Unsuccessful Use of Binaural Amplification by an Elderly Person

Transcription

1 J Am Acad Audiol 8 : 1-1 (1997) Unsuccessful Use of Binaual Amplification by an Eldely Peson Rose Chmiel* James Jege* Emily Muphy* Fancis Piozzolot Caolyn Tooley-Young* Abstact An eldely peson who pefeed and pefomed bette with monaual than with binaual amplification was extensively studied, both audiologically and neuopsychologically, in seach of an explanation fo the phenomenon. Paticula emphasis was placed on the study of dichotic speech peception, both behavioally and electophysiologically. Results suggest that ageelated changes in intehemispheic tansfe of auditoy input via copus callosum may undelie the pefeence fo monaual amplification. Implications fo the evaluation of amplification potential in eldely pesons ae discussed. Key Wods : pesbyacusis Aging, amplification, binaual, copus callosum, eldely, heaing aids, Abbeviations : ABR = auditoy bainstem esponse ; ALD = assistive listening device ; BTE = behind-the-ea heaing aid ; DPOAE = distotion-poduct otoacoustic emissions ; DSI = dichotic sentence identification test ; LVR = late vetex esponse ; MCR = message-tocompetition atio ; MLR = middle latency esponse ; NAL = National Acoustic Laboatoy of Austalia ; SBR = signal-to-babble atio ; SSI = Synthetic Sentence Identification Test espite the theoetical supeioity of binaual heaing (Haggad and Hall, 1982 ; D Books, 1984 ; Balfou and Hawkins, 1992), some heaing-impaied pesons pefe monaual to binaual amplification (Edman and Sedge, 1981 ; Scheus and Olsen, 1985 ; Stephens et al, 1991 ; Dempsey, 1994). Economic consideations ae undoubtedly the pivotal facto in many such cases ; the cost of two heaing aids is often beyond the use's means. Thee ae, howeve, othe individuals, especially in the eldely secto, who actually appea to function moe effectively with one heaing aid than with two. The pesent pape epots the esults of intensive testing of one such individual. We sought a bette undestanding of the basis fo the phenomenon. *Depatment of Otohinolayngology and Communicative Sciences, tdepatment of Neuology, Baylo College of Medicine, Houston, Texas Repint equests : James Jege, Taylocest, Houston, TX CASE HISTORY he subject of this epot, AK, is a 9-yeaold woman with a 13-yea histoy of gad- T ual decline in the heaing of both eas following aspiin theapy fo shoulde pain. Thee is no histoy o obvious evidence of stoke, dementia, neuologic o othe systemic disease. She has eceived homone theapy fo osteopoosis, but othewise has a negative medical histoy. AK is active and in good geneal health. She was fist evaluated by ou audiology sevice at the age of 87. She had been fitted with binaual aids at anothe cente and complained that they wee not satisfactoy, especially in the pesence of backgound noise. In the following sections, we pesent (1) basic audiometic data; (2) monaual auditoy evoked potential esults ; (3) behavioal and electophysiologic esults on a battey of dichotic speech tests ; (4) pefomance on a battey of neuopsychological tests ; and (5) the evaluation of heaing aid pefomance in both monaual and binaual modes.

