Smell perception plays an important role in eating behavior and might be involved in body weight gain. Since a body of literature implies that olfactory perception and function is hampered in obesity, we here investigate neuroanatomical correlates of this phenomenon. We assessed olfactory bulb volume with magnetic resonance imaging in 67 healthy participants with a body mass index from 18.9 to 45.4 kg/m2. Moreover, we obtained psychophysiological data on olfactory ability and self-report measurements on eating behavior. (...) Additionally, we collected parameters associated with metabolic health in obesity to investigate recently proposed mechanistic explanatory models of why olfaction may be altered in obesity. We showed that OB volume was significantly lower in participants with obesity when compared to those of normal weight. Moreover, we found weak to moderate negative correlations between OB volume and BMI and related measures of metabolic health, especially leptin, body fat percentage, waist-height ratio and insulin resistance. However, neither OB volume nor BMI were related to olfactory function in our young and healthy sample. Nevertheless, our results provide first indications that obesity is associated with brain anatomical changes in the OBs. (shrink)

There is increasing evidence for directional guidance of growing axons by molecular gradients in target tissues. Aside from biochemical studies on gradients and their role, the capability of axons to approach their target position from different aspects of a two-dimensional field is itself an indication for guidance by gradients. According to this criterion, such guidance is expected to be involved not only in map-formation in the visual system but also in targeting of receptor cell axons in the olfactory (...) class='Hi'>bulb. In this paper, physico-chemical concepts of visual mapping are adapted to olfactory targeting. In both cases there must be sophisticated processing of graded cues in the growing tip of the axon for growth cone navigation. In visual map formation, a target position is determined by influences of cues depending on the position of axonal origin; in olfactory targeting, however, these influences are expected to be based on properties of the receptor-cell-specific molecules (possibly including the receptor molecule itself), as well as by gene regulation affecting the levels of expression. According to this concept, the main role of molecules expressed in a receptor-cell-type specific manner is not matching specific counterparts on the target tissue, but instead quantitative modulation of growth cone steering for sensing the direction towards the target position. (shrink)

What is the function of new neurons entering the olfactory bulb? Many insights regarding the molecular control of adult neurogenesis have been uncovered, but the purpose of new neurons entering the olfactory bulb has been difficult to ascertain. Here, studies investigating the role of adult neurogenesis in olfactory discrimination in mice are reviewed. Studies in which adult neurogenesis is affected are highlighted, with a focus on the role of environment enrichment and what happens during ageing. (...) There is evidence for a role of adult neurogenesis in fine discrimination tasks, as underscored by studies that enhance adult neurogenesis. This is also observed in ageing studies, where older mice with reduced levels of adult neurogenesis perform poorly in olfactory discrimination. Differences in methodology that could account for alternative conclusions, and the importance of specificity in methods being used to investigate the effect of adult neurogenesis in olfactory performance are emphasized. (shrink)

The shapes of neurons and glial cells dictate many important aspects of their functions. In olfactory systems, certain architectural features are characteristics of these two cell types across a wide variety of species. The accumulated evidence suggests that these common features may play fundamental roles in olfactoryinformation processing. For instance, the primary olfactory neuropil in most vertebrate and invertebrate olfactory systems is organized into discrete modules called glomeruli. Inside each glomerulus, sensory axons and CNS neurons branch and (...) synapse in patterns that are repeated across species. In many species, moreover, the glomeruli are enveloped by a thin and ordered layer of glial processes. Theglomerular arrangement reflects the processing of odor information in modules that encode the discrete molecular attributes of odorant stimuli being processed. Recent studies of the mechanisms that guide the development of olfactory neurons and glial cells have revealed complex reciprocal interactions between these two cell types, which may be necessary for the establishment of modular compartments. Collectively, the findings reviewed here suggest that specialized cellular architecture plays key functional roles in the detection, analysis, and discrimination of odors at early steps in olfactory processing. (shrink)

