The mind's nose: Effects of odor and visual imagery on odor detection

fNIRS a novel neuroimaging tool to investigate olfaction, olfactory imagery, and crossmodal interactions: a systematic review

Olfaction is understudied in neuroimaging research compared to other senses, but there is growing evidence of its therapeutic benefits on mood and well-being. Olfactory imagery can provide similar health benefits as olfactory interventions. Harnessing crossmodal visual-olfactory interactions can facilitate olfactory imagery. Understanding and employing these cross-modal interactions between visual and olfactory stimuli could aid in the research and applications of olfaction and olfactory imagery interventions for health and wellbeing. This review examines current knowledge, debates, and research on olfaction, olfactive imagery, and crossmodal visual-olfactory integration. A total of 56 papers, identified using the PRISMA method, were evaluated to identify key brain regions, research themes and methods used to determine the suitability of fNIRS as a tool for studying these topics. The review identified fNIRS-compatible protocols and brain regions within the fNIRS recording depth of approximately 1.5 cm associated with olfactory imagery and crossmodal visual-olfactory integration. Commonly cited regions include the orbitofrontal cortex, inferior frontal gyrus and dorsolateral prefrontal cortex. The findings of this review indicate that fNIRS would be a suitable tool for research into these processes. Additionally, fNIRS suitability for use in naturalistic settings may lead to the development of new research approaches with greater ecological validity compared to existing neuroimaging techniques.

Odour-imagery ability is linked to food craving, intake, and adiposity change in humans

It is well-known that food-cue reactivity (FCR) is positively associated with body mass index (BMI)1 and weight change2, but the mechanisms underlying these relationships are incompletely understood. One prominent theory of craving posits that the elaboration of a desired substance through sensory imagery intensifies cravings, thereby promoting consumption3. Olfaction is integral to food perception, yet the ability to imagine odours varies widely4. Here we test in a basic observational study whether this large variation in olfactory imagery drives FCR strength to promote adiposity in 45 adults (23 male). We define odour-imagery ability as the extent to which imagining an odour interferes with the detection of a weak incongruent odour (the 'interference effect'5). As predicted in our preregistration, the interference effect correlates with the neural decoding of imagined, but not real, odours. These perceptual and neural measures of odour imagery are in turn associated with FCR, defined by the rated craving intensity of liked foods and cue-potentiated intake. Finally, odour imagery exerts positive indirect effects on changes in BMI and body-fat percentage over one year via its influences on FCR. These findings establish odour imagery as a driver of FCR that in turn confers risk for weight gain.

Olfactory imagery as a retrieval method for autobiographical memories

INTRODUCTION

The retrieval of autobiographical memories is influenced by several factors, such as sensory modality and the emotional salience of memory cues. This study aimed at investigating the interaction between sensory modalities (olfaction, vision) and emotional dimensions (valence, arousal) of imagery cues, on the frequency, quality, and age distribution of the autobiographical memories (AMs) elicited.

METHOD

A total of 296 females (aged between 18 and 35 years) received one out of eight brief instructions for olfactory or visual imagery. The participants were asked to create a mental image with either high arousal/positive valence, high arousal/negative valence, low arousal/positive valence, or low arousal/negative valence (e.g., 'imagine an unpleasant and arousing odor/scene'); no specific stimulus was mentioned in the instruction.

RESULTS

The approach used elicited imagery with autobiographical content in the majority of participants (78%). In terms of frequency, odor imagery, compared to visual imagery, turned out to be more effective at retrieving either unpleasant memories associated with experiences in adulthood, or pleasant childhood memories. In terms of quality, the imagery was rated as less vivid in the olfactory compared to the visual condition (irrespective of valence and arousal of the imagery instruction). Visual imagery was associated with the experience of more diverse emotions (happiness, sadness, anxiety, anger) than odor imagery, which was related primarily with disgust and happiness.

CONCLUSION

Our findings indicate that nonspecific imagery induction is a useful approach in accessing AM.

IMPLICATION

This approach presents promising clinical applications, such as in working with autobiographical memory narratives in psychotherapy.

