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Crossed hands strengthen and diversify proprioceptive drift in the self-touch illusion.

Kodaka K, Ishihara Y - Front Hum Neurosci (2014)

Bottom Line: Moreover, it is interesting that strong PD with dominance of the receptive hand, which did not appear in the uncrossed condition, was observed frequently.We also found that a small number of participants exhibited quite a different pattern of the PD in the identical posture.On the basis of the results, we analyze in detail how the dominant hand on the PD is determined in the STI.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Design and Architecture, Nagoya City University Nagoya, Japan.

ABSTRACT
In the self-touch illusion (STI), some can feel that both hands are touching each other even when they are separated actually. This is achieved by giving synchronized touches to both hands. Because the STI involves both hands (an administrating hand and a receptive hand) of a single person, two types of proprioceptive drifts (PDs) simultaneously occur in such a way that both hands are attracted to each other. It is known that the PD distance is generally larger for the administrating hand than for the receptive hand when the two hands are uncrossed. However, it remains unclear why such an asymmetrical relationship is observed universally. In this study, we conducted two types of experiment to induce the STI. The first experiment involved four conditions combining a factor of "whether the hands are uncrossed or crossed" and a factor of "whether the administrating hand is resting or active on the surface," with the receptive (left) hand located at the body's midline. The result demonstrated that crossing hands and resting on surface (ROS) induced the STI. Specifically, crossing hands enhanced the amount of PD distance by more than two or three times. Moreover, it is interesting that strong PD with dominance of the receptive hand, which did not appear in the uncrossed condition, was observed frequently. The second experiment collected seven "illusion-sensitive" participants from the first experiment, all of whom had a strong tendency to feel the self-touch, and examined the effect of the location of the body midline on the PD when hands are crossed with the administrating hand ROS. The result demonstrated that the dominant hand on the PD completely differed among participants, but was relatively stable over the midline position and time in the same person. We also found that a small number of participants exhibited quite a different pattern of the PD in the identical posture. On the basis of the results, we analyze in detail how the dominant hand on the PD is determined in the STI.

No MeSH data available.


Related in: MedlinePlus

Results of the directivity distribution of seven (A–G) “illusion-sensitive” participants for three types of body midline alignments in Experiment II. Each body midline alignment experiment contains five sessions. The individual data from each session are plotted as a small blank circle, while a large colored circle represents the average attractivity for each body midline alignment. The directivity values in the Crossed × ROS condition of Experiment I (including two sessions every participant) are depicted together with those in Experiment II by a small square, in the region of the Receptor-centered condition. Data of participant G in the Receptor-centered condition of the Experiment II was excluded because of low attractivity. Asterisks indicate that there is significant difference of directivity between two body midline alignments or that a series of attractivity in each body midline alignment are significantly different from zero (with one-tailed Welch's t-test, *p < 0.05, **p < 0.01, ***p < 0.001).
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Figure 9: Results of the directivity distribution of seven (A–G) “illusion-sensitive” participants for three types of body midline alignments in Experiment II. Each body midline alignment experiment contains five sessions. The individual data from each session are plotted as a small blank circle, while a large colored circle represents the average attractivity for each body midline alignment. The directivity values in the Crossed × ROS condition of Experiment I (including two sessions every participant) are depicted together with those in Experiment II by a small square, in the region of the Receptor-centered condition. Data of participant G in the Receptor-centered condition of the Experiment II was excluded because of low attractivity. Asterisks indicate that there is significant difference of directivity between two body midline alignments or that a series of attractivity in each body midline alignment are significantly different from zero (with one-tailed Welch's t-test, *p < 0.05, **p < 0.01, ***p < 0.001).

