As bitter as a trombone: synesthetic correspondences in nonsynesthetes between tastes/flavors and musical notes

In parallel to studies of various cases of synesthesia, many cross-modal correspondences have also been documented in nonsynesthetes. Among these correspondences, implicit associations between taste and pitch have been reported recently (Crisinel & Spence, 2009, 2010). Here, we replicate and extend these findings through explicit matching of sounds of varying pitch to a range of tastes/flavors. In addition, participants in the experiment reported here also chose the type of musical instrument most appropriate for each taste/flavor. The association of sweet and sour tastes to high-pitched notes was confirmed. By contrast, umami and bitter tastes were preferentially matched to low-pitched notes. Flavors did not display such strong pitch associations. The choice of musical instrument seems to have been driven primarily by a matching of the hedonic value and familiarity of the two types of stimuli. Our results raise important questions about our representation of tastes and flavors and could also lead to applications in the marketing of food products.     

Modality and variability of synesthetic experience

In synesthesia, stimulation of one sensory or cognitive pathway leads to additional, involuntary experiences in a second sensory or cognitive pathway. We here review previous surveys on this neurologically based phenomenon and report the results of 63 synesthetes who completed our Internet and paper questionnaire on synesthesia. In addition to asking for personal data and information on the participant's synesthesia, the questionnaire focused on the components of the inducer that elicit or modulate synesthesia. Synesthesia was most often developmental (92%) and of the grapheme-color type (86%). Sixty-two percent of the participants perceived time-related words in a spatial configuration. Music-color synesthesia was common (41%), and synesthesia for natural and artificial sounds (33%) was higher than in previous estimates. Eighty-one percent of participants experienced more than one form of synesthesia. Multimodal synesthesia, in which inducer and concurrent belong to 2 different sensory modalities, occurred in 92% of the participants. Overall, auditory stimuli were most often reported as inducers, and visual concurrents were most common. Modulations of the synesthetic experiences such as changes of the concurrent color, expansion within the same or to a different sensory modality, or reduction of the number of inducers over time were reported by 17% of participants. This challenges the presumed consistency of synesthesia and the adequacy of the test-retest consistency score still most commonly used to assess the veracity of reported synesthesia. Implications of the high prevalence of cross-modal synesthesia and the variability of synesthesia are discussed.     

Olfactory-induced synesthesias: a review and model

Recent reviews of synesthesia concentrate upon rare neurodevelopmental examples and exclude common olfactory-induced experiences with which they may profitably be compared. Like the neurodevelopmental synesthesias, odor-induced experiences involve different sensory modalities; are reliable, asymmetric (concurrents cannot induce), and automatic; and the inducer-concurrent relationship is learnt. Unlike neurodevelopmental synesthesias, these experiences are universal and their synesthetic nature goes unrecognized. Olfaction's ability to universally induce concurrents may result from its unique neuroanatomy, affording dual access to neocortex. We propose that concurrents arise here via a twofold process: by direct neocortical activation, which recovers a configural memory, and by attribution of this memory to the olfactory modality by thalamic attentional processes. The implications of this for other forms of synesthesia are then examined.     

Taste and Acquaintance

The analogy between gustatory taste and critical or aesthetic taste plays a recurring role in the history of aesthetics. Our interest in this article is in a particular way in which gustatory judgments are frequently thought to be analogous to critical judgments. It appears obvious to many that to know how a particular object tastes we must have tasted it for ourselves; the proof of the pudding, we are all told, is in the eating. And it has seemed just as obvious to many philosophers that aesthetic judgment requires first‐person experience. In this article we argue that, despite its initial appeal, the claim that gustatory and critical judgments are analogous in this way is mistaken. The two sorts of judgments are, as a matter of fact, similar in their epistemology, but earlier theorists have got things entirely backward—neither gustatory judgment nor aesthetic judgment requires first‐hand acquaintance with their objects. Our particular focus in this article is on arguing that first‐person experience is not required to know how an item of food or drink tastes. In fact, there are a wide variety of ways in which we can acquire this knowledge.     

Consistency and strength of grapheme-color associations are separable aspects of synesthetic experience

Consistency of synesthetic associations over time is a widely used test of synesthesia. Since many studies suggest that consistency is not a completely reliable feature, we compared the consistency and strength of synesthetes’ grapheme-color associations. Consistency was measured by scores on the Synesthesia Battery and by the Euclidean distance in color space for the specific graphemes tested for each participant. Strength was measured by congruency magnitudes on the Implicit Association Test. The strength of associations was substantially greater for synesthetes than non-synesthetes, suggesting that this is a novel, objective marker of synesthesia. Although, intuitively, strong associations should also be consistent, consistency and strength were uncorrelated, indicating that they are likely independent, at least for grapheme-color synesthesia. These findings have implications for our understanding of synesthesia and for estimates of its prevalence since synesthetes who experience strong, but inconsistent, associations may not be identified by tests that focus solely on consistency.     

