Abstract
The rubber hand illusion (RHI) is an illusion of the self-ownership of a rubber hand that is touched synchronously with one’s own hand. While the RHI relates to visual and tactile integration, we can also consider a similar illusion with visual and motor integration on a fake hand. We call this a “robot hand illusion” (RoHI), which relates to both the senses of ownership and agency. Here we investigate the effect of delayed visual feedback on the RoHI. Participants viewed a virtual computer graphic hand controlled by their hand movement recorded using a data glove device. We inserted delays of various lengths between the participant’s hand and the virtual hand movements (90–590 ms), and the RoHI effects for each delay condition were systematically tested using a questionnaire. The results showed that the participants felt significantly greater RoHI effects with temporal discrepancies of less than 190 ms compared with longer temporal discrepancies, both in the senses of ownership and agency. Additionally, participants felt significant, but weaker, RoHI effects with temporal discrepancies of 290–490 ms in the sense of agency, but not in the sense of ownership. The participants did not feel a RoHI with temporal discrepancies of 590 ms in either the senses of agency or ownership. Our results suggest that a time window of less than 200 ms is critical for multi-sensory integration processes constituting self-body image.
Highlights
Self-body recognition happens naturally in our body, but the mechanism of self-body recognition is not yet clear
The results showed that participants rated the 90-ms and 190-ms visual feedback delay conditions above 0 for both the ownership sense and the agency sense related questionnaire items (P < 0.01, t-test, False Discovery Rate (FDR)-corrected)
In the higher (590-ms) visual feedback delay condition, participants rated the ownership sense below 0 and the agency sense near 0 (P > 0.1). This result confirms that participants did not experience the ownership sense and the agency sense toward the virtual hand in the 590-ms visual feedback delay condition
Summary
Self-body recognition happens naturally in our body, but the mechanism of self-body recognition is not yet clear. According to Gallagher, the basis of self-body recognition comprises two sensory components, the sense of ownership and the sense of agency [1,2]. The definition of the sense of ownership is the conscious awareness that the body belongs to us. The definition of the sense of agency refers to the sense of authorship of a given action. The sense of ownership does occur toward our own body; there are a few cases in which we feel a sense of ownership of other objects. An example of this case is the rubber hand illusion (RHI)
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