I am a Marie-Skłodowska-Curie Actions post-doctoral research fellow at the Wellcome Centre for Human Neuroimaging in London, where I work with Prof. Karl Friston on multisensory weighting and integration in action and self-perception. I use virtual reality and bodily illusions to manipulate the perception of one’s body during rest and action. Then I look at how the brain adapts to these manipulations – how it changes its body representation or which actions it triggers. I like to interpret my empirical results within the active inference framework of brain function. Occasionally I also write about the philosophical implications of such interpretations.
Research Items (16)
One of the central claims of the Self-model Theory of Subjectivity is that the experience of being someone – even in a minimal form – arises through a transparent phenomenal self-model, which itself can in principle be reduced to brain processes. Here, we consider whether it is possible to distinguish between phenomenally transparent and opaque states in terms of active inference. We propose a relationship of phenomenal opacity to expected uncertainty or precision; i.e., the capacity for introspective attention and implicit mental action. Thus we associate introspective attention with the deployment of ‘precision’ that may render the perceptual evidence (for action) opaque, while treating transparency as a necessary aspect of beliefs about action, i.e., ‘what I am’ doing. We conclude by proposing how we may have to nuance our conception of minimal phenomenal selfhood and agency in light of this active inference conception of transparency-opacity.
To accurately guide one's actions online, the brain predicts sensory action feedback ahead of time based on internal models, which can be updated by sensory prediction errors. The underlying operations can be experimentally investigated in sensorimotor adaptation tasks, in which moving under perturbed sensory action feedback requires internal model updates. Here we altered healthy participants’ visual hand movement feedback in a virtual reality setup, while assessing brain activity with functional magnetic resonance imaging (fMRI). Participants tracked a continually moving virtual target object with a photorealistic, three-dimensional (3D) virtual hand controlled online via a data glove. During the continuous tracking task, the virtual hand's movements (i.e., visual movement feedback) were repeatedly periodically delayed, which participants had to compensate for to maintain accurate tracking. This realistic task design allowed us to simultaneously investigate processes likely operating at several levels of the brain's motor control hierarchy. FMRI revealed that the length of visual feedback delay was parametrically reflected by activity in the inferior parietal cortex and posterior temporal cortex. Unpredicted changes in visuomotor mapping (at transitions from synchronous to delayed visual feedback periods or vice versa) activated biological motion-sensitive regions in the lateral occipitotemporal cortex (LOTC). Activity in the posterior parietal cortex (PPC), focused on the contralateral anterior intraparietal sulcus (aIPS), correlated with tracking error, whereby this correlation was stronger in participants with higher tracking performance. Our results are in line with recent proposals of a wide-spread cortical motor control hierarchy, where temporoparietal regions seem to evaluate visuomotor congruence and thus possibly ground a self-attribution of movements, the LOTC likely processes early visual prediction errors, and the aIPS computes action goal errors and possibly corresponding motor corrections.
- Mar 2016
The brain constructs a flexible representation of the body from multisensory information. Previous work on monkeys suggests that the posterior parietal cortex (PPC) and ventral premotor cortex (PMv) represent the position of the upper limbs based on visual and proprioceptive information. Human experiments on the rubber hand illusion implicate similar regions, but since such experiments rely on additional visuo-tactile interactions, they cannot isolate visuo-proprioceptive integration. Here, we independently manipulated the position (palm or back facing) of passive human participants' unseen arm and of a photorealistic virtual 3D arm. Functional magnetic resonance imaging (fMRI) revealed that matching visual and proprioceptive information about arm position engaged the PPC, PMv, and the body-selective extrastriate body area (EBA); activity in the PMv moreover reflected interindividual differences in congruent arm ownership. Further, the PPC, PMv, and EBA increased their coupling with the primary visual cortex during congruent visuo-proprioceptive position information. These results suggest that human PPC, PMv, and EBA evaluate visual and proprioceptive position information and, under sufficient cross-modal congruence, integrate it into a multisensory representation of the upper limb in space.
