 1965). Relative intensity levels: Fletcher (1953) estab- lished relative intensities for the various phonemes of English. Haas (1970) adjusted his experimental phonemes to conform to these intensities, plus or minus 2 dB. Likewise, the experimental phonemes recorded by the four speakers for the present study have been electronically adjusted to meet the same standards. FletCher's criteria, and the results of both Haas' adjustments and those of the present investigator may be found in Appendix h. Organization of the Research Report Chapter I has been organized to provide an intro- duction to the problem of the cutaneous reception of infor- mation. It includes a brief overview of the types of inves- tigations which have been conducted by previous researchers, and cites some of the problems which have been encountered, as well as their implications for tactile speech reception. A statement of the purpose and importance of the investiga- tion has been presented, together with definitions of terms used throughout the study. I [I I II I‘ll-I‘ll" T ’(l 13 Chapter II consists of a review of the literature related to the reception of vibratory speech stimuli by the cutaneous receptors. Chapter III contains a description of the subjects, the equipment used, procedures employed, and statistical design followed in the study. Chapter IV presents the results of the study with respect to the questions posed in Chapter I, together with a discussion of those results. Chapter V consists of a summary statement, conclu- sions drawn from the results of the study, and the implica- tions for further research. CHAPTER II REVIEW OF THE LITERATURE Introduction In his unpublished doctoral thesis, Haas (1970) has extensively documented the literature pertaining to inves- tigations into the response of cutaneous receptors to pure tone and speech stimuli. Although this information is very interesting and informative, much of it is not immediately pertinent to the present study and will not be formally repeated here. However, it is appropriate to briefly sum- marize Haas' findings. For example, with regard to compar- isons between auditory and tactile channels, he indicated that various investigations showed that: 1. Although there are many similarities between taction and audition, there are so many differences that taction cannot be considered as a substitute for audition. 2. The tactile modality has its counterparts for the auditory concepts of intensity, frequency, duration, traveling waves, localization, recruitment, and neural inhibition. 3. The information transmitted to the nervous sys- tem by the tactile modality, with regard to the aforemen- tioned concepts, is "crudely molar compared to the sophisti- cated molecular capability of the human ear.” 1n 15 4. The limited capability of the skin to receive frequencies within the critical speech range is of primary significance. Looking at variables influencing vibrotactile thresholds, Haas noted that: 1. Most researchers agree that the fingertips are the most sensitive to vibrotactile stimulation of the various body sites tested. 2. Thresholds decrease in direct proportion to the extent of applied pressure or protrusion by the contactor. 3. Multiple simultaneous vibrator stimulation results in masking effects causing significant threshold elevations. 4. Large contactors result in an inverse relation- ship between the vibrotactile threshold and the contactor area, yielding a U-shaped curve with maximum sensitivity at 250 Hz, whereas when the contactors are small the threshold curves are independent of frequency, i.e., flat. 5. The role of adaptation is unclear. 6. The phenomenon of recruitment is present, but the metrics are not known. Haas further extensively documented research into the development and application of stimulus transmission systems; but since these systems have been used in attempts to transmit speech information, it is appropriate that they be dealt with more extensively in the pages that follow. 16 The same is true with respect to investigations into cuta- neous sensory reception of the speech code. History of Investigations into Cutaneous Speech Reception Whereas different aspects of tactile sensitivity have been the subject of research for a number of years, in- vestigation into the usefulness of the cutaneous system as a channel for the reception of the speech code grew out of Gault's work in the early 1920's. At first Gault considered the cutaneous channel to be equal to the auditory channel insofar as its potential to receive vibratory stimulation (Gault, 1934). His first experiment consisted of using a long speaking tube extended through several walls, with the subject seeking to discriminate between assorted tuning fork vibrations and speech sounds (Gault, 1924). His next inves- tigation involved the use of a device similar to the ear- piece of a telephone receiver. Again, tubes were used to transmit the speech signal from a room 35 feet away from the subject, with the subject seeking to discern the signal via his fingertips (Gault, 1926a). In 1928 Gault was assisted in his research by the Bell Telephone Laboratories, which helped develop a piece of equipment called the Teletactor. This device divided the speech signal into five frequency bands, each of which was then amplified and introduced to a different finger of one hand by means of simple vibrators. Each vibrator passed only one portion of the filtered speech signal, with a total ‘[ l{.[({c‘[‘lllll|lllll'|illllill! 