The Olfactory System and Profiling of Odour Stimuli - Research Proposal Example

The Influence Of Preference In The Verbal Profiling Of Odour Stimuli Allysha Ellicott [Name Of Institution] THE INFLUENCE OF PREFERENCE IN THE VERBAL PROFILING OF ODOUR STIMULI INTRODUCTION The olfactory system is characterised by having two discrete modes of stimulation (Chifala & Polzella, 2003, Rozin, 1982). Chemical stimuli can be transported to the olfactory receptors via the nose through sniffing (orthonasal perception) or via the release of volatile chemicals in the mouth during eating and drinking (Pierce & Halpern, 2004). These volatiles then ascend via the posterior nares of the nasopharynx to stimulate the olfactory receptors (retronasal perception). There are some relatively minor differences between the two modes of stimulation never the less they both result in binding to the same set of receptors (Burdach & Doty, 1987; Voirol & Daget, 1986).   WHAT ALLOWS US TO SMELL? DESCRIBING THE HUMAN OLFACTORY SYSTEM. For the purpose of this paper, the journey an odour takes from the nose into the brain is the main area of investigation. When we breathe in or sniff, odorant molecules enter the nasal passage where they bind to the receptors on the cilia that are located on the end of the olfactory receptor neurons (Hornung, 2006 cited in Hummel and Welge-Lussen, 2006). When odorants reach the olfactory receptors located in two discrete segments; one of these is accessed exclusively from the left nostril, and the other is accessed exclusively from the right which is found in the olfactory mucosa (Lanza & Clerico, 2003).  Each segment is covered with a layer of mucus that is vital for normal function (Pelosi, 2004). The mucus probably assists chemical stimuli to diffuse onto the olfactory receptor neurons, as well as removing stimuli after transduction. The receptor neurons project into the mucus, and the receptors are located on their cilia (for review, see Buck, 2004, 2000; Hildebrand & Shepherd, 2005). This is where they trigger a series of reactions that lead to the opening of ion channels in the membrane, causing an electrical signal in the cilium. This causes a change in the membrane potential at the tip of the olfactory receptors cell that in turn creates an electrical signal that flows along the axons which bundle together to form a olfactory nerve, which transmit to the olfactory bulb, the first destination of olfactory signal in the brain (Hornung, 2006 cited in Hummel and Welge-Lussen, 2006). Once the olfactory receptor neurons have reached the olfactory bulb they fan out and synapse in small round structures called glomeruli (Goldenstein, 2006).  Olfaction is unlike the wiring of other sense as olfaction is ‘ipsilateral’ meaning the right olfactory bulb receives information from the right nostril and the left olfactory bulb receives information from the left nostril, contrasted to the visual system where they cross over from right to left (Herz , 2001). Thus far, we have described the process of transduction and the organization of sensory information processing in the glomerular layer of the olfactory bulb. This information passes from the bulb into what’s commonly referred to as the olfactory trigone, which is the entry point into the brain. This olfactory tract then splits into three branches: the lateral, medial, and intermediate (Heimer, Van Hoesen, & Rosene, 2005).  Although well documented in animals the intermediate and medial branches are still elementary in research in humans (Gottfried, 2006, cited in Hummel and Lussen, 2006). The lateral branch is the most important, and projects to the entorhinal and piriform cortex and the amygdaloid complex, all of which are primarily located between the frontal and temporal lobe (Jones-Gotman & Zatorre, 2001). In addition, the piriform cortex is connected to the limbic system which is the brain structure responsible for emotion. The chief limbic structures that communicate with the olfactory system are the amygdale, hippocampus, and hypothalamus (Herz, 2001).  Three important sets of projections stem from these olfactory paleocortical areas: to the hypothalamus, to the mediodorsal nucleus of the thalamus, and to prefrontal cortex (Haberly, 1985 (2006). These latter two structures also project to each other, and the prefrontal cortex has reciprocal projections back to the piriform cortex. What arises from these olfactory structures unite on the orbital prefrontal cortex, agrandular insula, other amygdale subnuclei, thalamus, hypothalamus, basal ganglia, and hippocampus. This complex network of connections provides the neurological basis for odor-guided regulation and perception of behaviour, feeding, emotion, autonomic states and memory (Gottfried, 2006, cited in Hummel and Lussen, 2006). It is useful to draw a distinction between taste and smell, because these terms are commonly confused as they share many similarities.  