Matthew R Longo

Birkbeck, University of London · Department of Psychological Sciences

Research on media's effects on body perception has mainly focused on the role of vision of extreme body types. However, haptics is a major part of the way children experience bodies. Playing with unrealistically thin dolls has been linked to the emergence of body image concerns, but the perceptual mechanisms remain unknown. We explore the effects o...

When we interact with objects using our hands, we derive their size through our skin. Prolonged exposure to an object leads to a perceptual size aftereffect: adapting to a larger/smaller object makes a subsequently perceived object to appear smaller/larger than its actual size. This phenomenon has been described as haptic as tactile sensations with...

Despite our wealth of experience with our bodies, our perceptions of our body size are far from veridical. For example, when estimating the relative proportions of their body part lengths, using the hand as a metric, individuals tend to exhibit systematic distortions which vary across body parts. Whilst extensive research with healthy populations h...

Current models of mental body representations (MBRs) indicate that tactile inputs feed several of them for different functions, implying that altering tactile inputs may affect MBRs differently. Here we tested this hypothesis by leveraging Repetitive Somatosensory Stimulation (RSS), known to improve tactile perception by modulating primary somatose...

Interoceptive dysfunctions are increasingly implicated in a number of physical and mental health conditions. Accordingly, there is a pertinent need for therapeutic interventions which target interoceptive deficits. Heartrate and heartrate variability biofeedback therapy (HR(V)-BF), interventions which train individuals to regulate their cardiovascu...

Faces are a primary means of conveying social information between humans. One important factor modulating the perception of human faces is emotional expression. Face inversion also affects perception, including judgments of emotional expression, possibly through the disruption of configural processing. One intriguing inversion effect is an illusion...

When reproducing the remembered location of dots within a circle, judgments are biased toward the center of imaginary quadrants formed by imaginary vertical and horizontal axes. This effect may result from the heightened precision in the visual system for these orientations in a retinotopic reference frame, or alternately on the internal representa...

According to Newton's laws, the weight of a body part is equal to its mass times gravitational acceleration. Our experience of body part weight, however, is constructed by the central nervous system. No sensory receptors directly specify the weight of body parts, and the factors influencing perceived weight remain unknown. The perceived weight of h...

The somatosensory system is fundamental to the formation and maintenance of coherent mental representations of the human body. Traditional concepts of somatosensation have been shaped by the principles of somatotopic and hierarchical organization of the primary somatosensory cortex and the motor cortex. However, emerging research has shown that per...

Body posture and configuration provide important visual cues about the emotion states of other people. We know that bodily form is processed holistically, however, emotion recognition may depend on different mechanisms; certain body parts, such as the hands, may be especially important for perceiving emotion. This study therefore compared participa...

Tactile distance perception is influenced by stimulus orientation. On the hands or face, effects of orientation may originate from the mostly oval shape of receptive fields (RF) of which the long axis aligns with the proximodistal body axis. As tactile distance estimation relies on the number of RFs between stimuli, their alignment leads to a disto...

Orientation information contributes substantially to our tactile perception, such as feeling an object's shape on the skin. For vision, a perceptual adaptation aftereffect (tilt aftereffect; TAE), which is well explained by neural orientation selectivity, has been used to reveal fundamental perceptual properties of orientation processing. Neural or...

A recent perceptual illusion induces the feeling of having a sixth finger on one's hand. It is unclear whether the representation of supernumerary fingers is flexible for shape. To test whether we can embody a sixth finger with a different shape from our own fingers, we induced a sixth finger which curved laterally though 180°. Participants reporte...

Several studies have shown the presence of large anisotropies for tactile distance perception across several parts of the body. The tactile distance between two touches on the dorsum of the hand is perceived as larger when they are oriented mediolaterally (across the hand) than proximodistally (along the hand). This effect can be partially explaine...

Caregiver touch is crucial for infants' healthy development, but its role in shaping infant cognition has been relatively understudied. In particular, despite strong premises to hypothesize its function in directing infant attention to social information, little empirical evidence exists on the topic. In this study, we investigated the associations...

The English idiom “on the tip of my tongue” commonly acknowledges that something is known, but it cannot be immediately brought to mind. This phrase accurately describes sensorimotor functions of the tongue, which are fundamental for many tongue-related behaviors (e.g., speech), but often neglected by scientific research. Here, we review a wide ran...

Given humans’ ubiquitous visual experience of their own body, one reasonable assumption is that one’s perceptions of the lengths of their body parts should be accurate. However, recent research has shown that large systematic distortions of the length of body parts are present in healthy younger adults. These distortions appear to be linked to tact...

