Auditory Perception

First published Thu May 14, 2009; substantive revision Tue Apr 7, 2020

Auditory perception raises a variety of challenging philosophicalquestions. What do we hear? What are the objects of auditoryawareness? What is the content of audition? Is hearing spatial? Howdoes audition differ from vision and other sense modalities? How doesthe perception of sounds differ from that of colors and ordinaryobjects? This entry presents the main debates in this developing areaand discusses promising avenues for future inquiry. It discusses themotivation for exploring non-visual modalities, how audition bears ontheorizing about perception, and questions concerning the objects,contents, phenomenology, varieties, and bounds of auditoryperception.

1. Other Modalities and the Philosophy of Perception

The philosophy of sounds and auditory perception is one area of thephilosophy of perception that reaches beyond vision for insights aboutthe nature, objects, contents, and varieties of perception. This entrycharacterizes central issues in the philosophy of auditory perception,many of which bear upon theorizing about perception more generally,and it mentions outstanding questions and promising future areas forinquiry in this developing literature. Before beginning thesubstantive discussion of audition itself, it is worthwhile to discussthe motivation and rationale for this kind of work.

Philosophical thinking about perception has focused predominantly onvision. The philosophical puzzle of perception and its proposedsolutions have been shaped by a concern for visual experience andvisual illusions. Questions and proposals about the nature ofperceptual content have been framed and evaluated in visual terms, anddetailed accounts of what we perceive frequently address just thevisual case. Vision informs our understanding of perception’sepistemological role and of its role in guiding action. It is not agreat exaggeration to say that much of the philosophy of perceptiontranslates roughly as philosophy of visual perception.

Recently, however, other perceptual modalities have attractedattention (see, e.g., Stokes et al. 2015, Matthen 2015). In additionto auditory perception and the experience of sound, touch and tactileawareness have generated philosophical interest concerning, forinstance, the tactile and proprioceptive experience of space, theobjects of touch, whether contact is required for touch, and whetherdistinct modalities detect pressure, heat, and pain (see, e.g.,O’Shaughnessy 1989, Martin 1993, Scott 2001, Fulkerson 2013,2016). The unique phenomenology of olfaction and smells has been usedto argue that vision is atypical in supporting the transparency ofperceptual experience (Lycan 2000, 282; cf. Batty 2010) and thatperceptual objectivity does not require spatiality (Smith 2002, ch 5).Lycan (2000) even suggests that the philosophy of perception wouldhave taken a different course had it focused upon olfaction instead ofvision (see also Batty 2011). Some authors have appealed to taste andflavor to challenge traditional ways of dividing and counting senses(Smith 2015; cf. Richardson 2013).

This kind of work is philosophically interesting in its own right. Butit is also worthwhile because theorizing about perception commonlyaims to address general questions about perception, rather thanconcerns specific to vision. Hope for a comprehensive and generalunderstanding of perception rests upon extending and testing claims,arguments, and theories beyond vision. One might view work onnon-visual modalities as filling out the particulars required for athoroughly detailed account of perceiving that applies not just tovision but across the modalities. At least three approaches might beadopted, with potential for increasingly revisionist outcomes.

First, one might take work on non-visual modalities astranslating what we have learned from the visual case intoterms that apply to other modalities. This approach is relativelyconservative. It assumes that vision is representative or paradigmaticand that we have a good understanding of perception that is derivedfrom the case of vision. One example of this kind of approach would beto develop an account of the representational content of auditoryexperience.

Second, considering other modalities mightextend ourvision-based understanding of perception. Non-visual cases might drawattention to new kinds of phenomena that are missing from or notsalient in vision. If so, a vision-based account of perception issatisfactory as far as it goes, but it leaves out critical pieces. Forexample, speech perception, multimodal perception, and flavorperception might involve novel kinds of perceptual phenomena absentfrom the visual case.

Third, considering other modalities mightchallengevision-based claims about perception. If falsifying evidence isdiscovered in non-visual cases, then theorizing beyond vision mayforce revision of general claims about perception that are supportedby vision. For example, if olfactory experience is not diaphanous, butolfactory experience is perceptual, the transparency thesis forperceptual experience fails.

Finally, we might attempt to determine whether anyunifiedaccount exists that applies generally to all of the perceptualmodalities. We can ask this question either at the level of quitespecific claims, such as those concerning the objects of perception orthe nature and structure of content. We can ask it about therelationships among perceiving, believing, and acting. Or we can askit about the general theory of necessary and sufficient conditions forperceiving. Some philosophers, impressed by findings concerningnon-visual modalities, express skepticism whether a unified theoryexists (e.g., Martin 1992).

Whatever the approach, extending our knowledge about perception beyondthe visual requires systematic attention to individual modalities aswell as careful accounting in order to determine how the results bearon general questions about perception. Whatever the outcome, auditionis a rich subject matter in its own right, and investigating thissubject matter is crucial to our overall understanding ofperception.

2. The Objects of Auditory Perception

What do we hear? One way to address this question concerns theobjects of auditory perception.

2.1 Sounds

In the first instance, typical human perceivers hearsounds. Itis plausible that sounds are objects of auditory perception.

What are sounds? Sounds traditionally have been counted with colors,smells, and tastes assecondary,sensible, orsensoryqualities (see, e.g., Locke 1689/1975, Pasnau1999, 2000, Leddington 2019). However, recently it has been proposedthat sounds areindividuals to which sensible features areattributed. In particular, several philosophers have proposed thatsounds are public, distally-located, event-like individuals (Casatiand Dokic 1994, 2005, O’Callaghan 2007, Matthen 2010).

Four questions about audition’s objects define the debate andconstrain theories of sound (see also the entry onsounds, for extensive discussion).

2.1.1 Private or Public?

Are sounds private or public? Maclachlan (1989) argues that the soundswe hear aresensations (rather than, for instance, the pressurewaves that cause auditory experiences). Such sensations are internaland private, and we experience them directly, or without apparentmediation. On Maclachlan’s account, we hear the ordinary thingsand happenings that are thesources of sounds onlyindirectly, by means of inference from auditory data.

Maclachlan’s story is noteworthy partly because he uses hearingand sounds to motivate a general claim about perception. He claimsthat what seems perfectly intuitive and obvious in the case of soundsand hearing—that something other than material objects are thedirect objects of hearing; that the direct objects of audition areinternal; and that we indirectly hear things in the world by hearingtheir sounds—helps us to discover what is true of allperception. According to Maclachlan, for instance, seeing involvesdirect awareness of sensations of patterns of light, while surfacesand ordinary objects figure only indirectly and thanks to inferenceamong the intentional objects of sight. The case of sounds andaudition is important because it reveals that perceiving involvesawareness of sensations in the first instance, and of the externalworld only indirectly.

Maclachlan’s description of sounds and auditory experience hassome attractions. First, sounds are among the things we hear. Andsounds are among the direct or immediate objects of audition in therelatively innocuous sense that hearing a sound does not seem torequire hearing as of something else. Hearing a collision, on theother hand, may seem to require awareness as of a sound. Furthermore,sounds are unlike the ordinary material objects (e.g., bottles andstaplers) we see. You cannot reach out and grab a sound, or determineits temperature. Instead, sounds may strike us as byproducts oreffects of such ordinary things and their transactions. Sounds resultfrom activities or interactions of material bodies and thus areexperienced as distinct or independent from them (cf. Nudds 2001).Nevertheless, audition does afford some variety of awareness of thesources of sounds, or at least provides information about them.

However, the claim that sounds are sensations is unattractive. Goodreasons suggest that sounds are public rather than private, even ifsounds are not identical with ordinary objects and events such asclothespins and collisions. Suppose I am near the stage in a halllistening to some music, and that I have a headache. It is a confusionto think you could feel my headache, but I assume you hear the soundsI hear. Suppose I move to the back of the hall, and the headache thengets better. My experience of the sounds of the music differs once Iam at the back of the room, and my experience of the headache differs.The sound of the music itself need not differ (the musicians couldmake the same sounds), but the headache itself changes. The sounds cancontinue once I leave the room, but if I stop experiencing theheadache, it is gone. Moreover, the notion of an unfelt headache ispuzzling, but it makes good sense to say that a tree makes a soundwhen it falls in the woods without being heard. Finally, tinnitus, orringing of the ears, is an illusory or hallucinatory experience as ofa sound, but received wisdom maintains that there are no illusoryheadaches.

This suggests that audition does not providespecial reasons tobelieve that the objects of perception are private sensations. Sounds,construed as objects of auditory perception, plausibly inhabit thepublic world. (See the section3.1 Spatial Hearing for further discussion.)

