Indeed, it is fair to say that the principles of the visual system are not as settled as commonly stated either. What is the basis to examine olfaction in relation to vision then? Olfactory coding cannot be mapped one-to-one onto the characteristics of the visual pathway, and so analysis will engage with features of edge-detection and color vision to emphasize relevant differences with respect to overall perceptual integration. To compare perception in olfaction to vision thus must feature the coding processes that facilitate the identity and persistence of perceptual objects, regardless of whether these processes link to distinct, albeit overlapping, modules of a sensory system.
Overall, olfaction is highly susceptible to a number of causal factors: chemical, biological, and psychological. Setting up how these factors shape the perception of odors provides the background against which to evaluate the adequacy of the three philosophical criteria of objecthood in olfaction. It is quite common to describe smells with respect to their associated source objects.
Still, in the words of Magritte, This is not a pipe. So we are advised to question:. What is the output of the process of olfaction; more specifically, what defines the content of olfactory experience? An answer is hard to come by because olfactory responses do not appear to be stable but vary a lot, between people but also in the same individual.
Its variability is the reason why olfaction has long been excluded from theories of perception. It is also the reason why philosophical interest in olfactory theories was framed around the chemical stimulus as the stable element in the stimulus-response equation Lycan, , ; Batty, a , b , ; Young, ; Millar, Here, the reasoning goes that if it can be argued that odors are 1 rule-based representations of the stimulus, and 2 shown to be constant, meaning perspective invariant, as well as 3 distinct in their elemental composition in comparison with other odors, then smells form perceptual objects.
Perceptual variability, on this account, is seen as distortions or illusions that occur when some factors interfere with the normal causal process of perceptual object formation. The following subsections challenge this ontological premise of odor objecthood in the current philosophical debate. Specifically, it is shown that perceptual variation in olfaction is not a mark of subjectivity or distortion. Variability is not the same as subjectivity i. Of course, this statement about objectivity as grounded in the sensory coding mechanisms applies to vision as well.
Indeed, some variation also occurs in visual perception. That said the causal grounds and effects differ. Variation in vision routinely relates to higher-order processing. This effect is not related to visual receptor coding or sensitivities but linked to the computation of visual input in central processing.
Indeed, such shared grounds of variability should invite us to rethink the principles of vision. Still, at the periphery, the visual system is striking stable, discrete, and invariant in its conditions of feature extraction and integration. Meanwhile, the opposite is true in olfaction, as the following sections illustrate. In addition to higher-level integration and top-down effects also known in vision , olfaction is highly variable and lacks discrete feature extraction as well as coordinated feature integration already at the periphery in receptor coding different from vision.
This difference results in numerous effects of perceptual variation that are not accommodated by the notion of objecthood as derived from theories of vision. How do molecules result in mental images? Philosophical debate about olfactory objecthood centers on the chemical stimulus for its analysis of odor objects.
Most have argued that odors can be accommodated under a physicalist account: just like color is said to correlate with physical features, the visible spectrum, odors correspond to molecular features Lycan, ; Young, ; Millar, However, any stimulus-response model — regardless of modality — must be measured against the conditions of the sensory system. There are two responses to a comparison of light and odor chemistry for stimulus-response models. First, such naive physicalism does not hold in color vision either Matthen, ; Chirimuuta, Not all colors have a physical expression in wavelength.
Second, olfaction does not work like vision in its coding. Such coding differences are vital when it comes to the question of odor object formation. A comparison of visual with odor coding must address two issues in this context: what is the causal disposition of the chemical stimulus, and how does the stimulus interact with the sensory system i. Starting with the stimulus, the visual stimulus behaves in a predictable fashion: reflections of light rays in edge-detection have a precise angle.
The same cannot be said about the chemical stimulus of smell: odorants are unpredictable in their environmental trajectory. What about the predictability of the coded molecular features in smell? Here, a comparison with color vision illuminates the difference.