A substantial literature has described anisotropy of tactile distance perception across many body parts. In general, the distance between two touches is felt as larger when the touches are oriented with the mediolateral axis of the limbs than when oriented with the proximodistal axis. In this study, we investigated tactile distance perception acros...

Perceptual illusions of the distance between two touches have been used to study mental representations of the body since E. H. Weber’s classic studies in the nineteenth century. For example, on many body parts tactile distance is anisotropic, with distances aligned with body width being perceived as larger than distances aligned with body length o...

Neurocognitive models of higher-level somatosensory processing have emphasised the role of stored body representations in interpreting real-time sensory signals coming from the body (Longo, Azanon and Haggard, 2010; Tame, Azanon and Longo, 2019). The need for such stored representations arises from the fact that immediate sensory signals coming fro...

We can have a distorted perception of our body, instantly induced with multisensory illusions, anaesthesia or Virtual Reality, and recent studies show we can also feel extra body parts. Newport and colleagues (Newport et al., 2016) created an illusion that induces the feeling of having a sixth finger on one's hand, for a brief moment. By changing t...

Our body is central to our sense of self, and distorted body representations are found in several serious medical conditions. This paper reviews evidence that distortions of body representations are also common in healthy individuals, and occur in domains including tactile spatial perception, proprioception, and the conscious body image. Across dom...

Is there a way to visually depict the image people “see” of themselves in their minds’ eyes? And if so, what can these mental images tell us about ourselves? We used a computational reverse-correlation technique to explore individuals’ mental “self-portraits” of their faces and body shapes in an unbiased, data-driven way (total N = 116 adults). Sel...

Perception of distance between two touches varies with orientation on the hand, with distances aligned with hand width perceived as larger than those aligned with hand length. Similar anisotropies are found on other body parts (e.g., the face), suggesting they may reflect a general feature of tactile organization, but appear absent on other body pa...

Egocentric representations allow us to describe the external world as experienced from an individual’s bodily location. We recently developed a novel method of quantifying the weight given to different body parts in egocentric judgments (the Misalignment Paradigm ). We found that both head and torso contribute to simple alter-egocentric spatial jud...

The perceived distance between two touches is anisotropic on many parts of the body. Generally, tactile distances oriented across body width are perceived as larger than distances oriented along body length, though the magnitude of such biases differs substantially across the body. In this study, we investigated tactile distance perception on the b...

Background: Systematic perceptual distortions of tactile space have been documented in healthy adults. In isolated focal dystonia impaired spatial somatosensory processing is suggested to be a central pathophysiological finding, but the structure of tactile space for different body parts has not been previously explored. Objectives: The objectiv...

In a recent study, Lush et al. (Nat Commun 11, 4853, 2020) claimed that they found “substantial relationships” between hypnotizability and experimental measures of the rubber hand illusion. The authors proposed that hypnotizable participants control their phenomenology to meet task expectations arising from the experimental paradigm. They further s...

Perceptual completion is a fundamental perceptual function serving to maintain robust perception against noise. For example, we can perceive a vivid experience of motion even for the discrete inputs across time and space (apparent motion: AM). In vision, stimuli irrelevant to AM perception are suppressed to maintain smooth AM perception along the A...

Hands play a fundamental role in everyday behaviour. Nevertheless, healthy adults show striking misrepresentations of their hands which have been documented by a wide range of studies addressing various aspects of body representation. For example, when asked to indicate the location within the hand of the knuckles, people place them substantially f...

Naturally occurring high levels of caregiver touch promote offspring development in many animal species. Yet, caregiver touch remains a relatively understudied topic in human development, possibly due to challenges of measuring this means of interaction. While parental reports (e.g., questionnaires, diaries) are easy to collect, they may be subject...

Psychophysical experiments have demonstrated large and highly systematic perceptual distortions of tactile space. Such a space can be referred to our experience of the spatial organisation of objects, at representational level, through touch, in analogy with the familiar concept of visual space. We investigated the neural basis of tactile space by...

Egocentric frames of reference take the body as the point of origin of a spatial coordinate system. Bodies, however, are not points, but extended objects, with distinct parts that can move independently of one another. We recently developed a novel paradigm to probe the use of different body parts in simple spatial judgments, what we called the mis...

The possibility of being invisible has long fascinated people. Recent research showed that multisensory illusions can induce experiences of bodily invisibility, allowing the psychological consequences of invisibility to be explored. Here, we demonstrate an illusion of embodying an invisible face. Participants received touches on their face and simu...