17 range covered by all five vibrators of 0 to 2,600 Hz (Gault, 1928). Gault’s first experiment with the Teletactor employed a 28 year old deaf female. After practicing for 200 hours, she was able to distinguish about 50 percent of a list of 172 monosyllabic words (Gault, 1924). In another instance, following only 28 half-hour training sessions, a subject was able to judge which of 10 brief stimulus sen- tences had been presented to him, with about 75 Percent accuracy. However, it was reported that the results were significantly lowered with a change of speakers or a reduced rate of speaking (Gault, 1926b). Gault also experimented with the concurrent use of touch and vision (Gault, 1926c), using vibrotactile stimula- tion to help deaf students develop a feel for the rhythms of speech and to identify various types of speech patterns by their movements. He claimed that hearing people did this auditorily to the point where the ”movement" of spoken discourse provides cues which enable them to perceive its meaning, with rhythm, accent, and emphasis all making a con- tribution. He claimed that subjects could improve their understanding 40 to 100 percent over lipreading scores alone by combining taction with vision. He attributed this to the fact that taction helped the subjects get a feel of the rhythm of speech and provided help in perceiving words not easily distinguished by vision alone. His evidence sug- gested that, once trained, taction could be dispensed with and the benefits would still accrue. 18 Cloud (1933) reported on the use of Gault's Teletac- tor in an experiment using eight deaf children. He con- cluded that it aided in tone production, helped the subjects distinguish between long and short vowels, helped them recognize silent and unvoiced elements in words, enabled them more easily to discern and utilize the correct place- ment of accent in syllable combinations, aided in the cor- rection of omitted or added voiced speech elements, and resulted in smoother speech on the part of those children who used the Teletactor, as contrasted with those in the same age bracket who did not. Haas (1970) reported an experiment by Myers using a ”Shake-Table,” a single vibrator which stimulates the thumb and inner three fingers of the hand. Myers claimed an aver- age of 91 percent accuracy in discriminating between 16 sin- gle words after 8 training sessions. Another approach to vibrotactile stimulation has evolved as an attempt to circumvent the problems arising from the frequency range limitations of the cutaneous system. Equipment has been developed by various researchers which transposes the speech frequencies downward and transmits them over narrow low frequency bands. The first of these units was Dudley's Vbcoder, developed in 1936 (Dudley, 1933. The Vecoder derives a small set of measure signals repre- sentative of energy fluctuations in a corresponding set of speech frequency bands. The measure signals are then trans- mitted over narrow low-frequency channels. At the receiver, 19 the speech is approximately reconstructed by modulating the spectrum of a broad-band source in accordance with the fre- quency regions and amplitudes of the measure signals. Orig- inally, this reconstructed signal was presented acoustically to the listener. Application of the Vocoder technique to tactual stimulation was first attempted by Levine and others at the Massachussetts Institute of Technology, using a device called FELIX (Pickett and Pickett, 1963). FELIX divides the speech spectrum into seven frequency bands, deriving an approximate measure of the energy in each band. These mea- sures are then presented to the skin of the subject in the form of amplitude variations. Only a few preliminary trials were made with FELIX, according to Pickett and Pickett. They have reported that more recently Fant and his colleagues at the Speech Transmission Laboratory of the Royal Institute of Stockholm have developed a ten channel, two-hand type of Vbcoder. This device utilizes bone-conduction transducers, presenting the lowest frequency to the little finger on the left hand and progressing to the higher frequencies on the right hand. In the same article, Pickett and Pickett reported on using the ten-channel VOcoder in an experiment looking at the ability of subjects to discriminate between various vowel pairs and consonant pairs. They found results varying across the spectrum from fair success, through mod- erate, good, and consistent success for various vowel pairs, with vowel sounds of relatively greater duration yielding more consistent results. Looking at consonant pairs, the 20 results ranged from 22 percent to 99.5 percent discrimina- tion. One of the problems they noted was the masking effect which results from using multiple vibrators. Further, they commented on the fact that a ten-channel vibrating mechanism is cumbersome, suggesting that the maximum number which can be used profitably might be three or four discrete loci. Kringlebotn (1968) experimented with a five-vibrator tactual vocoder called Tactus. With it, he states: the speech signal . . . is divided down into the frequency range for tactual vibration b the suc- cessive multi-vibrator circuits. One bone conduc- tion] vibrator for each of five frequency ranges in the original speech thus provides a spatial pat- tern of vibrations to represent the speech frequency patterns. With this system, the pulse signal excites the first vibrator and then is divided down successively for the re- maining vibrators with pulse signals having frequencies one- half, one-fourth, one-eighth, and one-sixteenth of the ori- ginal frequencies. Using deaf children as subjects and closed choice experiments of limited complexity, Kringlebotn concluded that the apparatus showed promise: (1) as a sup- plement to lipreading under teaching conditions, (2) as an aid for the learning of lipreading. (3) as an aid in speech teaching and correction, and (4) as a rhythm