1

Smelling Matter Benjamin D. Young∗

Abstract: It is a tacit assumption of contemporary philosophy of perception that any evidence or conclusions drawn from vision will generalize across all perceptual modalities. While the objects of olfaction – smells – are intuitively individuated by reference to the ordinary objects from which they arise, this view is incorrect. This paper argues that smells are neither ordinary three-dimensional objects, identified according to the criteria employed to individuate visual or auditory objects, nor vapors (as Plato proposed), nor odors. Rather, smells are the chemical structures of molecular compounds within odor plumes. "Smell and its objects are much less easy to determine then what we have hitherto discussed; the distinguishing characteristic of smell is less obvious than those of sound or color."

- Aristotle DA, II 9 1. Introduction

What does your current location smell like? Close your eyes for a second. Can

you identify the things around you by smell? While we do not usually notice the odors

enveloping us, we surely do know what our environment looks like without being asked.

There is no doubt that we are primarily visual beings who sense and navigate the world

using vision, yet our behavior is also mediated by olfactory experiences.1 We are

constantly bombarded with smells, which continually shape our perception and

interactions with our surroundings.2 Intuitively, we smell ordinary three-dimensional

objects: the wet dog entering the elevator, the cookies from the bakery down the block,

or the musty rotting leaves outside the window on a warm autumn night. While smells

are commonly and intuitively individuated by reference to the ordinary objects from

which they arise, I will argue that this intuition is incorrect; the objects of olfaction (i.e.

what one smells) are the chemical structures of molecular compounds, which determine

the qualitative character of olfaction (i.e. how things smell).

While Plato, Aristotle and their Medieval Commentators engaged in a debate

regarding the nature and mechanisms of olfaction and how they differ from those of the ∗ I would like to thank Jesse Prinz and Richard Sorabji for their helpful feedback. 1 While human olfactory accuracy is excellent and on par with dogs, we systematically mistrust our olfactory abilities (Sela, and Sobel, 2010). 2 Olfaction guides our food choices (Fallon and Rozin, 1983), dietary preferences (Rozin, 1978; Rozin, et al. 1986; E. Rozin, S. Rozin, and E. Rozin, 1992), our selection of mates (Wilson and Stevenson, 2006) and social acquaintances (Li, et al., 2007) , and is responsible for identification of kin (Russell, 1976; Porter, Cernoch, and McLaughlin, 1983; Porter, et al. 1986).

Smelling Matter 2

other perceptual modalities,3 most of the recent work in the philosophy of mind and

perception takes vision as the primary modality of interest and tacitly assumes that any

evidence or conclusions drawn from its study can be generalized to all the perceptual

modalities. It is time to rectify contemporary philosophyʼs neglect of olfaction by re-

examining what the objects of our olfactory experiences are without simply assuming

that our best theory of vision will generalize to olfaction.

The focus of this article is the nature of smells – the objects that our olfactory

systems perceive in the world. I argue that the objects of olfactory perception are not,

as our common sense conception supposes, ordinary three-dimensional objects: What

we smell are neither ordinary three-dimensional objects, Platonic vapors, nor odors, but

rather the chemical structures of simple molecules (or mixtures of such) within odor

plumes. We literally smell the chemical structure of matter.

2. Olfactory objects are not ordinary Objects

Pre-theoretically our conception of an object is based on that of ordinary three-

dimensional objects. Apples, chairs, garbage trucks, and trees are all such objects; they

have clear boundaries as perceived by sight or touch. We certainly claim to have

olfactory experiences of ordinary objects. Commonly, we individuate smells by

reference to the objects from which they emanate. Our ordinary language usage most

likely derives from tracking olfactory experiences that are of ecological import,4 thus

making it natural to individuate the objects of olfactory experience by reference to the

ordinary objects from which we correlate their emanations. Intuitively we assume that

olfactory objects are ordinary objects, yet the spatiotemporal boundaries and chemical

composition of ordinary objects make them ill-suited to be the perceptual objects of

olfactory experiences.

3 Platoʼs theory of smell is contained within two paragraphs of the Timaeus 66d-67, while Aristotleʼs theory is developed in De Anima and De Sensu. Johansen (2006) provides a detailed assessment of the differences between Aristotleʼs theory in De Anima and De Sensu. Additionally, for an introduction to the Commentators debate over Plato and Aristotleʼs theories of olfaction see Kemp (1997). 4 Although ecological theories of the olfactory object are preferred by contemporary scientists, they are rejected for reasons discussed in Section 3.3.

Smelling Matter 3

The entities that are commonly thought of as having smells do not have the same

boundary conditions as ordinary objects. What we smell is spatially and temporally less

truncated then the object we identify by touch or sight. For example, the smell of

honeysuckle occupies a greater space, for a longer period of time, than the object (the

honeysuckle itself) that we identify tactilely and visually. Or consider the experience of

smelling the autumn leaves outside oneʼs window while sitting in a room. There is no

sense according to the ordinary object conception in which these entities are in the

room, yet the experience of smelling the leaves is certainly veridical and not a

hallucination (Batty, 2007).

Furthermore, it is an ill-advised theoretical starting point to assume that the

objects of olfactory experience is identical to those of visual or tactile experience, since

large portions of the ordinary object are unnecessary for generating an olfactory

experience (in contrast to what prima facie appears to be in the case of visual

experience).5 The average medium-sized object is composed of hundreds of different

molecules, yet only a dozen or so of these constitute its smell. Modern flavor and

fragrances houses are so profitable6 precisely because they are able to identify the

minimum number of chemical components of an ordinary object that are required to

produce an olfactory experience like that of smelling the object itself.7

A further problem for the ordinary object conception arises from cases of

olfactory misrepresentation (Lycan, 1996) where natural odors are mimicked using

synthetic chemical compounds. One can erroneously believe that one is smelling a rose

without there being a rose in the nearby environment, since there are synthetic chemical

compounds that mimic its odor; when smelling such a compound someone might quite

understandably come to both truly believe that it smells like a rose but falsely believe 5 It might be objected that this is unfair on the grounds that the visual experience of, say, a bowling ball does not require the presence of the ball in its entirety but merely a part of it. However, this might be taken to show that the ordinary object conception of visual experience is itself not tenable. Additionally, there is a longstanding debate within the philosophy of perception regarding whether we do in fact visually perceive aspects of an ordinary object that are not within our line of sight, such as the back of a bowling ball (Noë, 2005). 6 Flavor and Fragrance businesses generate multibillion-dollar revenues that on average exceed that of Hollywood and the entertainment industry. 7 Gilbert (2008) has a nice description of how the headspace model of International Flavors and Fragrances (IFF) is utilized in creating flavors and fragrances.

Smelling Matter 4

that the source of the smell is a rose. Such a case is neither one of perceptual

misrepresentation (e.g. it doesnʼt smell like a dog) nor one of hallucinatory experience

(there is something he is smelling). Rather, such a case involves a misrepresentation of

the actual source of the smell. Thus, ordinary objects should not be considered the

objects of our olfactory experience because we can have veridical perceptions of

olfactory qualities in the absence of the ordinary objects that produce them. If however

olfactory objects are not ordinary objects then do olfactory perceptions have objects at

all?

