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Perceptin & Psychphysics 1979, Vl. 26 (5), 43-48 Auditry mtin aftereffects D. WESLEY GRANTHAM and FREDERIC L.

1 Perceptin & Psychphysics 1979, Vl. 26 (5), Auditry mtin aftereffects D. WESLEY GRANTHAM and FREDERIC L. WIGHTMAN Nrthwestern niversity, Evanstn, Illinis 21 Observers were adapted t simulated auditry mvement prduced by dynamically varying the interaural time and intensity differences f tnes (5 r 2, H) presented thrugh headphnes. At 1-sec intervals during adaptatin, varius prbe tnes were presented fr I sec (the frequency f the prbe was always the same as that f the adaptatin stimulus). Observers judged the directin f apparent mvement ("left" r "right") f each prbe tne. At 5 H, with a 2-deg/sec adaptatin velcity, "statinary" prbe tnes were cnsistently judged t mve in the directin ppsite t that f the adaptatin stimulus. We call this result an auditry mtin aftereffect. In slwer velcity adaptatin cnditins, prgressively less aftereffect was demnstrated. In the higher frequency cnditin (2, H, 2-deg/sec adaptatin velcity), we fund n evidence f mtin aftereffect. The data are discussed in relatin t the well-knwn visual analg-the "waterfall effect." Althugh the auditry aftereffect is weaker than the visual analg, the data suggest that auditry mtin perceptin might be mediated, as is generally believed fr the visual system, by directin-specific mvement analyers. If ne gaes at a cntinuusly mving visual pattern fr 3 sec r mre, then shifts ne's gae t a statinary visual pattern, ne will typically reprt a strng perceptin f mtin in the directin ppsite t that f the riginal mvement. This type f mtin aftereffect is experienced ften in everyday life and can be quite cmpelling. Labratry investigatin f this and related phenmena (e.g., the "waterfall" and spiral aftereffects) has been extensive and has spanned mre than a century (see Whlgemuth, 1911, and Gates, 1934, fr reviews f the early wrk n visual aftereffects). The generally accepted explanatin fr visual mtin aftereffects is based n the presumed existence f mvement analyers in the visual system which are selectively tuned t mtin in a particular directin (Barlw & Hill, 1963; Sekuler & Pantle, 1967). Accrding t this view, gaing fr sme time at a stimulus mving in ne directin (the "inspectin" r "adaptatin" stimulus) fatigues the analyers which are specifically tuned t that directin. Subsequently, when the bserver gaes at a statinary pattern (the "test" stimulus), activity in the fatigued analyers remains depressed, and, hence, there is relatively mre activity in the analyers tuned t the ppsite directin. Perceptin is therefre f "ppsite" mvement. This research was supprted in part by NINCDS Grants NS1245 and NS5729. We are grateful t Lynn Halpern fr her assistance in the planning and executin f these experiments. Sme f the data were reprted at the 5th meeting f the Midwestern Psychlgical Assciatin, Chicag, May The current address f first authr is: Parmly Hearing Institute, Lyla niversity f Chicag, 6525 N. Sheridan Rad, Chicag, Illinis 626. This explanatin f visual mtin aftereffects enjys strng physilgical supprt, and, in fact, was riginally prmpted by the classic electrphysilgical wrk f Hubel and Wiesel (1962). These investigatrs fund single neurns in the eat's visual crtex which were specifically respnsive t mtin f a pattern in a particular directin. Barlw and Hill (1963) fund such directin-specific units als in the rabbit's retina, and shwed that the level f activity in these units declined with time f stimulatin, remained suppressed fr sme time after stimulatin ceased, then gradually rse back t baseline. This activity in singleunits is exactly parallel t the psychphysical effects f adaptatin, aftereffect, and decay f aftereffect. Directin-specific neurns have als been discvered in the auditry system. Altman and his clleagues have fund single units in the eat's inferir clliculus and medial geniculate bdy which respnded best t particular directins f mvement f a sund surce (simulated with headphne presentatin) (Altman, 1968; Altman, Syka, & Shmigidina, 197). Svijarvi and Hyvarinen (1974) fund the same selectivity in single units f the cat's auditry crtex when the stimuli were real sund surces mving in the vertical and hrintal planes. The parallels between the visual and auditry physilgical data suggest that there may be similar mechanisms underlying mtin perceptin in the tw mdalities. In particular, if there are directin-specific analyers in the auditry system, and if auditry mtin perceptin is mediated by the ttal activity f analyers tuned t ppsite directins, we wuld expect that auditry mtin aftereffects might be demnstrated psychphysically. 1 This paper reprts a Cpyright 1979 Psychnmic Sciety, Inc /79/1143-6$.85/

44 GRANTHAM AND WIGHTMAN preliminary experiment which deals with pssible aftereffects as a functin f tw variables: frequency f the stimulus and velcity f the auditry mvement.