Contemporary neuroscientific theories of consciousness are typically based on the study of vision and have neglected olfaction. Several of these (e.g. Global Workspace Theories, the Information Integration theory, and the various theories offered by Crick and Koch) claim that a thalamic relay is necessary for consciousness. Studies on olfaction and the olfactory system's anatomical structure show this claim to be incorrect, thus showing these theories to be either false or inadequate as general and comprehensive accounts of consciousness. Attempts to (...) rescue these theories by claiming that there is a structure in the olfactory system that is functionally equivalent to the thalamus in the visual system, such as the olfactory bulb or the olfactory cortex, are also shown to fail. If we wish to understand consciousness, we have to wake up and smell it. (shrink)

Chaos theory is a rapidly growing field. As a technical term, chaos refers to deterministic but unpredictable processes being sensitively dependent upon initial conditions. Neurobiological models and experimental results are very complicated and some research groups have tried to pursue the neuronal chaos. Babloyantz's group has studied the fractal dimension (d) of electroencephalograms (EEG) in various physiological and pathological states. From deep sleep (d=4) to full awakening (d>8), a hierarchy of strange attractors paralles the hierarchy of states of consciousness. In (...) epilepsy (petit mal), despite the turbulent aspect of a seizure, the attractor dimension was near to 2. In Creutzfeld-Jacob disease, the regular EEG activity corresponded to an attractor dimension less than the one measured in deep sleep. Is it healthy to be chaotic? An active desynchronisation could be favourable to a physiological system. Rapp's group reported variations of fractal dimension according to particular tasks. During a mental arithmetic task, this dimension increased. In another task, a P300 fractal index decreased when a target was identified. It is clear that the EEG is not representing noise. Its underlying dynamics depends on only a few degrees of freedom despite yet it is difficult to compute accurately the relevant parameters.What is the cognitive role of such a chaotic dynamics? Freeman has studied the olfactory bulb in rabbits and rats for 15 years. Multi-electrode recordings of a few mm2 showed a chaotic hierarchy from deep anaesthesia to alert state. When an animal identified a previously learned odour, the fractal dimension of the dynamics dropped off (near limit cycles). The chaotic activity corresponding to an alert-and-waiting state seems to be a field of all possibilities and a focused activity corresponds to a reduction of the attractor in state space. For a couple of years, Freeman has developed a model of the olfactory bulb-cortex system. The behaviour of the simple model without learning was quite similar to the real behaviour and a model with learning is developed. (shrink)

Olfactory rivalry can occur when a binary mixture is sniffed repeatedly, with one percept dominating then the other. Experiment 1 demonstrated olfactory rivalry using several new techniques. Experiments 2 and 3 examined whether participants can notice rivalry. Participants received trials composed of odor pairs: either a mixture followed by the same mixture; or a pure odor followed by the same pure odor. On some trials participants judged whether the two stimuli were the same or different, to see if (...) they could detect rivalry. On other trials participants judged the quality of each odor, allowing us to determine whether rivalry occurred. We found evidence for rivalry when we compared reports of odor quality for one stimulus and then the other, but no evidence that participants could detect this change. These findings are consistent with the idea that people can experience olfactory illusions, but may not know they have occurred. (shrink)

The philosophy of perception has been mostly focused on vision, to the detriment of other modalities like audition or olfaction. In this paper I focus on olfaction and olfactory experience, and raise the following questions: is olfaction a perceptual-representational modality? If so, what does it represent? My goal in the paper is, firstly, to provide an affirmative answer to the first question, and secondly, to argue that olfaction represents odors in the form of olfactory objects, to which (...) class='Hi'>olfactory qualities are attributed. In order to do this I develop an empirically adequate notion of olfactory object that is sensitive to the peculiarities of olfaction, and defend it against various objections. (shrink)

Much of the philosophical work on perception has focused on vision. Recently, however, philosophers have begun to correct this ‘tunnel vision’ by considering other modalities. Nevertheless, relatively little has been written about the chemical senses—olfaction and gustation. The focus of this paper is olfaction. In light of new physiological and psychophysical research on olfaction, I consider whether olfactory experience is object-based. In particular, I explore the claim that “odor objects” constitute sensory individuals. It isn’t obvious—at least at the outset—whether (...) they meet the widely accepted principles of object individuation and recognition at work in the visual and auditory cases. Among the general issues I consider, then, is whether these traditional principles form necessary, or simply sufficient, conditions on object perception. As we see, at the very least, considering the object-recognition model of olfaction challenges us to look more closely at well-entrenched models of object perception. But the payoff of doing so is high. We not only learn something about a modality that philosophers have historically neglected; by asking new questions and challenging old assumptions, we also further our understanding of perception in general. (shrink)

