Periodic Reporting for period 1 - Binding the Self (Binding the self: how cortical oscillations bind sensory stimuli into a multisensory representation of the physical self)
Período documentado: 2023-09-01 hasta 2025-08-31
Binding the Self tests the hypothesis that cortical oscillations serve as a temporal gateway for bodily perception, enabling the brain to bind self-related sensory signals into a coherent multisensory representation of the body. To achieve this aim, the project employs a multidisciplinary strategy that integrates innovative psychophysical paradigms with both correlational and causal neuroscientific approaches.
Multisensory integration refers to the brain’s ability to combine sensory information from different modalities into coherent perceptions. A fundamental challenge is determining which sensory signals should be integrated and which should be segregated. Signals originating from the same external object or event ought to be integrated, whereas those from different sources should not. Spatiotemporal correlations help solve this multisensory integration problem: when signals occur with minimal temporal discrepancy, they are more likely to stem from the same event and should therefore be bound together. By contrast, larger temporal discrepancies suggest distinct events, and integration should not occur. Therefore, temporal resolution of this integrative mechanism determines which signals are bound together across time and modalities to generate the perception of meaningful objects and events. In this regard, the notion of temporal binding window (TBW) refers to the temporal interval, variable across individuals, within which sensory stimuli are more likely to be integrated into a unified percept. An influential theory proposes that alpha oscillations discretize sensory input into perceptual frames, thereby determining temporal resolution of perception and the individual width of the TBW. According to this view, multisensory perception occurs within temporal windows defined by the frequency of alpha oscillations, such that individual differences in oscillatory frequency predict variability in temporal resolution.
In addition to combining or segregating sensory signals from external stimuli, the brain must determine whether to integrate or segregate signals originating from one’s own body. This is particularly important for the sense of body ownership—the perceptual experience of one’s limbs and body parts as one’s own. However, we still lack a mechanistic account of how the brain temporally integrates multisensory signals from the body itself. The aim of Binding the Self is to reveal the mechanism behind temporal integration of bodily signals, enhancing our knowledge of self-consciousness. Indeed, the role of brain oscillations in the fundamental sense of self and the distinction between self and non-self remains largely unexplored. Binding the self demonstrates that the frequency of cortical oscillations plays a crucial role in binding self-related sensory information into a coherent perceptual experience of one’s body and distinguishing this bodily self from external sensory events. This constitutes first evidence to link brain oscillations to such a foundational aspect of selfhood – the sense of bodily self. This overarching aim will be split into three objectives that will provide new scenarios to the mechanisms that allow us to bind the self:
1) The first objective is to demonstrate that temporal resolution of simultaneity perception correlates with temporal resolution of multisensory integration involved in body ownership, both when body ownership is induced by visuotactile information and when ownership is induced only by tactile and proprioceptive information alone in absence of vision.
2) The second objective is to demonstrate the role of parietal alpha oscillations in the temporal integration of somatosensory and bodily related visual signals, serving as the common electrophysiological mechanism underlying the temporal resolution of visuotactile processing in simultaneity and body ownership perception
3) The third objective is to investigate whether the temporal integration of bodily signals is supported by modality-specific oscillations, depending on the sensory modality through which the body is primarily perceived. Specifically, I hypothesize that beta oscillations mediate the temporal integration of bodily signals when body ownership is induced solely through proprioceptive and tactile cues in the absence of visual input.
Binding the Self will uncover the oscillatory mechanisms underlying temporal integration of bodily signals, advancing our understanding of self-consciousness. Without clarifying the electrophysiological basis of this integration, our knowledge of self-related multisensory processing will remain incomplete. The project is expected to open new lines of research on cortical oscillations and their role in fundamental aspects of selfhood, such as the sense of agency and sensory attenuation. Clinically, the findings will inform rehabilitation strategies for conditions involving distorted body ownership probably due to distorted temporal integration, including schizophrenia, eating disorders, and body identity disorders. Technologically, they will support the development of prosthetics and brain–machine interfaces by providing tools to enhance embodiment and sensory feedback, reducing rejection rates and improving quality of life. Overall, the expected impact of the project will bridge basic neuroscience, clinical rehabilitation, and neurotechnology, creating tangible societal value.