Odor imagery but not perception drives risk for food cue reactivity and increased adiposity

Mental imagery has been proposed to play a critical role in the amplification of cravings. Here we tested whether olfactory imagery drives food cue reactivity strength to promote adiposity in 45 healthy individuals. We measured odor perception, odor imagery ability, and food cue reactivity using self-report, perceptual testing, and neuroimaging. Adiposity was assessed at baseline and one year later. Brain responses to real and imagined odors were analyzed with univariate and multivariate decoding methods to identify pattern-based olfactory codes. We found that the accuracy of decoding imagined, but not real, odor quality correlated with a perceptual measure of odor imagery ability and with greater adiposity changes. This latter relationship was mediated by cue-potentiated craving and intake. Collectively, these findings establish odor imagery ability as a risk factor for weight gain and more specifically as a mechanism by which exposure to food cues promotes craving and overeating.

'Tasting Imagination': What Role Chemosensory Mental Imagery in Multisensory Flavour Perception?

A number of perplexing phenomena in the area of olfactory/flavour perception may fruitfully be explained by the suggestion that chemosensory mental imagery can be triggered automatically by perceptual inputs. In particular, the disconnect between the seemingly limited ability of participants in chemosensory psychophysics studies to distinguish more than two or three odorants in mixtures and the rich and detailed flavour descriptions that are sometimes reported by wine experts; the absence of awareness of chemosensory loss in many elderly individuals; and the insensitivity of the odour-induced taste enhancement (OITE) effect to the mode of presentation of olfactory stimuli (i.e., orthonasal or retronasal). The suggestion made here is that the theory of predictive coding, developed first in the visual modality, be extended to chemosensation. This may provide a fruitful way of thinking about the interaction between mental imagery and perception in the experience of aromas and flavours. Accepting such a suggestion also raises some important questions concerning the ecological validity/meaning of much of the chemosensory psychophysics literature that has been published to date.

Olfactory metacognition and memory in individuals with different subjective odor imagery abilities

Imagery vividness is one of the key indicators to evaluate the ability to generate mental images. There is large inter-individual variability in olfactory imagery (OI) abilities, however, little is known about the underlying factors for individual OI abilities. Using a word cueing imagery paradigm and the trial-by-trial imagery vividness rating method, participants with high or low OI abilities (differentiated by the Vividness of Olfactory Imagery Questionnaire) completed two OI tasks with either shorter (2 s) or longer (8 s) image generation time. Participants' olfactory function, olfactory-related working memory and episodic recognition memory were measured using validated methods. Moreover, olfactory metacognition was assessed using the Odor Awareness Scale (OAS) and the Importance of Olfaction Questionnaire (IOQ). Compared to participants with high OI abilities, those with low OI abilities reported less vivid odor images during OI tasks. For participants with low OI abilities, the imagery vividness significantly improved as the image generation time increased. There was no difference regarding olfactory perception or olfactory-related memory performances between the high and the low OI ability groups. However, participants with higher OI abilities had significant higher scores on the OAS and the IOQ, indicating a superior olfactory-related metacognition. These results provide evidences supporting the underlying factors that related to variances of subjective ability of generating vivid odor mental images.

Food Neophobia, Odor and Taste Sensitivity, and Overall Flavor Perception in Food

Smell, which allows us to gather information about the hedonic value of an odor, is affected by many factors. This study aimed to assess the relationship among individual factors, odor sensitivity, and enjoyment, and to evaluate how overall flavor perception and liking in actual food samples are affected by odor sensitivity. A total of 749 subjects, from four different Italian regions, participated in the study. The olfactory capabilities test on four odors (anise, banana, mint, and pine), as well as PROP (6-n-prpyl-2-thiouracil) status and food neophobia were assessed. The subjects were clustered into three groups of odor sensitivity, based on the perceived intensity of anise. The liking and intensity of the overall flavor were evaluated for four chocolate puddings with increasing sweetness (C1, C2, C3, and C4). The individual variables significantly affected the perceived intensity and liking of the odors. Even if all of the odor sensitivity groups perceived the more intensely flavored samples as the C1 and C4 chocolate puddings, the high-sensitivity group scored the global flavor of all of the samples as more intense than the low-sensitivity group. The low-sensitive subjects evaluated the liking of the sweeter samples with higher scores than the moderate-sensitive subjects, whereas the high-sensitive subjects gave intermediate scores. In conclusion, odor sensitivity plays a pivotal role in the perception and liking of real food products; this has to be taken into account in the formulation of new products, suitable for particular categories with reduced olfactory abilities.