Psychophysics of taste lateralization on anterior tongue

There have been very few investigations of the spatial properties of taste stimuli localized to specific areas of the oral cavity. This is surprising, since the spatial localization of taste sensations may contribute to the overall taste percept, much as do quality, intensity, and the temporal characteristics of tastes. The difficulty in eliminating the confounding factor of a tactile sensation may partially account for the paucity of such studies, since a gustatory stimulus cannot be presented as a liquid without a tactile component. As a step toward understanding the localizability of gustatory sensations, we designed a yoked stimulator and an experimental procedure to control for tactile cues. Lateral discrimination was evaluated at the tip of the tongue with four taste stimuli (sodium saccharin, sodium chloride, citric acid, and quinine hydrochloride) by presenting a taste and a blank solution simultaneously at two locations on the tongue. We found that subjects could lateralize all four taste stimuli in the absence of any discriminative tactile cues. Subjects' ability to lateralize varied as a psychometric function of the stimulus concentration. Detection thresholds, measured in a forced-choice two-interval staircase procedure with the same yoked stimulator that was used in the lateralization task, were always lower than lateralization thresholds, and both lateralization and detection thresholds were correlated within subjects. Subjects were unable to lateralize taste cues on a nongustatory surface under the upper lip at the highest tested concentrations, at which performance was 100% on a gustatory surface (dorsal anterior tongue). These results show that (1) taste compounds can be lateralized in the absence of any discriminative mechanical cue (but only on the gustatory epithelium) and (2) although the localization of a compound does not logically require conscious detection of the taste (cf. blind sight), subjects always detected a taste when they were able to lateralize.     

Crossmodal associations between flavoured milk solutions and musical notes

A number of crossmodal associations have now been described in the context of food evaluation, such as between tastes or flavours and musical notes (Crisinel & Spence, 2010b). Here we extend these findings by presenting flavoured milk solutions of varying fat contents. The participants in the present study matched a series of milk samples to musical notes. They chose both the pitch and the class of instrument that they felt was most appropriate for each sample. Participants also rated various features of the samples, such as their pleasantness, bitterness, or familiarity. Consistent associations between flavours and both pitch and instruments were confirmed. However, fat content did not influence either the pitch or instrument chosen, although it did have an effect on pleasantness and intensity ratings. These results demonstrate that flavour–sound associations are not restricted to basic tastes and flavours presented individually, but are still present in the context of more complex food stimuli. The present study opens the way for further investigations into the nature and characteristics of crossmodal associations (or correspondences) between more complex stimuli, both in the auditory and gustatory/olfactory modalities. This novel approach could lead to new insights into the representation of chemosensory stimuli in humans.     

A study of the science of taste: on the origins and influence of the core ideas

Our understanding of the sense of taste is largely based on research designed and interpreted in terms of the traditional four "basic" tastes: sweet, sour, salty, and bitter, and now a few more. This concept of basic tastes has no rational definition to test, and thus it has not been tested. As a demonstration, a preliminary attempt to test one common but arbitrary psychophysical definition of basic tastes is included in this article; that the basic tastes are unique in being able to account for other tastes. This definition was falsified in that other stimuli do about as well as the basic words and stimuli. To the extent that this finding might show analogies with other studies of receptor, neural, and psychophysical phenomena, the validity of the century-long literature of the science of taste based on a few "basics" is called into question. The possible origins, meaning, and influence of this concept are discussed. Tests of the model with control studies are suggested in all areas of taste related to basic tastes. As a stronger alternative to the basic tradition, the advantages of the across-fiber pattern model are discussed; it is based on a rational data-based hypothesis, and has survived attempts at falsification. Such "population coding" has found broad acceptance in many neural systems.     

Synaesthetic perception of colour and visual space in a blind subject: an fMRI case study

In spatial sequence synaesthesia (SSS) ordinal stimuli are perceived as arranged in peripersonal space. Using fMRI, we examined the neural bases of SSS and colour synaesthesia for spoken words in a late-blind synaesthete, JF. He reported days of the week and months of the year as both coloured and spatially ordered in peripersonal space; parts of the days and festivities of the year were spatially ordered but uncoloured. Words that denote time-units and triggered no concurrents were used in a control condition. Both conditions inducing SSS activated the occipito-parietal, infero-frontal and insular cortex. The colour area hOC4v was engaged when the synaesthetic experience included colour. These results confirm the continued recruitment of visual colour cortex in this late-blind synaesthetes. Synaesthesia also involved activation in inferior frontal cortex, which may be related to spatial memory and detection, and in the insula, which might contribute to audiovisual integration related to the processing of inducers and concurrents.     