3. Criteria of Visual and Auditory Objects

To assuage any worry that olfactory experiences might not be object-directed,

since the object of olfactory perception is not an ordinary three-dimensional object, I

argue in this section that olfactory objects satisfy the criteria typically used to ascertain

the nature of visual and auditory objects of perception, such as having spatiotemporal

boundaries, a mereologically-complex nature across time and presentations, and

separability from against a background. Additionally, this section should allay any

concerns regarding the promiscuity of the notion of object at play within the paper by

demonstrating that the perceptual objects of olfactory experience satisfy the criteria

used to individuate visual and auditory objects, thus the objective status of the olfactory

objects is on par with that of visual and auditory objects.8 While this generates support

for the claim that our olfactory perceptual states are object-directed, I argue that none of

these criteria adequately explain the robust nature of olfactory experiences.

3.1 Spatial Temporal Entities Our common sense conception of objects is shaped by vision and is of a

spatiotemporal entity with clear boundaries. Visual objects are prime examples of

perceptual objects in this sense, since they are either “punctate spatiotemporal clusters”

(Scholl and Pylyshyn 1999, p. 26) or spatiotemporally-bound entities that maintain their

8 Furthermore, section 5.3 outlines the properties of the olfactory perceptual object, thereby solidifying the claim that we smell objective entities with mereological structure on par with the objects of visual and auditory perception.

Smelling Matter 5

features when being moved through an environment (Matthen, 2005). As such, our

olfactory experiences are not object-directed. The lack of strict spatiotemporal

boundaries of smells has lead some philosophers to argue that olfaction is an outlier or

counter-example to this conception of a perceptual object and that olfactory experience

does not have, as a proper part, the location or direction of the olfactory object (Lycan,

2000; Smith, 2002; Matthen, 2005; Batty 2007; Peacocke, 2008). But they are

mistaken; although the olfactory object is more dispersed in time and space than visual

or auditory objects, olfaction satisfies both the spatial and temporal requirement, but in a

less truncated form.

Empirically it has been demonstrated that slight differences in the anatomical

structure of each nostril (Yeshurun et al., 2008) and the resulting binaural airflow (Zhou

and Chen, 2009) enable the localization of smells to within 7-10 degrees of their location

(von Bekesy, 1964). There has also been some research showing that olfactory objects

can be tracked through an environment across time (Porter et al., 2005, 2007).9 Thus,

the majority of philosophers who have claimed that the location or direction of the

olfactory object is not a proper part of olfactory experience are simply mistaken. The

olfactory object has spatial boundaries, but they are diffused across an environment in a

manner quite unlike visual objects.

It would be imprudent to claim that the olfactory object is not a spatial entity

simply because its boundary conditions are not as truncated, especially given the

empirical work that shows that the olfactory object can be demarcated given the

concentration gradient of the olfactory objectʼs odor plume.10 However, the ability to

demarcate olfactory objects requires changing oneʼs spatiotemporal relations relative to

the olfactory object by either sniffing or changing oneʼs position. Matthen (2005) argues 9 Batty (2010a, 2010c) dismisses these experimental results on the grounds that they are atypical of olfactory experience, perhaps due to assuming the correctness of the common sense conception of the phenomenology of olfaction However, without further argument as to why it is more authoritative and how the ʻtypicalityʼ of an olfactory experience is determined Battyʼs theory is highly questionable. 10 A perfumeʼs sillage is an excellent example of the spatial aspect of an olfactory object. In designing a new product, perfume chemists (perfumers) must consider a perfumeʼs sillage - the diffusion rate across space of a perfume. Some scents are designed to announce their wearerʼs presence or to turn the heads of those in a room; colognes are usually designed to be noticeable only within a small radius around the wearer.

Smelling Matter 6

that olfactory experiences are thus not object-directed because although olfactory

experience can, across time (i.e. diachronically), be aided by merely moving around, it

does not at a particular time (i.e. synchronically) present us with a spatiotemporally-

bound entity. This is not the case for visual experience: opening oneʼs eyes, one is

immediately presented with three-dimensional objects in a spatial environment.11 The

olfactory object might have spatial boundaries, Matthen claims, but its temporal aspect

makes it unlike the spatiotemporal bound entities of vision.

Matthenʼs line of argument is predicated on the assumption that olfactory

experiences can be identified and individuated merely by using phenomenal experience

(i.e. how things present themselves to us) as a guide. Lycan (2000) clearly states that

the reason olfactory experiences should not be considered to have a spatial aspect that

the synchronic experience of smells does not seem to contain any spatial information as

part of the experiential content. Even though, over time, one can locate and attend to

the source of an odor, these theorists deny that olfactory experience is inherently

spatial. Using this line of reasoning, Matthen (2005, p. 284) denies that our experiences

of smell can be characterized in the usual object-attribute form and claims that at best

smells have a primitive undifferentiated feature-location structure. Smith (2002) goes so

far as to use this line of reasoning to question whether physical objects are smelt at all.

Following their lead, Batty (2009, 2010a-c) concludes that the olfactory object is best

thought of as a loosely defined, spatiotemporal object (something surrounding me has a

11 The assumption that vision automatically presents us, synchronically, with spatial objects might be challenged because similar temporal processes occur in vision. To see things, oneʼs eyes must be in constant motion either through volitional control or through saccadic and microsaccadic movements. If oneʼs eyes were to stop moving oneʼs visual field would shrink and eventually turn a uniform grey. (This can easily be demonstrated by holding oneʼs eyeballs still in their sockets or by using a ganzfeld.) This presents a prima facie analogy to the role of inhalation in olfaction. If inhalation is excluded as either a part of the olfactory experience or an enabling condition of the olfactory percept, then why not saccadic eye movement? Anticipating this reply, Smith (2002) argues that sniffing is not equivalent to saccadic eye movements. While the latter is not under volitional control) the former always requires it whenlocating and moving towards a smell. However, some forms of saccadic eye movement required for visual perception are under volitional control in an analogous way to sniffing. Thus, Smithʼs claim is most charitably interpreted as one about the awareness of movement such that one is not usually aware of saccadic eye movements, but always aware of sniffing when attempting to locate a smell.

Smelling Matter 7

smell) that cannot be described in subject-predicate form unlike the objects of the other

sensations.

Phenomenologically if synchronic visual and olfactory experiences are

considered together, it might be admitted that the latter has fewer spatial qualities.

However, at times smells are presented as appearing from or at a location.

Phenomenological evidence may however be quite misleading. While I agree that the

phenomenology of experience should be accounted for in generating a theory,

phenomenology should not be the sole determining factor. Rather than denying that

olfactory experience has an inherent spatial aspect, I claim that there is a better

explanation for the apparent lack of spatial phenomenology.

Plato and Aristotle both correctly recognized that inhalation is necessary for

olfaction, and it is not usually accompanied by a conscious awareness of modulating

breathing. Most of the time, odors seemingly present themselves as if they have just

appeared before the nose or occurred within our nostrils. However, while breathing can

be volitionally controlled this is usually not noticed and is only attended to when sniffing

once an interesting olfactory object catches the attention. Furthermore, recent studies

on the role of sniffing suggest that the act of sniffing itself is part of the olfactory percept

(Sobel, et al., 1999; Kareken et al., 2004; Kepecs et al., 2006; Mainland, et al. 2006;

Koritnik et al., 2008;).

