Bodily illusions in young children: developmental change in visual and proprioceptive contributions to perceived hand position

Developmental changes of bodily self-consciousness in adolescent girls

The body and the self change markedly during adolescence, but how does bodily self-consciousness, the pre-reflexive experience of being a bodily subject, change? We addressed this issue by studying embodiment towards virtual avatars in 70 girls aged 10-17 years. We manipulated the synchrony between participants' and avatars' touch or movement, as well as the avatar visual shape or size relative to each participant's body. A weaker avatar's embodiment in case of mismatch between the body seen in virtual reality and the real body is indicative of a more robust bodily self-consciousness. In both the visuo-tactile and the visuo-motor experiments, asynchrony decreased ownership feeling to the same extent for all participants, while the effect of asynchrony on agency feeling increased with age. In the visuo-tactile experiment, incongruence in visual appearance did not affect agency feeling but impacted ownership, especially in older teenage girls. These findings highlight the higher malleability of bodily self-consciousness at the beginning of adolescence and suggest some independence between body ownership and agency.

Moving a missing hand: children born with below elbow deficiency can enact hand grasp patterns with their residual muscles

Children with a unilateral congenital below elbow deficiency (UCBED) have one typical upper limb and one that lacks a hand, ending below the elbow at the proximal/mid forearm. UCBED is an isolated condition, and affected children otherwise develop normal sensorimotor control. Unlike adults with upper limb absence, the majority of whom have an acquired loss, children with UCBED never developed a hand, so their residual muscles have never actuated an intact limb. Their ability to purposefully modulate affected muscle activity is often assumed to be limited, and this assumption has influenced prosthetic design and prescription practices for this population as many modern devices derive control signals from affected muscle activity. To better understand the motor capabilities of the affected muscles, we used ultrasound imaging to study 6 children with UCBED. We examined the extent to which subjects activate their affected muscles when performing mirrored movements with their typical and missing hands. We demonstrate that all subjects could intentionally and consistently enact at least five distinct muscle patterns when attempting different missing hand movements (e.g., power grasp) and found similar performance across affected and typically developed limbs. These results suggest that although participants had never actuated the missing hand they could distinctively and consistently activate the residual muscle patterns associated with actions on the unaffected side. These findings indicate that motor control still develops in the absence of the normal effector, and can serve as a guide for developing prostheses that leverage the full extent of these children's motor control capabilities.

Paradoxical decrease of imitation performance with age in children

Imitation development was studied in a cross-sectional design involving 174 primary-school children (aged 6-10), focusing on the effect of actions' complexity and error analysis to infer the underlying cognitive processes. Participants had to imitate the model's actions as if they were in front of a mirror ('specularly'). Complexity varied across three levels: movements of a single limb; arm and leg of the same body side; or arm and leg of opposite body sides. While the overall error rate decreased with age, this was not true of all error categories. The rate of 'side' errors (using a limb of the wrong body side) paradoxically increased with age (from 9 years). However, with increasing age, the error rate also became less sensitive to the complexity of the action. This pattern is consistent with the hypothesis that older children have the working memory (WM) resources and the body knowledge necessary to imitate 'anatomically', which leads to additional side errors. Younger children might be paradoxically free from such interference because their WM and/or body knowledge are insufficient for anatomical imitation. Yet, their limited WM resources would prevent them from successfully managing the conflict between spatial codes involved in complex actions (e.g. moving the left arm and the right leg). We also found evidence that action side and content might be stored in separate short-term memory (STM) systems: increasing the number of sides to be encoded only affected side retrieval, but not content retrieval; symmetrically, increasing the content (number of movements) of the action only affected content retrieval, but not side retrieval. In conclusion, results suggest that anatomical imitation might interfere with specular imitation at age 9 and that STM storages for side and content of actions are separate.

Dexamphetamine widens temporal and spatial binding windows in healthy participants

BACKGROUND

The pathophysiology of psychosis is complex, but a better understanding of stimulus binding windows (BWs) could help to improve our knowledge base. Previous studies have shown that dopamine release is associated with psychosis and widened BWs. We can probe BW mechanisms using drugs of specific interest to psychosis. Therefore, we were interested in understanding how manipulation of the dopamine or catecholamine systems affect psychosis and BWs. We aimed to investigate the effect of dexamphetamine, as a dopamine-releasing stimulant, on the BWs in a unimodal illusion: the tactile funneling illusion (TFI).

