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AUDIO/MARCH 198736
Early on around this magazine, there was a sort of Occam’ sAudio
Razor: “If a piece of gear measures well but soundsbad, it is bad,
but if it sounds good and measures poorly, it’s agood piece of
gear.” The idea behind the quasi-motto was tofree one’s ears, and
perception, from the tyranny of meters.Over the last four decades,
lots of midnight oil has beenburned trying to make measurements
mean something, whichusually wound up as an attempt to make gear
which alreadysounded good also measure well. On the hi-fi end of
things,at least, not much ef fort has been spent on what it means
to“sound good,” or “hear well,” or simply “hear .”
How we hear is an endlessly fascinating subject for somefew
audiophiles, most of whom know how easily any of thesenses—and
hearing is no exception—can be fooled. Indeed,stereo sound is an
illusion. If, however, you have ever listenedto a discussion of how
one hears at a hi-fi store, audio club oreven a learned society
convention, you have already foundout how few people are truly
knowledgeable in this area.
In an ef fort to free us from the tyranny that the ear is an
infallible judge of sound, I am proud and pleased to present an
article, with an illustrative Eva-Tone SoundSheet, by one ofthe few
true authorities in this field, Dr . Diana Deutsch, onwhat a
curious thing it is, our sense of hearing. — E.P.
In increasingly large numbers, peo-ple are choosing to listen to
musicthrough stereo headphones. Thisdevelopment has occurred
despite thefact that most recordings are notdesigned for headphone
listening, butrather to be played through loudspeak-ers. It is a
happy coincidence thatstereo recordings sound acceptableeither way.
Yet the creative opportuni-ties provided by headphone listeninghave
only just begun to be explored.
One highly successful use of head-phones involves binaural
recording.Two microphones are placed at the
ears of a dummy, and two very similarrecordings are produced
from these,differing only as would the sound sig-nals arriving at
the ears of a listenersituated in the same position. Whenthese
recordings are played backthrough stereo headphones, remark-able
realism is obtained.
There is, however , another use ofstereo headphones which takes
us inthe direction opposite that of increasedrealism, to an
unexpected and para-doxical world of illusion. Rather
thanpresenting highly similar signals to thetwo ears, entirely dif
ferent signals are
Illusions For StereoHeadphones
DR. DIANA DEUTSCH
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AUDIO/MARCH 1987 37
presented. Ef fects obtained with thistechnique are not only
startling to expe-rience, but also demonstrate certainproperties of
the hearing mechanismwhich might otherwise have
passedunrecognized.
Let us begin with a very simplesound pattern, which is
illustrated inFig. 1. A 400-Hz sine-wave tone isdelivered to one
ear , and at the sametime an 800-Hz sine-wave tone is deliv-ered at
equal amplitude to the otherear. When this combination lasts
for
Dr. Diana Deutsch has been a member of the research faculty of
the University ofCalifornia, San Diego, since 1970, the year she
was awarded a Ph.D in psycholo-gy from that institution. She is the
founding editor of Music Perception, a journalpublished by the
University of California Press; coauthor (with J. A. Deutsch)
ofPhysiological Psychology (Dorsey Press, 1966; Second Edition,
1973), and editorof The Psychology of Music (Academic Press, 1982).
In addition, she is an activemember of the Acoustical Society of
America and has served on the AdvisoryCouncil of the International
Association for the Study of Attention and Performance.She is a
Fellow of the American Association for the Advancement of Science
andof the Society of Experimental Psychologists. Recently made a
Fellow of the AudioEngineering Society, she was guest editor for a
special issue, entitled "AuditoryIllusions and Audio," of the
Society’s journal (Vol. 31, No. 9, Sept. 1983).
Illus
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AUDIO/MARCH 198738
several seconds, most people hearboth the high tone and the low
one, andcan localize them correctly.
Now let us consider a variant of thispattern which I devised.
(See Deutsch,D., “An Auditory Illusion,” Nature, Vol.251, 1974,
pgs. 307-309.) For the first250 mS, the 800-Hz signal is
presentedto the right ear and the 400-Hz signal tothe left. The
tones then interchangepositions, so that for the next 250 mSthe
400-Hz signal is presented to theright ear and the 800-Hz signal to
theleft. The tones then switch back to theiroriginal positions, and
the procedure isrepeated. So, as illustrated in Fig. 2A,each ear
receives a pattern that con-sists of two tones presented in
alterna-tion. Yet when the right ear receivesthe high tone, the
left ear receives thelow tone, and vice versa. This patternis given
in Sound Example 1. (Be sure,when listening to this and the
other
examples, that the loudspeakers onyour system are turned off,
and that thechannels are carefully balanced forloudness.)