Olfactory experiences, I claim, seem to lack a spatial phenomenology because

we do not commonly attend to our breathing patterns, which are both necessary for

olfactory experience and provide its spatial aspects. An awareness of the spatial

aspects of olfactory experience is given by diachronically attending to an olfactory

object, because attention is directed to breathing patterns and the movement of airflow.

Thus, although the spatiotemporal aspects of synchronic olfactory experience are not

commonly attended to, they are nevertheless present.

The objects of olfactory experience are spatiotemporally-bounded entities.

However, given the distinct spatial and temporal characteristics of smells, the criteria for

perceptual objects, as they are derived from vision, do not adequately capture the

Smelling Matter 8

nature of our olfactory experiences. More accommodating criteria are required, which

account for the variegated spatiotemporal nature of the objects of each modality.

3.2 Figure-Ground Separation The objects of auditory and olfactory perception have spatiotemporal boundaries

that exceed those of vision. Figure-ground separation can be used as a criterion, in

addition to spatial extent, to establish that olfactory objects are spatial. The olfactory

system is constantly bombarded by stimuli, yet we are able to separate and group

together stimuli that belong to one as opposed to another stimulus. The theory of

indispensable attributes (Kubovy, 1988; Kubovy and Van Valkenburg, 2001); – which

claims that essential attributes for each modality allow the perception of more than one

object at a time - is proposed to account for the ability for figure-ground separation and

as a general criterion for perceptual objecthood across modalities. For vision, the

essential attributes are claimed to be space and time, while for audition they are pitch

and time. While Kubovy and Van Valkenburg do not consider the case of olfaction, the

olfactory object satisfies this criterion of objecthood as well.

Chemicals, which could lead to olfactory experiences, constantly surround us.

Nonetheless different smells are separable from one another and detectable in the

environment. For instance, I can smell the roses within the bouquet of lilies and gerbera,

the rosemary on the roasted chicken, or the honeysuckle from the fresh-mown grass in

the meadow. Additional, empirical evidence for olfactory figure-ground separation may

be garnered from the overshadowing effect in odor mixture qualities. When combining

odorants in a mixture, if the constituents smell similar on their own it is often harder to

tease them apart when combined; conversely, if they smell dissimilar on their own it is

often quite easy to distinguish them within a mixture. However, in every variation of

similar and dissimilar pairings of odorants there is “evidence of overshadowing of one

component by another, depending upon the concentration level” (Kay et al., 2005, p.

727). Furthermore, if the concentration level of the overshadowed item is increased it is

possible to switch the overshadowing effect. Indeed, whether one smells an odor a

Smelling Matter 9

against a background of odor b (or vice-versa) can be manipulated merely by altering

the concentration levels of the components of a complex odor mixture

The olfactory object can meet the spatial criterion of a perceptual object using the

phenomenon of figure-ground separation. But the criterion still does not adequately

capture the nature of our olfactory experience. Odors can be recognized, discriminated

between, and identified across multiple contexts, presentations, and changes in their

properties. For example, the smell of a peach can be identified across changes in

intensity and concentration (when it is unripe, ripe, and overripe), and in different

contexts (as a fruity drink, in a baking pie, or in a perfume). Despite these changes, all

the various token olfactory experiences can still be recognized as all under a particular

type i.e. the peach smell.

3.3 Mereologically-Complex Entities

In an attempt to determine the nature of the auditory object, O'Callaghan (2008,

2009) suggests thinking about perceptual objects as entities with mereologically-

complex structures such that they can be recognized across contexts and changes in

properties. This approach to olfaction is seductive because it fits nicely with ecological

views of the olfactory object (Wilson and Stevenson, 2006; Gottfried, 2010). The

methodological assumption of ecological theories is that the olfactory object is to be

identified with the complex set of molecular compounds that enable us to track, locate,

and secure objects that are of value to us in maintaining our homeostatic needs. Such

theories define the olfactory object in terms of the function of olfaction in guiding the

ability to identify ecologically valuable information about the environment.

Wilson and Stevensonʼs (2006) theory is the most exhaustive scientific account

of the olfactory object that is in keeping with the criterion of a perceptual object as a

mereologically-structured entity. Central to this theory is the issue of how certain

chemicals can be recognized as bound together to form the perception of objects

despite the presence of countless other chemical structures in the environment. Given

their overall methodology, Wilson and Stevenson think that the perception of the

olfactory object partially depends upon ʻsyntheticʼ processing, such as memory

Smelling Matter 10

Figure 1. Polysantol – (4-Penten-2-ol, 3,3-dimethyl-5-(2,2,3-trimethyl-3-

cyclopenten-1-yl)) gives off a robust sandalwood smell.

processing that is modulated by the organismʼs current mental state, previous olfactory

states, expectations, and its situation. Thus, they identify the olfactory object with a

complex of molecular compounds, which is responsible for the ability to locate medium-

sized ordinary objects in the environment.

This ecological theory of the olfactory object - as a complex chemical mixture

composed of multiple molecular compounds that derive from an ordinary object - is not

satisfactory because simple molecular compounds can be recognized, identified, and

discriminated across contexts and against the background of other odors. Singular

synthetic molecules provide the simplest counter-example to Wilson and Stevensonʼs

ecological theory. For instance, Firmenichʼs Polysantol (See Figure 1) can be

recognized across presentations and varying levels of concentration.12 Wilson and

Stevensonʼs approach only accounts for complex mixtures. Simple odors composed of a

single molecular compound are experienced in the same manner as complex mixtures,

despite the fact that they are not mereologically-complex in the required ecological

sense.

Wilson and Stevensonʼs theory of the olfactory object is also not adequate

because it only generates a theory of how the perception of olfactory objects is

produced. While the theory provides an answer to how smells are recognized, identified,

and discriminated from one another, it provides no answer to the question of what

constitutes the olfactory quality of olfactory objects.

Olfactory experience is certainly object-directed, as it satisfies the

aforementioned spatiotemporal criteria used to ascertain the nature of the object of 12 One might debate whether the current formulation of Montaleʼs Aoud Pur Oriental contains this Polysantol or Firmenichʼs Oud Synthetic 10760 E (e.g. because they might be hard to discriminate between), but not, say whether it contains Givaudanʼs Black Agar Givco 215.

Smelling Matter 11

perception in vision and audition. The olfactory object has been shown to be a

spatiotemporal entity that can be separated from against a background of competing

stimuli, and maintain a mereological structure such that it can be recognized and

identified across changes in its location and properties. However, none of the criteria

discussed are sufficient to capture the nature of the olfactory object, which is less

spatiotemporally truncated than the objects of vision and audition, which at the same

time, is nevertheless mereologically-complex (even at the size of a simple molecular

compound).

4. Olfactory objects: Platonic vapors and odors

One suggestion that repeatedly appears in different guises in the literature is that

the olfactory object is the vapor, effluvia, or chemical gas given off by an ordinary object.