Multisensory integration refers to the brain’s ability to combine sensory information from different modalities into coherent perceptions. A fundamental challenge is determining which sensory signals should be integrated and which should be segregated. Signals originating from the same external object or event ought to be integrated, whereas those from different sources should not. Spatiotemporal correlations help solve this multisensory integration problem: when signals occur with minimal temporal discrepancy, they are more likely to stem from the same event and should therefore be bound together. By contrast, larger temporal discrepancies suggest distinct events, and integration should not occur. Therefore, temporal resolution of this integrative mechanism determines which signals are bound together across time and modalities to generate the perception of meaningful objects and events. In this regard, the notion of temporal binding window (TBW) refers to the temporal interval, variable across individuals, within which sensory stimuli are more likely to be integrated into a unified percept. An influential theory proposes that alpha oscillations discretize sensory input into perceptual frames, thereby determining temporal resolution of perception and the individual width of the TBW. According to this view, multisensory perception occurs within temporal windows defined by the frequency of alpha oscillations, such that individual differences in oscillatory frequency predict variability in temporal resolution.
In addition to combining or segregating sensory signals from external stimuli, the brain must determine whether to integrate or segregate signals originating from one’s own body. This is particularly important for the sense of body ownership—the perceptual experience of one’s limbs and body parts as one’s own. However, we still lack a mechanistic account of how the brain temporally integrates multisensory signals from the body itself. The aim of Binding the Self is to reveal the mechanism behind temporal integration of bodily signals, enhancing our knowledge of self-consciousness. Indeed, the role of brain oscillations in the fundamental sense of self and the distinction between self and non-self remains largely unexplored. Binding the self demonstrates that the frequency of cortical oscillations plays a crucial role in binding self-related sensory information into a coherent perceptual experience of one’s body and distinguishing this bodily self from external sensory events. This constitutes first evidence to link brain oscillations to such a foundational aspect of selfhood – the sense of bodily self. This overarching aim will be split into three objectives that will provide new scenarios to the mechanisms that allow us to bind the self:
1) The first objective is to demonstrate that temporal resolution of simultaneity perception correlates with temporal resolution of multisensory integration involved in body ownership, both when body ownership is induced by visuotactile information and when ownership is induced only by tactile and proprioceptive information alone in absence of vision.
2) The second objective is to demonstrate the role of parietal alpha oscillations in the temporal integration of somatosensory and bodily related visual signals, serving as the common electrophysiological mechanism underlying the temporal resolution of visuotactile processing in simultaneity and body ownership perception
3) The third objective is to investigate whether the temporal integration of bodily signals is supported by modality-specific oscillations, depending on the sensory modality through which the body is primarily perceived. Specifically, I hypothesize that beta oscillations mediate the temporal integration of bodily signals when body ownership is induced solely through proprioceptive and tactile cues in the absence of visual input.
Binding the Self will uncover the oscillatory mechanisms underlying temporal integration of bodily signals, advancing our understanding of self-consciousness. Without clarifying the electrophysiological basis of this integration, our knowledge of self-related multisensory processing will remain incomplete. The project is expected to open new lines of research on cortical oscillations and their role in fundamental aspects of selfhood, such as the sense of agency and sensory attenuation. Clinically, the findings will inform rehabilitation strategies for conditions involving distorted body ownership probably due to distorted temporal integration, including schizophrenia, eating disorders, and body identity disorders. Technologically, they will support the development of prosthetics and brain–machine interfaces by providing tools to enhance embodiment and sensory feedback, reducing rejection rates and improving quality of life. Overall, the expected impact of the project will bridge basic neuroscience, clinical rehabilitation, and neurotechnology, creating tangible societal value.
Binding the Self consists of two studies that demonstrate the role of alpha and beta cortical oscillations in the temporal integration of body-related sensory signals.
Study 1 integrates psychophysics, electroencephalography (EEG), brain stimulation, computational modeling, and a robot-assisted behavioral paradigm rooted in the bodily illusion framework to demonstrate that alpha frequency drives the temporal integration of tactile- and vision-related bodily signals, giving rise to the sense of body ownership. We employed a psychophysical version of the rubber hand illusion, combined with EEG and brain stimulation. In the classic illusion, participants experience synchronous touches on a visible rubber hand and their own hidden hand; after a brief period, most report perceiving the touches as arising from the rubber hand, which begins to feel as if it were part of their own body.