2.1.2 Proximal or Distal?

Are sounds proximal or distal? The customary science-based view holdsthat sounds are pressure waves that travel through a medium (see alsoSorensen 2008). On this account, sounds are caused by objects andevents such as collisions, and sounds cause auditory experiences.However, sounds are not auditorily experienced to travel through thesurrounding medium as waves do. Thus, if sounds are waves, then thesounds we hear may be proximal, located at the ear of the hearer.

Alternatively, some have argued that audition presents sounds as beinglocated in some direction at a distance (Pasnau 1999,O’Callaghan 2007, ch. 3, 2010). On such an account, soundscommonly appear auditorily to be in the neighborhood of their sourcesand thereby furnish useful information about the locations of thosesources. The sound of the drumming across the street seems to comefrom across the street but does not seem audibly to travel. Whensounds do appear to fill a room, sound seems located all around.Sounds that seem to “bounce” around a room appearintermittently at different locations rather than as travelingcontinuously from place to place. Experiencing a missile-like soundspeeding towards your ears illustrates the contrast with ordinaryhearing (O’Callaghan 2007, 35). Sounds, according to thisconception, ordinarily appear to have distal locations and to remainstationary relative to their sources.

If sounds are not usually experienced to travel, then unless auditoryexperience is illusory with respect to the apparent locations ofsounds, sounds themselves do not travel. Sounds thus are not identicalwith and do not supervene locally upon the waves, since waves travel(Pasnau 1999). Several philosophers have argued on these and relatedgrounds that sounds are located distally, near their sources (Pasnau1999, Casati and Dokic 2005, O’Callaghan 2007). On this view,pressure waves bear information about sounds and are the proximalcauses of auditory experiences, but are not identical with sounds.

One might object by resisting the phenomenological claim that weexperience sounds as distally located, for instance by suggesting thataudition is aspatial, or that audition is spatial but soundsources rather than sounds are auditorily localized (seesection3.1 Spatial Hearing for further discussion). Or, one might accept some measure ofillusion. Another possibility is that we experience only a smallsubset of the locations sounds occupy during their lifetimes (forinstance, while at their sources), and simply fail to experience wherethey are at other times. This avoids ascribing illusion. Finally,Fowler (2013) argues indirectly on the basis of echoes against distaltheories of sound.

2.1.3 Properties or Individuals?

Are sounds properties or individuals? Among both proximal and distaltheories, disagreement exists concerning the ontological category towhich sounds belong. Philosophers traditionally have understood soundsas properties—either as sensible or secondary qualities, or asthe categorical or physical properties that ground powers to affectsubjects. Commonly, sounds are attributed to the medium thatintervenes between sources and perceivers. More recently, however,some distal theorists have argued that sounds are properties of whatwe ordinarily understand as sound sources—bells and whistleshave orpossess rather thanmake orproduce sounds. Pasnau (1999), for instance, claims that soundsare transient properties that are identical with or supervene uponvibrations of objects. Kulvicki (2008) argues against transience in anattempt to subsume sounds to the model of colors, and claims thatsounds are persistent, stable dispositional properties of objects tovibrate in response to being “thwacked”. He distinguishes“having” a stable sound from “making” a soundon some occasion (manifesting the stable disposition). This accountimplies that sounds sometimes make sounds they do not have, and thatthey have sounds when silent. One also might ask whether events suchas collisions and strummings, rather than objects, bear sounds.Leddington (2019) recently has defended such an account.

A revisionist challenge comes from those who argue that sounds areindividuals rather than properties. Several arguments supportthis understanding. First, empirical work onauditory sceneanalysis suggests that one primary task of audition is to carve upthe acoustic scene into distinct sounds, each of which may possess itsown pitch, timbre, and loudness (Bregman 1990). Multiple distinctsounds with different audible attributes can be heard simultaneously.An analog of Jackson’s (1977, see also Clark 2000)manyproperties problem thus arises for audition since featureawareness alone cannot explain the bundling or grouping of audibleattributes into distinct sounds. Such bundling or grouping of audiblefeatures suggests that sounds are perceptible individuals to whichthese features are attributed.

Furthermore, the temporal characteristics of experienced soundssuggest that sounds are not simple qualities. Sounds audibly seem topersist through time and to survive change. A particular sound, suchas that of an emergency siren, might begin high-pitched and loud andend low-pitched and soft. This suggests that sounds are individualsthat bear different features at different times, rather than sensiblequalities.

Several responses to these arguments are available (see Cohen 2009 forthe most developed reply). One might argue that sounds are complexproperties, such as pitch-timbre-loudness complexes, instantiated at atime. To account for feature binding, one might hold that such complexproperties are ascribed to ordinary objects such as bells andwhistles. Or, one might hold that they are particularized properties,such as tropes. To accommodate sounds that survive change throughtime, a property account could hold that sounds are yet more complexproperties that have patterns of change built into their identityconditions. However, any such view differs a great deal from thefamiliar secondary or sensible quality view pioneered by Locke. Pitch,timbre, and loudness are better candidates for simple sensiblefeatures in audition (see section3.2 Audible Qualities).

2.1.4 Objects or Events?

If sounds are individuals, are they object-like or event-likeindividuals? Intuitively, the material objects we see are capable ofexisting wholly at any given moment, and all that is required toperceptually recognize such individuals is present at a moment. On theother hand, event-like individuals occupy time and need not existwholly at any given moment. Their individuation and recognitionfrequently appeal to patterns of features over time. Event-likeindividuals intuitively comprise temporal parts, while object-likeindividuals intuitively do not. The issue here is not the truth ofendurantism or perdurantism as an account of the persistence ofobjects or events. Instead, the issue concerns a difference in how weperceptually individuate, experience, and recognize individuals.

No contemporary philosopher has yet claimed that sounds are objectsin the ordinary sense. Those who argue that sounds areindividuals commonly point out that sounds not only persist andsurvive change (as do ordinary material objects), but alsorequire time to occur or unfold. It is difficult to imagine aninstantaneous sound, or one that lacks duration. Sounds are notcommonly treated as existing wholly at a given moment during theirduration. Indeed, the identities of many common sounds are tied topatterns of change in qualities through time. The sound of anambulance siren differs from that of a police siren precisely becausethe two differ in patterns of qualitative change through time. Thesound of the spoken word ‘team’ differs from that of‘meat’ because each instantiates a common set of audiblequalities in a different temporal pattern. These considerationssupport the view that sounds are event-like individuals (see Casatiand Dokic 1994, 2005, Scruton 1997, O’Callaghan 2007, Matthen2010).

This may bear on debates about persistence in the following way.Differences in the intuitive plausibility of endurantism andperdurantism may be grounded in facts about perception. In particular,vision may treat objects as persisting by enduring or being whollypresent at each time at which they exist, while audition may treat itsobjects as persisting by perduring or having temporal parts. This maystem from differences in perceptual organization. For instance,exhibiting a visible property profile at a time may suffice for beinga visual object of a given sort, while being an audible object of agiven sort may require exhibiting an audible property profile overtime.

2.2 Auditory Objects

Though most philosophers construe sounds either as properties or asevent-like individuals (see section2.1 Sounds), psychologists commonly have discussedauditory objects (see,e.g., Kubovy and Van Valkenburg 2001, Griffiths and Warren 2004, Healdet al. 2017). The target of such discussion is not simplyaudition’sintentional objects orproper (specificto audition) objects. The intended analogy is withvisualobjects. Talk of auditory objects gestures at the visual processesinvolved in perceptually discriminating, attentively tracking,recognizing and categorizing ordinary material objects. What justifiestalk ofobject perception in audition?

2.2.1 Object Perception in Audition

First of all, humans typically do not auditorily perceivethree-dimensional, bounded material objectsas such, though itis plausible to think we visually perceive them. Hearing does notresolve the edges, boundaries, and filled volumes in space that I see,and I do not hear audible items to complete spatially behind occludersas do visible surfaces of objects. If perceiving a three-dimensionalobject requires awareness of its edges, boundaries, and extension,perhaps in order to discriminate it from its surroundings, humanstypically do not auditorily perceive such objects.

Nevertheless, striking and illuminating parallels do exist between theperceptual processes and experiences that take place in vision andaudition. Such parallels may warrant talk of object perception in amore general sense that is common to both vision and audition(O’Callaghan 2008a).