Platonic Vapor theories maintain that olfactory objects are detached proper parts of the

ordinary object itself (e.g. one literally smells the blood of an Englishman). Odor theories

claim that olfactory objects are detached subsets of the ordinary object, which are not

themselves indicative of it. According to odor theories, the objects of our olfactory

experience are chemicals given off by the ordinary object, which are diffused in odor

plumes. Although one does not perceive the entire ordinary object, nor the form of the

object, some aspects of the object are responsible for our experience of smell.

4.1. Platonic Vapors

Platoʼs theory of smell consists of little more than two paragraphs within the

Timaeus (66d-67) in which he claims that the vapors of objects are smelt as they

transform from one elemental shape to another, although they cannot be identified with

these elements themselves. Ordinary objects, asserts Plato, give off particles as a

substance condenses or becomes gaseous. Ordinary objects are perceived as they

transform between elemental kinds such that the smells of objects are the aerated forms

of the objects proper. According to this view, the olfactory object (what is smelled) is not

the elemental object itself, since our nostril cannot accommodate entities of such size,

but rather the (Platonic) form of the object.

Smelling Matter 12

Plato, interpreted as holding the view that olfactory objects are detached proper

parts (or the forms) of the entire ordinary source objects, does not explicitly endorse the

ordinary object view. However, it nonetheless suffers from some of the same problems

detailed above. Olfactory objects are not ordinary medium-sized objects because only a

small chemical subgroup of its material makeup and certainly not the form of the entire

object is required for olfactory experience. Moreover, synthetic chemicals can be

manufactured that mimic the smell of natural objects, suggesting that not even the form

of ordinary objects is necessary for creating the experience of the same olfactory quality

(its smell).

4.2. Odors

Contemporary odor theories are an outgrowth of the vapor view, although they

pay no homage to their theoretical ancestors. Odor theories maintain that the olfactory

object is an odor, which is identified with a gaseous emanation of an ordinary object. For

instance, a rose exudes diffused parts of itself, which is what we smell. Most

philosophers who discuss olfaction assume that smells are odors (Lycan, 1996, 2000;

Tye, 2000, 2002; Smith, 2002; Matthen, 2005; Batty, 2007, 2009, 2010a, 2010b).

Odors, thus identified, are certainly an interesting perceptual object, since their

spatiotemporal boundaries are less truncated than those of the other modalities. What

makes odor theories enticing is that they can account for olfactory misrepresentation,

since the olfactory quality of an odor does not depend upon the ordinary object itself.

Additionally, since only diffused subparts of the object (and not the entire ordinary object

itself) are required to elicit a smell, odor theories can prima facie provide the resources

to explain how olfactory experience can be veridical even when the ordinary object is

not present in the immediate surroundings.

The odor theory is partially correct but does not provide an explanation of what it

is about the odor that makes it smell the way it does. Since the experience of a smell

changes across the spatially diffused odor and can be spotty across presentations

within the odorʼs gradient, odor theory needs to provide an explanation of how the

Smelling Matter 13

olfactory quality of an odor is identified and individuated. What is responsible for an

odor smelling as it does? That is, what determines the olfactory quality of an odor?

The most obvious reply would be to individuate the qualitative character of odors

by reference to the natural source from which they emanate (Tye, 2000, 2002).

However this would be to return to the ordinary object view that was already rejected in

Section 2. Olfactory qualities cannot be individuated by reference to ordinary objects

because not all their aspects are required to generate the relevant smells. Moreover it is

possible to have veridical olfactory experience of an olfactory quality in the absence of

any ordinary objects (e.g. a synthetic rose smell still smells just as sweet). Even if it

were possible to account for these phenomena by appealing to the typical source of an

odor, the odor theory would still not be able to generate an account of what determines

the quality of an olfactory object. Why is it that a particular synthetic rose smell has

almost exactly the same olfactory quality as a Gardenia? A way of specifying the

olfactory quality of an odor independent of its ordinary object source is needed.

5. Olfactory objects as chemical (material) objects

If olfaction is a perceptual modality that is sensitive to chemicals then prima facie

olfactory objects should be specified in light of chemistry. Since chemistry studies

matter, i.e. anything with mass and volume, the criteria of a material object ought to be

an object that has a chemical structure such that it has mass and occupies space. For

the case of human beings olfactory objects, can be specified by noting the size of

molecules (not larger than twenty chemical groups and no smaller than three) that are

biologically detectable.13 The general requirements for a material object to be classed

as an odorant is that it should be volatile, hydrophobic and have a molecular weight less

than ~300 daltons (Ohloff, 1986).14

13 Specifying the olfactory object in this manner rules out ordinary objects. While they might satisfy the criterion of having a chemical structure, mass and volume, their chemical size clearly falls well beyond our bounds of perception. 14 In humans, the cut-off point for a chemical structureʼs size having a quality of smell is not gradual. This was demonstrated by Wrobel and Wannagat (1982), who showed, using benzenoid musk, that replacing one of itsʼ carbon atoms with a larger silicon atom caused the entire molecule to become odorless.

Smelling Matter 14

In this section, I argue that the objects of olfaction are the chemical structures of

molecular compounds within an odor cloud (i.e. a diffusion of molecules in space and

time). This conception of olfactory objects combines the virtues of the ecological and

odor theories with the added advantages that it can accommodate simple molecular

compounds having a smell and provide an explanation of olfactory qualities (how things

smell).

5.1 Olfactory objects are the chemical structures of molecules

Olfactory objects are neither molecules nor the elements that compose them. I

argue, rather that olfactory objects are three-dimensional chemical structures of

molecules (see Figure 3). The structure of a molecule is neither an abstract property nor

a specification of the molecular compound, but rather itʼs three-dimensional structure in

space and time. While it is natural to think of molecular structure as two-dimensional in

a similar fashion to Figure 2, it is better to think of it as it is represented in Figure 3.

Empirical evidence supporting the identification of olfactory objects with the molecular

structures of elemental compounds can be derived from the leading scientific theories of

primary olfactory transduction, our physiological olfactory capacities, psychological

olfactory abilities, and animal models of olfaction.15

15 Since the olfactory system is ontogenetically ancient, a great deal can be inferred about human olfactory experiences from animal models. Aside from the fact that it is a generally accepted practice throughout the sciences, Aristotle (DA II 7 419a33 – b1, DAII 9, De Sensu 5) also supports the methodology of thinking of olfaction as lying on a continuum with other

Figure 2: Two-dimensional representation of Bisphenol A (4,4'-

(propan-2-ylidene)diphenol)

Figure 3: Three-dimensional representation of Bisphenol A (4,4'-

(propan-2-ylidene)diphenol)

Smelling Matter 15

It is uncontroversial within the scientific community that the cause and quality of

olfaction is the structure of the molecules that come into contact with the olfactory

epithelium. However, there is less consensus regarding what it is about that the

structure of molecules that determines its quality (i.e. smell). The leading scientific

theories (which both agree in principle with the identification of olfactory objects with

molecular structures) are that the olfactory quality of molecules is determined by either

their shape or the vibrational patterns of the functional groups within the molecule itself.

Since the issue of primary sensory transduction is still under debate, there is as yet no

empirical reason to prefer either of the theories and none of the arguments offered will

depend on them.