Surprisingly, this simple pattern isalmost never heard correctly
, andinstead gives rise to a number of illu-sions. Most people
obtain a perceptsuch as illustrated in Fig. 2B. This con-sists of a
single tone which switchesfrom ear to ear; as it switches, its
pitchsimultaneously shifts back and forthbetween high and low. In
other words,the listener hears a single high tone inone ear which
alternates with a singlelow tone in the other ear.
Clearly, there can be no simple basisfor this illusion. We can
explain the per-ception of alternating pitches by sup-posing that
the listener hears the tonespresented to one ear and ignores
theothers. But then we cannot explain whythese tones should appear
to be switch-ing between ears. Alternatively, we canexplain the
perception of a single tonewhich alternates from ear to ear by
sup-posing that the listener is constantlyshifting his attention
between left andright. But then the pitches of the tonesshouldn’t
change with changes in theirperceived locations. The illusion of
asingle tone that alternates simultane-ously both in pitch and in
location pres-ents us with a paradox.
The ef fect becomes even strangerwhen we consider what happens
whenthe earphone positions are reversed.The ear that had been
hearing the hightone continues to hear the high tone,and the ear
that had been hearing thelow tone continues to hear the low
tone!This creates the peculiar impressionthat the high tone has
migrated fromone earphone to the other, and that thelow tone has
also migrated in analo-gous fashion. The best way to experi-ence
this ef fect is to switch the ear-phones around several times while
thepattern is playing, and ask yourselfeach time which ear is
hearing the hightone. Most people find that the hightone appears to
stay in one ear and thelow tone in the other ear , regardless ofhow
the earphones are positioned.
Another interesting thing to try at thispoint is to begin by
listening to the illu-sion in stereo, and then change the set-ting
to mono, so that both ears nowreceive both channels. At this
pointyour percept should change dramatical-
ly: You should hear a single complextone coming simultaneously
from bothearphones, together with clicks occur-ring four times per
second. (The clicksare due to the transients produced byswitching
the signals between 400 and800 Hz). Then change the settingback to
stereo, and the illusion shouldreappear. Sound Example 2
presentsthe pattern in stereo, then in mono,and then in stereo
again.
How can we account for this illu-sion? Clearly , there is no
simpleexplanation. But if we assume thatseparate brain mechanisms
exist fordeciding what sound we hear and fordeciding where the
sound is comingfrom, we are in a position to advancean explanation.
The model is illustrat-ed in Figs. 3 and 4. To obtain the
per-ceived pitches, the frequencies arriv-ing at one ear are
attended to, andthose arriving at the other ear are sup-pressed.
However, each tone is local-ized at the ear receiving the
higherfrequency signal, regardless ofwhether a pitch corresponding
to thehigher or the lower frequency is in factperceived.
Figure 3 illustrates the model forthe case of a listener who
perceivedthe pitches corresponding to the fre-quencies delivered to
his right ear .When a high tone is delivered to hisright and a low
tone to his left, hehears a high tone, because this isdelivered to
his right ear . He alsolocalizes the tone in his right ear ,because
this ear is receiving the high-er frequency. But when a low tone
isdelivered to the right ear and a hightone to the left, he now
hears a lowtone, because this is delivered to hisright ear, but he
localizes the tone inhis left ear instead, because the leftear is
receiving the higher frequency .So he hears the entire sequence as
ahigh tone to the right which alternateswith a low tone to the
left. You cansee that reversing the earphone posi-tions wouldn’t
change this basic per-cept (the sequence would simplyappear to be
of fset by one tone).However, Fig. 4 illustrates the samemodel for
the listener who perceivesthe pitches corresponding to the
fre-quencies d elivered to h is l eft e arinstead, using the same
localizationrule. You can see that the identicalpattern is now
heard instead as a high
Mus
ic C
opyi
st: B
ert K
osow
Fig. 1—400-Hz sine-wave tone delivered to left ear and 800-Hz
toneto right ear.
Fig. 2—Octave illusion pattern, with400- and 800-Hz tones first
deliveredto left and right ears, respectively,and then
interchanging positionsevery 250 mS (A); and the most common
percept resulting from thatpattern (B).
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AUDIO/MARCH 1987 39
placed both ways. But left-handers did-n’t show this
tendency.
In a more extensive study , I dividedthe population of listeners
into threegroups on the basis of handedness,using the V arney and
Benton handed-ness questionnaire shown in Fig. 7.People scoring at
least nine out of 10“rights” were designated right-handers,those
scoring at least nine out of 10“lefts” w ere d esignated l
efthanders,and those with eight or fewer “lefts” or“rights” were
designated mixed-han-ders. Each group was then furtherdivided into
two on the basis of whether
or not the listener had a left- or mixed-handed parent or
sibling.