2 44 GRANTHAM AND WIGHTMAN preliminary experiment which deals with pssible aftereffects as a functin f tw variables: frequency f the stimulus and velcity f the auditry mvement. METHOD The Adaptatin Stimulus T prduce auditry mvement, we presented special stimuli t listeners thrugh headphnes. These stimuli (an example is shwn in Figure I) were binaural tnes with dynamically varying interaural tempral and interaural amplitude differences, prducing fr the listeners an intracranial acustic image which appeared t mve alng a path between the ears. We chse the nset interaural differences t simulate the psitin f a real surce situated in the hrintal plane 3 deg ff midline.' The interaural differences decreased linearly frm these values such that halfway thrugh the presentatin there were n interaural differences (simulating a sund surce straight ahead), and at stimulus ffset the differences were equal, but ppsite in sign t the nset inter aural differences (simulating a sund surce 3 deg ff midline t the ppsite side). One "sweep" f the adaptatin stimulus thus crrespnds, in terms f the changing interaural differences, t the mvement f a real sund surce in the hrintal plane frm 3 deg n ne side f the bserver t 3 deg n the ther side. The velcity f mvement f the adaptatin stimulus was manipulated by varying the duratin f sweep: sweep duratins f 2,, 1,, and 3 msec crrespnded, respectively, t adaptatin velcities f 3,, and 2 deg/sec (this parameter will hencefrth be referred t as velcity). The adaptatin stimulus was presented repeatedly, interrupted by 1 msec f silence between each "sweep." Thus, the auditry mvement we simulate is a sequence f left-t-right (r right-tleft) sweeps separated by silence. Prcedure We emplyed fur types f adaptatin stimulus, differing alng dimensins f frequency and velcity f (simulated) mvement. Three f the stimuli were 5-H tnes, presented at velcities f 3,, and 2 deg/sec, respectively. The furth was a 2,-H' tne presented at a velcity f 2 deg/sec. Fr each f these fur adaptatin stimuli, there were three pssible mdes f presentatin: left-t-right sweep, right-t-left sweep, and a cntrl cnditin that prduced n illusin f mvement. In this latter cnditin, tnes were presented with n interaural differences; the acustic image was that f a pulsing tne, the psitin f which remained fixed in the center f the head. Fr maximum efficiency in data cllectin, we emplyed a prbe technique t assess the effects f adaptatin. With this prcedure, the adaptatin stimulus remains fixed thrugh a blck f trials, and therefre bservers presumably remain in a "fully adapted state" while indicating their perceptins f varius (prbe) stimuli. During a single run (apprximately 8 min), ne f the 12 adaptatin stimuli (4 types x 3 presentatin mdes) was presented cntinually. At IO-sec intervals, the adaptatin stimulus was interrupted fr a I-sec presentatin f a test stimulus (the prbe) t which the bserver respnded by pressing ne f tw buttns, indicating whether he felt the prbe had mved "left" r "right" (bservers were instructed t guess if unsure). There were seven different prbe stimuli (t be described belw), each f which was presented six times in randm rder. Thus, 42 respnses were cllected during a "run." The prbe was always a single, I-sec presentatin f a tne f the same frequency as the adaptatin stimulus. It was presented at ne f seven velcities: deg/sec (ditic) r 1, 2, r 4 deg/sec, sweeping either left r right. As with the adaptatin stimuli, the mving prbe stimuli were synthesied t mve sym- TIME~ Figure 1. Representatin f the binaural stimulus emplyed t simulate left-t-right mvement. At stimulus nset, the wavefrm in the left ear (slid line) is mre intense and leads, in time, the wavefrm in the right ear (dtted line). At stimulus ffset, these lnteraural relatins are reversed. metrically abut midline. Velcity f the prbe was manipulated, nt by varying sweep duratin as was dne fr the adaptatin stimuli, but by varying the starting and ending psitins f the simulated mving surce (2, 1, and 5 deg ff midline, respectively, fr test velcities f 4,2, and 1 deg/sec). Fr each cmbinatin f adaptatin stimulus and prbe, respnses were cllected (nt all in a single sessin). The dependent variable was percent respnses "left." Subjects and Apparatus Three female bservers with clinically nrmal hearing were tested simultaneusly in 1 2-h sessins spread ver a 2-week perid. At least 6 h f training were prvided fr each bserver befre data were cllected. All experimentatin was cnducted in an lac sund-insulated chamber. Stimuli were delivered thrugh matched TDH-49 headphnes at a cmfrtable listening level (75 db SPL). Thrughut a sessin, a cntinuus, lw-level ( db SPL verall) 3,-H lw-pass Gaussian nise was present; this nise was presented ditically (identically in the tw ears) t prvide a centered backgrund image which bservers culd use fr reference. RESLTS The data are pltted in Figures 2-5 fr the fur types f adaptatin stimulus. In each figure, the percentage f respnses "left" is pltted as a functin f prbe stimulus velcity fr the three bservers (shwn separately in the three panels). The parameter is the "mde" f adaptatin (leftward, rightward, r cntrl). The data frm the cntrl cnditins suggest that, in the absence f directin-specific adaptatin, the bservers were generally unbiased in their respnses t the test stimuli: fr a statinary ( deg/sec) prbe, they respnded "left" abut 57 f the time. T the extent that there is a psitive aftereffect, the functin pltted fr the case f "leftward" adaptatin (triangles) shuld lie belw and t the left f the cntrl functin (bservers shuld tend t respnd "left" less ften), while the functin fr "rightward" adaptatin (squares) shuld lie abve and t the right f the cntrl data (shwing a tendency t respnd