Fingers have preferential associations with relative spatial locations. Tactile localisation is faster when the fingers are in these locations, such as when the index finger is in a relatively higher spatial position, and the thumb in a relatively lower position. However, it is unclear whether these associations are related to hands specifically, o...

Observers are able to make generally accurate judgments of the time-to-collision (TTC) of approaching stimuli. Traditional theories have emphasized the role of optical cues about the expansion of the retinal image in this ability. Recent work, however, has further emphasized the role of semantic information about the object. Here we investigate the...

Our body is central to our sense of self and personal identity, yet it can be manipulated in the laboratory in surprisingly easy ways. Several multisensory illusions have shown the flexibility of the mental representation of our bodies by inducing the illusion of owning an artificial body part or having a body part with altered features. Recently,...

The distances between pairs of tactile stimuli oriented across the width of the hand dorsum are perceived as about 40% larger than equivalent distances oriented along the hand length. Clear anisotropies of varying magnitudes have been found on different sites on the limbs and less consistently on other parts of the body, with anisotropies on the ce...

Recent research has shown that proprioception relies on distorted representations of body size and shape. By asking participants to localise multiple landmarks in space, perceptual body maps can be constructed. Such maps of the hand and forearm is highly distorted, with large overestimation of limb width compared to length. Here, we investigated pe...

Patients with the neurological syndrome known as body integrity dysphoria express a desire to amputate seemingly healthy parts of their body. A new study has found that this condition is linked to altered functional connectivity in a distributed neural network underlying body image.

Recent studies have demonstrated that mental representations of the hand dorsum are distorted even for healthy participants. Perceptual hand maps estimated by pointing to specific landmarks (e.g., knuckles and tips of fingers) is stretched and shrunk along the medio-lateral and the proximo-distal axes, respectively. Similarly, tactile distance perc...

Background: Pain and body perception are essentially two subjective mutually influencing experiences. However, in the field of musculoskeletal disorders and rheumatic diseases we lack of a comprehensive knowledge about the relationship between body perception dysfunctions and pain or disability. We systematically mapped the literature published abo...

Spatial distortions in touch have been investigated since the 19th century. For example, two touches applied to the hand dorsum feel farther apart when aligned with the mediolateral axis (i.e., across the hand) than when aligned with the proximodistal axis (along the hand). Stimulations to our sensory receptors are usually dynamic, where spatial an...

How do we ‘see’ ourselves in our mind’s eye? The question of how we represent our self has been at the centre of cultural practices across centuries, as the long tradition of self-portraits attests, and at the centre of our understanding of mental health issues such as body-image disorders. By implementing a reverse-correlation technique to measure...

Finger agnosia refers to a neurological condition in which patients with left posterior parietal lesions fail to identify their fingers, despite having relatively preserved abilities in sensation and skilled action. This dissociation suggests that the structural body representations (BSRs) may be distinct from sensorimotor representations. However,...

Categories provide a fundamental source of information used to structure our perception of the world. For example, when people reproduce the remembered location of a dot in a circle, they implicitly impose vertical and horizontal axes onto the circle, and responses are biased towards the center of each of the resulting quadrants. Such results revea...

Illusions of the perceived distance between two touches on the skin have been studied since the classic work of Weber in the 19th century. For example, anisotropies of perceived tactile distance have been consistently found on several body parts, including the hand dorsum, the forearm, and the face. In each case, tactile distances that are oriented...

Recent studies have reported that adaptation to extreme body types produces aftereffects on judgments of body normality and attractiveness, and also judgments of the size and shape of the viewer’s own body. This latter effect suggests that adaptation could constitute an experimental model of media influences on body image. Alternatively, adaptation...

The goal of this study is to determine how a self-avatar in virtual reality, experienced from different viewpoints on the body (at eye- or chest-height), might influence body part localization, as well as self-localization within the body. Previous literature shows that people do not locate themselves in only one location, but rather primarily in t...

The weightlessness experienced by astronauts has fascinated scientists and the public. On Earth, body weight is given by Newton’s laws as mass times gravitational acceleration. That is, an object’s weight is determined by the pull of gravity on it. We hypothesised that perceived body weight is – like actual weight – dependent on the strength of gra...

There are many similarities and differences between the human hands and feet. On a psychological level, there is some evidence from clinical disorders and studies of tactile localisation in healthy adults for deep functional connections between the hands and feet. One form these connections may take is in common high-level mental representations of...

