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Illusory body resizing typically uses multisensory integration to change the perceived size of a body part. Previous studies associate such multisensory body illusions with frontal theta oscillations and parietal gamma oscillations for dis-integration and integration of multisensory signals, respectively. However, recent studies support illusory changes of embodiment from visual-only stimuli. Multisensory resizing illusions can also reduce chronic pain, potentially through modulation of cortical body representations. This preregistered study (N=48) investigated differences between multisensory visuo-tactile and uni-modal visual resizing illusions using EEG. We hypothesised (1) stronger illusion in multisensory compared to uni-modal, and uni-modal compared to asynchronous (dis-integration) conditions, (2) greater parietal gamma during multisensory compared to uni-modal, and (3) greater frontal theta during asynchronous compared to baseline conditions. Results partially supported EEG hypotheses, finding increased parietal gamma activity comparing multisensory to unimodal visual conditions, whilst finding increased parietal theta activity when comparing asynchronous to non-illusion conditions. While results demonstrated that only 27% of participants experienced the illusion with visual-only stimuli, further analysis suggested that those who experience visual-only illusions exhibit a different neural signature to those who do not. Our results support the importance of multisensory integration for illusory changes in perceived body size. However, we also suggest that visual-only illusions can influence cortical body representations for a significant proportion of participants, which may have implications for the development of accessible visual-only chronic pain treatments.

There is now a considerable body of evidence to suggest that internal representations of the body can be meaningfully separated into at least two general levels; body image as a perceptual construct and body schema as a motor metric. However, recent studies with eating disordered individuals have suggested that there may in fact be more interaction between these two representations than first thought. We aimed to investigate how body image might act to influence body schema within a typical, healthy population. 100 healthy adult women were asked to judge the smallest gap between a pair of sliding doors that they could just pass through. We then determined whether these estimates were sufficient to predict the size of the smallest gap that they could actually pass through, or whether perceptual and attitudinal body image information was required in order to make these predictions. It was found that perceptual body image did indeed mediate performance on the egocentric (but not allocentric) motor imagery affordance task, but only for those individuals with raised body image concerns and low self-esteem; body schema was influenced by both the perceptual and attitudinal components of body image in those with more negative bodily attitudes. Furthermore, disparities between perceived versus actual size were associated with body parts that had larger variations in adipose/muscle-dependent circumference. We therefore suggest that it may be the affective salience of a distorted body representation that mediates the degree to which it is incorporated into the current body state.

Research has suggested that altering the perceived shape and size of the body image significantly affects perception of somatic events. The current study investigated how multisensory illusions applied to the body altered tactile perception using the somatic signal detection task. Thirty-one healthy volunteers were asked to report the presence or absence of near-threshold tactile stimuli delivered to the index finger under three multisensory illusion conditions: stretched finger, shrunken finger and detached finger, as well as a veridical baseline condition. Both stretching and shrinking the stimulated finger enhanced correct touch detections; however, the mechanisms underlying this increase were found to be different. In contrast, the detached appearance reduced false touch reports-possibly due to reduced tactile noise, as a result of attention being directed to the tip of the finger only. These findings suggest that distorted representations of the body could have different modulatory effects on attention to touch and provide a link between perceived body representation and somatosensory decision-making.

The dynamic flexibility of body representation has been highlighted through numerous lines of research that range from clinical studies reporting disorders of body ownership, to experimentally induced somatic illusions that have provided evidence for the embodiment of manipulated representations and even fake limbs. While most studies have reported that enlargement of body parts alters somatic perception, and that these can be more readily embodied, shrunken body parts have not been found to consistently alter somatic experiences, perhaps due to reduced feelings of ownership over smaller body parts. Over two experiments, we aimed to investigate the mechanisms responsible for altered somatic representations following exposure to both enlarged and shrunken body parts. Participants were given the impression that their hand and index finger were either longer or shorter than veridical length and asked to judge veridical finger length using online and offline size estimation tasks, as well as to report the degree of ownership towards the distorted finger and hand representations. Ownership was claimed over all distorted representations of the hand and finger and no differences were seen across ownership ratings, while the online and offline measurements of perceived size demonstrated differing response patterns. These findings suggest that ownership towards manipulated body representations is more bidirectional than previously thought and also suggest differences in perceived body representation with respect to the method of measurement suggesting that online and offline tasks may tap into different aspects of body representation.