This six-way division was found tocorrelate with how the octave
illusionwas perceived. Right-handers weremore likely to hear the
high tone on theright than were mixed-handers, andmixed-handers
were more likely to do so than were left-handers. And for allthree
handedness groups, those with-out left- or mixed-handed parents
orsiblings were more likely to hear thehigh tone on the right than
were thosewith left- or mixed-handed parents orsiblings. (See
Deutsch, D., “The
tone to the left alternating with a lowtone to the right.
In order to test this hypothesis, Idevised a new pattern,
illustrated inFigs. 5 and 6. You can see that one earreceives three
high tones followed bytwo low tones, while simultaneously theother
ear receives three low tones fol-lowed by two high tones. This
basicpattern is repeatedly presented, with-out pause. It was found
that, indeed,most people perceived a pattern ofpitches
corresponding to the frequen-cies presented either to the right or
tothe left. That is, they heard a repeatingpattern that consisted
either of threehigh tones followed by two low tones,or of three low
tones followed by twohigh tones. Also in confirmation of themodel,
each tone was localized in theear receiving the higher frequency
,regardless of whether a pitch corre-sponding to the higher or
lower fre-quency was in fact perceived.
So when a low tone was heard, itappeared to be coming not from
theearphone which was in fact deliveringit, but from the opposite
earphone.When a listener who heard the pitchesdelivered to his
right ear was present-ed with channel A to his right and chan-nel B
to his left, as shown in Fig. 5, heheard three high tones to his
right alter-nating with two low tones to his left.When the earphone
positions werereversed, as shown in Fig. 6, this listen-er now
heard two high tones to his rightalternating with three low tones
to hisleft! So the procedure of reversing theearphone positions
appeared to causethe channel to the right to mysteriouslydrop a
high tone and the channel to theleft to mysteriously add a low
tone!(See Deutsch, D. and P . L. Roll,“Separate ‘What’ and ‘Where’
DecisionMechanisms in Processing a DichoticTonal Sequence,” Journal
ofExperimental Psychology: HumanPerception and Performance , V ol.
2,1976, pgs. 23-29.
There is yet another surprisingaspect to this illusion:
Right-handersand left-handers dif fer statistically interms of
where the high and the lowtones appear to be localized. In
onestudy, I had people listen to this patternwith earphones
positioned first one wayand then the other. Most right-handersheard
the high tone on the right and thelow tone on the left, with
earphones
Right-handers and left-handers differ statistically in terms of
where high and low tones appear to be localized.
Fig. 4—Same as Fig. 3 but for “left-eared” listener .
Fig. 3—Perceived pitch and localization for “right-eared”
listener .
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AUDIO/MARCH 198740
Octave Illusion in Relation to Handed-ness and Familial
Handedness Back-ground,” Neuropsychologia, Vol. 21,1983, pgs.
289-293.)
How do these findings relate to theorganization of the brain in
relation tohandedness? In the large majority ofright-handers, the
left hemisphere of
the brain is dominant (i.e., speech isprocessed primarily in
this hemi-sphere). But this is true of only abouttwo-thirds of
left-handers, the remain-ing one-third being
right-hemispheredominant. W e also know that peoplewith left- or
mixed-handers in theirimmediate family are less likely to have
a pattern of dominance typical of right-handers than those with
only right-handers in their family. So this patternof results
indicates that we tend tolocalize the tones in this illusion
inaccordance with our patterns of hemi-spheric dominance.
Now, the perception of a single hightone in one ear which
alternates with asingle low tone in the other ear is mostcommonly
obtained. But some peopleexperience quite dif ferent illusions.Some
hear a single tone which switch-es from ear to ear , and whose
pitcheither remains the same or changesonly slightly as the tone
appears toshift in location. Other people obtain anumber of dif
ferent complex percepts,two of which are illustrated in Fig. 8.For
example, one person might hear alow tone which alternates from ear
toear and whose pitch shifts back andforth by a semitone, together
with anintermittent high tone in one ear .Another person might hear
a high tonealternating from ear to ear , with anintermittent low
tone in one ear . Yetother people find that the pitches of thetones
appear to change with continuedlistening. Large dif ferences in
timbreor sound quality are sometimesdescribed; for example, the
high tonesmay have a flute-like quality and thelow tones a
gong-like quality.
Complex percepts of the illusion aretypically unstable, so a
person maypass from one to another within a fewseconds and describe
the pattern asconstantly changing its character . Aconsiderably
higher proportion of left-handers obtain complex percepts thando
right-handers. This second hand-edness correlate is probably based
onanother relationship between handed-ness and brain organization.