Endogenous attention is crucial and beneficial for learning, selecting, and supervising actions. However, deliberately attending to action execution usually comes with costs like decreased smoothness and slower performance; it may severely impair normal functioning and, in the worst case, result in pathological behavior and self-experience. These ambiguous modulatory effects of attention to action have been examined on phenomenological, computational, and implementa-tional levels of description. The active inference framework offers a novel and potentially unifying view on these aspects, proposing that actions are enabled by attentional modulation based on expected precision of prediction errors in a brain's hierarchical generative model. The implications of active inference fit well with empirical results, they resonate well with ideomotor action theories, and they also tentatively reflect many insights from phenomenological analysis of the " lived body ". A particular strength of active inference is its hierarchical account of motor control in terms of adaptive behavior driven by the imperative to maintain the organism's states within unsurprising boundaries. Phenomena ranging from movement production by spinal reflex arcs to intentional, goal-directed action and the experience of oneself as an embodied agent are thus proposed to rely on the same mechanisms operating universally throughout the brain's hierarchical generative model. However, while the explanation of movement production and sensory attenuation in terms of low-level attentional modulation is quite elegant on the active inference view, there are some questions left open by its extension to higher levels of action control—particularly about the accompanying phenom-enology. I suggest that conceptual guidance from recent accounts of phenomenal self-and world-modeling may help refine the active inference framework, leading to a better understanding of the predictive nature of embodied agentive self-experience.
The term "minimal phenomenal selfhood" (MPS) describes the basic, pre-reflective experience of being a self (Blanke and Metzinger, 2009). Theoretical accounts of the minimal self have long recognized the importance and the ambivalence of the body as both part of the physical world, and the enabling condition for being in this world (Gallagher, 2005a; Grafton, 2009). A recent account of MPS (Metzinger, 2004a) centers on the consideration that minimal selfhood emerges as the result of basic self-modeling mechanisms, thereby being founded on pre-reflective bodily processes. The free energy principle (FEP; Friston, 2010) is a novel unified theory of cortical function built upon the imperative that self-organizing systems entail hierarchical generative models of the causes of their sensory input, which are optimized by minimizing free energy as an approximation of the log-likelihood of the model. The implementation of the FEP via predictive coding mechanisms and in particular the active inference principle emphasizes the role of embodiment for predictive self-modeling, which has been appreciated in recent publications. In this review, we provide an overview of these conceptions and illustrate thereby the potential power of the FEP in explaining the mechanisms underlying minimal selfhood and its key constituents, multisensory integration, interoception, agency, perspective, and the experience of mineness. We conclude that the conceptualization of MPS can be well mapped onto a hierarchical generative model furnished by the FEP and may constitute the basis for higher-level, cognitive forms of self-referral, as well as the understanding of other minds.
Spatially and temporally congruent visuotactile stimulation of a fake hand together with one’s real hand may result in an illusory self-attribution of the fake hand. Although this illusion relies on a representation of the two touched body parts in external space, there is tentative evidence that, for the illusion to occur, the seen and felt touches also need to be congruent in an anatomical reference frame. We used functional magnetic resonance imaging and a somatotopical, virtual reality-based setup to isolate the neuronal basis of such a comparison. Participants’ index or little finger was synchronously touched with the index or little finger of a virtual hand, under congruent or incongruent orientations of the real and virtual hands. The left ventral premotor cortex responded significantly more strongly to visuotactile co-stimulation of the same versus different fingers of the virtual and real hand. Conversely, the left anterior intraparietal sulcus responded significantly more strongly to co-stimulation of different versus same fingers. Both responses were independent of hand orientation congruence and of spatial congruence of the visuotactile stimuli. Our results suggest that fronto-parietal areas previously associated with multisensory processing within peripersonal space and with tactile remapping evaluate the congruence of visuotactile stimulation on the body according to an anatomical reference frame.