In our setup, we manipulated the timing of taps on the rubber hand relative to the participants’ real hand, introducing delays or advances of up to 500 ms, and asked participants to judge ownership after each trial in a detection-like task. Because longer delays progressively weakened the illusion, this approach allowed us to map the relationship between temporal delay and ownership judgments, quantifying the TBW of body ownership and perceptual sensitivity using signal detection theory (SDT). By comparing these measures with EEG recordings from the same participants, we examined the role of alpha oscillations in the temporal integration of sensory signals underlying body ownership.
All experiments also included a visuotactile simultaneity judgment task, in which participants judged whether brief tactile and external visual stimuli were simultaneous or delayed, providing a direct measure of the temporal resolution of multisensory perception. In Experiment 1, we found that the TBW and sensitivity for visuotactile simultaneity correlated with those for body ownership, consistent with the idea that individual alpha frequency (IAF) serves as a common electrophysiological mechanism for temporal integration of visual and somatosensory inputs. In Experiment 2, we found that IAF predicted participants’ TBW and sensitivity to both body ownership and visuotactile simultaneity. In Experiment 3, we tested the causal role of parietal alpha frequency in shaping TBW and perceptual sensitivity. Using transcranial alternating current stimulation (tACS), we selectively increased or decreased participants’ cortical alpha frequency and observed the predicted changes in temporal resolution.
Finally, to investigate the computational mechanism, we fitted behavioral data from Experiments 2 and 3 to a validated Bayesian causal inference model of body ownership. According to this model, body ownership arises from a probabilistic process in which the brain infers a common cause for unisensory inputs by integrating the prior probability of a common cause with sensory evidence, weighted by its reliability. Since IAF acts as a temporal perceptual frame, we hypothesized that it would be related to sensory reliability. Indeed, we found that IAF influences perceptual inference by modulating the reliability of multisensory asynchrony information.
Taken together, the psychophysical, EEG, brain stimulation, and computational modeling results of Study 1 provide conclusive evidence that alpha oscillations play a crucial role in mediating the temporal integration of visual and tactile signals in body ownership, determining the temporal resolution of self-related multisensory information processing.
Study 2 aimed demonstrate that beta frequency oscillations support the temporal integration of tactile and proprioceptive signals in generating the sense of body ownership in the absence of vision. Indeed, from Study 1 it remains unclear whether the temporal integration of non-visual bodily information—such as touch and proprioception—is mediated by the same alpha-based gating mechanism, or whether other frequency bands—such as beta oscillations—which are strongly implicated in somatosensory and motor processing, play a more central role.
To test this hypothesis, we developed a novel, robot-assisted psychophysical task designed to measure the temporal integration of somatic and proprioceptive information contributing to body ownership without visual input. Specifically, we implemented a psychophysical version of the somatic rubber hand illusion—a well-established paradigm for investigating how tactile and proprioceptive information contribute to the experience of body ownership. In the classical somatic rubber hand illusion, the experimenter guides the blindfolded participants’ left index finger to touch a right rubber hand, while simultaneously delivering tactile stimulation to the participant’s real right hand at the corresponding location. After a brief period of stimulation, most participants report the illusory sensation of touching their own right hand with their left index finger, despite physically interacting with a rubber hand. Crucially, this illusion breaks down when the movement of the left index finger and the tactile stimulation are temporally asynchronous, suggesting that the experience of body ownership, even in absence of vision, depends on the temporal congruency between proprioceptive and tactile signals. In our psychophysical adaptation of this paradigm, we employed a robot-assisted setup to precisely manipulate the timing of tactile events delivered to the rubber hand and the participant’s real hand. We systematically introduced temporal delays or advances of up to 400 ms and asked participants to judge whether they experienced the sensation of touching their own hand. In addition, similarly to Study 1, we included a propriotactile simultaneity judgment task to evaluate participants’ temporal resolution for proprioceptive and tactile integration. In this task, participants judged whether the touch they delivered to the rubber hand and the touch they received on their real hand occurred synchronously or asynchronously. By parametrically modulating the temporal delays, we were able to estimate the TBW for body ownership and simultaneity perceptions and assess their perceptual sensitivity using a signal detection theory (SDT) approach.