It con-cerns the degree to which one hemi-sphere of the brain is
dominant overthe other. In right-handers, there tendsto be a
pronounced dominance of theleft hemisphere, but in the
left-han-ders, patterns of dominance tend to beless pronounced.
The illusion is sometimes perceivedin a way that is analogous to
the per-ception of ambiguous figures in vision.As illustrated in
Fig. 9, the high tonemay first be heard on the right and thelow
tone on the left. Then after a fewseconds, the high tone will
switch tothe left and the low tone to the right.
The octave illusion may be heard in analogous fashion to the way
that we see ambiguous figures.
Fig. 6—Same as Fig. 5 but with earphone positions reversed.
Fig. 5—Three high tones followed by two low tones delivered to
right ear , simul-taneous with three low tones followed by two high
tones delivered to left ear .
-
Fig. 9—Possible instability of percept obtained from octave
illusion pattern.
AUDIO/MARCH 1987 41
After a few more seconds, the toneswill interchange positions
again, and soon. In a similar way, if we scrutinize theNecker cube
of Fig. 10, it will appear toswitch back and forth in orientation,
sothat the front face periodically changesplaces with the back
one.
If you consistently hear the hightone on the right and the low
tone onthe left when the stereo channels are inbalance, you might
find that you canachieve a “Necker cube” perceptinstead by
gradually altering balanceso as to increase the amplitude of
thesignal to the left ear relative to the right.At some stage, the
high tone will sud-denly appear to switch to the left andthe low
tone to the right. Havingreached this stage, shift the balanceback
a little so as to reduce the ampli-tude of the signal to the left
ear , untilthe tones appear to return to their orig-inal locations.
By shifting the balanceback and forth in this way, you may finda
point of equilibrium at which the toneswill appear to spontaneously
inter-change locations in space.
Playing w ith t he o ctave i llusion i nthis f ashion i s r
ather l ike s crutinizingsome of Escher ’s woodcuts. Take,
forexample his “Regular Division of thePlane III,” shown in Fig. 1
1. In theuppermost portion of this picture, theblack horsemen
clearly provide the fig-ure and the white horsemen theground. In
the lowermost portion, thissituation is reversed. But in the
mid-dle, there is a region of ambiguity inwhich your perception
alternatesbetween these two interpretations.
What happens when the pattern isplayed at dif ferent speeds?
SoundExample 3 presents the pattern firstat the original tempo of
four tones persecond. Then the tempo is graduallyincreased to 20
tones per second,and finally it is slowed down to onetone every
four seconds. You canhear the illusion sharpen as thetempo is
increased, and graduallydeteriorate as the tones are playedmore
slowly . At the slowest tempo,both of the simultaneously
soundedtones may be heard.
We may next ask what happenswhen the alternating tones are not
inoctave relation. Sound Example 4presents the pattern with tones
relatedby a minor third. You can hear that theimpression is quite
dif ferent, though anillusion is still produced.
What happens when the sounds arepresented through loudspeakers
ratherthan earphones? One experiment toinvestigate this question
was performedin an anechoic chamber . The listenerwas first
positioned so that one speakerwas exactly on his right and the
otherexactly on his left, as shown in Fig. 12.
When the octave illusion was played, ahigh tone appeared to be
coming fromthe speaker on the right, and itappeared to alternate
with a low tonecoming from the speaker on the left. Asthe listener
turned slowly, the high toneremained on his right and the low
toneon his left. When, however , the listen-
Fig. 8—Two alternative percepts obtained from octave illusion
pattern.
Fig. 7—Varney and Benton handedness questionnaire.
-
Fig. 11—Escher woodcut, “Regular Division of the Plane III,”
illustrating ambiguityof visual percept.
er came to face one speaker , with theother exactly behind him,
the illusionabruptly disappeared; a single com-plex tone was heard
instead, asthough coming simultaneously fromboth speakers. But as
he continued toturn, the illusion abruptly reappeared,with the high
tone still on his right andthe low tone on his left. In otherwords,
after he had turned 180°, itappeared as though the speaker thathad
been producing the high tone wasnow producing the low tone, and
thatthe speaker that had been producingthe low tone was now
producing thehigh tone!
The ef fect also works in certainnon-anechoic environments,
thoughthe acoustics of normal rooms candegrade the illusion
considerably .The following demonstration is, how-ever, generally
very successful:Begin by listening to the pattern withearphones in
their usual position.Then, while the pattern is playing,slowly
remove the earphones andbring them out in front of you, as
illus-trated in Fig. 13. If you obtain a clearand consistent
illusion in the firstplace, you will probably find that youcan
bring the earphones out a con-siderable distance before the ef
fectdisappears. There is another point ofinterest here. Once the
illusion islost, it is necessary to return the ear-phones
considerably closer (if notright back onto your ears) before it
isrecaptured.