Any living organism interacts with and responds specifically to environmental molecules by expressing specific olfactory receptors. In this paper, this specificity will be first examined in causal terms with particular emphasis on the mechanisms controlling olfactory gene expression, cell-to-cell interactions and odor-decoding processes. However, this type of explanation does not entirely justify the role olfactory receptors have played during evolution, since they are also expressed ectopically in different organs and/or tissues. Homologous olfactory genes have in fact (...) been found in such diverse cells and/or organs as spermatozoa, testis and kidney where they are assumed to act as chemotactic sensors or renin modulators. To justify their functional diversity, homologous olfactory receptors are assumed to share the same basic role: that of conferring a self-identity to cells or tissues under varying environmental conditions. By adopting this standpoint, the functional attribution as olfactory or chemotactic sensors to these receptors should not be seen either as a cause conditioning receptor gene expression, or as a final effect resulting from genetically predetermined programs, but as a direct consequence of the environmental conditions olfactory receptor genes have explored during evolution. The association of odorant patterns with specific environmental or contextual situations makes their relationship semiotically triadic, due to the emergence of an interpretant capable of perceiving odorants as meaningful signs out of a noisy background. This perspective highlights the importance of odorant-receptor relationships as respect to the properties of the interacting partners. It is our contention that only when taken together can these different explanatory strategies provide a realistic account of how olfactory receptor genes have been structurally and functionally modified during evolution. (shrink)

Mental Imagery, whereby we experience aspect of a perceptual scene or perceptual object in the absence of direct sensory stimulation is ubiquitous. Often the existence of mental imagery is demonstrated by asking one’s reader to volitionally generate a visual object, such as closing ones eyes and imagining an apple. However, mental imagery also arises in auditory, tactile, interoceptive, and olfactory cases. A number of influential philosophical theories have attempted to explain mental imagery in terms of belief-based forms of representation (...) using the Dependence Thesis, dependence upon means of access, such as enactivism, or in terms of the similarity of content with perceptual processing. The focus of this paper concerns the later approach and in particular assessing if Nanay’s promissory note that his theory is applicable to modalities other than vision, such as smell, seems likely to be of theoretical tender. The thesis argued for in this paper is that olfactory imagery exists and is best accounted for by considering it as a type of perceptual processing with a unique representational format relative to the olfactory perceptual modality. The paper concludes by summarizing the applicability of Nanay’s theory of mental imagery for olfaction and suggests some further issues that arise when transitioning to multi-modal mental imagery. (shrink)

This chapter argues that olfactory experiences represent either everyday objects or ad hoc olfactory objects as having primitive olfactory properties, which happen to be uninstantiated. On this picture, olfactory experiences reliably misrepresent: they falsely represent everyday objects or ad hoc objects as having properties they do not have, and they misrepresent in the same way on multiple occasions. One might worry that this view is incompatible with the plausible claim that olfactory experiences at least sometimes (...) justify true beliefs about the world. This chapter argues that there is no such incompatibility. Since olfactory experiences reliably misrepresent, they can lead to true and justified beliefs about putatively smelly objects. (shrink)

Domestic eco-efficient technologies, such as recycling bins and compact florescent light bulbs, are integral to the eco-modernisation project. To date, however, little research has examined their role in the production of 'sustainable citizens'. In response, this paper explores the productivities of commonplace domestic objects. It draws on qualitative research into a Sydney-based sustainable living programme called 'GreenHome', to examine how participants' environmental ethics became articulated through objects' use. This forges a form of embodied 'techno-ethics' that permeates socio-material relations beyond the (...) immediate. Therefore, this examination of the quotidian deployment of eco-efficient technologies, whilst not denying the problematic nature of technologically-dependant futures, suggests some positive outcomes from individuals' enrolment in domestic eco-modernisation. (shrink)