Perceiving objects requires parsing a perceptual scene into distinctunits that one can attend to and distinguish from each otherand from a background. In vision, bounded, cohesive collections ofsurfaces that are extended in space and that persist through time playthis role (see, e.g., Spelke 1990, Nakayama et al. 1995, Leslie et al.1998, Scholl 2001, Matthen 2005). In audition, as in vision, multipledistinct perceptible individuals might exist simultaneously, and eachmight persist and survive change (see the discussion of auditory sceneanalysis in section2.1 Sounds). A critical difference, however, is that while vision’s objectsare extended in space, and are individuated and recognized primarilyin virtue of spatial characteristics, audible individuals are extendedin time, and are perceptually individuated and recognized primarily invirtue of pitch and temporal characteristics (see, e.g., Bregman 1990,Kubovy and Van Valkenburg 2001). For instance, audible individualshave temporal edges and boundaries, and boundary elements can belongonly to a single audible individual. They also are susceptible tofigure-ground effects over time. One can, for instance, shiftattention among continuous audible individuals that differ in pitch.Furthermore, they are susceptible to completion effects over time inmuch the same way that visible objects are perceptually completed inspace. Seeing a single visible region to continue behind a barrier isanalogous to hearing a sound stream to continue through masking noise,which may take place even when there is no corresponding signal(Bregman 1990, 28). Finally, multiple distinct, discrete audibleindividuals, such as the temporally bounded notes in a tune, can formaudiblestreams that comprise a single perceptible unit. Suchstreams are subject to figure-ground shifts, and, like collections ofsurfaces, they can be attentively tracked through changes to theirfeatures and to one’s perspective. Though such complex audibleindividuals include sounds, they comprise temporally unifiedcollections of sounds and silence that are analogous to spatiallycomplex visible objects, such as tractors.

Such audible individuals are temporally extended and bounded, serve asthe locus for auditory attention, prompt completion effects, and aresubject to figure-ground distinctions in pitch space. For thesereasons, the auditory processes involved in their perception parallelthose involved in the visual perception of ordinary three-dimensionalobjects. The parallels suggest a shared sense in which vision andaudition involve a more general form of object perception (see, e.g.,Kubovy and Van Valkenburg 2001, Scholl 2001, Griffiths and Warren2004, O’Callaghan 2008a, Matthen 2010).

2.2.2 What is an Auditory Object?

What is the shared sense in which both visible and audible individualsdeserve to be called ‘objects’? Kubovy and Van Valkenburg(2001, 2003) define objecthood in terms of figure-ground segregation,which requires perceptual grouping. They propose thetheory ofindispensable attributes as an account of the necessary conditionson perceptual grouping (see also Kubovy 1981). Indispensableattributes for a modality are those without which perceptualnumerosity is impossible. They claim that while space and time areindispensable attributes for vision (and color is not), pitch and timeare indispensable attributes for auditory objects. Though they aremore skeptical about whether audition parallels vision, Griffiths andWarren (2004) sympathize with a figure-ground characterization butsuggest a working notion of an auditory object defined in terms of“an acoustic experience that produces a two-dimensional imagewith frequency and time dimensions” (Griffiths and Warren 2004,891).

O’Callaghan (2008a) proposes that both visible and audibleobjects are mereologically complex individuals, though their mereologydiffers in noteworthy respects. While vision’s objects possess aspatial mereology and are individuated and tracked in terms of spatialfeatures, audition’s objects have a temporal mereology and areindividuated and tracked in terms of both pitch and temporalcharacteristics. Discussion of auditory objects thus draws attentionto two roles that space plays in vision. First, there is the role ofspace in determining the structure internal to visible objects, whichfacilitates identifying and recognizing visible objects. Second, spaceserves as the external structure among visible objects, and iscritical in distinguishing objects from each other. In audition, timeplays a role similar to space in vision in determining the structureinternal to auditory objects. Pitch, on the other hand, serves as anexternal structural framework, along with space, that helps todistinguish among audible individuals.

Why is it useful to perceive such individuals in audition? Onepromising account is that they provide useful information about thehappenings that produce sounds. Carving the acoustic world intomereologically complex individuals informs us about what is going onin the extra-acoustic environment. It provides ecologicallysignificant information about what the furniture is doing, rather thanjust how it is arranged. It is one thing to perceive a tree; it isanother to hear that it is falling behind you.

Discussion of auditory objects and accounts of their nature andperception is relatively new among philosophers (see, e.g.,O’Callaghan 2008a, and essays in Bullot and Egré 2010,including Matthen 2010, Nudds 2010). Such work has led to thedevelopment of general accounts of perceptual objects designed toavoid visuocentrism (see, e.g., O’Callaghan 2016, Green 2019).This area is ripe for philosophical contributions.

2.3 Sound Sources

Sounds are among the objects of audition. Plausibly, so are complex,temporally extended individuals composed of sounds. Do we hearanything else? Reflectionsuggests we hear things beyond soundsand sound complexes. In hearing sounds, one may seem to experience thebackfiring of the car or the banging of the drum. One might hold thata primary part of audition’s function is to revealsoundsources, the things and happenings that make sounds.

2.3.1 Do Humans Hear Sound Sources?

If sounds were internal sensations or sense-data, then, as Maclachlan(1989) observes, we would hear sound sources only indirectly, in anepistemological sense, perhaps thanks to something akin to inference.Acquiring beliefs about the environment would require mediation bypropositions connecting experienced internal sounds with environmentalcauses.

If, however, sounds are properties attributed either to ordinaryobjects, as Pasnau (1999) and Kulvicki (2008) hold, or to events, asLeddington (2019) holds, then hearing a tuba or the playing of a tubamight only require hearing its sounds. Perceptually ascribing suchaudible attributes to their sources might ground epistemicallyunmediated awareness of tubas or their playings.

However, the individuals to which audible attributes are perceptuallyattributed need not be identical with ordinary objects or events.Instead, audible attributes may belong in the first instance tosounds. Sounds plausibly are distinct from ordinary or extra-acousticindividuals (O’Callaghan 2007, 2011). Suppose then that onecould not hear an ordinary object or event without there existing anaudible sound, as well as that sounds can mislead about their sources(it might sound like drumming but be hammering).

Given this, forming beliefs about ordinary things and happeningsconnected with sounds might seem to require inference, association, orsome otherwise cognitive process, and so awareness of a sound sourcemight appear to always involve more than perceptual awareness.According to such an account, awareness of environmental things andhappenings thanks to audition is epistemically mediated by awarenessas of sounds and auditory objects, but does not itself constituteauditory perceptual awareness as of those things and happenings. Youare inclined to think you hear the source because your representing orbeing aware of it co-occurs with, but is no more than a downstreamconsequence triggered by, your auditory experience.

Such an account is not wholly satisfactory. First, the phenomenologyof audition suggests something stronger than indirect, epistemicallymediated awareness of things such as collisions or guitar strummingsor lions roaring. Reflection suggests auditory awarenessas ofcollisions, strummings, and lions. Second, the capacity to referdemonstratively to such things and events on auditory grounds alsosuggests genuine perceptual awareness of them. Third, we commonlyperceptually individuate sounds in terms of their apparent sources,and our taxonomy reflects this. “What did you hear?”“I heard paper ripping,” or, “The sound of adripping faucet.” We distinguish two quite similar rattles oncewe hear one as of a muffler clamp and the other as of a loose fender.Furthermore, characterizing certain audible features and explainingperceptual constancy effects involving such features requires appealto sound sources. Handel says of timbre: “At this point, noknown acoustic invariants can be said to underlie timbre... The cuesthat determine timbre quality are interdependent because all aredetermined by the method of sound production and the physicalconstruction of the instrument” (Handel 1995, 441). Explainingloudness constancy—why moving to the back of the room does notchange how loudly the lecturer seems to speak—appeals to factsabout the sources of sounds (Zahorik and Wightman 2001). Auditoryprocessing proceeds in accordance with natural constraints concerningcharacteristics of sound sources, and information concerning sourcesshapes how auditory experiences are organized. This is to say thatprocesses responsible for auditory experience proceed as if acousticinformation is information about sound sources. Finally,audition-guided action supports the claim that we hear such things andevents. Turning to look toward the source of a sound or ducking out ofthe way of something we hear to be approaching—behaviors guidedby auditory experience—would make little sense if we heard onlysounds. In the first place, these reasons ground a case for thinkingthat auditory perceptual experience does not strictly end with soundsand auditory objects. In particular, awareness as of a source, even ifdependent upon awareness as of a sound, may be constitutive ofone’s auditory perceptual experience.