Taste is an anatomically discrete sense from smell and is characterised by four types of sensation (sweet, sour, salty, and bitter [and possibly a fifth, umami]), which are detected by receptors or ion channels located primarily on the tongue, but is influenced by the stimulation of the olfactory receptors (Goldstein, 2002). Olfactory information is received by the orbitaofrital cortex which also receives taste information and the location within the brain where by flavor is interoperated (Herz, 2001). The combination of nasal and oral stimulation is what creates the impression of flavor. Most basic tastants like sodium chloride, sucrose, quinine, and citric acid have no smell, just as many odor stimuli completely lack taste. The perception of flavor is typically confirmed, by placing a substance with a distinctive taste such a chewing gum or coffee on the tongue while the nose is firmly pinched to prevent retronasal olfaction. Flavour is difficult to identify, this is due to odour stimuli and is prevented from reaching the olfactory receptors by eliminating circulation of air through this channel. Both taste and smell are considered ‘gate keepers’ as they have a survival function as they can detect things the body should consume or would be bad for the body and therefore be rejected. This gatekeeper function is aided by a large emotional component, by assigning ‘good’ or ‘bad’ connotations to odors by the context they are encounted by means of semantic, social, emotional and physical associations.   Of all the senses, olfaction is predisposed to become associated with emotional meaning because of its neuroanatomical relationship with the amgala-hippocampal complex, this relationship will be discussed in length latter this paper (Herz, 2001). A further distinction is between the olfactory and nasal trigeminal systems. The nasal trigeminal system is mediated separately from the sense of smell, therefore often not appreciated as a contributing factor to olfaction. It refers to receptors located in the nasal passage and in all parts of the system that come into contact with inhaled substances. These receptors have at least two effects on olfaction (see Green & Lawless, 2000). First, the sensations they evoke, such as burning, itching, and stinging, are experienced as part of the spectrum of olfactory sensations (Laska, Distel, & Hudson, 2005). The trigeminal nerve is responsible for the tears produced from cutting onions or the possible sneeze from pepper. Second, trigeminal irritation appears to reduce the perceived intensity of pure odours such as acetone which is intense through to sweet rose which is mild (Cain & Murphy, 1980). This paper is primarily concerned with olfactory stimulation, however this is noteworthy in that it can causally affect the semantic profile given to an odor. Odours that do not stimulate the trigeminal system are extremely rare but include vanilla and hydrogen sulfide (rotten eggs) (Herz, 2001). Most general theories of imagery acknowledge the existence of imagery systems for modalities such as auditory and motor systems, though most of the research has been within the visual modality (Bensafi and Rouby, 2007). Although research has not always supported the existence of an olfactory image system, some research suggests that such a system may exist however it remains controversial (Bensafi and Rouby, 2007). Mental images are defined as ‘mental representations created in the absence of any extra stimulus’ (Freeman, 1981 cited in Bensafi and Rouby, 2007). Research has suggested that people can be polarised as ‘good’ or ‘bad’ imagers due to a large amount of variation in a persons ability to mentally evoke smells. Furthermore, verbal labels are not associated with odors as easily as they are with visual or other verbal stimuli. THE CONNECTION BETWEEN SENSES IN THE BRAIN It may be important to note that olfactory neurons happen to be unmyelinated, building olfaction the less paced of every one of the senses. It not merely takes the brain la lot more time to recognize olfactory spurs; the feeling of an aroma also persists for better lengths of moments than do vibrations of visualization or audition. The information that olfactory receptors are the single sensory receptors openly bare to the atmosphere may also assist elucidates the association connecting olfaction and memory. It may be that since olfactory receptors most voluntarily accept information from the outside world and for that reason are voluntarily competent to cipher reminiscences for effects like emotion or actions. It is first important to understand the nature of olfactory memory. Surely more investigation has been carried out in regions of visual and auditory knowledge but still a lot of qualities of odor reminiscence have yet to be definite. For instance, storeroom and decompose processes, individuality of reminiscence processes, are not yet implicit with reverence to olfaction (1996). Neurological imaging techniques could supplementary purify our accepting of the method odor memory works. Researchers asserted that odor memory is more than just a short-term constituent; more fresh research has maintained the subsistence of olfactory short-term remembrance (White & Treisman, 1997). Even though there is no proof for olfactory predominance (the experience in which stimuli offered at the start of a trial is memorized best), White and Treisman's experimentation does present momentous support for regency in olfaction (1997). The researchers elucidated this pronouncement by declaring that dominance is accounted for by practice, "a cognitive procedure that may not be obtainable for odours" (1997). WHAT