Renzo Lanfranco

Body ownership is not constructed unconsciously and then brought to awareness—it emerges directly in consciousness. A fundamental insight for understanding the bodily self, with clear implications for theories of consciousness. See PNAS article and thread below.

Why our physical bodies may be a core part of conscious experience – new research The brain’s sense of “this is my body” is tightly bound to conscious awareness – far more than many theories assume.

Also, check out my popular science article about this paper in @theconversation.com - theconversation.com/why-our-phys...

We thank @hakwan.bsky.social, Brian_Maniscalco, @smfleming.bsky.social, for their work on type-2 signal detection analysis, @kobedesender.bsky.social, Luc Vermeylen, Tom Verguts for their work on v-ratio, and @mariechancel.bsky.social for her work on RHI-based psychophysics. Please, share!

15/15 In sum, findings from a series of robust psychophysical experiments using signal detection analysis and computational modeling converge to suggest that body ownership multisensory processing occurs at the level of conscious processing.

14/15 We found that the rate of evidence accumulation for body ownership perception and for conscious awareness did not vary across visuotactile asynchronies, suggesting again that body ownership information is not processed in the absence of awareness.

13/15 Note that DDM produces several parameters that assess different dynamic aspects of perception, e.g., drift rate assesses accumulation speed and boundary separation assesses response caution as perceptual evidence is accumulated. v-ratio assesses accumulation speed for awareness.

12/15 What if the numbers of touches we chose aren't the most relevant ones? In Experiment 3, we implemented a sped-up version of our paradigm and applied drift-diffusion modeling (DDM) and v-ratio (a DDM variant of M-ratio) to test this in a dynamic framework.

11/15 Perception relies on evidence accumulation. To test whether the relationship between body ownership and awareness holds as evidence is accumulated, in Experiment 2, we varied the number of touches applied (3, 6, 9). We found conscious access remains constant across visuotactile asynchronies.

10/15 To test whether our findings are specific to body ownership rather than visuotactile processing, in Control Exp. 2, we used blocks of wood instead of rubber hands, and instead of ownership, we asked them to judge visuotactile synchronicity. Here, we did find differences in conscious access.

9/15 To ensure that participants focused on their feeling of ownership rather than on visuotactile synchronicity, in Control Exp. 1, we rotated the rubber hands by 90 degrees (which abolishes the RHI), and found chance sensitivity, suggesting that participants focused on ownership in the main Exp.

8/15 Body ownership processing and conscious access to body ownership arose together, ruling out unconscious processing. To test this further, we used a Bayesian hierarchical model of metacognitive efficiency (M-ratio): conscious access did not vary between asynchronies.

7/15 Using signal detection analysis, we found that the sensitivity of body ownership to visuotactile asynchrony was above chance from 31 ms of asynchrony, but not at 18 ms. We found equivalent results for the sensitivity of perceptual awareness to body ownership discrimination.

6/15 In our task, participants report which rubber hand feels most like theirs (2AFC discrimination) and the clarity of their experience (perceptual awareness scale) across different visuotactile asynchronies. Importantly, visuotactile synchrony is a proxy for visuotactile integration.

6/15 We used a novel and robust psychophysical paradigm that employs robotic arms to induce the RHI: one arm taps the hidden participant’s hand, while the other two tap two rubber hands on sight. One rubber hand is stroked in sync with the real hand, and the other is stroked with a varying delay.

5/15 Most studies have used questionnaires or indirect measures (e.g., Galvanic response) to assess body ownership, which cannot distinguish between conscious and unconscious processing or account for postperceptual factors (e.g., decision bias). How can we assess body ownership objectively, then?

4/15 RHI studies show that hand ownership is driven by the integration of visual, tactile, and proprioceptive cues, and can be explained by models of common cause inference: the feeling of ownership arises when the brain interprets these signals as having the same origin.

3/15 Researchers use bodily illusions like the rubber hand illusion (RHI) to study body ownership empirically and non-invasively: a rubber hand is stroked in sync with the participant’s hidden real hand, producing the illusion of owning the fake hand.

2/15 Body ownership is the perception that our body belongs to us, and over 25 years of research have shown that it relies on multisensory brain mechanisms capable of binding information from different senses together.

1/15 How does the perception of our bodily self arise in our conscious experience, and to what extent do we process body ownership information unconsciously? In this new study, we found that body ownership information processing doesn't occur outside of conscious awareness.

Conscious awareness, sensory integration, and evidence accumulation in bodily self-perception | PNAS Conscious awareness refers to the subjective experience of perceiving, thinking, and feeling and the ability to report these experiences. These per...

Happy to share our new and groundbreaking study on the relationship between conscious awareness and the sense of bodily self! With @brainself.bsky.social at @ki.se and out today in PNAS: www.pnas.org/doi/10.1073/...

Picture showing brain activation in a person with congenital blindness. Although early visual experience is essential for the proper development of visual cortex, Striem-Amit et al. show that the underlying connectivity structure of retinotopic mapping is retained even in congenitally blind individuals. This basic organisational principle emerges independently of visual input and persists despite lifelong experience-dependent plasticity.

Ella Striem-Amit (@striemamit.bsky.social) at Georgetown University is looking for a postdoc interested in brain plasticity and behavior in people born with blindness, deafness, or without hands, using behavioral paradigms, computational methods, and fMRI. Details at: apply.interfolio.com/177838 🧠🧪

Thanks to my co-authors Henrik Ehrsson, Marie Chancel, and Birgit Hasenack!

7/7 In sum, our findings suggest the integration of visual and tactile signals underlying body ownership remains effective as long as visual info. is available either to generate tactile predictions or to provide direct evidence of touch. However, occluding visual feedback alters perceptual bias.

6/7 These results expand those reported by Chancel & Ehrsson (2021) on how visually-driven tactile predictions affect the point of subjective equality in body ownership: doi.org/10.1016/j.co...

5/7 We also found a bias in hand ownership against the rubber hand that was touched by a robotic arm when its approaching movements were occluded, suggesting that even though vision and touch can be integrated as long as visually-driven predictions occur, there is still a perceptual bias.

4/7 Interestingly, we found that visual occlusion did not affect body ownership sensitivity, which suggests that as long as touch can be visually predicted, the feeling of ownership may arise in the rubber hand illusion.

3/7 Participants had to report in this 2AFC task which rubber hand felt more like their own. Using signal detection analysis, we quantified the sensitivity of their feeling of hand ownership to visuotactile synchrony, and the bias of their feeling of ownership towards the rubber hands.

2/7 Here, we induced the rubber hand illusion with two rubber hands, simultaneously, and varied the degrees of stimulation asynchrony between the real hand and the rubber hands, and visual feedback by occluding the approaching movements of the robotic arms or the touch itself on the real hand.

1/7 The sense of body ownership is crucial for distinguishing between internal and external sources of sensory information, and is the result of the brain's integration of vision, touch, and proprioception. The specific role of sensory predictions in shaping body ownership remains poorly understood.

I'm happy to share our preprint "Disentangling visually-driven tactile predictions from multisensory integration in body ownership". We show that tactile predictions in the rubber hand illusion are as important as feeling touch on the hand to elicit the feeling of ownership. osf.io/preprints/ps...