Objective: Medically unexplained symptoms (MUS) are increasingly being thought of as resulting from dysfunctional modulation of interoceptive sensory signals by top-down cognitive processes. The current study investigated whether individuals with a tendency toward MUS would be more susceptible to visual illusions that suggest tactile sensation on the skin in the absence of any actual somatosensory input. Method: Participants viewed real-time mediated reality video images of their own hand, either un-manipulated or digitally altered to display moving pixelated ‘static’ effect; the crawling skin illusion. The strength of various physical sensations during each condition were rated on a numeric scale and compared to standard measures of somatoform dissociation (Somatoform Dissociation Questionnaire 20). Results: Participants reporting a higher degree of somatoform dissociation were found to be more susceptible to somatic sensations across all conditions. Interestingly, participants who reported more visually-induced somatosensory sensations also felt less ownership over their digitally-presented hands. Conclusion: These findings support the proposed link between MUS and disturbances in body representation, and suggest that an over-reliance on top-down knowledge may interfere with current sensory inputs - contributing to symptom formation and maintenance in susceptible individuals.

When asked to judge the presence or absence of near-threshold tactile stimuli, participants often report touch experiences when no tactile stimulation has been delivered ('false alarms'). The simultaneous presentation of a light flash during the stimulation period can increase the frequency of touch reports, both when touch is and is not present. Using fMRI, we investigated the BOLD response during both light-present and light-absent false alarms, testing predictions concerning two possible neural mechanisms underlying these illusory touch experiences: activation of a tactile representation in primary somatosensory cortex (SI) and/or activation of a tactile representation in late processing areas outside of sensory-specific cortex, such as medial prefrontal cortex (MPC). Our behavioural results showed that participants made false alarms in light-present and light-absent trials, both of which activated regions of the medial parietal and medial prefrontal cortex including precuneus, posterior cingulate and paracingulate cortex, suggesting the same underlying mechanism. However, only a non-significant increase in SI activity was measured in response to false alarm vs. correct rejection trials. We argue that our results provide evidence for the role of top-down regions in somatic misperception, consistent with findings from studies in humans and non-human primates.

Recent studies have reported that in normal healthy individuals, the perception of illusory sensations in one modality can be induced by the presentation of a stimulus in another modality. These illusory sensations may arise from the activation of a tactile representation in memory induced by the non-target stimulus, in a process mirroring that thought to be responsible for many forms of medically unexplained symptoms. The reliability of illusory-touch reports was investigated here in two experiments with a novel perceptual paradigm designed to simulate the occurrence of somatoform symptoms in the laboratory. A concurrent light significantly increased the number of tactile stimuli reported, and resulted in a higher number of illusory-touch reports, while the modality of the trial start cue did not affect subsequent responses. In addition, a strong relationship was found between the rates of illusory sensations that participants produced in successive sessions, indicating that the tendency to report illusory sensations is a robust phenomenon.

The posterior parietal cortex (PPC) is thought to integrate different kinds of sensory information (e.g., visual, auditory, somatosensory) to produce multiple representations of space that are each associated with different types or combinations of action; such as saccadic eye movements and reaching or grasping movements of the upper limb. Lesion studies in monkeys and in humans have shown that reaching movements to visually defined and to posturally defined targets can be dissociated from one another; indicating that different regions of the parietal cortex may code the same movement in either extrinsic (visual) or intrinsic (postural) coordinates. These studies also suggest that regions within the posterior parietal cortex play an important role in maintaining an accurate and up-to-date representation of the current postural state of the body (the body schema). We used event-related functional magnetic resonance imaging (fMRI) to investigate those brain areas involved in maintaining and updating postural (i.e., non-visual) representations of the upper limb that participate in the accurate control of reaching movements. We show that a change in the posture of the upper-limb is associated with a significant increase in BOLD activation in only one brain region--the superior parietal cortex, particularly the medial aspect (precuneus). We note that this finding is consistent with the suggestion, based upon human neurological investigations and monkey electrophysiology, that this region of the PPC may participate in the dynamic representation of the body schema, and is the most likely location for damage leading to errors in visually guided reaching to non-foveated target locations. We also note that this brain area corresponds to a region of PPC recently identified as the human homologue of the Parietal Reach Region (PRR) observed in the monkey brain that has been thought to represent reaching movements in eye-centred coordinates.

We report a cross-cultural study designed to investigate crossmodal correspondences between a variety of visual features (11 colours, 15 shapes, and 2 textures) and the five basic taste terms (bitter, salty, sour, sweet, and umami). A total of 452 participants from China, India, Malaysia, and the USA viewed colour patches, shapes, and textures online and had to choose the taste term that best matched the image and then rate their confidence in their choice. Across the four groups of participants, the results revealed a number of crossmodal correspondences between certain colours/shapes and bitter, sour, and sweet tastes. Crossmodal correspondences were also documented between the colour white and smooth/rough textures on the one hand and the salt taste on the other. Cross-cultural differences were observed in the correspondences between certain colours, shapes, and one of the textures and the taste terms. The taste-patterns shown by the participants from the four countries tested in present study are quite different from one another, and these differences cannot easily be attributed merely to whether a country is Eastern or Western. These findings therefore highlight the impact of cultural background on crossmodal correspondences. As such, they raise a number of interesting questions regarding the neural mechanisms underlying crossmodal correspondences.

