Hit and False-Positive Rates for the Middle Latency Response in Patients with Central Nervous System Involvement

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1 J Am Acd Audiol 1 : (1999) Hit nd Flse-Positive Rtes for the Middle Ltency Response in Ptients with Centrl Nervous System Involvement Frnk Musiek* Lori Chrettet Tim Kelly* Wei Wei Lee* Erik Musiek~ Abstrct We sought to determine the test efficiency of the middle ltency evoked response for identifying or differentiting subjects with nd without centrl nervous system (CNS) involvement. Receiver operting chrcteristic curves were estblished for hit nd flse-positive rtes for 26 subjects with CNS lesions nd 26 control subjects mtched for ge nd hering sensitivity. The lesions involved but were not limited to the uditory regions of the CNS. Middle ltency evoked response ltency nd mplitude mesurements were mde for the N nd P wves recorded t C3 nd C electrode sites following stimultion of the left nd right ers. Intrsubject comprisons were mde for ipsilterl nd contrlterl stimultion/recording conditions. Amplitude mesures were superior to ltency mesures. For mplitude, percentge differences from contrlterl comprisons proved to be the most sensitive nd specific mesure. The clinicl implictions of findings re discussed. Key Words : Centrl uditory disorders, centrl uditory nervous system, centrl uditory processing, centrl nervous system, evoked potentils, middle ltency evoked response Abbrevitions : ABR = uditory brinstem response, CANS = centrl uditory nervous systems, CNS = centrl nervous system, MLR = middle ltency response, ROC = receiver operting chrcteristics he (uditory) middle ltency response (MLR) is series of verged neuroelectricl responses tht cn be recorded T from the sclp. Geisler et l (1958) were the first to report on these evoked potentils. Since 1958, the progress nd clinicl use of the MLR hs vried. Although flwed, erly reports tht *Section of Otolryngology, Deprtment of Surgery, Section of Neurology, Deprtment of Medicine, Drtmouth- Hitchcock Medicl Center, Lebnon, New Hmpshire ; tdeprtment of Audiology, Gylord Rehbilittion Hospitl, Wllingford, Connecticut ; *Deprtment of Otolryngology, Albert Einstein College of Medicine, Bronx, New York ; College of Willim nd Mry Willimsburg, Virgini Reprint requests : Frnk Musiek, Section of Otolryngology, Drtmouth- Hitch cock Medicl Center, One Medicl Center Drive, Lebnon, NH the MLR ws primrily ttributble to muscle rtifct hindered its cceptnce s reserch or clinicl procedure. Fortuntely, this is no longer the cse. A better understnding s to recording techniques, genertor sites, mturtionl influences, nd sleep effects hs mde the MLR more pplicble in both clinicl nd reserch settings (see Krus et l, 1994 ; Chermk nd Musiek, 1997). The dvent of the uditory brinstem response (ABR) lso plyed role in the increse in populrity nd use of the MLR. In mny cses, the ABR nd MLR re recorded simultneously, providing informtion bout considerble portion of the uditory pthwys. Recently, the MLR hs emerged s possible test for centrl uditory bnormlities. Studies show tht the MLR is often compromised in ptients with centrl uditory nervous system (CANS) lesions nd/or uditory processing prob-

2 Hit nd Flse-Positive Rtes for MLR/Musiek et l lems ssocited with lerning disbilities (Krus et l, 1994 ; Arehole et l, 1995 ; Chermk nd Musiek, 1997). Cliniclly, one fctor tht must be considered in the dignostic use of the MLR is its intersubject vribility. In norml popultions, the mplitude of the N P complex vries considerbly (Mdell nd Goldstein, 1972 ; Suzuki et l, 1983 ; Chmbers nd Griffiths, 1991 ; Musiek et l, 1994). Due to this mplitude vrince in norml ptients, dignostic efficiency ws compromised. Thus, other criteri nd strtegies emerged tht were more usble for seprting ptients with