indicator. ,Keidel (1958) experimented with storing speech sig- nals on magnetic tape, recorded at a rate of 15 inches per second, and then transposing the frequencies downward by manipulating the playback speed. The resultant speech sig- nals were then fed into a mechanical vibrator based on a 21 model developed by Bekesy in 1955 to further his study of the traveling wave theory. The model consisted of a plastic tube case around a brass tube with a slit in it. The tube complex, which was attached to the skin of the forearm, was filled with fluid and a vibrating piston within the tube set the fluid in motion. The result was that waves were pro- duced which traveled from hand to elbow. Keidel describes his adaptation of VOn Bekesy's model as follows: The physical features of the model permit spatial dispersion of the frequencies between 40 and 400 cps so that the surface of the model sensitive to 40 cps vibrates 30 cm distant from the point of vibration for 400 cps. When the volar side of the forearm is brought into contact with the vibrating surface of the model, each frequency excites another point of the skin within a length of 30 cm. Keidel (1968) was pleased with the results, reporting that he was able to train subjects to recognize three types of monosyllabic words, the three types differing with re- gards to their frequency range. In his doctoral dissertation, Johnson (1963) devised a system consisting of four loudspeakers, each two inches in diameter, which directly contacted the forearm of the sub- ject, with speech signals transmitted through the speakers. On the face of each speaker a fabric was attached. The speech signal vibrations activated the center of the fabric, producing an elliptical vibratory pattern on the forearm. With training, Johnson indicated that lipreading scores of experimental subjects were enhanced when this system was used. This, and the previously cited study by Kringlebotn using the Tactus vocoder, are in agreement as to the podtive 22 effect tactile stimulation can have on lipreading. As men- tioned earlier, Gault also felt that lipreading scores could be improved by supplementing vision with taction. He sup- ported his conclusions with evidence obtained in several studies (Gault, 1930a, 1927, 1930b). Also, using the Tele- tactor and lipreading combination, Ilieva (1934) reported an increment in correct responses as compared with the score obtained by vision alone. Geldard (1961), citing the various limitations of the cutaneous system and the problems inherent in trying to input ongoing speech, suggested that the best solution was to recode speech stimuli. Accordingly, he utilized the dimensions of locus, duration, and intensity to transpose language symbols into patterns over ten loci on the skin. This technique does not use speech sounds, per se, but pat- terns each letter of the alphabet, utilizing a 60 Hz sinus- oidal signal as the primary stimulus, varying its intensity and duration. Geldard called his system the ”vibratese language," and used the Bimorph as his vibrator. He claimed that his subjects had received up to 38 words per minute using this system. As was mentioned in Chapter I, electrocutaneous research has been attempted, as well. Geldard (1960) has indicated, however, that no practical system has been devel- oped to circumvent the problem of pain induced by electrical stimulation. 23 Research Specifically Pertinent to This Study Of major significance to the present investigation, in that this study is a direct outgrowth of it, is Haas' investigation into the vibrotactile absolute thresholds of English phonemes. Haas (1970) states that: With the use of a single, efficient vibrator, the Bimorph, the present study was successful to a signifi- cant degree in defining the information received from spoken phonemes via vibrotactile stimulation at the fingertip. Detection thresholds for 36 phonemes were found. Stimuli provided by utterances of the /s/ and /9/ phonemes could not elicit responses. Whether or not this can be attributed to limitations within the in- strumentation to move the skin at high frequency lev- els or to the inherent incapability of the cutaneous receptors to receive high frequency stimuli is not resolved. The literature does not provide convincing evidence for either case. Geldard has speculated that the cutaneous receptors have the potential, but as yet a transducer to provide efficient stimulation at high frequencies has not been developed (Haas, 1970). The graphic illustration of Haas' rankings of the phonemes by detectability thresholds is found in Appendix 1. Haas found that there was close agreement among the subjects' threshold scores, with closer agreement for con- sonant than for vowel sounds. Further, individual subject test-retest reliability was found to be excellent. In addition, he found that there was a strong relationship between the vibrotactile thresholds for spoken phonemes and the relative speech powers of the phonemes. Again, this relationship was more consistent for the consonant than the vowel sounds. Verillo (1966), in his research into the effects of varying pressure on cutaneous sensitivity, established that 24 thresholds for pure tone stimuli decrease in direct pro- portion to the extent of protrusion by the contactor. Verillo's findings supported earlier findings by Cohen and Lindley (1938) and Babkin, Rozen, Tumarkina, and Chernyak (1961). Weinstein (1968), investigating various vibrotactile parameters for pure tones, established that women demonstra- ted greater sensitivity to pressure than did men. In summary, with respect to research directly bearing on the questions posed by this study, Haas (1970) established vibrotactile thresholds for spoken English pho- nemes