Color vision is low dimensional: it is determined by one key parameter, the length of electromagnetic waves. Meanwhile, odorants are multi-dimensional; they are characterized by about 5, molecular parameters Keller and Vosshall, Odor chemistry is strikingly complex. The olfactory stimulus is structurally highly irregular in how its molecular features link to specific perceptual effects. Minimal alterations in chemical composition, sometimes just of one carbon atom or methyl group, can result in substantive qualitative shifts Rossiter ; Sell, Similarity in chemical structure does not necessitate similar odor quality: consider isosteric molecules, which are almost identical in shape and structure, yet have different odors.
In contrast to the visual system, olfactory quality is not reducible to a linear stimulus-response model. This applies to individual odorants.
- Upcoming Events;
- Main content!
- Book Of Minds And Molecules: New Philosophical Perspectives On Chemistry 2000?
- ACI 325.10R-95 - Report on Roller-Compacted Concrete Pavements.
- Point Defects in Solids: General and Ionic Crystals.
- Science (Vol. 311, No. 5760, January 2006).
- A theory of argumentation.
It is rendered even more visible in mixture perception. Commonly we do not perceive the smell of single odorants but mixtures. Molecules in a mixture regularly change their chemical properties and behavior, sometimes unpredictably.
- The Globalization of Business and the Middle East: Opportunities and Constraints.
- Boiling Point: The High Cost of Unhealthy Anger to Individuals and Society?
- Chemistry and a Theoretical Model of Science: On the Occasion of a Recent Debate with the Christies.
- Introduction to Automata Theory, Languages and Computation (Addison-Wesley Series in Computer Science).
Unlike light in vision, the causal disposition of the olfactory stimulus can alter. Mixture perception does not operate by neat additive principles of stimulus combination. Consider coffee aroma, which consists of several hundred of chemicals.
Emily R. Grosholz
None of these elements, in isolation, smells of coffee. Many of these individual components have a robust individual odor, such as indole with its overpowering fecal scent. In coffee aroma, this fecal smell is not present but blends with the other components to form a qualitatively new aroma. Odor chemistry involves several other effects involved in the masking and blending of aromatic compounds.
There is much more to be said about stimulus chemistry, of course. Suffice to say, the computation of odor from molecular structure is not straightforward. The interaction with the receptors are what really determines the causal disposition of the stimulus in relation to the sensory system, meaning what kinds of information the sensory system is able to pick up and process.
This brings us to the system selecting the input. The biology of olfaction is not less complicated. It involves receptor coding as well as the organization of neural activity. This article will focus primarily on receptor biology for brevity analysis of the neural organization of odor signaling in Barwich, The receptors alone give us plenty to talk about. Differences to vision emerge immediately.
The coding of primary colors, a central notion in visual perception, derives from the tuning of the three cones. To put this into perspective, human olfaction employs about different receptor types. This contrast in number is not the only remarkable feature of the olfactory system.
Olfactory receptors are also governed by different coding principles than vision. Odor receptors operate by combinatorial coding and are highly variable in their tuning to molecular features. What that means is that analogies to color vision break down: there is no set of primary smells coded by a set of receptors that, in their combination, explain the composition of other smells. Back to the subject of odor object formation, these two factors the mechanism of combinatorial coding, as well as variations and range in receptor tuning carry two significant consequences for the perception of odor:.
Combinatorial coding explains the vast amount of odors we can perceive, including the fact that we detect entirely new smells — immediately. Your nose does not have to evolve a new set of receptors to do this. It picks up distinct features e. For the identification of odor objects that means that there are odorants that did not exist in nature and have a quality that no human has smelled before, and which cannot be explained by reference to other odorants.
Plus, these odorants may not have any known semantic object associated with them like pee or rose. So, odor object coding must be understood in terms of receptor behavior. But receptor coding does not allow for straightforward stimulus-response mapping because:. Unlike vision, where the three cones are uniformly tuned to specific wavelengths, odor receptor coding is not uniform. Each of the receptors operates by a different receptive range, its own receptor chemistry. One could argue that vision also operates in a combinatorial way across the color cones to facilitate the calculation of colors without an associated spectrum, like pink.
