Odour perception: an object-recognition approach

Object recognition is a crucial component of both visual and auditory perception. It is also critical for olfaction. Most odours are composed of 10s or 100s of volatile components, yet they are perceived as unitary perceptual events against a continually shifting olfactory background (i.e. figure-ground segregation). We argue here that this occurs by rapid central adaptation to background odours combined with a pattern-matching system to recognise discrete sets of spatial and temporal olfactory features-an odour object. We present supporting neuropsychological, learning, and developmental evidence and then describe the neural circuitry which underpins this. The vagaries of an object-recognition approach are then discussed, with emphasis on the putative importance of memory, multimodal representations, and top-down processing.     

Dispositions and interferences

In this paper I argue that olfactory experience, like visual experience, is exteroceptive: it seems to one that odours, when one smells them, are external to the body, as it seems to one that objects are external to the body when one sees them. Where the sense of smell has been discussed by philosophers, it has often been supposed to be non-exteroceptive. The strangeness of this philosophical orthodoxy makes it natural to ask what would lead to its widespread acceptance. I argue that philosophers have been misled by a visuocentric model of what exteroceptivity involves. Since olfaction lacks the spatial features that make vision exteroceptive the conclusion that olfaction is nonexteroceptive can appear quite compelling, particularly in the absence of an alternative model of exteroceptivity appropriate to olfaction. I offer a model according to which odours seem to be external to the body because they seem to be brought into the nose from without by sniffing and breathing through the nostrils. I argue that some natural-seeming objections to this model rely on substantive assumptions about how the senses are distinguished from one another, and how perceptual experience is put together out of its modality-specific parts, that require defence.     

Editorial Notice

Abstract

John McDowell has claimed that the rational link between perceptions and empirical judgements allows us to perceive objects as belonging to a wider reality, one which extends beyond the objects perceived. In this way, we can be said to have a perceptual awareness of the world. I argue that McDowell's account of this perceptual awareness does not succeed. His account as it stands does not have the resources to explain how our perceptions can present objects as belonging to a wider reality, regardless of the judgements we make about that reality. I suggest that we can give a better account of this perceptual awareness of the world by appealing to transcendental phenomenology. A phenomenological study of perceptual experiences describes how they are structured by a sense of the perceived objects as belonging to a world containing other objects of possible perception. I shall outline this sense we have of the world, and argue that it allows us to perceive objects as belonging to a wider reality. Transcendental phenomenology can thus help to explain our perceptual awareness of the world.     

Smelling lessons

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 this paper, I consider the question: does human olfactory experience represents objects as thus and so? If we take visual experience as the paradigm of how experience can achieve object representation, we might think that the answer to this question is no. I argue that olfactory experience does indeed represent objects—just not in a way that is easily read from the dominant visual case.     

Making sense of the libertarian’s semantic claim about agential phenomenology

Libertarians about free will sometimes argue for their position on the grounds that our phenomenology of action is such that determinism would need to be false for it to be veridical. Many, however, have thought that it would be impossible for us to have an experience that is in contradiction with determinism, since this would require us to have perceptual experience of metaphysical facts. In this paper I show how the libertarian claim is possible. In particular, if experience depicts the world such that there is more than one physically possible future, then determinism would need to be false for that experience to be veridical. I show that we have experiences, or perceptual episodes, of this kind on the basis of recent work in the study of perception. Theorists in this area have argued that we have vision-for-action, and that what we visually perceive are not just objects but also possibilities for action. If we experience that it is possible that we ?, then we also experience that it is possible that we not ?. Furthermore, we probably experience more than one possibility for action at any one moment. I argue that these are physical possibilities, and therefore that we experience the world such that there is more than one physically possible future. So the libertarian claim about the semantics of agential phenomenology is highly plausible, even if this does not entail libertarianism.     

A Breath of Fresh Air: Absence and the Structure of Olfactory Perception

The question of whether we can perceive absences, in addition to ‘positives’, has received recent attention in the literature on the nature of vision and audition. The aim is to demonstrate that there can be objectless forms of perceptual consciousness; specifically, to show that such episodes can be distinguished from those in which there is merely no perception at all. The current article explores this question for the domain of olfaction, and argues that there can be experiences of the absence of odours, in addition to positive smell perception. Doing so sheds light upon the structure and spatial content of olfaction.     