CANS problems from those without them. Intrsubject rther thn intersubject mplitude comprisons were used in dignostic studies. This ws bsed on dt tht showed similr mplitudes recorded from similr sites on ech hemisphere in norml subjects (Kileny et l, 1987). However, this ws not the cse in subjects with centrl nervous system (CNS) lesions limited to one hemisphere (Krus et l, 1982 ; Kileny et l, 1987). In ptients with CNS involvement, MLR bnormlities re most often observed in the mplitude of the N-P wve on the side of the lesion. This mplitude reduction cn be detected by compring recordings from electrodes on both sides of the hed. The electrode nerest the lesion often yields reduced mplitude, nd this is clled the electrode effect (Krus et l, 1982 ; Kileny et l, 1987 ; Ibnez et l, 1989 ; Sheht-Dieler et l, 1991 ; Musiek et l, 1994). At times, there lso cn be n er effect, when one er yields significntly smller wve thn the other er t the vrious electrode sites. However, the er effect could be ipsilterl or contrlterl to the lesion (Ibnez et l, 1989 ; Musiek et l, 1994). To our knowledge, there is no cler tendency for the er effect to be either ipsilterl or contrlterl to the involved hemisphere. Unlike the more populr uditory brinstem response (ABR), ltency mesures for the MLR do not pper to be s sensitive s intrrsubject mplitude mesures to CANS compromise (Krus et l, 1982 ; Musiek nd Lee, 1997). It is known which mesurements of the MLR re dvntgeous for clinicl use, nd reports hve shown potentil dignostic vlue of the MLR in detecting centrl lesions, but little is known bout the sensitivity nd specificity of the MLR. We know of no reserch tht hs studied receiver operting chrcteristics (ROC) of the MLR in regrd to hit nd flse-positive rtes for popultions with nd without CNS involvement. Therefore, we studied lrge popultion of ptients with CNS involvement nd control group to derive ROC curves for hit nd flse-positive rtes for vriety of ltency nd mplitude criteri. Subjects METHOD Fifty-two subjects, divided into two groups of 26 subjects ech, prticipted in this study. One group served s control subjects (16 women, 1 men). The second group ws composed of ptients with mediclly confirmed lesions of the CANS (14 women, 12 men) (Tble 1). The subjects in the experimentl group hd lesions tht involved, but were not limited to, the centrl uditory system ccording to the ntomic boundries of Glburd nd Snides (198). The subjects in the two groups were mtched for ge (within 5 yers) nd for hering sensitivity (within 15 db for frequencies 5,, 2, nd 4 Hz) on n individul bsis. The ges of the subjects in the control group rnged from 17 to 64 yers (men 41.3 yers). The ges of the subjects in the experimentl group rnged from 16 to 64 yers (men 41.5 yers). Seven subjects in ech group presented with symmetric sensorineurl hering loss. All seven of these subjects in ech group demonstrted norml hering (2 db HL or better) t 5 Hz nd 35 db HL or better hering t nd 2 Hz. At 4 Hz, thresholds rnged from to 65 db HL in both groups. The remining subjects in both groups hd norml hering sensitivity (2 db HL or better for frequencies 5 through 4 Hz). The subjects with CNS involvement were ptients seen for udiologic evlution t the Drtmouth-Hitchcock Medicl Center or Gylord Rehbilittion Hospitl. The control subjects were volunteers, including some udiology ptients. Procedures Audiologic testing ws crried out in sound-treted room. All subjects were wke during MLR testing. The stimulus for the MLR ws -p sec electric squre wve pssed through ER-3A sound insert phones worn by the subjects. This click stimulus ws presented t rte of 9.8 per second. The coustic stimuli were presented t 6 db nhl to the right nd left ers of the subjects in monurl condition, nd the order of presenttion ws pseudorndomized. Impednce cross electrode sites ws 8 kilohms or less. 125