The main barrier to an alternative is that the relation between soundsand ordinary things or happenings is commonly understood ascausal (see, e.g., Nudds 2001). Awareness as of an effect doesnot itself typically furnish epistemically unmediated awareness of itscause. Seeing smoke is not seeing fire. The right sort of dependencebetween characteristics of the experience and the cause is notapparent, and awareness as of an effect does not by itself groundperceptual demonstratives that concern the cause. The metaphysicalindirectness of the causal relation appears to block epistemicdirectness (see O’Callaghan 2011a for further discussion).

2.3.2 The Mereology of Sounds and Sources

Is there another explanatory route? Suppose that instead of a causalrelation, we understand the relationship between sounds and sourcesmereologically, or as one of part to whole (seeO’Callaghan 2011a). Parthood frequently does ground perceptualawareness. For instance, seeing distinct parts of a surfaceinterrupted by an occluder leads to perceptual experience as of asingle surface (imagine seeing a dog behind a picket fence). Seeingthe facing surfaces of a cube affords awareness as of a cube, and wecan attentively track that same cube as it rotates and revealsdifferent surfaces. Suppose, then, that a sound is an event-likeindividual (recall, property accounts escape the worry). This event ispart of a more encompassing event, such as a collision or the playingof a trumpet, that occurs in the environment and that includes thesound. So, the typical horse race includes the sounds, and you mightauditorily perceive the racing in hearing some of its proper parts:the sounds. More specifically, you may hear the galloping thanks tohearing the sounds it includes. You may fail to hear certain parts ofthe racing event, such as the jockey’s glance back aftercrossing the wire, but you also fail to see parts of the race, such asthe misstep of the horse in second place. If the sounds are akin tothe audible “profile” of the event, analogous to thevisible surfaces of objects and visible parts of events, you mightthen enjoy auditory awareness as of the galloping of the horses invirtue of your awareness as of the sounds of the hooves. The sound isnot identical with the galloping, and it is not just a property or acausal byproduct of the galloping. It is a part of a particular eventof galloping. The metaphysical relation of part to whole, in contrastto that between effect and cause, might ground the sort ofepistemically unmediated awareness of interest (cf. Nakayama et al.1995, Bermúdez 2000, Noë 2004). Auditory perceptualawareness as of the whole may occur thanks to experiencing thepart.

One objection is that this mereological account of the relationbetween sounds and sources cannot account for hearing ordinaryobjects by hearing their sounds. You could not strictly hear atuba by hearing its sound because a tuba is not an event of which asound is a part. However, the sound is part of the event of playingthe tuba, and the tuba is a participant in that playing. So, thoughyou are not aware as of a tuba, you are aware as of an event thatinvolves a tuba. That perhaps is enough to explain talk of hearingtubas and to assuage the worry (for further discussion, see Young2018).

Another more serious objection contends that the events we seem tohear are ones that do not constitutively involve sounds or that mighthave taken place without sounds. For instance, we hear the collision,but the collision is something that could have occurred in a vacuumand not made a sound. (Note that this differs from the claim discussedbelow according to which sounds are identical with source events andso inaudibly exist in vacuums.) If so, the collision and the sounddiffer and the collision does not strictly include a sound. Thecollision therefore must have made the sound as a causal byproduct.This suggests that, strictly speaking, you could not hear that verycollision event (since it causes the sound). The best response is tobite the bullet and accept that events that do occur or that couldoccur in vacuums cannot be heard since they include no sounds. This isnot so bad, since you could hear a different, more encompassing eventthat includes a sound along with a collision. Alternatively, one mightsay the very same event that occurs in a vacuum also could occur inair, but that it would have involved a sound had it occurred in air.In that case, one can only hear such events when they occur in air andinclude a sound. The choice depends upon one’s metaphysics ofevents. In either case, it seems reasonable that token events that donot include sounds are inaudible.

Casati et al. (2013) sidestep some of these concerns by rejecting thedistinction between sounds and events that are typically understood assound sources. They propose to “Ockhamize” the“event sources” of sounds by identifying sounds withevents such as collisions and vibrations. The sound just is thecollision or the vibrating, whether or not it occurs in air. Thisaccount implies that sounds could exist in vacuums.

What hinges on the debate about hearing sources? The first upshot isepistemological and concerns the nature of the justification forempirical beliefs grounded in perceptual experience. The evidentialstatus of beliefs about what one perceptually experiences differs fromthat of beliefs about what is causally responsible for what oneperceptually experiences. So, whether or not we hear sound sourcesimpacts the epistemology of audition. The second upshot concerns therelation between audition and certain actions. If we hear only soundsand auditory objects, what appears to be effortless, auditorily guidedaction to avoid or orient toward sound sources requires anotherexplanation (because sounds are invisible and usually do no harm).Finally, it affects how we understand the adaptive significance ofaudition. Did audition evolve so as to furnish awareness of soundsalone, while leaving their environmental significance toextra-perceptual cognition, or did it evolve so as to furnishperceptual responsiveness to the sources of sounds?

3. The Contents of Auditory Perception

Another way to address the question, “What do we hear?”concerns thecontents of auditory perception. Two topics areespecially noteworthy in the context of related debates about visionand its contents. The first concerns the whether audition has spatialcontent. The second concerns the perception of audible qualities.Parallel questions can be raised without relying on the perceptualcontent framework, though important complications arise.

3.1 Spatial Hearing

One topic where the contrast between vision and audition has beenthought to be particularly philosophically significant concerns space.Vision is a robustly spatial perceptual modality. Vision furnishesawareness of space and spatial features. Some claim vision has aninherently spatial structure, or, further, that vision’s spatialstructure is a necessary condition on being visually aware of thingsas independent from oneself.

Hearing also provides information about space—humans learn aboutspace on the basis of hearing. If audition represents space or spatialfeatures, there is a natural account of being so informed. We mightform beliefs about spatial features of environments on the basis ofauditory perceptual experiences simply by accepting or endorsing whatis apparent in having those experiences.

But learning about spatial features on the basis of audition andaudition’s bearing information about space both are consistentwith entirely aspatial auditory phenomenology. For instance, volumemight bear information about distance, and differences in volume atthe two ears might bear information about direction. In that case,audition bears information about space, and learning about space onthe basis of audition is possible, but it does not follow thatauditory experience is spatial or that audition represents space.

3.1.1 Skepticism about Spatial Audition

Notably, a tradition of skepticism about audition’s spatialityexists in philosophy. Certainly, our capacity to glean informationabout space is less acute in audition than in vision. Vision revealsfine-grained spatial details that audition cannot convey, such aspatterns and textures. But philosophers who are skeptical aboutspatial audition are not just concerned about a difference in spatialacuity between audition and vision. Malpas says of theexpression, ‘the location of sound’:

I do not mean by ‘location’ ‘locality’, but‘the act of locating’, and by ‘the act oflocating’ I do not mean ‘the act of establishing in aplace’, but ‘the act of discovering the place of’.Even so ‘location’ is misleading, because it implies thatthere is such a thing as discovering the place of sounds. Since soundsdo not have places there is no such act. (Malpas 1965, 131)

O’Shaughnessy states, “…We absolutely neverimmediately perceive sounds to beat any place. (Inference fromauditory data being another thing)” (O’Shaughnessy 2002,446). The claim is that, in contrast to visible objects, audiblesounds are not experienced as having locations. Rather, we determinethe places of sounds and sources from acoustic features, such asloudness and interaural differences, that bear information aboutdistance and direction. We do not auditorily experience spatialfeatures.

This debate, and the purported contrast between vision and audition,has consequences for perceptual theorizing. One route to theconclusion that hearing sounds involves auditory awareness ofsensations involves denying that audition satisfies spatialprerequisites on experiencing sounds as objective or public. Forinstance, Maclachlan (1989) claims that audition’sphenomenology—in particular, its aspatialphenomenology—provides reasons to think sounds are sensations.Comparing sounds with pains, which we readily recognize as sensations,he says, “[A]lthough the sounds we hear are just as much effectsproduced in us as are the pains produced by pins and mosquitoes,there is no variety in the location of these effects [thesounds]. Because of the lack of contrast, we are not even aware thatthe sounds we hear are bodily sensations” (Maclachlan 1989, 31,my emphasis). Maclachlan means that, in contrast even to the case ofpains, which are felt at different bodily locations, sounds are notexperienced to be at differing locations, and so we are not eveninclined to recognize that they are bodily sensations. Maclachlan thensuggests that weassociate sounds with things and happeningsoutside the body rather than appreciate that they are effects in us.Given the lack of spatialvariation among experienced sounds,we projectively associate sounds with distal sources. This explanationassumes that experienced sounds exhibit no audibly apparent spatialvariation: sounds seem located at the ears or lack apparent locationaltogether. Denying that auditory experiences present sounds atvarying locations beyond the ears invites difficulty in finding aplace for sounds in the world. If audition is wholly aspatial, thismay encourage a retreat to the view that sounds lack locations outsidethe mind.