2 Jounal of the Ameican Academy of Audiology/Volume 8, Numbe 1, Febuay 1997 BASIC AUDIOMETRIC DATA n this section, we pesent data elating to the degee, configuation, and symmety of peipheal auditoy function. Measues include conventional pue-tone and speech audiomety, distotion-poduct otoacoustic emissions (DPOAEs), and monaual auditoy evoked potentials. Pue-Tone and Speech Audiomety Figue 1 shows conventional ai-conduction thesholds obtained at the fist evaluation, at the age of 87. Bone-conduction thesholds, tympanogams, and acoustic eflex thesholds wee all consistent with sensoineual loss. These data ae omitted fo the sake of claity. In the low-fequency egion, the ai-conducted theshold configuation ose fom about 6 db at 25 Hz to about 3 db at 2 Hz and the ight ea was slightly pooe than the left ea. In the high-fequency egion, thee was a steep decline in both eas and slightly geate loss in the left ea. The aveage of the HTLs at 5, 1, and 2 Hz (pue-tone aveage [PTA]) was 47 db fo the ight ea and 43 db fo the left ea. At a pesentation level of 8 db HL, phonemically balanced (PB) wod ecognition scoes wee 96 pecent fo the ight ea and 76 pecent fo the left ea. At the same pesentation level, Synthetic Sentence Identification (SSI) scoes (Jege et al, 1968) at db message-to-competition atio (MCR) wee 2 pecent fo the ight ea and 1 pecent fo the left ea. At the +1 db MCR, SSI scoes wee 1 pecent in both eas. S: AK Otoacoustic Emissions DPOAEs wee measued by means of a commecially available system (Etymotic Reseach, CUBeDIS'TM vesion 2.4). Pobe tone SPLs wee 65 db, the f2/fl atio was 1.2, and the amplitude of the 2f,f2 distotion poduct was plotted as a function of the f2 fequency. Figue 2 shows the esults fo ight and left eas. Inteestingly, distotion poducts ae elatively obust in both eas elative to the sensitivity loss. At 2 Hz, fo example, whee the theshold heaing level was 3 db in both eas, DPOAEs wee still 15 to 2 db above the noise floo. At 4 Hz, whee the theshold heaing levels wee 4 db in the ight ea and 5 db in the left ea, DPOAEs wee still 6 to 12 db above the noise floo. These esults suggest that at least pat of the theshold sensitivity loss in both eas is on a etocochlea basis. Of paticula inteest, moeove, is the obsevation that, in the fequency egion above 3 Hz, the left ea shows consistently stonge emissions than the ight ea, in spite of the pooe left-ea behavioal thesholds. This esult is not consistent with a geate cochlea deficit in the left ea than in the ight ea in this high-fequency egion. Monaual Auditoy Evoked Potentials This seies of measues evaluates the status of monaual pocessing at vaious levels of the ascending auditoy pathways. Auditoy evoked potentials wee measued in the ealy (auditoy bainstem esponse [ABR]), middle (middle latency esponse [MLR]), and late (late 2 F z. m c J db Pue Tone Audiomety I 1 J a W m -a c N -1 Right EaO Left Ea X J E m Figue 1 Pue-tone ai-conduction thesholds in subject AK, an 87-yea-old woman with a 1-yea histoy of pogessive bilateal heaing loss. Bone-conduction thesholds, tympanogams, and acoustic eflex thesholds wee all consistent with sensoineual heaing loss. These data ae omitted fo the sake of claity Fequency in khz Figue 2 Distotion-poduct otoacoustic emissions of subject AK. Note elatively obust emissions fom left ea, especially in the fequency ange above 3 Hz.

3 Binaual Amplification / Chmiel et al vetex esponse [LVR]) latency anges. Fo ABR, conventional clinical ecoding techniques wee employed. Activity at the vetex electode (C.) was efeed to ight and left ealobes with foehead as gound. Fo all late potentials, activity was ecoded at 18 active electodes aanged on the scalp accoding to the intenational 1-2 system and efeed to a common aveage efeence. ABR wavefoms wee unemakable. The wave V latency was 5.6 msec on each ea and amplitudes wee appoximately equal. A simila situation held fo the MLR and the LVR wavefoms. Latency of the positive peak Pa, measued at electode F., was about 4 msec fo each ea and amplitudes wee simila. Latencies of the negative peak Ni and the positive peak P2, measued