Behavior Research Methods & Instrumentation1975, Vol. 7 (5),447-451

An efficient method for dichotic tape preparation

C. K. LEONGInstitute of Child Guidance and Development, University of Saskatchewan

Saskatoon, Saskatchewan, Canada

The paper describes a simple but efficient method for dichotic tape preparation. The system ofinstrumentation together with checks for synchrony of stimuli and interstimulus intervals is explained.Methodological issues of onset synchrony and lag effect are discussed.

From the deceptively simple but ingeniousprocedures pioneered by Broadbent and Kimura indichotic tape preparation have evolved moresophisticated techniques as described by Irvine(1972), Rubino (1972), Studdert-Kennedy andShankweiler (1970), Yates, Smith, Burke, and Keane(1969), and Carr (Note 1). In essence, the procedureis as follows: (a) tryout recording of test materialsonto tapes with due regard for intensity and durationof the stimuli; (b) splicing of "best" stimuli fromtryouts onto d master tape loop; (c) rerecording ofbest stimuli from tryout tapes or from the master tapeloops through some kind of time control device toachieve synchrony on the final tape. In actualpractice, these steps are arduous and time­consuming. For example, the check of durationthrough a spectrogram and, more conveniently,through an oscilloscope is often difficult. Theexcursions above noise level for different phonemesembedded in different acoustic environments vary andmake for difficulties in determining onset synchrony.The splicing of tapes can be a frustrating experiencefor the novice. There is also a paucity of informationon the attempt to achieve synchrony. Rubino's (1972)method, though fairly detailed. raises some doubts asto the claim of onset synchrony of less than 5 msec inthe final tape. The minor flaw is his use of a tapespeed of 1-7/8 in. per second (ips), which reducessound fidelity. The major flaw is the reliance on the"instant stop" buttons for recording and themonitoring by ear to decide on the precise moment fordisengaging the buttons to begin transcription. Thus,his very refined S-msec onset difference between pairsof stimuli is more characteristic of computer­controlled instrumentation. Irvine's (1972) methodseems to achieve reasonable results, but could do withmore details explaining the precise procedure. Inneither case is there any indication of the technical

The writer would like to thank Dr. Burchard M. Carr ofOklahoma State University and W. Diachuk of the University ofAlberta for their suggestions. and Professor A. 1. Yates of theUniversity of Western Australia and the Editor of BehaviorResearch Methods & Instrumentation, for their comments on theearlier draft of this paper.

quality of the final tape, save the claim that synchronyis achieved. On the satisfactory solution of technicalproblems such as onset synchrony and verification ofinterstimulus intervals depend the results of anydichotic study, as emphasized by Yates (1972). Thepurpose of the present paper is to describe a simpleand yet efficient method for dichotic tape preparationtogether with a check for synchrony of stimuli.

SYSTEM OFINSTRUMENTATION

The system of instrumentation for the constructionof dichotic tapes consists of: (a) two high-quality dualchannel tape recorders (Sony 777-4J) withsolenoid-operated run and record functions and withtape lifters that can be deactivated when the machineis in stop mode; (b) a specially designed andconstructed cuing or control device for precise timealignment of stimulus materials; (c) a variable timer(a Heathkit sine-square audio generator) interfacedwith the control device to achieve the desired stimulusinterval. This is operationally defined as theduration between the onset of phonation of a stimulus(e.g .. digit) and the onset of phonation of the nextstimulus. As will be shown, the "beginning" of astimulus is not easy to determine. A slightmodification is made to the first tape recorder byremoving its Channel 2 input amplifier connectionfrom the quarter-track head and connecting it to theChannell half-track head. This enables theChannel 2 amplifier to be used as an amplifier for avoice-activated switch. The solenoid control providesthe necessary remote control with the capability ofbeing activated by voice impulses and deactivatedafter the desired interval from onset.

BASIC IDEA

The operational sequence in the tape preparation isas follows: (a) Preparation of tryout tapes by aphonetician with due regard to intensity and duration.An experienced speaker is trained to utter thestimulus signals, e.g., digits, at an even intensity asmonitored on a VU meter and to release the final

447

448 LEONG

flgure I. Systems block diagram fordichotic tape preparation.