This kind of strategy has companions and precursors. Lycan’ssuggestion that olfactory experiences are apparent as modifications ofone’s own consciousness depends heavily on the aspatialphenomenology of olfactory experience (Lycan 2000, 278–82). Eachrecalls the Kantian claim that objectivity requires space, or thatgrasping something as independent from oneself requires the experienceof space, a version of which is deployed by Strawson (1959, ch 2) inhis famous discussion of sounds.

Two lines of response are open. The first appeals to the thrivingempirical research program in “spatial hearing”(see, e.g., Blauert 1997). Scientists aim to discover the cues andperceptual mechanisms that ground spatial audition, such as interauraltime and level differences, secondary and reverberant signals, andhead-related transfer functions. Audition clearly cannot matchvision’s singular acuity—vision’s resolution limitis nearly two orders of magnitude better than audition’s(Blauert 1997, 38–9). Nevertheless, this research stronglysupports the claim that human subjects auditorily perceive suchspatial characteristics as direction and distance.

Second, a number of philosophers have objected onphenomenological grounds. Audition, they argue, involvesexperiencing or perceptually representing such spatial characteristicsas direction and distance (Pasnau 1999, Casati and Dokic 2005, Matthen2005, O’Callaghan 2007, 2010). Introspection and performancesupport the claim that sounds or sound sources are in many ordinarycases perceptually experienced as located in the environment at adistance in some direction. We hear the sound of the knocking overnear the door; we hear footsteps approaching from behind and to theleft; hearing sound to “fill” a room is itself a form ofspatial hearing. Though hearing is more error prone than vision, wefrequently do not need to work out the locations of sounds orsources—we simply hear them.

3.1.2 Strawson and the Purely Auditory Experience

A subtler form of skepticism about spatial audition aims just to blockthe requirements on objectivity. Strawson (1959) famously argues inChapter 2 ofIndividuals that because auditory experience isnotintrinsically spatial—spatial concepts have nointrinsic auditory significance—a purely auditory experiencewould be non-spatial. Thus, it would not satisfy the requirements onnon-solipsistic consciousness. Others have endorsed versions ofStrawson’s claim. “[T]he truth of a proposition to theeffect that there is a sound at such-and-such a position must consistin this: if someone was to go to that position, he would have certainauditory experiences,” states Evans (1980, 274).

The claim that audition is not intrinsically spatial admits at leasttwo readings. First, since Strawson suggests that audition mightinherit spatial content from other sense modalities, such as vision ortouch, it could mean that auditiondepends for its spatialcontent upon that of other modalities. If, unlike vision and touch,audition’s spatial capacities are parasitic upon those of othermodalities, audition is spatial only thanks to its relations to otherintrinsically spatial modalities. Second, it might be understood as aclaim about theobjects of audition. Strawson indicates thatsounds themselves are not intrinsically spatial. He says that althoughsounds have pitch, timbre, and loudness, they lack “intrinsicspatial characteristics” (1959, 65). Since these interpretationsare not clearly distinguished by Strawson, it is helpful to considerhis master argument.

Strawson claims that a purely auditory experience would benon-spatial. By “purely auditory experience” Strawsonmeans an exclusively auditory experience, or an auditory experience inabsence of experience associated with any other modality. However, ifany modalityin isolation ever could ground spatial experience,audition could. On one hand, given the mechanisms of spatial hearing,it is empirically implausible that a normal acoustic environment withrich spatial cues would fail to produce even a minimally spatialpurely auditory experience. Even listening only to stereo headphonescould produce a directional auditory experience. On the other hand, itdoes seem possible that there could be a non-spatial butimpoverished exclusively auditory experience if no binaural orother spatial cues were present. But similarly impoverished,non-spatial experiences seem possible for other modalities. Considervisually experiencing a uniform gray ganzfeld, or floatingweightlessly in a uniformly warm bath. Neither provides the materialsfor spatial concepts, so neither differs from audition in thisrespect. One might contend that we therefore lack a good reason tothink that,in contrast to a purely visual or tactileexperience, a purely auditory experience would be an entirelynon-spatial experience (see O’Callaghan 2010).

3.1.3 Does Audition Have Spatial Structure?

Nudds (2001) suggests another way to understand the claim, andinterprets Strawson as making an observation about the internalstructure of audition:

When we see (or seem to see) something, we see it as occupying or aslocated within a region of space; when we hear (or appear to hear) asound we simply hear the sound, and we don’t experience it asstanding in any relation to the space it may in fact occupy. (Nudds2001, 213–14)

Audition, unlike vision, lacks a spatial structure or field, claimsNudds. A purely auditory experience thus would not comprise a spatialfield into which individuals independent from oneself might figure.Following an example from Martin (1992), Nudds argues that whilevision involves awareness of unoccupied locations, audition does notinvolve awareness of regions of space as empty or unoccupied.Martin’s example is seeing the space in the center of a ringas empty. In audition, Nudds claims, one never experiences aspace as empty or unoccupied.

In response, one might simply deny a difference between vision andaudition in this respect. If one can attend to a location near thecenter of the visible ring as empty, one can attend to the locationbetween the sounding alarm clock and the slamming door as a placewhere there is no audible sound—as acoustically empty space. Ofcourse, auditory space generally is less replete than visual space,but this is contingent. Consider seeing just a few stars flickering onand off against a dark sky. Since such an experience may have spatialstructure, and since it is analogous to audition, one might on thesegrounds defend the claim that audition has spatial structure (see alsoYoung 2017).

3.1.4 How Spatial Audition Differs from Spatial Vision

What about the second way mentioned above to understandStrawson’s claim? Though audition’s status asintrinsically spatial may not differ from that of vision or touch,perhaps sounds are not intrinsically spatial. But without furtherargument, or a commitment to a theory of sounds, it is difficult tostate confidently the intrinsic features of sounds and thus whetherthey include spatial features. If, for instance, wavelength is among asound’s intrinsic features, sounds are intrinsicallyspatial.

Nonetheless, the claim might be that, as they are perceptuallyexperienced to be, sounds lack apparent intrinsic or non-relationalspatial features. Roughly, independent from spatial relations to othersounds, experienced sounds seem to lackinternal spatialstructure. That is why you cannot auditorily experience the emptyspace at the center of a sound or hear its edges. Interpreted assuch—that sounds are not experienced or perceptually representedto have inherent spatial features—the claim is plausible (thoughconsider diffuse or spread out sounds in contrast to focused orpinpoint sounds). It certainly marks an important difference fromvision, whose objects frequently not only seem to have rich internalspatial structure, but also are individuated in terms of inherentspatial features.

This difference, however, does not ground an argument that any purelyauditory experience is non-spatial or that sounds fail to satisfy therequirement on objectivity, since sounds’ being experienced tohave internal, intrinsic, or inherent spatial characteristics isnecessary neither for spatial auditory experience nor to experiencesounds as objective. Since sounds phenomenologically seem to belocated in space and to bear extrinsic spatial relations to eachother, auditory experience satisfies the requirements for objectivity,which need only secure the materials for a conception of a place forsounds to exist when not experienced.

So, vision and audition differ with respect to space in two ways.First, vision’s spatialacuity surpasses that ofaudition. Second, vision’s objects are perceptually experiencedto have richinternal spatial structure, and audition’sare not. However, given the spatial characteristics evident inaudition, such as direction and distance, the spatial status ofaudition presents no barrier to understanding its objects asperceiver-independent. The spatial aspects of auditory phenomenologythus may fail to ground an argument to the conclusion that sounds aremodifications of one’s consciousness. If that is the case, thenaudition provides no special intuitive support for accounts on whichprivate entities are the direct objects of perception.

3.2 Audible Qualities

3.2.1 Sounds and Colors

According to theories in which sounds are individuals, sounds are notsecondary or sensible qualities. But, humans hear audible qualities,such as pitch, loudness, and timbre, that are analogous to colors,tastes, and scents. Thus, familiar accounts of colors and othersensible attributes or secondary qualities might apply to the audiblequalities. For instance, pitches might be either dispositions to causecertain kinds of experiences in suitable subjects, the physical orcategorical bases of such dispositions, sensations or projectedfeatures of auditory experiences, or simple primitive properties of(actual or edenic) sounds.

Tradition suggests that the form of a philosophical account of visiblequalities, such as color, and their perception applies to othersensible qualities, such as pitch, flavor, and smell, and theirperception. Thus, according to tradition, if dispositionalism,physicalism, projectivism, or primitivism about sensible qualities istrue for features associated with one modality, it is true forfeatures associated with others. Despite tradition, we should be waryto accept that a theory of sensible qualities translates plausiblyacross the senses.