at electode C., wee appoximately 12 and 18 msec, espectively, in each ea. Again, amplitudes wee simila. DICHOTIC SPEECH TESTING ichotically pesented speech signals challenge the cental auditoy pocessing mech- D anisms of the binaual system. To detemine the status of AKs binaual pocessing capabilities, we administeed thee diffeent dichotic measues : the Dichotic Sentence Identification (DSI) Test (Fife et al, 1983) ; the Cued Listening Test (Jege and Jodan, 1992); and a newly devised dichotic PB wod test pocedue (Jege et al, 1995) designed to elicit P3 event-elated potentials sepaately fo ight-ea and left-ea vebal and nonvebal tagets. Figue 3 shows individual ea scoes on the DSI test unde a vaiety of expeimental conditions. When single sentences wee pesented monaually (lowest bas), scoes wee 1 pecent fo both ight and left eas. When a sequence of two sentences was pesented monaually, scoes wee 9 pecent in the ight ea and 75 pecent in the left ea. When pais of sentences wee pesented dichotically in a divided attention mode (espond to both eas), the ight ea scoe emained at 9 pecent but the left ea scoe dopped to 15 pecent, indicating a stiking ight-ea advantage, o left-ea disadvantage, in the dichotic listening mode. The emaining thee dichotic conditions epesent systematic manipulation of the dichotic sentence task in ode to detemine the extent to which the appaent left-ea disadvantage in the divided attention mode can be attenuated by lessening the cognitive load. In the focused attention mode, AK was equied to espond only to one cued ea. The M Postcued Pecued Focused Attention Divided Attention Two in Sequence Single Sentence Pecent Coect L Ea. ~ Right E Figue 3 Dichotic sentence identification test esults fo subject AK in six diffeent expeimental conditions. Note elatively constant left-ea scoes in dichotic mode despite manipulation of cognitive demand. ight ea was cued fo a block of 1 tials, then the left ea was cued fo anothe block of 1 tials. Hee, pefomance on the cued ight ea inceased to 1 pecent, but pefomance on the cued left ea, instead of impoving due to lessening of the cognitive demand, actually declined to 1 pecent. In the pecued condition, each tial was cued immediately befoe its pesentation athe than in blocked fashion. In the postcued condition, each tial was cued immediately afte its pesentation. In both of these individually cued conditions, left ea pefomance emained at the same level as in the blocked divided and focused attention modes. Figue 4 shows pefomance on the cued listening task (Jege and Jodan, 1992). In the sound field, AK listened fo a speech taget (the pesonal ponoun "I") embedded in a continuous naative. The same naative was pesented fom speakes located to the ight and to the left of AK but thee was a 6-second time delay between speakes. The to-be-attended speake was pecued ("listen ight " o "listen left") in blocks of five tagets each. Successive blocks wee pesented in andom ode. A total of five blocks was pesented to each side. Multitalke babble was pesented fom a loudspeake mounted diectly above AK in the sound-teated chambe. Coect taget identification as a function of signal-to-babble ation (SBR) is shown sepaately fo taget-ight and taget-left conditions. At the most favoable SBR (+1 db), thee was little diffeence between sides. But as the SBR became moe unfavoable, pefomance was substantially pooe fo the taget-left than fo the taget-ight condition. To exploe futhe the natue ofaks maked left-ea disadvantage on the dichotic sentence task, we constucted two additional dichotic measues, one vebal and one nonvebal. Both

