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Clark Shingledecker

Glenn Wilson

Karen Peio

Kirby Gilliland

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PROCEEDINGS of the HUMAN FACTORS SOCIETY-28th ANNUAL MEETlNG-1984EFFECT OF WORKLOAD ON THE AUDITORY EVOKED BRAlNSTEM RESPONSEKirby Gil li l and "Department of Psychology, University of Oklahoma, Norman, OklahomaClark ShingledeckerWorkload and Ergonomics Branch, Wright-Patterson Air Force Base, OhioGlenn Wilson and Karen PeioSystems Research Laboratories, Dayton, OhioABSTRACTThe purpose of this study was to explore the effect of workload level of a grammatical reasoningtask on the auditory brainstem evoked response. Ten male subjects were administered three diffi-culty levels of a grammatical reasoning task. Brainstem evoked responses were recorded beforeand after the randomly presented workload conditions, as well as during each workload condition.The results revealed a consistent increase in Wave VI latency during all workload conditions, butno apparent differentiation between workload condrtions , Post-test brainstem measures revealedthat latency of Wave VI did not recover to pre-test baseline levels.INTRODUCTIONRecent inve sti gations have demonstrated the utilityof electroencephalographic event-related potentials asmeasures of human cognition and task performance. Incoalescing these findings with more global human fac-tors engineering concerns, 0' Donnell (1979) has sug-gested that a number of EEG measures might provideconsiderable promise as metrics for workload assess-ment, among them the auditory evoked brainstem re-sponse(ABR).The ABR provides an exceptionally stable measureof neural functioning in the auditory pathway. The ABRis derived by aver-aging the first 10msec of multiple(1000 or more) auditory pathway evoked potentials,elicited by short-latency click or tone stimuli. Thisaverage evoked potential results in seven, vertex-pos-itive waves helieved to reflect sequential neural activ-ity at successively higher levels of the brainstem aud-itory pathway CJ ewettjRomano , & Williston, 1970;Jewett & Williston, 1971). The putative generators ofWave I through Wave VI I are the acoustic nerve, thecochlear nuclei, the superior olives, the lateral lem-niscus, the inferior colliculus, the medial geniculate,and the thalamocortical radiations, respectively(Stockard & Rossiter, 1977). Thus, the ABR posesas a highly desirable psychophysiological measurebecause it is highly stable within individuals andbecause of the apparent close relationship betweenthe waveform and specific neural structures.Another characteristic of the ABR is that it is pur-portedly insensitive to cortical activity variationsacross wakeful states, as well as sleep or even seda-tion. However, several problems mitigate the findingsof these investigations. For example, at least two of"{(This project was completed while the first authorwas sponsored as a Visiting Scientist through theAir Force System Command, University ResidentResearch Program at the Workload and ErgonomicsBranch, Wright-Patterson Air Force Base, Ohio.37these studies f ailed to analyze a complete complementof waves prior to Wave V (Mendel & Goldstein, 1969;Picton, Hillyard, Galambos, & Schiff, 1971). Of thetwo studies that explored sleep versus wakeful states,one failed to provide any s ystemanc analysisand both may have failed to consider that the wakefulcondition used may not have provided an adequaterange of arousal in relationship to the sleep condition(Amadeo & Shagass, 1973; Jewett & Williston, 1971).Of the four studies that examined resting versus taskperformance conditions, two studies failed to analyzea complete complement of waves (Mendel & Goldstein,1969; Picton et al. ,1971) and another confounded thetreatment conditions by providing a vigilance-typetask during the resting phase (Picton & Hillyard,1974). Only two studies included an analysis of WaveVI. One was compromised by several of the factorsmentioned above (Picton & Hillyard, 1974). The otherstudy reported no Wave"VI differences as subjectsperformed a dichotic listening task (Woods & Hillyard,1978). Additional problems such as a lack of controlfor sex of subjects, low numbers of subjects, and in-consistency among comparison groups make many ofthese earlier findings appear tenuous.There are also more recent studies which direct-ly question the presumed stability of the ABR in rela-tion to cortical state. Bullock (1982) reported length-ening of Wave I and Wave V latencies as a result ofexposure to a visual selective attention task. Lucas(1981,1982) has also demonstrated reductions in ABRWave I and Wave V amplitudes as a function of expo-sure to a visual attention task. Recent pilot data atthe Workload and Ergonomics Branch, Wright-Patter-son Air Force Base have revealed consistent Wave VIlatency increases during attention states. This addi-tional finding of Wave VI shifting is not surprisinggiven that examination of Wave VI is rarely includedin standard ABR analyses. (However, a reanalysisof the Bullock, 1982, data confirms the same patternof Wave VI shifting under attention conditions.)These latter investigations, as well as the previ-ous reassessment of earlier ABR research on cortical at UNIV OF