New research has found that blind individuals tend to have better interoceptive abilities than sighted individuals, particularly when it comes to detecting signals related to the heart. The new findings have been published in the Journal of Experimental Psychology: General.
The study aimed to investigate how blindness affects interoception, which refers to the ability to perceive internal bodily sensations. The researchers were specifically interested in examining how blindness affects cardiac interoception, which involves perceiving the sensations of the heartbeat.
The study was motivated by previous research that has shown that blindness can lead to heightened crossmodal plasticity, which is the ability of the brain to reorganize and compensate for sensory deprivation by enhancing other senses.
“I was interested in studying the impact of blindness on interoception, specifically on cardiac interoception, because while it is known that blind individuals have heightened abilities in processing exteroceptive information, such as hearing and touch, it was unclear whether their interoceptive abilities are also enhanced,” explained study author Dominika Radziun, a PhD candidate at the Department of Neuroscience at Karolinska Institutet in Stockholm.
“Interoception plays a critical role in our emotional experiences and bodily self-awareness, and understanding how lack of vision affects it can provide valuable insights into the extent of brain plasticity after visual loss. Furthermore, studying interoceptive processing in blind individuals could have important implications for improving the quality of life of blind individuals by informing interventions for conditions that affect interoception, such as anxiety disorders.”
The study involved 36 blind individuals and 36 sighted individuals who were matched for age and sex. All blind participants had blindness of peripheral origin and no other sensory impairments. The inclusion criteria for the study were complete blindness or minimal light sensitivity with no ability to functionally use this sensation, as well as no pattern vision.
The participants were asked to fill out a questionnaire regarding their bodily experiences at the beginning of the experiment, which measured interoceptive awareness using the Multidimensional Assessment of Interoceptive Awareness (MAIA) tool.
The participants were then asked to perform a heartbeat counting task, where they were instructed to silently count each heartbeat they felt in their body from the time they heard “start” to when they heard “stop.” The participants were not allowed to manually check their pulse or feel their chest with their hand. They were only allowed to feel the sensation of their heart beating.
After each trial, the participants were asked to rate their confidence in the perceived accuracy of their response on a scale ranging from 0 (total guess/no heartbeat awareness) to 10 (complete confidence/full perception of heartbeat). The task was repeated six times using intervals of 25, 30, 35, 40, 45, and 50 seconds, presented in a random order.
Before starting a task, participants had their heart rate measured for five minutes to establish a baseline reading. This was done using a device called a Biopac MP150 BN-PPGED pulse oximeter, which was attached to the participants’ left index finger and connected to a laptop running AcqKnowledge software. The software recorded the number of heartbeats within the preset time. Participants who could see were blindfolded during the task.
The researchers found that blind individuals had significantly better interoceptive accuracy than sighted controls, as reflected by their performance in the heartbeat counting task. The blind participants had a mean accuracy of 0.779, while the sighted participants had a mean accuracy of 0.630. There was no difference in the belief of performance accuracy. The results suggest that blindness enhances cardiac interoception, which may be due to crossmodal plasticity in the brain.
“The findings of our study suggest that blind individuals have a superior ability to accurately perceive their heartbeat, which is an important aspect of interoception,” Radziun told PsyPost. “This enhanced ability is likely due to the heightened brain plasticity that occurs in response to lack of vision. In short, sensory deprivation can lead to changes in brain function that may result in enhanced abilities in other senses.”
The participants also completed an assessment of tactile abilities. To test skin-sensing ability, they used a task where participants felt plastic domes with lines on them, and had to say whether the lines were horizontal or vertical. But the researchers found no significant correlation between interoceptive accuracy and tactile acuity in both the blind and sighted groups.
“As the lead researcher of this study, I can say that we were indeed surprised by the extent of the differences we observed between blind and sighted individuals in their ability to perceive their own heartbeat.,” Radziun said. “Additionally, it was interesting to see that the improvement in interoceptive accuracy did not extend to other aspects of interoceptive abilities, for example self-reported sensitivity to bodily signals.”
Radziun and her colleagues plan to conduct further studies to investigate how blind individuals perceive their own bodies. Specifically, they will explore if there are any changes in the structure of the visual cortex, which is typically responsible for processing visual information, that could explain the enhanced ability of blind individuals to sense signals from within their bodies.
“Our study only examined one submodality of interoception, cardiac interoception, and it remains unclear whether blindness affects other interoceptive modalities, such as respiratory or gastrointestinal interoception,” Radziun said. “Future research should investigate the effects of blindness on other interoceptive submodalities to gain a more comprehensive understanding of the extent of cross-modal plasticity after visual loss.”
The study, “Heartbeat Counting Accuracy Is Enhanced in Blind Individuals“, was authored by Dominika Radziun, Maksymilian Korczyk, Laura Crucianelli, Marcin Szwed, and H. Henrik Ehrsson.