Shifting gustatory thresholds and food cravings during pregnancy as expanding uterine-induced steady potential shifts within the insula: an hypothesis

A logical extrapolation from the principle that structure dictates function is that transient or anomalous experiences are consequences of simultaneous stimulations of proximal brain regions not typically co-activated. In this paper the occasional shifts in gustatory threshold during the menstrual cycle, the craving for unusual tastes experienced by some during pregnancies, and, the reports by postmenopausal women of the "burning mouth syndrome" are hypothesized to be artifacts of the proximity of gustatory and uterine representations within the female insula. Transient (menstrual) or tonic (pregnancy) stimulation within the uterus might shift the locus of neuronal activity within the insula to include adjacent gustatory neurons and consequently alter taste experiences. Specific tests of this hypothesis are suggested.     

Palatability shift of a salt-associated incentive during sodium depletion

Previous studies of natural palatability-sensitive reactions, elicited from rats by tastes, have indicated that the taste of concentrated NaCl becomes more palatable during states of body sodium depletion. A training procedure based upon “sensory preconditioning” or “irrelevant incentive” designs was used here to establish gustatory conditioned labels (quinine or citric acid) for either NaCl or fructose while rats were in a normal physiological state. Experiment 1 replicated demonstrations by others that gustatory conditioned labels for salt can attract and act as independent incentives during the salt appetite induced by sodium depletion. Experiment 2 used the taste reactivity measure to show that the enhanced palatability of the taste of NaCl transfers to produce enhanced palatability of the taste of the isolated conditioned label for salt in a state-dependent fashion. These results offer further support for the proposition that conditioned incentives not only predict hedonic events to follow, but themselves become attributed with the hedonic properties of their reinforcers.     

强联觉的认知加工模型及其脑机制

联觉是当个体感受到一种感觉刺激的同时体验到其它感觉的现象, 主要分为强联觉和弱联觉两种。本文主要介绍了强联觉的各种类型及其相关脑机制的研究, 分析和比较了前人从结构和认知加工角度建构的多个强联觉理论模型, 总结了这些模型对强联觉现象脑神经机制的解释。同时本文还探讨了强联觉与其它(如注意、记忆、创造力等)认知加工过程的关系, 对弱联觉(即联觉隐喻)的研究进展和不足也进行了分析和总结, 指出未来对联觉的研究趋势应集中在弱联觉的研究上。     

The impact of mediodorsal thalamic lesions on olfactory attention and flavor perception

Olfactory attention may be important in generating odor-induced tastes - an arguably universal form of synesthesia - by ensuring that the taste concurrent is captured by the nose and olfaction, not by the mouth and gustation (oral-capture). To examine the role of olfactory attention in generating odor-induced tastes and oral capture we tested a small sample (n = 4) of participants with likely impairments in olfactory attention - individuals with mediodorsal thalamic nucleus (MDNT) lesions. These participants were compared to two sets of controls on tests of olfactory attention, oral capture, odor and flavor perception, and control tasks. MDNT participants demonstrated impaired olfactory attention and enhanced oral capture. Greater oral capture was associated with greater olfactory attentional impairment. These findings imply that olfactory attention may be important in attributing odor-induced tastes to the olfactory modality. However, unlike for visual binding and for the neurodevelopmental synesthesias, where attention may be necessary to demonstrate both phenomena, olfactory attention deficits did not impair flavor binding or the experience of odor-induced tastes.     

Cortical substrates of taste aversion learning: dorsal prepiriform (insular) lesions disrupt taste aversion learning

The functional relation between restricted damage to ventral primary somatosensory neocortex and the ability of rats to acquire conditioned taste aversion (CTA( was examined by a combination of behavioral and neurohistological techniques. Lesions confined exclusively to the established gustatory neocortex (GN) did not disrupt CTA acquisition, nor did lesions confined to suprarhinal cortical areas ventral to the GN. Lesions that encroached on dorsal prepiriform and insular cortices produced CTA acquisition deficits and damaged a large proportion of efferent projections to the prefrontal and precentral neocortex. In a second experiment, lesions of dorsal prepiriform and insular cortices did not modify taste preference-aversion threshold to any of the four taste modalities. It is concluded tha ventral somatosensory neocortical fields, including the established GN, do not mediate CTA acquisition and that rhinal cortices ventral and posterior to the GN are preferentially involved in associative learning for tastes and illness.     