Perceptual consciousness plays no epistemic role

It is often assumed that perceptual experience provides evidence about the external world. But much perception can occur unconsciously, as in cases of masked priming or blindsight. Does unconscious perception provide evidence as well? Many theorists maintain that it cannot, holding that perceptual experience provides evidence in virtue of its conscious character. Against such views, I challenge here both the necessity and, perhaps more controversially, the sufficiency of consciousness for perception to provide evidence about the external world. In addition to motivating and defending the idea that unconscious perception can and does often provide evidence, I observe that whether or not perceptual phenomenology is relevant to the evidentiary status of perception depends on the nature of consciousness. And I argue that a well‐supported theory of consciousness—higher‐order thought theory—invites a striking conclusion: that perceptual phenomenology is not on its own sufficient to provide for evidence of the external world.     

The nature of perceptual constancies

Perceptual constancies have been studied by psychologists for decades, but in recent years, they have also become a major topic in the philosophy of mind. One reason for this surge of interest is Tyler Burge’s (2010) influential claim that constancy mechanisms mark the difference between perception and mere sensitivity, and thereby also the difference between organisms with genuine representational capacities and ‘mindless’ beings. Burge’s claim has been the subject of intense debate. It is becoming increasingly clear, however, that we cannot hope to settle this debate (as well as related debates in the philosophy of mind) without a clear and substantive theoretical account of what perceptual constancies are. In the first part of this paper, I argue that the standard definitions in the literature fall short of providing such an account. Still, as I aim to show in the second part of the paper, by taking a closer look at some of the paradigm examples, it is possible to construct a plausible general account of perceptual constancies that is both clear and substantive, and that can serve as a firm foundation for settling debates like the dispute about Burge’s ‘constancy mechanism criterion’ for perception.     

On A. D. Smith’s constancy based defence of direct realism

This paper presents an argument against A D Smith’s Direct Realist theory of perception, which attempts to defend Direct Realism against the argument from illusion by appealing to conscious perceptual states that are structured by the perceptual constancies. Smith’s contention is that the immediate objects of perceptual awareness are characterised by these constancies, which removes any difficulty there may be in identifying them with the external, or normal, objects of awareness. It is here argued that Smith’s theory does not provide an adequate defence of Direct Realism because it does not adequately deal with the difficulties posed by the possibility of perceptual illusion. It is argued that there remain possible illusory experiences where the immediate objects of awareness, which in Smith’s account are those characterised by perceptual constancies, cannot be identified with the external objects of awareness, contrary to Direct Realism. A further argument is offered to extend this conclusion to all non-illusory cases, by adapting an argument of Smith’s own for the generalising step of the Argument from Illusion. The result is that Smith’s theory does not provide an adequate Direct Realist account of the possibility of perceptual illusion.     

Up the nose of the beholder? Aesthetic perception in olfaction as a decision-making process

Is the sense of smell a source of aesthetic perception? Traditional philosophical aesthetics has centered on vision and audition but eliminated smell for its subjective and inherently affective character. This article dismantles the myth that olfaction is an unsophisticated sense. It makes a case for olfactory aesthetics by integrating recent insights in neuroscience with traditional expertise about flavor and fragrance assessment in perfumery and wine tasting. My analysis concerns the importance of observational refinement in aesthetic experience. I argue that the active engagement with stimulus features in perceptual processing shapes the phenomenological content, so much so that the perceptual structure of trained smelling varies significantly from naive smelling. In a second step, I interpret the processes that determine such perceptual refinement in the context of neural decision-making processes, and I end with a positive outlook on how research in neuroscience can be used to benefit philosophical aesthetics.     

The epistemic force of perceptual experience

What is the metaphysical nature of perceptual experience? What evidence does experience provide us with? These questions are typically addressed in isolation. In order to make progress in answering both questions, perceptual experience needs to be studied in an integrated manner. I develop a unified account of the phenomenological and epistemological role of perceptual experience, by arguing that sensory states provide perceptual evidence due to their metaphysical structure. More specifically, I argue that sensory states are individuated by the perceptual capacities employed and that there is an asymmetric dependence between their employment in perception and their employment in hallucination and illusion. Due to this asymmetric dependence, sensory states provide us with evidence.     

THE VISUAL EXPERIENCE OF CAUSATION

The thesis that we can visually perceive causal relations is distinct from the thesis that visual experiences can represent causal relations. I defend the latter thesis about visual experience, and argue that although they are suggestive, the data provided by Albert Michotte's experiments on perceptual causality do not establish this thesis. Turning to the perception of causality, I defend the claim that we can perceive causation against the objection that its arcane features are unlikely to be represented in experience.     

Spatial aspects of olfactory experience

Abstract

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.     