Sensory Cueing of Autobiographical Memories in Normal Aging and Alzheimer's Disease: A Comparison Between Visual, Auditory, and Olfactory Information

BACKGROUND

Alzheimer's disease (AD) is a chronic, neurodegenerative disease resulting in a progressive decline of autobiographical memories (AMs) which favors the development of psycho-behavioral disorders. One of the most popular psychosocial interventions in dementia care, Reminiscence Therapy, commonly uses sensory cueing to stimulate AMs retrieval. However, few empirical studies have investigated the impact of sensory stimulation on AMs retrieval in AD.

OBJECTIVE

Our goal was to determine the most relevant cue for AMs retrieval in patients with early to mild AD when comparing odors, sounds and pictures.

METHODS

Sixty AD patients, 60 healthy older adults (OA), and 60 healthy young adults (YA) participated in our study. Participants were presented with either 4 odors, 4 sounds, or 4 pictures. For each stimulus, they were asked to retrieve a personal memory, to rate it across 3 dimensions (emotionality, vividness, rarity) and then to date it.

RESULTS

Overall, results showed no clear dominance of one sensory modality over the others in evoking higher-quality AMs. However, they show that using pictures is the better way to stimulate AD patients' AM, as it helps to retrieve a higher number of memories that are also less frequently retrieved, followed by odors. By contrast, auditory cueing with environmental sounds presented no true advantage.

CONCLUSION

Our data should help dementia care professionals to increase the efficiency of Reminiscence Therapy using sensory elicitors. Other clinical implications and future directions are also discussed.

Olfactory-colour crossmodal correspondences in art, science, and design

The last few years have seen a rapid growth of interest amongst researchers in the crossmodal correspondences. One of the correspondences that has long intrigued artists is the putative association between colours and odours. While traditionally conceptualised in terms of synaesthesia, over the last quarter century or so, at least 20 published peer-reviewed articles have assessed the consistent, and non-random, nature of the colours that people intuitively associate with specific (both familiar and unfamiliar) odours in a non-food context. Having demonstrated such consistent mappings amongst the general (i.e. non-synaesthetic) population, researchers have now started to investigate whether they are shared cross-culturally, and to document their developmental acquisition. Over the years, several different explanations have been put forward by researchers for the existence of crossmodal correspondences, including the statistical, semantic, structural, and emotional-mediation accounts. While several of these approaches would appear to have some explanatory validity as far as the odour-colour correspondences are concerned, contemporary researchers have focussed on learned associations as the dominant explanatory framework. The nature of the colour-odour associations that have been reported to date appear to depend on the familiarity of the odour and the ease of source naming, and hence the kind of association/representation that is accessed. While the bidirectionality of odour-colour correspondences has not yet been rigorously assessed, many designers are nevertheless already starting to build on odour-colour crossmodal correspondences in their packaging/labelling/branding work.

Expertise Shapes Multimodal Imagery for Wine

Although taste and smell seem hard to imagine, some people nevertheless report vivid imagery in these sensory modalities. We investigate whether experts are better able to imagine smells and tastes because they have learned the ability, or whether they are better imaginers in the first place, and so become experts. To test this, we first compared a group of wine experts to yoked novices using a battery of questionnaires. We show for the first time that experts report greater vividness of wine imagery, with no difference in vividness across sensory modalities. In contrast, novices had more vivid color imagery than taste or odor imagery for wines. Experts and novices did not differ on other vividness of imagery measures, suggesting a domain-specific effect of expertise. Critically, in a second study, we followed a group of students commencing a wine course and a group of matched control participants. Students and controls did not differ before the course, but after the wine course students reported more vivid wine imagery. We provide evidence that expertise improves imagery, exemplifying the extent of plasticity of cognition underlying the chemical senses.

Study on the release and sensory perception of encapsulated d-limonene flavor in crystal rock candy using the time-intensity analysis and HS-GC/MS spectrometry

This research was conducted to evaluate encapsulated d-limonene perception and release in rock candy. Microcapsules with wall materials of 75/25 of gum Arabic/Maltodextrin by 20% of wall materials) were produced for using in rock candy. To evaluate the flavor release from rock candy by time-intensity method, a model system was developed and time-intensity sensory evaluation was conducted by trained sensory panelists in order to determine the effect of three different matrices (water, water and flavored rock candy, and water with flavored rock candy and citric acid (pH = 3) at three serving temperatures (10, 45, and 75°C) on the perception of d-limonene release. Results showed that release of d-limonene from flavored rock candy with acid citric (pH = 3) at 75°C had the highest perceived sensation whereas the matrix of microcapsule in water at 10°C had the lowest perception. On the other hand, increasing the temperature from 10 to 75°C had significant effects on the release and perception of d-limonene (p < .05). Headspace gas chromatography-mass spectrophotometry confirmed results from time-intensity sensory evaluation, which indicated that the release of d-limonene increased in the presence of sucrose and citric acid (pH = 3).