IS IT THAT WE SMELL? THE COMPOSITION OF ODORANTS. There has been a spike in research in olfaction over the past 10 years, however many details are still poorly understood as to how the molecule composition of an odorant translates into the psychological perception of olfaction (Herz, 2001; Zarzo and Stanton, 2006). Most everyday smells are comprised of a mixture of different air born components. The smell of chocolate is comprised of hundreds of volatile organic compounds, yet the olfactory system synthesises this into one odour. Due to the nature of odour perception, humans have great difficulty in identifying specific components within an odour blend. The theory of pattern activation is a widely regarded theory, however not yet proven, where by odorant receptors have different shapes (in a similar fashion to a lock and key method). How well an odour molecule is detected is determined by how well it fits into an olfactory receptor. Once a satisfactory number of molecules have stimulated a receptor it then fires an action potential. With biochemical and physiological evidence suggesting different patterns produce different electoral firings in the olfactory bulb whereby the theory states the activity in the olfactory bulb determines the scent we perceive (chocolate has a different pattern to vinegar) (Herz, 2001).  Only certain types of chemicals appear to be effective stimuli, that is, stimuli detectable by the olfactory system. First, they must fall within a certain range of solubility. Methane, for example, is relatively insoluble in water and odourless but can be smelled by divers as solubility increases with higher air pressure (Laffort & Gortan, 1987). Volatility, and hence molecular size, is a further limitation, with few chemicals being odorous if they exceed a molecular weight of around 300 (Ohloff, Winter, & Fehr, 2000). Studies have shown that even professional (wine tasters, perfumists, and sensory analysis) have no discriminatory advantage. Morrot, Brochet & Dubourdieu (2001) examined the study of enological tasting (wine tasters) who provide information about the visual, olfactory and gustatory properties of wine. By disguising the colour of wine consequently the categorisation given to the wine (as being a white or red wine) was primarily determined by hedonic criteria. Also in this same experiment experimenters changed the colour of the wine from white to red, with the tasters perceiving it as having the odour of a red wine, suggesting that it may be difficult to rely relying on visual sensory information. In general odour perception is highly plastic and depends on the sensory context, learning and past experience. WHY DO WE KNOW WHETHER WE LIKE OR DISLKIE WHAT WE SMELL? INVESTIGATING THE PERCEPTION OF SMELL. In general, society would like to perceive individuals as almost robotic or analytical when making perceptions about people, places and things. Social psychology has many plausible theories that inform human behaviour, specifically social cognition which ‘focuses on the way in which cognition is affected by wider and more immediate social contexts and how cognition affects our social behaviour’ (Vaughan and Hogg, 2005 p. 26). As such impression formation and person’s perceptions are important aspects of social cognition. As a result humans are influenced by an array of individual experiences and attitudes which precedes our behaviour and guides our choices, decisions and actions. What makes society able to believe individuals as analytical is that collectively we are often unaware of implicit attitudes, or the degree of social desirability bias individuals hold. Social psychology been able to successfully demonstrate that attitudes are learned rather than innate. However within olfactory perception there is a long standing debate as to whether our hedonic response are in fact innate or learned (Herz, Beland and Hellerstein, 2004). In odour research, a preference for a particular stimulus like an odour is a type of attitude, however it is labeled hedonic perception which refers to our attitude or state of mind as to whether we like or dislike something for example some people like the smell of skunks. The innate view of hedonic perception suggests we are born with a predisposition to like or dislike various smells, though widely held for animals it has not been validated for humans. The work of Sarah Herz (list all her work that I use in bib) has posed a convincing argument that olfaction is set up through experience and learning, whereby meaning becomes attached to an odor. To validate this theory Mennella and colleagues (1995) found infants of mothers who consumed distinctive smelling volatiles (garlic, cigarette smoke, alcohol) during pregnancy can scent the chemical composition of her amniotic fluid. With infants having an arbitrary pairing of these scents compared to infants who had not been exposed to these odors. Cross culturally research has confirmed hedonic evaluations exist for common everyday odors and odors considered offensive for example not everyone finds a skunk offensive. In the United States Military researchers tried to create a universally offensive ‘stink bomb’ however there was no unanimously considered unpleasant odor (Herz, 2001). There is also neuroantomy evidence