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.