Body perception and brain plasticity in blind and sighted individuals

Lack of vision is associated with large-scale brain plasticity. Vision, touch, proprioception, interoception, and other sensory modalities are thought to play a vital role in developing and maintaining bodily awareness. How do blind people perceive their bodies, and what kind of compensatory neuroplasticity processes are involved?

This thesis comprises a series of experiments focused on a profoundly understudied topic – the perception of one’s body following blindness.

Study I shows that blind individuals are significantly better at perceiving their heartbeats than sighted individuals. The results indicate that blind individuals experience signals from inner organs differently than sighted individuals, which has implications for further research on emotional processing and bodily awareness.

Study II provides a broader insight into tactile perception following blindness by studying discriminative and affective touch plasticity in blind and sighted groups. A key novel finding is changed pleasantness sensation due to affective touch, that is, slow, gentle, caress-like stroking of the skin, especially on the palm, in blind participants compared to sighted participants. The results have implications for understanding social and physical interactions in blind individuals.

Study III re-examines a classic paradigm to study multisensory bodily awareness, the somatic rubber hand illusion, in a large sample of blind participants with a well-matched sighted control group. The results present strong evidence that blind individuals are “immune” to this illusion which suggests that they rely more on unisensory processing rather than multimodal integration of sensory signals, compared to sighted individuals.

Study IV investigates the effect of short-term visual deprivation by a two-hour blindfolding procedure on the bodily senses of cardiac interoception, thermosensation, and discriminative touch in sighted participants. The results show no effect on these senses, which suggests that the changes observed in blind individuals on these sensory functions relate to their long-term lack of visual experience and associated brain plasticity changes.

Finally, Study V uses structural magnetic resonance imaging to analyze cortical thickness in a group of blind individuals and a matched sighted control group and relate the cortical thickness measure to the behaviorally registered changes in cardiac interoceptive accuracy. The key finding is that blind individuals with thicker occipital cortices are better at sensing their heartbeats; this finding advances our understanding of the limits of cross-modal plasticity following blindness and suggests that the visual cortex supports the awareness of inner bodily sensations in blind individuals.

Overall, this thesis is the first systematic characterization of differences and similarities between blind and sighted individuals in body perception and functioning of the bodily senses, opening a line of research with important links to mental health.

List of scientific papers

I. Radziun, D., Korczyk, M., Crucianelli, L., Szwed, M., & Ehrsson, H. H. (2023) Heartbeat counting accuracy is enhanced in blind individuals. Journal of Experimental Psychology: General. 152(7):2026-2039.
https://doi.org/10.1037/xge0001366

II. Radziun, D., Crucianelli, L., Korczyk, M., Szwed, M., & Ehrsson, H. H. (2023). The perception of affective and discriminative touch in blind individuals. Behavioural Brain Research. 444, 114361.
https://doi.org/10.1016/j.bbr.2023.114361

III. Radziun, D., Korczyk, M., Szwed, M., & Ehrsson, H. H. Are blind individuals immune to bodily illusions? Somatic rubber hand illusion in the blind revisited. [Manuscript]

IV. Radziun, D., Crucianelli, L., & Ehrsson, H. H. (2022). Limits of cross-modal plasticity? Short-term visual deprivation does not enhance cardiac interoception, thermosensation, or tactile spatial acuity. Biological Psychology. 168, 108248.
https://doi.org/10.1016/j.biopsycho.2021.108248

V. Stroh, A.-L.*, Radziun, D.*, Korczyk, M., Ehrsson, H. H., & Szwed, M. Enhanced cardiac interoceptive accuracy is related to cortical thickness of the occipital cortex in congenitally blind individuals. [Manuscript]