However, there exists a crucial difference between vision and olfaction in their mechanism of combinatorial coding. In color vision, all photoreceptors respond to the same stimulus property, wavelength, while the olfactory receptors respond to about 5, different parameters in a non-linear, non-additive fashion e. Consequently, feature extraction in olfaction is not homogenous; an issue highly relevant for signal integration and the question: which stimulus feature does a neural signal propagating receptor activation actually stand for?
What this difference amounts to is that, ultimately, odor qualities are determined by the constitution and coding of the receptors, not the chemical topology of the stimulus. In other words: olfactory receptors arrange the chemical similarity of odorants by different features than an analytical chemist would model these molecules. Stimulus coding at the receptor level is not coextensive with the chemical topology of the distal stimulus. In further consequence, it is anything but apparent that olfaction affords a position of representationalism.
Of Minds and Molecules: New Philosophical Perspectives on Chemistry
It is the receptors that count, not the stimulus. And the receptors do not afford a direct mapping of odor quality to molecular structure. This view becomes indisputable once we take a closer look at receptor genetics. Receptor genetics is one of the central causes for variation in olfactory responses. With a few exceptions, people typically have the same set of visual cones. Olfaction is different. Each person has a unique expression of receptor patterns in their nose, by default.
Does that imply that individual noses also smell the world differently? It looks that way! On top of that, the vast number of olfactory receptor genes in the human genome allows for many mutations to take effect. Such mutations lead to notable differences in the experience of odor. For instance, cilantro coriander is intensely disliked by some people, who perceive its aldehydes as soapy and pungent instead of fruity and green.
Next to differences in stimulus behavior, receptor coding and genetics, is receptor sensitivity. There are many odorants whose perception can vary substantially depending on receptor sensitivity. Take androstenone, a pig pheromone Wysocki and Beauchamp, Androstenone smells differently to people with varying receptor sensitivities.
Some people find it smells unpleasantly like urine, others perceive it as sweaty like body odor, and to others, it appears as woody, to a few it even comes off as vanilla or floral. It is not a matter of subjectivity either, as this perceptual divergence grounds in distinct, measurable causal differences. These are only some examples of how biology, not isolated stimulus chemistry, determines odor perception. What if we understood stimulus representation in terms of receptor patterns, instead of odor chemistry?
This strategy was pursued by Batty a , b and, to some extent, Millar conflating receptor coding with stimulus topology. Even in this modified account, the criterion of stimulus representation collapses. To explain this, it matters to disentangle the scientific notion of odor object from the philosophical concept. The scientific use of odor object refers to the neural signals as the target of scientific explanation.
Odor objects as receptor patterns determine the composition of the neural signal projected and organized throughout central processing by the olfactory system. This scientific notion is not co-extensive with the philosophical concept of odor object as defined above. Additionally, Wilson and Stevenson emphasized the need to consider context-dependence in processes of learning, instead of stable stimulus-response coding, as the basis of olfactory perception.
Identifying odor objects in the philosophical sense with combinatorial receptor patterns leads to conceptual pseudo-problems. Say, the epithelium of one person P1 expresses four of five receptors coding for a specific odorant like hedione, while another person P2 has all five.
Do they perceive the same olfactory object? If not, the notion of odor object for the criterion of stimulus representation breaks down. Do they perceive the same olfactory object in this case? Moreover, does only one of these two options have the same odor object, or both, or neither? Such game of definitions could be played ad absurdum without ever arriving at real insights into the nature of odor perception or objecthood. One may object that what counts is stability within rather than across individuals.
However, individuals undergo alterations in their receptor repertoire, too. This is not the case in vision. The upshot is that variability in perceptual responses is not necessarily an expression of subjectivity, but mirrors the causal mechanisms of the olfactory system. Variations in sensory coding determine and explain deviations in perceptual content. What constitutes objectivity in perception, therefore, are the causal principles of the system, not philosophical armchair intuitions about stimulus representation. Variation is not to be explained away as it constitutes the fundamental modus operandi of the olfactory system.