The format of mental imagery: from a critical review to an integrated embodied representation approach

The issue of the format of mental imagery is still an open debate. The classical analogue (depictive)-propositional (descriptive) debate has not provided definitive conclusions. Over the years, the debate has shifted within the frame of the embodied cognition approach, which focuses on the interdependence of perception, cognition and action. Although the simulation approach still retains the concept of representation, the more radical line of the embodied cognition approach emphasizes the importance of action and clearly disregards the concept of representation. In particular, the enactive approach focuses on motor procedures that allow the body to interact with the environment, whereas the sensorimotor approach focuses on the possession and exercise of sensorimotor knowledge about how the sensory input changes as a function of movement. In this review, the embodied approaches are presented and critically discussed. Then, in an attempt to show that the format of mental imagery varies according to the ability and the strategy used to represent information, the role of individual differences in imagery ability (e.g., vividness and expertise) and imagery strategy (e.g., object vs. spatial imagers) is reviewed. Since vividness is mainly associated with perceptual information, reflecting the activation level of specific imagery systems, whereas the preferred strategy used is mainly associated with perceptual (e.g., object imagery) or amodal and motor information (e.g., spatial imagery), the format of mental imagery appears to be based on dynamic embodied representations, depending on imagery abilities and imagery strategies.

Are Olfactory Images Sensory in Nature?

We investigated the features of olfactory mental images by comparing odour images with perceptual and semantic representations. Participants who were assigned to three groups made similarity judgments about 17 common odours by smelling odours, imagining odours, or on the basis of the meaning of odour source names. In the smelling group, every pair of odours was compared. In the imagining group, imagined odours were compared twice, both before and after associative learning of the odour/name combinations. In the meaning group, the odour source names were compared in terms of general word meanings. Nonmetric multidimensional scaling analysis was applied to each group of similarity data and three-dimensional sensory, mental, and semantic spaces were composed. 17 elements in the mental and semantic spaces were super-imposed onto the sensory space by Procrustes rotation. We found that the averaged distances of the 17 elements between the sensory and the mental spaces (either before or after learning) were smaller than those between the sensory and semantic spaces. We suggest that odour images have sensory features, especially after associative learning between perceived odours and their names.

The inability to self-evaluate smell performance. How the vividness of mental images outweighs awareness of olfactory performance

To rate one’s individual olfactory performance is difficult and in many cases differs clearly from validated objective olfactory performance measures. This study aimed to investigate the basis for this measurement drift between objective and subjective olfactory performance evaluation. In absence of an actual odor, one may imagine an olfactory stimulus to evaluate his subjective olfactory performance. Therefore, the impact of the vividness of mental images on self-evaluation of smell performance in patients with mild to severe olfactory dysfunction and healthy controls was investigated. Fifty-nine patients with peripheral olfactory dysfunction ranging from reduced olfactory function (hyposmia) to complete loss of olfactory perception (anosmia) and 16 healthy controls were included. Olfactory performance was assessed using the Sniffin’ Sticks battery, the vividness of olfactory mental images was evaluated using the vividness of olfactory imagery questionnaire (VOIQ). Decreased vividness of odor images was obtained for anosmic patients, and a trend of poorer odor imagery was determined in hyposmic patients. Multiple regression analyses revealed the VOIQ score as significant predictor for olfactory self-evaluation for hyposmic patients and healthy controls. In contrast, for anosmic patients, the only significant predictor for self-rating of olfactory performance was the threshold-detection-identification (TDI) score, measuring overall olfactory performance. The results of this study indicate that sensory perception and mental images are closely related to each other. Furthermore, subjects who were able to perceive odors, even to a smaller extent, rely on the vividness of their mental odor images to evaluate their olfactory performance. In contrast, anosmic patients rather trust in their knowledge that they are not able to perceive odors. We are therefore able to subjectively rate our olfactory performance levels, if we are not able to perceive odors, but not if we are able to perceive olfactory input.

