125 research outputs found
The Role of Optic Flow and Gaze Direction on Postural Control
Objective: The observers use the optic flow to control self-motion. However, the current state of knowledge indicates that it is difficult to understand how optic flow is used by the visual system without a direct measurement of the changes in the flow patterns caused by eye movements during natural behaviour. The purpose of this literature review is to highlight the importance of the integration between optic flow and eye movements for postural control. Methods: A literature review of the electronic papers through July 2022 was independently performed by three investigators. The selection of the studies was made by a search on PubMed, Scopus, and Google Scholar with two groups of selected keywords. We excluded papers performed on subjects with pathologies, children, and the elderly. Results: The results of this literature analysis highlight that eye movements are required to drive visual motion processing and heading perception in both static and dynamic contexts. Conclusion: Although we now know many neural mechanisms that process heading direction from the optic flow field, a consideration of optic flow patterns relative to gaze direction provides more detailed information on how the retinal flow field is used to control body balance. Doi: 10.28991/ESJ-2022-06-06-020 Full Text: PD
More than skin deep: body representation beyond primary somatosensory cortex
The neural circuits underlying initial sensory processing of somatic information are relatively well understood. In contrast, the processes that go beyond primary somatosensation to create more abstract representations related to the body are less clear. In this review, we focus on two classes of higher-order processing beyond somatosensation. Somatoperception refers to the process of perceiving the body itself, and particularly of ensuring somatic perceptual constancy. We review three key elements of somatoperception: (a) remapping information from the body surface into an egocentric reference frame (b) exteroceptive perception of objects in the external world through their contact with the body and (c) interoceptive percepts about the nature and state of the body itself. Somatorepresentation, in contrast, refers to the essentially cognitive process of constructing semantic knowledge and attitudes about the body, including: (d) lexical-semantic knowledge about bodies generally and one’s own body specifically, (e) configural knowledge about the structure of bodies, (f) emotions and attitudes directed towards one’s own body, and (g) the link between physical body and psychological self. We review a wide range of neuropsychological, neuroimaging and neurophysiological data to explore the dissociation between these different aspects of higher somatosensory function
Embodied learning of a generative neural model for biological motion perception and inference
Although an action observation network and mirror neurons for understanding the actions and intentions of others have been under deep, interdisciplinary consideration over recent years, it remains largely unknown how the brain manages to map visually perceived biological motion of others onto its own motor system. This paper shows how such a mapping may be established, even if the biologically motion is visually perceived from a new vantage point. We introduce a learning artificial neural network model and evaluate it on full body motion tracking recordings. The model implements an embodied, predictive inference approach. It first learns to correlate and segment multimodal sensory streams of own bodily motion. In doing so, it becomes able to anticipate motion progression, to complete missing modal information, and to self-generate learned motion sequences. When biological motion of another person is observed, this self-knowledge is utilized to recognize similar motion patterns and predict their progress. Due to the relative encodings, the model shows strong robustness in recognition despite observing rather large varieties of body morphology and posture dynamics. By additionally equipping the model with the capability to rotate its visual frame of reference, it is able to deduce the visual perspective onto the observed person, establishing full consistency to the embodied self-motion encodings by means of active inference. In further support of its neuro-cognitive plausibility, we also model typical bistable perceptions when crucial depth information is missing. In sum, the introduced neural model proposes a solution to the problem of how the human brain may establish correspondence between observed bodily motion and its own motor system, thus offering a mechanism that supports the development of mirror neurons
Visual and proprioceptive interaction in patients with bilateral vestibular loss