- Jan 2018
An important implication of several recent accounts of motor control is that sensory feedback from self-generated movements is relatively attenuated based on predictions issued by the agent's motor system. Such a relative attenuation of sensory information during actions has already been demonstrated in the somatosensory domain. Here, we used functional magnetic resonance imaging (fMRI) and a virtual reality-based setup to investigate a potential attenuation of brain responses to realistic visual movement feedback during active vs. passive right-hand movements. The participants’ right unseen hand was rotated either by the participants themselves or by the experimenter, while the participants received visual movement feedback via a photorealistic virtual 3D hand driven by their real hand movements, or received no visual feedback. We observed a significant interaction between movement type (active vs. passive) and movement feedback (vision vs. no vision) in the right superior temporal sulcus (STS), which showed relatively attenuated blood-oxygen-level dependent (BOLD) signal differences for movements with vs. without visual feedback when those movements were actively vs. passively executed. This finding suggests that STS activity caused by visual feedback from the moving body may be attenuated based on the agent's motor predictions.
To represent one’s upper limbs for action, the brain relies on a combined position estimate based on visual and proprioceptive information. Monkey neurophysiology and human brain imaging suggest that the underlying operations are implemented in a network of fronto-parietal and occipitotemporal cortical areas. Recently, a potential hierarchical arrangement of these areas has been proposed, emphasizing the posterior parietal cortex (PPC) in early multisensory comparison and integration. Here, we used functional magnetic resonance imaging (fMRI) and a virtual reality-based setup to briefly (0.5 s) present healthy human participants photorealistic virtual hands, of matching or nonmatching anatomical side, or objects at the same or a different location than their real hidden left or right hand. The inferior parietal lobe (IPL) of the left PPC showed a significant preference for congruent visuoproprioceptive hand position information. Moreover, the left body part-selective extrastriate body area (EBA; functionally localized) significantly increased its coupling with the left IPL during visuoproprioceptive congruence vs. incongruence. Our results suggest that the PPC implements early visuoproprioceptive comparison and integration processes, likely relying on information exchange with the EBA.
- Jun 2015
With congruent stimulation of one's limb together with a fake counterpart, an illusory self-attribution of the fake limb can be induced. Such illusions have brought profound insights into the cognitive and neuronal mechanisms underlying temporary changes in body representation, but to put them in perspective they need to be compared with ownership as experienced for one's real body. We used fMRI to compare the neuronal correlates of touch under different degrees of body ownership. Participants' left and right arms were stimulated either alone, or together with a fake counterpart while this stimulation was either synchronous, ambiguous, or asynchronous. Synchronous stimulation induced illusory fake arm ownership, but the brain still differentiated between touch to one's real arm and to an illusory "owned" arm: the degree of arm ownership was encoded positively by activity in the ventromedial prefrontal cortex and lateral occipitotemporal cortex, and negatively in the temporoparietal cortex. Conversely, the ventral premotor cortex responded more strongly to synchronous stimulation compared with asynchronous stimulation and with real arm only stimulation. These results offer new insights into the differential representation of the real body versus a body that is temporarily self-attributed following the resolution of multisensory conflict. © The Author (2015). Published by Oxford University Press. For Permissions, please email: email@example.com.
- Feb 2015
Neuroimaging has demonstrated that the illusory self-attribution of body parts engages frontal and intraparietal brain areas, and recent evidence further suggests an involvement of visual body-selective regions in the occipitotemporal cortex. However, little is known about the principles of information exchange within this network. Here, using automated congruent versus incongruent visuotactile stimulation of distinct anatomical locations on the participant's right arm and a realistic dummy counterpart in an fMRI scanner, we induced an illusory self-attribution of the dummy arm. The illusion consistently activated a left-hemispheric network comprising ventral premotor cortex (PMv), intraparietal sulcus (IPS), and body-selective regions of the lateral occipitotemporal cortex (LOC). Importantly, during the illusion, the functional coupling of the PMv and the IPS with the LOC increased substantially, and dynamic causal modeling revealed a significant enhancement of connections from the LOC and the secondary somatosensory cortex to the IPS. These results comply with the idea that the brain's inference mechanisms rely on the hierarchical propagation of prediction error. During illusory self-attribution, unpredicted ambiguous sensory input about one's body configuration may result in the generation of such prediction errors in visual and somatosensory areas, which may be conveyed to parietal integrative areas. Hum Brain Mapp, 2015. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.