Characterizing olfactory binary mixture interactions in Fischer 344 rats using behavioral reaction times

Response times provide essential subthreshold perceptual data that extend beyond accuracy alone. Behavioral reaction times (RTs) were used to characterize rats' ability to detect individual odorants in a series of complimentary binary odorant mixture ratios. We employed an automated, liquid-dilution olfactometer to train Fischer 344 rats (N = 8) on an odor identification task using nonreinforced probe trials. Binary mixture ratios composed of aliphatic odorants (citral and octanol) were arranged such that relative contributions of the 2 components varied systematically by a factor of 1% (v/v). Odorant concentrations for the target (S+), control (S-), and mixture (S+:S-) odorants were presented relative to threshold for each rat. Rats were initially trained to respond by licking at a spout to obtain liquid reward for either citral or octanol as the reinforced target (S+) odorant. After achieving 100% accuracy, rats were transferred to variable ratio (VR 2) reinforcement for correct responding. Nonreinforced probe trials (2 per block of 22 trials) were tested for each mixture ratio and recorded as either S+ (rats lick-responded in the presence of the mixture) or S- (rats refrained from licking), thereby indicating detection of the trained, S+ odorant. To determine the perceived salience for each ratio, RTs (latency from odorant onset to lick response) were recorded for each trial. Consistent with previous studies, RTs for both odorants were shortest (~150-200ms) when the probe trials consisted of a single, monomolecular component. Binary mixtures that contained as little as 1% of the S-, nontarget odorant, however, were sufficiently different perceptually to increase behavioral RTs (i.e., rats hesitated longer before responding); RTs changed systematically as a function of the binary ratio. Interestingly, the rate of RT change was dependent on which odorant served as the S+, suggesting an asymmetric interaction between the 2 odorants. The data demonstrate the value of behavioral RT as a sensitive measure of suprathreshold perceptual responding.

Smelling phenomenal

Qualitative-consciousness arises at the sensory level of olfactory processing and pervades our experience of smells to the extent that qualitative character is maintained whenever we are aware of undergoing an olfactory experience. Building upon the distinction between Access and Phenomenal Consciousness the paper offers a nuanced distinction between Awareness and Qualitative-consciousness that is applicable to olfaction in a manner that is conceptual precise and empirically viable. Mounting empirical research is offered substantiating the applicability of the distinction to olfaction and showing that olfactory qualitative-consciousness can occur without awareness, but any olfactory state that we are aware of being in is always qualitative. Evidence that olfactory sensory states have a qualitatively character in the absence of awareness derives from research on mate selection, the selection of social preference for social interaction and acquaintances, as well as the role of olfactory deficits in causing affective disorders. Furthermore, the conservation of secondary processing measures of olfactory valence during olfactory imagery experiments provides verification that olfactory awareness is always qualitatively conscious-all olfactory consciousness smells phenomenal.

The fate of the inner nose: odor imagery in patients with olfactory loss

Cerebral activations during olfactory mental imagery are fairly well investigated in healthy participants but little attention has been given to olfactory imagery in patients with olfactory loss. To explore whether olfactory loss leads to deficits in olfactory imagery, neural responses using functional magnetic resonance imaging (fMRI) and self-report measures were investigated in 16 participants with acquired olfactory loss and 19 control participants. Participants imagined both pleasant and unpleasant odors and their visual representations. Patients reported less vivid olfactory but not visual images than controls. Results from neuroimaging revealed that activation patterns differed between patients and controls. While the control group showed stronger activation in olfactory brain regions for unpleasant compared to pleasant odors, the patient group did not. Also, activation in critical areas for olfactory imagery was correlated with the duration of olfactory dysfunction, indicating that the longer the duration of dysfunction, the more the attentional resources were employed. This indicates that participants with olfactory loss have difficulties to perform olfactory imagery in the conventional way. Regular exposure to olfactory information may be necessary to maintain an olfactory imagery capacity.

Same same but different: the case of olfactory imagery

In the present work we present an overview of experimental findings corroborating olfactory imagery observations with the visual and auditory modalities. Overall, the results indicate that imagery of olfactory information share many features with those observed in the primary senses although some major differences are evident. One such difference pertains to the considerable individual differences observed, with the majority being unable to reproduce olfactory information in their mind. Here, we highlight factors that are positively related to an olfactory imagery capacity, such as semantic knowledge, perceptual experience, and olfactory interest that may serve as potential moderators of the large individual variation.