Several theorists argue that one does not experience something as being at or coming from a distance or direction in olfaction. In contrast to this, I suggest that there can be a variety of spatial aspects of both synchronic and diachronic olfactory experiences, including spatial distance and direction. I emphasise, however, that these are not aspects of every olfactory experience. Thus, I suggest renouncing the widespread assumption there is a uniform account of the nature, including the spatial nature, (...) of what is experienced in olfactory experience. (shrink)

In the contemporary analytic discussions concerning human olfactory perception, it is commonly claimed that (1) olfactory experiences are representations having content and (2) olfactory experiences represent odours, like coffee odour or vanilla odour. However, despite these common assumptions, there seems to be an ontological controversy between two views: the first states that odours are perceptually represented as features and the second states that they are represented as objects. In this paper, I aim to systematically address the Bfeature (...) or object^ status of represented odours by concerning whether odours are represented (a) as subjects of properties, (b) as mereological wholes, and (c) entities persisting in a way characteristic for objects. I argue that olfactorily represented odours constitute a sui generis category and cannot be easily classified as objects or features. Such investigations constitute a step in establishing whether various human modalities are unified by organising the environment according to the same categories. (shrink)

Although vision is the de facto model system of consciousness research, studying olfactory consciousness has its own advantages, as this collection of articles emphatically demonstrates. One advantage of olfaction is its computational and phenomenological simplicity, which facilitates the identification of basic principles. Other researchers study olfactory consciousness not because of its simplicity, but because of its unique features. Together, olfaction's simplicity and its distinctiveness make it an ideal system for testing theories of consciousness. In this research topic, the (...) results of recent research into olfactory consciousness are presented. (shrink)

It has been suggested that there maybe no olfactory illusions. This manuscript examines this claim and argues that it arises because olfactory illusions are not typically accompanied by an awareness of their illusory nature. To demonstrate that olfactory illusions do occur, the relevant empirical literature is reviewed, by examining instances of where the same stimulus results in different percepts, and of where different stimuli result in the same percept. The final part of the manuscript evaluates the evidence (...) favoring the existence of olfactory illusions, and then examines why they may not typically be accompanied by awareness. Three contributory mechanisms are discussed, relating to difficulty of verification and paucity of olfactory knowledge, the role of change blindness, and restricted access consciousness in this sense. (shrink)

The philosophy of perception has been dominated by vision, with very little discussion of the chemical senses – olfaction and gustation. In this second entry of a pair on olfactory experience, I consider what olfaction has to tell us about two issues: the nature of perceptual objects and the nature of perceptual properties and, in particular, the secondary qualities. Given the scant work on olfaction in the philosophical literature, my discussion not only surveys what philosophers have said about olfaction (...) so far, but considers the most plausible views and/or most pressing questions in each area of inquiry. (shrink)

Much of the philosophical work on perception has focused on vision. Recently, however, philosophers have been turning their attention to the ‘other modalities’. In a pair of entries, I consider olfaction—a sense modality that, along with gustation, has been largely overlooked by philosophers. In this first entry, I consider the challenge that olfactory experience presents to upholding a representational view of the sense modalities. It is common for philosophers to think that visual experience is world‐directed and, in particular, that (...) it is representational. World‐directed views contrast with subjectivist views—views according to which experiences are raw feels or mere sensations. Unlike visual experience, olfactory experience doesn't obviously support a representational view. Indeed, given its phenomenology, a subjectivist view of olfactory experience might seem unavoidable. But it is not. Once we begin to unravel ourselves from the dominant visual model of perception, we see that there is a representational view available that honors the phenomenology of olfactory experience. In turn, we learn that although there are some basic similarities between visual experience and olfactory experience, there are significant differences that prevent us from making easy generalizations from the visual case. (shrink)

The Westermarck effect (sexual inhibition among individuals raised together) is argued to be mediated olfactorily. Various animals, including humans, distinguish among individuals by scent (significantly determined by MHC genotype), and some avoid cosocialized associates on this basis. Possible models of olfactory mechanisms in humans are evaluated. Evidence suggests aversions develop during an early sensitizing period, attach to persons as much as to their scents, and are more powerful among females than among males. Adult to child aversions may develop similarly, (...) but more likely result from stimulus generalization. This hypothesis accords with current evidence and yields testable predictions (e.g., anosmia will prevent inhibition) that, should they be supported, will conclusively ground the Westermarck effect in a biological mechanism. (shrink)