using one adult male General American speaker, Verillo (1966) demonstrated that vibrotactile thresholds for pure tones improve with increased protrusion of the contactor into the skin's surface, and Weinstein (1968) found that, for pure tones, women displayed greater sensitivity to pressure than men. CHAPTER III SUBJECTS, MATERIALS, EQUIPMENT, AND PROCEDURES Four subjects were presented twenty experimental programs. The first four programs consisted of the deter- mination of intensity required for absolute detection thresholds of selected English phonemes for four separate speakers at a specified amount of applied contactor pres- sure. The second, third, fourth, and fifth sets of four programs were identical to the first set of four programs and to each other, with the single exception that the spec- ified amount of applied contactor pressure varied for each set. Subjects The four subjects, two males and two females, were between the ages of 24 and 30 years. None had known patho- logical conditions of the skin or central nervous system. All were either professionals or doctoral candidates in the field of Speech Pathology and Audiology. It was determined that more subjects were unnecces- sary, since Haas (1970) established that there was good agreement between subjects with respect to cutaneous thresh- olds for phonemes. Prior to each experimental session the four subjects 25 26 were given a practice session, using the reference phoneme /o/, with all conditions identical to those to be employed in the experiment. This practice session was used to re- acquaint the subjects with the nature of the stimuli and the task. Materials Four taped programs of recorded English phonemes comprised the stimulus materials for the study. The mag- netic recording tapes were Scotch brand, type 201. The phonemes employed were selected from those used by Haas, on the basis of mean threshold intensity. Haas' results may be examined in Appendix 1. Wherever a cluster of pho- nemes evidenced the same mean threshold intensity, random- ization was used to select one phoneme as representative of each cluster. 0n the other hand, if a phoneme stood alone, i.e., was not clustered with others with regard to mean threshold intensity, that phoneme was automatically selected By this means the phonemes /u/, /I/, /e/, fla/, /w/, /au/, /a/. /V/. /n/. /3/. /d3/. /b/. /t/. /3/. and /h/ were iso- lated. Next, in the interest of time required of the sub- jects under fatiguing experimental conditions, the preceding list was reduced to six phonemes. Again, Haas' mean thresh- old intensities were the reference and, using the criterion of at least a 3 dB span between adjacent phonemes, the experimental phonemes /u/, Akl, /a/, /n/, /b/, and /h/ were selected. These phonemes ranged along the continuum from Haas' best to his poorest obtained mean threshold intensifies. 27 The preceding phonemes, together with the reference phoneme [3/, were recorded in the indicated sequence, yield- ing the four master tapes. These tapes consisted of the reference phoneme and each of the stimulus phonemes being spoken five or more times by each of the four General Ameri- can speakers, i.e., an adult male, an adult female, a pre- adolescent male, and a pre-adolescent female. Each speaker was seated in a double-walled, sound-treated, prefabricated room. The microphone was placed approximately six inches from his lips at about a 45 degree angle. Recording proce- dures of Black (1949, 1952) and Fletcher (1953) were fol- lowed to obtain the best possible stress, duration, and nat- ural speech power. Each speaker was informed that he would be told the phoneme to be recorded as it was required. Upon being signalled to begin, he was to say the indicated pho- neme as naturally as possible, over and over again until he was signalled to stop, taking a breath between each utter- ance. The VU meter on the tape recorder was adjusted to 0 for the reference phoneme /o/, which was always the first phoneme to be recorded, for each speaker in turn. There- after, no further adjustments were made. Using the master tapes resulting from the foregoing procedures, the phonemes were dubbed onto an experimental tape and the best two utterances of each, as determined sub- jectively by the experimenter, were spliced into a new se- quence determined by the table of random numbers. The sequence for each speaker was separately randomized. 28 The resulting taped stimuli were played for critical review by three speech pathologists familiar with phonetic symbols. They were seated in a double-walled, sound treated, prefab- ricated room, and the tapes were played through the speech circuit of a Maico MA~24 audiometer. They were asked to record, in appropriate phonetic symbols, whatever sounds they heard. Their responses were analyzed,and if at least one of each of the recorded phonemes for each speaker did not elicit 100 percent agreement among the speech patholo- gists, a second recording session was scheduled and addi- tional utterances of the deficient phonemes were recorded. Again, the phonemes were submitted to evaluation by three speech pathologists and the results were analyzed. At this point, each speaker had produced at least one utterance of each of the selected phonemes which elicited 100 percent agreement by the speech pathologists. In those instances where more than one utterance for a given phoneme and a given speaker resulted in 100 percent agreement, an arbi- trary choice was made between the two, thus narrowing the stimulus phonemes to be used in the study to one utterance of each phoneme per speaker. These phonemes were then spliced back into the original sequence and four experi- mental tapes were prepared, each containing eight consecu- tive repetitions of each phoneme, for a total of fifty-six stimulus events per speaker, including the /a/. Each repetition was a replication of the original, single utter- ance previously selected. 