METHODS

We conducted a randomized, double-blind, counterbalanced placebo-controlled crossover study to investigate funnelling and errors of localization. We administered dexamphetamine (0.45 mg/kg) to 46 participants. We manipulated 5 spatial (5-1 cm) and 3 temporal (0, 500 and 750 ms) conditions in the TFI.

RESULTS

We found that dexamphetamine increased funnelling illusion (p = 0.009) and increased the error of localization in a delay-dependent manner (p = 0.03). We also found that dexamphetamine significantly increased the error of localization at 500 ms temporal separation and 4 cm spatial separation (p _interaction = 0.009; p _{500ms|4cm v. baseline} = 0.01).

LIMITATIONS

Although amphetamine-induced models of psychosis are a useful approach to understanding the physiology of psychosis related to dopamine hyperactivity, dexamphetamine is equally effective at releasing noradrenaline and dopamine, and, therefore, we were unable to tease apart the effects of the 2 systems on BWs in our study.

CONCLUSION

We found that dexamphetamine increases illusory perception on the unimodal TFI in healthy participants, which suggests that dopamine or other catecholamines have a role in increasing tactile spatial and temporal BWs.

The Relative Contributions of Visual and Proprioceptive Inputs on Hand Localization in Early Childhood

Forming an accurate representation of the body relies on the integration of information from multiple sensory inputs. Both vision and proprioception are important for body localization. Whilst adults have been shown to integrate these sources in an optimal fashion, few studies have investigated how children integrate visual and proprioceptive information when localizing the body. The current study used a mediated reality device called MIRAGE to explore how the brain weighs visual and proprioceptive information in a hand localization task across early childhood. Sixty-four children aged 4–11 years estimated the position of their index finger after viewing congruent or incongruent visuo-proprioceptive information regarding hand position. A developmental trajectory analysis was carried out to explore the effect of age on condition. An age effect was only found in the incongruent condition which resulted in greater mislocalization of the hand toward the visual representation as age increased. Estimates by younger children were closer to the true location of the hand compared to those by older children indicating less weighting of visual information. Regression analyses showed localizations errors in the incongruent seen condition could not be explained by proprioceptive accuracy or by general attention or social differences. This suggests that the way in which visual and proprioceptive information are integrated optimizes throughout development, with the bias toward visual information increasing with age.

Greater reliance on proprioceptive information during a reaching task with perspective manipulation among children with autism spectrum disorders

Difficulties with visual perspective-taking among individuals with autism spectrum disorders remain poorly understood. Many studies have presumed that first-person visual input can be mentally transformed to a third-person perspective during visual perspective-taking tasks; however, existing research has not fully revealed the computational strategy used by those with autism spectrum disorders for taking another person’s perspective. In this study, we designed a novel approach to test a strategy using the opposite-directional effect among children with autism spectrum disorders. This effect refers to how a third-person perspective as a visual input alters a cognitive process. We directly manipulated participants’ visual perspective by placing a camera at different positions; participants could watch themselves from a third-person perspective during a reaching task with no endpoint feedback. During a baseline task, endpoint bias (with endpoint feedback but no visual transformation) did not differ significantly between groups. However, the endpoint was affected by extrinsic coordinate information in the control group relative to the autism spectrum disorders group when the visual perspective was transformed. These results indicate an increased reliance on proprioception during the reaching task with perspective manipulation in the autism spectrum disorders group.

The rubber hand illusion in children: What are we measuring?

The rubber hand illusion (RHI) is a much-studied bodily illusion that has been used in a wide number of populations to investigate the plasticity of the mental body representation. In adult participants, the wide adoption of the illusion has led to a proliferation of experimental variations of the illusion, and with that, considerable apparent inconsistencies in both empirical results and conceptual interpretations. In turn, this makes it challenging to integrate empirical findings and to identify what those findings together can tell us about the representation of the body in the brain. More recently, scientists have started applying the illusion to populations of children, in order to better understand how body representations develop in both typically developing children and in clinical populations. With this field now starting to expand, we believe it is both urgent and important to prevent unintended methodological variability from hindering the consistency of the paediatric literature as it has the adult literature. With this aim in mind, we review the 12 currently available paediatric RHI studies, and summarise their key methodological choices and conceptual definitions. We highlight a number of important discrepancies, particularly where seemingly equivalent analysis choices might significantly affect the interpretation of results, and make recommendations for future studies. We hope this will allow this important and emerging field to benefit from the synergy that results from multiple studies using convergent and consistent empirical methods.