What happens if, instead of twoalternating tones, we present a
moreelaborate pattern? To examine thisquestion, I devised the
pattern shownin Fig. 14A and given in SoundExample 5. You can see
that this con-sists of a major scale whose succes-sive tones
alternate from ear to ear .The scale is played simultaneously
inboth ascending and descending form;when a tone from the ascending
scaleis in one ear, a tone from the descend-ing scale is in the
other ear . Figures14B and 14C show the ascending anddescending
components separately ,and you can see that the patternshown in
Fig. 14A is produced by thesuperposition of the patterns shown
inFigs. 14B and 14C. This sequence isplayed repeatedly without
pause.(See Deutsch, D., “T wo-ChannelListening to Musical Scales,”
Journal
AUDIO/MARCH 198742
Fig. 10—Necker cube, illustrating instability of visual
percept.
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AUDIO/MARCH 1987 43
of Acoustical Society of America, V ol.57, 1975, pgs.
1156-1160.)
This scale pattern also produces anumber of dif ferent
illusions. The onemost commonly experienced is illustrat-ed in Fig.
14D. A perceptual reorgani-zation occurs such that a melody
corre-sponding to the higher tones appears tobe coming from one
earphone, and amelody corresponding to the lowertones appears to
come from the other .When the earphone positions arereversed, the
higher and lower tonesusually maintain their apparent loca-tions.
So again, the procedure ofreversing the earphone positionsappears
to cause the higher tones tomigrate from one earphone to the
other,and the lower tones to migrate in anal-ogous fashion.
The ways in which the higher andlower tones are heard again
correlatewith handedness. Right-handers tendto hear the higher
tones on the rightand the lower tones on the left, but left-handers
don’t show this tendency .Some peo ple hear on ly the highertones,
and little or nothing of the lowertones. Interestingly, among those
whohear only the higher tones, a larger
number are able to localize them cor-rectly.
The scale illusion often works wellwith sounds presented through
stereo-phonically separated loudspeakers innormal room
environments. You maywant to listen to Sound Example 5 thisway,
making sure you are situatedroughly equidistant from the two
loud-speakers. Whether or not the spatialeffect works convincingly
in your envi -ronment, you should certainly experi-ence a
perceptual reorganization of themelodic lines, such that when the
chan-nels are played together in stereo, themelodies that you hear
are quite dif fer-ent from those that you hear when eachchannel is
played separately.
Variants of the scale illusion can eas-ily be produced. For
instance, SoundExample 6 presents a two-octave majorscale pattern,
switching from ear to ear(or from loudspeaker to loudspeaker) inthe
same way as before. This pattern isillustrated in Fig. 15. When the
twochannels are played together in stereo,most people hear a higher
scale whichmoves down an octave and back, andthey simultaneously
hear a lower scale,which moves up an octave and back,with the two
meeting in the middle. Butwhen you play each channel separately,the
tones are instead heard to be jump-ing around over a large pitch
range.Sound Example 7 presents another vari-ation, a one-octave
chromatic scalewhich alternates from ear to ear in thesame fashion,
as shown in Fig. 16. Asyet another variant, Sound Example 8presents
a two-octave chromatic scalewhich alternates in the same
fashion.This example is illustrated in Fig. 17.For all these
variants (as well as for theoriginal illusion), it is interesting
to listento each channel separately, and then togradually equalize
the balance of thechannels and experience the two melod-ic patterns
transforming into dif ferentones.
Similar effects can even occur in lis-tening to live music.
Figure 18 shows apassage from the last movement ofTchaikovsky’s
Sixth Symphony. As youcan see, the theme is formed of noteswhich
alternate between the first andsecond violins, while the second
voicealternates in converse fashion. A similararrangement holds for
the viola andcello parts. However , the voices aregenerally heard
instead as illustrated onthe right side of Fig. 18. It remains
a
Reversing the earphone positions does not usually reversethe
apparent left/right location of tones.
Fig. 14—Scale illusion using one-octave major scale. Sound
patterndelivered to right and left ears (A),based on ascending and
descendingscales (B and C), produces an illusorypercept (D).
Illus
tratio
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hilip
And
erso
n
Fig. 12—Octave illusion using loud-speakers; with speakers
exactly to leftand right of listener (A), with speakersexactly in
front of and behind listener(B), and after listener has turned 180
°(C).
Fig. 13—Octave illusion can be sustained even with earphones
infront of listener.