29 As the repetitions were taped, the relative inten- sities of the experimental phonemes were adjusted to meet the relative speech power dimensions as specified by Fletcher (1953). The strongest speech sound [3/, for example, is specified by Fletcher as being 28 dB stronger than the weak- est sound /9/. A level recorder (Bruel and Kjaer 2305) had been used to measure the relative intensities of the pho- nemes on the preliminary recordings. Comparing them to the values suggested by Fletcher, the amount of adjustment was determined and the peak values were equated at the time of preparation of the experimental tapes, as just mentioned, to the desired relative intensities, plus or minus 2 dB. The experimenter was fully aware of the fact that Fletcher's criteria were established using adults as subjects and therefore did not necessarily hold true for children. How- ever, the arbitrary decision was made to apply the criteria to all four speakers, adults and children alike, in order to control for individual speech power differences among speakers. Haas (1970) had already established that there was a strong positive relationship between phoneme thresh- olds and relative speech power. Therefore, if this is the sole variable active in determining vibrotactile thresholds for spoken phonemes, it could be expected that the present study would yield no significant differences due to speaker effect. On the other hand, by controlling for the speech power variable, information might be obtained as to whether or not there might be other variables, peculiar to the 30 individual speaker, which might be contributing factors in determining vibrotactile thresholds. The resulting experimental tapes were replayed through the level recorder for a final check of relative intensities. (See Appendix 4 for a description of the rela- tive intensity differences between the experimental phonemes and the stimulus phoneme, as specified by Fletcher, and as obtained by Haas and the present experimenter.) The intensity of the reference phoneme /a/, which Fletcher indicated was the phoneme with the highest inten- sity value, was used to determine the intensity level for the calibration tone. One minute of a 1,000 Hz sinusoidal tone was recorded at this level at the beginning of each experimental tape. An inter-stimulus interval of two seconds was left between each of the eight consecutive replications of each phoneme, and an inter-phoneme interval of six seconds was left between each set of eight phoneme replications. Neise spikes of approximately 15 dB were observed on the level recorder output. It was determined that these were the result of the activation of the on-off switch of the tape recorder. Although these were not audible through the earphones, they were spliced out as a safeguard against the possibility of their affecting tactile thresholds. A subject threshold data form was prepared for use during the experiments. (See Appendix 7.) 31 Equipment The following list constitutes the major instrumen- tation employed for this study: Tape Recorder I (Ampex AG 440B-4) Tape Recorder II (Ampex AG 600) Tape Recorder III (Viking 433) Microphone (Electrovoice 635A) Level Recorder (Bruel and Kjaer 2305) Audio Oscillator (Central Scientific Company) Commercial Test Room (Industrial Acoustic Company, Inc., double walled room, Model 10-1052) Audiometer (Maico MA—24) with Electrovoice SP-12 speaker Tactile Stimulus Transmission System with piezoelec- tric ceramic Bimorph (Clevite Corporation) Procedures All experimental sessions were conducted in a double walled, sound treated, prefabricated room. For each experi- ment each subject was seated beside a table with his right arm resting on a foam rubber pad the same height as the platform housing the Bimorph. The right hand, palm down, was placed on the handrest platform and the middle finger was placed in the finger cradle with the fingertip extended over the Lucite rod contactor, coupling the fingertip by contact at the innermost concentric fingerprint line. The finger and hand were secured for position by a single strap or adhesive tape. The finger cradle was then elevated to remove coupling with the contactor, and then lowered to the point where the subject just began to detect contact. Next, the finger cradle was lowered an additional number of grams dictated by the experiment being conducted. To insure against any perceived auditory signals 33 emanating from the Bimorph, all experiments were conducted with 80 dB SPL of broad band white noise projected into the sound field from the speaker in the test room via channel two of the Maico MA-24 audiometer. This level of masking was the same as that selected by Haas in that it is the standard level used by Geldard and Sherrick for experiments using the Bimorph at the Princeton Laboratory. Further, Haas conducted a sound pressure level analysis of the speech sounds emanating from the Bimorph, obtaining a maximum level of 54 dB SPL for the /o/, the loudest sound. Prior to the experiments the Maico MA-24 audiometer was calibrated to the Bimorph by obtaining voltage measure- ments across the electrical terminals to the transducer. Inspection of the results in Appendix 8 will reveal that at a 40 dB attenuator dial setting on the audiometer, the volt- age reading across the Bimorph was 1.6 volts. This level was arbitrarily chosen as the zero reference level for reporting the results of this study. Hence, a tactile threshold of 0 dB would be indicative of 1.6 volts across the Bimorph and an attenuator