3 Journl of the Americn Acdemy of Audiology/Volume 1, Number 3, Mrch 1999 Tble 1 Subjects with Centrl Nervous System Involvement Pthology Subject Locus of Lesion Right bsl gngli hemorrhge (internl cpsule) Left hemisphere CVA (superior temporl gyrus prietl lobe) Left hemisphere CVA (superior temporl gyrus, inferior prietl lobe) Left hemisphere CVA (superior temporl gyrus nd inferior prietl lobe) Left middle cerebrl rtery neurysm (superior temporl nd inferior prietl regions) Right temporl lobectomy (nterior/mid superior temporl gyrus) Left temporl lobectomy (nterior/middle superior temporl gyrus) Left hemisphere epileptic focus (superior, posterior temporl gyrus) Right temporl lobectomy (nterior/middle superior temporl gyrus) Left nd right hemisphere encephlitis (right temporl prietl re, left Heschl's gyrus) Right temporl lobe CVA (superior posterior temporl gyrus) Right hemisphere CVA (superior temporl gyrus, inferior prietl lobe) Left temporl lobe CVA (mid/posterior superior temporl gyrus) Left brinstem stroke (PICA) (inferior lterl pons superior lterl, medull) Left hemisphere CVA-AVM rupture (superior mid/posterior temporl gyrus, inferior prietl lobe) Left hemisphere CVA-bsl gngli infrct (internl cpsule) Right hemisphere CVA-bsl gngli nd cortex (internl cpsule extending superior temporl gyrus) Right temporl lobe CVA (posterior/superior temporl lobe) Left bsl gngli, thlmic nd pontine infrcts (internl cpsule?, MGB?, left lterl pons) Right hemisphere CVA bsl gngli infrct (internl cpsule extending to the superior, mid temporl lobe) Right temporl lobe CVA (posterior superior temporl gyrus) Left hemisphere CVA/bsl gngli infrct (midposterior temporl lobe, prietl lobe regions extending from bsl gngli insul internl cpsule) Left temporl lobe CVA (posterior superior temporl gyrus) Left temporl prietl CVA (inferior prietl lobe) Left temporl lobe CVA (superior/posterior temporl gyrus insul) Right temporl lobe CVA (posterior/superior temporl gyrus) CVA = cerebrovsculr ccident. Neuroelectricl ctivity ws detected by stndrd sclp electrodes ttched t C3 nd C4, which served s ctive sites. A clip electrode ttched to the contrlterl er served s the reference.the ground electrode ws plced t FP z. All wveforms were subjected to online nlog filtering (2 to 3 Hz) nd offline digitl filtering of vrying bndwidths to help define N nd P wves. Wveforms were displyed on 72-msec time window. One thousnd ccepted trils contributed to ech wveform, nd ll wveforms were replicted. If the replicted wveforms did not hve the sme ltency nd mplitude, n verge of the two wveforms ws tken. Ltency mesurements were tken for the N nd P wves of the MLR. Amplitude mesurements were tken for the N P complex. Ltencies were mesured from the onset of the stimulus to the most negtive repetble pek (N ) occurring between 12 nd 21 msec. The P ws determined s the most positive pek occurring between 21- nd 38-msec post-stimulus onset. Amplitude mesurements were tken from the trough of N to the pek of P. Mesurements Used in Anlyses ROC curves were estblished bsed on the two popultions in this study. The ROC curves were generted by plotting the hit rte by the flse-positive rte for vrious criteri (Turner et l, in press). This study nlyzed both ltency nd mplitude mesurements, which were tken ipsilterlly nd contrlterlly. The ipsilterl mesurement compred the MLR from the right er nd C4 electrode site with the MLR from the left er nd C3 electrode site. The contrlterl mesurement compred the MLR from the right er nd C3 electrode site with the MLR from the left er nd C4 electrode site. Therefore, in this pper, the ipsilterl nd contrlterl conditions refer to the electrode site on the hed nd the er stimulted (nd does not refer to electrode site in reltion to the side of the brin lesion).