Mentions: Figure 9 maps the distribution of the directivity values for the three body midline alignments of each of the seven participants (data of participant G in the Receptor-centered condition was excluded because of low attractivity). Participants A and D exhibited an admin-dominant PD revealed by significant positive directivity [one-tailed Welch's t-test comparison with zeroes, A: t(14) = 4.24, p < 0.001; D: t(14) = 5.82, p < 0.001]. Participant A exhibited relatively symmetric PD in the Receptor-centered condition whereas admin-dominant asymmetry strengthens when the body shifts leftward. Specifically, the directivity was more than 0.8 in four out of five sessions in the Admin-centered condition. Participant D maintained the admin-dominant PD independently of the body midline alignments, but a degree of the asymmetry depended on the alignments. In contrast, participants B, C, and G completely exhibited receptor-dominant PD revealed by significant negative directivity [B: t(14) = 4.93, p < 0.001; C: t(14) = 6.26, p < 0.001; G: t(9) = 3.57, p < 0.01]. In participant B, the tendency of having the receptor-dominant PD was fairly robust in both Symmetric and Admin-centered conditions though the intensity was not particularly large. Participant C exhibited significant receptor-dominant PDs in all three body midline alignments. Especially in the Admin-centered condition, the felt location of the receptive (left) hand shifted toward the place where the administrating (right) hand was placed, whereas the felt location of the administrating hand shifted even farther leftward from the original position, resulting in the high level of the negative directivity. Negative directivity was observed for almost all sessions in participant G but was especially robust in the Admin-centered condition. It is interesting that the receptor-dominant asymmetry in these three participants was maximized when the body midline was aligned at the administrating hand (Admin-centered condition). Finally, participants E and F did not exhibit specific asymmetry in the PD overall, unlike the aforementioned five participants. The directivity observed in participant E strongly varied among all body midline alignments. Specifically, it varied in the positive region for the Receptor-centered condition but mainly in the negative region for the Symmetric condition. Such randomness increased in the Admin-centered condition where both clearly positive and negative directivity (0.69 and −0.75) were observed during the five sessions. Conversely, participant F did not exhibit such a scattered distribution of the directivity. Almost all the directivity was relatively close to zero value, even though there was a significant receptor-dominant PD in the Symmetric condition.


Crossed hands strengthen and diversify proprioceptive drift in the self-touch illusion.

Kodaka K, Ishihara Y - Front Hum Neurosci (2014)

Results of the directivity distribution of seven (A–G) “illusion-sensitive” participants for three types of body midline alignments in Experiment II. Each body midline alignment experiment contains five sessions. The individual data from each session are plotted as a small blank circle, while a large colored circle represents the average attractivity for each body midline alignment. The directivity values in the Crossed × ROS condition of Experiment I (including two sessions every participant) are depicted together with those in Experiment II by a small square, in the region of the Receptor-centered condition. Data of participant G in the Receptor-centered condition of the Experiment II was excluded because of low attractivity. Asterisks indicate that there is significant difference of directivity between two body midline alignments or that a series of attractivity in each body midline alignment are significantly different from zero (with one-tailed Welch's t-test, *p < 0.05, **p < 0.01, ***p < 0.001).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4060641&req=5