3 ADITORYMOTIONAFTEREFFECTS 45,,. SO,, 11,, 2 KO ~ " ~~--~-.._--. Z SO 8 A.. <, / ~... / u,..."it 11 -l 2 TK ~ s 11 2 L TEST VELOCITY (OEG/SEC) Figure 2. Data fr three subjects. 5-H signal, 3-deg/sec adaptatin velcity. Percent left respnses is pltted as a functin f test stimulus velcity fr three cnditins f adaptatin: c,., leftward adaptatin;, rightward adaptatin;, statinary adaptatin (cntrl). "left" mre ften). When the adaptatin functins cincide with the cntrl functin, there is n evidence fr an auditry mtin aftereffect. Figures 2-4 plt the data btained using the 5-H adaptatin stimuli with sweep velcities f 3,, and 2 deg/sec, respectively. Fr the slwest velcity (Figure 2), nly ne listener (K.O.) shwed clear evidence f adaptatin, reflected in the relative psitins f the respnse functins fr the different directins f adaptatin. As adaptatin velcity increased (Figures 3-4), the aftereffect fr this subject became mre prnunced (the functins fr "left" and "right" adaptatin cnditins became increasingly divergent), and an effect became apparent fr the ther tw bservers as well. At 5 H, therefre, we may cnclude that the magnitude f the aftereffect fr ur three listeners is an increasing functin f adaptatin stimulus velcity, ver the range f velcities tested. Figure 5 shws the data cllected fr the 2,OOO-H adaptatin stimulus presented at a velcity f 2 deg/sec, At this higher frequency, there is little r n evidence fr mtin aftereffects. We shuld reemphasie at this pint that the mvement f the higher frequency adaptatin stimulus was judged (by ur listeners and by us) t be as salient as that f the lwer frequency stimulus. This equivalence f mvement perceptin acrss frequency is expected, based n subjects' equivalent perfrmance in lcaliing real (statinary) sund surces f different frequencies." Yet, despite equal apparent mvement f the adaptatin stimuli in the lw- and high-frequency cnditins represented in Figures 4 and 5, the mtin aftereffect is substantially reduced r cmpletely absent at the higher frequency. In ther wrds, we see a definite frequency effect in the measurement f auditry aftereffects. 8 s ~ u, 11 -l ~ L KO DISCSSION We cnclude that auditry mtin aftereffects can be demnstrated psychphysically if the right cmbinatin f stimulus parameters is used. Specifically, adaptatin with a 5-H tne sweeping repeatedly in ne directin at a velcity f 2 deg/sec prduced a ----ill,.... "... '5---",... ' ~,.. ' TEST VELOCITY )... 'a.. "~~~ -~----- (OEG/SEC) Figure 3. Data fr three subjects. SIlO-H signal, 6O-deg/sec adaptatin velcity. See captin fr Figure 2. R