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AUDIO/MARCH 198744
mystery whether Tchaikovsky intend-ed to create an illusion
here, orwhether he expected listeners to hearthis passage as in the
written score.
Why should we experience this illu-sion? Because of the
complexity ofour sound environment, we cannotrely on classical
localization cuesalone (such as dif ferences in ampli-tudes and
arrival times at each ear) todetermine the locations of
simultane-ously presented sounds. Therefore,other cues must also be
taken intoconsideration. One such cue is simi-larity of frequency
spectrum: Similarsounds are likely to be coming fromthe same
source, and dif ferentsounds from dif ferent sources. Sowith
patterns such as we have beenconsidering, it makes sense to
con-clude that tones in one frequencyrange are coming from one
source,and that tones in another frequencyrange are coming from a
dif ferentsource. W e therefore perceptuallyreorganize the tones on
the basis ofthis interpretation.
There is an interesting visual ana-log of this effect. In Fig.
19, we see aphotograph of a hollow mask, takenfrom the inside.
Although the featuresof the face, such as the nose, are pro-jecting
inward, away from us, we per-ceive the face as projecting
outward,towards us. Our expectations thatfaces should project
outward are sostrong that we perceive this picturequite
incorrectly. Further, we continueto do so despite our conscious
knowl-edge of the illusion.
So far, we have been consideringcases where the sounds
presentedthrough the two earphones (or loud-speakers) are
simultaneous. Whathappens when time dif ferences areintroduced? In
one experiment, Idevised two simple melodic patternsand asked
listeners to identify on eachtrial which one they had heard.
Thepatterns are shown in Figure 20.
In one condition, the tones com-prising the patterns were
presented tothe two ears simultaneously , asshown in Fig. 21A.
Under these cir-cumstances the patterns were easy toidentify, and
performance on the taskwas very good. In a second condition,the
tones were switched haphazardlybetween the ears, as shown in
Fig.21B. As can be heard in Sound
Despite our conscious knowledge of an illusion, we mayoften
continue to perceive what we hear incorrectly .
Fig. 16—Same as Fig 15 but using one-octave chromatic scale.
Fig. 15—Scale illusion using two-octave major scale.
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AUDIO/MARCH 1987 45
Example 9, the switching proceduremade the task much more dif
ficult.Most people found that their attentionwas directed to the
sounds coming fromone earphone or the other , and it wasvery dif
ficult for them to integrate thetwo into a coherent melody.
A third condition (Fig. 21C) wasexactly as the second, except
that themelody was accompanied by a drone.Whenever a tone from the
melody wasin the right ear, the drone was in the leftear, and
whenever a tone from themelody was in the left ear , the dronewas
in the right ear . So sounds wereagain presented to both ears
simultane-ously, even though the melody was stillswitching from ear
to ear , exactly asbefore. As can be heard in SoundExample 10, the
presence of the dronein the opposite ear caused the soundsto merge
perceptually , so that themelody could easily be
identified.Performance in this condition was againvery good. In a
fourth condition, shownin Fig. 21D, a drone again accompaniedthe
melody, but it was presented to thesame ear as the melody
component.This meant that input was again to oneear at a time. As
you can hear in SoundExample 11, it was again very difficult
tointegrate the dif ferent sounds. (SeeDeutsch, D., “Binaural
Integration ofMelodic Patterns,” Perception andPsychophysics, Vol.
25, 1979, pgs. 399-405.)
This experiment shows that whensignals are coming from two dif
ferentlocations, temporal relationshipsbetween them are important
determi-nants of how they are perceptuallygrouped together . When
both earsreceive input simultaneously , integra-tion of patterns is
easy . But whensounds arriving at the two ears areclearly separated
in time, we insteadfocus attention on one ear or the other ,and
find it much more dif ficult to com-bine the two into a single
perceptualstream.
What happens in the intermediatecase, where the signals to the
two earsare not strictly synchronous, but insteadoverlap in time?
In a further experi-ment, I found that this intermediate
caseproduced intermediate results.Identification of the melody with
a strict-ly synchronous drone in the oppositeear was easiest. Next
easiest identifi-cation of the melody was with an asyn-
Fig. 17—Same as Fig. 15 but using two-octave chromatic
scale.
Fig. 18—Passage from last movement of Tchaikovsky’s Sixth
Symphony, showingseparate parts for first and second violin, viola,
and cello (left), and how theseparts are usually perceived
(right).
Fig. 19—A visual example of perceptu-al rearrangement: Hollow
maskappears to project outward.
Pho
togr
aph:
Ben
Ros
e
-
chronous drone, while the worst resultswere with no drone.
Why should the perceptual systemfunction in this fashion?