5.2 Evidence for smelling the structure of matter 5.2.1 Physiological evidence

Evidence that the olfactory object is the molecular structure of matter can be

derived from studies on stimuli transduction by the olfactory system. While the Odotope

theory (Mori and Shepherd, 1994; Shepherd, 2005) and the biological spectroscope

theory (Turin, 1996, 2002, 2006; Turin and Yoshii, 2002) share the view that molecular

structures are olfactory objects and that a distributed activity pattern across multiple

olfactory receptor neurons (ORNs) determines the qualitative character of the olfactory

object, they disagree about the exact structural properties, and mechanisms of stimuli

transduction, responsible for it.

5.2.2 Psychological evidence for smelling matter

With the exception of perfume chemists16, most people would be surprised to

learn that they can detect, discriminate, and perhaps even identify the molecular

organisms. Animal models do not provide any further evidence for the claim that olfactory objects are the structures of molecular compounds, but only reinforce it (for example, both rodents and aphids can discriminate between enantiomers) For the sake of brevity, evidence from animal models in relation to human olfactory capacities is noted, where relevant, in the footnotes. 16 Burr (2007) gives a wonderful example of a perfume chemist, who can name the chemical structure of most of the common smells encountered when on a plane journey, from the lemon smell of the hot towels to the chemical odorants used in the bathroom disinfectants.

Smelling Matter 16

Figure 4: R-carvone and S-carvone

structure of the things they smell. However, the majority of people can discriminate

miniscule differences between and within the molecular structure of odorants. The

greatest source of evidence for this claim is the existence of enantiomers. Enantiomers

are molecular compounds whose structure and functional groups are identical, but

whose chiral properties (i.e. handedness) differ such that the molecules cannot be

symmetrically superimposed on top of each other. While most enantiomers have the

same smell (though both may not always be detectable by an individual), some do not.17

For example, R-carvone smells minty, while the S-carvone smells like caraway (Figure

4) (Boelens and van Gemert, 1993). Thus, the symmetry of the functional groups and

the orientation of a molecular compound are responsible for a different quality of smell.

Research on olfactory sensory conditioning also demonstrates, using classical

conditioning, that enantiomers can be discriminated despite subjects reporting that they

smell the same (Li et al., 2008). The results suggest that while optical isomers are

supraliminally indistinguishable, the two kinds of enantiomers can be discriminated

unconsciously, which can be interpreted as evidence that there are detectable

differences between the two types of smells.18

17 Since anosmia of a given enantiomer varies across populations, most flavor and fragrance products contain both enantiomers to ensure that the entire population is sensitive to the odor. The most exhaustive list of the smells of enantiomers is maintained by John Leffingwell. According to calculations of Leffingwellʼs listing in Turin (2006), 64% of enantiomers smell the same, 17% smell different and the remaining 19% are currently unknown. 18 Enantiomers have different behavioral effects across species. For instance Aphidius ervi is attracted to one enantiomer of nepetalactone (7S), but not the other (7R). When the two are combined the effect is an overall reduction in attraction (Glinwood et al., 1999). Further studies of enantiomers conducted on rats without any training, demonstrate that they are able to discriminate between R- and S- caravone, which as noted smells different to humans. With similar results to Li et al. (2008), Wilson and Stevenson (2006) have shown that, with some training, rats can learn to discriminate between limonene (R) and (S). These results further

Smelling Matter 17

In addition to being able to discriminate between the different versions of some

enantiomers we are also able to distinguish between aldehydes, compounds that differ

in one carbon group (Iamura et al., 1992). Our ability to discriminate between

aldehydes19 nicely demonstrates our sensitivity to changes in functional groups. The

case of aldehydes is intriguing because the smell of the compound changes as carbon

groups are added (Turin, 1996, 2006). The aldehydes from C-8 to C-12 all display an

interesting shift in smell as each carbon group is added: those with an even number of

carbon groups smell fruity, almost orange-like, while those with an odd number have a

floral, waxy odor (Arctander, 1994).

Further evidence that we are able to psychologically detect the structure of

molecular compounds is provided by the fact that we can detect the presence of

functional groups (Klopping, 1971). Functional groups are atomic groups within a

molecule that account for its chemical properties and structure. Interchanging functional

groups within molecules creates a predictable change in the qualitative character of

odorants (Turin and Yoshi, 2003). Thus, the identification of the olfactory object with the

structure of a molecular compound fits with these results, since the structure of a

moleculeʼs functional groups determines its characteristic smell in a predictable manner.

5.3 Olfactory properties

Having argued for the identification of the olfactory object with the chemical

structure of molecular compounds, what remains is specifying their properties. In

addition to the spatiotemporal properties of the olfactory object, which are best

determined empirically for each molecule or mixture according to the laws of chemistry,

I claim that olfactory objects have intensity, concentration, valence, and hedonic value.20

strengthen the claims that the object of olfaction is the molecular structure of chemical compounds and that the olfactory object is identical across species. 19 The reader may in fact have smelt Aldehydes, which are the primary synthetic ingredients of Chanel No. 5 and is what makes it so distinctive. 20 Experimental evidence that olfactory objects have these properties can be derived from the study by Li et al. (2008). While subjectsʼ were trained to discriminate between enantiomers that smell the same, their ratings of the valence, intensity, or familiarity of these structures were not affected. Since differences in the enantiomerʼs structure did not lead to a change in the

Smelling Matter 18

Intensity is simply the strength of the quality of smell. Concentration is best

thought of as the density of molecules of a particular odorant within its spatiotemporal

boundary.21 Thus, one might have a smell that is not intense, but highly concentrated.

For example, the intensity of Coumarin22 is quite weak, but walk through the menʼs

fragrance department of Macyʼs and the concentration level of these particles may

become unbearable.

The nauseating smell of the fragrance section of any department store also

provides an appropriate example of the property of valence23 (i.e. pleasantness) of an

odor. Pleasantness might better be thought of as a property of the olfactory object that

can vary across time and situations: steak always smells like steak, but if one has just

consumed thirty-two ounces of prime rib it might be the most repulsive thing one has

ever smelled.24 Finally, the hedonic value of olfactory objects should be distinguished

from, their valence. Some people may find the smell of skunks disgusting though the qualitative character of the olfactory object, it can be inferred that its properties remained the same. 21 Further evidence that concentration is a property of olfactory objects derives from the finding that as the level of concentration of an odorant increases in a given spatiotemporal location, a new olfactory percept is formed (McNamara et al., 2007), in the same way that changing the saturation of a given hue results in a different color. 22 Coumarin smells of golden, green, fresh, cut grass on a long, sunny, summer afternoon. 23 Yeshurun and Sobel (2010) have recently produced a rather exhaustive review of the literature on olfactory detection, discrimination, and identification. They claim that it is the molecular structure and pleasantness of an odor that determines the olfactory object, on the grounds that, based on the quality of smell, we are good at the first two and bad at the third, ,. Although this theory is certainly novel and interesting, their criteria of object-hood is unclear, especially given their claim that the olfactory object is a combination of external molecules together with a subjective judgment of pleasantness based on oneʼs homeostatic state. However, it might be possible to reject their theory on more substantial grounds by generating a more plausible explanation of the data cited in support of their theory. Yeshirun and Sobelʼs argument assumes that if we are bad at identification tasks, but good at labeling pleasantness, then the olfactory object must be determined by hedonic value. However, that we are poor at odor identification may better be explained by appeal to the linguistic deployment of concepts such that we are bad at naming and identifying olfactory objects. This makes the matter a performance issue rather than one involving the nature of the olfactory object itself. It is possible that the content of olfactory experiences cannot be fully captured using linguistic concepts alone, if for example the representational format of olfactory experience occurs in a combinatorial, but not classically-compositional, system. 24 There have been some cross-cultural studies demonstrating that judgments of valence are not innate, since they vary across cultures. For example, the smell of fish in certain island nations (e.g. Japan) is judged as neutral, while in landlocked nations (e.g. Bhutan) they are considered most unpleasant (see Gilbert, 2008, for a review of these studies).