46 GRANTHAM AND WIGHTMAN ---~...... 8...- qo II"" " 2 KO -, en ~, "'''!I en en SO ::: I- u, qo..j I- 2 ::: ""'&--ill '''...11 SO ' ~,A qo,,/ <, " 2 MS <, 'L... "'I!I..._- L TEST VELOCITY (OEG/SEC) R Figure 4.

4 46 GRANTHAM AND WIGHTMAN ---~ qo II"" " 2 KO -, en ~, "'''!I en en SO ::: I- u, qo..j I- 2 ::: ""'&--ill '''...11 SO ' ~,A qo,,/ <, " 2 MS <, 'L... "'I!I..._- L TEST VELOCITY (OEG/SEC) R Figure 4. Data fr three subjects. 5-H signal, 2-deg/sec adaptatin velcity. See captin fr Figure 2. a cnsistent tendency in all bservers t judge statinary stimuli as mving in the ppsite directin. Furthermre, as has been demnstrated fr visual mtin aftereffects (Sctt, Jrdan, & Pwell, 1963), the effect f auditry adaptatin was fund t cmbine algebraically with real mvement in prbe stimuli, such that the perceptin f mtin was either canceled r enhanced, depending n whether the mvement f the prbe was in the ppsite r same directin as the mvement f the adaptatin stimulus. We might cnsider as a wrking hypthesis that the widely accepted interpretatin f the visual "waterfall effect" might be applied t ur auditry data as well. Thus, the perceptin f mving sund surces is hypthesied t be mediated by directinspecific mtin analyers in the auditry system (the physilgical data cited earlier wuld place the analyers in the inferir clliculus and/r medial geniculate bdy). The mtin aftereffect reflects that activity in the set f analyers tuned t ne particular directin is temprarily depressed (fatigued by the previus expsure t mvement), allwing the relative activity f the analyers tuned in the ppsite directin t dminate during a neutral stimulus cn- ditin (nnmvement). The fact that the magnitude f aftereffect depends n the velcity f mtin wuld reflect the distributin fvelcities "preferred" by the ppulatin f analyers: thus, at 5 H, as the stimulus velcity decreases, it is "preferred" by fewer and fewer analyers, and the magnitude f the aftereffect shuld diminish. Finally, the fact that aftereffects are frequency-specific might indicate that the distributin f velcity "preferences" f the analyers depends n the stimulus frequency. Our failure t btain an aftereffect at 2, H may reflect that, f the subppulatin f mvement analyers tuned t 2, H, few r nne "preferred" a velcity f 2 deg/sec. At this higher frequency, a slwer velcity stimulus might have elicited the aftereffect (unfrtunately, we emplyed nly ne velcity at 2, H). This accunt f auditry aftereffects, brrwed in tt frm the visin literature, is f curse entirely speculative in the present cntext, and shuld be regarded cautiusly. We must stress that, while the visual mtin ("waterfall") aftereffect is quite a rbust phenmenn, easily demnstrated ver a wide range f stimulus cnditins, the auditry analg en en en ::: SO qo llj I u,..j I Z llj ::: 2 s qo 2 TK s qo 2 L HS TEST VELOCITY (OEG/SEC) R Figure 5. Data fr three subjects. 2,OOO-H signal, 2-deg/sec adaptatin velcity. See captin fr Figure 2.