Much of the philosophical work on perception has focused on vision, with very little discussion of the chemical senses—olfaction and gustation. In this paper, I consider the challenge that olfactory experience presents to upholding a representational view of the sense modalities. Given the phenomenology of olfactory experience, it is difficult to see what a representational view of it would be like. Olfaction, then, presents an important challenge for representational theories to overcome. In this paper, I take on this (...) challenge and argue for a representational account of olfactory experience that honors its phenomenology. (shrink)

Visual experience is often characterised as being essentially spatial, and auditory experience essentially temporal. But this contrast, which is based upon the temporal structure of the objects of sensory experience rather than the experiences to which they give rise, is somewhat superficial. By carefully examining the various sources of temporal variation in the chemical senses we can more clearly identify the temporal profile of the resulting smell and taste (aka flavour) experiences. This in turn suggests that at least some of (...) the objects of olfactory experience have significant temporal structure, including interactions between odorants and the body’s own sensory systems. This can help to inform our understanding not only of the metaphysics of olfaction, but the temporal structure of sensory processing and experience in other sense-modalities, including vision and audition. (shrink)

Amodal completion is the representation of those parts of the perceived object that we get no sensory stimulation from. While amodal completion is rife and plays an essential role in all sense modalities, philosophical discussions of this phenomenon have almost entirely been limited to vision. The aim of this paper is to examine in what sense we can talk about amodal completion in olfaction. We distinguish three different senses of amodal completion – spatial, temporal and feature-based completion – and argue (...) that all three are present and play a significant role in olfaction. (shrink)

Cannabis sativa L. is grown and marketed under a large number of named strains. Strains are often associated with phenotypic traits of interest to consumers, such as aroma and cannabinoid content. Yet genetic inconsistencies have been noted within named strains. We asked whether genetically inconsistent samples of a commercial strain also display inconsistent aroma profiles. We genotyped 32 samples using variable microsatellite regions to determine a consensus strain genotype and identify genetic outliers for four strains. Results were used to select (...) 15 samples for olfactory testing. A genetic outlier sample was available for all but one strain. Aroma profiles were obtained by 55 sniff panelists using quantitative sensory evaluation of 40 odor descriptors. Within a strain, aroma descriptor frequencies for the genetic outlier were frequently at odds with those of the consensus samples. It appears that within-strain genetic differences are associated with differences in aroma profile. Because these differences were perceptible to untrained panelists, they may also be noticed by retail consumers. Our results could help the cannabis industry achieve better control of product consistency. (shrink)

The common variety of incandescent light bulb has been in use for over a century, and although perhaps manufactured by highly technological systems, it is not a "high tech" device. Light bulbs are also found in nearly every home and business in this country. Because of these characteristics, the light bulb lends itself to use as a symbol of material things in modem industrial culture.

Clare Batty has recently argued that the content of human olfactory experience is 'a very weak kind of abstract, or existentially quantified content', and so that 'there is no way things smell'. Her arguments are based on two claims. Firstly, that there is no intuitive distinction between olfactory hallucination and olfactory illusion. Secondly, that olfaction 'does not present smell at particular locations', and 'seems disengaged from any particular object'. The present article shows both of these claims to (...) be false. It shows that naïve subjects find it quite natural to draw a distinction between olfactory hallucination and olfactory illusion. And it argues that the phenomenology of normal olfactory experience is of particular objects as having smells. Two confusions are responsible for Batty thinking otherwise: (1) Batty's examples are cases of extreme pungency, and she mistakes a peculiarity of intense perceptions for a property of olfaction more generally; (2) Batty focuses on very short time slices and so confuses limitations on the information carried by a single sniff for a limitation on the logical form of all olfactory content. (shrink)

This book reconsiders the major current topics in the philosophy of perception using olfaction as the paradigm sense. The author reveals how many of the most basic concepts of philosophy of perception are based on peculiarities of visual perception not found in other modalities, and addresses how different the philosophy of perception would be if based on olfaction. The book addresses several aspects of olfaction, including perceptual qualities, percepts, olfaction and cognitive processes, and consciousness. The first part of the book (...) considers perception with respect to its ability to guide behaviors and to make information available to cognitive processes. The author continues by addressing the differences between conscious and non-conscious olfactory perception, and presents an argument for an important role of attention in conscious processes. The book concludes by discussing the function of conscious brain processes and their link to guiding behaviors in complex situations. (shrink)