dial setting on the audiometer of 40 dB. Likewise, a tactile threshold of 10 dB would be indicative of 5.0 volts across the Bimorph and an attenuator dial setting on the audiometer of 50 dB. All stimulus materials were amplified and attenuated by the Maico MA-24 audiometer and transmitted via the speech circuit of channel one, which permitted one dB adjustments of the intensity of the signal. The equipment range was 34 120 dB, which theoretically permitted 80 dB of amplification above the 40 dB dial setting of the audiometer which repre- sented tactile zero. However, due to the nature of the test materials and limited applied voltage tolerance of the Bi-« morph, a range of only 40 dB, i.e., 40 to 80 dB on the at- tenuator dial of the audiometer, was utilized. The order in which the five experimental pressure levels were presented was the same for each of the four subjects. It was arbitrarily decided to begin with 15 grams in order to have the ”easier” threshold judgments first, to be followed by what might prove to be more difficult judgments. At any rate, based on Haas' results, it was known that thresholds could be elicited at 15 grams, whereas it was hypothesized that more pressure might result in damp- ing effects and less pressure might result in an inability to discern vibrations sufficiently to establish consistent thresholds. Experiment I. The purpose of this experiment was to determine the intensities required to elicit detection thresholds for the selected phonemes, for each of the four experimental speakers, with 15 grams of contactor pressure beyond that point where the subject first detected contact. The order of speaker presentation to the subjects was ran- domized (see Appendix 9). Prior to each experimental session, the subject was presented with the following written instructions: 35 The purpose of this session is to determine what intensity is required in order for you to determine the presence of a tactile sensation at a given pres- sure setting. Each stimulus event represents an English phoneme. We are interested in absolute de- tection thresholds. Please respond on every occa- sion that you detect a vibration on your fingertip. Respond by briefly pressing the button provided. Most of the stimuli will be presented around your threshold. As a result, this task will require constant concentration on your part. Several pre- sentations will be given for each phoneme. There will be both ascending and descending series. The first presentation of a phoneme, before all the series for that phoneme, will be rather strong. This will alert you to the nature of the sensation for that particular phoneme. There will be one prac- tice phoneme followed by six experimental phonemes for each of four speakers. A masking noise will be intro- duced into the test suite during threshold testing. Between phonemes, and between speakers while the stim- ulus tapes are being changed, the masking noise will be discontinued. This will indicate to you that we have completed the threshold series for a phoneme, and for a speaker, respectively. When the masking noise is re-introduced the presentation of the next phoneme will begin. Remember that the first stim- ulus for each phoneme will be strong. Since the pressure contact of the Bimorph ”needle" is one of the variables being investigated, you are asked to maintain the position of your right hand in the cradle throughout the test session. The session will last approximately one hour. Before presenting the practice phoneme,the calibra- tion tone was used to adjust the output gain of the Maico MA-24 audiometer to zero on the VU meter. This step was repeated for each of the four speakers. The practice ses- sion utilized the reference phoneme /o/, with all conditions identical to those employed in the experiment itself. Following the practice session, the psychophysical method of limits was used to elicit the detection thresholds of the six experimental phonemes. For all subjects, with 36 each phoneme, there were two ascending and two descending series of stimuli, with an ascending series presented first, followed by a descending series, etc. Prior to the first ascending series the alerting signal, utilizing the experi- mental phoneme, was presented at the maximum intensity em- ployed in the experiment (i.e., 40 dB re the calibration tone at 1.6 volts, which corresponded to 80 dB on the atten- uator dial). This was followed by a stimulus of very low magnitude which was progressively increased until detected. The intensity at this point of detection was recorded as the threshold for that first ascending series. The signal was further augmented by 1 dB steps and responses were noted for three additional trials, at which time the process was re- versed and the descending series was begun, reducing the stimulus by 1 dB steps until it was no longer detected, re- cording the last detected signal as threshold for that series. Attenuation was then continued for three additional trials, at which time the second ascension was initiated, to be followed by the second descension in turn. The average score for the four series was recorded as the absolute de- tection threshold for that given phoneme. The subject was instructed to respond by pressing a signal button. Phoneme presentation order was determined randomly. Experiment II. The purpose of this experiment was to determine the intensities required to elicit detection thresholds for the selected phonemes, for each of the four 37 experimental speakers, with 20 grams of contactor pressure beyond that point where the subject first detected contact. The order of speaker presentation to the subjects was ran- domized (see Appendix 9). General procedures followed were the same as