OKLAHOMA LIBRARIES on January 20, 2016pro.sagepub.comDownloaded from PROCEEDINGS of the HUMAN FACTORS SOCIETY-28th ANNUAL MEETlNG-1984state influences, suggest that ABR may very well, beinfluenced by cortical state, and therefore be useful asa workload measure. The purpose of this investigationwas to examine the influence of workload level of-a gram-matical reasoning task on the components of the ABR.METHODSubjectsTen male subjects (ages 2G-36yrs) served as sub-jects. Each subject was screened for drug (caffeine,nicotine, alcohol) and medication use prior to thestudy. All subjects had normal hearing and 20/20natural or correctecl vision.ProcedureEach subject was instrumented with Beckman, sil-ver-silverchloride electrodes at vertex (Cz) and mas-toids for ipsilateral ABR recording. The subject wasthen seated in a sound attenuated booth in a semi-reclinedposition with a push button response pad held in bothhands.Three workload levels of the U. S. Air Force Cr:i-terion Task Set, Grammatical Reasoning Task werepresented to the subject in random order on a CRTmonitor. This task is comprised of statements whichdefine the ordinal relationship between two (or insome cases, more) symbols, followed by the actualsymbols in some order. The subject simply respondstrue or false in relationship to the symbol orderingpresented. Difficulty of the task is regulated by thenumber of symbol relationships presented and the tense(posrtive or negative) of the relationship. In this study,the Low Workload condition consisted of one-statement,positi ve tense cases; 1. e., " # FOLLOWS ~, -- *# ."The Moderate Workload condition consisted of one-statement, negative tense cases; i.e., "# DOES NOTFOLLOW ~, -- *#." And, the High Workload conditionconsisted of two-statement, positive tense cases; I.e.," # FOLLOWS~' ~'PRECEDES @-- #*@." Therelative difficulty of these conditions has been estab-lished through prior standardization studies of theCriterion Task Set (Shingledecker, personal commun-ication, December 1983). Task performance sessionslasted approximately three minutes at each workloadlevel with a two minute rest period between workloadsessions.Auditory brainstem evoked potentials were record-ed during each workload ses si on , as well as during apre- and post-test baseline period. The ABR data ~erecorded on a Nicolet CA1000 Clinical Averager. Thebroadband click stimuli (center frequency 2 KHz) werepresented at a rate of 11.1 c/sec, at 75 dB SL, with aduration of 100 usec. Low and high pass filters were150 and 3000 Hz, respectively. A total of 2000 clicktrials were averaged for each ABR recording. TheseABR data were collected as part of a larger study inwhich other EEG measures were recorded; however,only the ABR results will be reported here.RESULTSMANOVA analysis of latency and amplitude ABRdata yielded only a significant difference for the latencydata, £. (28,66) = 3.07, £<..001 (Wilks' !::..) ANOVA38analyses of the latency data yielded significant differ-ences for Wave I (£.(4,36)= 5.73, £ <. •OD, Wave II I(£.(4,36) = 3.15, £< .05), Wave V (!'(4,36) = 3.63,P.< .05), and Wave VI (£.(4,36) = 14.20, p.< .0001).Multiple comparison tests (Scheffe , 1953) failed toreveal any significant differences among conditionsfor Waves I I I and V. A significant difference atWave I was found between the Moderate and Low Work-load conditions only. At Wave VI, all workload con-ditions produced latencies which were significantlylonger than the pre-test baseline latency. Also, thepost-test baseline was significantly longer than thepre-test baseline latency. No significant differenceswere found in either the ANOVA or multiple compari-son tests of the amplitude data for any waveform com-ponent.A MANOVA analysis of interpeak latencies wasalso significant, !' 06,64) = 4.29, P.<. .001 (Wilks I !).ANOVA analyses yielded significant differences forthe I-I I I, I-V, and I-VI interpeak intervals. Forthe I-I II interpeak interval, multiple comparisonsyielded a significant difference between the ModerateWorkload condition and all other conditions exceptLow Workload. The I-I I I interval was longer duringModerate Workload as compared to the other conditions.For the I-V interpeak interval, the only multiple com-parison that was significant revealed a longer inter-val during Moderate Workload as compared to the pre-test baseline. The multiple comparison test resultsfor the I-VI interpeak interval were similar to theWave VI latency data, i.e., the I-VI interpeak laten-cy was significantly shorter during pre-test baselineas compared to all other conditions.Means and standard deviations for Wave VI latencyand the Wave I-VI interpeak latency are presented inTable 1.Table 1.Means and standard deviations for Wave VIlatency and Wave I-VI interpeak latency forbaseline and workload conditions.Condition VI Latency I-VI LatencyPretest Baseline 7.32 (.24) 5.71(.25)Low Workload 7.49(.28) 5.90 (.30)Moderate Workload 7.46 (.29) 5.92 (.30)High Workload 7.51 (.29) 5.88 (.28)Post-test Baseline 7.45 (.30) 5.82 (.27)DISCUSSIONThe results of this study suggest that the auditorybrainstem evoked response is affected by cognitiveworkload, as compared to prior resting conditions.This seemed especially true for Wave VI, the medialgeniculate. The ABR