4 Hit nd Flse-Positive Rtes for MLRnVlusiek et l Absolute ltency nd mplitude difference between ipsilterl nd contrlterl mesurements were used. We lso used percentge difference for mplitude mesurements, which ws computed s follows : lrger mplitude - smller mplitude difference = smller mplitude RESULTS Ltency of the N Wve The criteri used for developing the ROC curves for N ltency were ltencies in 1-msec steps (rnge : >17 msec to >21 msec). As shown in Figures l, lb, nd lc, the ipsilterl nd contrlterl mesurements hve similr curves, indicting only mediocre hit nd flse-positive rtes. This sitution is improved only slightly by combining ipsilterl nd contrlterl indices. b so mse > msec >2 sec >21 msec Ipsilterl Only >17 msec >18 msec Contrlterl Only Ltency of the P Wve The P ;A wve criteri were estblished using 1- or 2-msec steps (rnge : >28 to >36 msec) to derive the ROC curves. As shown in Figures 2, 2b, nd 2c, the contrlterl condition yields the best ROC curve. The ROC curves re similr for bsolute ltencies of more thn 3 msec. Flse-positive rtes were low. Agin, the hit rtes were only fir. Percent Amplitude Difference of N-P Amplitude differences in percent were estblished using the formul mentioned bove. The ROC curve ws estblished using nine points, rnging from greter thn 1 percent difference to greter thn percent difference for ipsilterl-only, contrlterl-only, nd ipsilterl nd contrlterl-combined conditions. Figures 3, 3b, nd 3c reflect tht the contrlterl-only condition yields the best results. Of note is the result showing tht 5 percent mplitude difference for the contrlterl-only condition comprisons yields percent flsepositive rte. C s 6 - x 4 - x 2 - ROC-Absolute N Ltency / >2 msec >21 msec Ipsilterl & contrlterl >19 msec >18 msec >17 msec Absolute Amplitude Difference of NP Another nlysis performed ws bsolute differences in mplitude. Although this mesurement hs inherent problems (i.e., gret intersubject vribility in MLR mplitude), the contrlterl-only condition gin showed good hit nd flse-positive rte. Criteri rnged Figure 1 The ROC curves for hit nd flse-positive rtes for N bsolute ltency mesures for () ipsilterl condition, (b) contrlterl condition, (c) ipsilterl nd contrlterl conditions combined (ltency criteri re shown in msec long the grph line). 127

5 Journl of the Americn Acdemy of Audiology/Volume 1, Number 3, Mrch 1999 ROC-Absolute P Ltency lpsillerl Only ROC-Amplitude % Difference Ipsilterl Only >15% >1% so >2% 6 - d 1 m 4 - >3 msec x >32 msec >28 msec >29 msec o'~ m d N 2 4 >75% >4% >5% >25% >3% 2 >34 msec >36 msec Flse-Positive Rte (% Flse-Positive Rte (%1 b ROC-Absolute P Ltency Contrlterl Only b ROC-Amplitude % Difference Contrlterl Only Bo - >28 msec w m x 6-4 >34 msec 2 7 >36 msec >29 msec >3 msec p >32 msec ROC-Absolute Pe Ltency Ipsilterl &. Contrlterl C Flse-Positive Rte (%1 ROC-Amplitude % Difference Ipsilterl & Contrlterl Bo - d m 2 d l 6-4 % Figure 2 The ROC curves for hit nd flse-positive rtes for P bsolute ltency mesures for () ipsilterl condition, (b) contrlterl condition, (c) ipsilterl nd Contrlterl conditions combined (ltency criteri re shown in msec long the grph line). Figure 3 The ROC curves for hit nd flse-positive rtes for percentge of mplitude difference for () ipsilterl condition, (b) contrlterl condition, (c) ipsilterl nd contrlterl conditions combined (percentge difference criteri re shown long the grph line). 128

6 Hit nd Flse-Positive Rtes for MLR/Musiek et l ROC-Absolute Amplitude Difference Ipsilterl Only from microvolt differences of >.1 to >.6 (Figs. 4-c). o ' o m W x 'x b so- 6-4 C 2- ) 8 -I ~~>.1 wv >.15 rvr >.2 wv, 2 ~ ROC-Absolute Amplitude Difference Contrlterl only >.t4 p v >.5 wv V r 2> 6 ~L >.;KV ) i 1 2! )..i> >.15 wv /.1 wv ) ROC-Absolute Amplitude Difference Ipsilterl & Contrlterl >.4 wv - 5 ~V >.6 wv J >.3 pv >.2 ~v,->.1 wv / >.15 [V y 2, t 44 6 i 8 Figure 4 The ROC curves for hit nd flse-positive rtes for bsolute mplitude difference for () ipsilterl condition, (b) contrlterl condition, (c) ipsilterl nd contrlterl conditions combined (bsolute difference criteri re shown in volts long the grph line). T DISCUSSION he MLR is potentilly useful dignostic test for identifying centrl uditory bnor- mlities (Krus et l, 1982 ; Kileny et l, 1987 ; Ibnez et l, 1989 ; Sheht-Dieler