The long developmental trajectory of body representation plasticity following tool use

Humans evolution is distinctly characterized by their exquisite mastery of tools, allowing them to shape their environment in more elaborate ways compared to other species. This ability is present ever since infancy and most theories indicate that children become proficient with tool use very early. In adults, tool use has been shown to plastically modify metric aspects of the arm representation, as indexed by changes in movement kinematics. To date, whether and when the plastic capability of updating the body representation develops during childhood remains unknown. This question is particularly important since body representation plasticity could be impacted by the fact that the human body takes years to achieve a stable metric configuration. Here we assessed the kinematics of 90 young participants (8-21 years old) required to reach for an object before and after tool use, as a function of their pubertal development. Results revealed that tool incorporation, as indexed by the adult typical kinematic pattern, develops very slowly and displays a u-shaped developmental trajectory. From early to mid puberty, the changes in kinematics following tool use seem to reflect a shortened arm representation, opposite to what was previously reported in adults. This pattern starts reversing after mid puberty, which is characterized by the lack of any kinematics change following tool use. The typical adult-like pattern emerges only at late puberty, when body size is stable. These findings reveal the complex dynamics of tool incorporation across development, possibly indexing the transition from a vision-based to a proprioception-based body representation plasticity.

Hand size representation in healthy children and young adults

Whereas we experience our body as a coherent volumetric object, the brain appears to maintain highly fragmented representations of individual body parts. Little is known about how body representations of hand size and shape are built and evolve during infancy and young adulthood. This study aimed to investigate the effect of hand side, handedness, and age on the development of central hand size representation. The observational study with comparison groups was conducted with 90 typically developing Belgian school children and young adults (48 male and 42 female; age range = 5.0-23.0 years; 49 left-handed and 41 right-handed). Participants estimated their hand size and shape using two different tasks. In the localization task, participants were verbally cued to judge the locations of 10 anatomical landmarks of an occluded hand. An implicit hand size map was constructed and compared with actual hand dimensions. In the template selection task, the explicit hand shape was measured with a depictive method. Hand shape indexes were calculated and compared for the actual, implicit, and explicit conditions. Participants were divided into four age groups (5-8 years, 9-10 years, 11-16 years, and 17-23 years). Implicit hand maps featured underestimation of finger length and overestimation of hand width, which is already present in the youngest children. Linear mixed modeling revealed no influence of hand side on finger length underestimation; nonetheless, a significant main effect of age (p = .001) was exposed. Sinistrals aged 11 to 16 years showed significantly less underestimation (p = .03) than dextrals of the same age. As for the hand shape, the implicit condition differed significantly with the actual and explicit conditions (p < .001). Again, the implicit shape index was subjected to handedness and age effects, with significant differences being found between sinistrals and dextrals in the age groups of 9 and 10 years (p = .029) and 11 to 16 years (p < .001). In conclusion, the implicit metric component of the hand representation in children and young adults is misperceived, featuring shortened fingers and broadened hands since a very young age. Crucially, the finger length underestimation increases with age and shows a different developmental trajectory for sinistrals and dextrals. In contrast, the explicit hand shape is approximately veridical and seems immune from age and handedness effects. This study confirms the dual character of somatoperception and establishes a point of reference for children and young adults.