) INPUT AMPLI­FIER CONNt:CTlON REMOVEDFllOM QUARTER - TRACK HUDAND CONNECTED 10 CHANNt:Llie I) HALF - TRACK HUD.THUS C2 ."PLIFIEIl KRYES., AN .IIPLIFIEIl FOR AVOICE ACTIVATED SWlltH.

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stops. Each digit is recorded a number of times. andthe recordings are played through a Bruel and Kjaersound-pressure-level recorder to obtain a record of theintensity of each digit. One example of each digit ischosen so that the final list contains only digits ofabout the same intensity. Imbalance in intensity isequalized to 75 dB SPL ±1/2 dB as measured by thesound-pressure equipment for a l,OOO-Hz calibrationtone equated to the intensity of the vocalic portion ofthe stimuli. (b) Recording of best samples from tryouttapes above onto one track of a second or master tapein such a way that the stimuli (digits. for example) tobe used sequentially in the same series will follow onefrom the other at a speed slower than that required inthe final tape. Take as an example the three-digit pair5-9-8. in Track 1, and 6-1-2. in Track 2. If theinterstimulus interval is 1 sec. all that is required forthe master tape is recording at a constant rate.separating the immediately adjoining digits in thesequence in the same track (5-9 or 9-8) greater thanI sec. Other than this steady pace. no precise intervalis needed at this stage. In practice. the 3- to 5-secseparation time is monitored on a Hunter decadeinterval timer.· Also. the corresponding stimuli forTrack 2 (6-1-2) are recorded on the same track of themaster tape. This is done by recording all the seriesfor Track 1 first and then all the series for Track 2. orby alternating each corresponding series betweenTrack I and Track 2 (such as 5-9-8 followed by 6-1-2)before going back to the next series in Track 1. thenthat in Track 2. This latter method of alternatingbetween tracks is more efficacious. (c) When thestimuli of matched intensity and duration withintolerance limits are properly recorded as in (b) onto amaster tape. the latter is set in the first tape recorderin readiness for rerecording onto the two tracks of thesecond recorder to achieve onset synchrony. Theinterfacing of the two dual-channel recorders (thecontrol device and the Heathkit timer) is shown in thesystems diagram in Figure 1. Power supply and con­trol logic diagrams are shown in Figures 2 and 3.respectively.

RECORDING OF STIMULI AND CHECKING

The basic principle is to use the voice impulses ofthe prerecorded stimuli on the master tape to activate.via the control device interfaced with the Heathkittimer. and thence the solenoid control. the secondtape recorder which will thus start slightly ahead ofthe actual digits to be recorded. As the operationadvances. with the desired interstimulus interval seton the timer linked to the control device. the latter"senses" the digits one at a time from theamplification on Channel I. This sensing enables thesecond recorder to start. overcome inertia. pick upspeed. and attain steady state by the time the actualinformation arrives from the modified playback headof the matched Sony 777-4J and with a tape speed of7.5 ips. This use of the voice activation anddeactivation and the adjustable Heathkit timer forvarying time intervals enables the digits to be recordedwithin the time duration specified. When recording ofeach series on Track I of the second tape recorder iscompleted as detailed. the second tape is wound backto specified marks on both the tape and recorder deckfor approximate alignment in readiness forsynchrony. The same process is repeated for therecording of the corresponding series on Track 2 insynchrony with those digits already recorded onTrack 1. When this is accomplished for oneseries-pair ~:i:~. the same procedure is repeated withthe next series on Track I. which is paired with itscorresponding series on Track 2. Preceding the testitems. sufficient tape length is allowed for theinsertion of instructions binaurally while adequateresponse time is given between each series. Thisresponse time can be augmented by stopping the taperecorder manually when it is found that the subjectneeds more time to make a verbal report.

Following completion of the final tape. synchronycan be tested on a polygraph (Hewlett-Packard 760preamplifier with two-channel printout at varyingrates from 0.25 to 100 mm/sec). The use of theapparatus is practical and provides an easy-to-read

DICHOTIC TAPE PREPARATION 449

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Figure 2. Power supply diagram for system of instrumentation.

printout for comparisons of onset, offset, andinterstimulus intervals of stimuli. From the tapes,synchrony falls within 5 msec and interstimulusintervals are held constant within the same tolerancelimit. An example of the verification is shown inFigure 4.