et l, 1991 ; Musiek nd Lee, 1997), but informtion is lcking on its hit nd flse-positive rtes for popultions with CNS lesions. To our knowledge, no studies hve ttempted to construct ROC curves for the MLR bsed on results from control subjects nd those with CNS lesions. We sought to supply this informtion to better evlute the dignostic vlue of the MLR. To evlute the hit nd flse-positive rtes of the MLR we used two min indices : those of ltency nd mplitude. These indices cn be mesured in reference to the er stimulted nd/or the electrode position on the hed. Other mesurements could hve been used, but in our opinion the dded complexity of dditionl electrodes nd er comprisons would increse clinicl difficulty nd would dd little to the understnding of the MLR's dignostic vlue. Ltency The ROC curves for the bsolute ltencies of the N nd P wves of the MLR indicted only moderte hit nd flse-positive rtes for the mesurements conducted. This finding is consistent with other reports showing little effect of centrl lesions on ltencies of the MLR (Kileny et l, 1987 ; Musiek et l, 1994 ; Musiek nd Lee, 1997). The P wve ltency mesure yields better ROC curves compred to the N ltencies. Krus et l (1982) nd Kileny et l (1987) reported little effect of ltencies of the MLR for temporl lobe lesions, but there ppered to be greter effect on P wves thn on N wves. Ibnez et l (1989) reported tht N ltency ws seldom influenced by CNS lesions. Others report similr findings (Sheht-Dieler et l, 1991 ; Musiek et l, 1994). Celebisoy et l (1996), however, reported similr ltency bnormlities for N nd P in ptients with multiple sclerosis, but in this study bnorml N nd P ltencies occurred in only smll portion of ptients. The MLR P wve, however, hs been shown to shift in ltency in ptients with temporl lobe lesions (Ho et l, 1987 ; Sheht-Dieler et l, 1991). However, even 129

7 Journl of the Americn Acdemy of Audiology/Volume 1, Number 3, Mrch 1999 in reports tht show n extension of the P in temporl lobe involvement, the finding is not consistent nd does not occur in high percentge of subjects with CNS involvement (Ho et l, 1987, Sheht-Dieler et l, 1991). The contrlterl-only recording condition (compring C3 nd right-er stimultion with C4 nd left-er stimultion) nd the combined condition for the P provided better ROC curves thn did the ipsilterl-only condition. For the ipsilterl, contrlterl, nd combined conditions, P ltencies exceeding 3 msec yielded low flse-positive rte even though the hit rte ws mediocre. Criteri of ltencies tht exceed 29 msec yield cliniclly uncceptble flse-positive rte. The 3-msec ltency criterion, lthough not highly sensitive, could be vluble cliniclly becuse when this vlue is exceeded it is likely tht CNS involvement is present if peripherl hering sensitivity is essentilly norml. Similr ltency findings hve been reported by others (Celebisoy et l, 1996). Amplitude Some uthors suggest tht mplitude is better index thn ltency for dignostic use of the MLR (for review, see Chermk nd Musiek, 1997). Other uthors suggest tht intrsubject comprisons for the MLR (e.g., comprisons cross electrodes or comprisons between ers) re the more vluble dignosticlly (Kileny et l, 1987 ; Musiek et l, 1994). This is primrily becuse there is gret vribility in mplitude of the MLR wves in subjects who hve norml uditory systems (Musiek, 1991 ; Hll 1992). Therefore, s with ltency mesurements, we mde ipsilterl nd contrlterl comprisons for individul subjects. We reviewed mplitude differences by percentge of difference s well s on n bsolute voltge bsis. The contrlterl-only condition provided the best ROC curve (see Fig. 3b) nd proved better thn combining both ipsilterl nd contrlterl conditions. Although the combined condition yielded better hit rte, its flse-positive rte ws much higher thn tht of the contrlterl-only condition. A similr trend ws noted for bsolute mplitude differences, lthough overll percentge differences were slightly better thn the bsolute vlues. Percentge differences in mplitude rnging from >5 percent to >2 percent for the contrlterl condition would seem to be cliniclly useful criteri. The hit rtes re not exceptionl but the flse-positive rtes re good. Other MLR studies must be performed tht exmine the 2 percent to 5 percent mplitude difference