Fig 1.
Experimental set-up and events sequence.
The participant sat at a table with the forearm hidden from view and placed inside a box. Before stroking, the participant judged the felt position of her own index finger by means of a ruler. After making a proprioceptive judgment, the rubber hand was made visible and stroked synchronously or asynchronously with the participant’s hidden hand for 2 min. After stroking, the participant was again asked to judge the position of her index finger. Finally, the participant filled in the RHI questionnaire. This sequence was the same for synchronous and asynchronous stroking of the right and the left hand, thus resulting in a total of 4 conditions.
Fig 2.
Boxplot of the scores for the experimental statements in the young, middle-aged, and older adult groups.
In the synchronous stroking condition (gray columns), scores for all experimental statements were higher in the young and the older adult groups than in the middle-aged group. This pattern qualitatively describes a characteristic U-shape of the illusory embodiment of the rubber hand across different stages of life. Between-group differences were found also for the asynchronous stroking condition (gray-striped columns) at statements 2 and 3. The scores for these statements were higher in the young adult group than in the other two groups. *Significant values (p<0.05); °outliers (e.g., values falling between 1.5 and 3 times above or below the interquartile range); # extreme outliers (e.g., values more than three times above or below the interquartile range). Red bars represent median values.
Fig 3.
Boxplot of proprioceptive drift in the young adults, middle-aged, and older adults groups.
Proprioceptive drift was similar between groups in both the synchronous (gray columns) and the asynchronous (gray-striped columns) stroking conditions, suggesting that age does not affect the illusory displacement of the real hand towards the rubber hand. °Outliers (e.g., values falling between 1.5 and 3 times above or below the interquartile range); # extreme outliers (e.g., values more than three times above or below the interquartile range). Red bars represent median values.