to suggest the orbitfrontal cortex (the area of the brain responsible for processing olfaction) is also the area whereby the brain assigns hedonic meaning (Davidson, 2000 cited in Herz, et al, 2004). TO BE ENDED WITH CONSCIOUS PERCEPTION IS A INDIVIDUAL EXPERIENCE Within olfaction researchers there is individual variation in odor perceptions (eg intensity, quality, sensitivity). Contemporary theories in human cognition and perception, such as the ideas expressed in detection theory, attempt to account for the variability within individuals (Dalton, year to be confirmed). Detection theory suggests that ‘initial reception (sensitivity) and subsequent evaluations (criterions) of a stimulus are determinants of the perceptual response’ (Dalton, year to be confirmed, p. 448). Several experiments have demonstrated enhanced discrimination following mere exposure to a set of odors. Rabin (1988) had a group of participants profile a set of seven odors of low familiarity and near neutral hedonic tone using the Dravnieks (1985) Atlas of Odor profiling. In the subsequent same-different discrimination test their performance—equivalent to about 88% correct—was significantly better than that of the two nonexposed control groups. Enhancement of performance in such tests of odor discrimination can be obtained following prior exposure even when no task is required of participants. Jehl, Royet, and Holley (2003) gave different groups 0, 1, 2, or 3 exposures to sets of odors, asking participants to sniff each odor for 4 seconds and remain silent. A subsequent same-different test revealed that discrimination performance increased with prior exposure, mainly reflecting decreased false-alarm rates. The strength of such study is it allows a plausible conclusion that the degree to which an odor feels familiar or novel appears, along with its intensive, qualitative, and emotional dimensions, to be an intrinsic part of odor perception. HOW DO WE DESCRIBE AN ODOUR? ODOUR PROFILING Most people have difficulty in naming an odour that they smell this is because of a difficulty in accessing relevant verbal labels; olfaction is notably a non-verbal sense than vision or hearing as both are intrinsically reliant on language. In general people can name a similar odour, an object evoking that odour, a category of smell, a place that the smell may have come from and eliciting visual image of the object or the place where they smelt it (Royet, Paugam-Moisy, Rouby, Zighed, Nicoloyannis, Amghar and Sicard, 1996). Lawless and Engen (1977) named this ‘tip of the nose’ phenomenon, parallel to the ‘tip of the tongue’ phenomenon (cited in Royet, et al., 1996). Odour profiling is an attempt to exemplify odour stimuli by their components, in order to overcome any ‘tip of the nose’ difficulties. Methods for exemplifying odours have applications in a variety of disciplines such as food aromas, fragrance chemistry, and perfume research. There are two main methods that are used to produce multidimentional profiles reference odorant methods and the semantics method. In reference odorant method an odour is rated for similarities in direct comparison to a series of reference odours, whilst more objective it is time consuming method (Dravniek, 1982). In contrast semantic method is logistically simpler, allows for rapid generalisations and is more common methodology. It is the process where by words (verbs nouns) are used as to a target odours applicability to a set of odour descriptors (Dravniek, 1982). As it has been put forward in this paper, odour perception is highly emotive and varies exceedingly between individual. Consequently if open or unrestricted descriptions are used to categorise a smell, there would undoubtedly be subjective descriptors such as ‘dry, fresh, powerful, tender, or feminine’ which are all open to interpretation (Zarzo and Stanton, 2006). Olfaction industry professionals (e.g., sensory evaluation panels, expert tasters, perfumers, flavorists, and wine tasters has expressed the need for a standardized descriptive system that captures the differences between odours and promotes communication between specialists. Semantic profiling has consequently become a popular system, which a target odor is evaluated in relation to a standard list of verbal descriptors such as ‘…………… (e.g., Dravnieks, 1985). Harper, Bate-Smith, and Land (2006) pioneered the first system of this kind by collecting a large number of terms used to describe odor quality. These were then winnowed down to a set of 44 items, against which participants evaluate the target odor. Dravnieks (1985) later extended the number of items in his widely used list to 146 in favourably Atlas of Odor Profiling. There is, however, no strict limit on the number of items that could be included, apart from obvious practical considerations like participant fatigue. These systems allow an odor to be profiled quite rapidly, with participants rating each descriptor on degree of presence (effectively a similarity rating). The profile developed for a particular odor using this technique shows high test-retest reliability (Dravnieks, 1982). Noticably a key strength of Dravnieks Atlas of Odor profiling is the descriptors used are both nouns and verbs, and are drawn from other sensory modalities, particularly vision.  