Smelling Matter 19

experience of so doing nevertheless quite pleasant.25 While the properties of valence

and hedonic value are certainly a matter of learning and enculturation, intensity and

concentration seem to be neurophysiologically-driven.

6.1 Objection 1: But arenʼt smells subjective?

It is often claimed that smells and how they smell are subjective. An extremely

charitable interpretation of this claim is that the hedonic value, or valence of an olfactory

object is subjective. However, attributing this level of sophistication to the average

person, regarding olfactory properties, is implausible. Moreover the claim of subjectivity

is typically made about the very objects of olfactory experience rather than how they

smell (its quality). Indeed, it is more probable that our intuition about the subjectivity of

smells can be traced back to sensational theories of the olfactory object.

Sensational views of olfaction (Locke, 1690; Reid, 1764; Peacocke, 1983, 2003)

claim that smells are subjective objects that require a perceiver or mind to exist. Smells

are merely sensations within the mind. According to this view, the smell of a rose does

not objectively inhere within the rose itself and the only time a rose smells like anything

is when it is being smelled. As argued in Section 5, the olfactory object (what we smell)

is the chemical structure of molecular compounds, which determines its quality (what it

smells like). Since chemical structures are certainly mind-independent, external objects,

whose qualities are accessible in an objective manner across subjects, sensational

views are simply wrong.26

The olfactory object is not a subjective entity. The quality of an olfactory object

can be identified and individuated using its chemical structure. What something smells

25 While an extremely intense odor might cause a shift in valence, Wilson and Stevenson (2006) are careful to point out that intensity is a property separable from hedonic value. 26 The same reply can be used against projectionist views of olfaction. Perkins (1983) argues for an indirect-realist, projectionist account of smell such that the smell of an object does not inhere within the object itself and is not due to the causal powers of the object to cause in us a certain sensation. Rather, he claims, when smelling something, there is a disposition to judge that the ordinary object itself is attributed with the relevant olfactory property. So we are only indirectly (i.e. not directly) aware of the chemical structure that is responsible for our sensation of smell. The object of smell is an internal sensation, which is later projected upon the object that caused it. However, as argued, olfactory properties inhere in, and are intrinsic to, the chemical structure of odors.

Smelling Matter 20

like is not in the mind of the beholder, rather we can individuate the subjective qualities

of an olfactory experience in an objective and publicly assessable manner using

chemical structures. Metaphysical and epistemological issues about the kinds of

material entities that are to be considered olfactory objects need to be kept separate.

Metaphysically, everything composed of matter that has a molecular structure has a

smell. How we know about the smell of matter is an epistemic issue best left open for

empirical discovery. Relative to human beings, the material objects that are olfactory

objects can be specified by finding the size of molecules that are biologically detectable,

and discerning the conditions necessary for these chemical structures to be perceived

(See Section 5). However, our biological limitations should not lead us to exclude the

chemical structures outside of this range from having a smell, since there might be

beings with different biological systems who can smell what we cannot. (Similarly, it

should not be assumed that the limits of the color spectrum begin and end with our own;

there might be some species who perceive colors in the ultraviolet or infrared

electromagnetic frequencies.)

6.2. Objection 2: If we smell the chemical structure of matter, do we see photons too?

It might be objected that if the theory of olfactory objects presented here is

extended to vision, it creates the absurd conclusion that what we see are photons. The

visual system is sensitive to the wavelengths of photons at the first stage of stimuli

transduction within the retina, since these are the environmental stimuli received by the

rods and cones of the eye. Thus, the stimuli received by the visual system are just

photons of given energy states. However, it should not be assumed, without argument,

that the proffered theory of olfactory objects can be generalized as a theory of the

objects of the other perceptual modalities. The objects of visual experience are best

treated in the way outlined in Section 3.1, that is, in terms of spatiotemporal entities that

have clear boundaries.

Although the visual system is stimulated by photons, they are not what it is

primarily sensitive to. The primitives of the visual system are not infinitesimal dots, but

Smelling Matter 21

lines and edges, whose encoding begins to occur at the ganglion level of

photoreceptors (one step up from the rods and cones). We see three-dimensional

objects when we open our eyes. We see structured, spatiotemporal objects with clear

boundaries, such as coffee mugs, tables, and this article in front of you. The visual

system is wonderfully organized to be sensitive to the lines, edges, and their

orientations, that compose an ordinary object. The visual system is sensitive to photons

with differing energy levels in a way that is dependent upon the surfaces they have been

reflected by. However, these entities are neither detectable nor can they be

discriminated at either the physiological or psychological level. What is visually

perceived are the spatiotemporal properties of bound, ordinary objects. Moreover, none

of the arguments adduced for the view that the olfactory object is not an ordinary object

apply to the objects of visual experience.

The olfactory system is sensitive to the chemical structures of molecular

compounds and these are what are perceived as smells. In olfaction, the objects that

olfactory receptors are sensitive to are the very same entities that can be physiologically

and psychologically detected and discriminated. The olfactory quality of olfactory objects

is constituted by the three-dimensional chemical structures of the molecular

compounds, as derived from the composition and placements of its functional groups.

This is a very strong reason against the extension of the theory of olfactory objects to

the case of vision.

6.3. Objection 3: We donʼt report smelling chemical structures. Our olfactory experiences seem to present themselves to us as subjective

sensations within our own consciousness, rather than - as argued here - experiences of

external, structured molecular compounds. While having an olfactory experience, most

people do not report being aware of the posits of chemistry. Although flavor and

fragrance chemists have olfactory experiences of the chemical structures of molecular

compounds, for the rest of us, chemistry is something to be endured in high school. The

simplest reply to this objection is that since smells are the objects of olfaction, and

smells are the chemical structures of molecular compounds, the mode of presentation of

Smelling Matter 22

our experience of smells need not be as of such entities having this or that molecular

structures.27

The objection that this is not how the awareness of smells presents itself tacitly

assumes that the olfactory object must be specified by appeal to the awareness of

experiential content. Such awareness is typically claimed to occur against the

background of deployed concepts. To be aware of a smell (i.e. the chemical structure of

a molecular compound) as the very compound it is would require the use of a vast

repertoire of concepts from chemistry, which most of us do not possess or deploy on a

regular basis. This lack of conceptual sophistication does not prevent us from having the

same type of olfactory experience. After all, someone might understandably claim to

detect a sweet, flowery putrid undertone in Chanel No. 5, yet at the same deny that their

experience is of a large concentration of Aldehydes. While our awareness of the

olfactory experience does not commonly present us with the posits of chemistry, this

does negate that our olfactory experiences are of the three-dimensional structure of

molecular compounds, rather it is more indicative of our conceptual repertoire. Perhaps

this partially explains the temptation of individuating smells using ordinary objects or

their effluvia (odor theories) as we commonly use these entities to talk about smells, but

this way of talking is a short hand that we utilize as an imperfect crutch to compensate

for our feeble chemical vocabulary.