Temporal rela-tionships between sound signals pro-vide important
cues as to whether theyare coming from the same source orfrom dif
ferent sources. So we shouldexpect that the more clearly signals
atthe two ears are temporally separated,the more we should treat
them as com-ing from separate sources, and so themore we should
tend to group them byspatial location. If such grouping werestrong
enough, it should prevent usfrom linking together sounds
arisingfrom these different sources.
To place these findings in a moregeneral context, we may note
that thecomposer Berlioz has argued for thecompositional importance
of spatialarrangements. As he wrote in hisTreatise on
Instrumentation:
I want to mention theimportance of the dif ferentpoints of
origin of the tonalmasses. Certain groups of anorchestra are
selected by thecomposer to question andanswer each other; but
thisdesign becomes clear andeffective only if the groupswhich are
to carry on the dia-logue are placed at a sufficientdistance from
each other. Thecomposer must therefore indi-cate in his score their
exactdisposition. For instance, thedrums, bass drums, cymbals,and
kettledrums may remaintogether if they are employed,as usual, to
strike certainrhythms simultaneously. But ifthey execute an
interlocutoryrhythm, one fragment of whichis given to the bass
drums andcymbals, the other to kettle-drums and drums, the ef
fectwould be greatly improvedand intensified by placing thetwo
groups of percussioninstruments at the oppositeends of the
orchestra, that isat a considerable distancefrom each other.
The experiments that we have beendescribing indicate that
spatial arrange-ments of instruments should indeed
AUDIO/MARCH 198746
Fig. 21—Patterns of Fig. 20, with tones presented to two ears
simultaneously(A), switching haphazardly between ears (B),
switching haphazardly and accom-panied by a drone in the opposite
ear (C), and switching haphazardly andaccompanied by a drone in the
same ear (D).
Fig. 20—Simple melodic patterns usedto examine effects of time
differenceson perception.
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AUDIO/MARCH 1987 47
have profound ef fects on how music isperceived. When a rapid
pattern oftones is distributed between two sets ofinstruments, and
these tones are clearlyseparated in time, we may be unable
tointegrate them so as to form a coherentmelody. If, however , the
tones overlapin time, such integration is more readilyachieved. But
there is a trade-of f: Asthe temporal overlap is increased,
ourability to identify the locations of differentsounds decreases,
and when the tonesare simultaneous, spatial illusions tendto
occur.
Let us finally return to the question ofhow perception of
simultaneous tones isaffected by whether the higher tone is tothe
right and the lower to the left, or viceversa. As we have seen in
the octaveand scale illusions, right-handers tend tohear the higher
tones on the right andthe lower tones on the left, regardless
oftheir actual locations. So combinationsof the
“high-right/low-left” type tend to becorrectly localized, and
combinations ofthe “high-left/low-right” type tend to
bemislocalized. Other recent experimentshave shown this to be true
in more gen-eral settings also. And in further study Ifound that,
in addition, there is anadvantage to the “high-right/low-left”
dis-position in terms of how well the pitchesof the tones are
perceived. (SeeDeutsch, D., “Dichotic Listening toMelodic Patterns
and Its Relationship toHemispheric Specialization of
Function,”Music Perception , V ol. 3, 1985, pgs.127-154.)
Now, to the extent that ef fects of thissort occur in listening
to live music, wemay advance the following line of rea-soning. In
general, seating arrange-ments for contemporary orchestras aresuch
that, from the performers’ point ofview, instruments with higher
registerstend to be to the right, and instrumentswith lower
registers to the left. As anexample, Fig. 22 shows a seating
planfor the Chicago Symphony, viewed fromthe rear of the stage. In
the string sec-tion, the first violins are to the right of
thesecond violins, which are to the right ofthe violas. These are,
in turn, to the rightof the cellos, which are to the right of
thebasses. In the brass section, the trum-pets are to the right of
the trombones,which are to the right of the tuba. Noticealso that
the flutes are to the right of theoboes, and the clarinets to the
right ofthe bassoons. The same general princi-
ple holds for choirs and other singinggroups. Since it is
important that the dif-ferent performers in an ensembleshould be
able to hear each other aswell as possible, we may conjecture
thatthis type of arrangement has evolved bytrial and error because
it is conducive tooptimal performance.
But this presents us with a paradox.Since the audience sits
facing theorchestra, as shown in Fig. 23, this left-right
disposition is, from their point of
view, mirror-image reversed: Instru-ments with higher registers
are now tothe left, and instruments with lower reg-isters to the
right. So from the audi-ence’s standpoint, this arrangement issuch
as to cause perceptual dif ficulties.In particular, instruments
with low regis-ters which are to the audience’ s rightshould tend
to be poorly perceived andlocalized.