Colors and odors are associated; for instance, people typically match the smell of strawberries to the color pink or red. These associations are forms of crossmodal correspondences. Recently, there has been discussion about the extent to which these correspondences arise for structural reasons (i.e., an inherent mapping between color and odor), statistical reasons (i.e., covariance in experience), and/or semantically-mediated reasons (i.e., stemming from language). The present study probed this question by testing color-odor correspondences in 6 different cultural groups (Dutch, Netherlands-residing-Chinese, German, Malay, Malaysian-Chinese, and US residents), using the same set of 14 odors and asking participants to make congruent and incongruent color choices for each odor. We found consistent patterns in color choices for each odor within each culture, showing that participants were making non-random color-odor matches. We used representational dissimilarity analysis to probe for variations in the patterns of color-odor associations across cultures; we found that US and German participants had the most similar patterns of associations, followed by German and Malay participants. The largest group differences were between Malay and Netherlands-resident Chinese participants and between Dutch and Malaysian-Chinese participants. We conclude that culture plays a role in color-odor crossmodal associations, which likely arise, at least in part, through experience.

Theory suggests that a tendency to experience distortions in somatosensory awareness is associated with physical symptom reporting (i.e., somatization) but empirical evidence for this is lacking. This article describes research designed to test this hypothesis.Somatosensory distortion was operationalized as the frequency of illusory touch experiences (i.e., false alarm rate) on the Somatic Signal Detection Task. Two studies correlated false alarms on this task with physical symptom reporting on the 15-item Patient Health Questionnaire, the first using a nonclinical sample (n = 35), the second using a clinical sample of endoscopy patients who were identified as having either medically explained (n = 25) or medically unexplained symptoms (n = 30).Scores on the 15-item Patient Health Questionnaire were positively correlated with false alarm rate in both studies (r = 0.288-0.506), even after controlling for trait anxiety, depression, anxiety (standardized β range = 0.793-0.932, all p.0001) and (in Study 2) somatosensory amplification and hypochondriacal worry (standardized β range = 0.345-0.375, both p.05). There was no difference in false alarm rate between patients with medically explained and medically unexplained symptoms (medically explained median range = 6.8 [3.7] to 6.8 [4.0] versus medically unexplained median range = 4.3 [3.9] to 5.6 [3.1], both p.1).There seems to be a robust link between physical symptom reporting and the tendency to experience somatosensory distortion, consistent with recent cognitive theories. It may be possible to reduce the impact of somatization by developing treatments that target this tendency.

When attempting to detect a near-threshold signal, participants often incorrectly report the presence of a signal, particularly when a stimulus in a different modality is presented. Here we investigated the effect of prior experience of bimodal visuotactile stimuli on the rate of falsely reported touches in the presence of a light. In Experiment 1, participants made more false alarms in light-present than light-absent trials, despite having no experience of the experimental visuotactile pairing. This suggests that light-evoked false alarms are a consequence of an existing association, rather than one learned during the experiment. In Experiment 2, we sought to manipulate the strength of the association through prior training, using supra-threshold tactile stimuli that were given a high or low association with the light. Both groups still exhibited an increased number of false alarms during light-present trials, however, the low association group made significantly fewer false alarms across conditions, and there was no corresponding group difference in the number of tactile stimuli correctly identified. Thus, while training did not affect the boosting of the tactile signal by the visual stimulus, the low association training affected perceptual decision-making more generally, leading to a lower number of illusory touch reports, independent of the light. © 2011 Elsevier B.V.

Strong associations exist between specific odours and colours, and these associations have been found to be both consistent within populations and over time (Gilbert et al., 1996). Experimental manipulations of these associations have shown that both taste and odour perception rely heavily upon visual cues (e.g., Blackwell, 1995; Sakai et al., 2005); participants often make errors in odour judgements when stimuli have been artificially coloured (Morrot et al., 2001), and the presence of a strongly-associated colour can greatly enhance the detection of an odour and the intensity of aromas or flavours (Zellner and Kautz, 1990; Zellner and Whitten, 1999), as well as preference and enjoyment (Herz, 2001; Herz and Beland, 2004). Such associations between colour and odour appear to be based on prior experience (Blackwell, 1995; Morrot et al., 2001; Sakai et al., 2005; Stevenson and Oaten, 2008), and odours are usually perceived alongside visual, taste and tactile sensations, as well as higher order cues such as shape, size and object labelling. As such, an odour maybe perceived quite differently depending upon its current multisensory context, and experiencing an odour without these additional cues is likely to be different from experiencing the odour in a natural multisensory environment. Here we explore if odour-evocative words, rich in semantic connotations, differ in their colour associations compared to those associated with just odour. Twenty individuals were tested in each of four geographical locations; Germany, Malaysia, The Netherlands and the United States of America. Participants chose the three colours they most closely associated with both odours and odour-words from a chart of 36, using Xperiment software (www.xperiment.mobi). Preliminary results indicate that there were differences between odour-evocative words and odour cues in terms of the associated colours, for all populations.