Imagining handwriting movements in a usual or unusual position: effect of posture congruency on visual and kinesthetic motor imagery

Motor imagery has been used in training programs to improve the performance of motor skills. Handwriting movement may benefit from motor imagery training. To optimize the efficacy of this kind of training, it is important to identify the factors that facilitate the motor imagery process for handwriting movements. Several studies have shown that motor imagery is more easily achieved when there is maximum compatibility between the actual posture and the imagined movement. We, therefore, examined the effect of posture congruency on visual and kinesthetic motor imagery for handwriting movements. Adult participants had to write and imagine writing a sentence by focusing on the evocation of either the kinesthetic or visual consequences of the motion. Half the participants performed the motor imagery task in a congruent posture (sitting with a hand ready for writing), and half in an incongruent one (standing with arms crossed behind the back and fingers spread wide). The temporal similarity between actual and imagined movement times and the vividness of the motor imagery were evaluated. Results revealed that temporal similarity was stronger in the congruent posture condition than in the incongruent one. Furthermore, in the incongruent posture condition, participants reported greater difficulty forming a precise kinesthetic motor image of themselves writing than a visual image, whereas no difference was observed in the congruent posture condition. Taken together, our results show that postural information is taken into account during the mental simulation of handwriting movements. The implications of these findings for guiding the design of motor imagery training are discussed.

Auditory-induced body distortions in children and adults

Recent studies have shown that body-representations can be altered by dynamic changes in sound. In the so-called “auditory Pinocchio illusion” participants feel their finger to be longer when the action of pulling their finger is paired with a rising pitch. Here, we investigated whether preschool children - an age group in which multisensory body-representations are still fine-tuning - are also sensitive to this illusion. In two studies, sixty adult and sixty child participants heard sounds rising or falling in pitch while the experimenter concurrently pulled or pressed their index finger on a vertical (Experiment 1) or horizontal axis (Experiment 2). Results showed that the illusion was subjected to axis and age: both adults and children reported their finger to be longer in Experiment 1, but not in Experiment 2. However, while in adults the feeling of finger elongation corresponded to a recalibration of the fingertip’s felt position upwards, this was not the case in children, who presented a dissociation between the feeling of finger elongation and the perceived fingertip position. Our results reveal that the ‘auditory Pinocchio illusion’ is constrained to the vertical dimension and suggest that multisensory interactions differently contribute to subjective feelings and sense of position depending on developmental stage.

Proprioceptive accuracy in Immersive Virtual Reality: A developmental perspective

Proprioceptive development relies on a variety of sensory inputs, among which vision is hugely dominant. Focusing on the developmental trajectory underpinning the integration of vision and proprioception, the present research explores how this integration is involved in interactions with Immersive Virtual Reality (IVR) by examining how proprioceptive accuracy is affected by Age, Perception, and Environment. Individuals from 4 to 43 years old completed a self-turning task which asked them to manually return to a previous location with different sensory modalities available in both IVR and reality. Results were interpreted from an exploratory perspective using Bayesian model comparison analysis, which allows the phenomena to be described using probabilistic statements rather than simplified reject/not-reject decisions. The most plausible model showed that 4-8-year-old children can generally be expected to make more proprioceptive errors than older children and adults. Across age groups, proprioceptive accuracy is higher when vision is available, and is disrupted in the visual environment provided by the IVR headset. We can conclude that proprioceptive accuracy mostly develops during the first eight years of life and that it relies largely on vision. Moreover, our findings indicate that this proprioceptive accuracy can be disrupted by the use of an IVR headset.

Cortical signatures of vicarious tactile experience in four-month-old infants

The human brain recruits similar brain regions when a state is experienced (e.g., touch, pain, actions) and when that state is passively observed in other individuals. In adults, seeing other people being touched activates similar brain areas as when we experience touch ourselves. Here we show that already by four months of age, cortical responses to tactile stimulation are modulated by visual information specifying another person being touched. We recorded somatosensory evoked potentials (SEPs) in 4-month-old infants while they were presented with brief vibrotactile stimuli to the hands. At the same time that the tactile stimuli were presented the infants observed another person's hand being touched by a soft paintbrush or approached by the paintbrush which then touched the surface next to their hand. A prominent positive peak in SEPs contralateral to the site of tactile stimulation around 130 ms after the tactile stimulus onset was of a significantly larger amplitude for the "Surface" trials than for the "Hand" trials. These findings indicate that, even at four months of age, somatosensory cortex is not only involved in the personal experience of touch but can also be vicariously recruited by seeing other people being touched.