5 ADITORY MOTION AFTEREFFECTS 47 that we have measured is relatively subtle, apparently demnstrable nly in relatively few circumstances. This great difference in the strength f the visual and auditry aftereffects is illustrated in the methds used t measure them: While duratin f apparent mtin is the typical measure f the strength f visual aftereffects, the auditry aftereffect was much t transitry t allw such a measurement (all auditry aftereffects disappeared within 1-3 sec). Instead, we had t emply a tw-alternative ("right"-"left") frced-chice paradigm t reveal the existence f the auditry effect. Given that auditry mtin aftereffects can be demnstrated with apprpriate stimulus cnditins, we may speculate as t whether the effect is truly an auditry phenmenn, r is mediated by the visual, kinesthetic, and/r prpriceptive systems. In ther wrds, des the perceptin f auditry mtin during the adaptatin perid affect ther systems (visual rientatin, musculature f the eyes, pstural attitude, etc.), such that the reprted mvement f the auditry prbe stimuli is due t sme kind f adaptatin in these systems, and nt specifically t auditry adaptatin? Alng these same lines, we might ask whether the auditry mtin aftereffect is a sensry effect at all, as ppsed t a nnsensry phenmenn (e.g., a change in judgmental bias r adaptatin level). There are several features f ur data which suggest that the btained aftereffect is indeed a purely auditry phenmenn. That it is nt mediated by the visual system is clear, since the tempral parameters in the tw cases are nt f the same rder f magnitude. Nte that we fund best auditry aftereffects fr adaptatin velcities f 2 deg/sec. The best visual aftereffects are btained with adaptatin velcities f 4-6 deg/sec (Sekuler & Gan, 1963). Therefre, the auditry effect is nt a simple translatin f, auditrystimulatinint visual space. Mre generally, the "frequency effect" bserved in ur data (see Figures 4-5) suggests that the auditry mtin aftereffect is nt mediated by anther system (sensry r nnsensry), but that its basis is purely auditry. In ther wrds, since the frequency cntent f the stimulus is critical in determining whether r nt the auditry aftereffect ccurs, any intervening system which wuld mediate the effect wuld have t be frequency-specific. Rather than implicate sme ther frequency-dependent system as a mediatr, it seems mst parsimnius t cnclude that the auditry system itself is directly affected by the prlnged mtin stimulatin, resulting in the effects we have measured. SMMARY AND CONCLSIONS With apprpriately chsen stimulus cnditins, bservers' judgments f auditry mtin in the hri- ntal plane are clearly and cnsistently affected by their immediately previus experience with auditry mvement. The fact that auditry mtin aftereffects are frequency-specific (they ccur at 5 H, but nt at 2, H) suggests that the effects are specific t the auditry system (i.e., they are nt likely mediated by anther sensry system, nr are they likely based n judgmental criterin shifts). Althugh the auditry mtin aftereffect is weaker than the "waterfall" effect in visin, we feel that the parallel results suggest that analgus mechanisms underlie mtin perceptin in the tw mdalities. In particular, auditry mtin perceptin might be mediated by directin-specific mvement analyers in the auditry system. This interpretatin wuld be cngruus with the auditry neurphysilgical data cited earlier, in which single units were reprted t respnd selectively t mtin in ne particular directin. Additinal psychphysical wrk, fcusing n stimulus frequency, velcity, and the manner in which auditry mtin is prduced, will hpefully reveal whether the analg between visual and auditry mtin perceptin will ultimately prve useful. REFERENCES ALTMAN, J. A. Are there neurns detecting directin f sund surce mtin? Experimental Neurlgy, 1968,22, ALTMAN, J. A., SYKA, J., & SHMIGIDINA, G. N. Neurnal activity in the medial geniculate bdy f the cat during mnaural and binaural stimulatin. Experimental Brain Research, 197, 1, BARLOW, H. B., & HILL, R. M. Evidence fr a physilgical explanatin f the waterfall phenmenn and figural aftereffects. Nature, 1963,2, EHRENSTEIN, W. H. Directin-specific acustical aftereffects. Jurnal fthe Acustical Sciety famerica, 1978, 64, S35(A). FEDDERSON, W. E., SANDEL, T. T., TEAS, D. C., & JEFFRESS, L~. Lcaliatin f high-frequency tnes. Jurnal f the AcusticalSciety famerica, 1957,29, GATES, L. W. The after-effect f visually bserved mvement. American Jurnal fpsychlgy, 1934,46, HARRIS, J. D., & SERGEANT, R. L. Mnaural/binaural minimum audible angles fr a mving sund surce. Jurnal fspeech & Hearing Research, 1971, 14, HBEL, D. H., & WIESEL, T. N. Receptive fields, bincular interactin, and functinal architecture in the eat's visual crtex. Jurnal fphysilgy, 1962,1, MILLS, A. W. On the minimum audible angle. Jurnal f the Acustical Sciety famerica, 1958,3, MOLINO, J. A. Psychphysical verificatin fpredicted interaural differences in lcaliing distant sund surces. Jurnal f the Acustical Sciety famerica, 1974,55, SANDEL, T. T., TEAS, D. C., FEDDERSON, W. G., & JEFFRESS, L. A. Lcaliatin f sund frm single and paired surces. Jurnal f the Acustical Sciety f America, 1955, 27, SCOTT, T. R., JORDAN, A. E., & POWELL, D. A. Des visual aftereffect f mtin add algebraically t bjective mtin f the test stimulus? Jurnal fexperimental Psychlgy, 1%3, 66, SEKLER, R. W., GANZ, L. Aftereffect f seen mtin with a stabilied retinal image. Science, 1963, 139,