Figure 9: Results of the directivity distribution of seven (A–G) “illusion-sensitive” participants for three types of body midline alignments in Experiment II. Each body midline alignment experiment contains five sessions. The individual data from each session are plotted as a small blank circle, while a large colored circle represents the average attractivity for each body midline alignment. The directivity values in the Crossed × ROS condition of Experiment I (including two sessions every participant) are depicted together with those in Experiment II by a small square, in the region of the Receptor-centered condition. Data of participant G in the Receptor-centered condition of the Experiment II was excluded because of low attractivity. Asterisks indicate that there is significant difference of directivity between two body midline alignments or that a series of attractivity in each body midline alignment are significantly different from zero (with one-tailed Welch's t-test, *p < 0.05, **p < 0.01, ***p < 0.001).
Mentions: Figure 9 maps the distribution of the directivity values for the three body midline alignments of each of the seven participants (data of participant G in the Receptor-centered condition was excluded because of low attractivity). Participants A and D exhibited an admin-dominant PD revealed by significant positive directivity [one-tailed Welch's t-test comparison with zeroes, A: t(14) = 4.24, p < 0.001; D: t(14) = 5.82, p < 0.001]. Participant A exhibited relatively symmetric PD in the Receptor-centered condition whereas admin-dominant asymmetry strengthens when the body shifts leftward. Specifically, the directivity was more than 0.8 in four out of five sessions in the Admin-centered condition. Participant D maintained the admin-dominant PD independently of the body midline alignments, but a degree of the asymmetry depended on the alignments. In contrast, participants B, C, and G completely exhibited receptor-dominant PD revealed by significant negative directivity [B: t(14) = 4.93, p < 0.001; C: t(14) = 6.26, p < 0.001; G: t(9) = 3.57, p < 0.01]. In participant B, the tendency of having the receptor-dominant PD was fairly robust in both Symmetric and Admin-centered conditions though the intensity was not particularly large. Participant C exhibited significant receptor-dominant PDs in all three body midline alignments. Especially in the Admin-centered condition, the felt location of the receptive (left) hand shifted toward the place where the administrating (right) hand was placed, whereas the felt location of the administrating hand shifted even farther leftward from the original position, resulting in the high level of the negative directivity. Negative directivity was observed for almost all sessions in participant G but was especially robust in the Admin-centered condition. It is interesting that the receptor-dominant asymmetry in these three participants was maximized when the body midline was aligned at the administrating hand (Admin-centered condition). Finally, participants E and F did not exhibit specific asymmetry in the PD overall, unlike the aforementioned five participants. The directivity observed in participant E strongly varied among all body midline alignments. Specifically, it varied in the positive region for the Receptor-centered condition but mainly in the negative region for the Symmetric condition. Such randomness increased in the Admin-centered condition where both clearly positive and negative directivity (0.69 and −0.75) were observed during the five sessions. Conversely, participant F did not exhibit such a scattered distribution of the directivity. Almost all the directivity was relatively close to zero value, even though there was a significant receptor-dominant PD in the Symmetric condition.

Bottom Line: Moreover, it is interesting that strong PD with dominance of the receptive hand, which did not appear in the uncrossed condition, was observed frequently.We also found that a small number of participants exhibited quite a different pattern of the PD in the identical posture.On the basis of the results, we analyze in detail how the dominant hand on the PD is determined in the STI.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Design and Architecture, Nagoya City University Nagoya, Japan.

ABSTRACT
In the self-touch illusion (STI), some can feel that both hands are touching each other even when they are separated actually. This is achieved by giving synchronized touches to both hands. Because the STI involves both hands (an administrating hand and a receptive hand) of a single person, two types of proprioceptive drifts (PDs) simultaneously occur in such a way that both hands are attracted to each other. It is known that the PD distance is generally larger for the administrating hand than for the receptive hand when the two hands are uncrossed. However, it remains unclear why such an asymmetrical relationship is observed universally. In this study, we conducted two types of experiment to induce the STI. The first experiment involved four conditions combining a factor of "whether the hands are uncrossed or crossed" and a factor of "whether the administrating hand is resting or active on the surface," with the receptive (left) hand located at the body's midline. The result demonstrated that crossing hands and resting on surface (ROS) induced the STI. Specifically, crossing hands enhanced the amount of PD distance by more than two or three times. Moreover, it is interesting that strong PD with dominance of the receptive hand, which did not appear in the uncrossed condition, was observed frequently. The second experiment collected seven "illusion-sensitive" participants from the first experiment, all of whom had a strong tendency to feel the self-touch, and examined the effect of the location of the body midline on the PD when hands are crossed with the administrating hand ROS. The result demonstrated that the dominant hand on the PD completely differed among participants, but was relatively stable over the midline position and time in the same person. We also found that a small number of participants exhibited quite a different pattern of the PD in the identical posture. On the basis of the results, we analyze in detail how the dominant hand on the PD is determined in the STI.

No MeSH data available.


Related in: MedlinePlus