The Role of Age on Multisensory Bodily Experience: An Experimental Study with a Virtual Reality Full-Body Illusion

A growing body of evidence demonstrated that it is feasible to induce ownership over an artificial body to alter bodily experience. However, several uncharted aspects about full-body illusion applications need to be tackled before a complete exploitation of these methods in clinical practice. This work is devoted to explore possible individual age-related differences in shaping changes in body representations induced with a full-body illusion. A total of 40 women were divided into two different age groups according to the median of the variable age. Participants estimated the width of three different body parts (i.e., shoulders, abdomen, and hips) before the entire illusion was induced (baseline), and after the synchronous and the asynchronous conditions. Results revealed that 26-to-55-year-old participants were more resistant to changes induced by the bodily illusion, whereas 19-to-25-year-old participants underestimated their bodies after both conditions. The findings were discussed in terms of the literature exploring age differences in responses to bodily illusion, which could suggest a Bayesian mechanism underlying these individual differences.

Neural predictors of motor control and impact of visuo-proprioceptive information in youth

For successful motor control, the central nervous system is required to combine information from the environment and the current body state, which is provided by vision and proprioception respectively. We investigated the relative contribution of visual and proprioceptive information to upper limb motor control and the extent to which structural brain measures predict this performance in youth (n = 40; age range 9-18 years). Participants performed a manual tracking task, adopting in-phase and anti-phase coordination modes. Results showed that, in contrast to older participants, younger participants performed the task with lower accuracy in general and poorer performance in anti-phase than in-phase modes. However, a proprioceptive advantage was found at all ages, that is, tracking accuracy was higher when proprioceptive information was available during both in- and anti-phase modes at all ages. The microstructural organization of interhemispheric connections between homologous dorsolateral prefrontal cortices, and the cortical thickness of the primary motor cortex were associated with sensory-specific accuracy of tracking performance. Overall, the findings suggest that manual tracking performance in youth does not only rely on brain regions involved in sensorimotor processing, but also on prefrontal regions involved in attention and working memory. Hum Brain Mapp 38:5628-5647, 2017. © 2017 Wiley Periodicals, Inc.

The Development of Tactile Perception

Touch is the first of our senses to develop, providing us with the sensory scaffold on which we come to perceive our own bodies and our sense of self. Touch also provides us with direct access to the external world of physical objects, via haptic exploration. Furthermore, a recent area of interest in tactile research across studies of developing children and adults is its social function, mediating interpersonal bonding. Although there are a range of demonstrations of early competence with touch, particularly in the domain of haptics, the review presented here indicates that many of the tactile perceptual skills that we take for granted as adults (e.g., perceiving touches in the external world as well as on the body) take some time to develop in the first months of postnatal life, likely as a result of an extended process of connection with other sense modalities which provide new kinds of information from birth (e.g., vision and audition). Here, we argue that because touch is of such fundamental importance across a wide range of social and cognitive domains, it should be placed much more centrally in the study of early perceptual development than it currently is.

Associations Between Interoceptive Cognition and Age in Autism Spectrum Disorder and Typical Development

Interoceptive awareness is linked to emotional and social cognition, which are impaired in individuals with autism spectrum disorder (ASD). It is unknown how this ability is associated with age in either typical or atypical development. We used a standard test of interoceptive accuracy (IA) to investigate these questions in children and adults with and without ASD. Perceived number of heartbeats over 4 time intervals was compared with actual heart rate to determine IA. Effects of group, age, IQ, heart rate, and mental counting ability on accuracy were assessed using multiple regression. Post hoc correlations were performed to clarify significant interactions. Age was unrelated to IA in both groups when IQ ≥115. When IQ <115, this relationship was positive in typical development and negative in ASD. These results suggest that cognitive ability moderates the effect of age on IA differently in autism and typical development.

The Development of a Cross-Modal Sense of Body Ownership

In this study, we investigated the contribution of tactile and proprioceptive cues to the development of the sense of body ownership by testing the susceptibility of 4- to 5-year-old children, 8- to 9-year-old children, and adults to the somatic rubber-hand illusion (SRHI). We found that feelings of owning a rubber hand in the SHRI paradigm, as assessed by explicit reports (i.e., questionnaire), are already present by age 4 and do not change throughout development. In contrast, the effect of the illusion on the sense of hand position, as assessed by a pointing task, was present only in 8- to 9-year-old children and adults; the magnitude of such capture increased with age. Our findings reveal that tactile-proprioceptive interactions contributed differently to the two aspects characterizing the SRHI: Although the contribution of such interactions to an explicit sense of self was similar across age groups, their contribution to the more implicit recalibration of hand position is still developing by age 9.