The impact of expertise in olfaction

Olfactory expertise remains poorly understood, most likely because experts in odor, such as perfumers, sommeliers, and oenologists, are much rarer than experts in other modalities, such as musicians or sportsmen. In this review, we address the specificities of odor expertise in both odor experts and in a priori untrained individuals who have undergone specific olfactory training in the frame of an experiment, such as repeated exposure to odors or associative learning. Until the 21st century, only the behavioral effects of olfactory training of untrained control individuals had been reported, revealing an improvement of olfactory performance in terms of sensitivity, discrimination, memory, and identification. Behavioral studies of odor experts have been scarce, with inconsistent or inconclusive results. Recently, the development of cerebral imaging techniques has enabled the identification of brain areas and neural networks involved in odor processing, revealing functional and structural modifications as a function of experience. The behavioral approach to odor expertise has also evolved. Researchers have particularly focused on odor mental imagery, which is characteristic of odor experts, because this ability is absent in the average person but is part of a perfumer’s professional practice. This review summarizes behavioral, functional, and structural findings on odor expertise. These data are compared with those obtained using animals subjected to prolonged olfactory exposure or to olfactory-enriched environments and are discussed in the context of functional and structural plasticity.

Olfactory perception, cognition, and dysfunction in humans

The main functions of olfaction relate to finding food, avoiding predators and disease, and social communication. Its role in detecting food has resulted in a unique dual mode sensory system. Environmental odorants are 'smelled' via the external nostrils, while volatile chemicals in food-detected by the same receptors-arrive via the nasopharynx, contributing to flavor. This arrangement allows the brain to link the consequences of eating with a food's odor, and then later to use this information in the search for food. Recognizing an odorant-a food, mate, or predator-requires the detection of complex chemical blends against a noisy chemical background. The brain solves this problem in two ways. First, by rapid adaptation to background odorants so that new odorants stand out. Second, by pattern matching the neural representation of an odorant to prior olfactory experiences. This account is consistent with olfactory sensory physiology, anatomy, and psychology. Odor perception, and its products, may be subject to further processing-olfactory cognition. While olfactory cognition has features in common with visual or auditory cognition, several aspects are unique, and even those that are common may be instantiated in different ways. These differences can be productively used to evaluate the generality of models of cognition and consciousness. Finally, the olfactory system can breakdown, and this may be predictive of the onset of neurodegenerative conditions such as Alzheimer's, as well as having prognostic value in other disorders such as schizophrenia. WIREs Cogn Sci 2013, 4:273-284. doi: 10.1002/wcs.1224 For further resources related to this article, please visit the WIREs website.

A preliminary investigation of olfactory function in olfactory and auditory-verbal hallucinators with schizophrenia, and normal controls

INTRODUCTION

It is well established that people with schizophrenia have impaired olfactory perception. However, another olfactory abnormality that occurs in schizophrenia--olfactory hallucinations (OHs)--has received almost no attention.

METHODS

This preliminary study compared a small sample of olfactory (OH; n=14) and auditory-verbal (AVH; n=11) hallucinators with schizophrenia, with matched healthy controls (NC; n=21), on tests of odour detection threshold, identification, and hedonics, and bespoke tests relating to possible causes of OHs.

RESULTS

Both OH and AVH participants were equally impaired on tests of odour identification, but neither had any impairment in detection. However, although the AVH group had hedonic impairments, these were not evident in the OH and NC groups. Examination of the possible causes of OHs revealed abnormalities in olfactory habituation. In addition, we observed a far greater rate of past episodes of brief unconsciousness in the OH group.

CONCLUSIONS

The presence of habituation deficits and past episodes of brief unconsciousness, and absence of olfactory affective impairment, have not been identified before as correlates of OHs, suggesting these factors may be worthy of further investigation.

The effects of visual imagery on face identification: an ERP study

The present study tested the hypothesis that the effects of mental imagery on subsequent perception occur at a later matching stage in perceptual identification, but not in the early perceptual stage as in perceptual detection. The behavioral results suggested that the effect of visual imagery on visual identification is content-specific, i.e., imagining a congruent face facilitates face identification, whereas a mismatch between imagery and perception leads to an interference effect. More importantly, the ERP results revealed that a more negative N2 response to the subsequent visual face stimuli was elicited over fronto-central sites in the mismatch and no-imagery conditions as compared to that in the match condition, with the early P1 and N170 components independent of manipulations. The latency and distribution of the neural effects demonstrate that the matching step, but not the earlier perceptual process, is affected by the preceding visual imagery in the context of face identification. We discuss these results in a broader context that the imagery-perception interaction may depend on task demand.