It is not all clear what can be doneabout this. We can’t simply
mirror-image
The spatial arrangements of instruments should indeed have
profound effects on how music is perceived.
Fig. 23—Same as Fig. 22 but as viewed from audience.
Fig. 22—Seating plan for Chicago Symphony, as viewed from rear
of stage.
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AUDIO/MARCH 198748
reverse the orchestra, because then theperformers wouldn’t be
able to heareach other so well. Suppose, then, thatwe turned the
orchestra 180°, as awhole, so that the players had theirbacks to
the audience. This wouldn’tprovide a solution, because then
thebrasses and percussion would be clos-est to the audience, and so
woulddrown out the strings. Suppose, then,that w e “
retrograde-inverted” t heorchestra so that they had their backs
tothe audience, with the brasses and per-cussion farthest away and
the stringsthe closest. This wouldn’t provide asolution either ,
because then the con-ductor wouldn’t be able to hear thestrings,
and so wouldn’t be able to con-duct efficiently.
One solution (suggested by my col-league Robert Boynton) would
be toleave the orchestra as it is, but havethe a udience h anding u
pside-downfrom the ceiling! (See Fig. 24.) Thissolution is,
however, unlikely to be pop-ular with concert-goers! On the
otherhand, for the case of sounds repro-duced in stereo, an obvious
suggestionpresents itself: Try reversing the chan-
nels on your system. This solution isnot without its drawbacks;
the musicwon’t sound the same as in concerthalls, and the
arrangement will be unfa-miliar even as a reproduction. But youmay
want to try the experiment anyway.
Finally, I should mention that most ofthe perceptual ef fects
described hereoccur even though the listener has fullinformation as
to what the sound pat-tern really is. There are other cases
inlistening to music, however , in whichprior knowledge of the
music has a pro-found influence on how it is perceived.One such ef
fect, which I originallydemonstrated using the tune “Y
ankeeDoodle,” is particularly striking. If youplay a well-known
melody, but displaceits individual notes at random into dif-ferent
octaves, people will be unable torecognize the melody unless they
aregiven clues on which to base a hypoth-esis (such as its rhythm,
its contour ,and so on). But if you give the listenerthe name of
the melody beforehand,this problem essentially disappears.(See
Deutsch, D., “OctaveGeneralization and Tune Recognition,”Perception
and Psychophysics, Vol. 11,
1972, pgs. 411-412.)Sound Example 12 presents anoth-
er well-known melody , with its tonesplaced haphazardly in
different octavesin this fashion. Listen to this example,and try to
identify the tune. Then listento Sound Example 13, which
presentsthe same melody without the octave-randomizing
transformation. Finally ,listen to Sound Example 12 again, andyou
will find that the melody is nowmuch easier to follow.
This little experiment can also easi-ly be performed by anyone
with accessto a musical instrument. Make sure,though, that you
don’t give your sub-jects any hints as to what the melodyis, and
that you scramble the octavesvery well, or they might recognize
themelody on the basis of a small part thatwas left intact. Also,
choose a melodythat is as free of rhythmic cues as pos-sible, or
they might be able to make theright guess on the basis of the
rhythmalone. If you follow this procedure, it’ spretty sure to
work!
Additional ReadingBerlioz, H., Treatise on Instru-
mentation, I. Strauss, editor , and T.Front, translator (E. F .
Kalmus,1948).
Butler, D., “Melodic Channeling in aMusical Environment,”
presented atthe Research Symposium on thePsychology and Acoustics
of Music,Kansas, 1979.
Deutsch, D., “Auditory Illusions,Handedness, and the
SpatialEnvironment,” Journal of the AudioEngineering Society, Vol.
31 (1983),pgs. 607-622.
Deutsch, D., “Musical Illusions,”Scientific American , V ol.
233(1975), pgs. 92-104.
Deutsch, D., “The Processing of PitchCombinations,” The
Psychology ofMusic, D. Deutsch, editor(Academic Press, New York,
1982).
Machlis, J., The Enjoyment of Music,Fourth Edition (Norton, New
Y ork,1977).
Varney, N. R. and A. L. Benton, “TactilePerception of Direction
in Relationto Handedness and FamilialHandedness
Background,”Neuropsychologia, Vol. 13 (1975),pgs. 449-454.
Zangwill, O. L., Cerebral Dominance
If a familiar melody is played with its notes displaced in
different octaves, people will be unable to recognize it.
Fig. 24—One way to optimize the left-right arrangement of an
orchestra, both forthe players and the audience.
Illus
tratio
n: P
hilip
And
erso
n
Audio_1987_36_48