With equalizing of intensity of stimuli on themaster tape, another attempt should be made tofurther ensure equal intensity between the channelson the final tape. One way to achieve this is to directthe stimulus materials to a compressor amplifier or toplay the final tape through a Shure audio-mixer. The

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Figure 3. Control logic diagram for system of instrumentation.

450 LEONG

SUMMARY AND DISCUSSION

FIgure 4. Sample polygraph tracings on a reduced Kale (orlalnalprintout on 25 mm/.ec) of dichotic digiti to show synchrony,Interstlmulus Interval, and duration of digit sequences. Tracings Intop record show 9·3·) In Channel) and 8·'·9 In Channel 2 (fromtop downl. Tracings In bottom record show 2·'·4·2·3 and 5·6·)·4·2In Channel) and Channel 2. respectively.

three-digit series). However, once well versed with thesystem. the actual preparation of a 15-itemed tapewith three-digit pairs on the average should takeabout 6 to 8 h. One difficulty relates to the limitationsimposed by the mechanical aspect of evenhigh-quality tape recorders, which in turn affect ratesof presentation. It takes some time for a tape recorderto get started. pick up speed. attain the steady staterequired to make a recording without disturbing theacoustic patterns. The time required is estimated ataround ISO/200 msec with the matched Sony 777-4J.Added to this is the duration needed to utter asyllable, which clusters around 350/400 msec within arange of 350 to 500 msec, as found by the writer. Thiscompares with the tinding of Yates et al. (1%9) ofvariations between 407 and 553 msec and with that ofStuddert-Kennedy and Shankweiler (1970) of a rangeof 300 to SOO msec for natural CVC syllables. Somevariation is needed for maximum intelligibility assyllables have natural acoustic durations. Thus. for aspoken syllable or a digit to be recorded with thepresent system. or for that matter the other systemsoutlined. the operation takes about 550/600 msec.This raises doubts as to the claim or the precisemeaning of the often-mentioned "two pairs persecond" in the literature. From empirical tindings •the only acceptable explanation of the assertion is thatof "the interval between the beginning of one digitand that of the next was I sec" (Broadbent &Gregory. 1%1, p. 106).

The "beginning of one digit" is explained byStuddert-Kennedy and Shankweiler (1970) as the tirstexcursions above noise level in an oscillographicrecord, that is sustained and followed by clearperiodicity. In actual practice, the instant of onset fora monosyllable is generally difficult to determine sincethe beginning of phonation is not marked by a singleevent having a conspicuous acoustic correlate which iseasily displayed on a cathode ray tube of atwo-channel storage oscilloscope. This difficulty isminimized by the use of test materials which beginwith plosive consonants. By so doing, the point wherethe speech signal departs from ambient backgroundnoise to a fast rising aperiodic excitation of voicingcan be agreed upon consistently. The departure fromambient background noise serves as the operationallydetined point of "onset." The tinding by Berlin.Lowe-Bell. Cullen. Thompson, and Loovis (\973) andLowe, Cullen, Berlin, Thompson. and Willett (1970)of differential perception affected by 30- to 60-mseclag effect further highlights the problems related toonset synchrony.

The present system of instrumentation also showsthat the acoustic qualities of phonemes are important.During the preparation of tapes, it was found that thecontrol device worked well with pure tones whichwould activate and deactivate the second taperecorder precisely within the desired time interval.

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question of intelligibility of dichotic stimuli is a vexedone. An attempt is made to ensure, on the part ofthesubjects. perfect intelligibility at 75 dB SPL of allmonaural individual digits and of samples of dichoticpairs. The fusion effect demonstrated by Day (Note 2),such that dichotically presented nonsense words"banker," given to one ear. and "lanket," to the otherear. are fused to produce "blanket," provides someinsight into the combination of speech informationcentrally. As far as could be ascertained. thefusion effect of the dichotic pairs studied is negligible.

