Do Lower-Limb Amputees Pay Attention to Their Prosthetic Foot When Walking?
It doesn’t seem obvious, but humans are wired to control biological body parts and receive information by directing attention toward them. This is called “body-specific attention,” which explains why it’s often harder for amputees to feel comfortable using their prosthetic legs.
But the more someone uses their prosthetic foot, the closer they get to experiencing “embodiment,” or the ability to perceive the prosthesis as a part of their body. So, researchers sought to find out how prosthetic foot users achieve embodiment and how much attention is given to prosthetic feet when walking.
Importance of embodiment
Recent studies have reported that the more a prosthetic limb is used, the more it is perceived to be a part of the body. Therefore, the embodiment of the prosthesis is vital for re-learning how to walk.
Research has also shown that persons with limb loss who can walk with a prosthetic limb have higher survival rates and lower rates of re-amputation than those who can’t walk. This makes it crucial for patients to understand how to use their prosthesis during walking rehabilitation. However, the process of embodiment is unclear.
To use the prosthetic foot well, people with lower-limb loss need to direct their attention to it as they would to their biological body parts. Researchers have reached this conclusion because the brain typically directs attention to natural body parts to perform any intended action accurately.
Previous studies have shown that a visual detection task can determine body-specific attention. This phenomenon indicates that the brain directs attention to the body and regulates the amount of information from the limb to help control movement. Moreover, researchers have found that this body-specific attention is an intrinsic process that spontaneously directs attention to specific body parts.
This body-specific attention is an intrinsic process that spontaneously directs attention to specific body parts.
Findings indicate that people with lower-limb amputation who use their prosthetic leg well direct more attention to the prosthetic foot, as they experience the prosthetic foot as their own body part. But the evidence still needs to be clarified.
So, researchers from Tohoku University Hospital in Japan embarked on a new study to examine whether lower-limb amputees direct attention toward their prosthetic foot. The hypothesis is if people with limb loss could use their prosthetic foot well, the attention directed toward the prosthetic limb would increase.
The study used data from Tohoku University Hospital in Japan from 2012 through 2017. A total of 11 inpatients and outpatients participated in the study and received physical therapy at the hospital to re-learn how to walk using a prosthetic foot.
The researchers administered measurements in two periods: the initial stage and the final stage. The initial stage was one month after patients began using the prosthetic foot in rehabilitation. The final stage was when patients walked independently immediately before getting discharged from the hospital.
In the initial and final stages of walking rehabilitation, a visual detection task assessed attention to the prosthetic foot and healthy foot. Moreover, the subjective embodiment of the prosthetic foot was evaluated using the phrase, “I felt as if the prosthetic foot was my foot.”
The study found that attention to the prosthetic foot was typically low initially but increased in the final stage. During the initial stage, attention given to the prosthetic foot was lower than to the sound side foot. But, in the final stage, the former increased. The researchers also found that there was no significant difference between the attention to the prosthetic foot and the sound side foot in the final stage.
According to the researchers, the study’s results show that the prosthetic foot’s embodiment score was higher in the final stage than in the initial stage. This indicates that the study participants felt the prosthetic foot was a part of their own body.
Furthermore, findings in previous studies have reported that the subjective embodiment of a prosthetic limb, such as a rubber hand, is caused by multi-sensory integration, including not only visual and somatosensory input but also active movement. Given the limited somatosensory information from the prosthesis, using the prosthetic limb leads to the integration of visual information and movement of the limb, which results in a subjective embodiment.
Use of the prosthetic foot leads to the integration of visual information and movement of the limb, resulting in subjective embodiment.
And when embodiment is achieved, prosthetic users perceive not only a lightening of prosthesis weight but also experience an increase in walking speed and a decrease in physical and mental fatigue.
What do you think of these findings? Have you achieved a sense of embodiment with your prosthetic foot?