Debates about sensible qualities and their perception begin withconcerns about whether sensible features can be identified with orreduced to any objective physical features. What follows has two aims.The first is to give a sense of how such debates might go in the caseof audible qualities. The focus is on pitch, since pitch is oftencompared to color, and the case of color is well known (for discussionof similar questions concerning timbre, see Isaac 2017). The second isto point out the most salient differences and similarities between thecases of color and pitch that impact the plausibility of argumentstranslated from one case to the other.

First, I consider two noteworthy arguments that are founded on aspectsof color perception. Each aims to establish that the colors weperceive cannot be identified with objective physical features.Neither argument transposes neatly to the case of pitch. Thus, weshould not assume arguments that are effective in the case of colorhave equal force when applied to other sensible qualities. Colorperhaps is a uniquely difficult case.

Second, however, I discuss two respects in which pitch experience issimilar to color experience. It is instructive that these aspects ofpitch experience do raise difficulties for an objective physicalaccount of pitch that are familiar from the case of color.

3.2.2 Pitch, Timbre, and Loudness

What are pitch, timbre, and loudness? Pitch is a dimension along whichtones can be ordered according to apparent “height”. Thepitch of fingernails scratching a blackboard generally is higher thanthat of thumping a washtub. Loudness can be glossed as the volume,intensity, or quantity of sound. A jet plane makes louder sounds thana model plane. Timbre is more difficult to describe. Timbre is aquality in which sounds that share pitch and loudness might differ.So, a violin, a cello, and a piano all playing the same note differ intimbre. Sometimes timbre is called “tone color”.

Physics and psychoacoustics show that properties including frequency,amplitude, and wave shape determine the audible qualities sounds(auditorily) appear to have. To simplify, take the case of pitch,since pitch often is compared to color. Not all sounds appear to havepitch. Some sounds appear to have pitch thanks to a simple,sinusoidal pattern of vibration at some frequency in an objector in the air. Some sounds appear pitched thanks to a complex patternof vibration that can be decomposed into sinusoidal constituents atmultiple frequencies, since any pattern of vibration can be analyzedas some combination of simple sinusoids. Sounds appear pitched,however, just when they have sinusoidal constituents, orpartials, that all are integer multiples of a commonfundamental frequency. Sounds with pitch thus correspond toregular orperiodic patterns of vibration that differ infundamental frequency and complexity. Simple sinusoids and complexwaveforms match in pitch (though they typically differ in timbre) whenthey share fundamental frequency. This is true even when the complextone lacks a sinusoidal constituent at the fundamental frequency,which is referred to as the phenomenon of themissingfundamental.

3.2.3 Is Pitch Physical?

A straightforward account identifies pitch with periodicity (perhapswithin some range). Having pitch is being periodic (seeO’Callaghan 2007, ch. 6). Periodicity can be expressed in termsof fundamental frequency, so individual pitches are fundamentalfrequencies. This has advantages as an account of pitch. It capturesthe linear ordering of pitches. It also explains the musicalintervals, such as the octave, fifth, and fourth, for example, whichare pitch relations that hold among periodic tones. Musical intervalscorrespond to whole-number ratios between fundamental frequencies.Sounds that differ by an octave have fundamental frequencies thatstand in 1:2 ratios. Fifths involve a 2:3 relationship, fourths are3:4, and so on. This also allows us to revise the linear pitchordering to accommodate the auditory sense in which tones that differby an octave nonetheless are the same pitch. If the pitch ordering isrepresented as a helix, upon which successive octave-related tonesfall at a common angular position, each full rotation representsdoubling frequency.

Is the periodicity theory of pitch plausible as an account of theaudible features we perceive when hearing sounds? If so, thenobjective physicalism about at least some sensible qualities mightsucceed.

3.2.4 Disanalogies with Color

The periodicity theory of pitch fares better on two counts thantheories that identify colors with objective physical properties.

First, consider the phenomenological distinction betweenuniqueandbinary hues. Some colors appear to incorporate othercolors, and some do not. Purple, for instance, appears both reddishand bluish; red just looks red. Some philosophers contend that theleading physical theories of color cannot explain the unique-binarydistinction without essentially invoking the color experiences ofsubjects. How, for instance, do reflectance classes identified withunique hues differ from those associated with binary hues?

Consider a related issue concerning pitch. Some tones with pitch soundsimple, while other pitched tones, such as sounds of musicalinstruments, auditorily appear to becomplex and to havediscernible components. However, the difference between audibly simpleand audibly complex pitched tonesis captured by the simplicityor complexity of a sound’s partials. Simple tones are sinusoids,and complex tones have multiple overtones. So, one response is to holdthat the unique-binary color distinction and the simple-complex pitchdistinction are disanalogous. Unlike the case of color, one mightcontend, no pitch that is essentially a mixture of other pitchessolely occupies a distinctive place in pitch space.

Second, considermetamerism. Some surfaces with very differentreflectance characteristics match in color. Metameric pairs share noobvious objective physical property. Some philosophers argue thatunless color experience fails to distinguish distinct colors, metamerspreclude identifying colors with natural physical properties ofsurfaces (see the entry oncolor).

Now consider the case of pitch. Are there pitch metamers? Some soundswith very different spectral frequency profiles match in pitch. Asimple sinusoidal tone at a given frequency matches the pitch of eachcomplex tone with that fundamental frequency (even those that lack aconstituent at the fundamental). But, again, the case of pitch differsfrom the case of color. For each matching pitch, a single naturalproperty does unify the class. The tones all share a fundamentalfrequency.

3.2.5 Analogies with Color

Two kinds of argument familiar from the case of color are equallypressing when applied to the case of pitch.

First, arguments fromintersubjective variation transpose.Actual variations in frequency sensitivity exist among perceivers; forinstance, subjects differ in which frequency they identify as middleC. If there is no principled way to legislate whose experience isveridical, pitch might be subjective or perceiver-relative. Oneresponse is that, in contrast to the case of unique red, there is anobjective standard for middle C: fundamental frequency. But, whosepitch experience has the normative significance to settle thefrequency of middle C?

Some might wonder whether there is a pitch analog of the trouble posedby the kind of variation associated withspectrum inversion inthe case of color (see the entry oninverted qualia). Spectral shift in pitch, sometimes dramatic, commonly occurs aftercochlear implant surgery. This is not spectral inversion for pitch;but, a dramatic shift makes most of the same trouble as inversion. Notquite all the trouble, since cochlear implants preserve the pitchordering and its direction. But, there could be a cochlear implantthat switched the placement of electrodes sensitive to 100 hertz and1000 hertz, respectively; and there could be one that reversed theentire electrode ordering. This goes some distance to grounding theconceivability of a pitch inversion that reverses the height orderingof tones.

Second, consider an argument that frequencies cannot capture therelational structure among the pitches. This is looselyanalogous to the argument that physicalism about color fails tocapture the relational structure of the hues—for instance, thatred is more similar to orange than either is to green. In the case ofpitch, psychoacoustics experiments show that perceived pitch does notmap straightforwardly onto frequency. Though each unique pitchcorresponds to a unique frequency (or small frequency range), therelations among apparent pitches do not match those amongfrequencies. In particular, equivalent pitch intervals do notcorrespond to equal frequency intervals. For example, the effect uponperceived pitch of a 100 hertz change in frequency varies dramaticallyacross the frequency range. It is dramatic at low frequency and barelydetectable at high frequency. Similarly, doubling frequency does notmake for equivalent pitch intervals. A 1000 hertz tone must be tripledin frequency to produce the same increase in pitch as that produced byquadrupling the frequency of a 2000 hertz tone. Apparent pitch is acomplex function of frequency; it is neither linear nor logarithmic(see, e.g., Hartmann 1997, ch 12, Gelfand 2004, ch 12, Zwicker andFastl 2006, ch 5). Pitch scales that capture the psychoacoustic dataassign equal magnitudes, commonly measured in units calledmels, to equal pitch intervals. Themel scale of pitchthus is an extensive or numerical pitch scale, in contrast to theintensive frequency scale for pitch. The former, but not the latter,preserves ratios among pitches.

S. S. Stevens famously argued on the basis of results drawn frompsychoacoustic experiments that pitch is not frequency (see, e.g.,Stevens et al. 1937, Stevens and Volkmann 1940). In light of similarresults, contemporary psychoacoustics researchers commonly reject theidentification of pitch with frequency or periodicity. The receivedscientific view thus holds that pitch is a subjective or psychologicalquality that is no more than correlated with objective frequency (see,e.g., Gelfand 2004, Houtsma 1995). Pitch, on this understanding,belongs only to experiences. The received view of pitch thereforeimplies an error theory according to which pitch experience involves awidespread projective illusion.