While there is a growing philosophical interest in analysing olfactory experiences, the mereological structure of odours considered in respect of how they are perceptually experienced has not yet been extensively investigated. The paper argues that odours are perceptually experienced as having a mereological structure, but this structure is significantly different from the spatial mereological structure of visually experienced objects. Most importantly, in the case of the olfactory part-structure, the classical weak supplementation principle is not satisfied. This thesis is (...) justified by referring to empirical results in olfactory science concerning the human ability to identify components in complex olfactory stimuli. Further, it is shown how differences between olfactory and visual mereologies may arise from the way in which these modalities represent space. (shrink)

Our sense of smell pervasively influences our most common behaviors and daily experience, yet little is known about olfactory consciousness. Over the past decade and a half research in both the fields of Consciousness Studies and Olfaction has blossomed, however, olfactory consciousness has received little to no attention. The olfactory systems unique anatomy, functional organization, sensory processes, and perceptual experiences offers a fecund area for exploring all aspects of consciousness, as well as a external perspective for re-examining (...) the assumptions of contemporary theories of consciousness. It has even been suggested that the olfactory system may represent the minimal neuroanatomy that is required for conscious processing. Here, we seek contributions that should serve as the foundation for future research concerning consciousness using olfaction as a model. -/- Given the variegated nature of research on consciousness, we seek original papers including review articles, original research, and theoretical contributions concerning the nature of olfactory consciousness. The scope of the special edition widely incorporates olfaction as it relates to Consciousness, Awareness, Attention, Phenomenal- or Access-Consciousness, and Qualia. Research concerning olfaction and cross-modal integration as it relates to conscious experience is also welcome. -/- As the initial foray into this uncharted area of research, we welcome contributions from across all disciplines contributing to cognitive neuroscience, including neurobiology, neurology, psychology, philosophy, linguistics, and computer sciences. It is our hope that this special edition will serve as the impetus for future interdisciplinary research on olfaction and consciousness. (shrink)

Philosophical research into olfaction often focuses on its limitations. We explore instead an underappreciated capacity of the sense of smell, namely, its role in interpersonal experience. To illustrate this, we examine how smell can enable continuing connections to deceased loved ones. Understanding this phenomenon requires an appreciation of, first, how olfaction's limitations can facilitate experiences of the deceased person and, second, how olfaction enables experiences of what we refer to as the ‘olfactory air’ of a person. This way of (...) experiencing someone privileges their status as an environmentally situated human animal. (shrink)

One of the crucial characteristics of the olfactory modality is that olfactory experiences commonly present odours as pleasant or unpleasant. Indeed, because of the importance of the hedonic aspects of olfactory experience, it has been proposed that the role of olfaction is not to represent the properties of stimuli, but rather to generate a valence-related response. However, despite a growing interest among philosophers in the study of the chemical senses, no dominant theory of sensory pleasure has emerged (...) in the case of human olfaction. The aim of this paper is to develop an argument based on the way in which olfactory valence is neurally encoded; one that demonstrates an advantage of the indicative representational approach to olfactory valence over approaches that characterise valence in terms of desires or commands. The argument shows that it is plausible to understand olfactory valence, at least in part, in terms of indicative representations. (shrink)

We can learn much about perceptual experience by thinking about how it can mislead us. In this paper, I explore whether, and how, olfactory experience can mislead. I argue that, in the case of olfactory experience, the traditional distinction between illusion and hallucination does not apply. Integral to the traditional distinction is a notion of ‘object-failure’—the failure of an experience to present objects accurately. I argue that there are no such presented objects in olfactory experience. As a (...) result, olfactory experience can only mislead by means of a kind of property hallucination. The implications of my arguments are twofold. First, we see that accounts of representational content cannot always be based on the visual model. And, secondly, we see that we must recast the notion of nonveridicality, allowing for a notion of non-veridical experience that is disengaged from any particular object. (shrink)