7. Conclusion

Our intuitions and everyday linguistic practices often serve as a theoretical

starting point in philosophy, yet they are not always accurate guides. We certainly do

talk about smells and claim that our olfactory experiences are object-directed. In

everyday life, smells are individuated using our intuitive grasp of ordinary objects,

thereby making the emanations of ordinary three-dimensional objects, picked out

visually, our most natural conception of the olfactory object. However, our pre-

theoretical intuitions and linguistic practices are themselves theory-laden. In this article I

27 If the claim that experiences of olfactory objects have intentional content is accepted then it is generally agreed that we cannot quantify into intentional attributions, such as reports about beliefs or perceptual experience (See Frege, 1892/1997; Quine, 1953, 1956; Davidson, 1969).

Smelling Matter 23

have argued that our folk conception of smells is incorrect, since it tacitly assumes an

inappropriate conception of the olfactory object that is borrowed from the study of vision.

While we are doubtlessly primarily visual creatures, the workings of the visual system,

and what we know about it, should not be the sole arbiter on what the proper objects of

perception are.

The best theory of visual objects does not adequately capture the nature of

olfactory experience. The perceptual object of olfaction is not an ordinary object and the

criteria typically used to ascertain and individuate visual and auditory objects do not fully

account for the apparent properties of olfactory objects. Our olfactory experiences are

of objects that are both spatiotemporally less truncated than those of vision and

audition, and - at the same time - are caused by such minuscule entities as simple

synthetic molecular compounds. These aspects of the olfactory object generate

sufficient reason enough to reject ecological theories of olfaction, yet at the same time

provide evidence that olfactory experiences are of external objects in our environment.

Contemporary Odor theories are also inadequate because they either cannot account

for the qualitative nature of olfactory objects (what objects smell like) or are empirically

untenable.

We smell the chemical structure of molecular compounds within odor plumes.

This theory of the olfactory object was supported by appeal to empirical evidence

regarding our physiological and psychological abilities to detect, distinguish, and

recognize the chemical structure of molecular compounds. So conceived, an

explanation of what determines the olfactory qualities of such objects was provided,

namely that the smell of each olfactory object is constituted by the structure of the

chemical compound as determined by its functional groups. We smell types of matter

and not subjective entities; the way such things smell are objective facts about the

nature of the material fabric of reality and not about some (private) subjective realm of

experience. Finally, olfactory objects are neither similar to those found in vision nor what

would be pre-theoretically expected (based on our linguistic practices and our first-

person phenomenological reports of olfactory experience). We smell the chemical

structure of matter and it is this that smells.

Smelling Matter 24

References:

Arctander, S., 1994. Perfume and Flavor Chemicals. Carol Stream, IL: Allured Publishing.

Aristotle, 1984a. De Anima. In The Complete Works of Aristotle, vol. 1, edited by Jonathan Barnes. Princeton, NJ: Princeton University Press, 641-692.

Aristotle. 1984b. De Sensu. In The Complete Works of Aristotle, vol. 1, edited by Jonathan Barnes. Princeton, NJ: Princeton University Press, 693-713

Batty, C. E., 2007. Lessions in Smelling: Essays on Olfactory Perception, Linguistics and Philosophy, the MIT Press, Cambridge, MA.

———. 2009. ʻWhat's that Smell?ʼ, Southern Journal of Philosophy 27, 321-348. ———. 2010a. ʻWhat the Nose Doesn't Knowʼ. Journal of Consciousness Studies 17, 10-17. ———. 2010b. ʻScents and Sensibiliaʼ. American Philosophical Quarterly 47, 103-118. ———. 2010c. ʻA Representational Account of Olfactory Experienceʼ. Canadian Journal of

Philosophy Boelens, M. H., and van Gemert ,L. J.ʼ 1993. ʻSensory properties of optical isomersʼ. Perfumer

and Flavorist 18: Nov-Dec. Burr, C., 2007. The Perfect Scent. Holt, Henry & Company, Inc. Fallon, A. E., Rozin, P., 1983. ʻThe psychological bases of food rejections by humansʼ. Ecol

Food Nutr 13: 15-26. Gibson, J. J., 1966. The Senses Considered as Perceptual Systems. New York: Houghton

Mifflin Company. Gilbert, A. N., 2008. What the Nose Knows: The Science of Scent in Everyday Life. New York,

NY, Crown Publishers. Glinwood, R.T., Du, Y.J., Powell, W., 1999. ʻResponses to aphid sex pheromones by the pea

aphid parasitoids Aphidius ervia and Aphidius eadyiʼ. Entomol Exp Appl 92: 227-232. Gottfried, J. A., 2010. ‘Central mechanisms of odour object perception’. Nature Reviews

Neuroscience 11, 628–641. Iamura, K., Mataga, N. and Mori, K., 1992. ʻCoding of odor molecules by mitral/tufted cells in

rabbit olfactory bulb. I. Aliphatic compoundsʼ. J. Neurophysiol., 68, 1986–2002. Johansen, T. K., 1996. ʻAristotle on the Sense of Smellʼ. Phronesis XLI/I: 1-20. ———. 2006. ʻWhat's New in the De Sensu? The place of De Sensu in Aristotleʼs Psychologyʼ.

In Common to body and soul: Philosophical approaches to explaining living behaviour in antiquity (edited by R.King). Berlin: Walter De Gruyter.

Kareken, D. A., Sabri, M., Radnovich, A. J., Claus, E., Foresman, B., Hector, D. and Hutchins, G. D., 2004. ʻOlfactory System activation from sniffing: effects in piriform and orbitofrontal cortexʼ. NeuroImage 22: 456-465.

Kepecs, A., Uchida, N. and Mainen, Z. F., 2006. ʻThe Sniff as a Unit of Olfactory Processingʼ. Chemical Senses 31: 167-179.

Kemp, S., 1997. ʻA Medieval Controversy about Odorʼ. Journal of the History of the Behavioral Sciences 33 (3): 211-219.

Klopping H.L., 1971. ʻOlfactory theories and the odors of small moleculesʼ. J Agric Food Chem 19: 999-1004

Koritnik, B., Azam, S., Andrew, C. M., Leigh, P. N. and Williams, S. C.R., 2008. ʻImaging the brain during sniffing: A pilot fMRI studyʼ. Pulmonary Pharmacology & Therapeutics: 1-5.

Kubovy, M., 1988. ʻShould we resist the seductiveness of the

Smelling Matter 25

space:time::vision:auditionanalogy?ʼ. Journal of Experimental Psychology: Human Perception and Performance,14(2): 318-20.

Kubovy, M. and Valkenburg, D. V., 2001. ʻAuditory and visual objectsʼ. Cognition 80: 97- 126.