To summarize the methodological aspects ofdichotic tape preparation, it is pertinent to retlect onsome difficulties encountered. Considerable opera­tional skills are required in making dichotic tapes,given the equipments described. Rerecording is oftenrequired to ensure that the stimuli fall withinreasonable time limits (e.g., less than 2.5 sec for a

With speech sounds. sound streams in differentphonemic environments and with different signal-to­noise ratio might trigger off the second recorder aheadof the stipulated time, thus throwing synchrony intoslight disarray. This can happen when the intensity istoo high, such as with the immediate onset of voicingin "one" as compared with "five." It can happen alsowith decreased signal-to-noise ratio, as with acompressed tape compressed on a BA-43/45 AGCProgram Amplifier Unit 11455. This unexpected..filtering" is double-edged. On the one hand, it alertsthe researcher to the need to carefully control intensityand other acoustic qualities prior to attemptingsynchrony. It also points to the vulnerability of anelectronic/mechanical system short of computercontrol in response to complex speech codes. Asdemonstrated with discrete pure tones, were themostly monosyllabic stimuli (speech segments) strictlylinear, the instrumentation would work perfectly tospecification. As it is, speech is also multidimensionaland the experimentation with the dichotic systemprovides some indirect evidence for this. Up till now,there has been considerable effort in improving thetechnical quality of dichotic tapes. Perhaps the role ofthe ipsilateral pathways and the "psychologicalmoment" of the lag effect in the context of speechlateralization (see Belin et al., 1973) should deservegreater attention. From the evidence that dichoticlistening involves an additive central process whichcombines speech information from both ears (Cullen.Thompson, Hughes, Berlin, & Samson, 1974), thedifferential roles of acoustic, phonetic, and linguisticparameters should also be further investigated.

REFERENCE NOTES

I. Carr. B. M. A new system for preparing dichotic listeningtapes. Paper presented at the annual convention of the AmericanSpeech and Hearing Association. Chicago. November 1969.

DICHOTIC TAPE PREPARATION 451

2. Day. R. Digit-span memory in language-bound andstimulus-bound subjects. Haskins Laboratories: Status Report onSpeech Research. SR-34. 1973, 127-139.

REFERENCES

BERLIN. C. I., LOWE-BELL, S. S., CULLEN, J. K., JR.,THOMPSON. C. L., & LOOVIS, C. F. Dichotic speech perception:An interpretation of right-ear advantage and temporal offseteffects. Journal of the Acoustical Society of America,1973.53.699-709.

BROADBENT. D. E., & GREGORY. M. On the recall of stimulipresented alternately to two sense organs. Quarterly JournalotExperimental Psychology, 1961. 13, 103-109.

CULLEN. 1. K.. JR.. THOMPSON, C. L.. HUGHES, L. F., BERLIN.C. I .. & SAMSON. D. S. The effect> of varied acoustic parametersof performance in dichotic speech perception tasks. Brainand Language. 1974, 1, 307-322.

IRVINE. 1. W Handedness preference. manual dexterity, earasymmetry in dichotic listening and grade 2 reading proficiency.Unpublished doctoral dissertation, University of Alberta, 1972.

Lows. S. S.. CULLEN, 1. K., JR.. BERLIN,C. I., THOMPSON, C. L.,& WILLETT. M. E. Perception of simultaneous dichotic andrnonotic monosyllables. Journal of Speech and HearingResearch. 1970. 13. 812-822.

RUBINO, C. A. A simple procedure for constructing dichoticlistening tapes. Cortex, 1972. 8, 335-338.

STUDDERT-KENNEDY, M., & SHANKWEILER, D. Hemisphericspecialization for speech perception. Journal of the AcousticalSociety C!fAmerica, 1970, 48, 2, Pt. 2, 579-594.

YATES, A. 1. Technical, methodological and theoreticalproblems in dichotic stimulation research. AustralianPsychologist. 1972.7.2-19.

YATES, A. 1., SMITH, P. J., BURKE, B. D., & KEANE, M. A. Atechnique for the construction of discrete dichotic stimulationmaterial. Behavior Research Methods & Instrumentation,1969.1.257·258.

(Received for publication February 12, 1975;revision received April I, 1975.)