Following bilateral vestibular loss (BVL) patients gradually adapt to the loss of vestibular input and rely more on other sensory inputs. Here we examine changes in the way proprioceptive and visual inputs interact. We used functional magnetic resonance imaging (fMRI) to investigate visual responses in the context of varying levels of proprioceptive input in 12 BVL subjects and 15 normal controls. A novel metal-free vibrator was developed to allow vibrotactile neck proprioceptive input to be delivered in the MRI system. A high level (100 Hz) and low level (30 Hz) control stimulus was applied over the left splenius capitis; only the high frequency stimulus generates a significant proprioceptive stimulus. The neck stimulus was applied in combination with static and moving (optokinetic) visual stimuli, in a factorial fMRI experimental design. We found that high level neck proprioceptive input had more cortical effect on brain activity in the BVL patients. This included a reduction in visual motion responses during high levels of proprioceptive input and differential activation in the midline cerebellum. In early visual cortical areas, the effect of high proprioceptive input was present for both visual conditions but in lateral visual areas, including V5/MT, the effect was only seen in the context of visual motion stimulation. The finding of a cortical visuo-proprioceptive interaction in BVL patients is consistent with behavioural data indicating that, in BVL patients, neck afferents partly replace vestibular input during the CNS-mediated compensatory process. An fMRI cervico-visual interaction may thus substitute the known visuo-vestibular interaction reported in normal subject fMRI studies. The results provide evidence for a cortical mechanism of adaptation to vestibular failure, in the form of an enhanced proprioceptive influence on visual processing. The results may provide the basis for a cortical mechanism involved in proprioceptive substitution of vestibular function in BVL patients
Visuo-vestibular mechanisms of bodily self-consciousness
Bodily self-consciousness is linked to multisensory integration and is particularly dependent on vestibular perception providing the brain with the main sensory cues about body motion and location in space. Vestibular and visual inputs are permanently balanced and integrated to encode the most optimal representation of the external world and of the observer in the central nervous system. Vection, an illusory self-motion experience induced only by visual stimuli, illustrates the fact that the visual and the vestibular systems share common neural underpinnings and a similar phenomenology. Optokinetic stimulation inducing vection and direct vestibular stimulation induce whole-body motion sensations that can be used to explore multisensory interactions. A failure in visuo-vestibular integration, artificially induced by the methods of cognitive psychology or in pathological conditions, has also been reported to altered own body perception and bodily self-consciousness. The respective contributions of the vestibular and visual systems to bodily self-consciousness amongst other polymodal sensory mechanisms, and the neural correlates of visuo-vestibular convergence, should be better understood. We first performed a neuroimaging study of brain regions where optokinetic and vestibular stimuli converge, using 7T functional magnetic resonance imaging in individual subjects. We identified three main regions of convergence: (1) the depth of supramarginal gyrus or retroinsular cortex, (2) the surface of supramarginal gyrus at the temporo-parietal junction, (3) and the posterior part of middle temporal gyrus and superior temporal sulcus. Then, we aimed to induce the embodiment of an external fake rubber hand through visuo-tactile conflict - the so-called rubber hand illusion paradigm, and studied how this integration is modulated by vection. Subjects experiencing vection in the direction of the rubber hand mislocalised the position of their real hand towards the rubber hand indicating that visuo-vestibular stimuli can enhance visuo-tactile integration. We also investigated if visuo-proprioceptive and tactile integration in peripersonal space could be dynamically updated based on the congruency of visual and proprioceptive feedback. A pair of rubber hands or feet provided visual feedback. Fake and real limbs were crossed or uncrossed. We showed that sensory cues were integrated in peripersonal space, dynamically reshaped but only for hands. Finally, we investigated a rare case of an illusory own body perception in an epileptic patient suffering from multiple daily disembodiments during seizures. Seizures were associated to a focal cortical microdysplasia juxtaposed to a developmental venous anomaly in the left angular gyrus, a brain region known to be important for visuo-vestibular integration and bodily self-consciousness. Our results characterize the inferior parietal lobule as a crucial structure in merging visual, vestibular, tactile and proprioceptive inputs, allowing the emergence of the global and unified experience of being âI.â Multisensory body representation can be reshaped transiently using visual and vestibular signals or in relation to a medical condition affecting the temporo-parietal junction. The integration of visual and vestibular signals, aims to adapt dynamically our internal representations to constant changes occurring in our environment
Influenza dell'optic flow sul controllo posturale
The study of optic flow on postural control may explain how self-motion perception contributes to postural stability in young males and females and how such function changes in the old falls risk population.