Li, W., Moallem, I.;,Paller, K. A. and Gottfried, J. A., 2007. ʻSubliminal Smells Can Guide Social Preferencesʼ. Psychological Science 18 (12): 1044-1050.

Li, W., Howard, J.D., Parrish, T.B. and Gottfried, J. A., 2008. ʻAversive Learning Enhances Perceptual and Cortical Discrimination of Indiscriminable Odor Cuesʼ. Science 319: 1842-1845.

Locke, J., 1959/1690. An Essay Concerning Human Understanding. A. C. Fraser (ed.). New York, NY: Dover Publications.

Lycan, W. G., 1996. Consciousness and Experience. Cambridge MA: MIT Press. ———. 2000. ʻThe Slighting of Smellʼ. In Of minds and molecules; new philosophical

perspectives on chemistry. Oxford; New York: Oxford University Press. Mainland, J., and Sobel, N., 2006. ʻThe Sniff is Part of the Olfactory Perceptʼ. Chemical Senses

31: 181-196. Matthen, M., 2007. Seeing, Doing, and Knowing. Oxford: Oxford University Press. McNamara, A. M., Magidson, P.D., Linster, C., 2007. ʻBinary Mixture Perception is affected by

Concentration of Odor Componentsʼ. Behavioral Neuroscience 121 (5): 1132-1136. Mori, K., and Shepherd, G. M., 1994. ʻEmerging principles of molecular signal processing by

mitral/tufted cells in the olfactory bulbʼ. Cell Biology 5: 65-74. Noë, A., 2005. Action in Perception. Cambridge MA: MIT Press. O'Callaghan, C., 2007. Sounds. Oxford: Oxford University Press. ———. 2008. ʻObject Perception: Vision and Auditionʼ. Blackwell Philosophy Compass: 1-28. Ohloff, G., 1986. ʻChemistry of odor stimuliʼ. Experientia 42: 271-279. Peacocke, C., 1983. Sense and Content. Oxford: Claredon Press. ———. 1986. ʻAnalogue contentʼ. Proceedings of the Aristotelian Society 60,1-17. ———. 1989. ʻPerceptual contentʼ. In J. Almog, J. Perry, and H. Wettstein (Eds.),

Themes from Kaplan. New York: Oxford University Press. ———. 2008. ʻSensational properties: Theses to accept and theses to rejectʼ. Revue

Internationale de Philosophie 62: 7-24. Perkins, M., 1983. Sensing the World. Indianapolis, Indiana: Hackett Publishing. Plato, 1997. Complete Works. J.M. Cooper and D.S. Hutchinson (eds.). Indianapolis, and

Cambridge: Hackett Publishing. Porter, J., Anand, T., Johnson, B.N., Khan, R.M. and Sobel, N., 2005. ʻBrain Mechanisms for

Extracting Spatial Information from Smellʼ. Neuron 47: 581-592. Porter, J., Craven, B., Khan, R.M., Chang, S.J., Kang, I., Judkewitz, B., Volpe, J.,

Settles, G., and Sobel, N., 2007. ʻMechanisms of scent-tracking in humansʼ. Nature Neuroscience 10 (1): 27-29.

Porter, R.H., Balog, R.D., Cernoch, J.M. and Franchi, C., 1986. ʻRecognition of kin through characteristic body odorsʼ. Chem Senses 11: 389-395.

Porter, R.H., Cernoch, J.M. and McLaughlin, F.J., 1983. ʻMaternal recognition of neonates through olfactory cuesʼ. Physiol Behav 30: 151-154.

Porter R.H. and Winberg J., 1999. ʻUnique salience of maternal breast odors for newborn infantsʼ. Neuroscience and Biobehavioral Reviews , 23, 439–449

Smelling Matter 26

Reid, T., 1997/1764. An Inquiry into the Human Mind. D. R. Brookes, (ed.). Edinburgh, UK: Edinburgh University Press.

Rozin, E., Rozin, S. and Rozin, E., 1992. ʻEthnic Cuisineʼ. In Flavor principle cook book. E. Rozin (ed.). East Rutherford, NJ: Penguin Group.

Rozin, P., 1978. ʻThe use of characteristic flavourings in human culinary practiseʼ. In Flavour: Its chemical behavioural and commercial aspects, 101-127. Boulder, CO: Westview Press.

Rozin, P., Hammer, L., Oster, H. and Marmora, V., 1986. ʻThe childʼs conception of foodʼ. Appetite 7: 141-151.

Russell, M. J., 1976. ʻHuman olfactory communicationʼ. Nature 260: 520-522. Scholl, B. and Pylyshyn, Z., 1999. ʻTracking multiple items through occlusion: Clues to

visual objecthoodʼ. Cognitive Psychology 38: 259-90. Sela, L. and Sobel, N., 2010. ʻHuman Olfaction: a constant state of change-blindnessʼ. Exp

Brain Res:1-17. Shepherd, G. M., 2005. ʻOutline of a Theory of Olfactory Processing and its Relevance to

Humansʼ. Chemical Senses 39 (S1): i3-i5. Smith, A. D., 2002. The Problem of Perception. Cambridge, MA.: Harvard University Press. Sobel, N., Khan, R. M., Saltman, A., Sullivan, E.V. and Gabrieli, J. D. 1999. ʻThe world smells

different to each nostrilʼ. Nature 402:35. Turin, L., 1996. ʻA Spectroscopic Mechanism for Primary Olfactory Receptionʼ. Chemical

Senses 21(6): 773-791. ———. 2002. ʻA Method for the calculation of odor character from molecular structureʼ. Journal

of theoreticla biology 216: 367-385. ———. 2006. The secret of scent: adventures in perfume and the science of smell. New York,

NY: HarperCollins. Turin, L. and Yoshii, F., 2002. ʻStructure–odor relations: a modern perspectiveʼ. In: Handbook

of Olfaction and Gustation (edited by R. Doty). New York, NY: Marcel Dekker. Tye, M., 2000, Consciousness, Color, and Content. Cambridge, MA: The MIT Press. ———. 2002. ʻRepresentationalism and the Transparency of Experienceʼ. Nous 36(1): 137-

151. von Bekesy, G., 1964. ʻOlfactory analogue to directional hearingʼ. Journal of Applied

Physiology 19(3): 369-373. Wilson, D. A. and Stevenson, R. J., 2006. Learning to Smell. Baltimore, MD: The

Johns Hopkins University Press. Wrobel, D. and Wannagat, U., 1982. ʻSila substituted perfumes 4 Sila derivatives of some

musk scentsʼ. Journal of Organomertallic Chemistry 225: 203-210. Yeshurun, Y., Dudi, Y., and Sobel, N., 2008. ʻWorking Memory Across Nostrilsʼ. Behavioral

Neuroscience 122(5): 1031-1037. Zelano, C. Montag, J., Johnson, B., Khan, R. and Sobel, N., 2007. ʻDissociated

Representations of Irritation and Valence in Human Primary Olfactory Cortexʼ. Journal of Neurophysiology 97: 1969-1976.

Zhou, W. and Chen, D., 2009. ʻBinaural Rivalry between the Nostrils and in the Cortexʼ. Biology 19(18): 1561-1565.