What is the argument against the periodicity theory of pitch? Comparean argument against reflectance physicalism about color. Reflectancephysicalism identifies each hue with a class of reflectances.Periodicity physicalism identifies each pitch with a fundamentalfrequency. In both cases, each determinate sensible feature isidentified with a determinate physical property. In the color case, itis objected that reflectance classes do not bear the relations to eachother that the colors bear. In the pitch case, the frequencies do notbear the relations to each other that the pitches bear. Thus, if therelational features among a class of sensible qualities are essentialto them, an account that does not accurately capture those relationsfails. Frequencies, according to this line of argument, do not standin the relations essential to pitch.

This, of course, is a quite general phenomenon among sensiblequalities. Brightness and loudness vary logarithmically with simplephysical quantities. Even if we identified candidate molecules forsmells, nothing suggests physical similarities would mirror theirolfactory similarities.

In the case of pitch and other sensible features that can be put in alinear ordering, one might respond that the relational order isessential while the magnitudes are not. In that case, if pitch isfrequency, pitch experience has the right structure, but distortsmagnitudes of difference in pitch. This retains the periodicity theoryand explains away the results in terms of pitch experiences.

Nonetheless, Pautz (2014, 3.5) has replied that this partial erroraccount cannot be reconciled with certain types of possibleintersubjective difference. So, suppose instead we accept that the melscale is well-founded and that it accurately captures essentialrelationships among pitches. This does not by itself imply aprojective or subjective theory of pitch. Pitches might bedispositions to produce certain kinds of experiences, or they might besimple or primitive properties. It also is open to seek a moreadequate physical candidate for pitch. For instance, pitches might befar more complex physical properties than frequencies. Such physicalproperties may be of no interest in developing the simplest, mostcomplete natural physical theory, but they may be anthropocentricallyinteresting.

It is an important question whether a physical theory of sensiblefeatures should just provide a physical candidate for each determinatesensible feature, or whether the physical relationships among thosephysical candidates should capture the structural relations amongsensible qualities (and, if so, which structural relations it shouldcapture). This is an example of how considering in detail the natureand the experience of sensible qualities other than color promisesinsights into traditional debates concerning the sensible qualities.Pautz (2014) offers an empirically-grounded argument concerning avariety of sensible qualities, including audible qualities, thatadvances such discussion.

4. Varieties of Auditory Perception

4.1 Musical Listening

Musical listening is a topic that bears on questions about therelationship between hearing sounds and hearing sources. While thephilosophy of music has its own vast literature (see the entry onthe philosophy of music), musical experience has not been used as extensively to exploregeneral philosophical questions about auditory perception. Thissection discusses links that are relevant to advancing philosophicalwork on auditory perception.

4.1.1 Acousmatic Experience

An account of listening to pure or non-vocal music should capture theaesthetic significance of musical listening. Appreciating musicis appreciating sounds and sequences, arrangements, or structures ofsounds. Thus, the temporal aspects of auditory experiences arecritical to appreciatively listening to music.

One might go further and hold that sounds are all that matters inmusic. In particular, some have argued that appreciatively listeningto music demands listening in a way that abstracts from theenvironmental significance, and thus from the specific sources, of thesounds it includes (Scruton 1997, 2–3). Suchacousmaticlistening involves experiencing sounds in a way that is“detached from the circumstances of their production,”rather than “as having a certain worldly cause” (Hamilton2007, 58; see also Hamilton 2009). Listening to music and beingreceptive to its aesthetically relevant features requires notlistening to violins, horns, or brushes on snare drums. It requireshearing sounds and grasping them in a way removed from their commonsources. Hearing a high fidelity recording thus furnishes anaesthetically identical musical experience despite having a speakercone rather than a violin as source. “The acousmatic experienceof sound is precisely what is exploited by the art of music”(Scruton 1997, 3).

This suggests an intuitive difference between music and visual artssuch as painting and sculpture. As Kivy (1991) explains, it isdifficult even with the most abstract paintings and sculptures to seethem in a way that takes them to be entirely formal or abstract. Thatis, it is difficult to avoid seeing pictures and sculptures asrepresentational. In contrast, it seems easier to listen attentivelyto the formal acoustical features of musical sounds, without beingcompelled to think of what makes them.

Musical listening thus may be thought to provide a prima facieargument against the claim that in hearing sounds one typically hearssound sources such as the strumming of guitars and bowing of violins.If such “interested” audition were the rule, musicallistening would be far more challenging.

4.1.2 Acousmatic Listening as Attention to Sounds

Acousmatic experience, however, may be a matter ofattention.Nothing prevents focusing one’s attention on the sounds andaudible qualities without attending to the instruments, acts, andevents that are their sources, even if each is auditorily available.That musical listening requires effort and training supports the ideathat one can direct attention differently in auditory experience,depending on one’s interests. Caring for an infant and safelycrossing the street require attending to sound sources, whilelistening with aesthetic appreciation to a symphony may requireabstracting from the circumstances of its production, such as thefinger movements of the oboist. This response holds that musicallistening is a matter of auditorily attending in a certain way. It isattending to features of sounds themselves, but does not imply failingto hear sound sources.

The acousmatic thesis is a limited view about which aspects of thethings one can auditory experience are aesthetically significant.These include audible aspects of sounds themselves, but exclude, forexample, other contents of auditory experience. However, room existsfor debate over the aesthetically significant aspects of what you hear(see Hamilton 2007, 2009). For example, one might argue that liveperformances have aesthetic advantages over recordings because onehears theperformance of the sounds and songs, rather thantheir reproduction by loudspeakers (cf. Mag Uidhir 2007).Circumstances of sound production, such as that skillful gesturesgenerate a certain passage, or that a particularly rare wood accountsfor a violin’s sounds, might be aesthetically relevant in a waythat outstrips the sounds, and some such features may be audible inaddition to sounds. For instance, hearing the spatial characteristicsof a performance may hold aesthetic significance beyond the tones andstructures admitted by traditional accounts of musical listening.Composers may even intend “spatial gestures” among aspectsessential for the appreciation of a piece (see, e.g., Solomon 2007).To imagine auditorily experiencing the spatial characteristics ofmusic in a way entirely divorced from the environmental significanceof the sounds is difficult. Appreciating the relationship betweenexperiences of sounds and of sources makes room for a view of theaesthetic value of musical listening that is more liberal thanacousmatic experience allows.

4.2 Speech Perception

4.2.1 Is Speech Special?

Speech perception presents uniquely difficult twists, and fewphilosophers have confronted it directly (Appelbaum 1999, Trout 2001a,Matthen 2005, ch 9, and Remez and Trout 2009 are recent exceptions).Something striking and qualitatively distinctive—perhapsuniquely human—seems to set the perception of speech apart fromordinary hearing. The main philosophical issues about speechperception concern versions of the question, Is speech special? (SeeO’Callaghan 2015 for a comprehensive review and discussion.)

How does perceiving speech differ from perceiving ordinarynon-linguistic sounds? Listening to music and listening to speech eachdiffer from listening to other environmental sounds in the followingrespect. In each case, one’s interest in listening is to somedegree distanced from the specific environmental happenings involvedin the production of sounds.

But this is true of listening to music and of listening to speech fordifferent reasons. In music, it is plausible that one’s interestis in the sounds themselves, rather than in the sources of theirproduction. However, speech is a vehicle for conventional linguisticmeaning. In listening to speech, one’s main interest is in themeanings, rather than in the sources of sound. Ultimately, theinformation conveyed is what matters.

Nevertheless, according to the most common philosophicalunderstanding,perceiving spoken utterances is just a matter ofhearing sounds. The sounds of speech are complex audible soundstructures. Listening to speech in a language you know typicallyinvolvesgrasping meanings, but grasping meanings requiresfirst hearing the sounds of speech. According to this account,grasping meanings itself is a matter of extra-perceptualcognition.

The commonplace view—that perceiving speech is a variety ofordinary auditory perception that just involves hearing the sounds ofspeech—has been challenged in a number of ways. The challengesdiffer in respect of how speech perception is held to differ fromnon-linguistic audition.