4 Jounal of the Ameican Academy of Audiology/Volume 8, Numbe 1, Febuay 1997 U N U C U a SBR in db Figue 4 Cued listening test esults fo subject AK at fou signal-to-babble atios. wee based on the dichotic pesentation of pais of PB wods. In addition, both wee cast in the "oddball" paadigm useful fo ecoding eventelated potentials fom electoencephalic activity. In both the vebal and nonvebal vesions of the oddball paadigm, the "fequent" event was the simultaneous pesentation of two andomly selected PB wods spoken by the same male talke. Fo the vebal task, the "ae" event was the occuence of a taget wod hyming with "book" (e.g., "look," "took," "cook," etc.), also ecoded by the same male talke. Fo the nonvebal task, the ae event was a change in gende of the talke fom male to female. In each mode, vebal and nonvebal, a total of 3 wod pais was pesented in succession. Thee wee 9 ae o taget events and 21 fequent o nontaget events (a pioi pobability 3%). Rae events wee andomly intespesed among fequent events with the single constaint that a ae event could not occu moe than twice in succession. Both vebal and nonvebal tagets wee pesented to the ight ea on half of the ae tials and to the left ea on the othe half. In each mode, esponses to nontagets (fequent events) to ight- and to left-ea tagets (ae events) wee aveaged sepaately. Electoencephalogaphic activity was ecoded fom gold-cup scalp electodes affixed accoding to the intenational 1-2 system. Ocula activity was monitoed by electodes above and below the left eye. Individual epochs wee ejected automatically wheneve electical activity exceeded 3 l.,v Afte the pesentation of each wod pai, AK esponded by pushing one of two buttons aanged vetically on a esponse boad. The uppe button indicated that a taget wod had been head in eithe ea. The lowe button signaled that a nontaget wod pai had been head. Reaction times (elapsed time fom wod-pai onset to button push) wee automatically ecoded. Figue 5 shows eaction times fo the ight and left eas fo both vebal and nonvebal tagets. The expected left-ea disadvantage in the vebal mode is evident. Inteestingly, moeove, the nonvebal tagets show a ight-ea, athe than a left-ea, disadvantage. Coect esponses wee faste fo ight-ea vebal tagets and fo left-ea nonvebal tagets. Figue 6 shows aveaged wavefoms ecoded at the P3 electode (left of P.) fo ight-ea and left-ea tagets in both the vebal and nonvebal tasks in ou expeimental subject (S : AK). Each wavefom is the subtaction of the fequent (nontaget) wavefom fom the ae (taget) wavefom. The event-elated potential, usually efeed to as the P3 o P3 esponse because of positivity in the post-stimulus inteval beyond 3 msec, is clealy evident in the ight-ea esponse to vebal tagets and in the left-ea esponse to nonvebal tagets. Thee was vitually no P3 esponse to vebal tagets pesented to the left ea, and a geatly attenuated esponse to nonvebal tagets pesented to the ight ea. Fo compaative puposes, we pesent, in Figue 7, analogous data obtained fom a 78-yea-old man with a simila degee of loss but without behavioal evidence of a lage dichotic asymmety. In this contol subject (S : Contol), thee was a slightly lage ight-ea esponse in the vebal mode, and a slightly lage left-ea esponse in the nonvebal mode, but the amplitude diffeences wee much smalle Vebal Reaction Time Task Nonvebal " Right Ea la Left Ea Figue 5 Reaction times fo ight and left eas of subject AK on dichotic PB wod pais pesented as vebal (phonemic taget) o nonvebal (voice gende taget) dichotic tasks.

5 Binaual Amplification / Chmiel et al Nonvebal Vebal Nonvebal Vebal Figue 6 Paoo wavefoms at electode P3 fo ight and left eas of subject AK on dichotic PB wod pais pesented as vebal (phonemic taget) o nonvebal (voice gende taget) dichotic tasks. than those of AK. Figue 8 plots the amplitude diffeence, at peak positivity, between tagetight and taget-left wavefoms fo both subjects in the vebal and nonvebal modes. Ou expeimental subject (AK) shows a substantially lage left-ea disadvantage in the vebal mode and a substantially lage ight-ea disadvantage in the nonvebal mode. Figue 9 compaes maps of the topogaphic distibution of evoked voltages acoss the suface of the scalp at the positive peak of the P3 wavefom (defined by the wavefom at the P3 electode) in subject AK (Fig. 9A) and in the contol subject (Fig. 9B). In the contol subject, the distibution of positivity was centeed at the P3 electode and was simila in all fou conditions. In subject AK, howeve, the topogaphic distibution of positivity was centeed ove the Vebal Nonvebal Msec Figue 7 Paoo wavefoms at electode P3 fo