Study I: The aim was to examine the optic flow effect on postural control in young people (n=24), using stabilometry and surface-electromyography. Subjects viewed expansion and contraction optic flow stimuli which were presented full field, in the foveral or in the peripheral visual field. Results showed that optic flow stimulation causes an asymmetry in postural balance and a different lateralization of postural control in men and women. Gender differences evoked by optic flow were found both in the muscle activity and in the prevalent direction of oscillation. The COP spatial variability was reduced during the view of peripheral stimuli which evoked a clustered prevalent direction of oscillation, while foveal and random stimuli induced non-distributed directions.
Study II was aimed at investigating the age-related mechanisms of postural stability during the view of optic flow stimuli in young (n=17) and old (n=19) people, using stabilometry and kinematic. Results showed that old people showed a greater effort to maintain posture during the view of optic flow stimuli than the young. Elderly seems to use the head stabilization on trunk strategy.
Visual stimuli evoke an excitatory input on postural muscles, but the stimulus structure produces different postural effects. Peripheral optic flow stabilizes postural sway, while random and foveal stimuli provoke larger sway variability similar to those evoked in baseline. Postural control uses different mechanisms within each leg to produce the appropriate postural response to interact with extrapersonal environment. Ageing reduce the effortlessness to stabilize posture during optic flow, suggesting a neuronal processing decline associated with difficulty integrating multi-sensory information of self-motion perception and increasing risk of falls
Multisensory mechanisms of body ownership and self-location
Having an accurate sense of the spatial boundaries of the body is a prerequisite for
interacting with the environment and is thus essential for the survival of any organism with
a central nervous system. Every second, our brain receives a staggering amount of
information from the body across different sensory channels, each of which features a
certain degree of noise. Despite the complexity of the incoming multisensory signals, the
brain manages to construct and maintain a stable representation of our own body and its
spatial relationships to the external environment. This natural “in-body” experience is such
a fundamental subjective feeling that most of us take it for granted. However, patients with
lesions in particular brain areas can experience profound disturbances in their normal sense
of ownership over their body (somatoparaphrenia) or lose the feeling of being located
inside their physical body (out-of-body experiences), suggesting that our “in-body” experience depends on intact neural circuitry in the temporal, frontal, and parietal brain regions.
The question at the heart of this thesis relates to how the brain combines visual, tactile, and
proprioceptive signals to build an internal representation of the bodily self in space.
Over the past two decades, perceptual body illusions have become an important tool for
studying the mechanisms underlying our sense of body ownership and self-location. The
most influential of these illusions is the rubber hand illusion, in which ownership of an
artificial limb is induced via the synchronous stroking of a rubber hand and an individual’s
hidden real hand. Studies of this illusion have shown that multisensory integration within
the peripersonal space is a key mechanism for bodily self-attribution. In Study I, we
showed that the default sense of ownership of one’s real hand, not just the sense of rubber
hand ownership, also depends on spatial and temporal multisensory congruence principles
implemented in fronto-parietal brain regions. In Studies II and III, we characterized two
novel perceptual illusions that provide strong support for the notion that multisensory
integration within the peripersonal space is intimately related to the sense of limb ownership, and we examine the role of vision in this process. In Study IV, we investigated a fullbody version of the rubber hand illusion—the “out-of-body illusion”—and show that it can
be used to induce predictable changes in one’s sense of self-location and body ownership.
Finally, in Study V, we used the out-of-body illusion to “perceptually teleport” participants
during brain imaging and identify activity patterns specific to the sense of self-location in a
given position in space. Together, these findings shed light on the role of multisensory
integration in building the experience of the bodily self in space and provide initial
evidence for how representations of body ownership and self-location interact in the brain
Central Adaptation after Peripheral Vestibular Injury
This
thesis
examines
how
the
human
brain
adapts
after
peripheral
vestibular
injury.
Vestibular
perceptual
function
is
used
as
a
probe
of
cortical
vestibular
function.