4.2.2 The Objects of Speech Perception

First, consider theobjects of speech perception. What are theobjects of speech perception, and do they differ from those ofordinary or non-linguistic auditory perception? According to thecommonplace understanding, hearing speech involves hearing sounds.Thus, hearing spoken language shares perceptual objects with ordinaryaudition. Alternatively, one might hold that the objects of speechperception are not ordinary sounds at all. Perhaps they arelanguage-specific entities, such asphonemes orwords.Perhaps, as some have argued, perceiving speech involves perceivingarticulatory gestures or movements of the mouth and vocalorgans (see the supplement onSpeech Perception: Empirical and Theoretical Considerations). Note that if audition’s objects typically include distalevents, speech in this respect is not special, since its objects donot belong to an entirely different kind from ordinary sounds.

4.2.3 The Contents of Speech Perception

Second, consider thecontents of speech perception. Does thecontent of speech perception differ from that of ordinary audition? Ifit does, how does the experience of perceiving speech differ from thatof hearing ordinary sounds? Perceiving speech might involve hearingordinary sounds but auditorily ascribing distinctivefeaturesto them. These features might simply be, or comprise, finer grainedqualitative and temporal acoustical details than non-linguistic soundsaudibly possess. But perceiving speech also might involve perceivingsounds as belonging tolanguage-specific types, such asphonemes, words, or other syntactic categories.

Furthermore, speech perception’s contents might differ in a moredramatic way from those of non-linguistic audition. Listening withunderstanding to speech involves graspingmeanings. Thecommonplace view is conservative. It holds that grasping meanings isan act of theunderstanding rather than of audition. Thus, thedifference between the experience of listening to speech in a languageyou know and the experience of listening to speech in a language youdo not know is entirelycognitive.

But one might think that there also is aperceptual difference.A liberal account of this perceptual difference holds that perceivingspeech in a language you know may involve hearing soundsasmeaningful or auditorily representing them as having semanticproperties (see, e.g., Siegel 2006, Bayne 2009, Azzouni 2013, Brogaard2018; cf. O’Callaghan 2011b, Reiland 2015). Alternatively, amoderately liberal account holds that the perceptual experience ofspeech in a language you know involves perceptually experiencinglanguage-specific but nevertheless non-semantic features. Forinstance, O’Callaghan (2011b) argues that listening to speech ina familiar language typical involves perceiving its phonologicalfeatures.

4.2.4 Is Speech Perception Auditory?

Third, consider theprocesses responsible for speechperception. To what extent does perceiving speech implicate processesthat are continuous with those of ordinary or general audition, and towhat extent does perceiving speech involve separate, distinctive, ormodular processes? While some defendgeneral auditory accountsof speech perception (see, e.g, Holt and Lotto 2008), some argue thatperceiving speech involves dedicated perceptual resources, or even anencapsulated perceptual system distinct from ordinary non-linguisticaudition (see, e.g., Fodor 1983, Pinker 1994, Liberman 1996, Trout2001b). These arguments typically are grounded in several types ofphenomena, including themultimodality of speechperception—visual cues about the movements of the mouth andtongue impact the experience of speech, as demonstrated by the McGurkeffect (see the section4.3 Crossmodal Influences);duplex perception—a particular stimulus sometimescontributes simultaneously both to the experience of an ordinary soundand to that of a speech sound (Rand 1974); and thetop-downinfluence of linguistic knowledge upon the experience of speech. Areasonable challenge is that each of thesecharacteristics—multimodality, duplex perception, and top-downinfluence—also is displayed in general audition.

See the supplement onSpeech Perception: Empirical and Theoretical Considerations.

4.3 Crossmodal Influences

4.3.1 Crossmodal Illusions

Auditory perception of speech is influenced by cues from vision andtouch (see Gick et al. 2008). The McGurk effect in speech perceptionleads to an illusory auditory experience caused by a visual stimulus(McGurk and Macdonald 1976). Do such multimodal effects occur inordinary audition? Visual and tactile cues commonly do shape auditoryexperience. The ventriloquist illusion is an illusory auditoryexperience of location that is produced by an apparent visible soundsource (see, e.g., Bertelson 1999). Audition even impacts experiencein other modalities. The sound-induced flash effect involves a visualillusion as of seeing two consecutive flashes that is produced when asingle flash is accompanied by two consecutive beeps (Shams et al.2000, 2002). Such crossmodal illusions demonstrate that auditoryexperience is impacted by other modalities and that auditioninfluences other modalities. In general, experiences associated withone perceptual modality are influenced by stimulation to other sensorysystems.

4.3.2 Causal or Constitutive?

An important question is whether the impact is merely causal, orwhether perception in one modality is somehow constitutively tied toother modalities. If, for instance, vision merely causally impactsyour auditory experience of a given sound, then processes associatedwith audition might be proprietary and characterizable in terms thatdo not appeal to other modalities. Relying on information from visionor touch could simply improve the existing capacity to perceive space,time, or spoken language auditorily. On the other hand, coordinationbetween audition and other senses could enable a new perceptualcapacity. In that case, audition might rely constitutively on anothersense.

A first step in resolving this question is recognizing that crossmodalillusions are not mere accidents. Instead, they are intelligible asthe results of adaptive perceptual strategies. In ordinarycircumstances, crossmodal processes serve to reduce or resolveapparent conflicts in information drawn from several senses. In doingso, they tend to make perception more reliable overall. Thus,crossmodal illusions differ fromsynaesthesia. Synaesthesia isjust a kind of accident. It results from mere quirks of processing,and it always involves illusion (or else is accidentally veridical).Crossmodal recalibrations, in contrast, are best understood asattempts “to maintain a perceptual experience consonant with aunitary event” (Welch and Warren 1980, 638).

In the first place, the principled reconciliation of information drawnfrom different sensory sources suggests that audition is governed byextra-auditory perceptual constraints. Moreover, since conflictrequires a common subject matter, such constraints must concern commonsources of stimulation to multiple senses. If so, audition and visionshare a perceptual concern for a common subject matter. And thatconcern is reflected in the organization of auditory experience. Butthis by itself does not establish constitutive dependence of auditionon another sense.

However, the perceptual concern for a common subject matter could bereflected as such in certain forms of auditory experience. Forinstance, the commonality may be experientially evident in jointlyperceiving shared spatio-temporal features, or in the perceptualexperience of audio-visual intermodal feature binding. If so, someforms of auditory perceptual experience may share with vision a commonmultimodal or amodal content or character (see O’Callaghan2008b, Clark 2011). More to the point, if coordination with anothersense enables a new auditory capacity, then vision or touch could havea constitutive rather than merely causal impact upon correspondingauditory experiences.

4.3.3 Multimodality in Perception

What hangs on this? First, it bears on questions aboutaudition’s content. If we cannot exhaustively characterizeauditory experience in terms that are modality-specific or distinctiveto audition, then we might hearas of things we can see orexperience with other senses. This is related to one puzzling questionabout hearing sound sources: How could you hear as of something youcould see? Rather than just a claim about audition’s contentthat requires further explanation, we now have a story about whythings like sound sources figure in the content of auditoryexperience. Second, all of this may bear on how to delineate whatcounts as auditory perception, as opposed to visual or even amodalperception. If hearing is systematically impacted by visual processes,and if it shares content and phenomenology with other senseexperiences, what are the boundaries of auditory perception?Multimodal perception may bear on the question of whether there areclear and significant distinctions among the sense modalities (cf.Nudds 2003). Finally, multimodal perceptual experiences, illusions,and explanatory strategies may illuminate the phenomenologicalunity of experiences in different modalities, or the sense inwhich, for instance, an auditory experience and a visual experience ofsome happening comprise a single encompassing experience (see theentry onthe unity of consciousness).

We can ask questions about the relationships among modalities indifferent areas of explanatory concern. Worthwhile areas for attentioninclude the objects, contents, and phenomenology of perception, aswell as perceptual processes and their architecture. Crossmodal andmultimodal considerations might shed doubt on whether vision-basedtheorizing alone can deliver a complete understanding of perceptionand its contents. This approach constitutes an importantmethodological advance in the philosophical study of perception (forfurther discussion, see O’Callaghan 2012, 2019, Matthen 2015,Stokes et al. 2015).

5. Conclusion and Future Directions

Considering modalities other than vision enhances our understanding ofperception. It is necessary to developing and vetting an adequatecomprehensive and general account of perception and its roles.Auditory perception is a rich territory for philosophical explorationin its own right, but it also provides a useful contrast case in whichto evaluate claims about perception proposed in the context of vision.One of the most promising directions for future work concerns thenature of the relationships among perceptual modalities, how theserelationships shape experience across modalities, and how they mayprove essential to understanding perception itself. Philosophical workon auditory perception thus is part of the advance beyond consideringmodalities in isolation from each other.

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