In Experiment 1, we found that TBW and sensitivity to propriotactile simultaneity predicted the TBW and sensitivity of body ownership, suggesting a shared temporal processing mechanism. In Experiment 2, we showed that invidual beta frequency (IBF) predicted the temporal integration of propriotactile signals underlying body ownership in the absence of vision, as well as the perception of propriotactile simultaneity. Participants with faster IBF exhibited narrower TBWs and greater perceptual sensitivity. Finally, In Experiment 3, we found that IBF did not correlate with the TBWs or sensitivities related to visuotactile simultaneity and visuotactile-induced body ownership, indicating a modality-specific role of IBF in propriotactile integration.
These findings are significant as they reveal that the sense of body ownership can be supported by modality-specific oscillatory dynamics. While Study 1 highlighted the role of alpha oscillations in the integration of visual and somatosensory information, current results demonstrate that beta rhythms—rather than alpha—play a central role when the body is perceived through tactile and proprioceptive cues alone.
Study 1 integrates psychophysics, electroencephalography (EEG), brain stimulation, computational modeling, and a robot-assisted behavioral paradigm rooted in the bodily illusion framework to demonstrate that alpha frequency drives the temporal integration of tactile- and vision-related bodily signals, giving rise to the sense of body ownership. We employed a psychophysical version of the rubber hand illusion, combined with EEG and brain stimulation. In the classic illusion, participants experience synchronous touches on a visible rubber hand and their own hidden hand; after a brief period, most report perceiving the touches as arising from the rubber hand, which begins to feel as if it were part of their own body.
In our setup, we manipulated the timing of taps on the rubber hand relative to the participants’ real hand, introducing delays or advances of up to 500 ms, and asked participants to judge ownership after each trial in a detection-like task. Because longer delays progressively weakened the illusion, this approach allowed us to map the relationship between temporal delay and ownership judgments, quantifying the TBW of body ownership and perceptual sensitivity using signal detection theory (SDT). By comparing these measures with EEG recordings from the same participants, we examined the role of alpha oscillations in the temporal integration of sensory signals underlying body ownership.
All experiments also included a visuotactile simultaneity judgment task, in which participants judged whether brief tactile and external visual stimuli were simultaneous or delayed, providing a direct measure of the temporal resolution of multisensory perception. In Experiment 1, we found that the TBW and sensitivity for visuotactile simultaneity correlated with those for body ownership, consistent with the idea that individual alpha frequency (IAF) serves as a common electrophysiological mechanism for temporal integration of visual and somatosensory inputs. In Experiment 2, we found that IAF predicted participants’ TBW and sensitivity to both body ownership and visuotactile simultaneity. In Experiment 3, we tested the causal role of parietal alpha frequency in shaping TBW and perceptual sensitivity. Using transcranial alternating current stimulation (tACS), we selectively increased or decreased participants’ cortical alpha frequency and observed the predicted changes in temporal resolution.
Finally, to investigate the computational mechanism, we fitted behavioral data from Experiments 2 and 3 to a validated Bayesian causal inference model of body ownership. According to this model, body ownership arises from a probabilistic process in which the brain infers a common cause for unisensory inputs by integrating the prior probability of a common cause with sensory evidence, weighted by its reliability. Since IAF acts as a temporal perceptual frame, we hypothesized that it would be related to sensory reliability. Indeed, we found that IAF influences perceptual inference by modulating the reliability of multisensory asynchrony information.
Taken together, the psychophysical, EEG, brain stimulation, and computational modeling results of Study 1 provide conclusive evidence that alpha oscillations play a crucial role in mediating the temporal integration of visual and tactile signals in body ownership, determining the temporal resolution of self-related multisensory information processing.
Study 2 aimed demonstrate that beta frequency oscillations support the temporal integration of tactile and proprioceptive signals in generating the sense of body ownership in the absence of vision. Indeed, from Study 1 it remains unclear whether the temporal integration of non-visual bodily information—such as touch and proprioception—is mediated by the same alpha-based gating mechanism, or whether other frequency bands—such as beta oscillations—which are strongly implicated in somatosensory and motor processing, play a more central role.