We assessed lateralization of brain function during mental rotation, measuring the scalp distribution of a 400-600 ms latency event-related potential (ERP) with 128 recording electrodes. Twenty-four subjects, consisting of equal numbers of dextral and sinistral males and females, performed a mental rotation task under two response conditions (dominant non-dominant hand). For males, ERPs showed a right parietal bias regardless of response hand. For females, the parietal ERPs were slightly left-lateralized when making dominant hand responses, but strongly right-lateralized when making non-dominant hand responses. These results support the notion that visuo-spatial processing is more bilaterally organized in females. However, left hemisphere resources may be allocated to response preparation when using the non-dominant hand, forcing visuo-spatial processing to the right hemisphere.

Our visual experience of the world around us remains stable despite constant changes in the relationship between direction of gaze and the location of visual objects in our environment brought about by eye movements. Presaccadic activity, first observed in the monkey lateral intraparietal (LIP) area

Associations between colour and odour are likely culturally specific. Exposure to a new culture’s cuisine and food customs however may alter these associations. Here we test for cultural colour–odour association differences and whether exposure to a new culture impacts upon these associations. Participants were given 14 odours and choose from a chart of 36 randomly presented colours which of 3 colours they most associated with each odorant, and which of 3 colours was least associated with each. Data collection was done on Android and Apple iPod devices using Xperiment software (see www.xperiment.mobi). In the first study, we tested equal numbers of Dutch and Chinese participants living in the Netherlands (n = 20 per group). In the second study we tested equal numbers of Malay and Malaysian-Chinese participants living in Malaysia (n = 20 per group). Preliminary results indeed indicate that the cultures in both studies did differ from each other in terms of colour–odour pairings. Further analyses are ongoing.

Experimental studies have demonstrated that it is possible to induce convincing bodily distortions in neurologically healthy individuals, through cross-modal manipulations; such as the rubber hand illusion (Botvinick and Cohen, 1998), the parchment skin illusion (Jousmaki and Hari, 1998) and the Somatic Signal Detection Task (SSDT; Lloydet al., 2008). It has been shown previously with the SSDT that when a tactile stimulus is presented with a simultaneous light flash, individuals show both increased sensitivity to the tactile stimulus, and the tendency to report feeling the stimulus even when one was not presented; a tendency which varies greatly between individuals but remains constant over time within an individual (McKenzieet al., 2010). Further studies into tactile stimulus discrimination using the Somatic Signal Discrimination Task (SSDiT) have also shown that a concurrent light led to a significant improvement in people’s ability to discriminate ‘weak’ tactile stimuli from ‘strong’ ones, as well as a bias towards reporting any tactile stimulus as ‘strong’ (Poliakoffet al., in preparation), indicating that the light may influence both early and later stages of processing. The current study investigated whether the tendency to report higher numbers of false alarms when carrying out the SSDT is correlated with the tendency to experience higher numbers of cross-modal ‘enhancements’ of weak tactile signals (leading to classifications of ‘weak’ stimuli as strong, and ‘strong’ stimuli as ‘stronger’). Results will be discussed.

Studies into tactile detection have found that a simultaneous light stimulus affects judgments of the presence or absence of a near threshold tactile stimulus, leading to higher numbers of false alarms, whereby participants report feeling a touch in the absence of a stimulus, as well as modest improvements in tactile sensitivity (Lloydet al., 2008; McKenzieet al., 2010, 2012). Anecdotally, the reported intensity of the bi-modal stimuli was also enhanced — an effect that was investigated in the current studies. In Experiment 1 participants discriminated between ‘weak’ and ‘strong’ tactile stimuli, which were accompanied by a light flash on 50% of trials. We observed a bias towards classifying light-present vibrations as ‘strong’ regardless of signal strength, as well as some evidence for improved accuracy in discrimination. In Experiment 2, participants gave a subjective intensity rating on a 6-point scale, which showed an increase in magnitude ratings for both ‘weak’ and ‘strong’ vibrotactile stimuli when the light was present. This shows that a simultaneous light can both improve tactile discrimination and lead to both types of tactile stimulus being rated as stronger. Primary somatosensory cortex may underlie these effects, as it receives direct projections from visual cortex and indirect projections from association areas of the brain. However, it is as yet unclear whether or not these effects are due to the same underlying mechanism, or at which processing stage they occur. Therefore, we are currently exploring the neural underpinnings of this amplification effect using both fMRI and EEG.