Does somatosensation change with age in children and adolescents? A systematic review

BACKGROUND

Somatosensory modalities, such as touch, proprioception and haptic ability, greatly influence the achievement of developmental milestones for children. Describing somatosensory impairment, natural variability and typical or expected developmental changes across age groups will help establish frameworks for intervention in clinical populations. This systematic review aimed to determine how different somatosensory modalities develop across childhood into adolescence to use as a point of reference for children at risk of somatosensory impairment.

METHODS

Searches of five electronic databases were undertaken through EBSCO-host (MEDLINE, CINAHL, PsycINFO, SPORTDiscus and ERIC) for studies measuring at least one somatosensory modality in typically developing individuals between birth and 18 years and analysed by age. Characteristics of studies were collected including country of origin, sample size, demographics and outcome measure used. Quality assessment and data extraction were performed by two independent reviewers.

RESULTS

Twenty three cross-sectional studies were included from a total of 188 articles retrieved: 8 examined aspects of touch, 5 proprioception and 10 haptic ability. Variability of study designs and variation in assessment tools precluded any formal meta-analysis.

CONCLUSIONS

Somatosensation matures through childhood into adolescence; however, the present review found the pattern of somatosensory development varied depending on the assessment tool used and the aspect of somatosensation being measured, making it difficult to describe typical performance. There is a need for comprehensive assessment batteries to measure the somatosensation, including touch, proprioception and haptic ability, of children at risk of somatosensory impairment to aid in the development of effective interventions.

Proprioceptive-Visual Integration and Embodied Cognition: A Developmental Perspective

The present study addressed whether a spatial matching task relying on inter-sensory judgments might be influenced by the transition between egocentric and decentered mode of thinking. Thirty-six children aged 5, 7, or 9 years performed a paramedian correspondence task with conditions requiring inter-sensory integration (visual-proprioceptive) and a problem-solving task. The visual information was given through a mirror that perturbed the sensory judgments in the paramedian correspondence task. The results did not corroborate the hypotheses; nevertheless, the increasing importance of proprioception in the perceptual judgments for older children suggests that although younger children may be body centered (egocentric mode of thinking), older children seemed more able to use body to mediate their perceptual judgments.

Over my fake body: body ownership illusions for studying the multisensory basis of own-body perception

Which is my body and how do I distinguish it from the bodies of others, or from objects in the surrounding environment? The perception of our own body and more particularly our sense of body ownership is taken for granted. Nevertheless, experimental findings from body ownership illusions (BOIs), show that under specific multisensory conditions, we can experience artificial body parts or fake bodies as our own body parts or body, respectively. The aim of the present paper is to discuss how and why BOIs are induced. We review several experimental findings concerning the spatial, temporal, and semantic principles of crossmodal stimuli that have been applied to induce BOIs. On the basis of these principles, we discuss theoretical approaches concerning the underlying mechanism of BOIs. We propose a conceptualization based on Bayesian causal inference for addressing how our nervous system could infer whether an object belongs to our own body, using multisensory, sensorimotor, and semantic information, and we discuss how this can account for several experimental findings. Finally, we point to neural network models as an implementational framework within which the computational problem behind BOIs could be addressed in the future.

Developmental changes in the visual-proprioceptive integration threshold of children

The ability to detect artificially induced visual-proprioceptive asynchrony reflects an awareness of the first-person experience of self-generated movement. The current study assessed children's (5- to 8-year-olds) and adults' ability to integrate asynchronous visual and proprioceptive stimulation by delaying the visual feedback of self-generated action in videos. Children and adults observed a monitor showing their movements of a joystick at varying delay durations and were then asked to make judgments on whether their movements appeared to be delayed or live. Children demonstrated age-related differences in their reporting of delay judgments across all delay conditions. Adults' performances on the same task exceeded those of children. The results of this study provide a mapping of visual-proprioceptive integration abilities in 5 to 8 year old children. The age-related increase in sensitivity to visual-proprioceptive asynchrony is suggestive of increasing sensitivity to the temporal properties of multisensory feedback of self-generated movement with development.