A
paradigm
determining
vestibular
perceptual
thresholds
to
yaw
axis
rotation
by
a
method
of
limits
is
described.
Asymmetry
in
the
thresholds
is
induced
in
normal
subjects
with
galvanic
vestibular
stimulation.
In
patients
with
acute
vestibular
neuritis,
perceptual
thresholds
were
bilaterally
elevated,
with
less
asymmetry
when
compared
to
the
brainstem
reflexive
function.
Thresholds
were
measured
in
a
prospective
longitudinal
study
in
vestibular
neuritis
patients,
assessed
acutely
and
at
follow-‐up
(n=16).
Assessments
comprised
vestibular
caloric
testing,
visual
dependency
measures,
questionnaire
measures
of
symptom
load,
anxiety,
depression
and
fear
of
body
sensations.
Clinical
recruitment
found
a
low
rate
of
correct
diagnoses
by
referring
clinicians.
Symptomatic
outcome
at
follow-up
was
associated
with
increased
visual
dependence,
asymmetric
caloric
function,
increased
anxiety
and
depression.
It
was
also
associated
with
increased
fear
and
anxiety
of
body
sensations
present
acutely,
suggesting
this
may
be
predisposing.
The
anatomical
substrate
of
central
compensation
was
investigated
in
patients
with
bilateral
vestibular
failure
(n=12)
and
normal
controls
(n=15)
using
functional
MRI.
A
novel
air
turbine-powered
vibrating
device
was
developed
to
provide
high
and
low
levels
of
proprioceptive
stimulus
to
neck
rotator
muscles.
This
was
combined
with
a
horizontal
visual
motion
paradigm
in
a
factorial
design.
A
lateralised
interaction
was
found
in
the
lateral
occipital
visual
processing
areas
in
the
avestibular
patients.
In
addition
to
the
known
visual-vestibular
interaction,
this
demonstrates
a
visuo-proprioceptive
interaction,
which
may
reflect
compensation
after
vestibular
injury. Conclusions:
Vestibular
perceptual
function
can
be
measured
in
disease,
and
is
elevated
in
patients
with
acute
peripheral
vestibulopathy.
Specific
psychological
and
physiological
factors
associated
with
clinical
recovery
after
vestibular
neuritis
are
proposed.
Functional
MRI
shows
that
proprioceptive
signals
interact
with
visual
motion
signals
in
patients
with
vestibular
failure
Sensorimotor integration processing in Diabetic Retinopathy and Diabetic Peripheral Neuropathy
This study evaluated the direct link between visual perception and related motor output responses during an optic flow stimulation which induced a perception of forward movement, and during a driving task using a simulator. The experiments focussed on the evaluation of two different complications of diabetes, diabetic retinopathy and diabetic peripheral neuropathy (DPN), in order to evaluate the different contributions of both central and peripheral nervous factors in affecting the sensorimotor integration process in diabetes.
Study I. The aim was to assess how optic flow processing contributes to the control of posture and whether it requires the predominant activation of cortical networks involved in motion perception or the intervention of subcortical loops.
People with retinopathy and people who had undergone laser treatment showed a higher postural instability compared to control subjects. Differing retinal functionality produced different postural strategies. Based on these findings, postural control seems to be a process dependent on perceptual analysis via feed-forward cortical circuits.
Study II. The aim was to assess whether diabetes was associated with alterations of visual gaze behaviour and/or neuromuscular impairment that might adversely affect driving performance.
The potential for impaired driving performance with diabetes seems to be represented by diminished eye-steering coordination. While proprioception function seems to indicate the potential for improvement, a slower production of strength in the plantar flexor muscles seems not to influence accelerator pedal control during a driving simulation task in people with diabetes (with and without diabetic peripheral neuropathy).
These results confirm the role of visual perception and eye movements in guiding human movements during dailylife activities. In particular, we demonstrated the detrimental effects of diabetes and the different contribution of diabetic retinopathy and diabetic peripheral neuropathy in affecting both central and peripheral components of the sensorimotor integration process
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