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The rubber foot illusion.

Crea S, D'Alonzo M, Vitiello N, Cipriani C - J Neuroeng Rehabil (2015)

Bottom Line: Lower-limb amputation causes the individual a huge functional impairment due to the lack of adequate sensory perception from the missing limb.The development of an augmenting sensory feedback device able to restore some of the missing information from the amputated limb may improve embodiment, control and acceptability of the prosthesis.The results, collected from 19 healthy subjects, demonstrated that it is possible to elicit the perception of possessing a rubber foot when modality-matched stimulations are provided synchronously on the biological foot and to the corresponding rubber foot areas.

View Article: PubMed Central - PubMed

Affiliation: The BioRobotics Institute, Scuola Superiore Sant'Anna, viale Rinaldo Piaggio, Pontedera (PI), Italy. s.crea@sssup.it.

ABSTRACT

Background: Lower-limb amputation causes the individual a huge functional impairment due to the lack of adequate sensory perception from the missing limb. The development of an augmenting sensory feedback device able to restore some of the missing information from the amputated limb may improve embodiment, control and acceptability of the prosthesis.

Findings: In this work we transferred the Rubber Hand Illusion paradigm to the lower limb. We investigated the possibility of promoting body ownership of a fake foot, in a series of experiments fashioned after the RHI using matched or mismatched (vibrotactile) stimulation. The results, collected from 19 healthy subjects, demonstrated that it is possible to elicit the perception of possessing a rubber foot when modality-matched stimulations are provided synchronously on the biological foot and to the corresponding rubber foot areas. Results also proved that it is possible to enhance the illusion even with modality-mismatched stimulation, even though illusion was lower than in case of modality-matched stimulation.

Conclusions: We demonstrated the possibility of promoting a Rubber Foot Illusion with both matched and mismatched stimulation.

No MeSH data available.


Related in: MedlinePlus

Experimental setup. The participant is looking at the rubber foot, placed in front of him while his real foot is hidden from view
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Fig1: Experimental setup. The participant is looking at the rubber foot, placed in front of him while his real foot is hidden from view

Mentions: Nineteen able-bodied volunteers (10 females) participated in this study after signing a written informed consent. All experimental procedures were performed according to the standards set by the declaration of Helsinki for medical research involving human subjects. Each participant sat comfortably on a bed with both legs lying in a supine position and with his/her right leg out of sight, behind a screen. The participant was instructed to fix his/her sight on a rubber foot (single-axis foot, Ottobock Gmbh) during the experiment. Modality-matched and modality-mismatched stimulation conditions were tested. During the modality-matched conditions, congruent stimulation was delivered on the real and the rubber feet, using two paintbrushes, as in the original RHI experiment. In the modality-mismatched conditions the stimulation was incongruent; the rubber foot, in full view, was manually stimulated with the paintbrush while the hidden real foot was stimulated by small vibrators taped on the first and second toes, triggered off by a keypad, as in our previous studies [9, 10] (as depicted in (Fig. 1)). Each vibrator (8 mm diameter, 3.4 mm height, 0.7 g weight) could be selectively activated to vibrate at a pre-defined vibration frequency (165 Hz) and force amplitude (0.36 N; i.e. largely supra-threshold) or deactivated. As soon as a specific key on the keypad was pressed, the corresponding unit would start vibrating, until the key was released. The time delay between the pressure of a key and starting of perceivable vibration can be considered negligible (i.e. <10 ms). Paintbrush stimulations on the rubber foot were applied on the areas corresponding to where the vibrators were placed on the real foot, i.e. on the first and second toes. Details on this set-up can be found in [14]. Both the congruent and incongruent conditions were tested with either synchronous or asynchronous stimulation (a temporal delay of about 0.5 s was included between stimulations) for a total of four combinations. The asynchronous conditions were included as control conditions for the synchronous ones. The four combinations of modality and timing (congruent synchronous - CS, congruent asynchronous - CA, incongruent synchronous - IS and incongruent asynchronous - IA) were tested twice for each subject; 50 % of the trials (balanced across conditions) ended with a threat stimulus, i.e. a needle was used to stab the rubber foot, in order to measure the SCR (as in the conventional RHI experiment [7]). Each trial lasted 150 s; in previous studies the stimulation duration was ranged from a minimum of 45 s [9] to a maximum of 240 s [15]. The order of execution of the trials was randomized across the participants.Fig. 1


The rubber foot illusion.