To test this hypothesis, we developed a novel, robot-assisted psychophysical task designed to measure the temporal integration of somatic and proprioceptive information contributing to body ownership without visual input. Specifically, we implemented a psychophysical version of the somatic rubber hand illusion—a well-established paradigm for investigating how tactile and proprioceptive information contribute to the experience of body ownership. In the classical somatic rubber hand illusion, the experimenter guides the blindfolded participants’ left index finger to touch a right rubber hand, while simultaneously delivering tactile stimulation to the participant’s real right hand at the corresponding location. After a brief period of stimulation, most participants report the illusory sensation of touching their own right hand with their left index finger, despite physically interacting with a rubber hand. Crucially, this illusion breaks down when the movement of the left index finger and the tactile stimulation are temporally asynchronous, suggesting that the experience of body ownership, even in absence of vision, depends on the temporal congruency between proprioceptive and tactile signals. In our psychophysical adaptation of this paradigm, we employed a robot-assisted setup to precisely manipulate the timing of tactile events delivered to the rubber hand and the participant’s real hand. We systematically introduced temporal delays or advances of up to 400 ms and asked participants to judge whether they experienced the sensation of touching their own hand. In addition, similarly to Study 1, we included a propriotactile simultaneity judgment task to evaluate participants’ temporal resolution for proprioceptive and tactile integration. In this task, participants judged whether the touch they delivered to the rubber hand and the touch they received on their real hand occurred synchronously or asynchronously. By parametrically modulating the temporal delays, we were able to estimate the TBW for body ownership and simultaneity perceptions and assess their perceptual sensitivity using a signal detection theory (SDT) approach.
In Experiment 1, we found that TBW and sensitivity to propriotactile simultaneity predicted the TBW and sensitivity of body ownership, suggesting a shared temporal processing mechanism. In Experiment 2, we showed that invidual beta frequency (IBF) predicted the temporal integration of propriotactile signals underlying body ownership in the absence of vision, as well as the perception of propriotactile simultaneity. Participants with faster IBF exhibited narrower TBWs and greater perceptual sensitivity. Finally, In Experiment 3, we found that IBF did not correlate with the TBWs or sensitivities related to visuotactile simultaneity and visuotactile-induced body ownership, indicating a modality-specific role of IBF in propriotactile integration.
These findings are significant as they reveal that the sense of body ownership can be supported by modality-specific oscillatory dynamics. While Study 1 highlighted the role of alpha oscillations in the integration of visual and somatosensory information, current results demonstrate that beta rhythms—rather than alpha—play a central role when the body is perceived through tactile and proprioceptive cues alone.
Binding the Self demonstrated through two studies that alpha and beta oscillations are crucial for the temporal integration of bodily sensory information, such that participants with faster oscillations exhibit smaller TBWs and greater sensitivity to body ownership. Specifically, parietal individual alpha oscillations support the integration of somatosensory information with bodily-related visual input, whereas individual beta frequency temporally integrates somatosensory and proprioceptive information to generate the sense of body ownership in the absence of vision. Overall, these findings establish that alpha frequency plays a pivotal role in bodily self-awareness by influencing the temporal integration versus segregation of bodily signals—processes that are essential for perceiving one’s body as one’s own and for distinguishing self-related from external sensory information. Brain oscillations, therefore, are fundamental to how the brain constructs a coherent sense of bodily self. Moreover, the oscillatory mechanisms underlying body ownership are modality-specific, with beta oscillations supporting purely somatosensory integration and alpha oscillations supporting visuotactile integration.
It is widely accepted that body ownership depends on multisensory integration, but the electrophysiological mechanism allowing the temporal integration of different bodily sensory information is still unknown. Previous EEG studies revealed alpha power modulation during perception of body ownership. However, alpha desynchronization was interpreted as multisensory area activation, leaving the mechanism through which the parietal cortex integrates self-related sensory signals unclear. Previous fMRI and ECoG experiments have highlighted activity in the posterior parietal cortex that reflects the temporal integration of visuotactile signals in bodily illusion, but the neurophysiological mechanism by which this activity is achieved remains poorly understood. Binding the Self’s results indicate a mechanistic role of parietal alpha and beta frequency in temporally integrating visuotactile signals for body ownership and simultaneity perception, going beyond the sate of the art. Additionally, Binding the Self provides the most robust evidence to date for the role of alpha oscillations in the temporal resolution of perception more broadly. We also present a novel computational explanation of how alpha frequency modulates perceptual temporal resolution via its influence on sensory uncertainty, addressing and resolving recent debates on this topic, such as the negative findings reported by Burgers and Noppeney (2022) in Nature Human Behaviour.