48 GRANTHAM AND WIGHTMAN SEKLER, R., & PANTLE, A. A mdel fr after-effects f seen mvement. Visin Research, 1967,7,427-439. SOVIJARVI, A. R. A., & HYVARINEN, J.

6 48 GRANTHAM AND WIGHTMAN SEKLER, R., & PANTLE, A. A mdel fr after-effects f seen mvement. Visin Research, 1967,7, SOVIJARVI, A. R. A., & HYVARINEN, J. Auditry crtical neurns in the cat sensitive t the directin f sund surce mvement. Brain Research, 1974,73, STEVENS, S. S., & NEWMAN, E. B. The lcaliatin f actual surces f sund. American Jurnal f Psychlgy, 1936, 48, WOLGEMTH, A. On the after-effect f seen mvement. British Jurnal fpsychlgy, 1911, Mngraph Supplement I, NOTES 1. Ehrenstein (1978) has recently reprted that expsure t auditry mvement affects an bserver's subsequent lcaliatin f a statinary auditry bje in particular, the apparent psitin f a surce is displaced abut 2 deg t the side ppsite the directin f mvement f a previus adaptatin stimulus. Althugh this "auditry displacement aftereffect" is relevant t mechanisms underlying ur perceptin f auditry (static) space, if directin-specific mtin analyers exist, we wuld predict that a statinary test stimulus (presented after adaptatin t mvement), shuld nt nly be displaced, but shuld appear t mve. T date there have been n reprts f such an auditry mtin aftereffect. 2. Frm a sund surce in the hrintal plane lcated 3 deg ff midline, the wavefrnt arrives at the nearer ear abut.25 msec befre it arrives t the farther ear (independent f frequency). The interaural intensity difference f the sund frm this surce depends n its frequency cntent: fr a 5OD-H tne, the difference is abut 3 db; fr a 2,-H tne, the difference is abut 7 db. These measurements have been made by Feddersn, Sandel, Teas, and Jeffress (1957). 3. By emplying apprpriate interaural parameters, we were able t prduce mvement at 2, H which was as salient as that at 5D H (see Ftnte 2). Thus, in terms f the perceptin f mvement f the adaptatin stimulus, the lw-frequency and high-frequency cnditins were equivalent. 4. Althugh the classic paper by Stevens and Newman (1936) reprted that tnes arund 2,-4, H are lcalied less precisely than tnes f lwer (r higher) frequency, mre recent studies have revealed that this frequency effect is small r negligible, especially in the regin arund midline (Harris & Sergeant, 1971; Mills, 1958; Mlin, 1974; Sandel, Teas, Feddersn, & Jeffress, 1955). (Received fr publicatin April 12, 1979; revisin accepted September 21, 1979.)

AP Biology Lab 12: Introduction to the Scientific Method and Animal Behavior

AP Biology Lab 12: Introduction to the Scientific Method and Animal Behavior Name: AP Bilgy Lab 12: Intrductin t the Scientific Methd and Animal Behavir Overview In this lab yu will: -Observe an rganism and design an experiment t investigate their respnses t envirnmental variables.