The ability to recognize and identify particular objects through time and space is perhaps the most convincing or intuitive criterion of perceptual objecthood. Its effects are salient in vision. The brain is an extraordinary organ in how it makes sense of visual input hitting the retina from all sorts of angles and constructing a tractable image that exhibits a constancy of features across changing perspectives and lighting circumstances.
Next to variations of perspective are other challenges to visual processing; e.
On the other hand, we can detect invariant features of a perceptual object despite shifts in perspective. These types of constancy imply that there are specific causal features that ensure stability in the mental representation of odor objects. Odors do not have a discrete identity retained throughout various perspectives, sensory and cognitive. Three examples should hammer this point home.
First, there is the mechanism of selective adaptation in olfaction Hettinger and Frank, The reason for that is, again, receptor behavior. Odor receptors habituate quickly to a stimulus. Moreover, olfactory receptors habituate and desensitize at different speeds. So if one smells an odor blend for a while, the receptors get desensitized to some of its stronger ingredients while others, to which receptors are still responsive, become more prominent in return. In reply, consider the next case. Second, an olfactory mixture can, when perceived under altering perspectives, be experienced as having different conceptual categories.
In a study by Herz and von Clef , participants smelled identical pairs of five mixtures, each administered with different verbal labels e. Subjects reported that the mixtures smelled different, although each pair of vials contained the same stimulus. The same stimulus can elicit a markedly different phenomenological experience, as well as qualitative category, depending on changes in the context of its exposure. Different semantic associations result in diverging perceptions of the same stimulus simply by experiencing an odor with a different conceptual tag.
Indeed, descriptions of an odor vary significantly if a source object is visible or not; a fact that the German psychologist Hans Henning recognized as early as Henning, A third case will dissolve also this objection. In a presentation at Columbia University in , the master perfumer Christophe Laudamiel distributed smelling strips scented with sulfurol to an audience.
Similar books and articles
People smelling it at first were uncertain regarding its quality. It smelled somewhat organic, perhaps a little meaty or sweaty, but also of something else. Laudamiel proceeded to show an image of warm milk. The audience murmured in agreement. Of course, it smelled like warm milk! Laudamiel continued by showing another image, this time of ham. The audience was startled. The strip with sulfurol suddenly smelled like ham. Laudamiel repeated his demonstration, alternating between the images of warm milk and ham. The perceptual switch continued to occur with the alternating images.
The moral of the story is that, yes, we can recognize and assign a stimulus with general classes of odor qualities like milk or ham. But the mere fact that our sensory system facilitates perceptual categorizations of input information does not mean that there is a discrete and constant perceptual object assigned to a stimulus. In contrast with color vision, the border separating sensory input from cognitive judgment appears less categorical in smell than in vision.
One reason for this is that the same olfactory stimulus, in different contexts, alters its perceptual meaning. Butyric acid can be perceived as Parmesan as well as vomit because it is an element of both, Parmesan and vomit aroma. Odor signals are ambiguous and underdetermined with respect to the conceptual identity of their source objects. This ambiguity resides on the periphery and does not constitute higher-level effects of illusions, distortions, or bias.
Instead, variation in olfaction is explained by receptor coding and stimulus behavior in the environment. On the one hand, receptor coding: unlike visual cones, the olfactory receptors do not have a consistent, designated receptive range that picks out this, only this, and no other feature. Instead, they are broadly tuned and combinatorial. On the other hand, stimulus behavior: the stimulus itself is promiscuous in its occurrence; odorants frequently overlap in their occurrence in different mixtures and environments, so much so that they can get associated with various source objects of distinctly different conceptual identities.
Therefore, odor identification is not poor as argued by Young, ; it is conceptually underdetermined. In conclusion, odors are not perspective-invariant like visual objects. Olfactory processing, in light of its inherent sensory underdetermination at the periphery, is fundamentally shaped by other sensory and higher-level cognitive processes e.