Crea S, D'Alonzo M, Vitiello N, Cipriani C - J Neuroeng Rehabil (2015)

Experimental setup. The participant is looking at the rubber foot, placed in front of him while his real foot is hidden from view
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4559902&req=5

Fig1: Experimental setup. The participant is looking at the rubber foot, placed in front of him while his real foot is hidden from view
Mentions: Nineteen able-bodied volunteers (10 females) participated in this study after signing a written informed consent. All experimental procedures were performed according to the standards set by the declaration of Helsinki for medical research involving human subjects. Each participant sat comfortably on a bed with both legs lying in a supine position and with his/her right leg out of sight, behind a screen. The participant was instructed to fix his/her sight on a rubber foot (single-axis foot, Ottobock Gmbh) during the experiment. Modality-matched and modality-mismatched stimulation conditions were tested. During the modality-matched conditions, congruent stimulation was delivered on the real and the rubber feet, using two paintbrushes, as in the original RHI experiment. In the modality-mismatched conditions the stimulation was incongruent; the rubber foot, in full view, was manually stimulated with the paintbrush while the hidden real foot was stimulated by small vibrators taped on the first and second toes, triggered off by a keypad, as in our previous studies [9, 10] (as depicted in (Fig. 1)). Each vibrator (8 mm diameter, 3.4 mm height, 0.7 g weight) could be selectively activated to vibrate at a pre-defined vibration frequency (165 Hz) and force amplitude (0.36 N; i.e. largely supra-threshold) or deactivated. As soon as a specific key on the keypad was pressed, the corresponding unit would start vibrating, until the key was released. The time delay between the pressure of a key and starting of perceivable vibration can be considered negligible (i.e. <10 ms). Paintbrush stimulations on the rubber foot were applied on the areas corresponding to where the vibrators were placed on the real foot, i.e. on the first and second toes. Details on this set-up can be found in [14]. Both the congruent and incongruent conditions were tested with either synchronous or asynchronous stimulation (a temporal delay of about 0.5 s was included between stimulations) for a total of four combinations. The asynchronous conditions were included as control conditions for the synchronous ones. The four combinations of modality and timing (congruent synchronous - CS, congruent asynchronous - CA, incongruent synchronous - IS and incongruent asynchronous - IA) were tested twice for each subject; 50 % of the trials (balanced across conditions) ended with a threat stimulus, i.e. a needle was used to stab the rubber foot, in order to measure the SCR (as in the conventional RHI experiment [7]). Each trial lasted 150 s; in previous studies the stimulation duration was ranged from a minimum of 45 s [9] to a maximum of 240 s [15]. The order of execution of the trials was randomized across the participants.Fig. 1

Bottom Line: Lower-limb amputation causes the individual a huge functional impairment due to the lack of adequate sensory perception from the missing limb.The development of an augmenting sensory feedback device able to restore some of the missing information from the amputated limb may improve embodiment, control and acceptability of the prosthesis.The results, collected from 19 healthy subjects, demonstrated that it is possible to elicit the perception of possessing a rubber foot when modality-matched stimulations are provided synchronously on the biological foot and to the corresponding rubber foot areas.

View Article: PubMed Central - PubMed

Affiliation: The BioRobotics Institute, Scuola Superiore Sant'Anna, viale Rinaldo Piaggio, Pontedera (PI), Italy. s.crea@sssup.it.

ABSTRACT

Background: Lower-limb amputation causes the individual a huge functional impairment due to the lack of adequate sensory perception from the missing limb. The development of an augmenting sensory feedback device able to restore some of the missing information from the amputated limb may improve embodiment, control and acceptability of the prosthesis.

Findings: In this work we transferred the Rubber Hand Illusion paradigm to the lower limb. We investigated the possibility of promoting body ownership of a fake foot, in a series of experiments fashioned after the RHI using matched or mismatched (vibrotactile) stimulation. The results, collected from 19 healthy subjects, demonstrated that it is possible to elicit the perception of possessing a rubber foot when modality-matched stimulations are provided synchronously on the biological foot and to the corresponding rubber foot areas. Results also proved that it is possible to enhance the illusion even with modality-mismatched stimulation, even though illusion was lower than in case of modality-matched stimulation.

Conclusions: We demonstrated the possibility of promoting a Rubber Foot Illusion with both matched and mismatched stimulation.

No MeSH data available.


Related in: MedlinePlus