Phenomenal evidence and factive evidence

Perceptions guide our actions and provide us with evidence of the world around us. Illusions and hallucinations can mislead us: they may prompt as to act in ways that do not mesh with the world around us and they may lead us to form false beliefs about that world. The capacity view provides an account of evidence that does justice to these two facts. It shows in virtue of what illusions and hallucinations mislead us and prompt us to act. Moreover, it shows in virtue of what we are in a better epistemic position when we perceive than when we hallucination. In this paper, I develop the capacity view, that is, the view that perceptual experience has epistemic force in virtue of the epistemic and metaphysical primacy of the perceptual capacities employed in perception. By grounding the epistemic force of experience in facts about the metaphysical structure of experience, the capacity view is not only an externalist view, but moreover a naturalistic view of the epistemology of perceptual experience. So it is an externalist and naturalistic alternative to reliabilism. I discuss the repercussions of this view for the justification of beliefs and the epistemic transparency of mental states, as well as, familiar problem cases.     

Inter-species variation in colour perception

Inter-species variation in colour perception poses a serious problem for the view that colours are mind-independent properties. Given that colour perception varies so drastically across species, which species perceives colours as they really are? In this paper, I argue that all do. Specifically, I argue that members of different species perceive properties that are determinates of different, mutually compatible, determinables. This is an instance of a general selectionist strategy for dealing with cases of perceptual variation. According to selectionist views, objects simultaneously instantiate a plurality of colours, all of them genuinely mind-independent, and subjects select from amongst this plurality which colours they perceive. I contrast selectionist views with relationalist views that deny the mind-independence of colour, and consider some general objections to this strategy.     

Naïve realism without disjunctivism about experience

I argue that the possibility of non-perceptual experience need not compel a naïve realist to adopt a disjunctive conception of experience. Instead, they can maintain that the nature of perceptual and hallucinatory experience is the same, while still claiming that perceptual experience is presentational of the objects of perception. On such a view the difference between perceptual and non-perceptual experience will lie in the nature of the objects that are so presented. I will defend a view according to which in non-perceptual experience one is presented with mere universals, while in perceptual experience one is presented with the instantiation of a universal by a particular. This is to adopt disjunctivism about the objects of experience, about that which is apparently present in experience.     

Seeing absence

Intuitively, we often see absences. For example, if someone steals your laptop at a café, you may see its absence from your table. However, absence perception presents a paradox. On prevailing models of perception, we see only present objects and scenes (Marr, Gibson, Dretske). So, we cannot literally see something that is not present. This suggests that we never literally perceive absences; instead, we come to believe that something is absent cognitively on the basis of what we perceive. But this cognitive explanation does not do justice to the phenomenology. Many experiences of absence possess immediate, perceptual qualities. One may further argue that the ability to detect certain absences confers strong adaptive advantage and therefore must be as primitive and fundamental to humans as seeing positive things. I argue that we can literally see absences; in addition to representing objects, perception represents absences of objects. I present a model of seeing absence based on visual expectations and a visual matching process. The phenomenon of seeing absence can thus serve as an adequacy-test for a theory of perceptual content. If experiences of absence are possible, then we have another reason (following Siegel) to reject the view that perceptual content is restricted to colors and shapes. Furthermore, if the proposed account is correct, then we have grounds for dissociating seeing absence from other imagery-based phenomena termed “perceptual presence-in-absence” (Noë, Macpherson).     

The Sense of Touch: From Tactility to Tactual Probing

Because philosophical reflections on touch usually start from our ability to perceive properties of objects, they tend to overlook features of touch that are crucial to correct understanding of tactual perception. This paper brings out these features and uses them to develop a general reconception of the sense of touch. I start by taking a fresh look at our ability to feel, in order to reveal its vital role. This sheds a different light on the skin's perceptual potential. While it is commonly observed that tactile experiences have two intentional objects, an external object and one's own body, I will advance a more accurate alternative: in tactile experiences, one becomes aware of what one's body undergoes. This alternative not only fits better with tactility's vital role; it is also key to explaining how active touching provides for a unique contribution to our perceptual relation to material objects. By thus connecting tactility's vital role to the way we rely on touch while manipulating objects, this essay offers a cross-sectional survey of our tactile powers that reveals the interplay between sensing and touching.     

On the Perception of Structure

Many of the objects that we perceive have an important characteristic: When they move, they change shape. For instance, when you watch a person walk across a room, her body constantly deforms. I suggest that we exercise a type of perceptual constancy in response to changes of this sort, which I call structure constancy. In this paper I offer an account of structure constancy. I introduce the notion of compositional structure, and propose that structure constancy involves perceptually representing an object as retaining its compositional structure over time. I argue that compositional structure is represented in visual phenomenology, and I also assemble empirical evidence in support of the claim that compositional structure is recovered by the visual system. Finally, I draw out consequences of this account. I argue that structure constancy has implications for the predictive capacities of perception, and that the phenomenon places important constraints on viable accounts of both the format and reference frame of visual experience.