This is because linguistics is associated to other senses, as such olfaction rely on words; very few pertain to olfaction alone (pungent is an exception).  Thus an odour might be described in terms of the substance/object it orientated from (fishy or chocolate), or from a more general contrived group (e.g., floral, citrus, animal-like).  Simple colours might be used (e.g., green), as well as tactile labels (sharp, heavy, light), gustatory labels (sweet, sour) and even auditory labels (soft).   Descriptors can even be emotions (sickening). More recent attempts at defining primary odor qualities have also met with problems. Amoore (2001) identified terms used by chemists to describe odors. These were then analyzed to identify those most commonly used. Seven terms were identified: ethereal, camphor, minty, floral, musky, putrid, and burnt. Amoore and Venstrom (2005) found significant correlations between the terms characterizing particular chemicals and their molecular shape, suggesting seven or so primary qualities and hence receptors. However, Amoore's other approach, the identification of specific anosmias—analogous to the study of anomalous color vision—revealed a much larger number of specific anosmias (about 43 at last count; Amoore, 1982), and this finding is difficult to reconcile with the earlier conclusion of seven primaries. Overall, attempts to identify odor primaries must be judged as unsuccessful. WHAT AFFECTS THE WAY WE PROFILE AN ODOR? THE INFLUENCE OF EMOTION AND MEMORY ON HEDONIC PERCEPTION. Historically, the process of odor perception is considered a classic information-processing task being data (sensory) driven. The basic assumption of information processing is that information is encoded by sensory memory and processed through working memory and long term memory before a decision is made about the output. In contrast concept driven or ‘top down’ processing relies on information already in memory such as expectations, emotional state to guide perception. With laboratory studies making a convincing argument that ‘top down’ processing affects our perception of odours. Extending the findings to a generalized environment O’Mahoney (1978) used radio and television as a medium for informing audiences that a certain frequency could produce the perception of an odor. With many audience members making reports of discomfort and allergic reactions. As such the power of suggestion is a powerful tool in odor perception. A common western culture example is aromatherapy with the odour of lavender commonly used in bath oils and soaps due to its relaxation effects. Consequently certain individual beliefs heavy influence associations learnt about human’s perception of odours. How the individual brain routes emotion is still uncertain. Studies by means of electrophysiological and set procedures recommend that the amygdala exercises an essential character in emotional handing out in humans. The study that electrical stimulus and seizures alerts on the person amygdala regularly creates terror or other emotional rejoinders that give strong proof associating the amygdala in emotional dispensation in humans. On the other hand, sabrasion of the amygdala in humans hardly ever fabricate the gathering of emotional abnormalities connected with sets of the amygdala in non-humans, apart from when amygdala injury occurs in combination with disperse cerebral sickness. The awareness of smell is conquered by a hedonic (appeal -repulsiveness) measurement, and any contact to odorants produces healthy advancement and removal responses. For instance, the smell of an object on fire can call to mind potently moreover terror and extraction responses or pleasure and approach responses, which depends on the conditions adjoining odor perception. Such occurrence imitate the inextricable anatomical associations amid the mammalian limbic and the olfactory systems CONCLUSION Descriptor profiling is a very common technique both in research and industry (e.g., Moskowitz and Barbe1977, Chu and Resurreccion 2005). The future research should attempt to test one of the assumptions of profiling; that it is an effective analytical technique, where individuals are able to reliably extract the component qualities of an odour. Should confounding variables such as hedonic preference be identified, then it would suggest that more information needs to be gathered from participants in a profiling task, or that alternative analytical techniques might be more appropriate to characterise odours. It is hypothesised that odours that are liked by a subgroup of a panel will differ in its profile that if it is not liked. Such a finding would suggest flaws exist in the commonly accepted practice of averaging odour stimulus profiles, and that knowledge of individual preferences would allow a better understanding of the true sensory characteristics of odours. REFERENCES Bensafi, M. and C. Rouby (2007). "Individual differences in odor imaging ability reflect differences in olfactory and emotional perception." Chemical Senses 32(3): 237-244. Herz, R. S. (2001). "Ah, Sweet Skunk! We Like or Dislike What We Smell "   Retrieved 21.3.08, 2008, from http://www.dana.org/news/cerebrum/detail.aspx?id=1428. Herz, R. S. (2004). 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