differences observed did notdifferentiate in any systematic manner across the YKJrk-load conditions represented in this study, however.Also, the failure of the post-test ABR (at 5 min follow-ing the last workload session) to return to pre-testbaseline levels suggests a protracted recovery at UNIV OF OKLAHOMA LIBRARIES on January 20, 2016pro.sagepub.comDownloaded from PROCEEDINGS of the HUMAN FACTORS SOCIETY -28th ANNUAL MEETlNG-1984period for Wave VI shifting in rel ation to cogru tiveworkload condiuons .While significant differ-ences were found at ear-lierwave components of the ABR, only those found at WaveVI were consistently affected by all workload condl-trons , However, the effects found at other wave com-ponents seemed to invol ve longer latency at ModerateWorkload as compared to other conditions or pre-testbaseline. Of the three workload condi tions, the Mod-erate condition was the only one which utilized the neg-ative tense in the or-dinal position statements (e. g. ,1, DOES NOT FOLLOVJ #). Since the difficulty r-atingof these tasks was based primarily on reaction timeand self-reported workload level, these ABR findingssuggest that a different relationship may be revealedthrough ABR measurement than through performanceor self-report measures.These results present additional evidence that theABR is s en s it i ve to workload, i.e., cor-tical ac n vitylevel. Unlike previous studies (Lucas, 1981, 1982),no consistent Wave I or Wave V alter-ations were found ..Not unlike much of the previous research on ABRandcortical act iv i ty level, no evidence was found forperipheral gating. However, the evidence presentedin this study does suggest that some form of processingor some allied processing mechanism seems to occurquite early (approximately 7.0 to 8.0 ms ec) afterstimulus presentation. These data support the viewthat some ABR components do appear to be s en s it iveto workload demand or cortical activation state. Thus,ABR may hold potential as a measure of workload.REFERENCESAmadeo, M., & Shagass, C. Brief latency click evokedpote nn al s during waking and sleep in man. fSycho-physiology, 1973, 1:.2, 244-250. --Bullock, W. B. Age and attention effects on the audit-ory brainstem response. A paper presented at theSociety for Psychophysiological Research MeetingMinneapolis, Minn., October, 1982.Jewett, D.L. & Romano, M.N., & Williston, J.S.Human auditory evoked potentials: possible brain-stem components detected at the scalp. Science,1970, 167, 1517-1518.Jewett, D. r:;- & Williston, J . S. Auditory-evoked farfields averaged from the scalp of humans. Brain,1971, 94, 681-696. --Lucas, J. H-:-The role of efferent inhibition in humanauditory attention: An examination of the auditorybrainstem potentials. 1nternational Journal ofNeur-os c ience , 1981, 12, 137-145. ----Lucas, J. H. The effects Ofattention and voluntarymiddle ear muscle contractions on the human aud-itory brainstem pot enti al s . A paper presented atthe Society for Psychophysiological ResearchMeeting, Minneapolis, Minn., October, 1982.Mendel, M. I. & Goldstein, R. The effect of test con-di n ons on the early components of the averagedelectroencephalograph response. Journal S?!~and Hearing, 1969, g, 344-350.0' Donnell, R. D. Contributions S?! psychophysiologicaltechnigues ~ aircraft design and other operationalproblems. AGARD-AG-244, 1979.Picton, TW. & Hillyard, S .A. Human auditory evokedpotentials I I: Effects of attention. Electroenceph-39alography ~ni ClImcal NeurophyslOlogy, 1974,36, 191-199.Picto~T.W., HIllyard, S.A., Galambos, R. &Schiff, M. Human auditor-y attention: A centralor peripheral process? Science, 1971, 173,351-353. -Scheffe, H. A method for judging all contrasts in theanalysis of vanance. Brornet rrka , 1953, 53,347-358. --Stockard, J. J. & Rossiter, V. A. Climcal pathologic-al correlates of bramstem auditory responseabnormalmes . Neurology, 1977, 27, 316-325.Woods, D.L. & HIllyard, S.A. Attention at thecocktail party: Brainstem evoked responsesreveal no peripheral gan ng . In D.A. Ottof Ed . )MultIdISCIplInary perspectives !..!:!. event-relatedbrain 'p'?.!.ential !,~search. l'roceedmgs of theFourth International Congress on Event-RelatedSlow Potentials of the Brain, Henderson, NorthCarolina, April, 1976. EPA-600/9-77-043,December 1978. at UNIV OF OKLAHOMA LIBRARIES on January 20, 2016pro.sagepub.comDownloaded from 

Effect of Workload on the Auditory Evoked Brainstem Response

 The purpose of this study was to explore the effect of workload level of a grammatical reasoning task on the auditory brainstem evoked response. Ten male subjects were administered three difficulty levels of a grammatical reasoning task. Brainstem evoked responses were recorded before and after the randomly presented workload conditions, as well as during each workload condition. The results revealed a consistent increase in Wave VI latency during all workload conditions, but no apparent differentiation between workload conditions. Post-test brainstem measures revealed that latency of Wave VI did not recover to pre-test baseline levels. </jats:p

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Effect of Workload on the Auditory Evoked Brainstem Response

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