ight and left eas of eldely subject without dichotic deficit on dichotic PB wod pais pesented as vebal (phonemic taget) o nonvebal (voice gende taget) dichotic tasks Amplitude Diffeence at P3 (Taget Right - Taget Left) in RV Figue S Compaison of ea diffeence scoes of Paoo amplitude fo subject AK and eldely contol subject without dichotic deficit. P3 electode fo ight-ea vebal tagets but disappeaed fo left-ea vebal tagets. In the case of nonvebal tagets, the situation was evesed. The aea of positivity was lage fo left-ea but much smalle and displaced to the left tempoal egion fo ight-ea tagets. These maps highlight the asymmety in AK's esponses to dichotic stimuli, and the fact that this asymmety can be evesed by alteation of the taget speech featue fom vebal to nonvebal. They also suggest a shift in the oientation of the dipole geneating the esponse to nonvebal tagets deliveed to the ight ea. NEUROPSYCHOLOGICAL TEST RESULTS A battey of neuopsychological tests was administeed in ode to assess AK's geneal intelligence, easoning ability, language compehension, visual easoning ability, memoy, psychomoto skills, and pesonality. We also included measues specifically elevant to callosal function. All measues wee administeed in thei standad manne accoding to published instuctions, scoing citeia, etc. The complete battey, selected scoes, and the intepetation of each test esult ae summaized in Table 1. The esults of this test battey showed evidence consistent with AK's age and educational backgound. On measues of geneal intellectual and easoning ability, she scoed just above the noms fo he age fo both vebal and nonvebal skills. He psychomoto abilities wee also in the aveage ange, but with a substantial discepancy in pefomance between the

6 Jounal of the Ameican Academy of Audiology/Volume 8, Numbe 1, Febuay 1997 S : AK n +4.. Vebal, LE Vebal, RE i -4. Nonvebal, LE A Nonvebal, RE S : Contol +2.. Vebal, LE il Vebal, RE -2. v+4.. i "Illmi Nonvebal, LE ~ Nonvebal, RE s -4. B Figue 9 Topogaphic bain maps showing distibution of P.,oo auditoy event-elated potentials acoss suface of scalp. A...subject AK, B...eldely subject without dichotic deficit. ight and left hands. The ight hand was supeio in all cases. Memoy evaluation evealed expected age-elated difficulties. No psychological o adjustment poblems wee evealed by the evaluation. The Telephone Dialing Test equies the ecollection of digits in the pesence of auditoy distaction. Hee, esults wee consistent with the audiologic findings of pocessing difficulty in the pesence of competing continuous discouse (e.g., SSI). The esults of two tests, the Taffic Reaction Time test and the Haptic Naming Test, showed esults consistent with a deficit in intehemispheic communication. On the Haptic Naming Test, AK had consideable difficulty naming objects out of view with he left hand. On the Taffic Reaction Time Test, she had faste eaction times when infomation was pesented to the ipsilateal visual field (i.e., when she attempted to stop a ca with he ipsilateal foot) than when it was pesented to the contalateal field. EVALUATION OF HEARING AID PERFORMANCE n ode to detemine the extent to which AKs cental auditoy pocessing abilities impacted the use of amplification, we measued sentence identification in the pesence of competing continuous discouse unde fou conditions of conventional heaing aid amplification : (1) unaided, (2) aided in the ight ea only, (3) aided in the Table 1 Summay of Neuopsychological Test Results Measue Scoe Intepetation Raven Pogessive 65th pecentile " Matices Boston Naming Test 7th pecentile Mufti-Scoe Depession Inventoy ITPA Visual Closue Westen Aphasia Battey NEO Five Facto Inventoy Bief Symptom Index Selective Reminding Test Gooved Pegboad Test Finge Tapping Test Delayed Non-Matching to Sample Haptic Naming - ight hand 8/8 Haptic Naming - left hand 5/8 S11 Telephone Dialing Test 2th pecentile SI Taffic Reaction Time Test Left field-left foot 78 msec Left field-ight foot 912 msec SI Right field-ight foot 695 msec Right field-left foot 14 msec SI " = within nomal limits ; tsi = significant impaiment.