These results have important implications because they can inform research on other aspects of self-consciousness, such as the sense of agency, thereby opening new lines of investigation. Temporal contingencies between actions and their outcomes are a crucial mechanism for the sense of agency, and the speed of cortical oscillations may prove equally relevant in this domain. Binding the Self also introduces new tools for studying body ownership, such as the psychophysical somatic RHI and tACS. The psychophysical somatic RHI can be employed to investigate the representation of the body in individuals with congenital or acquired blindness, offering a more efficient way to study embodiment without relying on visual cues. More broadly, Binding the Self suggests that multisensory representations of the self and the external environment are two sides of the same coin. Researchers and clinicians studying conditions characterized by distorted body representation—such as schizophrenia, eating disorders, or body identity disorder—can benefit from these findings. Compared to healthy controls, individuals with schizophrenia, for instance, often display abnormally large TBWs, which may contribute to experiencing the body as fragmented. The evidence that bodily sensory stimuli are temporally integrated by IAF/IBF also holds potential for applications in prosthetics and brain–machine interfaces. Combining EEG with brain stimulation, start-ups specialised in prosthetic interface devices could facilitate the embodiment of robotic devices by modulating on-line the temporal resolution of perception Indeed, some patients who have undergone limb amputation reject prostheses because they do not perceive them as part of their body. Optimizing rehabilitation in these patients is of high societal importance, since many of those who reject prostheses are young adults with many years of potential employment and active social participation ahead.
It is widely accepted that body ownership depends on multisensory integration, but the electrophysiological mechanism allowing the temporal integration of different bodily sensory information is still unknown. Previous EEG studies revealed alpha power modulation during perception of body ownership. However, alpha desynchronization was interpreted as multisensory area activation, leaving the mechanism through which the parietal cortex integrates self-related sensory signals unclear. Previous fMRI and ECoG experiments have highlighted activity in the posterior parietal cortex that reflects the temporal integration of visuotactile signals in bodily illusion, but the neurophysiological mechanism by which this activity is achieved remains poorly understood. Binding the Self’s results indicate a mechanistic role of parietal alpha and beta frequency in temporally integrating visuotactile signals for body ownership and simultaneity perception, going beyond the sate of the art. Additionally, Binding the Self provides the most robust evidence to date for the role of alpha oscillations in the temporal resolution of perception more broadly. We also present a novel computational explanation of how alpha frequency modulates perceptual temporal resolution via its influence on sensory uncertainty, addressing and resolving recent debates on this topic, such as the negative findings reported by Burgers and Noppeney (2022) in Nature Human Behaviour.
These results have important implications because they can inform research on other aspects of self-consciousness, such as the sense of agency, thereby opening new lines of investigation. Temporal contingencies between actions and their outcomes are a crucial mechanism for the sense of agency, and the speed of cortical oscillations may prove equally relevant in this domain. Binding the Self also introduces new tools for studying body ownership, such as the psychophysical somatic RHI and tACS. The psychophysical somatic RHI can be employed to investigate the representation of the body in individuals with congenital or acquired blindness, offering a more efficient way to study embodiment without relying on visual cues. More broadly, Binding the Self suggests that multisensory representations of the self and the external environment are two sides of the same coin. Researchers and clinicians studying conditions characterized by distorted body representation—such as schizophrenia, eating disorders, or body identity disorder—can benefit from these findings. Compared to healthy controls, individuals with schizophrenia, for instance, often display abnormally large TBWs, which may contribute to experiencing the body as fragmented. The evidence that bodily sensory stimuli are temporally integrated by IAF/IBF also holds potential for applications in prosthetics and brain–machine interfaces. Combining EEG with brain stimulation, start-ups specialised in prosthetic interface devices could facilitate the embodiment of robotic devices by modulating on-line the temporal resolution of perception Indeed, some patients who have undergone limb amputation reject prostheses because they do not perceive them as part of their body. Optimizing rehabilitation in these patients is of high societal importance, since many of those who reject prostheses are young adults with many years of potential employment and active social participation ahead.