for Experiment I. Experiment III. The purpose of this eXperiment was to determine the intensities required to elicit detection thresholds for the selected phonemes, for each of the four experimental speakers, with 10 grams of contactor pressure beyond that point where the subject first detected contact. The order of speaker presentation to the subjects was ran- domized (see Appendix 9). General procedures followed were the same as for Experiment I. EXperiment IV. The purpose of this experiment was to determine the intensities required to elicit detection thresholds for the selected phonemes, for each of the four experimental speakers, with 25 grams of contactor pressure beyond that point where the subject first detected contact. The order of speaker presentation to the subjects was ran- domized (see Appendix 9). General procedures followed were the same as for Experiment I. Experiment V. The purpose of this experiment was to determine the intensities required to elicit detection thresholds for the selected phonemes, for each of the four 38 experimental speakers, with 5 grams of contactor pressure beyond that point where the subject first detected contact. The order of speaker presentation to the subjects was ran- domized (see Appendix 9). General procedures followed were the same as for Experiment I. CHAPTER IV RESULTS AND DISCUSSION This chapter contains the basic data obtained and discussions of their significance with regard to the four experimental questions posed in this study, as follows: 1. Does varying the speaker affect the threshold level for phonemes? 2. Does variation in contactor pressure influence the threshold level for phonemes? 3. Does the sex of the receiver (subject) affect the threshold level for phonemes? 4. Are there interactions attributable to manipulation of the speaker-pressure, speaker-sex of subject, or pressure-sex of subject variables? Analysis of variance was accomplished with a three-factor design with repeated measure (Winer, 1962). In addition, agreement among subjects' absolute thresholds was investigated. Each subject's responses to the six selected phonemes were ranked and comparisons were accomplished, for each pressure separately, using the non- parametric Coefficient of Concordance (Kendall's W) (Downie & Heath, 1965). Finally, the mean thresholds in the current study, for the adult male speaker with 15 grams of contactor pres- sure beyond the point where the subject first began to 39 4O detect contact, were compared with those obtained by Haas (1970). The statistical procedure used was the Spearman-R Rank Correlation for the two sets of ranks (Siegel, 1950). It will be noted that whereas six experimental pho- nemes were chosen to be used in this study, only five of the six appear in the figures and tables illustrating the re- sults. The missing phoneme is /h/. The reason for its omission is the fact that no subject responded to this pho- neme at any pressure, for any speaker, in the present study. Discussion of this phenomenon will by presented in the appropriate section of this chapter. Effects of Speakerplgontactor PressuggL and Sex of Receiver Each phoneme was analyzed separately by a three- factor analysis of variance design with repeated measures in order to determine whether or not there were any signi- ficant threshold deviations resulting from the experimental conditions. Factors included speaker, pressure, and sex of the receiver. Possible interactions of these factors were also investigated. Phoneme /u/. At each of five experimental sessions each of four subjects was stimulated with the vibrotactile form of the phoneme /u/ spoken by each of four different speakers. The experimental sessions differed only in terms of the amount of pressure presented to the subjects finger- tip by the Bimorph's contactor rod. Two ascending and two descending thresholds were established, the mean of the four 41 comprising each subject's absolute threshold. Figures 2 and 3 present the absolute threshold re- sults in the form of histograms. Table 1 presents the sta- tistical data obtained by analysis of variance. There were no significant effects attributable to any of the three variables or to interactions among them. Table 1. Phoneme /u/. Analysis of Variance: Threshold Data —: Source d/f Sums of Squares Mean Squares F-Ratio P 4 95.398 23.849 0.162 PSx 4 76.470 19.117 0.130 P(I/Sx) 8 1173.622 146.702 Sp 3 67.058 22.352 0.528 Spr 3 76.786 25.595 0.605 Sp(I/Sx) 6 253.646 42.274 81 1 3.570 3.570 0.005 I/Sx 2 1235.577 617.788 PSp 12 59.841 4.986 0.346 PSpr 12 58.947 4.912 0.340 PSp(I[Sx) 24 3451223 14.405 P: pressure Sp: speaker Sx: sex of receiver (subject) I/Sx: individual subjects within sex 4.760 required for significance at the 0.05 level of confidence Phoneme_/A[.’ At each of five experimental sessions each of four subjects was stimulated with the vibrotactile form of the phoneme [A/ spoken by each of four different speakers. The experimental sessions differed only in terms of the amount of pressure presented to the subject's finger- tip by the Bimorph's contactor rod. 