Let us finish this section by applying these insights into odor biology to the criterion of perceptual constancy, as outlined in Millar Take the first type of perceptual constancy: completeness. However, a complex, unified experience is not indicative of discrete perceptual objects or migraines would meet that criterion; can a migraine be complete? Plus, a unified sensory experience does not entail object recognition and identification. In fact, integrated perceptual experience and object recognition and identification reflect distinct processing stages also in vision, think agnosia.
The main point in need of attention is the second type of perceptual constancy: that perceptual objects have invariant features that allow them to be viewpoint independent. The reason why olfaction does not offer viewpoint independent perception is plain yet cannot be stressed enough: its coding differs from vision. Consider how perceptual constancy is achieved in vision. In parallel with the distinctly spatial coding of retinal input and its cortical projections, the perceptual representation of visual objects builds on specific spatial features, such as edges and boundaries, orientation, directionality, and extension Churchland, Specifically, shape detection in vision builds on particular viewpoint invariant features in edge-detection, such as T-junctions defining the boundaries of objects and Y-junctions marking areas where surfaces join Oram and Perrett, Based on these junctions, our visual system can calculate regularities in perspective, e.
Optical illusions routinely build on this peculiarity in visual processing e. In effect, the possibility of viewpoint invariant spatial features in vision is a result of the topographically distinct projection of signals from retinal cells sensitive to light contrast center-surround cells to cells in the primary visual cortex and their hierarchical integration from simple cells to more complex cells Hubel, What kinds of features are extracted by the olfactory system that might allow for feature-invariant representation?
Feature extraction in edge-detection, as well as color vision, is much more confined and discrete compared to olfactory receptor tuning and combinatorics. In odor coding, there is no single definite parameter like light contrast in edge-detection, or wavelength in color vision that could operate as a viewpoint invariant feature. In a sense, the olfactory brain has to do some guesswork because odor receptors respond to several kinds of features as they are broadly tuned. Say, a receptor can be tuned to molecules with a particular polar surface area as well as odorants with atom groups in a specific orientation or a functional group e.
The interpretation of such underdetermined input signal thus depends on other, parallel signals. On a neural level, feature coding is not viewpoint invariant either. Additionally, the neural representation of odors differs fundamentally from the topographic organization in vision. Thus, they represent contingent neural associations with an odor, not constancy in the way the visual system facilitates perspective-invariant perception through consistent and stable feature coding.
Overall, olfaction lacks a principal feature by which to calculate regularities or parallel structures like in vision, and as required for perceptual constancy if understood as perspectival invariance. In olfaction, we do not have a comparable set-up in its coding principles. While the olfactory system facilitates perceptual categorizations of stimulus information, it does not provide a comparable invariance in feature coding like edge-detection in vision.
Notably, this applies also to the olfactory bulb, not only piriform cortex. While the implications of this finding are yet to be determined, clear is that this may revise understanding of odor coding and further differentiate it from vision. Ultimately, the process of categorization lumping information into groups does not require the notion of objecthood.
Figure-ground segregation allows the perceiver to pick out specific information against a noisy background. The cocktail party effect, referring to instances when one can hear someone saying their name in a chattering crowd, is an example of how the brain can filter and prioritize auditory information Cherry, Olfaction, too, allows for figure-ground segregation.
Smelling wine aroma, e. Figure-ground segregation in olfaction has to do with stimulus saliency. Sommeliers evaluate a wine by focusing on distinct criteria of observational likeness with other wine profiles. They can point to subtle flavor notes that the layperson may have missed but, after paying attention, is also able to perceive. During this process, wine tasters, as well as perfumers for that matter, have to search for olfactory qualities in a complex mixture.
They are taking several steps of sniffing, comparing and evaluating their perception against cognitive templates because these fragrant notes in complex mixtures do not reveal themselves all at once Smith, ; Todd, Figure-ground segregation in odor perception is not immediate; it is a process of perceptual grouping that involves sequential processing of attention and iterative interpretation. To be good at wine tasting requires perceptual expertise, acquired by a prolonged training of particular perceptual grouping techniques.
