Biology subjects

Johannsen, L.

Publications and source records attributed to Johannsen, L..

3 recordsLinked to original sources

bioRxiv2025

Embodiment of a functionally altered virtual arm in children and adults

While the embodiment of non-human body parts is well-established, the precise conditions that facilitate this remain incompletely understood. One critical yet underexplored factor is whether the non-human body part affords greater or lesser functionality than its biological counterpart. This study investigated how the sensorimotor capabilities of a dynamic virtual arm modulate the experience of embodiment. Given that childrens body representations are widely considered to be more flexible than those of adults, they may be especially suited to embodying functionally altered virtual bodies. To test this, both child and adult participants engaged in goal-directed forward reaching movements with a virtual arm to feed animals within an immersive virtual environment. Reaching functionality was systematically manipulated via changes in visual gain, adjusting the arms length and functionality from a normal (100%) condition, to be slightly reduced (80%); slightly increased (120%); or markedly increased (400%). Our findings reveal that extreme alterations in reaching functionality (400% visual gain) significantly reduced subjective ratings of limb ownership, an effect most evident in adult participants. Despite these perceptual disruptions, participants across all ages adjusted their reach kinematics in ways that reflected an integration of the virtual arms perceived capabilities with the physical limitations of their own bodies. Interestingly, children responded to the altered embodiment with more cautious and less refined movement strategies than adults, suggesting developmental differences in adaptive motor control over non-human bodies. Moreover, across both age groups, exposure to functionally enhanced virtual arms led to increased subjective estimates of reaching affordances, highlighting the influence of altered sensorimotor feedback on perceived action capabilities. Collectively, these results demonstrate that the sense of body ownership, the accuracy of body representations, and the properties of sensorimotor control are closely associated with bodily function. Moreover, while children may exhibit greater tolerance to functional alterations in terms of perceived ownership, they do not show superior motor control. These findings reveal that sensorimotor function and developmental factors interact to shape the boundaries of embodiment in virtual contexts.

animal behavior and cognition↗

bioRxiv2024

The balance stabilising benefit of social touch: influence of an individual's age and the partner's relative body characteristics

Interpersonal touch (IPT) is a successful strategy to support the stability of and individuals body balance during a multitude of activities in daily life, including physical education and therapy. Despite common practice, however, the influence of an individuals anthropometry and other personal characteristics, such as age, balancing skills, motor experience, and sex as well as interindividual differences in these characteristics between interaction partners on the balance stabilising benefit of social touch is unknown. We assessed an individuals balance stability and change due to IPT provision during single-legged stance in 72 pairs (age range 4 to 63 years) under four sensory conditions: with or without vision in combination with IPT or without. Two participant subgroups were created: one of more vulnerable with low stability and one of more stable, mature participants. Best fitting multiple linear regression models, including moderating variables, for explaining the benefit of IPT in each visual condition indicated that without vision, an individuals benefit of IPT was determined by their balancing skill and the partner-related difference in balancing skill but not by any other factors or partner-related differences. Especially vulnerable individuals improved considerably with IPT when vision was unavailable. With vision complementing IPT, however, an individuals age-dependent motor developmental potential became an additional moderating factor. These findings indicate that the extent to which IPT is benefitting mutual balance stabilisation does not depend on biomechanical factors. Instead, the IPT benefit emerges as a product of both partners sensorimotor capabilities moderated by a persons motor developmental potential when visual feedback could be utilised. We discuss a theoretical framework that accounts for the observed dependencies of the effect of haptic social support on balance control. Significance StatementThis work contributes to a better understanding of the factors influencing the benefit of interpersonal touch for balance stabilization across a wide age range from children to senior adults. It is the first work that investigates the role of both individual factors and relative differences between interaction partners on the amount of benefit of IPT and takes moderating factors such as age-related motor developmental potential, sex, and body mass index into account. Future studies can build on this work when selecting or simulating an optimal partner, especially for individuals with postural instability, for example due to age or sensorimotor deficits.

neuroscience↗

bioRxiv2019

Robotic light touch assists human balance control during maximum forward reaching

ObjectiveWe investigated how light interpersonal touch (IPT) provided by a robotic system supports human individuals performing a challenging balance task compared to IPT provided by a human partner. BackgroundIPT augments the control of body balance in contact receivers without a provision of mechanical body weight support. The nature of the processes governing the social haptic interaction, whether they are predominantly reactive or predictive, is uncertain. MethodTen healthy adult individuals performed maximum forward reaching (MFR) without visual feedback while standing upright. We evaluated their control of reaching behaviour and of body balance during IPT provided by either another human individual or by a robotic system in two alternative control modes (reactive vs predictive). ResultsChanges in reaching behaviour under the robotic IPT, such as lower speed and straighter direction were linked to reduced body sway. MFR of the contact receiver was influenced by the robotic control mode such as that a predictive mode reduced movement variability and increased postural stability to a greater extend in comparison to human IPT. The effects of the reactive robotic system, however, more closely resembled the effects of IPT provided by human contact provider. ConclusionThe robotic IPT system was as supportive as human IPT. Robotic IPT seemed to afford more specific adjustments, such as trading reduced speed for increased accuracy, to meet the intrinsic demands and constraints of the robotic system. Possibly, IPT provided by a human contact provider reflected reactive interpersonal postural coordination more similar to the robotic systems follower mode. PrecisInterpersonal touch support by a robotic system was evaluated against support provided a human partner during maximum forward reaching. Human contact receivers showed comparable benefits in their reaching postural performance between the support conditions. Coordination with the robotic system, nevertheless, afforded specific adaptations in the reaching behaviour.

neuroscience↗