7 Binaual Amplification / Chmiel et al left ea only, and (4) aided binaually In addition, we compaed ight-ea aided and left-ea aided amplification though an assistive listening device (ALD). Conventional heaing aids wee fit using a Fonix 65-C Real-Ea Measuement System. Fom the pue-tone audiometic data, the desied fequency esponse of the heaing aid was detemined using the National Acoustic Laboatoies' (NAL) pocedue (Byne and Dillon, 1986). Real-ea insetion gain measuements wee obtained unaided and with the heaing aid coupled to the system. Then, a compute algoithm was initiated, which povided an estimate of the best fit of the gain and fequency esponse of the heaing aid to the NAL taget. The heaing aid was adjusted until the fequency esponse matched as closely as possible the NAL taget esponse. Figue 1 shows the esult of soundfield testing of a pogammable behind-the-ea (BTE) aid fitted eithe to the ight ea, the left ea, o both eas (binaual). Test mateials wee SSI sentences pesented fom a loudspeake at degees azimuth eithe in quiet (no competition) o while competing continuous discouse was pesented fom a loudspeake at 18 degees azimuth at vaying MCR atios. Results show that pefomance was best when the ight ea was aided, pooest when the left ea was aided, and intemediate when both eas wee aided. Figue 11 shows the esult when the ALD was tested with the same mateials. Pefomance was almost within nomal limits when the ight ea was aided, but pooe when the left ea was aided. DISCUSSION u subject, AK, is typical of many eldely heaing-impaied pesons who, in spite of elatively symmetic sensitivity loss, appea to function bette with monaual than with binaual amplification. She was initially fitted with binaual aids but neve found this aangement satisfactoy. She is a satisfied use of ight monaual amplification but does badly when any amplification is attempted on the left ea. Subject AK illustates the binaual intefeence phenomenon descibed by Jege et al (1993). The pesentation of vebal infomation to the left ea appeas to intefee with vebal pocessing by the ight ea. At least thee possible explanations suggest themselves : (1) a geate peipheal deficit on the left ea leading to imbalance in, o asynchony of, binaual input, (2) a cognitive Figue 1 Evaluation of heaing aid pefomance fo subject AK, using SSI sentences. Compaison of unaided scoes with aided scoes fo monaual ight, monaual left, and binaual fittings. deficit limiting successful use of binaual input, o (3) an auditoy pocessing deficit limiting successful use of binaual input. The possibility of a geate peipheal (i.e., cochlea) deficit on the left side must be consideed since audiometic theshold HTLs wee slightly pooe at fequencies above 2 Hz on the left ea. The diffeence was 2 db in favo of the ight ea at 3 Hz, 1 db at 4 Hz, and 1 db at 6 Hz. In futhe suppot of a peipheal asymmety is the fact that thee was a 2 pecent diffeence in PB wod ecognition scoes-a significant diffeence by the Thonton and Raffin (1978) test. Aguing against peipheal asymmety as the basis fo the appaent binaual intefeence effect, howeve, ae the DPOAEs (see Fig. 2). If emission amplitude indexes hai cell status (Kemp, 1978 ; Pobst et al, 1987), then we must conclude that, in the egion above 3 Hz, the 1 c m m 4 m SSI Assistlve Listening Device Evaluation S : AK Left Ea-ALD IR Right Ea-ALD MCR In db I I 1 Quiet Figue 11 Compaison of pefomance of assistive listening device fitted eithe to ight o left eas of subject AK.

8 Jounal of the Ameican Academy of Audiology/Volume 8, Numbe 1, Febuay 1997 left ea has bette, not wose, cochlea eseve than the ight ea. Futhe agument against the left peipheal hypothesis lies in the dichotic data fo vebal and nonvebal tasks (see Figs. 5-9). Hee, it is clea that asymmeties in eaction time and P3 amplitude can be evesed, fom a leftea deficit to a ight-ea deficit, by simply changing the to-be-attended speech featue, of the same monosyllabic wods, fom phonemic to voice gende. It is difficult to econcile this esult with a left-sided cochlea effect. The possibility of a cognitive deficit that limits the successful use of binaual input must cetainly be consideed in anyone in the 87- to 9-yea ange. Aguing fo such a deficit ae the monotic data fo identifying two sentences in sequence (see Fig. 3). Hee, two andomly selected DSI