Tool use leads to plastic changes in sensorimotor body representations underlying tactile perception. The neural correlates of this tool-induced plasticity in humans have not been ad-equately characterized. The present study used event-related brain potentials to investigate the stage of sensory processing modulated by tool use. Somatosensory evoke...

This chapter will focus on the claim that our self-conception is flexible, such that our thoughts about ourselves do not ultimately determine what kind of thing we are. We will review virtual reality research that seems promising as a means of investigating our self-conception. But we will raise certain key methodological issues with this research...

Psychophysical experiments have demonstrated large and highly systematic perceptual distortions of tactile space. We investigated the neural basis of tactile space by analyzing activity patterns induced by tactile stimulation of nine points on a 3 × 3 square grid on the hand dorsum using functional magnetic resonance (fMRI). We used a searchlight a...

Traditional conceptions of peripersonal space emphasised its role in the organisation of skilled action. However, two other aspects of this representation have also been highlighted, namely, its defensive and social aspects. Indeed, having a distinct representation of the space close to the body is crucial for preparing defensive responses to noxio...

Perceived limb position is known to rely on sensory signals and motor commands. Another potential source of input is a standard representation of body posture, which may bias perceived limb position towards more stereotyped positions. Recent results show that tactile stimuli are processed more efficiently when delivered to a thumb in a relatively l...

Our body is a volumetric, 3-dimensional object in the world, and we experience it as such. Existing methods for measuring the perceptual body image, however, have been based on judgments of 1-dimensional length or 2-dimensional images. We developed a new approach to the 3-D perceptual body image of the fingers by asking people to judge whether each...

It is currently not fully understood where people precisely locate themselves in their bodies, particularly in virtual reality. To investigate this, we asked participants to point directly at themselves and to several of their body parts with a virtual pointer, in two virtual reality (VR) setups, a VR headset and a large-screen immersive display (L...

New research demonstrates systematic errors of tactile localisation, involving confusions of body parts and body sides. Such errors do not follow the organisation of topographic maps in somatosensory cortex, suggesting that tactile localisation involves coding of abstract features of limbs.

The perceived distance between two touches has been found to be larger for pairs of stimuli oriented across the width of the body than along the length of the body, for several body parts. Nevertheless, the magnitude of such biases varies from place to place, suggesting systematically different distortions of tactile space across the body. Several...

A large body of research has suggested that localisation of the hand in external space relies on distorted representations of the hand. We developed a paradigm for measuring implicit perceptual maps of the hand (Longo & Haggard, 2010, Proc Natl Acad Sci USA, 107, 11727–11732), which show systematic deviation from actual hand shape, including overes...

The processing of touch depends of multiple factors, such as the properties of the skin and type of receptors stimulated, as well as features related to the actual configuration and shape of the body itself. A large body of research has focused on the effect that the nature of the stimuli has on tactile processing. Less research, however, has focus...

We experience our body as a 3D, volumetric object in the world. Measures of our conscious body image, in contrast, have investigated the perception of body size along one or two dimensions at a time. There is, thus, a discrepancy between existing methods for measuring body image and our subjective experience of having 3D body. Here we assessed in a...

The notion of a personal space surrounding one's ego-center is time-honored. However, few attempts have been made to measure the shape of this space. With increasing use of virtual environments, the question has arisen if real-world aspects, such as gender-effects or the shape of personal space, translate to virtual setups. We conducted two experim...

Perceiving the external spatial location of body parts using position sense requires that immediate proprioceptive afferent signals be integrated with information about body size and shape. Longo and Haggard (Proc Natl Acad Sci 107:11727–11732, 2010) developed a method to measure perceptual hand maps reflecting this metric information about body si...

The Rubber Hand Illusion (RHI) has been widely used to investigate the perception of the bodily self. Commonly used measures of the illusion are self-report questionnaires and proprioceptive drift of the participants’ hands towards the rubber hand. Recent studies have shown that these measures can be dissociated, suggesting they may arise from dist...

It is currently not well understood whether people experience themselves to be located in one or more specific part(s) of their body. Virtual reality (VR) is increasingly used as a tool to study aspects of bodily perception and self-consciousness, due to its strong experimental control and ease in manipulating multi-sensory aspects of bodily experi...

The complete merged raw dataset, with variable annotations. (XLSX)

The set of survey questions the participants answered on paper at the end of the experimental session. (PDF)

Faces are complex, multidimensional, and meaningful visual stimuli. Recently, Araragi, Aotani, & Kitaoka (2012) demonstrated an intriguing face size illusion whereby an inverted face is perceived as larger than a physically identical upright face. Like the face, the human body is a highly familiar and important stimulus in our lives. Here, we inves...