A century of imagery research: reflections on Cheves Perky's contribution to our understanding of mental imagery

We review contemporary scientific research on the relationship between visual perception and visual mental imagery in the context of Cheves Perky's (1910) landmark article on imagery and imagination. This body of research has firmly established a strong connection between the psychology of imagery and perception and has contributed a strong voice to the imagery debate. We then use the concept of embodiment to discuss additional avenues of inquiry at which Perky's work hinted. These include a more thorough examination of the relationship between imagery and emotion, the creative, active aspects of imagery and imagination, and the methods we can bring to bear on understanding imagery and imagination as a human experience.

Olfactory predictive codes and stimulus templates in piriform cortex

Neuroscientific models of sensory perception suggest that the brain utilizes predictive codes in advance of a stimulus encounter, enabling organisms to infer forthcoming sensory events. However, it is poorly understood how such mechanisms are implemented in the olfactory system. Combining high-resolution functional magnetic resonance imaging with multivariate (pattern-based) analyses, we examined the spatiotemporal evolution of odor perception in the human brain during an olfactory search task. Ensemble activity patterns in anterior piriform cortex (APC) and orbitofrontal cortex (OFC) reflected the attended odor target both before and after stimulus onset. In contrast, prestimulus ensemble representations of the odor target in posterior piriform cortex (PPC) gave way to poststimulus representations of the odor itself. Critically, the robustness of target-related patterns in PPC predicted subsequent behavioral performance. Our findings directly show that the brain generates predictive templates or "search images" in PPC, with physical correspondence to odor-specific pattern representations, to augment olfactory perception.

Odor recognition without identification

Odors are notoriously difficult to identify, yet an odor can often lead to a sense of recognition, despite an inability to identify it. In the present study, we examined this phenomenon using the recognition-without-identification paradigm. Participants studied either odor names alone or odor names that were accompanied by scratch-and-sniff stickers containing their corresponding scents. At test, the participants were presented with blank scratch-and-sniff stickers, half of which corresponded to items that were studied and half of which did not. The participants attempted to identify each test odor, as well as to rate the likelihood that it corresponded to a studied item. In addition, the participants indicated whether they were in a tip-of-the-tongue (TOT) state for a given odor's name. Odor recognition without identification was found, but only when the participants had actually smelled the test odor at study; it was not found when the participants only studied odor names and were then tested with odors, suggesting that this effect is an episode-specific, perceptually driven phenomenon. Despite this difference, an overall TOT-attribution effect, whereby recognition ratings were higher during TOT states than during non-TOT states, was shown across conditions.

The effect of early experience on odor perception in humans: psychological and physiological correlates

The olfactory function in humans is characterized by wide variability between individuals. One of the prominent factors that contribute to this plasticity is early exposure. The present study examined how brain activity is modulated by such olfactory experience. To this end, two groups of people living in France but originating from different cultures ("European-French" (EF, 18 subjects) vs. "Algerian-French" (AF, 19 subjects)) were tested, and their perceptual and physiological responses to the smells of mint (presumed to be experienced earlier in life by "Algerian-French" subjects) and of rose (control odorant) were compared. Neurophysiological responses were obtained in the form of chemosensory event-related potentials (CSERP). The results confirmed that the AF group was exposed to Mint tea earlier than the EF group. On the perceptual level, when asked to associate the smell of mint with objects or events retrieved from memory, the discourse of AF subjects included more "experience-oriented" associations than that of EF subjects. This was associated with longer P2 latency in CSERPs in response to the smell of mint in the AF group. These findings highlight the plasticity of behavioral and neural olfactory processes as a result of differential lifetime exposure.

An fMRI investigation on image generation in different sensory modalities: the influence of vividness

In the present fMRI study the issue of the specific cortices activation during imagery generation in different sensory modalities is addressed. In particular, we tested whether the vividness variability of imagery was reflected in the BOLD signal within specific sensory cortices. Subjects were asked to generate a mental image for each auditory presented sentence. Each imagery modality was contrasted with an abstract sentence condition. In addition, subjects were asked to fill the Italian version of the Questionnaire Upon Mental Imagery (QMI) prior to each neuroimaging session. In general, greater involvement of sensory specific cortices in high-vivid versus low-vivid subjects was found for visual (occipital), gustatory (anterior insula), kinaesthetic (pre-motor), and tactile and for somatic (post-central parietal) imagery modalities. These results support the hypothesis that vividness is related to image format: high-vivid subjects would create more analogical representations relying on the same specific neural substrates active during perception with respect to low-vivid subjects. Results are also discussed according to the simulation perspective.