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Ion n. ans Inns Io: no: mmm¢mmm nqamu mudzmm mmm Hoxdcam Seam Ammo» soaumanaaco um ooo.a Hon naaosam nachos mpaob n.a on ma ov macaw ca oasmmoam nN ON na mmmqdeO£ H HHHH U NNI—‘O N NNCDJI' l-' N O \O H \l O H PM4 «we 0 0 ON» 22.4 22.6 22.7 23.2 2501 30.1 43.3 44.3 * 0 dB re 1.6 volts across Bimorph for 1,000 Hz calibration tone APPENDIX 2 CHARACTERISTICS OF THE BIMORPH 83 APPENDIX 2 CHARACTERISTICS OF THE BIMORPH The material comprising this appendix, including the three Figures. is taken directly from Haas (1970), pages 65-71, and 135. The Bimorph vibrator employed in this study (PZT-5B) measures 1 1/4 inches in length, 1/8 of an inch in width. and 0.021 of aninch in thickness. The device uses flexure responsive piezoelectric elements as transducers for mechanical output as a function of electrical input. A Bimorph is a 0.002 inch thick brass plate with a ceramic material bonded to the top and bottom surfaces. Figure [14] illustrates this arrangement. The framework for housing the Bimorph involved a cantilever mounting. also illustrated in Figure In order to respond flexurally to the input signals. the Bimorph must have its two active cera- mic plates oppositely polarized. This produces Oppositely direct transverse strains which result in bending or deflection of the free end. Motion sensitivity is derived in terms of deflection per unit of applied voltage. The maximum for applied voltage is 260 volts. Any excess over this amount may cause destruction of the vibrator. The cantilever mounting for the Bimorph also served as the means of electrical contact. Spe- cifically, this was achieved by connections to the two brass plates forming the clamp to hold the top and bottom surfaces of the vibrator. The skin-contactor coupler was a Lucite rod. 1/8 inch in diameter. The contactor was secured to the outermost free end of the Bimorph by a small (2-48) flat head screw. The screw was at- tached with epoxy glue. This arrangement allows for fastening contactors of various sizes. The desired length of the contactor was dictated by the design of the plexi-glass hand-rest platform in relation to the adjustable finger cradle of the apparatus. Figure [[3 illustrates this arrangement. The construction provided an 1/8 inch extension Electrical Contacts Brass -——- ___‘ g.— Clamp 84 Signal Field Direction of Strain r---Poling Field Bimorph Figure 14. Cantilever Mounted Bimorph up 83 Bimorph // Lucite rod —— Figure 15- . 85 ~Dynamomet er /Hand-rest platform Finger cradle Finger cradle adjustment Apparatus for Housing Bimorph (PZT-SB) 86 .aocm Heapsoo mcasaOnud was .aoom pace .acpuhm scunmaamsdha nsfiaaaam no aanwdgn capaaunom .oH unawam #NIdS nopoaoavafl coda: £00m QQmBzoo ’ ‘ an: Egg r nounooom oada w iv zoom Emma HOOn nosnouucana malnoum _ 4 madmaos sans—am 87 of the Lucite rod above the handrest platform. The adjustable finger cradle could be lowered to a posi- tion whereby it was exactly parallel to the hand- rest platform. This allowed variation in adjust- ment of the pressure against the contactor by the fingertip up to no grams. The site on the integu- ment for coupling was the inner-most concentric fingerprint line of the third finger of the right hand, the inner-most papillary ridge. According to the Clevite Corporation. the mass loading of the Bimorph by the Lucite contactor rod presents no significant deterent to the performance of the vibrator. The loading by the fingertip. however. does influence an interaction between deflection rate and voltage. Resonant frequency is not affected. . . . A design chart was provided by the manufacturer which was used to determine the specifications for applied voltage, pressure at the contactor. and for the length and width of the Bi- morph . . . . An ll 1/2 inch high plexi-glass post was at- tached to the vibrator end of the hand-rest plat- form. A 3 l/2 inch long plexi-glass support plate was secured to the top of the post and extended over the finger cradle. A dynamometer scaled in grams, was suSpended from the support plate and coupled to the finger cradle by a 2 1/2 inch string. Thus, as the finger cradle is lowered the relative pres- sure can be read directly from the dynamometer. Figure El‘fl depicts this construction. The PZT-SB was chosen for this study because of the higher voltage limit. The PZT-S series all provide relatively flat frequency response charac- teristics from 15 to 20.000 Hertz according to the Clevite Corporation Technica;;§ublication PD-9247. The resonant frequency for this model series was computed as 300 kHz from a "Resonant Frequency Nomograph" provided on p. h of this publication. APPENDIX 3 A COMPARISON OF METHODS FOR DETERMINING ABSOLUTE VIBBOTACTILE THRESHOLDS 88 APPENDIX 3 A COMPARISON OF METHODS FOR DETERMINING ABSOLUTE VIBROTACTILE THRESHOLDS In his investigation. Haas (1970) used the psycho- physical method of limits to determine absolute vibrotactile thresholds. Specifically. he used eight threshold measures. four ascending and four descending. and took their mean as the absolute threshold. In order to conserve time in what was expected to be a fatiguing series of experimental condi- tions in the present study, the feasibility of using only four threshold measures. i.e., two ascending and two de- scending. was investigated. Looking at the six experimental phonemes to be used in the present study. and utilizing Haas' raw data, a com- parison was made between the absolute thresholds Haas would have obtained using only his first four thresholds to com- pute the mean and those he actually obtained with the series of eight thresholds. Table lh contains the results for all six of Haas' subjects, each presented separately. It will be noted that differences obtained were in- significant. without exception. Further. all subjects ranked the six experimental phonemes identically under both conditions. This held constant within and between subjects. On the basis of these results. it was decided that it would be acceptable to use only four threshold series. _ A 8 Threshold X 4 Threshold X 89 A Comparison of Means for Four Versus Eight Phoneme Thresholds. Table 1“. Subject 221431 0 O O O O 0 000000 55524602 3%120 1.1.23 ...... 3816.40 1123 uAanbh 000000 865952 0 o o o o o n.520u9 1222 538880 0 O O O O . 4620:49 1222 uAanbh 430823 0 O O O O 0 000000 607612 0 503928 11122 uAanbh 000000 5/0. 58 91 .U