sentences ae pesented sequentially to one ea. The subject's task is simply to identify which 2 sentences, fom a closed list of 1, wee head. In the absence of cognitive deficit, this task is odinaily executed without difficulty, even by pesons with substantial peipheal sensitivity loss. Individual ea accuacy scoes ae usually 1 pecent. But AK's pefomance fell to 9 pecent, fo the ight ea, and to 75 pecent, fo the left ea, indicating some difficulty in immediate memoy. Since memoy fo two sentences is citical to adequate dichotic pefomance in the divided-attention mode, the left-ea deficit in this condition might be explained by a memoy poblem. The inteaction of such a memoy deficit with poblems in attention and speed of mental pocessing might conceivably esult in moe sensoy oveload when both eas ae amplified than when only one ea is amplified. Aguing against cognitive deficit, howeve, as an explanation fo the left-ea dichotic deficit ae the esults of the emaining dichotic conditions of Figue 3. If cognitive dysfunction is the basis fo the left-ea deficit in the divided attention mode, then the deficit should be attenuated by switching to the focused attention mode. Hee, only one ea must be attended. The othe can be ignoed, thus lessening the memoy load. The pecued and postcued modes epesent futhe manipulation of the cognitive demands of the task. In the case of a dichotic asymmety due to cognitive deficit, the ea diffeence should be geatest in the divided attention mode, less in the focused attention mode, then pogessively geate in the pecued and postcued modes. But AK showed vitually no effect fom this cognitive manipulation. The ea asymmety noted in the divided attention mode emained constant acoss all dichotic conditions. Thus, while cognitive deficits in memoy, attention, and speed of pocessing may cetainly be pesent, they do not appea to explain the left dichotic deficit. Futhe agument against the cognitive deficit hypothesis is the fact that the geneal esults of the neuopsychological evaluation wee within nomal limits. The thid possibility, an auditoy pocessing deficit impacting binaual input, seems moe consistent with the available data. The most pesuasive agument comes fom the dichotic esults illustated in Figues 5 to 9. They demonstate a patten not unlike that of patients who have undegone commissual section (Milne et al, 1968; Spaks and Geschwind, 1968). When the dichotic task is vebal, the left ea pefoms pooly, but when the dichotic task is nonvebal, the patten eveses and the ight ea pefoms less well than the left ea. Futhe suppot fo this view is povided by the neuopsychological evaluation. Results achieved by expeimental manipulation of the neuopsychological tests evealed a patten of pefomance much like that seen in callosal agenesis patients (Feis and Dosen, 1975) and in some callosectomy patients (Spey, 1974). The impotant ole of the copus callosum in mediating vebal esponses to left-ea input has been extensively studied (Milne et al, 1968; Spaks and Geschwind, 1968 ; Lindeboom and Host, 1988 ; Rao et al, 1989 ; Kaga et al, 199). That thee is age-elated change in the human copus callosum is also well documented (Byne et al, 1988 ; Witelson, 1989 ; Yoshii and Duaa, 1989 ; Allen et al, 1991 ; Doaiswamy et al, 1991 ; Weis et al, 1991 ; Laissy et al, 1993). That such change can affect the efficiency of intehemispheic tansfe has also been documented (Goldstein and Shelly, 1974). Thus, the necessay conditions can be mashaled to suppot the hypothesis that, in aging, thee may be a significant loss of efficiency of intehemispheic tansfe of auditoy infomation though the copus callosum. As a esult, the left ea is at an inceased disadvantage fo the pocessing of vebal tasks. The pesent esults on subject AK demonstate this effect both behavioally and electophysiologically. We suggest that AK's difficulty with binaual amplification may be explained by age-elated pogessive atophy and/o demyelination of copus callosal fibes, esulting in delay o othe loss of the efficiency of intehemispheic tansfe of auditoy infomation in a manne simila