between sites. Although this rnge of mplitude differences seems to hold promise s criteri for clinicl use, the high degree of vribility found in ptients with CNS lesions rgues for more dt. The nture, size, nd locus of CNS lesions re seldom even similr cross ptients, nd therefore findings my vry (Musiek et l, 1994). This, in turn, my influence the determintion nd selection of prticulr MLR criterion. This is lso why we re reticent to suggest specific criterion nd prefer to discuss rnge of criteri tht my be useful. Contrlterl versus Ipsilterl The present findings indicte, especilly for mplitude, tht the contrlterl recording conditions yield better ROC curves compred to the ipsilterl recording condition. These findings re consistent with the report by Ibnez et l (1989). It is interesting to note tht the MLR does not seem to be consistent in regrd to er lterlity effects in ptients with lesions. Ptients with CNS lesions my hve bnorml MLRs for the er ipsilterl or contrlterl to the involved hemisphere (Ibnez et l, 1989). However, evidence indictes tht the electrode over or closest to the lesion yields reduced mplitude (Krus et l, 1982). The mesurements used in this study re promising wy of tking into ccount both of these effects on the MLR wveform. It is not cler why the contrlterl mesures re more sensitive thn the ipsilterl mesures, but severl fctors cn be considered. One fctor hs n ntomic bsis. It is well known tht the contrlterl fferent uditory pthwy hs more fibers compred to the ipsilterl pthwy. Some MLR dt indicte tht in norml subjects the contrlterl MLR is lrger in mplitude compred to the ipsilterl MLR (Ibnez et l, 1989 ; Sheht-Dieler et l, 1991). These ntomic nd MLR dt my be consistent with the dipole orienttion for the MLR (Pool et l, 1989). The contrlterl MLR recording my reflect the disruption of the dipole more redily thn the ipsilterl MLR ; hence, there is greter differentil when compring ech pthwy's resultnt MLR. The contrlterl route lso covers greter neurl re thn does the ipsilterl route nd thus my be more susceptible to compromise by lesion. Upon reinterprettion of Ibnez et l's dt (1989), we

8 Hit nd Flse-Positive Rtes for MLRnVlusiek et l similrly found tht contrlterl mesures were more sensitive thn ipsilterl mesures. These contrlterl MLR findings my be relted to the contrlterl er effects noted on centrl uditory behviorl tests. As shown mny times, scores on vrious behviorl tests of centrl uditory function will be decresed in the er opposite the hemisphere with the lesion (see Musiek nd Brn, 1991, for review). In this sitution, the contrlterl pthwy for given er is dmged, mking tht er more dependent on the ipsilterl pthwy, which is weker. However, for the opposite er its contrlterl pthwy is intct, yielding norml score. Thus, when the two contrlterl systems re compred, the one with the lesion provides the lower score. This mechnism my be similr for the MLR. Study Implictions The present study hs severl implictions for clinicl dignostic udiology. Our dt re consistent with those of reports indicting tht the mplitude mesurements re of greter vlue thn MLR ltency mesurements in the identifiction of CNS lesions (Ibnez et l, 1989). It is importnt to tke into ccount the ltency mesures for the MLR, but this index usully provides little differentil dignostic informtion. The hit nd flse-positive rtes reported in this study show wht cn be chieved with the MLR in situtions where CANS integrity is in question. In these cses, the clinicin must mke decisions bout which tests cn be used to best provide informtion bout CANS sttus. Informtion on hit nd flse-positive rtes is importnt since it llows the clinicin to evlute the MLR for the purpose of CANS ssessment. In similr mnner, the present study provides informtion on hit nd flse-positive rtes tht cn be used to compre with other electrophysiologic nd behviorl tests of centrl uditory function (Chermk nd Musiek, 1997 ; Hurley nd Musiek, 1997). This enbles the clinicin to select centrl tests with the best sensitivity nd specificity for centrl uditory test bttery. Moreover, the ROC curves represent new informtion for the MLR tht cn be pplied cutiously to estblish pss-fil criteri for mking clinicl decisions. The ROC curves lso provide reference for comprison to future studies on the