Perceptual and sensorimotor differences between "good" and "poor" olfactory mental imagers

Like odor perception, odor imagery is characterized by wide variability between individuals. The present two-part study sought to assess whether this inter-individual variability is underlain by behavioral differences in actual odor perception. In study 1, subjects judged the intensity, pleasantness, familiarity and edibility of 3 odorants. Participants were split into two olfactory imagery groups ("good" versus "poor" olfactory imagers) according to their scores on an imagery questionnaire. Results showed that good olfactory imagers judged all odors as more familiar and more edible than did poor olfactory imagers. Study 2 sought to determine whether these effects derived from a particular strategy of reenacting olfactomotor responses to smells on the part of good olfactory imagers, by recording their sniffs during odor perception. Results revealed that good olfactory imagers sniffed all odors longer and, again, judged these same odors as more edible and familiar. This supports the hypothesis of more complete odor processing and better access to odor semantics in good olfactory imagers.

Comparing Mental Imagery across the Sensory Modalities

Previous studies using introspective reports have suggested that although mental images can contain elements referring to all sensory modalities, visual images tend to be experienced as most vivid, whereas olfactory and gustatory images tend to be least vivid. However, these studies have typically used arbitrarily selected events and objects as the to-be-imagined stimuli, which may have biased cross-modal comparison. Therefore, in the present study participants were instructed to imagine an event or product of their choice that elicited a conspicuous or characteristic appearance, sound, feel, smell, or taste. The results showed that the types of events imagined differed considerably across modalities. Similar to previous studies in this area, we found that the reported image quality was consistently highest for vision and audition, and lowest for smell.

Hypnotizability-related integration of perception and action

Hypnotizability is a cognitive trait able to modulate many behavioural/physiological processes and associated with peculiar functional characteristics of the frontal executive system. This review summarizes experimental results on hypnotizability-related differences in sensorimotor integration at a reflex and an integrated level (postural control) and suggests possible interpretations based on morpho-functional considerations. In particular, hypnotizability-related differences in spinal motoneurones excitability are described, and the role of attention and imagery in maintaining a stable upright stance when sensory information is reduced or altered and when attention is absorbed in cognitive tasks is discussed as a function of hypnotic susceptibility. The projections from prefrontal cortex to spinal motoneurones and the balance between the activation of the right and left cortical hemisphere are considered responsible for the hypnotizability-related modulation of reflex responses, while the differences in postural control between subjects with high (highs) and low (lows) hypnotic susceptibility are considered a possible consequence of the activity of the locus coeruleus, which is also involved in attention, and of the cerebellum, which might be responsible for different internal models of postural control. We suggest a highly pervasive role of hypnotic susceptibility in human behaviour through the modulation of the integration of perception and action, which could be relevant for neurorehabilitative treatments and for the adaptation to special environments.

Olfactory Imagery and Repetition Priming

This study examined the impact of odor naming and imagery ability on the capacity of female participants to form odor images, as indexed by a novel olfactory repetition priming task. Experiment 1 involved three conditions – olfactory and visual imagery priming, and a no-prime control. Odor imagery priming was only obtained in good odor namers. Experiment 2 used the same conditions, but altered the nature of the hit-rate trials to test how odor imagery might facilitate performance in good odor namers. Odor imagery priming was again obtained only in good odor namers and this effect appeared to result from generic activation of olfactory processing caused by trying to imagine a smell. Experiment 3 examined whether this latter effect might be generated semantically, but no evidence for this was obtained. Together, these findings suggest that trying to form an odor image can facilitate performance by producing a generic state of activation, which only benefits existing odor-name associations. While this effect is mediated via perceptual processes it may occur independently of a conscious image.

Which format for odor images?

Olfactory mental images are defined as short-term memory representations of olfactory events that give rise to the experience of "smelling with the mind's nose." The present paper reviewed converging evidences that support the view that as visual mental images, odor mental images preserve some aspects of olfactory percepts. The role of olfactomotor mechanisms in recalling olfactory mental images from long-term memory to short-term memory is also discussed.