9 Binaual Amplification / Chmiel et al to that ecently suggested by Jege et al (1995). Such loss could explain the deficits in left-ea pefomance when AK esponded to dichotic pesentation of vebal mateials, and the deficits in ight-ea pefomance fo the nonvebal task. To the extent that such faulty intehemispheic tansfe affects the utilization of subtle binaual cues, eldely pesons like AK may expeience a vaiety of poblems involving sound localization, auditoy space, and the effective use of binaual heaing aids. AN IMPORTANT CLINICAL IMPLICATION n ecent yeas, we have seen a majo paadigm shift, among audiologists, away fom speech audiometic assessment of heaing aid pefomance and towad eal-ea measuement of fequency esponse. The case fo this shift was stated most eloquently by Hawkins et al (1987) : Recent data concening the test-etest vaiability of wod ecognition scoes... and the lack of suppot fo the undelying assumptions of the compaative heaing aid evaluation that uses wod ecognition scoes... have cast doubt on both the eliability and the validity of this appoach. A popula altenative in heaing aid selection utilizes audiogambased pesciptions of appopiate amplification and the measuement of unaided and aided sound-field thesholds. (p. 56) The pesent case illustates the hazads of such a naow appoach to heaing-aid evaluation and fitting, especially as it applies to eldely pesons and binaual amplification. In the case of AK, neithe the pue-tone audiogam no pesciptions of appopiate amplification based on eal-ea measues evealed, o even hinted at, the fact that binaual amplification was inappopiate fo this individual. In point of fact, it was speech audiomety that highlighted the poblem. Beginning with the PB wod scoes, followed by the DSI scoes, then pogessing though the cued listening test scoes and ending with the dichotic vebal and nonvebal tasks, thee was a consistent left-ea deficit fo vebal tasks. The consequence of this unilateal deficit was well illustated in the evaluation of heaing aid pefomance and in AK's eaction to monaual vesus binaual amplification. Acknowledgment. This wok was suppoted, in pat, by eseach gant AG-8958 fom the National Institute on Aging, and by the Ethel andalbet Hezstein Foundation. We ae gateful to John Allen and Heny Lew fo assistance in data collection and analysis. REFERENCES Allen L, Richey M, Chai Y, Goski R. (1991). Sex diffeences in the copus callosum of the living human being. J Neuosci11 : Balfou P, Hawkins D. (1992). A compaison of sound quality judgments fo monaual and binaual heaing aid pocessed stimuli. Ea Hea 13 : Books D. (1984). Binaual benefit - when and how much? Scand Audiol 13 : Byne W Bleie R, Houston L. (1988). Vaiations in human copus callosum do not pedict gende : a study using magnetic esonance imaging. Behav Neuosci 12 : Byne D, Dillon H. (1986). The National Acoustic Laboatoies' (NAL) new pocedue fo selecting the gain and fequency esponse of a heaing aid. Ea Hea 7: Dempsey J. (1994). Heaing aid fitting and evaluation. In : Katz J, ed. Handbook of Clinical Audiology. 4th ed. Baltimoe : Williams & Wilkins, Doaiswamy P, Figiel G, Husain M, McDonald W Shah S, Boyko O, J E, Kishnan K. (1991). Aging of the human copus callosum : magnetic esonance imaging in nomal voluntees. JNeuopsychiaty Clin Neuosci 3: Edman S, Sedge R. (1981). Subjective compaisons of binaual vesus monaual amplification. Ea Hea 2: Feis G, Dosen M. (1975). Agenesis of the copus callosum. 1. Neupsychological studies. Cotex 11 : File R, Jege J, Belin C, Tobey E, Campbell J. (1983). Development of a dichotic sentence identification test fo heaing-impaied adults. Ea Hea 4:3-35. Goldstein S, Shelly C. (1974). Revesal of expected tansfe as a function of inceased age. Pecept Mot Skills 38 : Haggad M, Hall J. (1982). Foms of binaual summation and the implications of individual vaiability fo binaual heaing aids. Scand Audiol Suppl 15 : Hawkins D, Montgomey A, Posek R, Walden B. (1987). Examination of two issues concening functional gain measuements. J Speech Hea Disod 52 : Jege J, Alfod B, Lew H, Rivea V Chmiel R. (1995). Dichotic listening, event-elated potentials, and intehemispheic tansfe in the eldely. Ea Hea 16 : Jege J, Jodan C. (1992). Age-elated asymmety on a cued-listening task. Ea Hea 13 : Jege J, Silman S, Lew H, Chmiel R. (1993). Case studies in binaual intefeence : conveging evidence fom behavioal and electophysiologic measues. J Am Acad Audiol 4: Jege J, Speaks C, Tammel J. (1968). A new appoach to speech audiomety. J Speech Hea Disod 33 :

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