Essentially, this expertise builds on the disposition to separate sensory information and focus on salient features. Essentially, figure-ground segregation is a process that facilitates perceptual categorization, not perceptual objecthood. A distinction introduced by Smith explains this difference. Smith, using the example of taste, distinguishes between, on the one hand, the causal disposition of a stimulus to elicit a certain range of perceptual qualities and, on the other hand, the perceptual expression of said causal features as a phenomenal quality.
This distinction is crucial for understanding olfaction because the perceptual expression of an odor does not correlate undeviatingly with the causal disposition of its stimulus: First, the same stimulus can elicit different qualitative experiences in individuals e. Second, a complex stimulus can be perceived differently in its qualitative notes if perceivers group its features differently.
For example, two wine critics may describe the bouquet of a wine in separate qualitative terms simply because different features in the wine appear salient to them in their perceptual evaluation, and so they pay attention to different olfactory notes in their characterization Smith, a , b. That does not make the wine different. They might even come to the same conclusion identifying the specific type of wine, its vineyard and year. But their perceptual sequence of evaluating the wine may differ. On this account, figure-ground segregation can result in varying yet equally accurate perceptual groupings of the same stimulus.
It is instructive to think of perceptual object formation as just one example of how the senses act as perceptual systems. Some sensory systems may afford the formation of perceptual objects. But that does not say that the notion of perceptual objecthood is fundamental to the process of sensory perception in every modality. Publication Timeline. Most widely held works by Nalini Bhushan. Of minds and molecules : new philosophical perspectives on chemistry by Nalini Bhushan 17 editions published in in English and held by 1, WorldCat member libraries worldwide "Of Mind and Molecules is the first anthology of its kind devoted exclusively to work in the philosophy of chemistry.
Its essays, authored by chemists and philosophers working independently and as teams, address a variety of topics that are central to any articulation of a comprehensive philosophy of chemistry. The author's own chapters on the work of this period contextualize the philosophical essays collected and connect them to broader intellectual, artistic and political movements in India.
This book yields a new understanding of cosmopolitan consciousness in a colonial context, of the intellectual agency of colonial academic communities, and of the roots of cross-cultural philosophy as it is practiced today. It transforms the canon of global philosophy, presenting for the first time a usable collection and a systematic study of Anglophone Indian philosophy.
Many historians of Indian philosophy see a radical disjuncture between traditional Indian philosophy and contemporary Indian academic philosophy that has abandoned its roots amid globalization. The book provides a corrective to this common view. The literature collected and studied is at the same time Indian and global, demonstrating that the colonial Indian philosophical communities were important participants in global dialogues, and revealing the roots of contemporary Indian philosophical thought.
The scholars whose work is published here will be unfamiliar to many contemporary philosophers. But the reader will discover that their work is creative, exciting, and original, and introduces distinctive voices into global conversations. These were the teachers who trained the best Indian scholars of the post-Independence period. They engaged creatively both with the classical Indian tradition and with the philosophy of the West, forging a new Indian philosophical idiom to which contemporary Indian and global philosophy are indebted.
Contrary thinking : selected essays of Daya Krishna by Daya Krishna 9 editions published in in English and held by 1, WorldCat member libraries worldwide Daya Krishna was easily the most creative and original Indian philosopher of the second half of the twentieth century. His thought and philosophical energy dominated academic Indian philosophy and determined the nature of the engagement of Indian philosophy with Western philosophy during that period. Krishna's thought and publications address a broad range of philosophical issues, including issues of global philosophical importance that transcend considerations of particular traditions; issues particular to Indian philosophy; and issues at the intersection of Indian and Western philosophy.
TransBuddhism : transmission, translation, transformation by Jay L Garfield 8 editions published in in English and held by WorldCat member libraries worldwide The global spread of Buddhism is giving rise to new forms of religious complexity, both in the West and in Asia. This collection of essays examines the religious and cultural conversations that are occurring in this process from a diverse range of disciplinary, methodological, and literary, perspectives, including philosophy, ethnography, history, and cultural studies.