Beyond visual imagery: How modality-specific is enhanced mental imagery in synesthesia?

Synesthesia based in visual modalities has been associated with reports of vivid visual imagery. We extend this finding to consider whether other forms of synesthesia are also associated with enhanced imagery, and whether this enhancement reflects the modality of synesthesia. We used self-report imagery measures across multiple sensory modalities, comparing synesthetes’ responses (with a variety of forms of synesthesia) to those of non-synesthete matched controls. Synesthetes reported higher levels of visual, auditory, gustatory, olfactory and tactile imagery and a greater level of imagery use. Furthermore, their reported enhanced imagery is restricted to the modalities involved in the individual’s synesthesia. There was also a relationship between the number of forms of synesthesia an individual has, and the reported vividness of their imagery, highlighting the need for future research to consider the impact of multiple forms of synesthesia. We also recommend the use of behavioral measures to validate these self-report findings.     

Behavioral interference and C/EBPbeta expression in the insular-cortex reveal a prolonged time period for taste memory consolidation

Memory consolidation is defined as the time window during which the memory trace is susceptible to behavioral, electrical, or pharmacological interventions. Here, we presented rats with two novel tastes at consecutive time intervals. Clear interference was evident when a novel taste formed the second taste input whereby, surprisingly, the time window for interference was found to last more than 10 h. In addition, we detected an increase of C/EBPbeta protein expression in the gustatory cortex 18 h after novel taste learning. This modulation was attenuated by a subsequent novel taste. Our findings reveal temporal constraints and a lingering nature of taste memory consolidation.     

Implicit and explicit spatial-numerical representations diverge in number-form synesthetes

In number-form (NF) synesthesia—a condition in which people report vivid, automatic and consistent mental layouts for numerical sequences—numbers and space are closely linked. These explicit associations are similar to the implicit associations demonstrated by the Spatial-Numerical Association of Response Codes (SNARC) effect. Thus, NF synesthesia offers a unique opportunity to investigate spatial-numerical associations. We tested implicit and explicit representations in NF synesthetes using a multiple case-study design. Over two sessions, synesthetes participated in a semi-structured interview focusing on the nature of their associations, as well as SNARC and number line estimation tasks. Contrary to our hypotheses, only one synesthete demonstrated SNARC effects congruent with her reported form, whereas two others exhibited SNARC effects that were the opposite of their explicit NFs. While this inconsistency between implicit and explicit representations may indicate separate underlying cognitive mechanisms, factors such as task-specific constraints and strategic variability must also be considered.     

Predicting language: MEG evidence for lexical preactivation

It is widely assumed that prediction plays a substantial role in language processing. However, despite numerous studies demonstrating that contextual information facilitates both syntactic and lexical–semantic processing, there exists no direct evidence pertaining to the neural correlates of the prediction process itself. Using magnetoencephalography (MEG), this study found that brain activity was modulated by whether or not a specific noun could be predicted, given a picture prime. Specifically, before the noun was presented, predictive contexts triggered enhanced activation in left mid-temporal cortex (implicated in lexical access), ventro-medial prefrontal cortex (previously associated with top-down processing), and visual cortex (hypothesized to index the preactivation of predicted form features), successively. This finding suggests that predictive language processing recruits a top-down network where predicted words are activated at different levels of representation, from more ‘abstract’ lexical–semantic representations in temporal cortex, all the way down to visual word form features. The same brain regions that exhibited enhanced activation for predictive contexts before the onset of the noun showed effects of congruence during the target word. To our knowledge, this study is one of the first to directly investigate the anticipatory stage of predictive language processing.     

Gastrointestinal reactivity in rats lacking anterior insular neocortex

Behavioral and physiological studies have shown that the insular neocortex participates in a wide variety of special visceral processes, in particular, the higher-order integration of taste stimuli and the regulation of autonomic activity. The present experiment examined the involvement of the anterior insular (gustatory) neocortex (AIGN) in gastrointestinal reactivity and taste learning in rats by the use of a modified taste aversion training procedure. Normal rats and rats lacking AIGN demonstrated similar "illness thresholds" to the early onset symptoms of ingested LiCl. Conversely, animals lacking AIGN showed significant impairments in taste aversion learning ability. From a consideration of several research findings it is concluded that animals lacking AIGN can normally perceive tastes and illness, but these animals experience reliable impairments in taste aversion learning ability.