MLR. Compring ipsilterl er nd electrode results with contrlterl er nd electrode results yields mesurements tht cn be ccomplished esily for clinicl use ; this pproch cn lso provide lterlity mesurements. Certinly, more detiled mesurements cn be mde by exmining vrious er nd electrode interctions, but the more simple pproch ws selected for this report. This mesurement pproch is cliniclly dptble nd does not scrifice sensitivity nd specificity. CONCLUSIONS T he present study estblishes ROC curves for hit nd flse-positive rtes for control subjects nd those with CNS lesions involving, but not limited to, the uditory regions. The ROC curves indicte tht MLR mplitude mesures re more vluble dignosticlly s compred to ltency mesures. The contrlterl MLR mplitude mesurements lone were superior to ipsilterl-only or ipsilterl nd contrlterl mesurements combined. It ws lso noted tht percentge of mplitude differences were superior to bsolute mplitude differences. Finlly, the MLR contrlterl mplitude mesurements indicted tht 2 percent difference provided the best hit nd flse-positive rtes, lthough low flse-positive rtes were obtined for 3 percent through 5 percent differences. REFERENCES Arehole S, Augustine L, Simhdri R. (1995). Middle ltency response in children with lerning disbilities : preliminry findings. J Commun Disord 28 : Celebisoy N, Aydogdu 1, Ekmekci O, Akurekli O. (1996). Middle ltency uditory evoked potentils (MLAEPs) in MS. Act Neurol Scnd 93 : Chmbers R, Griffiths S. (1991). Effects of ge on the dult uditory middle ltency response. Her Res 51 :1-1. Chermk GD, Musiek FE. (1997). Centrl Auditory Processing Disorders. Sn Diego : Singulr Publishing Group. GlburdA, Snides F. (198). Cytorchitectonic orgniztion of the humn uditory cortex. J Comp Neurol 19: Geisler C, Frishkopf L, Rosenblith W (1958). Extr crnil responses to coustic clicks in mn. Science 128 : Hll, JW 111. (1992). Hndbook of Auditory Euoked Responses. Boston : Allyn & Bcon. Ho K, Kileny P, Pccioretti D, McLen D. (1987). Neurologic, udiologic, nd electrophysiologic sequele of bilterl temporl lobe lesions. Arch Neurol 44 :

9 Journl of the Americn Acdemy of Audiology/Volume 1, Number 3, Mrch 1999 Hurley RM, Musiek FE. (1997). Effectiveness of three centrl uditory processing (CAP) tests in identifying cerebrl lesions. J Am Acd Audiol 8: Ibnez V, Deiber P, Fischer C. (1989). Middle ltency uditory evoked potentils nd corticl lesions : criteri of interhemispheric symmetry. Arch Neurol 46 : Kileny P, Pccioretti D, Wilson A. (1987). Effects of corticl lesions on middle ltency uditory evoked responses (MLR). Electroencephlogr Clin Neurophysiol 66 : Krus N, Kileny P, McGee T. (1994). Middle ltency uditory evoked potentils. In : Ktz J, ed. Hndbook of Clinicl Audiology. 4th Ed. Bltimore : Willims & Wilkins, Krus N, Ozdmr O, Hier D, Stein L. (1982). Auditory middle ltency response in ptients with corticl lesions. Electroencephlogr Clin Neurophysiol 5: Mdell JR, Goldstein R. (1972). Reltion between loudness nd the mplitude of the erly components of the verged electroencephlic response. J Speech Her Res 15 : Musiek FE. (1991). Auditory evoked responses in site of lesion ssessment. In : Rintelmnn WF, ed. Hering Assessment. 2nd Ed. Boston : Allyn & Bcon. Musiek FE, Brn JA. (1991). Assessment of the humn uditory system. In : Altschuler R, Bobbin R, Clopton B, Hoffmn D, eds. Neurobiology of Hering: The Centrl Auditory System. New York: Rven Press, Musiek FE, Brn JA, Pinheiro M. (1994). Neuroudiology Cse Studies. Sn Diego : Singulr Publishing Group. Musiek FE, Lee W. (1997). Conventionl nd mximum length sequences middle ltency response in ptients with centrl nervous system lesions. J Am Acd Audiol 8: Pool KD, Finitzo T, Tzong-Hong, Rogers J, Pickett R. (1989). Infrction of the superior temporl gyrus : description of uditory evoked potentil ltency nd mplitude topology. Er Her 1 : Sheht-Dieler W Shimizu H, Solimn S, Tus R. (1991). Middle ltency uditory evoked potentils in temporl lobe disorders. Er Her 12 : Suzuki T, Hirbyshi M, Kobyshi K. (1983). Auditory middle ltency responses in young children. Br JAudiol 17 :5-9. Turner RG, Robinette M, Buch CD. (In press). Clinicl decision nlysis. In : Musiek FE, Rintelmnn WF, eds. Contemporry Perspectives in Hering Assessment. Boston : Allyn & Bcon.