The rubber hand illusion (RHI) is a paradigm used to induce an illusory feeling of owning a dummy hand through congruent multisensory stimulation. Thus, it can grant insights into how our brain represents our body as our own. Recent research has demonstrated an involvement of the extrastriate body area (EBA), an area of the brain that is typically implicated in the perception of non-face body parts, in illusory body ownership. In this experiment, we sought causal evidence for the involvement of the EBA in the RHI. Sixteen participants took part in a sham controlled, 1 Hz repetitive transcranial magnetic stimulation (rTMS) experiment. Participants received (RHI condition) or asynchronous (control) stroking and were asked to report the perceived location of their real hand, as well as the intensity and the temporal onset of experienced ownership of the dummy hand. Following rTMS of the left EBA, participants misjudged their real hand's location significantly more toward the dummy hand during the RHI than after sham stimulation. This difference in "proprioceptive drift" provides the first causal evidence that the EBA is involved in the RHI and subsequently in body representation and further supports the view that the EBA is necessary for multimodal integration.
- Oct 2013
The Rubber Hand Illusion (RHI) is an established paradigm for studying body ownership, and several studies have implicated premotor and temporo-parietal brain regions in its neuronal foundation. Here we used an automated setup to induce a novel multi-site version of the RHI in healthy human participants inside an MR-scanner, with a RHI and control condition that were matched in terms of synchrony of visual and tactile stimulation. Importantly, as previous research has shown that most of the ownership-related brain areas also respond to observed human actions and touch, or body parts of others, here such potential effects of the experimenter were eliminated by the automated procedure. The RHI condition induced a strong ownership illusion; we found correspondingly stronger brain activity during the RHI versus control condition in contralateral middle occipital gyrus (mOCG) and bilateral anterior insula, which have previously been related to illusory body ownership. Using independent functional localizers, we confirmed that the activity in mOCG was located within the body-part selective extrastriate body area (EBA). Crucially, activity differences in participants' peak voxels within left EBA correlated strongly positively with their behavioral illusion scores. Thus EBA activity also reflected interindividual differences in the experienced intensity of illusory limb ownership. Moreover, psychophysiological interaction analyses (PPI) revealed that contralateral primary somatosensory cortex had stronger brain connectivity with EBA during the RHI versus control condition, while EBA was more strongly interacting with temporo-parietal multisensory regions. In sum, our findings demonstrate a direct involvement of EBA in limb ownership.
- Apr 2011
The subjective location of the Self in the body is a traditionally problematic question, and it can only be addressed from the first-person perspective. However, this does not preclude an empirical approach to the question. In the present study, we examined whether a large sample of participants would be willing and able to determine the perceived location of their Self. The main goal was to assess current beliefs about the nature of the Self and its assumed relation to specific bodily organs. Eighty-seven participants indicated the center of their Self by placing crosshairs on human silhouettes and abstract, non-human silhouettes with varying anatomy. Results show a clearly dominant role of the brain and the heart for Self-location in humans, but only of the brain for Self-location in abstract creatures. Moreover, results reveal that people believe there is one single point inside the human body where their Self is located.
Awards & Achievements (5)
Award · Jun 2016
OHBM Merit Abstract Award
Award · Jun 2013
OHBM Trainee Abstract Award
Scholarship · Aug 2008
Fulbright Student Program Travel Grant
Scholarship · Aug 2008
Cornell-Heidelberg Exchange Program
Scholarship · Oct 2005
Studienstiftung des deutschen Volkes Student Scholarship